Delaware announces two more cases of West Nile Virus in horses

DOVER, Del. – The Office of the State Veterinarian announced today Delaware’s fourth and fifth cases of West Nile Virus (WNV) found in horses in 2018. Three previous cases of WNV in horses were reported in 2018, two in August and one in September.

The fourth case of WNV confirmed in a Delaware horse occurred in a 1-year-old Standardbred mare residing in Kent County. The horse received veterinary care for loss of control of limbs and buckling over in the front limbs which began on October 11. Clinical signs progressed to inability to rise, muscle twitching, and stupor. The horse was euthanized on October 15 due to the severity of its illness. She had not been vaccinated for WNV. New Bolton Center Clinical Pathology Laboratory reported positive WNV results on October 19.

The fifth infected horse is a 6-year-old Belgian mare residing in Kent County that was evaluated by a veterinarian for whole body stiffness, acting sore, and abnormal mentation consisting of aggression with a date of onset of October 12, 2018. Diagnostic specimens were submitted to the National Veterinary Services Laboratory, which confirmed the diagnosis on October 23. The mare had never been previously vaccinated against WNV. She was treated supportively and her condition was improving as of October 18.

West Nile Virus and Eastern Equine Encephalitis (EEE) are diseases transmitted to horses via the bites of mosquitoes. Humans can also be infected with WNV and EEE, but transmission requires a mosquito bite and the virus cannot be directly transmitted between horses, or between horses and people. Signs of infection in horses include fever (although not always with WNV), anorexia, head pressing, depression or personality change, wobbling or staggering, weakness, blindness, convulsions, muscle spasms in the head and neck, or hind-limb weakness. If owners notice any of these signs in their horses, they should contact their veterinarian immediately. Two cases of WNV were confirmed in Delaware horses in 2017.

The Department of Natural Resources and Environmental Control’s (DNREC) Mosquito Control Section has seen an increase of WNV found in wild birds and sentinel chickens this year throughout the state. There have been a total of eight EEE-positive sentinel chickens and WNV has been detected in 66 sentinel chickens and 37 wild birds. So far in Delaware in 2018, eight cases of WNV have been found in humans.

Even though we are nearing the end of the mosquito season, the State Veterinarian urges horse owners to contact their veterinarians as soon as possible to have horses and other equines vaccinated against WNV and EEE. Neither disease has a specific drug treatment, and EEE infections in horses are fatal in 70 to 90 percent of cases, and WNV in 30 percent of cases.

Horse owners can take several additional steps in the barn and around the farm to help protect horses from mosquito bites. Horses should be kept inside during dawn and dusk, which are peak hours for mosquito activity. Topical insect repellents labeled for use on horses may be applied. The wind generated by fans installed in horse stalls can also help deter mosquitoes. Old tires and containers should be disposed of and standing water eliminated. Water troughs or buckets should be emptied, cleaned, and refilled every 2-3 days if possible to remove any mosquito eggs or larvae.

For more information about WNV or EEE:
• To report suspected cases of human West Nile Virus, call the DPH Office of Infectious Disease Epidemiology at 888-295-5196.
• Animal health questions should be directed to the Delaware Department of Agriculture at 800-282-8685 (Delaware only) or 302-698-4500. Ask for the Poultry and Animal Health Section.
• Questions about the state’s mosquito control program or mosquito biology should be directed to the Delaware Department of Natural Resources and Environmental Control’s Mosquito Control Section at 302-739-9917.

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Media Contact: Stacey Hofmann, 302-698-4500, stacey.hofmann@delaware.gov


DNREC’s Mosquito Control Section announces expanded detection of Eastern Equine Encephalitis

Continued awareness and precautions encouraged

The logo for the Department of Natural Resources and Environmental ControlDOVER (Sept. 20, 2018) – The recent detection of Eastern Equine Encephalitis (EEE) in sentinel chickens monitored for mosquito-borne diseases by the DNREC Division of Fish & Wildlife’s Mosquito Control Section reinforces the fact that mosquitoes remain active and that precautions should continue to be taken to avoid mosquitoes whose bites could transmit EEE and other mosquito-borne diseases.

