Category Archives: Mosquitoes

Malaria, Dengue, Mosquitoes – evolving in the urban environment

As the world increasingly urbanizes, we need to address the role of urban ecosystems and the evolution of disease vectors and organisms.  Marina Alberti and colleagues explained that …

“Recent studies show that cities might play a major role in contemporary evolution by accelerating phenotypic changes in wildlife, including animals, plants, fungi, and other organisms. Many studies of ecoevolutionary change have focused on anthropogenic drivers, but none of these studies has specifically examined the role that urbanization plays in ecoevolution or explicitly examined its mechanisms.”

In their own study they looked at “five types of urban disturbances including habitat modifications, biotic interactions, habitat heterogeneity, novel disturbances, and social interactions.” The researchers learned that, “clear urban signal; rates of phenotypic change are greater in urbanizing systems compared with natural and nonurban anthropogenic systems.” They concluded that there is need to continually “uncover insights for maintaining key ecosystem functions upon which the sustainability of human well-being depends.”

Of particular concern in the area of tropical health are the unique urban manifestations of diseases like yellow fever, dengue and malaria. Although Zika virus, for example, was first discovered in forests, it has adapted to an urban cycle involving humans and domestic mosquito vectors in tropical areas where dengue is endemic. Musso and Gubler in their review further explain that although there may be sylvatic cycles of Dengue, “Arboviruses such as DENV have adapted completely to humans and can be maintained in large tropical urban centers in a mosquito-human-mosquito transmission cycle that does not depend on nonhuman reservoirs.”

Weaver et al. note that Zika in spreading to Asia, “emerged on multiple occasions into urban transmission cycles involving Aedes (Stegomyia) spp. Mosquitoes.” In addition it can be hypothesized that phenotypic changes in Asian lineage ZIKV strains made rare disease outcomes such as congenital microcephaly and Guillain-Barré more common and visible.

According to Estelle Martin and co-researchers, “Puerto Rico, a major metropolitan center in the Caribbean, has experienced increasingly larger and clinically more severe epidemics following the introduction of all four dengue serotypes.” They found that Dengue serotype 4 replaced earlier strains and that “this epidemic strain progressed rapidly, suggesting that the epidemic strain was more fit, and that natural selection may have acted on these mutations to drive them to fixation.”

In addition to virus evolution, mosquito changes have been documented by Caroline Louise and colleagues in “One of the world’s largest urban agglomerations infested by Ae. aegypti … the Brazilian megalopolis of Sao Paulo.”  They detected microevolution despite a short observational period and stress the implications of the “rapid evolution and high polymorphism of this mosquito vector on the efficacy of control methods.”

“The adaptation of malaria vectors to urban areas is becoming a serious challenge for malaria control,” is a major concern of Antonio-Nkondjio and co-workers. They found, “rapid evolution of pyrethroid resistance in vector populations from the cities of Douala and Yaoundé,” Members of this team also learned that the M form of Anopheles gambiae predominated in the centre of urban agglomerates in Cameroon. Previously it was known that larval habitats polluted with decaying organic matter as found in densely populated urban agglomerates, were unsuitable for Anopheles gambiae. The recent study showed that the “M form showed greater tolerance to ammonia (arising from organic matter) compared to the S form. This trait may be part of the physiological machinery allowing forest populations of the M form to colonize polluted larval habitats.”

The evolutionary response of vectors and disease organisms to urban environments needs continued monitoring. Urban disease control and elimination efforts must adapt to such adaptations in the disease process.

Decreasing Household Costs of Dengue Prevention at Low-Altitudes in Colombia …

… Redirecting Resources into the Hands of People Who Slap Mosquitoes Everyday.

Class members from the course “Social and Behavioral Foundations of Primary Health Care” at the Johns Hopkins Bloomberg School of Public Health write a policy advocacy blog as part of their assignments. Here we are sharing the blog posted by . read more on this and other SBFPHC blog posts by clicking here

Squito(Photo by James Gathany)

Colombia bears high burdens associated with dengue.  During the 2010 epidemic, disability-adjusted-life-years lost were 1178.93 (per 1 million inhabitants) versus just 88.38 averaged for 2011-2012.  Rodriguez et. al (2016) estimated economic burdens higher than $129.9 million USD each year, with most of the burden at the individual household level (46%, 62%, and 64%) for preventing/controlling mosquitos.

