Recent research into mosquitos and the deadly dengue virus shows new promise for preventing transmission of the disease. Roughly 50 to 100 million cases of infection are reported annually, and several tropical countries saw an increase in their numbers during 2013. In Costa Rica for example, the number of registered cases more than doubled, increasing by 27,000 to an unprecedented 52,247 infections. While eliminating standing water where the mosquitos can breed and other preventative measures are encouraged, health organizations are asking for a world-wide effort to prevent transmission. The Costa Rican Social Security Fund estimated last years disability payments from dengue infection cost the country $816,000.
Research efforts into mosquito prevention have proven difficult and at times dangerous. For example, the use of spatial repellents such as mosquito coils and candles which release a chemical that drives mosquitos away has been shown to be toxic to human health. In a study done on the toxic effects of mosquito coils commonly used in Asia and South America researchers found them to contain heavy metals, allethrin, phenol, and o-cresol; which create a toxic smoke that will cause adverse effects on consumers. These effects were likened to smoking several packs of cigarettes.
This type of dengue and malaria research, prevention through spatial repellents such as coils, is the precise research being conducted at the University of Notre Dam which was just awarded $23 million by the Bill & Melinda Gates Foundation. Though the chemical ingredients and side effects on humans of the “new method of mosquito control” used in the study have not yet been released, even if they are deemed non-toxic to humans it still will not lower the number of mosquitos which can transmit the virus. Spatial repellents can only for protect people in an enclosed area where fumes of the repellent are dispersed.
Discoveries such as a dengue vaccine have often been discussed for preventing the spread of the deadly disease, but due to the very nature of the infection and reinfection researchers say it is unlikely a viable vaccine will be available anytime soon. Once an individual has contracted dengue and developed antibodies, either by mosquito bite or vaccination, they are more likely to contract a more serious and more lethal form of the disease if infected a second time, which can lead to hemorrhagic fever.
However, one recent discovery into a special kind of insect bacteria could hold great promise in the prevention of mosquito-borne diseases with no cost to human health. Researchers with the Eliminate Dengue Program, an international scientific collaboration, are using a strain of Wolbachia bacteria from fruit flies to reduce the mosquito’s capacity to transmit disease.
They have infected the A. aegypti mosquito, a common carrier of dengue, with the bacteria and studied its effects in the mosquitos bodies as well as its spread through wild mosquito population in the area. They found the bacteria greatly reduced the replication of the virus inside the mosquitos, and that the mosquitos were carrying the bacteria on through subsequent generations. They also reported that there were no local transmissions (human infections) where the Wolbachia infected mosquitoes had been released.
The program will be conducting large-scale trails in dengue-endimic countries including Vietnam, Indonesia, Brazil, and Columbia to determine whether releasing mosquitoes with Wolbachia bacteria can actually reduce the infection rate in those communities. Early research shows the bacteria has the potential to reduce the transmission of other viruses such as yellow fever and the parasites that cause malaria. Discoveries such as the use of bacteria on the actual mosquitos are of high importance in preventing the spread of deadly mosquito-borne disease such as dengue because they do not present any toxic side-effects on human health.
By Mimi Mudd