New Jersey Department of Health and Senior Services
West Nile Virus Fact Sheet
February 23, 2001
Q. What is West Nile virus
encephalitis?
A. West Nile virus encephalitis is a mosquito-borne viral disease, which can
cause an inflammation of the brain. The West Nile virus (WNV) is commonly found
in Africa, West Asia, the Middle East and Europe, and is closely related to St.
Louis encephalitis virus, which was found in New Jersey in 1964 and 1975. For
the first time in North America, WNV was confirmed to be present in the New York
metropolitan area during the summer and fall of 1999. WNV successfully
over-wintered in the northeastern United States and was present in humans,
horses, birds and mosquitoes in 2000, and preparations are being made to monitor
for WNV activity again in 2001.
Q. How do people get West Nile
Virus encephalitis?
A. WNV is transmitted to people by the bite of a mosquito that has become
infectious after feeding on a bird infected with the virus. Birds serve as the
reservoir hosts of WNV, and the principal vector in the transmission from one
bird to another is the northern house mosquito, Culex pipiens and other Culex
mosquitoes. WNV has also been found in several species of Aedes mosquitoes,
which could serve as bridge vectors by picking up the virus from birds and then
transmitting it to humans or horses.
Q. How many cases of West Nile
virus infection occurred in New Jersey in 2000?
A. Six residents of New Jersey, out of a total of 55 which initially met WNV
testing criteria, were confirmed to be positive for WNV, with 1 death in 2000.
New York City reported 14 cases, including 1 death and Connecticut reported 1
case in 2000.
Q. What are the symptoms of West
Nile virus infection?
A. Most infections produce no symptoms in people, or are mild or moderate.
Symptoms may include: fever, headache, and body aches, often with skin rash and
swollen lymph glands. More severe infections may be marked by headache, high
fever, neck stiffness, muscle weakness, stupor, disorientation, convulsions,
paralysis, coma and rarely death.
Q. What tests does the New Jersey
Department of Health and Senior Services (DHSS) do to determine a human case of
West Nile virus encephalitis?
A. To screen potential cases for WNV, blood and spinal fluid samples are
sent to the DHSS Laboratory for an ELISA antibody test.
Q. What is a confirmatory test?
A. If the first test is positive, samples are sent to the national Centers
for Disease Control and Prevention (CDC) to repeat the first test and perform
PCR tests, followed by a serum neutralization test on the initial and a second
specimen for final confirmation.
Q. How is West Nile encephalitis
treated?
A. There is no specific therapy. In more severe cases, intensive supportive
therapy is indicated, ie. hospitalization, IV fluids, airway management,
respiratory support (ventilator) if needed, prevention of secondary infections
(pneumonia, urinary tract, etc.) and good nursing care.
Q. What is the incubation period
in humans?
A. Usually 5 to 15 days from the time a mosquito carrying the WNV infects a
person.
Q. Where did the 6 people with
West Nile virus encephalitis in New Jersey become infected?
A. The patients were residents of 5 different counties, but it is not
possible to determine where each patient was bitten by infectious mosquitoes. It
is most important that residents in all parts of the State take preventive
measures to reduce the risk of mosquito bites as outlined in this Fact Sheet and
other educational materials.
Q. Should outdoor activities in
August and September be cancelled when there is evidence of West Nile virus
activity?
A. There is no reason to change plans for outdoor activities, but common
sense precautions should be taken to avoid mosquito bites, particularly at dusk
and early evening.
Q. What proportion of people die
when infected with WNV?
A. Since the majority of infected persons are asymptomatic, the fatality
rate is much less than 1%. However, case fatality rates for hospitalized
patients may range from 3% to 15%, and are highest in the elderly.
Q. Can you get WNV directly from
crows or from other people?
A. There is no evidence that a person can get the virus from handling live
or dead infected birds. However, avoid barehanded contact when handling any dead
animal. WNV is NOT transmitted from person to person. There is some evidence
that crow-to-crow transmission fo WNV is possible without mosquito
vectors.
Q. What is the basic transmission
cycle for WNV?
A. Mosquitoes become infected by feeding on infected birds, which have virus
circulating in their blood. After an incubation period of 10 days to 2 weeks,
the infected mosquitoes can then transmit the virus to other animals or humans when
biting to take a second blood meal.
