Swine flu may be hogging the headlines, but H1N1 is far from the only disease worrying researchers. The worldwide spread of HIV in the early 1980s marked the dawn of what many scientists believe is the age of pandemics, when diseases emerge from remote areas and strike people everywhere.
Blame the destruction of rainforests, the ubiquity of international travel and inadequate public health services in developing countries. Whatever the reason, it’s clear that what happens in the jungle no longer stays in the jungle. “In 1918, it took three years for the flu virus to get around the world,” says Dr. Parviez Hosseini, a senior research fellow with the Wildlife Trust, “but H1N1 traveled through vast parts of the world in just three months.”
“In 1918, it took three years for the flu virus to get around the world, but H1N1 traveled through vast parts of the world in just three months.”
Researchers studying the origins of HIV now believe that a form of the virus first infected humans in the 1930s. That means there are diseases out there now that could infect millions in the decades to come. But what are they? And which are the most dangerous? The greatest future threat could be a virus that researchers haven’t yet identified. “It’s a lot like predicting hurricanes and cyclones,” Hosseini says. “We know there’s a general phenomenon, but we can’t necessarily predict that there will be a disease of a particular severity next February.”
The majority of emerging infectious diseases originated in animals; they’re called zoonoses. Others threats come from forms of long-recognized illnesses that have become resistant to drugs. Here’s a sampling of what scientists around the world are watching:
1. Avian Influenza A (H5N1). In birds, this virus is highly contagious and can be deadly, according to the Centers for Disease Control. In general, bird flu does not cross over to humans. But of those few strains that have made the leap, H5N1 has infected the most people; more than half of those infected have died. As of last month, the World Health Organization reported 442 cases worldwide since 2003 and 262 deaths. The victims are usually children or young adults who have had direct or close contact with infected poultry or contaminated surfaces. Scientists worry that H5N1 may someday change in a way that will allow it to spread more easily and start a pandemic.
2. Chikungunya. A mosquito-borne disease, this virus has been blamed for many epidemics in Africa and Asia since it was first isolated in Tanzania in 1953. More recently, it has been found in Europe. Although fatalities are rare, the disease is debilitating, with patients suffering from fever, headaches, vomiting, rashes, and muscle and joint pain.
3. Dengue Hemorrhagic Fever (DHF). Another mosquito-borne infection, dengue is found primarily in urban and rural tropical and subtropical regions. The World Health Organization estimates that close to 40 percent of the world’s population lives in areas at risk for dengue, with about 50 million annual cases. DHF is a potentially fatal complication of dengue that was first recognized about 60 years ago. It’s the leading cause of hospitalization and death for children in dengue-prone areas. Four different but related viruses cause dengue. People who recover from one virus are immune to it, but may still be vulnerable to others. More than one dengue infection appears to increase the risk of DHF.
4. Ebola Hemorrhagic Fever and Marburg Hemorrhagic Fever. Ebola is the best-known member of this family of viruses. First discovered in 1976, it is often fatal. Symptoms come on suddenly and include a rash, fever, headaches, and vomiting along with internal and external bleeding. Although so far it has affected only people in Africa, scientists are concerned that Ebola could spread through an infected passenger on a plane. Marburg is much rarer. It was first recognized in 1967, when lab workers in Germany and Yugoslavia became ill after exposure to infected African monkeys. Since then, there have been a few scattered reports of the illness. About a quarter of cases are fatal, according to the Centers for Disease Control.
5. Extensively Drug-Resistant Tuberculosis (XDR TB). Although a number of medications are effective for TB, this bug fights off most of them. It’s estimated that there are at least 40,000 cases a year in 49 countries. Researchers suspect the number may be increasing because many TB patients don’t take their medicines regularly and get sick again, which increases their chances of getting the drug-resistant disease. The Centers for Disease Control say the risk of XDR TB in this country is still relatively low, but that could change if the disease spreads in other countries.
6. Helminths (parasitic worms). It’s estimated that almost 3 billion people around the world (including more than 40 million Americans) are infected with helminths such as flatworms, thorny-headed worms, or roundworms. They can live inside the gastrointestinal tract or, the case of roundworms, in the lymphatic system. People infected with helminthes are more vulnerable to other diseases.
7. Hendra Virus Disease and Nipah Virus Encephalitis. Scientists think both of these related viruses originated in the bat family. Human cases so far are relatively rare, and neither disease has been reported spreading from human to human. Hendra was named after the Brisbane, Australia, suburb where it was first reported in 1994. The virus apparently passed from infected horses to humans. Of the three reported Hendra cases, two were fatal, according to the Centers for Disease Control. Nipah was first spotted in a 1998-99 outbreak in Malaysia that killed about 100 people, who apparently got the disease from contact with infected pigs. Twelve more outbreaks have been reported in South Asia since then.
8. Japanese Encephalitis. It’s the leading cause of viral encephalitis in Asia, with up to 50,000 cases reported annually, according to the Centers for Disease Control; 30 percent of those cases are fatal and another 30 percent of patients have serious ongoing neurological problems. So far, less than one case a year has been reported among U.S. civilians or military personnel living in or traveling to Asia but researchers are concerned because it appears that the mosquito-borne virus may be expanding its range.
Barbara Kantrowitz is a contributing editor at Newsweek and co-author of The Menopause Book (Workman Publishing, 2009).