Hantavirus Remains Rare, but Potentially Deadly

Jamie Childs, Sc.D., is a senior research scientist and lecturer in the Department of Epidemiology of Microbial Diseases at the Yale School of Public Health. His research is focused on the ecological dynamics of directly transmitted zoonotic viruses, including the hantaviruses, arena viruses and rabies, as well as vector-borne bacteria. Prior to coming to Yale, he served as the chief of the Viral and Rickettsial Zoonoses Branch at the Centers for Disease Control and Prevention. Dr. Childs and his colleagues started studying hantavirus in the alleys and streets of Baltimore where rats were common and they did their viral work at high containment laboratories at the U.S. Army Research Institute for Infectious Diseases. He was also the environmental investigation team leader during the 1993 outbreak in the four-corners region of the Southwestern United States. More recently, Dr. Childs has been interviewed by national media on the current and deadly outbreak of hantavirus in California.

Most people in the United States have limited experience or knowledge of hantavirus. How is this disease transmitted?

JC: Hantaviruses are maintained in various species of rodents that serve as reservoir hosts. Humans are believed to become infected when they inhale virus present in the excreta or secretions shed from an infected rodent or through direct contact with rodents. Currently four species of rodents, commonly called the deer mouse, white-footed mouse, rice rat and the cotton rat, have been associated with hantavirus pulmonary disease in humans. Sin Nombre virus from deer mice causes the majority of hantaviral disease in the United States.

Do mosquitoes also play a role in its transmission?

JC: No

Where is the disease most prevalent and how common is it in the United States?

JC: Hantavirus infection and Hantavirus pulmonary syndrome (HPS) are rare occurrences; the CDC has reported more than 600 cases in the United States since 1993. Most cases have been reported from the Southwestern part of the country where the original 1993 outbreak occurred, followed in order of number of cases in the Northwest, the Midwest and the Eastern states. The predominance of cases in the West are associated with the deer mouse, which is far less common in the East.

Has it occurred on the East Coast or New England?

JC: Cases have been reported from Maine, Vermont, New York, Massachusetts, Rhode Island, North Carolina, Pennsylvania, Virginia, West Virginia and Florida. It is sometimes difficult to identify where exactly infection occurred as the state reporting the case was not the state of where the individual was believed to be exposed (the cases from Massachusetts and Rhode Island are believed to have contracted their infections elsewhere). Overall, the Eastern United States has reported about 3 percent of the cases occurring in this country.

What conditions have to be present for an outbreak?

JC: Although many factors contribute to the sporadic or sometimes clustered (in time and space) cases of HPS, the presence of rodents is a universal condition. The presence of rodents within human habitations poses a special risk and in the late fall deer mice and white-footed mice frequently invade houses to over-winter . Conditions that increase rodent populations, such as mild winters and abundant rainfall resulting from El Nino events in the Southwestern United States, allow for greater survival of over-wintering mice and an early increase in food resources that contribute to rapid population increases. More mice increase the probability of human-rodent contact. Additionally, deer mice are most abundant in biomes, such as those dominated by pinyon-juniper in the western United States, where humans tend to prefer to live and visit.

What are the major symptoms of hantavirus?

JC: HPS is usually associated with a prodromal phase in which respiratory symptoms may be absent. Fever and myalgias are the most common complaints during this time and gastrointestinal symptoms may also occur. Normally hospital admission only occurs after the onset of respiratory symptoms. Following the prodromal phase, typically lasting less than a week, a cardiopulmonary phase occurs marked by coughing, shortness of breath and tachycardia. These signs and symptoms appear abruptly (24 to 48 hours after hospital admission) and pleural effusions and the resulting hypoxia often require intubation and mechanical ventilation. Patients with severe disease often die with hypoxia and cardiac dysrhythmia within two weeks following onset, many die within 48 hours of admission. The convalescent stage of HPS may last months. Some cases of HPS are less severe with only modest respiratory symptoms.

If infected, what are the chances for survival?

JC: Approximately 65 percent of patients with HPS survive.

What treatments are available to someone who is infected with the disease?

JC: The major treatment is supportive care during the cardiopulmonary phase of the disease including intubation and mechanical ventilation. At least two antiviral drugs for treating hantaviral disease are being investigated. Open-label treatment with intravenous ribavirin (classified then as a investigational new drug and not routinely available) of some HPS cases occurring in 1993-1994 did not indicate a marked approval.