Deployment of new combination insecticidal bednets in Africa to combat pyrethroid resistance in malaria mosquitoes
- Impact Case Studies
4 December 2020
Malaria prevention in Africa is dependent on Insecticide Treated Nets (ITNs) which prevented 500 million malaria cases from 2000-2015.
However, until 2017, all insecticides used in ITNs were pyrethroids and LSTM’s research has highlighted the public health threat from pyrethroid resistance.
so my name’s professor hilary ransom and
i work in the department of vector
biology Liverpool School of Tropical
Medicine and the department here has got
an international reputation for its work
on insecticide resistance particularly
in mosquitoes and for many years now
we’ve been looking at what they’re the
causes and the consequences of
resistance are for disease control
because lsdm is a real focus on on
translation we our work doesn’t just
look at at the describing a problem
because clearly resistance is a very big
problem for disease control particularly
for control of malaria and dengue but we
also work with multiple stakeholders to
try and develop and implement solutions
to the problem we were one of the first
groups to identify the problem of
pyrethroid resistance in malaria
mosquitoes in Africa and we spent many
years looking at what the cause is
what’s the molecular mechanisms
responsible for that resistance and we
identified one of the most potent
resistance mechanisms and that is over
expressional increased levels of a
family of enzymes known as cytochrome
p450s now there’s a known an inhibitor
that can can block the action of these
enzymes it’s a chemical known as PB o so
we were then able to work with
stakeholders and Industry and partners
to look at how we might be able to use
this information about the main
resistance mechanisms to develop new
nets that were would overcome resistance
so now that one of the big innovations
in the terms of malaria vector control
is the use of nets containing PB o s
they contain the pyrethroids insecticide
Plus’s inhibitor there’s resistance
makers and PB o and PB o bed nets are
now being rolled out and across many
countries in Africa another example
where our work on on mosquito biology
and behavior has led to two real
innovations in this space is the work
that we’ve been doing on looking at how
mosquitoes actually interact with a bed
net so look by doing some some filming
of how mosquitoes
somebody sleeping under a net as they
try and enter a house to try and get a
blood meal we found that the mosquitos
predominantly come to the surface of the
net the top surface of the net and that
information has been invaluable for net
manufacturers to think of innovative new
ways in which they might apply
insecticides to Nets so for example
we’ve looked at putting barriers just on
the nets that contain a different on the
top of the nets that just contain
another insecticide that maybe might be
too costly to put over the entire net
and this enables us to expand the range
of insecticides that can be used
LSTM has pioneered research into the causes, consequences and rapid spread of pyrethroid resistance in African malaria vectors and provided practical solutions to combat the problem. The outputs of this research, which span the translational pipeline, have alerted international agencies to the problem, defined the scale and complexity of the issue, informed the development of new classes of insecticides and next-generation ITNs using insecticide or insecticide/synergist combinations, and informed national and global policy on when, and where, the new products should be deployed for maximum public health impact.
Designing new approaches for resistance monitoring, LSTM has evaluated alternative bioassays; these have been incorporated into WHO guidelines (2016) and discussions are ongoing on the incorporation of alternative assays for new insecticides. These measures have strengthened resistance monitoring and helped operational decision-making.
Understanding the genetics and behaviour of mosquitoes has been key in understanding and combatting insecticide resistance and has been pivotal in the development of mitigating strategies. Our work on pyrethroid resistance mechanisms has led to several new classes of ITNs, including PBO-pyrethroid nets that are now being included in many national net distribution schemes across Africa, whereas our studies on mosquito behaviour have led the development and field testing of nets that can utilise insecticides previously discounted from the use on nets, given their cost or toxicity. We also play a major role in the evaluation of new classes of ITNs and are currently leading the entomological evaluation of the largest ever trial of a vector control tool, a trial of PBO-pyrethroid ITNs in Uganda.
Research Outputs
Barnes KG, Weedall GD, Ndula M, Irving H, Mzihalowa T, Hemingway J, Wondji CS. 2017. Genomic Footprints of Selective Sweeps from Metabolic Resistance to Pyrethroids in African Malaria Vectors Are Driven by Scale-up of Insecticide-Based Vector Control.(link is external)(opens in a new tab)PLoS Genet 13: e1006539.
Implications of insecticide resistance for malaria vector control with long-lasting insecticidal nets: a WHO-coordinated, prospective, international, observational cohort study.(link is external)(opens in a new tab) Lancet Infect Dis. 2018 Jun; 18(6): 640–649. doi: 10.1016/S1473-3099(18)30172-5
Churcher TS, Lissenden N, Griffin JT, Worrall E, Ranson H. 2016. The impact of pyrethroid resistance on the efficacy and effectiveness of bednets for malaria control in Africa.(link is external)(opens in a new tab) Elife 5.
