Image: Dengue
James Gathany  /  CDC
Although killer diseases such as dengue fever are long-forgotten by Americans, they still plague millions worldwide — and these infections could start becoming more widespread in the U.S. Some, such as dengue fever, are spread by infected mosquitoes.
By contributor contributor
updated 3/10/2009 9:09:37 AM ET 2009-03-10T13:09:37

To most Americans, diseases with names like dengue fever, chikungunya, malaria, Chagas and leishmaniasis might sound like something out of a Victorian explorer’s tales of hacking through African jungles. Yet ongoing epidemics of these diseases are killing millions of people around the world. Now, disease experts are increasingly concerned these and other infections may become as familiar in the United States as West Nile or Lyme disease.

Few believe Americans face a killer epidemic from tropical diseases. But scientists who specialize in emerging infectious diseases say such illnesses may become more common here as the economic downturn batters an already weakened public health system , creating environmental conditions conducive to infectious diseases spread by insects or other animals. At the same time, such vector-borne diseases are capable of spreading around the world much more rapidly due to massive south-to-north immigration, rapid transportation, and global trade.

“We truly did become a global village,” said Duane Gubler, Director of the Duke/NUS Graduate School of Medicine Emerging Infectious Disease Program in Singapore. “It has been a sequence of events over a period of 30 years and has come to a head in the last ten years. So we have sounded the alarm.”

Budget cuts over a period of years have left public health at all levels of government underfunded by $20 billion, according to a report published in the U.S. in October by the non-partisan Trust for America’s Health. 5 deadly infections

The recession has only piled on the pain, with states and counties being especially hard hit. For example, Washington's King County was forced to cut roughly $19 million out of public health in its 2009 budget.

Funding was surprisingly tiny even before the recession. “When I started at the CDC in the summer of 2001, I was told my branch budget was zero,” said Dr. James Maguire, former chief of the CDC’s parasitic diseases branch and now a Harvard professor. “It was always pretty sparse.” Currently, the budget for the branch is thought to be less than $75,000, not including staff salaries. (The agency was unable to provide a definite amount.) The total for all emerging diseases was $130.3 million for fiscal 2008. By comparison the CDC expects to spend about $103.7 million on anti-tobacco promotions. The 2009 CDC budget for chronic disease prevention, which includes heart disease, diabetes and stroke, is more than $932 million.

A significant amount of the CDC funding for emerging diseases goes to salaries and state and local health departments, explained Dr. Ali Kahn, deputy director of the National Center for Zoonotic, Vector-Borne and Enteric Diseases at the CDC, “There is no doubt we could do a lot more in the U.S. and worldwide with additional funds,” said Kahn.

The recession has weakened the government's ability to develop better treatments, vaccines or prevent an epidemic, experts said.

“States do not have resources to keep people on board and these people are monitoring diseases, the epidemiologists doing shoe leather investigations,” said Jeffrey Levi, executive director of Trust for America’s Health. “You cannot turn them on and off with a switch. If you lose them you’ve lost them forever.”

Once ‘conquered,’ now returning
Diseases such as Chagas and leishmaniasis affect more than 13 million people around the world each year, according to experts. These vulnerabilities in America’s disease defensive shield comes at a time when worldwide changes have boosted the ability of such diseases to spread.  Cities in tropical Asia and Africa, for example, “have gone from 4 million to 15 million people,” Gubler explained. “These are mega cities that have inadequate housing, water and sewer treatment, waste management,” Gubler said. “This creates ideal conditions for transmission of all kinds of infectious diseases.”

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American health officials thought they had conquered most such diseases after World War II through a combination of mosquito-killing campaigns and public health measures like draining swamps, improved housing, better sewage and waste control. As a result, medical professionals turned their attention to conditions like cancer and diabetes.

“That’s what I call the period of complacency,” Gubler said. “It set in during the 1970s after the war on infectious disease had been declared won.”

But it wasn’t won.

In a June 2008 article in the journal PLOS Neglected Tropical Diseases, Dr. Peter Hotez, chairman of the department of microbiology, immunology and tropical medicine at George Washington University in Washington, D.C. wrote that Americans living in poverty, immigrants and those living in medically underserved regions suffer from a host of such diseases, including Chagas, dengue and leishmaniasis. 

Increasingly, these diseases pose a risk to the rest of the country. For example, in 2007, in the middle of a drought that should have prevented large-scale mosquito breeding, Kern County, Calif. became the national epicenter of West Nile disease, which emerged in Africa and is spread by mosquitoes.

At least 140 confirmed cases, and four deaths, were recorded. At first, public health officials were mystified. They soon realized that because the county was an early victim in the national housing collapse, foreclosed and abandoned homes sat with partially filled swimming pools and spas serving as mosquito love motels.

Ten years ago, managers of hunting dog kennels in upstate New York began to notice that some of the foxhounds had contracted a mysterious illness.

“I got a call from the caretaker of the dogs at Millbrook Hunt Club,” recalled Richard Ostfeld, an animal ecologist at the nearby Cary Institute of Ecosystem Studies, Millbrook, N.Y. “The dogs were extremely sick. They were losing their hair, bleeding from their noses and mouths, having seizures, wasting. Some were dying. I wanted to be helpful, but I didn’t know what to do.”

When experts from the CDC and Walter Reed Army Medical Center in Washington, D.C. finally identified the illness, they realized foxhounds in New York were dying of visceral leishmaniasis, a parasitic disease usually found in places like Brazil, the Middle East and India. The disease is transmitted by a type of sand fly.

Investigators still aren't sure how the foxhounds caught the disease. At the time when Ostfeld and a group of interns set traps on the institute's 2000 acres, they found sand flies all over the place.

