Category Archives: Mosquitoes

Manufacturing Mosquito Nets ‘At Home’

The technology of insecticide treated nets (ITNs) to prevent malaria has been around for over three decades. ITNs have evolved from a process of semi-annual soaking and impregnating nets with a safe insecticide at the household or community level to long lasting insecticide-treated nets (LLINs) where the insecticide is integrated into the nets during the manufacturing process. The challenge has always been guaranteeing enough currently treated nets to cover the population and impede malaria transmission.

IMAG0170Recently Rwanda announced its intentions to establish LLIN manufacturing in-country. The Ministry of Trade and Industry has begun screening of bidders. The government’s main rationale for this move is projected the need for a large and continuous supply of LLINs in the country through 2020, “making it a prudent to set up a production plant in the country.” When this information was shared with our malaria/tropical health update mailing list a number of readers expressed interest and hope that their own governments would follow suit. This post provides some background for readers to consider.

The idea of locally made mosquito nets is not new. MacCormack and Snow documented that, “95% of people were already sleeping under locally-made DSCN5582nets,” in The Gambia in the 1980s. Likewise in Burkina Faso it was common to find nets made from imported materials or local cotton that were sewn by local tailors.

The idea of drawing on the combination of local or regional textile and chemical industries to produce an ITN kit containing both net and approved insecticide for home/community soaking was tested in several countries by the USAID sponsored NetMark project between 1999–2009. Although the project made ITNs available at reduced prices and resulted in gains in  awareness, ownership, and use of nets, “none of the countries reached the ambitious Abuja targets.”

NARCHOct03 012Even at reduced prices the ITNs made available through this commercial sector approach were still more expensive than most families could afford. In addition partway through the project the emphasis shifted from local products to imported LLiNs leaving a leaving a very bitter taste, particularly in Nigeria with its large industrial sector, in mouths of the textile and chemical partners who during malaria partners meetings at the time expressed a sense of betrayal.

A-Z Olyset Commercial BagTalk arose in Nigeria about the potential for starting LLIN production in the country, but no one stepped forward with funding or technical assistance. In the meantime, on the other side of the continent, A to Z Textiles of Tanzania entered into a partnership and by 2003 LLINs were being produced in Arusha.  Sumitomo Chemical provided a royalty-free technology license to the company for its Olyset LLINs. “By 2010, Olyset Net production capacity (at A to Z) reached 30 million LLINs per year, creating 8,000 jobs; more than half of the global Olyset Net output and an outstanding contribution to the local economy.”

Over the years A to Z Textiles were hard pressed, just like the few other LLIN manufacturers, to meet global demand. Over the period, the focus changed from protecting young children and pregnant women to universal coverage of the population. Also research and actual use found that the lifespan of an LLIN was not the 5 years as initially projected, but more like two. These factors meant that supply could rarely meet demand for regular replacement nets. No wonder Rwanda wants its own LLIN factory!

ITNs Use TanzaniaIn addition to supply issues, does local availability of LLINs make a difference in fighting malaria? Regular studies by the Demographic and Health Survey group of USAID in Tanzania found that ITN use increased over time by children below five years of age. The most recent survey still shows that the 2010 Abuja target of 80% was not met (let alone a target of universal coverage), but the findings hint at the importance of having locally available LLINs.

Let’s wish Rwanda success in establishing its LLIN manufacturing capacity. For colleagues in Nigeria and elsewhere who have expressed interest in this issue, your advocacy work is just beginning.

 

World Mosquito Day Is Not Just About Malaria

World Mosquito Day Block the BiteOur colleagues at Roll Back Malaria remind is that 20 August is marked annually as World Mosquito Day since doctor Sir Ronald Ross first identified female Anopheles mosquitoes as the vector that transmits malaria between humans. This year, 2015 is the 118th annual observance.

It may seem obvious to state, but while malaria is carried by mosquitoes, not all types of mosquitoes carry malaria. And more specifically our control measures for combating the anopheles mosquitoes that carry malaria are not specifically aimed at aedes or culex. This has not stopped public health workers in the field, and health worker trainees in the classroom from broadcasting messages to the public implying that the control and destruction of any mosquito will prevent malaria.

