MARYLAND WEST NILE VIRUS SUMMARY, 2000

The Maryland Department of Health and Mental Hygiene (DHMH), in collaboration with the Maryland Department of Agriculture (MDA) and the Maryland Department of Natural Resources (DNR), implemented a surveillance plan for West Nile virus (WNV) detection activities. The plan highlighted four major components of WNV surveillance: mosquito, avian, veterinary, and human. The following summarizes surveillance findings in 2000:

Major Components:

1. Mosquito Surveillance:
MDA sampled fourteen jurisdictions throughout Maryland January 1 - December 31, 2000. A total of 93,848 mosquitoes were submitted for WNV testing; all mosquito samples were negative for WNV.

2. Avian Surveillance:
Live Bird Surveillance: Fourteen sentinel chicken flocks consisting of four birds each (56 total birds) were established by MDA in ten jurisdictions May 21 - September 28. Chicken sera were collected bi-weekly; all 559 chicken sera samples tested negative for WNV antibody. Another component of live bird surveillance was an ongoing wild and captive bird serosurvey, conducted by the DNR Fish and Wildlife Health Program. In 2000, 265 wild bird blood samples were submitted to the National Wildlife Health Center; all avian samples were negative for viral isolation of WNV.

Dead Bird Surveillance: The Maryland WNV Reporting Hotline, a toll-free, 24-hour hotline staffed by DNR and DHMH personnel, was launched on May 19, 2000. Staff provided general information concerning WNV and coordinated dead bird pick-up by contacting local health departments (LHDs) with appropriate specimen reports. LHDs selected birds and delivered them to DHMH Laboratories for WNV testing. A total of 13,605 calls were received in 2000, with 66% of calls reporting dead/dying birds. A total of 893 birds were tested for WNV by reverse transcriptase polymerase chain reaction (RT-PCR). Fifty (50) birds tested positive (48 crows, 2 blue jays). The 50 positive birds were collected in a five week period, between September 13 and October 20 from eight jurisdictions: Anne Arundel (2), Baltimore City (29), Baltimore Co. (9), Charles (2), Frederick (1), Howard (3), Montgomery (3), and Prince George's (1). Dead bird pickup ceased October 31, 2000.

3. Veterinary Surveillance:
All Maryland veterinarians registered with the Maryland State Board of Veterinary Medical Examiners were contacted by the Maryland State Public Health Veterinarian in a mass mailing alerting them to the clinical signs and symptoms of West Nile and other arboviral infections in horses (equines). Ten (10) equine specimens, one pygmy goat and one deer were submitted for RT-PCR testing; all samples were negative for WNV. From mid-September until December 31, randomly selected bats that were rabies negative (n=40) were submitted for WNV testing; all bats tested negative for WNV.

4. Human Surveillance:
Guidelines were issued to all LHDs concerning enhanced passive surveillance of human encephalitis and aseptic meningitis cases in order to confirm or rule out WNV as a cause. The Acting State Epidemiologist notified, by letter, infection control professionals, emergency department directors, and physicians in Maryland hospitals of the existence of the human arbovirus surveillance project and requested reports of any suspected encephalitis or meningitis cases to the appropriate LHDs. DHMH Laboratories offered serologic testing of human blood and cerebrospinal (CSF) specimens. From May 1 - November 30, a total of 203 Maryland residents were tested for WNV infection; all 203 tested negative for WNV antibody.

Other components:

Mosquito Control:
MDA implemented an aggressive mosquito control program using ground spraying of the adulticide Permethrin in two square mile areas surrounding all WNV-positive findings. In addition to adulticiding efforts, routine mosquito larviciding occurred in spring, 2000.

Pesticide Toxicity Surveillance:
Surveillance of acute pesticide-related toxicity in humans was conducted by DHMH at four Baltimore City sentinel hospitals for five days immediately following mosquito adulticiding, and five Montgomery Co. hospitals for three days immediately following adulticiding. All nine hospital emergency departments (EDs) reported that no people presented to the EDs with symptoms that the patient attributed to pesticide spraying. The Maryland Poison Control Center (Baltimore) and the National Capital Area Poison Control Center (DC) reported a total of 208 calls over a 30-day period related to WNV activity and/or subsequent spraying. Ten callers reported symptoms that they attributed to spraying; no callers were hospitalized.

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Maryland Department of Health & Mental Hygiene — Epidemiology & Disease Control Program