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New Viral Encephalitis Marked by Muscle Weakness.

Encephalitis fears are abating in New York City, but the epidemiologic thriller is not over.

Experts report that the cause of the infectious disease is a new arbovirus. Potential cases were being detected beyond the New York metropolitan area, in Connecticut and New Jersey, at press time.

No new cases have occurred in New York City since the insecticide spraying program started in September, but there may be pockets of the virus still around, Dr. Rick Conetta, director of the critical care unit at Flushing Hospital Medical Center in Queens, told FAMILY PRACTICE NEWS.

Dr. Conetta and his colleagues knew an outbreak was afoot when a cluster of patients with a puzzling picture of encephalopathy was admitted to his service at Flushing Hospital Medical Center.

The profound muscle weakness of the patients, which progressed to the point of total paralysis, made the physicians suspect they were dealing with an unusual disease.

And now, as more of the viral DNA sequence is decoded, scientists suspect that the etiologic agent is a new variant of either the Australian Kunjin virus or the West Nile virus, neither of which have been seen before in the Western Hemisphere (Lancet 354[9186]:1261-62, 1999).

The detective work started in August when four patients, all residents of the Whitestone area of Queens, presented within an 11-day span with the same clinical picture: high fever, confusion, and generalized muscle weakness.

All of the patients, aged 60-87, had been previously healthy and active, Dr. Conetta said. Some had been outside working in their gardens where they could have been exposed to mosquitoes harboring the virus.

The patients first developed fever up to 104 [degrees] F, accompanied by mental status changes that progressed to coma. Within a few days of the initial symptoms, they developed generalized muscle weakness to the point of respiratory paralysis, requiring ventilatory support.

In the 10 years that he has been the director of the critical care unit, Dr. Conetta has never seen anything like this outbreak. "To see four people come from the same area be this acutely ill at the same time is unusual."

Spinal tap revealed a picture of aseptic meningitis--the spinal fluid had a high protein content with lymphocytes. Smears and cultures for routine organisms were negative, so the physicians suspected viral meningitis or meningoencephalitis. CT scans of the brain were also negative.

They persisted in the work-up. "What was peculiar was the muscle weakness," Dr. Conetta said. Most encephalitides progress to seizure activity but do not cause muscle weakness. None of these patients had seizures, only muscle weakness, "so we knew it was something strange," he added. Acute Guillian-Barre syndrome was strongly suspected, but electromyography did not confirm this diagnosis.

Soon after the fourth patient was admitted to the critical care unit, the Flushing Hospital physicians contacted the New York City Department of Health, alerting them to a possible outbreak of an unusual viral illness.

Samples sent to the Centers for Disease Control and Prevention in Atlanta were serologically positive for St. Louis encephalitis virus, which was initially thought to be the culprit. But some of the patients had equivocal titers, "which was unusual, since we would have expected all of them to have positive titers," given the full-blown course of the illnesses, Dr. Conetta said.

At the same time that people were falling ill, a rash of dead birds, including crows and exotic zoo birds, were observed in the region. Genomic sequencing of a pathogen isolated from the brains of these birds suggested a virus similar to the West Nile virus. Serologies for the West Nile virus were performed; all four patients in the original cluster had positive titers.

Interestingly, although the West Nile virus is known to infect birds, death has never been observed before, said Dr. Rima Khabbaz of the CDC. Birds are suspected to be the reservoir of the mosquito-transmitted virus.

Dr. Ian Lipkin and his colleagues at the emerging diseases laboratory at the University of California, Irvine, have since isolated the virus from the brains of four encephalitis victims. The genomic sequence suggests that the new virus is a distinct strain that may be closer to the Australian Kunjin virus than the West Nile virus, Dr. Lipkin said in an interview.

As of Oct. 15, there have been 55 laboratory-positive cases and 6 fatalities; none of the patients had onset of the illness after Sept. 17 (MMWR 48[39]:890-92, 1999).

Muscle weakness is present in only a minority of patients with St. Louis encephalitis, whereas muscle weakness is present in a majority of the new viral illness that he has seen, Dr. Conetta said. Fortunately, management is the same for both illnesses: vector control and supportive care.

Since notifying the New York City Department of Health, Dr. Conetta has seen three more confirmed cases at Flushing Hospital. Among the four original cases, there were three deaths due to complications or withdrawal of life support. These patients had multisystem organ failure and brain damage. One patient recovered and is now in rehabilitation.

Diagnosing the New Variant of Encephalitis

Profound muscle weakness in the setting of high fever and mental confusion should ring warning bells for the new arboviral encephalitis that struck the New York metropolitan area.

Even though cold weather signals the end of mosquito season, physicians in the Northeast region should remain vigilant for the triad of high fever, mental status changes, and muscle weakness, according to Dr. Rick Conetta.

If a patient is mildly ill and at home, no specific testing is needed. But a patient sick enough to be hospitalized should be tested for antibodies to West Nile virus or the newly identified strain.
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Publication:Family Practice News
Date:Nov 1, 1999
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