In terms of health communication, if we convince people that any mosquito carries malaria, but institute measures like long lasting insecticide-treated nets and indoor residual spraying aimed at anopheles mosquitoes, we may lose some credibility as people will still see other types of mosquitoes flying about. And then when people develop another febrile illness from bites of those other mosquitoes, they may not differentiate illness types, but say our interventions do not work.

Old poster on malaria-mosquito presentionThe conflation of all mosquitoes with malaria is seen clearly in the image at the right from a common malaria poster. The dirty gutters may contain culex larvae; the cans and bottles may contain aedes larvae. Obviously none of these mosquito species is good for human health, so can we achieve clarity in health communication about mosquito-borne disease on World Mosquito Day and thereafter?

We often forget that people in the community are quite observant of their environment; sometimes more so the the public health inspectors who try to teach them about ways of preventing malaria by reducing mosquito breeding. Villagers deal with mosquitoes on a daily basis and can distinguish the coloring and posture of the different species.

Instead of telling people what to do, it would be more helpful for public health workers to engage in dialogue with people to learn what they know about different types of mosquitoes and different forms of febrile illness. Maybe by learning first from the people, health workers can then become better teachers about integrated vector management.

PS – maybe we can also educate the mass media to stop putting pictures of Aedes aegypti on their malaria stories!

Moving toward Malaria Elimination through Integrated Vector Control

As malaria control efforts are scaled up and sustained, we expect a drop in prevalence to the point where Ministries of Health may no longer devote a whole operational unit – a National Malaria Control Program – to the disease. This does not mean that malaria programming stops, otherwise countries would experience a resurgence.

Pf_mean_2010_NAMWe can learn from countries like Namibia and Rwanda that are on the frontline of malaria elimination efforts. In Namibia, “The National Vector-borne Disease Control Program (NVDCP) at the Namibia Ministry of Health and Social Services effectively controls the spread of malaria with interventions such as spraying dwellings with insecticides, distributing mosquito nets treated with insecticides, using malaria tests that can give accurate results within 15 minutes, and distributing medicines that kill the parasite.”

The NVDCP falls under the Primary Health Care Services Directorate with its five divisions: Epidemiology; Public and Environmental Health Services; Family Planning; Information, Education and Communication (IEC); Disability Prevention and Rehabilitation. Contrary to what one might think, malaria activities are not lost, but are teaming up with international partners like UCSF Global Health Group’s Malaria Elimination Initiative, the Novartis Foundation for Sustainable Development, the London School of Hygiene and Tropical Medicine, the Clinton Health Access Initiative and the Bill & Melinda Gates Foundation.

In Rwanda we now have the Malaria and Other Parasitic Diseases Division (MOPDD) within the Rwanda Biomedical Center within the Ministry of Health. Major donors like the US Presidents Malaria Initiative are supporting the MOPDD to achieve Rwanda’s national strategic plan of reaching the pre-elimination stage by 2018.

PAMCA logo smEven if a country is still highly malaria endemic, it is important to ensure that integrated vector management is taking place so that in the future the country’s malaria efforts will have a strong ‘home base’ to approach elimination. This is why the opportunity presented by upcoming the Second Pan-African Mosquito Control Association is important.  According to the organizers …

The 2nd Pan African Mosquito Control Association (PAMCA) Conference themed, “Emerging mosquito-borne diseases in sub-Saharan Africa” will be held in Dar-es- Salaam, Tanzania, from 6-8th October 2015. The 2nd Annual PAMCA conference will build on the momentum generated following the successful hosting of the 1st PAMCA Annual Conference in Nairobi, Kenya. The main objective is to bring professionals, students, research institutions and other stakeholders working in mosquito control and mosquito-borne diseases research together under common agenda to discuss the challenges of emerging and re-emerging mosquito-borne diseases across the African continent. The conference will seek to illuminate this subject of emerging mosquito-borne diseases and develop progressive resolutions that will serve as guidelines to tackling this challenge going forward. The conference will also offer a platform for participants to exchange knowledge and ideas on mosquito control, forge new collaborations and strengthen existing ones.

