final program.qxd - Parallels Plesk Panel

OP 8.2
West Nile Virus Infection in Humans: An Emergent Disease
James J. Sejvar, MD
Division of Vector-Borne Infectious Diseases and Division of Viral and Rickettsial
Diseases
National Center for Infectious Diseases - Centers for Disease Control and Prevention
Atlanta GA USA
West Nile Virus Infection
West Nile virus (WNV), an arthropod-borne flavivirus, has historically been associated
with infrequent epidemics of febrile illness in parts of Africa, Asia, and Europe. More
recently, outbreaks of WNV have increased both in frequency and in disease severity.
Since approximately 1996, epidemics and epizootics of WNV have occurred in Romania,
France, Tunisia, Russia, and other European countries. However, the emergence and
subsequent spread of WNV in North America has resulted in the largest outbreaks of
arboviral encephalitis in the Western hemisphere, with a resultant expansion in our
understanding of the clinical spectrum of human illness.
Transmission of WNV involves mosquito vectors and birds as amplifying hosts; e
xperience in North America has suggested great differences in vector competence, which
can influence human disease burden. Natural infection in humans is acquired through
bites from infected mosquitoes; however, several other modes of transmission have been
recognized, including transmission through blood transfusions, organ transplantation, and
transplacental transmission from infected mother to fetus.
Approximately 80% of human infections with WNV remain clinically silent. Most
symptomatic individuals develop West Nile fever, characterized by fever, chills, headache,
and fatigue. Most people recover completely, although recent data suggest that some
persons continue to experience persistent overwhelming fatigue. Non-neurologic clinical
manifestations, including rhabdomyolysis, ocular disease, and myocarditis, have been
described in case reports. More severe illness is seen in patients developing West Nile
neuroinvasive disease (WNND), which includes meningitis, encephalitis, and a
poliomyelitis-like syndrome. Elderly persons and immunocompromised individuals are at
greater risk of developing WNND. West Nile meningitis is characterized by fever,
meningismus, and headache; most persons recover uneventfully. West Nile encephalitis
is characterized by altered mental status or other neurologic deficits, and may range in
severity from a mild confusional state to severe encephalopathy and death. Movement
disorders including positional tremor, myoclonus, and parkinsonism, are frequently seen.
West Nile poliomyelitis is due to involvement of the lower motor neurons of the spinal cord,
similar to the syndrome produced by poliovirus infection. It is characterized by acute,
asymmetric weakness; brainstem involvement may result in acute neuromuscular
respiratory failure, associated with high morbidity and mortality. Clinical outcomes of
WNND vary, with some individuals experiencing persistent headaches, movement
disorders, cognitive difficulties, and fatigue. In West Nile poliomyelitis, persistent long-term
limb weakness and disability appear to be the rule.
There is no definitive treatment for WNV disease. Several therapies, including interferon-,
antisense nucleic acid agents, and antivirals, have either not been assessed in
randomized clinical trials or have not shown promising results. An intravenous
immunoglobulin product with high titers of anti-WNV antibodies is currently under
investigation. Several vaccines are in development and are undergoing clinical trials.
The future pattern of WNV in the Western hemisphere and elsewhere is unclear;
however, heavy viral activity has been observed in North America for several consecutive
years, lower level activity continues in several European countries, and WNV has been
detected in Central America. This suggests that WNV will continue to be a source of
considerable human morbidity and mortality for the foreseeable future.
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