Q. Why are crows, but not most
other dead birds, tested for WNV?
A. In 1999 and 2000, there was a large die-off of American crows from WNV in
New Jersey and other states. Although other birds also can become infected with
the virus, the mortality rate is much lower in other birds. Because crows are
extremely susceptible to WNV, they are very useful as a sentinel animal to
monitor viral activity. In 2000, 1,283 birds (over 95% of them crows) were
confirmed to be positive for WNV from 18 counties in New Jersey. Since the first
positive crows were collected in late May, long before any human or horse cases,
the crow surveillance provided an early warning of WNV activity.
Q. What other kinds of
surveillance are conducted to detect WNV activity in New Jersey?
A. As part of a multi-agency plant to monitor WNV and prevent virus
transmission in 2000, surveillance activities were conducted in all 21 counties
to detect and monitor the virus in crows, hawks, falcons, urban birds, sentinel
chickens, horses and mosquitoes, as well as surveillance for human cases. A
total of 1,283 birds from 18 counties, 82 mosquito pools from 11 counties, 4
sentinel chickens from 4 counties and 28 horses from 11 counties were confirmed
to be positive for WNV. There was evidence of WNV in all but 1 New Jersey county
in 2000. Extensive surveillance activities, with some modifications, are planned
for 2001.
Q. What agencies conduct the
surveillance and provide mosquito control services?
A. The WNV surveillance plan is coordinated among a number of agencies,
including the State Mosquito Control Commission, the State Departments of Health
and Senior Services, Environmental Protection, and Agriculture; Rutgers
University, 21 county mosquito control agencies, local health departments, and
physicians and hospitals, in addition to the national Centers for Disease
Control and Prevention (CDC) and other states in the region.
The primary responsibility for mosquito control rests with the 21 county mosquito control agencies, which conduct many activities, including: education, surveillance, source reduction and biological and chemical control of larval and adult mosquitoes.
Q. Can West Nile virus cause
illness in dogs and cats?
A. The virus apparently does not usually cause illness in dogs and cats. WNV
was isolated from a cat in New Jersey in 1999, but this is the only case
recorded in cats. A serosurvey of dogs and cats in the New York WNV epidemic
area in 1999 showed a low infection rate in healthy dogs and cats. There is no
evidence that a dog or cat can transmit the virus to humans or animals.
Q. Can WNV cause death in horses?
A. Of the 28 New Jersey horse cases in 2000, 8 either died or had to be
euthanized. In horses, the virus can interfere with normal central nervous
system functioning and cause inflammation of the brain. Most horses recover from
the infection. As with other animals, horses become infected by the bite of
infectious mosquitoes.
Q. Is there a vaccine to protect
horses from WNV infection?
A. No vaccine is available at this time, but an experimental vaccine may be
available sometime in 2001. The vaccine for Eastern equine encephalitis (EEE)
will not give cross protection against WNV.
Q. What can I do to reduce my
risk of becoming infected with WNV?
A. Eliminate stagnant water around the home in discarded tires, blocked
gutters, unclean birdbaths, poorly maintained pools, and any type of receptacle
with decaying organic matter.
Limit outdoor activities at dawn, dusk and in the early evening, when possible.
Wear long-sleeved shirts and long pants whenever you are outdoors.
Make sure screen doors and windows are in good condition.
When going outside, use an effective skin or clothing mosquito repellent. Always use a repellent according to instructions on the product label.
Q. Who can I contact to ask about
mosquito control spraying in my area?
A. You can call your county mosquito control agency. As the pesticide
applicator, with professional staff licensed to apply mosquito larvicides and
adulticides, the county agency can answer questions about insecticide
applications in your community.
Q. Where can I get more
information about WNV?
A. the pamphlet "Mosquito Borne Viruses of New Jersey" and
information about mosquito control around the home are available from your local
health department and county mosquito control agency.
The following web sites are a source
for additional information:
New Jersey Department of Health and Senior Services (www.state.nj.us/health)
New Jersey Department of Environmental Protection (www.state.nj.us/dep/mosquito)
New Jersey Mosquito Homepage (www.njmosquito.org)
New Jersey Department of Agriculture (www.state.nj.us/agriculture)
Centers for Disease Control and Prevention (www.cdc.gov)