The Pan American Health Organization/World Health Organization (PAHO/WHO) is offering to provide technical cooperation to support pilot studies of new mosquito control technologies, as part of its response to the Zika epidemic first detected in Brazil in 2015, which has spread to 33 countries and territories in the Americas.
New tools under development to combat the Aedes mosquito that transmits Zika virus include Wolbachia bacteria, genetically modified mosquitoes, and others.
"The most important tool in the fight against Zika, and at the same time, dengue and chikungunya, is the control of Aedes aegypti mosquitoes that transmit these diseases. Since these mosquitoes live in and around houses, it will take a concerted effort with participation of the community to reduce the number of mosquitoes in the Americas. We are also looking urgently at improved control methods including insecticides and other technologies, "said Dr. Marcos Espinal, director of communicable diseases at PAHO.
The World Health Organization's Vector Control Advisory Group has recommended the carefully planned pilot deployment of new tools, accompanied by rigorous independent monitoring and evaluation.
"The most advanced techniques are those that use Wolbachia bacteria and transgenic mosquitoes, so we want to offer technical support to countries who want to study these technologies to combat Zika virus as well as dengue and chikungunya, which are transmitted by the same mosquito," added Espinal.
These include the release of mosquitoes carrying Wolbachia bacteria, which propagates itself in the population. The symbiotic bacteria suppress the development of the virus in the mosquito and control transmission. The other tool consists of OX513A transgenic male mosquitoes which are released periodically to suppress the wild population. Aedes larvae carrying the OX513A gene develop normally, but die before becoming an adult.
The WHO group examined new vector control technologies and recommended starting studies regarding the future implementation of some of these technologies for controlling the Aedes mosquito. It concluded that more evidence is required before pilot deployment of three other tools could be considered. These include sterile insect technique, vector traps and attractive toxic sugar baits that kill mosquitoes.
The new Technical Advisory Group on Entomology in Public Health at PAHO is seeking ways to strengthen control programs of the Aedes aegypti vector, given that some of the problems in controlling Aedes include the adaptation of the mosquito, human movement, monitoring, resistance to pesticides, and their resilience.
"PAHO will provide technical assistance to countries that want to implement pilot projects for these technologies to combat the vector that transmits Zika, dengue, and chikungunya, all arbovirus transmitted by the same mosquito," said Harold Bezerra, PAHO's regional advisor on entomology. PAHO is building a network of entomologists and epidemiologists who can give direct advice to countries in vector control.
The vector control group, at its recent meeting in Geneva, suggested the implementation of two of the new tools, at a pilot level of limited duration under operational conditions, accompanied by rigorous monitoring and evaluation.
Use of bacteria such as Wolbachia, which does not infect humans or other mammals and are found in 60% of common insects, such as butterflies and fruit flies, has been underway for some time. In Australia, Brazil, Indonesia and Viet Nam, Wolbachia-carrying mosquitoes have been released to help control dengue fever. When females mate with the bacteria- carrying mosquitoes their eggs do not hatch, thus reducing the population.
The other recommended tool for pilot studies is to reduce the mosquito population through genetic manipulation. OX513A is a transgenic strain of Aedes aegypti, in which larvae develop normally but die before becoming functional adults. This technology has demonstrated the ability to reduce Aedes aegypti in field tests on a small scale in parts of Brazil and some Caribbean islands.
In both cases, more data on the epidemiological impact of the Wolbachia and transgenic mosquito strains are needed to gather necessary evidence to expand their use beyond the trial stages.
PAHO has intensified its integrated surveillance strategy for Zika virus infection in the Americas, but the exact burden of disease in the region is not yet well known. It is also working to continue training primary health care workers in identifying and reporting Zika cases, and helping the countries strengthen laboratory capacities.