A recent article in “The Scientist Online” detailed an experiment in Australia where Aedes aegypti mosquitoes were infected with a bacterium called Wolbachia which prevented the mosquitoes from transmitting the virus that causes Dengue Fever1. “Dengue infects up to 50 million people worldwide every year, according to the World Health Organization2.” It is a viral disease found commonly in the tropics and causes fever, rash, and joint pain. While most patients recover completely, in 2008 the disease was responsible for over 400 deaths in Cambodia alone2. Finding a way to control the disease at the source would be of great benefit to both humans and animals especially if Wolbachia infected mosquitoes would also be unable to spread other diseases.
There are several significant diseases that afflict animals which are spread my mosquitoes. Some of these are; Canine and Feline Heartworm, Equine Eastern, Western, and Venezuelan Encephalitis Virus, Equine Infectious Anemia, and West Nile Virus. With the exception of heartworm disease there is no treatment for these infections. Basic mosquito management which I have detailed in a previous article on Malaria, is essential, but it is impossible to completely eliminate these flying parasites. Since the most effective method of control is pesticides, another avenue of prevention would be magnificent.
Researchers have known for several years that Wolbachia infected mosquitoes were unable to spread Dengue Fever, unfortunately the bacterium wasn’t easily spread to other mosquitoes1. In fact, the bacteria can only be spread through the mosquitoes reproductive tissues. Because of this the practicality of using the bacterium as a large scale control of the disease was severely limited. The breakthrough came when the Australian researchers were able to inoculate the mosquito’s ovaries. Their offspring and succeeding generations were then subsequently infected and resistant to Dengue Fever1.
Scientist’s don’t know how Wolbachia prevents transmission of Dengue Fever. They speculate that it may prevent viral growth in the mosquito’s tissues or that it may boost the mosquito’s immune system and kill the virus before they can inject it into another host.
It is not yet known if Wolbachia infected mosquitoes will be unable to transmit other diseases, but the prospect is at least encouraging. The other question is whether other types of mosquitoes such as the genus Culex, which is responsible for spreading heartworm infestations, or Anopheles which spreads Malaria would respond so favorably to Wolbachia infection. Further research should provide the answers.
1. Dengue-Resistant Mosquitoes; Tia Ghose August 24, 2011
2. Dengue fever killed 407 people in Cambodia last year; USA Today January 4, 2008