West Nile virus has been detected for the first time this year in Delaware, in chickens that are monitored by the Mosquito Control Section of the Department of Natural Resources and Environmental Control.
West Nile virus has been detected for the first time this year in blood samples taken from Delaware’s sentinel chickens that are systematically monitored for mosquito-borne diseases.
The samples were collected as part of a statewide surveillance program conducted by the Mosquito Control Section of the Department of Natural Resources and Environmental Control (DNREC), according to a DNREC press release.
No cases of West Nile in humans or horses have yet been found in Delaware this year.
The positive results from two sentinel chickens sampled by Mosquito Control were reported to DNREC late Friday by the Delaware Division of Public Health Laboratory. One was sampled on Aug. 18 from a sentinel chicken station in the Colonial Heights section of southwestern Wilmington and the other on Aug. 19 at a station located east of Dover near Kitts Hummock, according to Mosquito Control Section Administrator William Meredith, Ph.D.
These two sentinel chicken stations are among 24 caged chicken stations operated statewide by Mosquito Control. The sentinel chickens are humanely kept and tended in the field. If exposed to West Nile and eastern equine encephalitis (EEE) viruses – both of which can affect humans and horses – the chickens develop antibodies that enable them to survive. Their blood is tested every two weeks for these antibodies, indicative of virus transmission to the birds.
In past years, West Nile most often has first surfaced by mid-July, making this year’s first occurrence in mid-August rather late this summer. In addition, to date, West Nile has not been found in any sick or dead wild birds, and even the number of virus-suspect birds collected by Mosquito Control for testing – just 10 - has been far below the numbers of previous years. In recent years, the virus has often first appeared in wild birds during June, but Meredith noted the absence of virus findings in wild birds this year might in part be caused by the public now having less concern about this disease, and hence not reporting virus-suspect wild birds.
“All of this might point to a relatively light year in Delaware for West Nile virus, but nobody really knows for sure what the remainder of the year holds in store. Concerns for mosquito-borne disease transmissions now really won’t subside until much cooler autumn temperatures set in, lasting in most years until mid-October and sometimes even beyond,” Meredith said.
Meredith added that the significance of finding West Nile virus in sentinel chickens is that virus transmission has occurred at essentially ground level, where the virus might just as readily have been transmitted to humans, depending upon the species of mosquitoes transmitting the virus to the chickens.
Nationwide, on Aug. 19 the Centers for Disease Control and Prevention reported statistics that compared to the past several years seem to indicate a decrease: 236 human cases of West Nile virus in 28 states, with the most cases occurring in California, Mississippi, Colorado, North Dakota, South Dakota and Texas. Two deaths have been reported so far: one in Mississippi and one in Arizona. On a regional basis for 2008, two human cases of West Nile have been reported in New York, plus one case each from Connecticut, Pennsylvania and West Virginia. No human cases have been reported as of yet in New Jersey, Delaware, Maryland or Virginia.
West Nile virus has been present every year in varying degrees in Delaware since 2001. The worst West Nile outbreak in Delaware occurred in 2003, with 17 confirmed human cases and 2 fatalities, plus 63 horse cases.
“While the finding of West Nile virus in two sentinel chickens thus far this year is not cause for alarm, it serves as a good reminder for people to take common-sense precautions against mosquito bites,” Meredith said. Precautions include wearing long-sleeved shirts and long pants when outdoors in mosquito-prone areas, applying insect repellent containing 10-30 percent DEET in accordance with all label instructions, and avoiding mosquito-infested areas or times of peak mosquito activity around dusk, dawn or throughout the evening.
To reduce mosquito-breeding, people should drain or remove items that collect water, such as buckets, birdbaths, rain barrels, old tires, flowerpot liners, depressions in tarps covering boats, clogged rain gutters, and unused swimming pools.
An effective equine vaccine now exists to protect horses from West Nile virus and EEE, but there are no approved West Nile or EEE vaccines for humans. The majority of humans infected with West Nile virus typically have only symptoms similar to a mild flu, if they show any signs at all; 20 percent of those infected develop a mild illness which includes fever, body and muscle aches, headache, nausea, vomiting and rash.
A very small percentage of patients, usually the elderly, develop severe neurological disease that results in meningitis or encephalitis (inflammation of the brain), occasionally leading to deaths. Symptoms of a severe case of West Nile may include sudden onset of severe headache, high fever, stiff neck, confusion and muscle weakness. Individuals with these symptoms should see their physician immediately.
Delaware’s Acting State Veterinarian, Dr. Caroline Hughes, said, “I am urging horse owners to assist with prevention efforts by making sure their horses are vaccinated against West Nile virus. There is a very effective vaccine that is available to horse owners through their veterinarians. Two doses of the vaccine three weeks apart are necessary for immunization. After the initial two vaccinations, a yearly booster is needed. If horses have not been vaccinated or have only recently been vaccinated, owners should keep horses inside during peak mosquito times, i.e., dawn, dusk, and throughout the night.”
Suspect sick or dead wild birds for the species of interest (crows, blue jays, cardinals, robins, hawks and owls) when monitoring for West Nile virus can be reported to the Mosquito Control Section from Monday through Friday between 8 a.m. and 4 p.m. by calling:
New Castle County and northwestern Kent County (Glasgow office):
Remainder of Kent County and all of Sussex County (Milford office):
Calls made after business hours or during weekends or holidays can be recorded on a taped message. Callers should give their name, phone number, address and brief message about the finding. However, the public should be aware that some calls left more than 24 hours before Mosquito Control can review them (usually between Friday evening and Sunday morning) unfortunately usually result in the bird conditions becoming too deteriorated for virus testing.
The Mosquito Control phone numbers above should also be used for citizens to report intolerable numbers of biting mosquitoes. The section uses this information about severe mosquito nuisance situations to help determine when and where to provide control services.
For more information about mosquito biology/ecology and mosquito control, please contact the Mosquito Control Section’s Dover office at 302-739-9917.
For more information about West Nile virus in humans and related medical issues, please contact the Division of Public Health at 1-888-295-5156.
For more information about West Nile virus in horses and equine vaccines, contact the Department of Agriculture’s Poultry and Animal Health Section staff at 302-698-4500 or 800-282-8685 (Delaware only).