Tiono AB, Ouédraogo A, Ouattara D, Bougouma EC, Coulibaly S, Diarra A, Faragher B, Guelbeogo Page 11 of 37 et al, Ranson H, Lindsay SW. Efficacy of Olyset Duo, a bednet containing pyriproxyfen and permethrin, versus a permethrin-only net against clinical malaria in an area with highly pyrethroid resistant vectors in rural Burkina Faso: a cluster-randomised controlled trial. (link is external)(opens in a new tab)Lancet. 2018 Aug 18;392(10147):569-580. PMID:30104047
GPD Murray, N Lissenden, J Jones, V Voloshin, KH Toé, E Sherrard-Smith, GM Foster, TS Churcher, JEA Parker, CE Towers, WM Guelbeogo, Sagnon N’Falé, H. Ranson, D. Towers, P. J. McCall. Barrier bednets target malaria vectors and expand the range of usable insecticides.(link is external)(opens in a new tab) Nature Microbiology,5, 40–47 (2020). https://doi.org/10.1038/s41564-019-0607-2
Reducing Malaria Prevalence in Africa Through New Classes of Insecticide-Treated Nets
Widespread use of insecticide treated nets (ITNs) has dramatically reduced the incidence of malaria in Africa but resistance to pyrethroid insecticides in Anopheles mosquitoes is eroding their efficacy.
In this seminar LSTM Professor Hilary Ranson, Professor Martin Donnelly, Professor Philip McCall, Dr David Weetman and Dr Gareth Lycett highlight how research from the Department of Vector Biology at LSTM on the mechanisms underpinning pyrethroid resistance, and the behavioural response of mosquitoes to ITNS has led to the development of new classes on ITNs mosquitoes. They will highlight how, by working in partnership with different sectors we have developed the evidence base for the public health value of these nets that has led to their widespread deployment across Africa to combat resistant mosquito populations.
okay so welcome everyone um to this series to one of the series of seminars we’re giving on the
translational impact of our work here at the lstm um as you’ll be aware one of the three key aims of
lstm is to maximize the translational impact of our work and translation in this case in a public health sense
and so we have a number of groups uh five presenters from across the vector department who are presenting
a a sort of an evolving narrative if you will around our work in insecticide resistance and
vector behavior and how that’s been led into real world impacts on malaria transmission principle in sub-saharan africa
but how it’s led to the development of new vet control tools and how from a mechanistic understanding of
insecticide resistance and behavior we’ve transitioned through product development into
public health impact and policy change on a global scale so that’s what we’re hoping to to capture
today um this is a um a work package from a number of groups across the school
and what i really want to emphasize it’s very much in association with and in many cases led by partners in the
global south and it’s been a a research um area which has been going on for approximately 20
years within the school so that’s also why reflected on we have quite senior presenters here
um who are at the outset of these projects early career researchers and i also really just wanted to emphasize that a lot of this work has
been driven by successes of cadres of highly talented and very gifted um early career research and that will
be reflected in the acknowledgment slides and that’s but that’s why we have this presenter composition
so we’re going to kick off with uh dr david wheatman department who’s going to talk us through some of the mechanistic
understanding and then we’ll have fingers crossed a sort of a scientific relay where we’ll pass on to other members of
the department who will talk about their specific areas of interest and how they’ve moved the story forward so welcome and
over to you dave okay thanks very much
[Music]
um okay so it’s um i’m going to be starting out the the first of the um present
sub presentations if i by looking at the role that lstm and of course many others have played in um advocacy
specifically focusing on um developing the the evidence base to show
the importance of insecticide treated nets but also the threat to that uh that importance that is posed
by uh pyrethroid resistance so although use of um
bed nets for protection against flying insects and the diseases they they they may carry it’s been around for
hundreds or probably thousands of years a big revolution really came out or
became possible from the sort of early 70s onwards with the development of synthetic pyrethroids so
synthetic peripherals
neurotoxins that um fast acting and really importantly in addition to
although they’re very good at killing insects they’re very very safe for humans that means that they can be
used to treat materials that can be in close contact with people
and this property meant that they were highly suitable for treating bed nets and this this led to
the um development of bed nets or treatments for bed nets which were then tested in a number of
randomized control trials and the results overall from from these
were to the point in the early 2000s was summarized by
the cochrane review by christian langler and the take on message from this was that
insecticide treated nets can reduce deaths in children by a fifth and episodes by half
there are a number of trials but one that i particularly like to highlight here which was led by cdc and camry
and research from the university of amsterdam was conducted in assembly in kenya and
the reason why i highlight this one in particular i mean the results from several trials were very consistent in showing that there was a
strong impact was because this probably provided the strongest evidence for a community benefit and the
community benefits demonstrated because the protective efficacy that was shown by um
insecticide treated nets that were were present within control compounds was also
found outside of those compounds at least within a relatively short space and this strongly suggested
that people were getting protection even if they were not sleeping under a treated nest
and therefore there was a strong community benefit as in mosquitoes were most likely being killed and that’s this
reduction in the population as a whole was protecting the wider area it does indeed suggest a major benefit of
the insecticide treated nets and subsequently these these became long-lasting insecticidal nets
which were treated for the lifespan of the net comes from the pyrethroid treatment itself and the killing effect
so the um the evidence was really crystallized for how strongly um
the impact of treated nets was a has been on malaria control you know in a landmark paper from samira
batting colleagues which many of you are probably familiar with and this compared the the the uh
plasmodium falciparum positivity raising in children at a point of 2000 and 2015
and the heat map comparing the a and the b their left and right shows a dramatic decline from 2000 2015
but of course many factors were changing not just the mass distribution of bed nets what their geospatial model was able to
show was what percentage of that decrease was attributed to bed nets and it was very major indeed
almost um around about 70 percent of that decrease was attributable to bed nets so really demonstrated
with with very good clarity just how important treated bed nets have been for the
decline seen in malaria control unfortunately nothing comes for free and
the fact that it was only pyrethroids that have the required safety profile for treatment of bed nets also it has
been for a long time means that they were affected they’ve effectively been used as a monotherapy
throughout the time that the mass distribution has been going on there’s been a lot of
bioasset testing going on across africa particularly using the whole tube bioassay
methodology and this produced lots of data points which enabled research from from lstm to
put together a time series and demonstrate that whether we look at different types of vectors so we’ve got
a novelist gangnam guy at the top on the left anopheles finesses bottom bottom left
there’s really quite strong declines in mortality caused by pyrethroid insecticides
over time as we move through from the 90s to 2015.
