Infection: Hantavirus Infection
Infection: Hantavirus Infection
Hantavirus infection is more commonly called hantavirus pulmonary syndrome or HPS in the United States. It is a rare but potentially fatal disease that people get by breathing in the virus from the dried urine, feces, or saliva of its vectors —infected mice or rats. Hantavirus infection is classified as both an emerging infectious disease and a zoonosis (disease transmitted from animals to humans).
The most distinctive symptom of hantavirus infection is its effect on the patient's lungs and breathing. After an incubation period of several days to several weeks, the infected person develops symptoms that can easily be mistaken for the flu or food poisoning. In the second phase, however, the patient has trouble breathing and may die as the lungs fill up with fluid and other body organs begin failing.
Anyone can get hantavirus infection from infected mice. However, most reported cases are in middle-aged adults. People of both sexes and all races can get the infection. Men are at somewhat greater risk than women, however, because they are more likely to be employed in occupations that expose them to infected mice. Hantavirus infection had been reported in thirty states in the United States as of 2008. It is most likely to occur in the spring and summer as the weather warms and people spend more time outdoors. It can also occur in the fall, when the rodents that carry the virus seek shelter from the cold weather in houses or barns.
Some people are at greater risk of hantavirus infection:
- People who live in New Mexico, Colorado, Arizona, California, Utah, Texas, Washington, Idaho, and Montana.
- Farmers, ranchers, and field hands
- Field biologists and veterinarians
- People who work in grain elevators, feed lots, or feed mills
- Utility workers, plumbers, and electricians
- Construction workers and building contractors
- Hikers and campers
Hantaviruses are RNA viruses that enter the body when people breathe dust contaminated by the urine, feces, or saliva of rodents. They sometimes breathe in this contaminated dust while working in a mouse-infested building, cleaning out a barn or shed, or hiking or camping in an area where infected mice build their burrows. When a person breathes in the dust, the virus particles enter the tissues lining the nose, throat, and lungs.
People can also take in the virus if they touch an object that has been contaminated by rodent droppings and then touch their mouth or nose. It may take anywhere from one week to five weeks for the disease to incubate. In a very few cases, people have been infected with hantavirus after being bitten by an infected mouse, but this method of transmission is unusual. As far as is known, people cannot get hantavirus infection through direct contact with an infected person.
The early stage of the disease is often misdiagnosed as flu or food poisoning because the person may have muscle ache and pains like those of flu or have nausea, vomiting, and diarrhea resembling the signs of food poisoning. This stage of the illness lasts from a few hours to several days. Other early symptoms of hantavirus infection are:
- Fever between 101 and 104°F (38 and 40°C)
- A dry cough
- Rattling noises in the lungs
In the second stage of the disease, the body responds to the virus that is infecting the tissue lining the lungs by secreting large amounts of fluid in order to get rid of the virus. The fluid, however, makes it hard for the person to breathe. Eventually the patient's blood pressure drops, an abnormal heart rhythm may develop, and one's breathing and blood circulation fails.
Discovery of an Emerging Disease
The Indian Health Service and the CDC were puzzled by an outbreak of a new disease in the Four Corners region of the American Southwest in May 1993. A young, healthy Navajo man died shortly after having difficulty breathing. His fiancé had died several days earlier after having similar symptoms. Five other cases followed. The CDC sent special investigators to find the cause. Chief investigator Terry Yates (1950–2007) traced the disease organism to deer mice. An unusually large number of deer mice thrived in spring 1993 due to heavy rains that provided a bumper crop of food for the mice.
The cause of the deaths was a new virus in the hantavirus family called Sin Nombre virus or SNV. Since 1993, several other hantaviruses carried by different species of rats and mice in Florida, Louisiana, Rhode Island, and New York have been identified. The CDC also found that several mysterious deaths in the United States before 1993 had been caused by a hantavirus; the earliest known case concerned a Utah man in 1959.
The name “hantavirus” itself comes from the Hantaan River in South Korea, where the first virus in this family was discovered by researcher Dr. Lee Ho-Wang in 1976. Dr. Ho-Wang had been looking for the cause of a hemorrhagic fever that
had been killing thousands of people in Siberia, China, and Korea since the 1930s. About 2,300 American soldiers were infected by the hantavirus during the Korean War (1950–1953), and about 800 died as a result.
The diagnosis of hantavirus infection is based on the patients' history, including their occupational history or other evidence that they were exposed to mice and rats or their droppings. Hantavirus infection can be distinguished from influenza, bubonic plague, and other conditions that may cause painful breathing through a blood test. In most cases the doctor will also order a chest x ray to look for fluid buildup in the lungs.
There is no drug that can cure hantavirus infection. The patient's best chance of recovery is being placed on a respirator to help him or her breathe. Another form of treatment that helps some patients is extracorporeal membrane oxygenation, or ECMO. It is a technique in which the patient's blood is pumped through a machine that removes carbon dioxide and adds oxygen to the blood. The oxygenated blood is then returned to the patient's body.
In the early 1990s hantavirus infection was almost always fatal. Better understanding of the disease, however, has reduced the death rate to about 50 percent. Patients who survive, however, recover completely without long-term damage to their lungs.
There is no vaccine to prevent hantavirus infection. The risk of hanta-virus infection can be lowered considerably, however, by taking proper precautions to keep buildings free of rodents and to minimize exposure to them outdoors. The CDC recommends the following steps:
- Seal up holes, cracks, and other gaps that might allow mice to get into a house or barn.
- Get rid of any food sources (pet food, garbage cans, animal feed) within 100 feet (30 meters) of the house.
- Cut grass short near the house and keep shrubbery trimmed. Use mousetraps inside the house; disinfect dead rodents before disposing of them.
- Treat rodent droppings with chlorine bleach or another disinfectant before sweeping or vacuuming them. Wear rubber gloves during cleaning.
- Wear a respirator when cleaning, repairing, or working in a rodent-infested building.
It is difficult to predict whether hantavirus infection will become more common in the United States and Canada over the next few decades. On the one hand, hantaviruses may spread to parts of North America where the infection has not yet been reported. On the other hand,
doctors are now better trained to recognize the disease early and hospitalize patients quickly. It is also possible that an effective vaccine will be developed at some future point.
SEE ALSO Influenza; Plague
WORDS TO KNOW
Emerging infectious disease (EID): A disease that has become more widespread around the world in the last twenty years and is expected to become more common in the future.
RNA virus: A virus whose genetic material is composed of ribonucleic acid (RNA) and does not need DNA to copy itself and multiply.
Vector: An animal that carries a disease from one host to another.
Zoonosis: A disease that can be transmitted from animals to humans.
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Available online at http://www.montana.edu/wwwpb/pubs/mt9404.html (accessed April 19, 2008). This Web site contains detailed information about mouse-proofing houses and other preventive measures.