Earlier this summer, it looked like folks in Mississippi could breathe a sigh of relief regarding West Nile virus. There had been no new cases of West Nile virus in humans, and fewer cases found in birds and horses. But now there have been three human deaths in Mississippi from the disease that claimed one life in 2003.
In early September Mississippi State Department of Health (MSDH) confirmed two new cases of West Nile virus, one from Hinds County and one from Coahoma County. There was an additional human death in West Nile virus from a previously reported case in Washington County.
That brings the state’s total number of identified human cases of West Nile virus to 17 thus far in 2004. For the same time period last year, Mississippi reported 53 human cases of West Nile virus and one death.
Although fewer cases of West Nile has been reported this year, state residents need to remain vigilant to avoid getting mosquito bites that could lead to developing the disease.
“We expect West Nile virus to remain in Mississippi indefinitely, even though the level of transmission may vary from year to year,” said state epidemiologist Dr. K. Mills McNeil. “Thus far, we have seen a continued decrease in the number of human cases of West Nile virus reported each year in Mississippi after a peak incidence in 2002.
“There are a number of factors that influence the level of West Nile virus transmission. Educating Mississippians about the simple, inexpensive methods of prevention and protection is crucial to lower numbers. We do know that our Fight the Bite campaign has changed the behavior of Mississippians and we also know our numbers are reduced this year.”
McNeil said factors that affect the rates of West Nile virus infections include seasonal variables such as temperature and rainfall that influence the number of mosquitoes at any given time. Also, the abundance of specific types of mosquitoes that are able to serve as effective vectors (carriers) of West Nile virus is a factor.
Finding the cases
Better surveillance may also pick up cases of West Nile virus that were unreported in the past.
“Mosquito-borne viruses are identified every year in Mississippi, and our improved statewide surveillance system for West Nile virus and other mosquito-borne viruses helps us successfully detect these cases,” McNeil said. “Mississippians can reduce their risk of contracting West Nile virus by taking simple precautions. Such measures include removing sources of standing water; avoiding mosquito-prone areas, especially at night when mosquito activity is highest; wearing protective clothing when in mosquito-prone areas; and using insect repellents that contain DEET when outdoors.”
Symptoms of West Nile virus infection are often mild or flu-like and may include fever, headache, nausea, vomiting, a rash, muscle weakness and swollen lymph nodes. In a small number of people, infection can cause encephalitis or meningitis, which may result in paralysis, coma and possibly death.
It has been speculated that growing immunity in birds and migratory bird movements may play a role in the decline in incidences of West Nile virus. Dr. James Jarratt, Mississippi State University Extension entomologist, said when West Nile virus first entered the eastern U.S. and moved across the country, it was common to see a lot of West Nile virus in the areas affected.
“But as it progressed, birds become more tolerant of the disease,” Jarratt said. “They don’t develop it to the point that once a mosquito feeds on a bird, it is enough to give it to mosquitoes and then to people. It is beginning to look like the worst cases have passed this area of the country. There may be a few cases but not as many as there were a couple of years ago.”
The number of cases reported in Mississippi this year is similar to that in other Southeastern states, although Louisiana with 34 cases exceeds those from other states in the region.
The Web site (http://www.cdc.gov/ncidod/dvbid/westnile/surv&control04Maps.htm) provides the latest update on West Nile virus cases by state. The case counts posted by the Center for Disease Control on this Web site lag behind the real-time counts by a week or more, but they are representative of the disease transmission patterns in a region. As shown by the national map, presently the highest rate of West Nile virus transmission is being seen in the western states, particularly New Mexico, Arizona, Colorado, California and Nevada.
Contact MBJ contributing writer Becky Gillette at firstname.lastname@example.org.
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