and to put this into a spatial and temporal context um penny hancock was a member of
catherine moyes team who’s been working with mike coleman janet hemingway and various
other people from uh teams at lstm have shown that um over time
pyrethroid resistance has both spread and intensified as moving through 2015 through to 2017.
with particularly strong resistance in west africa
and obviously the this change over time does certainly
correlate with the the mass distribution of bed nets and the the
up-to-date data for this are present in the plot on the right but what um the model also showed
was that by looking at over a hundred potential explanatory variables and this was
particularly strong in the the west african component of the model itn coverage was really strongly
correlated with the the changes in um pyrethrum the variation in pyrethroid
insecticide mortality and this this was true but spatially and
temporally and so although based on correlation it strongly implicates
that pyrethroid resistance is being driven at least in a large part by the increased coverage of bed nets
treated with pyrethroids so this is based on data from who
bioassays and whether this actually reflects an operational change you know does it
mean that there’s a derailment of malaria control has been a a a long-running argument that really has
uh required um data to address this so that
there are a number of studies coming from groups at london school working in benin who when they compared
bed nets that were treated or untreated and these were bed nets that were quite well worn so they had
holes they were finding that there was very little difference um
between the treated and the untreated if they were looking at mosquitoes from a resistant area and listen in contrast to
susceptible mosquitoes similarly a work from the avec net project
led by lstm was showing just how dramatic the the the difference in mortality
for mosquitoes explained to exposed to various types of pyrethroid treated nets were between the the local resistant
population population of burkina faso compared to susceptible strains as kasumu strain
so really look it does indeed appear that the the nets are not quite doing everything they should do at least under
these test conditions but that’s that’s not quite the same as
um finding a a major impact within a control situation
and so to look into this the whl commissioned a major research study multi-center
study spread across five countries which was aiming to to look at what the
impact of pyrethroid resistance on the effectiveness of um of insecticidal
tools particularly long-lasting insecticidal nets treated with pyrethroids were
and this the the study involved overall looking at about 80 000 mosquitoes across almost 280 locations
across multiple time points involved testing about 50 000 children for uh malaria parasites
and about forty thousand were assessed for um clinical instances of malaria so a
really huge study and again this was led by um lstm
so the results from this were in some ways quite surprising i guess at the time in that um of the the five countries
within each one there were variations into clusters with relatively higher and lower resistance
and the comparison was made between whether there was an impact of this difference
in cluster resistance on whether net users were favored or
or non-users were more favored and the the consistent message coming from the
study was that um even in areas of relatively higher insecticide resistance
net users still had a substantial benefit so suggesting that um the personal
protective effect that’s provided by the barrier net the barrier from the net even if the priority is not killing effectively is
still really really important so this this was slightly at odds with
the the very early results that suggest a major community uh impact from the pyrethrum on bed nets
or apparently so to look into this further um tom churchill
modern modelling studying collaboration with henry ranson’s group and this was looking at to make a
metronome modeling metro analysis from experimental hut studies and these
were conducted across a wide variety of different resistance settings and involving sleepers under bed nets
these looked at blood feeding inhibition which is a commonly recorded measure in in heart trials and also the mortality
difference being that blood feeding inhibition suggests a measure of personal protection the bed’s stopping the mosquito getting a
blood mail whereas mortality indicates community protection something that’s going to suppress the population
and the plot on the right shows how the probability of different events so probability of a mosquito being
killed or blood fed as you move towards the bottom right or whether they’re deserved from fading
and exit the house in the middle against the um
survival link resistance testing and the modelling results showed really quite clearly that
high resistance was required to reduce the personal protective effect but the community effect
can be reduced at far lower resistance levels and this modeling result really helped to tie up
some of the other uh results that we were saying both from the the who impacts trial and the early
results from assemble bay so pass over now to gareth who’ll be talking about um
mechanisms of insecticide resistance thanks dave um in this second part of
the talk um we’ll be discussing how and why we need to delineate
the key mechanisms of resistance in anopheles mosquitoes
could have the next slide please and so the research behind looking into
the mechanisms of resistance has been going on for many years within the department and has involved
many many different partners throughout the globe um and many
past and present members of the vector group have been involved in this work and all these folk together have been at
the forefront of the discovery of these mechanisms in anopheles mosquitoes why do we need
to know what the mechanism of resistance is in the mosquito well once you know what the mechanism of
resistance is you can you can find other chemicals or other approaches
to attack these resistant mosquitoes and so much of the work that’s been gone
on in department in the past 15 years has been looking at the different mechanisms of resistance
anopheles like most insects have got four main mechanisms that are involved in
resistance this includes the modification or the
evolution of changes in the cuticle which slows penetration of insecticides into the
into the mosquito you also get changes in target site so you get mutations in the target site for
the insecticides which stops the insecticide binding and functioning but
keeps that mutation keeps the function of that protein going so the mosquito survives
other work that’s going on in the department so we’re looking at all these different mechanisms more recently the
another mechanism is sequestration and these are these are proteins produced by the mosquito that are able to bind