We hope that colleagues will submit abstracts soonest focusing on the various conference themes:

  • Emerging mosquito-borne diseases: new Public Health challenges
  • Mosquito resistance to insecticides and population genetics
  • Translating research into practice: Linking interventions to mosquito behavior
  • Multidisciplinary approaches to tackling mosquito-borne disease
  • Mosquito biology & ecology
  • Impact of climate change on mosquito control

 

Indoor Residual Spraying – not a one-trick pony

Jasson Urbach and Donald Roberts claim that the malaria fight is hurt by flimsy anti-DDT research as they opine in Business Day (South Africa) on 9th May 2014. They are particularly exercised by an article on possible DDT effects on bird egg shells. Despite the controversy sparked by the article, there is no evidence that any individual country nor WHO itself is recommending removal of DDT from the arsenal of chemicals used in indoor residual spraying (IRS) to control malaria.

PMI: http://www.pmi.gov/how-we-work/technical-areas/indoor-residual-spraying

PMI: http://www.pmi.gov/how-we-work/technical-areas/indoor-residual-spraying

There is something about DDT that raises hackles among proponents and detractors. But malaria vector control planners do have choices. WHO recommends 14 insecticides for indoor residual spraying against malaria vectors as seen below in an list updated on 25 October 2013:

  1. DDT
  2. Malathion
  3. Fenitrothion
  4. Pirimiphos-methyl
  5. Pirimiphos-methyl
  6. Bendiocarb
  7. Propoxur
  8. Alpha-cypermethrin
  9. Bifenthrin
  10. Cyfluthrin
  11. Deltamethrin
  12. Deltamethrin
  13. Etofenprox
  14. Lambda-cyhalothrin

Ironically DDT tops the list.  No chemical is 100% safe, so the caveat with any of these chemicals is that, “WHO recommendations on the use of pesticides in public health are valid ONLY if linked to WHO specifications for their quality control. WHO specifications for public health pesticides are available on the Internet.

Interestingly, a bigger concern should be the potential for mosquitoes to develop resistance to any of the above mentioned insecticides.  This is why it is important to avoid putting all our eggs – soft or hard shelled – in one basket. Ideally insecticides should be rotated often to prevent resistance from developing.

Decisions to embark on IRS and choice of insecticides should be based on national and sub-national environmental and epidemiological characteristics, not emotional attachment to any particular product.

Know Your Mosquitoes

Recently we have seen some online discussion about mosquitoes biting 24/7, and while this is true, it is not all species of mosquitoes that bite all the time – only that anytime during the day/night one might be bitten, but by different types of mosquitoes, carrying different diseases at different times. Below is a chart that tries to draw some of the distinctions among the different types of mosquitoes.  It is not all inclusive. Some references are listed at the end. Finally there is an abstract about possible changes in malaria mosquito biting behaviors, although we should use caution in that this has not been verified universally.

mosquito-types-sm.jpg

Reference Links

  • How Mosquitoes Work. http://science.howstuffworks.com/zoology/insects-arachnids/mosquito1.htm
  • Be vigilant to different mosquito breeding grounds. http://www.fehd.gov.hk/english/safefood/images/Pestnews_9e.pdf
  • Biological Notes on Mosquitoes. http://www.mosquitoes.org/LifeCycle.html
  • Mosquito. From Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Mosquito
  • Anopheles Mosquitoes. http://www.cdc.gov/malaria/about/biology/mosquitoes/
  • Differentiate Culex, Anopheles and Aedes Mosquitoes. http://profwaqarhussain.blogspot.com/2012/10/differentiate-culexanopheles-and-aedes.html
  • Flight performance of the malaria vectors Anopheles gambiae and Anopheles atroparvus. http://www.ncbi.nlm.nih.gov/pubmed/15266751

