NurseWeek: Global Swarming

Global swarming
Migration of birds, insects and other species triggers rise in infectious diseases – and places new demands on health care

By Diane Sussman
September 18, 2000
Photo: Montgomery County (Md.) Department of Health and Human Services

The West Nile virus has been responsible for several deaths in the U.S. over the past two years. The virus is carried by mosquitoes that contract the virus from infected birds.


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Hanta. Nipah. Hendra. Ebola. West Nile. Arena. Lassa. With their exotic names and distant origins, they suggest scourges of the past, such as smallpox, vanquished by vaccines, antibiotics and modern hygiene. But the past few years have brought striking episodes of the devastating effects of emerging and dormant viruses, serving as a powerful reminder of how susceptible the human population is and how quixotic the concept of conquering the world’s viruses ultimately may prove to be.

Consider these recent incidents:

Last month, an 83-year-old Israeli man died of complications of West Nile virus, the same virus that killed seven people and sickened 62 in the New York metropolitan region last summer. Five elderly people have been diagnosed with the virus this year, although none have died. The mosquitoborne virus, which causes encephalitis and meningitis, was unknown in the Western Hemisphere before last year. Outbreaks in Israel, Romania and South Africa during the past 40 years have killed hundreds and sickened thousands.
One hundred people dead and 1 million pigs slaughtered in Malaysia because of the newly discovered Nipah virus. Researchers isolated strains of the deadly virus in urine collected from a type of fruit bat. It made itself known when it crossed over to pigs, then humans. The CDC has put Nipah in the class of viruses called paramyxoviruses, which includes Hanta, HIV, measles, mumps and Hendra. There is no known cause or cure.
Four cases of hantavirus, one fatal, were reported in California this spring, all in the rural, mountainous regions of Yolo and Mono counties. Spread primarily by deer mice, the virus was rarely seen outside the arid Southwest until last year. Infection leads to hantavirus pulmonary syndrome, a potentially fatal illness that starts with a fever and can progress to shortness of breath severe enough to warrant intubation.
California also is the new home of arenavirus, a rodentborne virus never before seen in North America. The virus, usually found only in South America and Africa, killed a teen-age girl from Oakland in April. Arenaviruses cause hemorrhagic diseases, including Argentine hemorrhagic fever, Lassa fever, Bolivian hemorrhagic fever and lymphocytic choriomeningitis.
In 1994, Hendra virus, transmitted by fruit bats, killed 14 racehorses and two people, including the horses’ trainer, in Australia.

Unforeseen trends
Infectious diseases are now the world’s leading killer of children and young adults, accounting for 13 million deaths per year, said David Heymann, MD, executive director for communicable diseases for the World Health Organization. One in two of those deaths occurred in developing countries.

In the United States, mortality from infectious diseases increased 58 percent from 1980 to 1992, according to a study published in the Jan. 6, 1999, issue of the Journal of the American Medical Association, a trend that was unforeseen. According to the National Center for Health Statistics Division of Vital Statistics, the number of deaths in the United States each year from all non-HIV-related infectious diseases combined is 37,826, higher than the number of suicides.

If the trend was unforeseen, it is because antibiotics and vaccines have made the world complacent, said Don Henderson, MD, director of the Johns Hopkins University Center for Civilian Biodefense Studies in Baltimore. "What is happening now is not surprising, or shouldn’t be surprising," he said. "I think we’ve gone through a period when we believed we had whipped infectious diseases. But mutations and change are part of nature. What is surprising is the frequency and severity of the outbreaks."

Also surprising is the sheer number of new infectious diseases, not to mention new places where old ones are landing. "We’re testing a lot more now because we have so many more viruses now," said Carol Glaser, MD, medical officer for the California Department of Health Services’ viral disease laboratory. "The old pathogens haven’t gone away, and there are all these new pathogens to consider."

Experts are mostly at a loss to explain why so many viruses are emerging now, as well as how they migrate beyond customary boundaries and spread from one species to another.

Frequent explanations are global warming, global travel, global commerce, a change in the distribution of disease-carrying animals and insects, population movement due to civil wars and natural disasters, and the migration patterns of birds, bats and insects. A 1992 Institute of Medicine report also listed IV drug use and risky sexual practices, increased human contact with rain forests and other wilderness habitats, and increased urbanization and crowding.

West Nile virus probably was imported on a bird, CDC spokesman Tom Skinner said. But what bird, and where it came from, is unknown, he said. Tests in New York point to the house sparrow as a reservoir, along with crows, but the virus originally could have flown in on a gull that shared a tick with an altogether different bird. But it is also possible the virus entered the United States in the blood of a tourist from Israel, which experienced an outbreak in 1998.

Diagnostic difficulties
Not surprisingly, the unfamiliarity of these viruses already has led to misdiagnoses and incorrect treatment. Difficulty in diagnosing West Nile virus is being blamed for the death of an elderly New York man and for the misdiagnosis of a teen-age boy.

In the first case, a 69-year-old man who reported progressive weakness was diagnosed with Guillain-Barré syndrome. West Nile virus was not diagnosed for two weeks, but by then he was severely paralyzed and on a ventilator.

In the second case, a 15-year-old boy was hospitalized after three days of fever, headache, vomiting and confusion. The boy eventually recovered but spinal and blood tests later revealed infection with the virus.

And when the Nipah outbreak occurred in Malayasia, health care workers initially believed they were dealing with Japanese encephalitis, which has similar symptoms of fever, aches and coma. Health care workers had to rethink their diagnosis when pigs started dying, too, which does not happen with Japanese encephalitis. Several of those who were infected had been inoculated against Japanese encephalitis, further complicating the diagnosis.

"The truth is, it’s really tricky because you have nonspecific symptoms that look like the flu," Glaser said. "And it may be the flu, or it may not be the flu."

Fighting back
Recognizing the need for stepped-up efforts to combat infectious diseases, the CDC’s National Center for Infectious Diseases has called for action:

Strengthen infectious disease surveillance and response.
Integrate laboratory science and epidemiology to optimize public health practice.
Strengthen public health infrastructures to support surveillance and research and to implement prevention control programs.
Ensure prompt implementation of prevention strategies and enhance communication of public health information about emerging diseases.

Lindsay Martinez, MD, communicable diseases specialist for WHO, calls epidemiological investigation and laboratory diagnosis the "two pillars" of a good surveillance system. "Effective response to outbreaks depends on accurate confirmation of diagnosis, in every region of the world, preferably as close as possible to the affected site," Martinez said.

Several states – California, New York and Tennessee among them – have added new surveillance and diagnostic programs, Glaser said. California has long used flocks of "sentinel chickens" as a means of tracking infection in the bird population and has begun cooperating with the CDC on an encephalitis program designed to take a comprehensive look at outcome, etiology and causes of the disease, she said.

Yet at a time when infectious diseases are on the rise, only 1 percent of the nation’s health care budget is devoted to prevention efforts, the CDC said.

This will have to change, Henderson said. "There’s no way around it, it’s going to cost us some money. We need to educate and cultivate the medical community, and that is going to take resources," he said.

"Eternal vigilance is the only solution," he added. "I think Joshua Lederburg, the Nobel laureate, said it best. He said viruses are man’s only real competitors for domination of the planet."