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Mosquito-borne illness remains unpredictable

West Nile virus on the decline?

In a year filled with bad news, Mississipians got some good news from the Mississippi State Department of Health (MSDH) recently. After some re-figuring, it was discovered the number of human cases of West Nile virus (WNV) in 2008 was less than previously reported. The number of Mississippians afflicted with the mosquito-borne disease last year was down compared to 2007 and was the mildest since 2004.

In 2008, there were 65 confirmed human cases and three deaths attributed to WNV. MSDH previously reported 101 cases during the peak months of the WNV season last year. However, in October 2008 the Centers for Disease Control and Prevention (CDC) informed states that a WNV test used by a private laboratory reported inaccurate results. The CDC and MSDH repeated many of these tests, and some individuals previously reported as Mississippi cases did not test positive for WNV, resulting in a reduction in the total number of reported cases for 2008.

During the 2008 WNV season, confirmed human cases were reported in Calhoun, Forrest (four), Hinds (21), Jackson, Jasper, Jones (10), Lamar, Lawrence, Leake, Leflore (four), Lincoln (three), Madison (six), Marion (three), Monroe, Neshoba, Panola, Pearl River, Rankin (two), Scott and Simpson counties.

The adjusted WNV figures are down more than 50 percent compared to 2007 when 136 human cases were identified. And, 2007 was a milder year for WNV. Since the disease was discovered in Mississippi in 2002, the state has ranked in the top 10 in the nation in reported human cases every year with the exception of 2003, when it ranked 16th.

The state saw 193 human cases of WNV in 2002, 83 cases in 2003, 52 cases in 2004, 70 cases in 2005 and 184 cases in 2006.

The three WNV deaths (in Forrest, Hinds and Panola counties) were also low, though not a record. In 2002, there were a staggering 12 deaths attributed to WNV. The worst year was 2006 with 14 deaths, as opposed to the best year, 2003, when there were only two fatalities.

These numbers leave Currier to be cautiously optimistic about 2009. WNV has shown to be anything but predictable.

“Although we are pleased with the low numbers of West Nile virus cases (in 2008), it is important that all Mississippians continue to protect themselves and their family members to reduce the risk of contracting West Nile virus and other mosquito-borne illnesses,” said Dr. Mary Currier, state epidemiologist. “Mosquito-borne diseases occur statewide and throughout the year in Mississippi.”

Currier said she could not attribute the decline in WNV cases to any one factor, though she hoped MSDH’s anti-WNV education campaign “Fight the Bite” played a significant role.

Currier could also not forecast 2009 being an even better year. She pointed to WNV’s up-and-down numbers over the years and said Mississippian’s best bet this year is to remain vigilant.

Another reason for caution is that WNV is not the only mosquito-borne disease with which Mississippi has to contend. For example, there were three cases of LaCrosse encephalitis, two cases of flavivirus (also carried by ticks) and Jamestown Canyon virus. While these diseases have been identified in the past and their occurrence in 2008 does not mean larger outbreaks are ahead, they still should make locals wary.

“This is not the time to let our guard down,” Currier added.

Symptoms of WNV include fever, headache, nausea and vomiting, rash, muscle weakness and/or swollen lymph nodes. In a small number of cases – less than one percent – severe illness can result in paralysis, coma and death.

Finally, there was yet more good news in 2008 as there were no human cases of St. Louis encephalitis or eastern equine encephalitis reported. These diseases have been regularly identified in Mississippi in prior years.

Contact MBJ staff writer Wally Northway at wally.northway@msbusiness.com.

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