Effects of changing mosquito host searching behaviour on the cost effectiveness of a mass distribution of long-lasting, insecticidal nets: a modelling study. Malaria Journal 2013, 12:215 doi:10.1186/1475-2875-12-215. Olivier JT Briët (olivier.briet@unibas.ch). Nakul Chitnis (nakul.chitnis@unibas.ch)

Abstract: Background The effectiveness of long-lasting, insecticidal nets (LLINs) in preventing malaria is threatened by the changing biting behaviour of mosquitoes, from nocturnal and endophagic to crepuscular and exophagic, and by their increasing resistance to insecticides. \

Methods: Using epidemiological stochastic simulation models, we studied the impact of a mass LLIN distribution on Plasmodium falciparum malaria. Specifically, we looked at impact in terms of episodes prevented during the effective life of the batch and in terms of net health benefits (NHB) expressed in disability adjusted life years (DALYs) averted, depending on biting behaviour, resistance (as measured in experimental hut studies), and on pre-intervention transmission levels.

Results: Results were very sensitive to assumptions about the probabilistic nature of host searching behaviour. With a shift towards crepuscular biting, under the assumption that individual mosquitoes repeat their behaviour each gonotrophic cycle, LLIN effectiveness was far less than when individual mosquitoes were assumed to vary their behaviour between gonotrophic cycles. LLIN effectiveness was equally sensitive to variations in host-searching behaviour (if repeated) and to variations in resistance. LLIN effectiveness was most sensitive to preintervention transmission level, with LLINs being least effective at both very low and very
high transmission levels, and most effective at around four infectious bites per adult per year. A single LLIN distribution round remained cost effective, except in transmission settings with a pre-intervention inoculation rate of over 128 bites per year and with resistant mosquitoes that displayed a high proportion (over 40%) of determined crepuscular host searching, where some model variants showed negative NHB.

Conclusions: Shifts towards crepuscular host searching behaviour can be as important in reducing LLIN effectiveness and cost effectiveness as resistance to pyrethroids. As resistance to insecticides is likely to slow down the development of behavioural resistance and vice versa, the two types of resistance are unlikely to occur within the same mosquito population. LLINs are likely cost effective interventions against malaria, even in areas with strong resistance to pyrethroids or where a large proportion of host-mosquito contact occurs during times when LLIN users are not under their nets.

——–

Finally please note that one malaria intervention alone will not solve our problems so we need to apply a mix that includes Nets, Indoor Residual Spraying, Diagnosis with mRDTs, Appropriate treatment with Artemisinin-based Combination Therapy, Intermittent Preventive Treatment, one day a vaccine and others …

Malaria Vector Bionomics During the Dry Season in Nchelenge District, Zambia

Smita Das and Douglas E Norris of the Johns Hopkins Bloomberg School of Public Health Department of Molecular Microbiology and Immunology and Johns Hopkins Malaria Research Institute have written our guest blog posting based on a poster they presented at the recent JHU Global Health Day.

picture1-smita-das-and-douglas-norris-jhmri-sm.jpgAs part of the International Centers of Excellence in Malaria Research (ICEMR) in Southern Africa project, mosquito collections are being conducted in Nchelenge District in Luapula Province, Zambia. Nchelenge experiences hyperendemic malaria despite continued implementation of indoor residual spraying (IRS) and long-lasting insecticide nets (LLINs) as control measures.

Center for Disease Control light trap (CDC LT) and pyrethroid spray catch (PSC) collections performed during the wet season in April 2012 revealed the presence of both Anopheles gambiae s.s. and An. funestus s.s. Both species were highly anthropophilic and the Plasmodium falciparum sporozoite infection rate in An. funestus was higher compared to An. gambiae.

In the dry season collections, An. funestus continued to be the dominant species with even fewer An. gambiae caught compared to the wet season.  Due to the abundance of An. funestus and high human malaria infection rates in Nchelenge, it is predicted that the human blood index and entomological inoculation rate for An. funestus is higher than that of An. gambiae in both seasons.