"That was very eye-opening to me, that a tropical disease may not occur (here) but could potentially occur because the vector occurs outside its current range,” said Ostfeld. “And by the way, we also found literally hundreds of anopheles mosquitoes, the American malaria mosquito thought to be wiped out in the 1950s.”

Diseases knocking on America's door
What worries officials most is not that somebody could step off an airplane with a disease, but that the bugs would become widespread in the U.S. In the 1980s, an invasive mosquito species known as the Asian Tiger, an aggressive biter, arrived in a shipment of tires. It and another invasive species, the yellow fever mosquito, have colonized territory from the Mexican border to downtown Chicago. Both can transmit dengue, chikungunya and malaria.

5 deadly infections

Last fall, researchers from Texas A&M and the CDC looking for organisms carrying Chagas, including “kissing bugs,” reported that “over half of the new specimens found inside or near houses were infected” with the parasite. The bugs were found all over Texas often “in close proximity to human settings,” which suggested “the presence of an active peridomestic Chagas disease transmission cycle.”

There are more than five tropical diseases knocking on America’s door that concern public health experts.

Leishmaniasis is caused by a protozoa spread through phlebotomine sand fly bites. The most common cutaneous form of the disease causes skin lesions that can take months or even years to heal. Some forms can result in terrible facial deformities. Visceral leishmaniasis can cause a swollen spleen and liver, fever, weight loss, anemia, miscarriage and death.

Over 1,000 military personnel serving in Iraq have contracted cutaneous forms of the disease. A few have had visceral forms. Fortunately, both forms can be treated with anti-parasitic drugs. It also means that veterans can, and do, bring the parasite back into this country.

Cutaneous leishmaniasis has occurred in south Texas for years. In April of 2008, doctors in north Texas reported nine cases in people who had not traveled out of the region, meaning it originated in the state.

Chagas is a serious and growing problem in the U.S., although there are no specific statistics of infection rates, according to experts. “We do not have enough data to say what the magnitude is,” explained Caryn Bern, a Chagas expert at the CDC’s parasitic diseases branch. “There is a lot of speculation all over the map, anywhere from 100,000 to 1 million.” Bern estimates between 100,000 and 200,000 people living in the U.S. who have undiagnosed Chagas.

Because the disease has a long, silent chronic phase, people may have no symptoms at all, but still be infected with the parasites. Eventually, about 30 percent will suffer life-threatening symptoms, such as heart failure.

Bern and other Chagas experts believe that a significant number of heart disease cases in this country are actually Chagas disease. Yet few doctors recognize it or even think of testing for it. It can easily be missed in its acute phase, too, since symptoms, like swelling around the site of infection or fever, can be mild.

Chagas is curable when symptoms first appear, with drugs available only from the CDC. The drugs themselves can have severe side-effects, including Stevens-Johnson Syndrome, a potentially fatal dermatological condition.

Since screening of the nation’s blood supply started in 2007, 782 undiagnosed cases of Chagas have been discovered. Most of those cases were in immigrants from Latin America where Chagas is widespread. But early numbers showed that about 10 percent may have been contracted within the U.S. Many of these cases show up in the poor who don’t have access to quality medical care. They often go untreated.

Dengue, a mosquito-borne viral disease is sometimes called “break-bone fever” for the severe joint pain that accompanies it. The World Health Organization estimates that 2.5 billion people in 100 countries, including the U.S., are now at risk.

In 2005, 16 people in Brownsville, Texas came down with a severe form called dengue hemorrhagic fever. “Widespread appearance of dengue in the continental United States is a real possibility,” immunologist Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and Dr. David Morens, Fauci's senior advisor, warned in the Journal of the American Medical Association.

Dengue has a long history here. An epidemic swept through Philadelphia in 1780 and periodic outbreaks have plagued Hawaii. Last year, 3,346 people in Puerto Rico caught it. There is no vaccine or treatment. Roughly 1 to 2 percent of victims die. Though most live, the experience can be excruciating.

Video: Bill Gates bugs out By 1970, malaria, which had once plagued people from Manhattan’s Madison Avenue to rural Tennessee, was declared eradicated. But in 1999, two people in Suffolk County, New York were diagnosed with it. About 1,000 to 1,500 travelers every year enter the U.S. infected with malaria parasites, but the New York patients had not traveled anywhere. In 1999 and 2000, a few domestic cases showed up in Virginia and Maryland. In 2003, eight cases were found in Florida.  

These numbers are puny compared to the global burden of malaria. Roughly 300 to 500 million people around the world are infected with malaria parasites every year, and about 1 million die. 

Malaria can be treated with drugs, although the parasites have displayed an annoying ability to develop resistance to them. In the 1950s, there was great hope that a vaccine for malaria had been found. Fifty years later, scientists are still hoping.

Chikungunya, a viral illness transmitted by mosquitoes, causes headache, fever, nausea, vomiting, and muscle and joint pain. It was first isolated in 1953 and remained obscure until 2005 when a few cases were reported on islands in the Indian Ocean. Since then, it has sprinted across Asia and Africa.

Then, in 2007, it shocked disease experts by starting an outbreak in north-central Italy. “That’s about 44 degrees north latitude,” noted Michael Reiskind, assistant professor of entomology at Oklahoma State University who has studied the role of mosquitoes as disease vectors. “That’s roughly the same as Anne Arbor, Michigan.”

As yet, there have been no confirmed cases of local transmission of chikungunya within the continental U.S., although about 37 travelers came home with it in 2007. Most of the 37 patients had visited India before reaching the U.S. However, Harvard’s Maguire warned, “I think this could pull a West Nile on us.”  

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