Tag Archives: mosquito

Sterile or Feral? Preventing Dengue Fever via Mosquito Population Control

Contributed by Guest Blogger: E. Doyle ’14

In order to disseminate successfully, viruses, being immobile, must adapt and evolve to utilize their surroundings to effectively propagate. One group of viruses that’s done this particularly well are the Flaviviruses, which are transmitted to humans via bites by infected mosquitoes. Though beneficial for the spread of the virus, Flaviviruses such as yellow fever, dengue fever, and West Nile virus cause a significant amount of serious and painful illnesses and even death in human beings. Of particular concern are the dengue fever outbreaks that have, according to the CDC, recently been common in many parts of the world. Since there is no cure for this virus, prevention is the only way to stop the spread. Scientists are currently looking to do this by controlling the mosquito population.
In a recent study, scientists considered two known methods of mosquito population control (sterilization of male mosquitoes, and genetic alteration of male mosquitoes that would cause them to be genetically programmed to die, as well as any offspring they produced) and mathematically projected how these methods would be most effectively utilized. The variable in this experiment was the frequency of the release of the mosquitoes altered by these two techniques. Would fewer mosquitoes be produced if these altered males were released frequently in small bursts, or less frequently in larger numbers? The projected effectiveness of the different timelines was shown by the calculated number of mosquitoes present in the environment afterwards, keeping in mind the as well as the mating competitive ability of mosquitoes that have been altered to control their reproductive success. If the altered males are able to mate as successfully as the wild type males are and lower the population of mosquitoes below a certain level, the virus will no longer successfully transmit.
Though genetically altered or sterilized male mosquitoes may often lose out when it comes to reproductive success, as has been shown in other real-life experiments, the numbers showed that the release of these mosquitoes into the environment still works when they are released very frequently rather than at lower frequencies. It should be kept in mind, however, that releasing these mosquitoes more frequently also results in higher costs. Also, since the results of these experiments were merely projected using mathematical analysis, it begs the question of whether the anticipated results of frequent mosquito release would be as successful in real life as they are on the page.


Septic Tanks: urban breeding grounds for virus-carrying mosquitoes

Contributed by Guest Blogger: L. Herrera-Torres ’14

Like in several other landforms in tropical regions, Puerto Rico is victim to seasonal increases in the Dengue fever and West Nile Virus, which are transmitted via the mosquitoes Aedes aegypti and Culex quiquefasciatus respectively. In order to test whether or not active septic tanks with raw sewage provide an adequate environment for the development of mosquitoes (particularly Aedes aegypti) and therefore aid in the spread of these diseases, a test was conducted in a southern municipality of Puerto Rico, called Salinas. In the community of Playa-Playita 89 septic tanks with varying structural integrity and water quality were sampled for the presence and abundance of mosquito larvae using floating funnel traps and 93 septic tanks were tested for the presence and abundance of adult mosquitoes using screened, plastic emergence traps.
Predictably, Culex quinquefasciatus, the vector of West Nile virus, which has been proven to thrive in polluted waters, was found in 74% of the septic tanks in larval form and in 97% in adult form. However, the results of vector for Dengue fever (the main focus of the experiment) were more surprising.
Previously Ae. Aegypti was known to be well adapted to urban areas and were often found in artificial containers, but it was still generally accepted that these larvae developed in clean water. However in 18% of the septic tanks sampled revealed that Ae. Aegypti was present in this water despite its contamination and had a positive association with the cracking of septic tank walls, uncapped tanks, and larger tank surface area. Similar results were found for Ae. Aegypti adults. 49% of the tanks showed both their presence and abundance as well as their positive correlation with cracking, uncapping, and septic water pH. The correlation between the amount of larvae collected from the septic tanks and the amount of adult mosquitoes recorded strongly insinuates that this environment is conducive to mosquito reproduction and development and is not just a resting place as others have suggested.
These findings led the researchers to believe that Ae. Aegypti can develop in sewage water and that septic tanks provide ideal conditions for mosquito productivity and can serve as potential to maintain dengue transmission during the dry season.