insecticide before it can reach its target site so there’s some work now going on
on sequestration um but it has to be said most of the work
today has involved looking at detoxification and these these are enzymes which break down
insecticides so the mosquitoes can produce enzymes in different parts of the body which can break down insecticides
and this even though we’re different members of the department are looking at all different aspects of resistance
and the mechanisms of resistance we’ll focus on detoxification enzymes today
and can we have the next slide please
um and it’s it has been known for for a long time that there are three classes of enzymes
three super families of enzymes um that are mainly involved in uh resistance to insecticides these
are glutathione s transferases carboxylase rases and p450s which which will be a main
focus for us today because uh how we’ve discovered their central role in
pyrethroid resistance and so this this map is indicating um
through works with partners how um mosquitoes have been examined by
biochemical aspects of the marquis those have been examined to look at these enzyme activities
and in many cases where you we’re picking up resistance you see elevated activities of these enzymes
and as a as i mentioned the p450 enzymes are
of a white are elevated in um many many different populations
um kind of the next slide the problem with studying these super families of um
detoxifying enzymes is that they in mosquitoes there is in anopheles
mosquitoes there are over 100 different p450s and all together there’s over about 400
different enzymes which may be involved and they all have similar activities so
if you’re trying to find which ones are involved with resistance to pyrethroids in this case it’s quite a
hard job to delineate which which p450s are involved in that breakdown of pyrethroids
and this slide just goes as is showing some of the different tools that have
been used to examine which genes to try and find out which of these genes are involved in resistance
and like most of science the paradigm shifts in knowledge really come through
technology technological advances and the vector group and their partners have been quite at the forefront of
early adoption of these technologies so this includes the transcriptomic analysis
through initially small microarrays and then whole transcriptome arrays
where you’re trying to find out which genes which specific genes are regulated in
individual resistant mosquitoes which ones are produced at higher levels
there’s also movement into slip arrays so looking at single nucleotide polymorphisms
so rather than looking at which ones are up regulated you’re looking for mutations
in the in the the metabolic genes that may be associated with the
resistance so you can study the evolution of um resistance and see if there’s um
common snips amongst these resistant genes and this lends itself to to diagnostics
so once once you can um identify polymorphisms you can get diagnostics and go and have
track and traits to follow the early production of resistance in the field
um we’ve also developed transgenic analysis and in
vitro analysis to look at the function of these individual genes and finally with an advent of
fairly cheap whole genome sequencing it’s now possible to compare resistant mosquitoes from many different
populations to to look at individual genes and how how mutations or duplications of those
genes are associated with the resistance phenotype developing
so all of these tools have been used over a 15-year period to to delineate the enzymes involved
get the next slide please and this slide shows
how the data from multiple different analysis transcriptomic analysis has
been used to narrow down the number of in this case p450 genes that are involved
in resistance so this together with much of the genomic work has enabled us to narrow down the field
of potential genes that p450 genes that are involved in pyrethroid resistance
and here you can see um numbers of different populations of of
um anopheles um taken from areas
um throughout sub-saharan africa and then doing transcriptomics to see which ones are upregulated
and what you can find is there’s a small subset of p450s that are commonly found up regulated in
in the anopheles mosquitoes um this is not to say these are the only
genes that are involved but these these are the the key ones that keep on cropping up
in mosquitoes from different areas um could have the next slide please
and so from all this work we can narrow down and the potential candidate genes that are
involved and in the next couple of slides i’ll show how we can take
these candidate genes and show that they do they are in fact involved in the
resistance phenotype and producing the resistance phenotype and so this first slide shows in vitro
assays to examine the activities of these p450 enzymes
and so this is quite a high throughput technique and so you can take a whole series of
the p 450 genes clone them into e coli and express the recombinant protein
in e coli and then mix this recombinant protein with insecticide in this case the pyrethroids
and then do mass spec and hplc to determine uh do they produce metabolites is there a
metabolism going on of these pyrethroids and to summarize many years work it appeared that some of
the key p450 candidates were sip six p three and
six m two these showed high activity against different types of pyrethroids and also and
have become key metabolic resistance candidates okay on the next slide please um
to take this further and so we’ve shown that [Music]
we were then able to put these individual genes into mosquitoes into susceptible
mosquitoes and over express the different these two p450s to produce mosquitoes that originally
susceptible but just over expressed one of one of these p450s
and so these mosquitoes are producing quite a lot of p450 of in this case m2 there’s six m2
and when we do bio assays on these mosquitoes we can see that just over expressing one of these um
give rise to resistance in these mosquitoes to permethrin and delta methamphetamine
so m2 and p3 6m2 and p3 give resistance to permethrin p3 shows a
lot more activity against um deltamethrin whereas neither seem to work against gdt interestingly the
the p3 also metabolizes a different totally different class of insecticides the carbamates or at least then diet
carb in this case and so we’ve been able to go from hundreds of p450s in the mosquito to
show that a small subset of these are
involved
one key aspect is um the ability to produce molecular diagnostics
and this allows um track and trace and exterminate of um mosquitoes
in an ideal situation and the in vivo and in vitro screening
of um i’ve been of different p450s allows the pipeline to be developed to
screen new insecticides to see if these insecticides are going to be broken down by the enzymes that we know are in
mosquitoes already so we can screen to find the most potent insecticides that are going to avoid these resistant