The Colombian Ministry of Health and Social Protection uses the 1,800m elevation mark when allocating money to low-altitude departments for dengue-related expenditures.  This suggests that only half of Colombia’s 47 million residents are at risk for dengue.  However, many people vacation at low altitudes where they risk becoming infected and bringing dengue back home.  If low-altitude residents were better equipped to control mosquitos, then both residents and visitors would be better protected.  Unfortunately, low-altitude residents shoulder a greater financial burden for mosquito prevention than the government.  Rodriquez et al. (2016) reported that almost $85 million USD was the highest household burden (for prevention alone) between 2010 and 2012, while the highest government burden was only $35 million USD (for prevention, awareness campaigns, and control combined).

If the Ministry of Health and Social Protection’s vision of equity-based protection and healthcare resources for all is to come to fruition, more money must flow into prevention and control.  Residents should not have to buy expensive sprays when they already live in poverty.  If Ministry-controlled finances were earmarked for inexpensive yet effective household supplies, such as curtains and water container covers, then less money would be required for treatment.  I advocate for reshuffling some of the dengue-related funds to reflect the prevention priority; increase amounts for household prevention and decrease treatment allocations.

Let’s not make low-altitude residents choose between buying expensive sprays or food to eat.  It’s hard enough already just to slap together supper.

Mosquito-Borne and Tick-Borne Illness in Florida: Importance of Surveillance

Class members from the course “Social and Behavioral Foundations of Primary Health Care” at the Johns Hopkins Bloomberg School of Public Health write a policy advocacy blog as part of their assignments. Here we are sharing the blog posted by “jleblan5jhmiedu“. read more on this and other SBFPHC blog posts by clicking here. This posting is particularly relevant today on World Mosquito Day.

Vector-borne diseases make up some of the more common infections throughout the globe. The Centers for Disease Control and Prevention acknowledges mosquito-borne denque mosqdiseases, such as West Nile Virus, and tick-borne infections, such as Lyme disease, have a great impact on the United States. These vectors have found favor in climate change as they continuing to breed and pose a public health risk; carrying infectious agents that may be transmitted to humans through a bloodmeal.

In 2014, the State of Florida Department of Health published their mosquito borne diseases surveillance guidebook. Within these guidelines, specific mosquito-borne infections were addressed in regards to both detecting and preventing such diseases. Unfortunately, since this publication, the Zika virus outbreak developed and was found to have recently reached Miami-Dade county in Florida, where locally transmitted cases were confirmed. Given these locally acquired infections in Florida, the surveillance guidelines should be updated accordingly.

FL Zika

Number of Florida Acquired Zika Virus (gray line: per million)

While the Northeastern regions of the US are known to have their “tick season” in the Spring and Summer, Florida’s climate allows for a year-long risk of contracting a tick-borne diease. The standard lab diauos in newsgnostic criteria for Lyme disease, the ELISA, detects antibodies against the bacterium, Borelia burgdorferi sensu stricto. However, it has continued to demonstrate poor sensitivity and overall reliability. Research from the University of North Florida has identified different strains of Borrelia that cause disease in humans. Thus, should one be infected with one of the different strains of Borrelia, one’s test is likely to be negative despite having actual disease. In recent years, Florida was found to have a 140% increase in Lyme disease cases since 1993 while reports of other tick-borne diseases have also increased. Hence, Florida researchers and public health professionals must partner together to revise and implement more up-to-date/accurate screening and awareness for vector-borne diseases.

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.



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.


Reference Links

  • How Mosquitoes Work.
  • Be vigilant to different mosquito breeding grounds.
  • Biological Notes on Mosquitoes.
  • Mosquito. From Wikipedia, the free encyclopedia.
  • Anopheles Mosquitoes.
  • Differentiate Culex, Anopheles and Aedes Mosquitoes.
  • Flight performance of the malaria vectors Anopheles gambiae and Anopheles atroparvus.

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 ( Nakul Chitnis (

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.