An increase in West Nile virus (WNV) cases in Mississippi in August doesn’t necessarily mean the state will end up with a worse year overall from 2005, says Dr. Mills McNeill, the state’s epidemiologist.
In early August the Mississippi Department of Health (MDH) confirmed five new human cases of WNV: three in Forrest County and two in Lauderdale County. These new cases increase the total human cases of WNV in Mississippi this year to 17 with two resulting in death. This time last year, Mississippi reported nine human cases and no deaths.
“We are seeing a little increase thus far,” McNeill said. “However, all cases need to be tallied at the end of the year before we can make valid comparisons. The reason for that is we have no way of knowing exact transmission patterns from year to year. We expect to see the majority of cases in the July-August-September time frame. But that can vary depending on rainfall amounts and frequency, and factors we have little control over like the virus reservoir in birds, and the number of the vector mosquitoes that can transmit the disease to humans.”
McNeill said while the state has gotten off to a pretty brisk start for the WNV season, the patterns of illness aren’t the same each year. The state has seen sporadic cases as late as October. One year the peak might be in August, and another year in September.
“It is highly variable from year to year,” McNeill said.
A week-to-week comparison shows a small increase thus far this year. But the health department will have to wait until the end of the season to make any real comparisons.
“I would also add that since we know about 80% of human infections produce no serious illness, we are only seeing those patients who become sufficiently ill to go to physicians, the physician suspects WNV and orders a test. It is difficult to track the true number of cases, but that is the best information we have.”
Of the 17 WNV reported in humans thus far this year, Forrest County has had nine cases. Lauderdale County has had two cases, and Bolivar, Copiah, Lamar, Monroe, Pike and Scott have each had one case.
Symptoms of WNV are often mild, similar to the flu, and may include fever, headache, nausea, vomiting, a rash, muscle weakness or swollen lymph nodes. The illness is considered an important public health threat because in a small number of people, infection can result in encephalitis or meningitis, which can lead to paralysis, coma and possibly death.
Local health officials in Forrest County, in particular, have been working closely with city and county officials tracking the incidence of WNV. The health department has increased the number of media releases to insure the public understands there is an increase in cases in that area of the state.
No matter where you live in the state, the health department urges residents to “fight the bite” by following simple protective measures that reduce mosquito exposure. That starts with avoidance of mosquitoes as much as possible.
“Avoid exposure during peak biting hours,” McNeill said. “This is primarily dusk to dawn. Of course, the evening hours are when people would be out of doors barbequing and other normal summer activities. What we encourage everyone to remember is if you are going to be out, use mosquito repellent, and wear long sleeves and long pants.”
Home and business owners are also advised to deny mosquitoes the conditions they need to breed. Mosquito species that are best at transmitting WNV don’t fly far and breed in small pockets of water like clogged gutters, flowers pots, buckets, bird baths and old tires. Experts recommend changing the water in bird baths at least weekly, turning buckets and flower pots upside down and removing trash like old tires or cans that might hold water.
“Fortunately, none of these kinds of measures cost much money or are hard to do,” McNeill said. “And they can really have an impact on the potential number of WNV mosquitoes in a given locale. Fountains, as long as they have moving water, the WNV virus carriers would not find that a favorable breeding site.”
For ditches and ponds, he recommends larvicides, which are available for purchase at home improvement stores. And mosquito fish (Gambusia affinis) and other types of fish can control mosquito populations in ponds.
Many businesses are located in areas where the city or county has mosquito control capability. McNeill recommends that if business owners notice a problem, they should work with local mosquito control authorities for advice.
Businesses with activities that take employees out into the woods where they might encounter dead birds can help by reporting those to the health department. Birds are a reservoir for WNV, and dead birds can be evidence of the virus. McNeill said the state has good bird death reporting and WNV testing throughout the state.
“But certainly we always welcome help from any quarter,” he said.
To report a dead bird or for more information about WNV, please call 1-877-WST-NILE (1-877-978-6453).
When spending time outdoors for business or pleasure, the first defense is long sleeved shirts and long pants. A good mosquito repellent is also advised. McNeill said repellents containing DEET are the best.
“We strongly emphasize the safety and effectiveness of DEET,” McNeill said. “There are others out there that are good. But the best advice the CDC and other expert sources is that if you are going to be out extended periods of time, DEET is probably the best.”
There have been some public concerns about the safety of DEET, but McNeill said there are no health problems when used according to manufacturer’s directions. DEET works; the military has used it successfully for years.
“It has a proven track record when applied correctly,” he said.
Contact MBJ contributing writer Becky Gillette at firstname.lastname@example.org.