mechanisms and importantly we can because we know
the p450s are mainly involved in resistance if we can block p450 activity we can
overcome resistance to the pyrethroids and extend the use of the pyrethroids
and so with that i’ll pass on to phillip
[Music] thank you and
so uh next time
having demonstrated the importance of the p450s this uh was exploited because the
people on detoxify was a well-known potent inhibitor of the cytochrome p450
um enzyme so this meant there was a an immediate message to respond with a new type of bed net
next slide and pretty quickly sumitomo investigared and began to
produce nets and treated with pbo plus pyrenees so we still depend on pyrethroids but as
garrosh said we’re extending the lifespan through the use of this inhibitor and
interestingly at the same time this was happening vestigaard um vestige bednet
the primary three only has pbo on the roof which was a decision made
based upon work from our department which showed that in a very crude early experiment
the importance of the roof as a primary location where mosquitoes were in awfully
mosquito landed next slide but that those crude investigations really
didn’t tell us enough it was important to to make a decision on using and treating the roof only but we
expected there was a lot more information to be gleaned if we could only see more of what was happening around the bed net so we worked with university
warwick engineers to develop this tracking system which was portable enough that we could use it
in a hut and and look at the behavior of wild mosquitoes
at a bed net in sub-saharan africa and this early work was done in tanzania
so top left shows the the the tracking system and the top right image b
um shows a probably about 20 second burst of activity of a
number of mosquitoes actually getting through a hole in the net to reach somebody inside and the bottom
of me shows what happens when you track 25 mosquitoes over a period of about one hour next
slide so how does an itn work well this is this was um
this view here is this movie shows what was really quite revelatory at the time
we had never really realized that the mosquito is in flight the holes and she’s not
actually resting on the net so she’s visiting the part of the body above the torso and head
not quite exclusively but predominantly and uh from this we were able to measure a lot
of them detail next slide please so first point here is that a bed net an
itn is a human baited trap without the the human sleeper inside
the nest really has no function it doesn’t attract and doesn’t kill mosquitoes
when it is a fully functional the majority of contacts with the beginner are made above the torso
or the head of the sleeper and in fact this as i said as we saw they don’t rest for
long periods but this constant flight activity of relentlessly trying to get reached the host
means they accumulate contact with it with the redneck surface and a fatal or lethal dose
is received on a fresh net in about 90 seconds possibly less in some cases and
the mosquito comes in attacks right away and in our test of one to two hours in
duration the majority of mosquitoes are killed within 10 minutes of arrival at the bed net
but the important thing here as well is that the the profile of arrival the pattern of the predominant arrival at the top of
the net you can see by these figures on the right um the treaty that on the bottom and the
untreated net with the hosts in the middle the darker patterns are on the roof of the night in all cases
so while the numbers of mosquitoes attacking are reduced or numbers of contacts the attack rates reduce and the the
behavior shifts from high contact to low contact modes the top of the net remains the
predominant area of activity next slide
and that’s shown quite clearly here so these three images show the an untreated unbaited net on the left
an untreated human bait in the middle we see the huge increase in activity and the dominant activity on the roof of
the knife in this case over the entire surface of the net when you put insecticide on the net
the color change shows you as you can see from the key on the bottom that the mosquito activity ends
far earlier in the one hour sequence so the profile is the same across all three different um
treatments if you like and important also as you look above the night itself in the space above the
net there’s also considerable activity and much of what was happening up here were
mosquitoes flying back and forth and what purpose we don’t know but not
making any contact with the bed net itself so we wondered if we could exploit that
behavior by putting simply putting a barrier up there which they were going to bump into next
slide and innovation seems a very strong word
for sticking a barrier in somebody’s in the path of a moving animal but that’s all it amounted to so here
that the top image shows a sleeper with a mosquitoes around the net and adding the vertical panel um
and you can see that on the bottom left it shows in the situ in arcane of faso this was sufficient to
really increase the amount of contact the mosquito made with the insecticide and you can see a couple of tracks there
in the middle showing individual mosquitoes and the left-hand side avoiding it and
then the right there’s the right one which collides with the barrier and with the net itself the advantage of
the roof of the night is that up here the sleeper will never contact us even
in daytime usage it’s out of the way of children it can be sort of ignored
not entirely of course but it does mean you can have a safer net you could potentially use insecticides
that we wouldn’t have been able to use previously on a bed net and potentially
new insecticides that might cost a lot more than the existing pyrethroids
could be used by treating only the barrier perhaps so we did some assays in liverpool
before we moved to a hut trial in burkina faso next night
and so shown here we have them three treatments
so the the green shows the a permanent a permanent two a standard pyrethroid
treated bed mat with a barrier made of the same material and the blue one
is a barrier made out of neonicotinoid which didn’t work very well so we didn’t
continue with it and the yellow and the brown economy show um the yellows are permanent too with an
organophosphate barrier so here we’re using a barrier that would kill the highly resistant vector population we were dealing with
and the brown one is um an untreated bed net with organophosphate on the barrier only
and you can see straight away that the the organic phosphate first of all is very effective because that’s the
insecticide to which the population of mosquitoes are susceptible but what’s remarkable
in some ways is that the untreated knight with the organophosphate barrier is so extremely
efficient in the left-hand side in terms of killing effect and not that we’re advocating untreated
