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 Information provided by the Section of Communicable Disease Control and Veterinary Public Health of the Missouri Department of Health and Senior Services
Every spring and summer, as mosquito numbers and activity increase, people across the United States are at risk of being infected by viruses spread by these pests. Infection may result in encephalitis, or inflammation of the brain, which is a very serious and even life-threatening condition.
In Missouri, diseases such as St. Louis and eastern equine encephalitis are a potential threat each year, but they have been overshadowed recently by the much-publicized West Nile encephalitis. West Nile virus was first discovered in the United States in New York City in 1999 and spread to other states in the Northeast and along the Atlantic seaboard during 2000. West Nile virus invaded the Midwest in 2001, and by the fall of that year had been identified in eight crows in eastern Missouri.
The life cycle of these mosquitoborne viruses is complex. Reservoirs include wild and domestic birds, small rodents and other mammals, and perhaps even reptiles and amphibians. Vectors for these viruses include mosquitoes that feed on both birds and mammals. Horses and humans are accidentally infected when the level of virus activity in normal hosts becomes so great that it begins to "spill over" into other species.
The Missouri Department of Health and Senior Services (MDHSS) has conducted surveillance for this group of illnesses for many years. With the threat of introduction of West Nile Virus into the state, these surveillance activities were expanded during 2000 and 2001. This season, in a cooperative effort with numerous partners, the following activities will be conducted:
- Passive surveillance for mosquitoborne illnesses in humans, which are reportable by statute in Missouri. Local health departments should encourage arboviral testing of patients presenting with aseptic meningitis and viral encephalitis if mosquitoborne illness has not already been ruled out.
- Active surveillance for equine cases of western and eastern equine encephalitis (WEE and EEE). Designated equine veterinary practitioners are contacted weekly throughout the mosquito season to see if they have diagnosed or suspect cases of these diseases in horses under their care.
- Surveillance of mosquito populations. MDHSS contracts with several local health departments to conduct mosquito-trapping programs. Some local health departments conduct mosquito-trapping programs using local funding. Personnel from Southeast Missouri State University (SEMSU) conduct a mosquito-trapping program in southeast Missouri under a contract with MDHSS.
- Surveillance for human cases of arboviral disease. MDHSS contracts with local health departments to conduct active human case surveillance for mosquitoborne illnesses (with emphasis on WN fever).
If you would like more information on this program please contact the Section of Communicable Disease Control and Veterinary Public Health at telephone 573-751-6113.
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