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Arboviruses Mosquito-borne viruses are part of a group of pathogens known as arthropod-borne viruses, or arboviruses. Blood-sucking insects usually spread arboviruses. One arbovirus that has generated much interest and news is the West Nile virus. Other mosquito-related illnesses not covered in this article* include malaria, Dengue fever, yellow fever, California serogroup, Japanese, and Western Equine encephalitides. There are more than 100 arboviruses that can cause human diseases, including encephalitis (or swelling of the brain). Most people infected with arboviruses do not have symptoms or may develop flu-like symptoms, but in a small number of cases, some infections can cause coma or death. Arboviruses are most often detected during the summer months because that is when mosquitoes are most active. The organisms in which viruses survive the winter remain largely unknown. Transmission Few of the 2,000 species of mosquitoes carry microorganisms that cause disease in people. The source, maintenance, and transmission of the viruses are subjects still under study by researchers at the Harvard School of Public Health (HSPH) and elsewhere. Arboviruses require a host (usually a bird or small mammal) in which they maintain themselves in nature and a vector, such as a mosquito, to get around and infect other organisms. Female mosquitoes may ingest a virus from an infected host and later pass the infection in their saliva when they bite another animal. Of the animals on which mosquitoes feed, birds are among the best-known hosts for arboviruses. Humans and other animals such as horses are dead-end hosts for most arboviruses; they do not pass the virus to others or back to mosquitoes. HSPH research of birds as hosts Birds tend to collect in flocks that create available populations on which the mosquitoes may feed and in which viruses may amplify. HSPH researchers are investigating factors such as: Types of bird. Certain birds such as crows, starlings, and robins may serve as better hosts.Roost loyalty. The likeliness of birds returning to the same roost seems to increase their chance of maintaining the virus. Roost density. The number of birds roosting at the same place seems to play a role in virus amplification. Frequency of contact with mosquitoes. Birds that remain calm when they are bitten by mosquitoes seem to receive fewer bites than those that flutter a lot. Control Methods Public health agencies attempt to reduce the spread of arboviruses through a variety of methods. One of the most common methods of mosquito control is the placement of chemicals that kill mosquito larvae in storm drains and other places where water collects and mosquitoes breed; the chemicals are generally non-toxic to humans and other animals such as dogs and cats. Sometimes agencies spray pesticides from trucks, helicopters or planes. There are some basic ways people can decrease their personal risk of contracting an arbovirus. See What You Can Do. This document has been assembled to give information to the public and is for informational purposes only. Brand names have not been mentioned, nor do we endorse any particular product.©2000 President and Fellows of Harvard College. All rights reserved. |
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The Mosquito: An Awesome Predator