Test results reported to the Mosquito Control Section last week by the Delaware Division of Public Health Laboratory indicated EEE-positive chickens from three additional stations of the 20 stations monitored by the Mosquito Control Section throughout the state. Two of these positive stations were in New Castle County and one in Sussex County, increasing the total number of EEE-positive sentinel chicken stations this year to six: three in New Castle County and three in Sussex County. This higher-than-average detection rate for EEE suggests increased EEE activity and distribution in Delaware.

Eastern Equine Encephalitis is a rare, but potentially fatal, viral disease spread by mosquitoes, and is considered one of the more serious mosquito-borne illnesses. Although there is an EEE vaccine for horses, an EEE vaccine is not available for people. No human cases of EEE have been reported to date this year in Delaware.

Anyone in an area where the virus is circulating can be infected with EEE. The risk is highest for people exposed to high numbers of mosquito bites, including people who live in, visit, or work outside in areas with high mosquito populations where there is greater exposure to potentially infected mosquitoes. Those over age 50 and under age 15 appear to be at greatest risk for developing severe disease when infected with EEE.

While most patients infected with EEE have no apparent illness, severe cases of EEE (involving encephalitis, an inflammation of the brain) begin with the sudden onset of headache, high fever, chills, and vomiting. The illness may then progress into disorientation, seizures, or coma. Symptoms of EEE often appear four to 10 days after being bitten by an infected mosquito. Approximately 33 percent of EEE cases lead to death, and many of those who do survive experience significant brain damage. There is no specific treatment for EEE; care is based on symptoms. If you think you or a family member may have contracted EEE, it is important to consult your health care provider for proper diagnosis.

In response to DNREC’s recent EEE detections, along with ongoing West Nile virus activity, the Mosquito Control Section will increase mosquito population surveillance in areas where these detections have occurred and take mosquito control actions as warranted to include possible aerial spraying and/or fogging with a spray truck. However, the best protection to lessen the chance of contracting a mosquito-borne disease is to avoid mosquito bites by:

  • Properly using insect repellent containing DEET whenever outdoors;
  • Covering up exposed skin as much as possible by wearing long-sleeved shirts and pants; and
  • Avoiding known high mosquito population areas or being outside during times of peak mosquito activity, typically dawn and dusk.

In addition to avoiding mosquito bites, the Mosquito Control Section advises residents to also reduce mosquito breeding habitat on their individual properties and communities/neighborhoods by draining or removing items that collect water, such as discarded buckets or containers, uncovered trash cans, stagnant birdbaths, unprotected rain barrels or cisterns, old tires, upright wheelbarrows, flower pot liners, depressions in tarps covering boats, clogged rain gutters, corrugated downspout extenders and unused swimming pools.

The Mosquito Control Section also encourages residents to report intolerable numbers of biting mosquitoes by calling the numbers below 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

For more information about:

  • Mosquito biology/ecology and control – Contact the Mosquito Control Section’s Dover office at 302-739-9917.
  • Reporting WNV-suspect wild birds, or for requests for mosquito relief – For upstate areas from Dover north, contact Mosquito Control’s Glasgow field office at 302-836-2555; for downstate areas south of Dover, contact Mosquito Control’s Milford field office at 302-422-1512.
  • WNV or EEE in humans and related medical issues – Contact the Delaware Division of Public Health at 888-295-5156.
  • Animal health questions should be directed to the Delaware Department of Agriculture at 800-282-8685 (Delaware only) or 302-698-4500. Ask for the Poultry and Animal Health Section.
  • For more information on West Nile Virus or Eastern equine encephalitis – Visit the CDC website, www.cdc.gov/ncidod/dvbid/westnile/index.htm.

Contact: Joanna Wilson, DNREC Public Affairs Office, 302-739-9902

Vol. 48, No. 253


DNREC’s Mosquito Control Section announces year’s first finding of West Nile virus in wild birds

DOVER – The Department of Natural Resources and Environmental Control’s Mosquito Control Section, in conjunction with Delaware’s Division of Public Health and Department of Agriculture, has announced the first detection this year of West Nile virus (WNV) in wild birds, indicating the recurrence of this mosquito-borne disease in Delaware. WNV was detected in the first wild bird collected and tested by Mosquito Control this year, a crow found June 29 in southwestern Sussex County, and reported as WNV-positive July 5 by the Public Health Laboratory. Another crow collected in Sussex County also was reported as WNV-positive four days later.

