US authorities begin hunting for dead birds infected with West Nile virus*

Authorities of Suffolk County have activated a hotline for local
residents to report occurrences of dead birds that may be infected with
West Nile virus. Birds infected with that virus can often be found at
pools or any other open source of water due to their thirst which they
suffer from because of the viral infection. Specialists of the Suffolk
County Department for Health Services will follow such reports to pick
up crows, blue jays, hawks, falcons, owls, exotic or unusual bird species.

West Nile virus (or WNV) is a virus of the family Flaviviridae; part of
the Japanese encephalitis (JE) antigenic complex of viruses, it is found
in both tropical and temperate regions. It mainly infects birds, but is
known to infect humans, horses, dogs, cats, bats, chipmunks, skunks,
squirrels, and domestic rabbits. The main route of human infection is
through the bite of an infected mosquito.

Image reconstructions and cryoelectron microscopy reveal a 45-50 nm
virion covered with a relatively smooth protein surface. This structure
is similar to the dengue fever virus; both belong to the genus
Flavivirus within the family Flaviviridae. The genetic material of WNV
is a positive-sense, single strand of RNA, which is between 11,000 and
12,000 nucleotides long; these genes encode seven non-structural
proteins and three structural proteins. The RNA strand is held within a
nucleocapsid formed from 12 kDa protein blocks; the capsid is contained
within a host-derived membrane altered by two viral glycoproteins.

W.N.V. has three different effects on humans. The first is an
asymptomatic infection; the second is a mild febrile syndrome termed
West Nile Fever; the third is a neuroinvasive disease termed West Nile
meningitis or encephalitis. In infected individuals the ratio between
the three states is roughly 110:30:1.

The second, febrile stage has an incubation period of 3-8 days followed
by fever, headache, chills, diaphoresis, weakness, lymphadenopathy, and
drowsiness. Occasionally there is a short-lived truncal rash and some
patients experience gastrointestinal symptoms including nausea,
vomiting, loss of appetite, or diarrhea. All symptoms are resolved
within 7-10 days, although fatigue can last for some weeks and
lymphadenopathy can take up to two months to resolve.

The more dangerous encephalitis is characterized by similar early
symptoms but also a decreased level of consciousness, sometimes
approaching near-coma. Deep tendon reflexes are hyperactive at first,
later diminished. There are also extrapyramidal disorders. Recovery is
marked by a long convalescence with fatigue.

More recent outbreaks have resulted in a deeper study of the disease and
other, rarer, outcomes have been identified. The spinal cord may be
infected, marked by anterior myelitis with or without encephalitis.
WNV-associated Guillain-Barré syndrome has been identified and other
rare effects include multifocal chorioretinitis (which has 100%
specificity for identifying WNV infection in patients with possible WNV
encephalitis), hepatitis, myocarditis, nephritis, pancreatitis, and
splenomegaly.

The virus is transmitted through mosquito vectors, which bite and infect
birds. The birds are amplifying hosts, developing sufficient viral
levels to transmit the infection to other biting mosquitoes which go on
to infect other birds (in the Western hemisphere the American robin and
the American crow are the most common carriers) and also humans. The
infected mosquito species vary according to geographical area; in the US
Culex pipiens (Eastern US), Culex tarsalis (Midwest and West), and Culex
quinquefasciatus (Southeast) are the main sources.