Deadly Tropical Disease Arrives on U.S. Shores

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Deadly Tropical Disease Arrives on U.S. Shores

Chikungunya, a severe and sometimes deadly infectious disease that has devastated the islands of the Indian Ocean, has arrived in the United States.

Colorado, Louisiana, Maryland, Minnesota and at least a half-dozen other states have reported cases of travelers returning from visits to Asia and East Africa sick with the mosquito-borne virus, according to the U.S. Centers for Disease Control and Prevention. Chikungunya can cause fever, chills, nausea, headache, rash, crippling joint pain and even neurological damage. There is no drug treatment, just bed rest, fluids and mild pain medication.

"This virus has exploded," said French scientist Philippe Parola, before presenting his findings last week at the 55th annual American Society of Tropical Medicine and Hygiene conference. "People must start to pay attention."

From the Indian Ocean islands of Mayotte, Reunion and the Seychelles, to 150 provinces of India, chikungunya has infected more than 1.3 million people in just the past 20 months.

Even more alarming, international travel has dramatically increased chikungunya's global reach. According to the most recent edition of the journal Emerging Infectious Diseases, hundreds of visitors to outbreak areas are returning home -- to Europe, South America, Canada and, now, the United States -- infected with a disease unfamiliar to most physicians in the West.

"We believe this type of outbreak could occur in other regions of the world where competent vectors (mosquitoes) are prevalent," wrote Parola in the journal article. He also believes chikungunya could end up being more dangerous to public health than West Nile virus. First appearing in this country in 1999, West Nile has killed more than 700 people, but for it humans are "dead-end" hosts -- the virus cannot be passed person-to-person by a single mosquito -- whereas with chikungunya they are not.

At the conference, Parola further detailed the extent to which chikungunya (which means "illness of the bended walker" in Tanzania) has become a global disease.

France has reported 850 cases of travel-associated chikungunya, the United Kingdom 93 and the United States at least a dozen, according to the CDC. Other chikungunya-infected travelers have been diagnosed in Belgium, French Guyana, Hong Kong, Italy, Kenya, Malaysia, Martinique, Norway, Switzerland and Sri Lanka.

Although chikungunya was discovered in East Africa in the 1950s, it has caused only 18 major epidemics since that time. But a disease that was little written about in the textbooks and previously thought to be benign appears now to have increased both in frequency and severity, hallmarks of a re-emerging infectious disease.

At least 200 of the 1,415 infectious diseases known to man are either emerging for the first time or re-emerging. And 75 percent of them -- including 11 of the last 12 discovered -- are, like chikungunya, zoonotic, which means they can pass from animal to human. Chikungunya originated in wild primates but now circulates independently with the help of mosquitoes.

The two main mosquito species involved in the transmission of chikungunya (Aedes aegypti and Aedes albopictus) can be found in dozens of countries around the world and in at least half the states in America. That fact alone, wrote Walter Tabachnick, director of the Florida Entomology Laboratory, in a newsletter two weeks ago, "should send a chill through U.S. mosquito and public health workers."

"Is there a threat that an infectious patient can meet a competent vector (mosquito) in the U.S. and Europe? Why not?" said Parola. "We still don't know how it gets established, though. And we don't know the future if that happens. But is there a risk? Yes, there is a risk."

With international travel reaching levels of nearly three-quarters of a billion people a year, according to the World Tourism Organization, coupled with the annual movement of another 12 million refugees and immigrants, it is no surprise that even a rare virus like chikungunya, which has killed more than 250 people on Reunion, could find its way to the four corners of the Earth.

Immigration to the United States just from Africa -- the original source of the majority of new and re-emerging zoonoses, including chikungunya -- increased a staggering 670 percent from the 1980s to the 1990s.

"Are we going to keep seeing the next emerging disease? That's how we've set ourselves up," said Emily Zielinski-Gutierrez, a behavioral scientist at the National Center for Infectious Diseases and a conference speaker. "We're close to everywhere else in the world, and we need to understand what's going on everywhere. People are moving; their food comes from all over. This is a small world."

Peter Daszak from the Consortium of Conservation Medicine in New York City has confirmed that fact by measuring emerging disease hot spots. In a poster presentation at the conference given by a colleague, Marm Kilpatrick, a surprising discovery was announced: Most emerging infectious diseases occur in the northeastern United States, western Europe, Japan and southeastern Australia.

Daszak and his research team cite population density, latitude and rainfall as significant predictors of emerging disease events, along with high rates of HIV/AIDS, which make patients particularly vulnerable to other infections.

"When you have a lot of HIV -- people who are immunosupressed -- you have a lot of disease popping up," Kilpatrick said.

France's vulnerability lay in its relationship to Reunion, a paradisiacal vacation spot not unlike the Bahamas and a popular destination for the French. In his hometown of Marseille, which has approximately the same population as Indianapolis, Parola has treated 46 cases of travel-associated chikungunya this year.

"For us, chikungunya fever was a few lines in a tropical medicine book," said Parola. "Now we see many cases and have noticed that after nine months half the patients are cured, but half still have severe arthritis, especially in their hands, wrists and ankles."

One hopeful aspect for many U.S. residents is that winter and summer in the Indian Ocean are the reverse of those seasons in North America.

Travelers returning, say, to the Midwest from a vacation in Reunion, would most likely be doing so in the winter when few mosquitoes are breeding.

The likelihood, then, of a sick traveler passing the virus to another person by way of a mosquito would be much diminished.

The Southern states, however, where some mosquitoes are present year-round, are a different story.

"If they get the virus down there, then it could spread all over the U.S.," said Charles Calisher, a well-known virologist at Colorado State University who was attending the conference. "The CDC or state health departments would have to tell people. If they don't and if this gets into the country, it could get established. You can't just hope for the best."

Calisher, who also is a 27-year veteran of the CDC, believes too many governmental health and disease agencies have been integrated into the Department of Homeland Security, and subsequently have lost their mission.

"I'm of the opinion that this homeland is not secure and we're not prepared," said Calisher. "All this about hundreds of billions of (bioterrorism) dollars, and transferring people around under homeland security -- no one knows what they're supposed to be doing."

Because of chikungunya's human-to-human transmission -- Parola reports at least one case of a nurse becoming infected after taking a blood sample from a patient -- Calisher is not hopeful that the disease will ever be eradicated.

"If you could ever stamp out the last human case, that might be the end of it," he said, "but that's not possible. . . . We've been lucky so far. There really haven't been many serious infectious epidemics in the United States. But as far as chik is concerned, I think it's a crapshoot."