The peak time of year for transmission of WNV, along with Delaware’s other mosquito-borne disease of concern, Eastern equine encephalitis (EEE), is from about mid-August into mid-October. During most years, evidence of WNV is first found upstate later in the season.

“Heavy rainfall amounts three times above normal from mid-May to mid-June caused a serious irruption of adult mosquitoes statewide, with conditions worse downstate than upstate,” said Mosquito Control Section Administrator Dr. William Meredith with DNREC’s Division of Fish & Wildlife. “But with extensive aerial spraying, we have now knocked back mosquito numbers in Delaware. We are hoping this early virus detection does not foreshadow abnormal mosquito-borne disease activity later in the year.”

The first finding of mosquito-transmitted virus in Delaware also serves as a good reminder for people to continue taking common-sense precautions against mosquito bites. 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. The possibility of mosquito-borne disease transmissions will not subside until cooler autumn temperatures set in, usually in mid-October and sometimes later.

To reduce mosquito-breeding habitat and chances of disease transmission, residents should drain or remove from outdoor areas all items that collect water, such as discarded buckets or containers, uncovered trashcans, stagnant birdbaths, unprotected rain barrels or cisterns, old tires, upright wheelbarrows, flowerpot liners, depressions in tarps covering boats, clogged rain gutters, corrugated downspout extenders and unused swimming pools.

In addition to wild bird testing, the Mosquito Control Section also operates 20 monitoring stations with caged chickens in the field statewide from early July into October. The sentinel chickens are humanely kept and tended. Sentinel chickens bitten by mosquitoes carrying WNV or EEE develop antibodies that enable them to survive, with both WNV or EEE affecting humans and horses, but which cannot be transmitted between horses or from horses to people. Chicken blood from each monitoring station is tested every week for the antibodies, which indicate exposure to the mosquito-borne viruses. Mosquito Control also conducts statewide monitoring to determine the types and population abundances of the 19 mosquito species of most concern through a statewide network of 25 stationary adult light trap stations, and assesses larval mosquito populations by sampling aquatic habitats around the state.

No approved WNV or EEE vaccines are available for humans, according to Delaware’s Division of Public Health. The majority of people infected with WNV will not show any symptoms; 20 percent develop a mild illness, which may include fever, body and muscle aches, headache, nausea, vomiting, and rash. A small number of people infected develop serious illness, with young children, pregnant women, senior citizens and individuals with immuno-compromised systems being particularly vulnerable. Neurological symptoms including paralysis and possibly death may occur.

Effective EEE and West Nile vaccines are available for horses through veterinarians, according to the Delaware Department of Agriculture’s State Veterinarian’s Office. Both WNV and EEE cause severe, and sometimes fatal, infections in horses. Signs of infection in horses include fever (although not always with WNV), anorexia, head pressing, depression or personality change, wobbling or staggering, weakness, blindness, convulsions, muscle spasms in the head and neck, or hind-limb weakness. If owners notice any of these signs in their horses, they should contact their veterinarian immediately.

Horse owners can take several steps in the barn and around the farm to help protect horses from WNV and EEE. Horses should be kept inside during dawn and dusk, which are peak hours for mosquito activity. Topical insect repellents labeled for use on horses may be applied. The wind generated by fans installed in horse stalls can also help deter mosquitoes. Old tires and containers should be disposed of and standing water eliminated. Water troughs or buckets should be emptied, cleaned, and refilled every 2-3 days if possible to remove any mosquito eggs or larvae.

For more information about:

  • Mosquito biology/ecology and control – Contact the Mosquito Control Section’s Dover office at 302-739-9917.
  • Reporting WNV-suspect wild birds, or for requests for mosquito relief – For upstate areas from Dover north, contact Mosquito Control’s Glasgow field office at 302-836-2555; for downstate areas south of Dover, contact Mosquito Control’s Milford field office at 302-422-1512.
  • WNV or EEE in humans and related medical issues – Contact the Delaware Division of Public Health at 888-295-5156.
  • WNV or EEE in horses and equine vaccines – Contact the Department of Agriculture’s Poultry and Animal Health Section at 302-698-4500 or 800-282-8685 (Delaware only).
  • For more information on West Nile virus or Eastern equine encephalitis – Visit the CDC website, www.cdc.gov/ncidod/dvbid/westnile/index.htm

Media contact: Joanna Wilson, DNREC Public Affairs, 302-739-9902

Vol. 48, No. 187

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