The multiple blood feeding behavior and insecticide resistance status of both malaria vectors will also be explored as this can give us an idea of estimating the transmission potential of these mosquitoes. The vector data in Nchelenge present unique opportunities to further our understanding of malaria transmission and the implications for malaria control in high-risk areas.

Modeling Malaria – getting a handle on vectors

Models represent reality but the closer they come to reality, they better they are at helping us plan.  A session at the American Society of Tropical Medicine and Hygiene yesterday addressed the modeling process for vector control.

VECNet is developing the capacity to take data from multiple sources to tailor vector populations and behavior to local situations. Such models need to consider vector bionomics/population variables, weather/climate/environment, and effectiveness of deployed vector control strategies.

a-stephensi-map-project-2.jpgModelers encourage us to think beyond existing malaria control strategies and consider a varierty of mosquitoe behaviors beyond direct feeding on humans and immediate resting thereafter. Such understandings can lead us to ask whether new interventions could be directed at other vector bevahiors such as …

  • laying eggs (oviposition)
  • feeding on sugars
  • seeking hosts
  • mating
  • resting generally

In short, we were challenged to look at aspects of vector biology that have been ignored or unknown in the past.

nga_gambiae_ss-sm.pngThe MAP project out of Oxford is also beginning detailed mapping of vectors by region and utlimately my country.  Globally there are 41 dominant vector species, so the work ahead is immense, but some mapping has started with three in a program called Risk Mapper.

The session also included product impact estimation. This should help program planners decide on hypothetical outcomes of investments in different existing interventions and even consider possible outcomes were new interventions developed to address the other aspects of mosquito behavior outlined above – e.g. traps, repellents.

The modeling process requires a lot of data that needs to be updated as control interventions proceed. Such data requires a strong corps of entomologists and health information systems staff that many countries lack.  Hopefully modeling efforts will also include these elements of human resource development.

Ivermectin against malaria: novel idea, but can it be scaled

Several news sources have picked up on a new article in the American Journal of Tropical Medicine and Hygiene that reported when communities take annual ivermectin doses for controlling onchocerciasis and lymphatic filariasis, they may also be protecting themselves or their neighbors from malaria. Specifically the researcheds reported that ivermectin Mass Drug Administration (DA) “reduced the proportion of Plasmodium falciparum infectious Anopheles gambiae sensu stricto (s.s.) in treated villages in southeastern Senegal.”

The process works the same way that ivermectin treats head lice in that when insects take a bloodmeal from someone who has swallowed the drug, the medicine kills the insect. Sarah Boseley points out that some of the attractions of ivermectin are that it has been safely used in humans for 30 years and that it is inexpensive.

The Merck company has been supplying ivermectin (under its brand name Mectizan) free through the Mectizan Donation Program (MDP) to the African Program for Onchocerciasis Control for 16 years.  Over time coverage has reached over 100,000 villages in 18 African countries. Annual distribution in Africa contrasts with more frequent distribution in the smaller focal transmission points in Latin America where the diseases has almost been completely eliminated.

MDP reports that, “Currently, more than 70 million treatments are approved for onchocerciasis in Africa and Latin America and 80 million for lymphatic filariasis in Africa and Yemen each year.” That is a lot of free medicine and one of the largest and far reaching corporate social responsibility programs known.

Back to Senegal – the researchers found that the effect of ivermectin on mosquitoes lasted up to two weeks. They also raise the question of whether more frequent ivermectin distribution in onchocerciasis or filariasis MDA communities during the main malaria transmission season would be feasible.  Possibly a small scale operations research proposal could be submitted to the Mectizan Expert Committee.

cdi_report_08.jpgOf importance is the fact that the Community Directed Treatment with Ivermectin (CDTI) approach utilized by APOC projects has been tested and found quite accommodating to the addition of other Community Directed Interventions (CDI) such as community case management of malaria, ITN delivery and use monitoring and Vitamin A distribution among other basic health services.

