An outbreak of disease in New York City in August, which was originally diagnosed as St Louis encephalitis, has turned out to be West Nile-like virus, a virus never before found in the United States. Previous outbreaks have occurred in Uganda, Israel, Romania and south Africa.
The health commissioner for New York state, Dr Antonia Novello, reported last week that 48 laboratory positive cases of West Nile-like virus had been identified. A total of eight people have died during the outbreak, all of whom experienced symptoms of clinical encephalitis.
The correct identification of the disorder is being attributed, in part, to conscientious detective work by Dr Tracey McNamara, a Bronx Zoo pathologist, who became concerned at the large number of crows dying around the zoo during the summer. Then, early in September, the zoo lost several exotic birds.
Postmortem examinations in these birds showed varying degrees of meningoencephalitis and severe myocarditis. Tissue samples were sent to laboratories for further study.
Testing at the federal Centers for Disease Control and Prevention (CDC) indicated that the samples contained material closely related to West Nile virus. In other tests at the CDC, a West Nile-like virus genomic sequence identical with that derived from the bird isolates was observed in a human brain specimen from an encephalitis case.
Concurrently, specimens of brain tissue from three human encephalitis cases, sent to the Emerging Disease Laboratory, at the University of California at Irvine, were reported as positive for West Nile-like virus by genomic analysis.
The West Nile virus is transmitted to humans from mosquitoes that have bitten infected birds. At the beginning of September New York City began aerial and ground spraying of pesticides to reduce the mosquito population.
Surveillance for new, human West Nile virus cases will be conducted until several weeks after the first frost, when mosquito activity is expected to subside.
Dr Duane Gubler, the director of the division of vector borne infectious disease at the CDC, said, “These viruses do travel with birds, and bird migration has been in process now for a better part of the month. There is a good possibility that this virus has already been taken to areas further south.”
A report on West Nile-like viral encephalitis can be found in the CDC’s Morbidity and Mortality Weekly Report of 1 October (at www.cdc.gov).
Figure.
AP PHOTO/WANDERLAN P. SILVA
New York City Health Department official applies larvicide to a swimming pool to kill disease-carrying mosquitoes