nets but it does demonstrate it within with the correct or potent insecticide the barrier alone can do the job
that the entire bed net was doing in terms of killing on the right side the right figure shows
personal protection so these were bed knits with holes and as you can see that the permanent
tube with the organophosphate barrier is by far the best actually improves on the on the
pyrethroid only p2 in green but you can see that the the untreated
net with holes in it you’re actually a loss in person protection though
this wasn’t quite significant um next slide please so working with them
our colleagues in imperial and they modeled um what the effect would be
like if we have replaced the current permanent tube redness used widely in burkina faso
with the permanent two and these uh organophosphate barriers and you can see the
if continuing with the standard permanent two in gray and it’s you’ve reached that point in a
three years time and the the two other nets are not really significantly difficult but
what’s remarkable again here the untreated net actually is so slightly but not significantly better
than the permanent two so again the the untreatedness plus effective barrier it has the potential
to be um as or maybe even more effective than the current basic permanent two
which is used wide across africa and so since then next slide
we’ve been we’ve gone to a prototype working with vestigaard the bedroom manufacturer to produce a
permanent three um barrier net so this is basically a regular permanent three
with an additional barrier a longitudinal vary running from head to toe this time and and this just contains the same
material as the the blue roof of the bed net so the the reason we did this rather than use any
other insecticides was the idea was that we would get this in approved hopefully
more rapidly by using existing um chemistries and not having to worry about
registration new chemistries but get it and get the concept tested in africa and
as early as possible and uh with that i’ll leave you to the next
speaker
martin put your mic on
thank you gareth um so sorry hopefully by now you’ve got an understanding of how the ls team and
partners lstm team and partners have been developing an understanding of how behaviorally mosquitoes intersect with the net
surface leading to this treatment of insecticide and pdo on the top and also that
mechanistic understanding of resistance but a key component running alongside this was related to
advocacy um what we were very concerned about is that um we needed to sensitize a variety
of stakeholders sort of who and the other normative bodies industry partners um the scientific and
public health communities as a large to the the inherent dangers of insecticide resistance as
dave spoke about earlier pyrethroid nets at the point were used as a monotherapy and so as we
know with amr the emergence of resistance is a major threat and we needed to get the community to start to think about
how what’s the strategy for transitioning and so we use that with it with variety of sort of opinion pieces
um and also sort of use case scenarios uh trying to sensitize the community about how resistance could potentially
impact um public health impacts of malaria and running alongside that we were
generating the evidence base so these are some um a cochrane review led through the lstm by
kathleen and hillary and colleagues and in in association with the cochrane infectious disease research group so
they were collating the evidence for what actually is the impact of pbo and pyrethroids used in concerts
on entomological and epidemiological indicators of malaria and i appreciate the slide on the font
on this are very small but the take home here is that they identified around 180 190 different studies which investigated
the use of pbo and pyrethroids on a variety of outcomes both entomological and epidemiological
and only 15 of those met the criteria for inclusion in this review and only one of those was actually an
epidemiological trial so the see the outcome of this review is actually they found strong evidence on
that in areas of high insecticide resistance pbo nets resulted in an increase in mosquito mortality and
reduced blood feeding rates and and we could infer that it’s likely to therefore have an impact on malarial transmission rates
and the one clinical study which was that led by an attached approach off which was conducted in mohasa
in sorry malabar in tanzania showed that there was a reduction in malaria prevalence in
those communities where pvo nets were used in and the control group there was
standard nets so there was some emergent epidemiological evidence of impact um
can i go back one please dave um and so alongside this um you saw earlier the
work that tom churchill and hillary’s and colleagues conducted looking about use cases for
um pbo nets and so the lstm groups started to to work with who to
development the evidence and interim recommendations for for where we may want to think about deploying these
sort of second generation nets um and so the ento evidence the cochrane
review and and natasha prosper’s trial um and the advocacy from some lstm staff
members resulted in a who coming out with an interim recommendation that these pyrethroid pvo nets were
a new class of insecticides and that’s particularly important because at present before this point they are bundled in
with nets as a whole and so there was no incentive for manufacturers to move into that market because there’s no sort of differential
purchasing power for the two net types this is only an interim recommendation because w
stipulated that they required evidence from two epidemiological trials of the impacts of pbo
before they could move to full recommendation and sort of full classifications pbo was a as a new net type which had properties
which would delay the emergence of resistance um and so that data
was generated from a second uh trial and this was conducted in association with idrc
london school ministry of health in uganda ucsf and it’s funded by we see the
funders across ivcc and the gates foundation and this was a cluster randomized control trial which was embedded within
a universal coverage campaign conducted by the the ministry of health of uganda and so
essentially what it’s again trying to do is evaluate both the epidemiological and entomological impact of um pdo nets
versus withstand nets and the primary outcome here was looking at parasite prevalence in
children between the ages of two and ten we also looked at anemia rates in the subset of children
and also um vector density as a sort of a corollary of hopefully the impact we were hoping to
see so it’s it’s notionally a forum trial though it was powered for
two arms so essentially a pbo versus non-pvo comparison and i think it’s important to point at the randomization process um
we stratified it both on the east and the west of the country because work led through by dave wheatman had
