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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