West Nile virus (WNV) has been detected in Delaware in blood samples taken from DNREC’s sentinel chickens that are monitored for mosquito-borne diseases. The samples are collected as part of a statewide surveillance program conducted by DNREC’s Mosquito Control Section. No cases of West Nile virus have been found in horses or humans so far in Delaware this year, with two cases found in wild birds in August.
The virus-positive chicken results were reported to DNREC by the Delaware Division of Public Health Laboratory. The chicken was sampled at a monitoring station along the Delaware River in southeast Wilmington on Aug. 25, according to Mosquito Control Section Administrator Dr. William Meredith of the Division of Fish and Wildlife. Based upon these positive virus findings, Mosquito Control will increase its mosquito population monitoring activities in this area and take appropriate mosquito control actions.
Mosquito Control operates 20 monitoring stations with caged chickens statewide. The sentinel chickens are humanely kept and tended in the field. Sentinel chickens bitten by mosquitoes carrying WNV or eastern equine encephalitis (EEE) – both of which can affect humans and horses – develop antibodies that enable them to survive. Their blood is tested every two weeks for these antibodies, which indicate exposure to these viruses.
The first indications of mosquito-borne viruses in Delaware for 2014 occurred earlier this summer in wild birds, involving two WNV-positive crows collected in August, one from north Wilmington and the other from the Hartly area in northwestern Kent County.
“So far in 2014, mosquito populations and occurrence of mosquito-borne illnesses have been a bit below normal, probably due to a relatively cool and dry summer,” Dr. Meredith said, noting Delaware’s numbers are similar to what’s happening across the country. Nationwide through Aug. 26, 2014 the federal Centers for Disease Control (CDC) has reported 297 WNV human cases with 12 deaths, with California, Louisiana, Texas and Arizona having the most cases, he said. In the mid-Atlantic region this year, two WNV human cases each have been reported in New York, New Jersey and Pennsylvania, with one death, plus one WNV human case in the District of Columbia, and no human cases in Virginia. Maryland reported its first WNV human case last week.
The worst year on record for WNV was in 2003, with 9,862 human cases and 264 deaths nationwide. That year, the worst West Nile outbreak in Delaware also occurred, with 17 confirmed human cases and two fatalities, plus six equine cases. In 2012, there was a resurgence nationwide of WNV involving 5,674 human cases and 286 deaths, with nine WNV human cases in Delaware and one death, but no horse cases due to equine vaccinations. Last year, nationwide numbers declined to 2,469 human cases.
Dr. Heather Hirst, State Veterinarian with the Delaware Department of Agriculture, said effective equine vaccines exist to protect horses from WNV and EEE. “I am urging horse owners to assist with prevention efforts by making sure their horses are vaccinated against both WNV and EEE,” Dr. Hirst said. “Initially, two doses of the vaccine are necessary for immunization. After the initial two vaccinations, a yearly booster is needed. Horse owners should consult their local veterinarian for advice on vaccination protocols. 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.”
There are no approved WNV or EEE vaccines for humans. The majority of humans infected with WNV typically have symptoms similar to a mild flu, if they show any symptoms at all; 20 percent 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 resulting in meningitis or encephalitis (inflammation of the brain), or acute flaccid paralysis, and sometimes death. Symptoms may include sudden onset of severe headache, high fever, stiff neck, confusion and muscle weakness. Individuals with these symptoms should see their physician immediately.
“Most people bitten by an infected mosquito won’t get sick,” said Dr. Karyl Rattay, Division of Public Health Director. “Others are not as lucky. The risk of severe disease, such as meningitis and encephalitis, increases with age resulting in the elderly being at higher risk for complications.”
“This finding of West Nile virus in Delaware serves as a good reminder for people to take common-sense precautions against mosquito bites,” Meredith said. These 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 night.
“We know that insect bites are not only annoying and sometimes painful, but can be dangerous as well,” Dr. Rattay said. “It’s better medicine to prevent insects from biting you at all. Use insect repellant whenever outdoors.”
To reduce mosquito-breeding, Meredith said people should drain or remove items that collect water, such as discarded buckets or containers, uncovered trash cans, stagnant birdbaths, unprotected rain barrels or cisterns, old tires, upright wheelbarrows, flowerpot liners, depressions in tarps covering boats, clogged rain gutters, downspout extenders, and unused swimming pools.
“The possibility of mosquito-borne disease transmissions won’t subside until cooler autumn temperatures set in, usually in mid-October and sometimes even later,” Meredith added.
To help determine when and where control services are needed, Mosquito Control encourages residents to report intolerable numbers of biting mosquitoes by calling the numbers below. Staff answers phones between 8 a.m. and 4 p.m. Monday through Friday. Callers after business hours or during weekends or holidays should leave their name, phone number, address and a brief message.
- Glasgow Office, serving New Castle County and northern Kent County (including the Dover area): 302-836-2555
- Milford Office, serving Sussex and southern Kent Counties: 302-422-1512
Source: September4, 2014 News Release from the Delaware Department of Natural Resources and Environmental Control
For more information on WNV in horses, please visit our previous post http://extension.udel.edu/equine/2013/08/23/protect-your-horses-from-west-nile-virus/