identified p450 mediated resistance in the east of uganda but we didn’t really know much about what was going on in west uganda at the
time so it’s important showing how our knowledge of the mechanisms has been important for informing epi trials and
something similar is now happening in the democratic republic of congo in in in another trial there
so essentially it’s a a two-on trial but we have two different manufacturers providing nets we have non-pbo nets
from olisette and their pdo olisette plusnet and from investigate france and we have
permanent two and permanent three permanent three being the pbo treated net so they were distributed run by as part
of universal coverage campaign um what you can see on the extreme right there is that there are approximately
16 million nets distributed to 104 health sub districts um across the
uganda and those are also appearing in the sort of the colored hsds in the central map
we have balance between our pvo and non-pdo arms around 52 um around 52. um hst is receiving the
pbo or non-pvo and what we’re doing is visiting the communities on a six monthly basis at baseline
6 12 18 and 25 months looking at parasite prevalence in uh 10
enumeration areas um and so 20 that’s 50 health households five households per enumeration area and
in 20 of those households we’re also doing vector density measurements using proca pack sort of aspirators
um again referring back to sort of dave’s talk he’s showing there that the um parasite
prevalation decreased across both ends of the trial so we’re looking at as you move across this box whisker
plot from baseline 6 12 and 18 months and you can see it in the red is non-pbo and blue is pvo
you can see that there’s a mark falling parasite prevalence at 6 12 and 18 months so there’s a there’s
still an impact of using nets as dave was saying it may well be that they’ve lost their their community effect with certain that personal
protection uh at least some degree of that personal protection remains but what’s key here is that you can see
when you compare it 6 12 and 18 months parasite prevalence is significantly lower in the pbo arms and so
just to put some numbers on that if we look at parasite prevalences so this is a ratio of prevalence in pvo versus non-pvo communities and what
we can see is that parasite prevalence fell by about 26 in those pbo communities and that effect
was uh seen at 8 12 18 and although the data on published yet also 25 months so we do see a prolonged
impact of pvo seeing much lower probability significantly that prevalences in those pbo
users using communities um and just for those of you an informatical bent this data was
replicated by the the anopheles density so again same six 12 and 18 months time point
we saw between an 86 and a 75 reduction in the number of monopolies resting in in houses so good
evidence of entomological impact as well so so the the the results of this is
essentially now we have the evidence from a second epidemiological trial of the enhanced benefits of pbo nets so pbo
coming out overcoming p450s in an area of relatively high pyrethroid resistance
where we know it’s mediated via by p450s there is a significant advantage to those communities who are using pvo nets
versus non-pvo nets and so now we have the second evidence base for an epic trial to move
or help who move towards making that full recommendation around the use of peos
so with that i thank you and i pass on to hillary
thank you martin so next please dave so as a result of the work that
we’ve been doing um over the past um 19 years i think now on building and synthesizing the
evidence um on the efficacy of of pbo nets or leading up to
to the development and the um building the evidence base and on the ethics of the nets and i work on
mapping the distribution and the impact of insecticide
resistance and the um combined with work with who and other policy making bodies
this has led to the deployment of pbo nets in africa to combat pyrethroid
resistance so you can see here this this graph on the slide here
shows the um proportion of nets the total net distributions uh
deliveries to sub-saharan africa over the past three years and in pink that’s indicating the
proportion of those nets that are pyrethroid pbo nets so approximately somewhere between 150 and 200 million
nets are distributed to africa every year and in um in the first three quarters of
2020 18 of those nets were um pbl nets about 29 million pbo nets have
been um deployed in in africa so far this year and to combat pyrethroid
resistance now um pyruvate pbo nets are seen um by many as being sort of an interim
solution because as pyrethroid intensity of pyrethroid resistance increases there will likely come a point
at which the um pbo can no longer synergize the pyrethroids and
and it’s that’s been shown in the models and there’s some evidence from from uh laboratory studies although not
yet seen in the field but they’re seen as essentially a sort of stop gap um while we get new
nets um on the market and you can see on this graph here that in black there’s already some of those
nets being used in africa and these are known as joule dual ai or dual active ingredient
nets that contain pyrethroids so all nets still contain pyrethroids because they’re fast and
knock down effect um but also a second insecticide so it might be chlorofenapere in the
case of interceptor g2 nets or other nets have insect growth regulators
on them so there’s already some um some new nets
that are um with more than one insecticide that have been uh used or evaluated in the field
deployed and evaluated as as they’re used um you can go to next please
um the work of lstm though is looking to to ensure the sustainability of the um
net market so we have developed a pipeline for screening new compounds coming from industry partners and
working closely with ivcc so we have the the light facility that
um hosts the largest collection of pyrethroid
um resistant or populations of mosquitoes that are are resistant to um a
different chemistries um and um they
so uh um and so we can use these um in vivo screens to determine whether um uh the the mosquitoes
uh whether these new chemistries will actually kill resistant mosquitoes
and then we have the in vitro screening and pipeline that gaf has already described where we can look and see
whether the individual enzymes are elevated in resistant mosquitoes can metabolize these new
chemistries and potentially cause cross-resistance and then we have um the transgenic
mosquitoes where we can actually test in vivo to see whether um the the new
chemistries are um can confer across resistance to uh um there’s already existing
cross-resistance and this is also um underpinned by a an increasing number
of behavioral assays that um that philips group have developed in order to
to see how the mosquitoes respond to these new chemistries either alone or in
combination with pyrethroid nets so next please so this screening
