Vector Control: Our Best Chance in the Fight Against Zika

Aedes aegypti in the Americas

Latin America is currently fighting to prevent the diseases transmitted by the Aedes aegypti mosquito: Zika, Dengue, and Chikungunya. There are significant and ongoing outbreaks of these diseases in Latin America, including Brazil, Mexico, Argentina, Peru, and Colombia, to name a few [1-5]. Anyone who has watched the news recently knows that Brazil is the epicenter of the Zika virus outbreak; additionally, dengue is endemic to the country. However, they are not alone – other countries in Latin America are fighting simultaneous outbreaks. Countries in Latin America are taking a variety of approaches to fight and prevent A. aegypti from proliferating in these already endemic areas. Techniques employed range from environmental sanitation, chemical control, physical control, to educational campaigns. Additionally, given the seriousness of the situation, novel approaches are being considered, such as genetic modification or radiation of the A. aegypti mosquitos.

Environmental Sanitation

The main mode of prevention for these diseases is to limit mosquito contact through vector control [6]. This is primarily done by eliminating habitats that favor the procreation and proliferation of the mosquito [7]. It is important to note that the exception to this is the Zika virus where it has been discovered that sexual (person-to-person) transmission may play a greater role than previously thought [8]. A. aegypti is a “container breeder” and will breed wherever water accumulates [10], even very small amounts, therefore elimination of open sources of stagnant water is the main preventative measure used. Health departments in affected municipalities often form sanitation brigades that go out into the community and visit homes to eliminate or modify sources of stagnant water such as potted plants, toilets, and water leaks. Solid waste such as old tires, open water bottles, and discarded containers are also a hazard because they have the potential to accumulate water and must be eliminated. Water storage containers in homes are fitted with tight lids or mesh screens by the brigades to prevent mosquitos from laying eggs [7, 9, 10,].

Chemical Control

The life cycle stage of the A. aegypti mosquito determines the type of chemical control measure that can be used. Larvicides, such as Temefos, are used to kill the mosquito in its immature, larval, stages in water containers that cannot be eliminated [6]. During emergency situations, like those that many communities in Latin America are currently experiencing, targeted outdoor residual space spraying is employed. In communities where homes are not adequately screened or air-conditioned, residual indoor spraying is recommended with ultra low volume doses of adulticides, such as deltamethrin and bifenthrin [11]. Finally, in extreme outbreak situations, widespread outdoor space spraying of pesticides is used. This is used as a last-resort measure with rapidly effective treatment in order to reach wide areas. To do the widespread spraying, ultra low volume dose machines are mounted onto trucks and/or aircrafts and the pesticides are dispersed in an aerosol of ultrafine droplets [6, 11]. However, in order for this technique to be effective, the pesticide must come into direct contact with the mosquitoes.

Physical Control

Physical control measures for the A. aegypti mosquito include both physical methods to catch the mosquitos, as well as physical barrier methods. A physical control method is placing oviposition, egg-laying medium on sticky traps in homes to lure female mosquitos and trap them. Some barrier methods include installing screens on windows in the home, wearing protective clothing, like long sleeve shirts and pants, and installing bed nets. Bed nets can be treated with insecticide such as Permethryn to prevent mosquitos from making contact and to kill them at the same time.

Educational Campaigns

Educational campaigns are used concurrently with the environmental sanitation chemical control, and physical control methods in order to inform members of the community of ways to safely protect themselves and rid their communities of the A. aegypti mosquito. In these campaigns, city health departments, in conjunction with sanitation brigades, go out into the community to teach residents and students about the A. aegypti life cycle, how the mosquito reproduces, and ways to eliminate breeding habitats [12]. Some locations such as Rosario, Argentina have dedicated “days of sanitation” or “overhaul weekends” like the one that that Dominican Republic conducted at the end of June 2016. During these sanitation days, everyone works together to eliminate vector-breeding sites in the community and is involved in education campaigns at the same time [13, 14]. The aim of these campaigns is to assist and teach the communities how to eliminate the vector so that they can know the importance of sanitation in disease control, and continue the efforts on their own.

Novel Approaches

There are several novel approaches being discussed as an effort to fight the A. aegypti mosquito. An approach that has been come up a lot recently is the genetic modification (GM) of the male A. aegypti mosquito. The GM male mosquito carries a dominant lethal gene, which is then passed down to its offspring upon mating. The gene causes the mosquito larvae from maturing and thus breaking the mosquito’s life cycle [15, 16]. This approach was successfully tested in the Cayman Islands in 2010 [15] and in June of 2016 was reintroduced in order to prevent Zika and dengue outbreaks [17]. In 2012, Brazil established a farm for GM A. aegypti mosquitos (18) as an effort to reduce dengue outbreaks, and is using this approach in certain areas to fight the current Zika outbreak [19]. According to the United States Food and Drug Authority (FDA) the use of genetically modified mosquitos is safe [20] and Key West, Florida may soon be the first location in the US to test these GM mosquitos [20]. Sterilization through radiation of the male A. aegypti mosquito is another novel approach that has been utilized [15, 21], however it has been shown to not be as effective as the GM mosquitos [22]. Similar to the GM approach, radiation sterilizes male mosquitos so that when they mate, none of the eggs laid would be viable.

It is important to note that no one method by itself is completely effective. Vector control is most effective through a combination of all of these methods [7].

[1] http://espanol.cri.cn/2786/2016/06/23/1s386644.htm

[2] http://larepublica.pe/impresa/sociedad/778842-se-han-reportado-22-mil-casos-de-dengue-este-ano

[3] http://www.diariouno.com.ar/para-reducir-el-dengue-insisten-el-trabajo-la-temporada-invernal-20160619-n967250

[4] http://www.elpais.com.co/elpais/cali/noticias/esperamos-300-casos-microcefalia-asociados-zika-este-ano-ins

[5] http://www.unionjalisco.mx/articulo/2016/06/17/salud/guadalajara/jalisco-es-septimo-en-casos-de-dengue

[6] http://www.cdc.gov/chikungunya/resources/vector-control.html

[7] http://www.who.int/denguecontrol/control_strategies/control_strategy_vector/en/

[8] http://www.cdc.gov/zika/transmission/sexual-transmission.html

[9] http://www.who.int/denguecontrol/control_strategies/environmental_management/en/

[10] http://www.who.int/emergencies/zika-virus/articles/mosquito-control/en/

[11] http://www.cdc.gov/zika/public-health-partners/vector-control-us.html

[12] https://www.diariodemorelos.com/noticias/ense%C3%B1an-en-escuelas-contra-brotes-de-dengue-zika-y-chikungunya