The availability of tens of millions of exra ivermectin doese in communities where MDA is already occurring is unknown at present, let alone the feasibility of starting free ivermectin in malarious areas that have no onchocerciasis or filariasis.  In addition, for onchocerciasis, the idea time for distribution is before the rainy season so that microfilariae loads are seriously reduced before the black fly vectors emerge. This timing may not benefit malaria control fully.

Regardless of the unknowns, it is encouraging that people are thinking of synergistic ways to control the various endemic diseases that inflict suffering on poor communities.

Mosquito Mis-Match

dscn3027sm.jpgVisiting a clinic in Binji Local Government Area of Sokoto State Nigeria today we saw the attached poster.  In fact there were three copies posted on walls in the public waiting areas. It was not clear whether this poster was intended as a job aid (reminder) for the health staff or a public education poster. If the latter, there is too much happening on the poster for it to be a good BCC material.

The main concern about this poster is that it implies that all mosquitoes are responsible for malaria. The pictures in fact implicate other mosquitoes such as the culicine species and Aedes aegypti.  Covering pots and getting rid of old cans and bottles will prevent mosquito breeding, but more than likely will prevent yellow fever, not malaria.

Clearing dirty gutters can prevent breeding of culex and the various viral diseases they carry, but not malaria. Yes, we want people to prevent mosquito breeding generally, as there appear to be no ‘good’ mosquitoes, but promising that preventing breeding of non-anophelene species will prevent malaria is misinformation.

We can be straightforward with the public and say there are many types of mosquitoes, and they carry many different diseases. It helps to prevent the breeding of all, but as different ones breed in different places, we can not expect every action will result in the prevention of malaria. We also need to stress that not all fevers are malaria, and we need testing to ensure the right medicine is given, not ACTs for dengue or west nile virus (which are carried by the other mosquitoes – adding to the public’s confusion).
At present there are two major vector control measures recommended by the RBM community – insecticide treated bednets and indoor residual spraying.  A few places have been successful with limited larviciding, but since breeding sites are ubiquitous, this is an almost never ending activity.  Lets focus on what is feasible.

Finally we need to recall that when we talk to local people about mosquito breeding, they may not understand what we mean by mosquito larvae.  Among the Yoruba, for example, these larvae are called tanwiji and are thought to be a different animal from actual mosquitoes themselves.  People have been confused by attempts at BCC on larval control thinking that health workers are saying that swallowing the tanwiji causes malaria.

Again, for now lets make headway with our treated nets and appropriately targeted IRS.  If we can achieve those coverage targets, the 2015 Millennium Development Goals will be achievable.

Mosquitoes also do not want to be infected

When the small copepod or cyclops swallows a guinea worm larva, seeing it as food, several things may happen as the larva develops – either someone swallows the cyclops when drinking the pond water, continuing the guinea worm cycle, or the larva grows so large that the cyclops is destroyed. Control measures have included putting temephos in ponds to kill the cyclops. All of these mean death for the cyclops. None of these alternatives bode well for the cyclops.

dscn0333-sm.jpgIt is not surprising to learn, as reported in PLoS Biology that disease vectors or intermediate hosts themselves are not very ‘happy’ to get infected with disease organizms that are later passed to humans. In essence Anophleles gambiae mosquitoes have genes that encode ‘essential components of the mosquito immune defense against malaria parasites.’

Furthermore, these genes are not static. Rottschaefer and colleagues report that, “Our data indicate that functionally variable APL1 alleles are evolutionarily maintained to combat diverse pathogens, perhaps including but probably not restricted to Plasmodium species.”

Most malaria control measures to date that involve the vector are aimed at killing, repelling or sterilizing.  These range from the newest, a toxic sugar bait, to the widely used instecticide treated bednets. There is exploration into a human vaccine that would prevent the parasite from developing in the mosquito.

While mosquitoes are certainly a nuissance in their own right, they are not necessarily the main enemy in the fight against malaria. We should certainly continue using bednets and indoor spraying and in appropriate cases larviciding, as major gains have been made from these. It would be hard though to completely eliminate the vectors.  Therefore continued research is needed on vaccines and genetic modifications that make mosquitoes a hostile host to plasmodium species.