pipeline is proving to be very useful for industry partners as it
can provide this early warning system for um indicating whether there’s any
potential cross-resistance new chemistries and it’s actually already led to the changing in priorities of um
but from some of the leading inside manufacturers to change their lead chemistry and identify a more effective backup
compound um for after following this pipeline and finding potential resistance
mechanisms so next please so i hope that um
these these presentations today are sort of given a snapshot of the work in the in the research programs across
the department and shown how that there that we’re working together to try
and ensure that the future viability of of bed nets because bed nets um as
you heard earlier from dave they’ve really proved to be one of the most effective non-pharmaceutical public
health interventions globally and it’s really critical for the future success
of malaria control that we can preserve the efficacy of this this important tool
so i sort of sort of work from these multiple research groups across the department
only some of which have have presented today um is is really ensuring that we’ve got
continued innovation in this space and using an interdisciplinary approach to and working with with stakeholders
and with partners across the globe um to maximize the research uptake uh um
and ensure that we’ve got continued continue new innovation in the bednet space so finally then
the last slide i’d just like to to repeat martin’s comments at the beginning and acknowledge members of the vector
department past and present this work has been going on for many many years and involves it has
involved a huge number of different staff in lstm and of course also would not be
possible at all without our large numbers of partners our funders but also key to this are many southern
partners that we’ve worked with over the years um to to deliver that on this research
so i’ll end there and okay martin thank you uh
thank you all the presenters and um had a little bit of a technological glitch there hopefully you you may have lost the present to you
hope that didn’t um impact your enjoyment so we still have uh five minutes for questions
so uh if you if you you want to ask a question um please um edit it into the the
chat box and we’ll do our best to get it to okay so graham graham small has written
in um i felt like a dj to what extent can transgenic lines expressing particular
mechanisms of resistance be used not only to confirm the role of these mechanisms in cross-resistant
but also their fitness cost in the absence of insecticide selection so i guess that’s a question for you gareth about the select and fitness
effects of these mutations in transgenics yeah thanks martin well that’s yeah that’s a great question graeme
um the transgenic lines we’re going to need quite a lot of optimization to look at
fitness costs so it’s quite feasible these days to knock out individual genes and so you
could imagine knocking out some of the um some of the p450s and seeing what
effect that has on resistance but also you can do fine mutagenesis
and change the some of the target sites and then just those small modifications
you could look at the fitness cost of those at the moment the lines we have overexpressed
to a large extent and so of of the different people 50s we’ve got and so with those
they’re going to have some fitness costs which will be probably up and above what they they have in the wild where
the expression is lower and so you can you could fine tune over expression to specific tissues
potentially to look at that but that with the ones we have at the moment it’s it wouldn’t really be feasible
or fair to look at the the effect of of um on fitness but it
you can you could do something like that for target site mutations quite easily with
crispr not crispr mutagenesis which is what we’re doing at the moment so
do you want to take on that and talk about observation studies in the wild and how you can look at adaptive around vgse for example
so i think uh oh oh sorry um we got another question so for dr
whitman uh do you know why the resistance in western africa seems so much stronger and more prevalent
is it down to increase bed net use or is that something else um so i don’t think there’s any evidence
that it is actually down to um increased bed net use or or distribution
um the bed nets are not the only selective force that
has led to insecticide resistance or pyrethroid resistance and certainly what preceded the um the
onset of strong pyrethroid resistance which was particularly noticeable in in west africa or to some extent in
sudan as well was really quite strong ddt resistance so um
it could suggestion would probably be that there’s been a relatively bigger impact
of agricultural selection in west africa with a long use of ddt given that’s very
cheap and quite for many years anyway it’s quite effective in agriculture selected for insight mutation mechanisms
in particular which um very effective for ddt resistance but also have carryover
effects for pyrethroid resistance not as strong as for ddt but gives that
that sort of leg up of resistance in west africa which has then been sort of taken on and
expanded particularly with metabolic resistance um by the distribution of pyrethroid
nets so i think it’s almost more just that west africa had a bit of a head start um over over others rather than
necessarily a greater selection from their bets
okay are there any other questions we haven’t got anything coming through on the chat
um five seconds uh okay so um i guess it’s almost two
o’clock so um really just to to thank you all for your attendance virtually and um thank all the
presenters and just to to again fully acknowledge that this work is is is part of lstm’s
collaborative efforts in developing um translational tools for public health impact
um and really just to thank all our partners past present and hopefully future both here in the uk and
in the global south so thank you all um and i hope you enjoyed all you found that informative thank you
ESSENTIALs
The ESSENTIALs project is the latest programme led ny the Vector Biology Department, developing, performing and evaluating new entomological assays to determine the performance of new classes of nets against different mosquito populations across Africa.
ESSENTIALs will determinine whether a combination of entomological monitoring and mathematical modelling, could be used to predict the efficacy of future new classes of ITNs without the need for lengthy and costly clinical trials.
Partnership for Increasing the Impact of Vector Control
Supported by long term mentorship from LSTM and rigorous evaluation of the capacity needs in-country, this partnership will generate new knowledge and tools, strengthen research capacity, and reinforce links between researchers and policy-makers, leading to reduced disease burden and increased resilience for responding to outbreaks.