Hanta virus, a distant cousin of the Ebola virus, has been recognized as a cause of disease for many years. In the United States, disease caused by Hanta virus has probably always existed, but in such low numbers that it was not recognized.

A 1993 outbreak of fatal respiratory illness on an Indian reservation in the Four Corners area (the border of Utah, Colorado, New Mexico, and Arizona) led epidemiologists to the discovery of Hanta virus as the causative agent. Since that discovery, Hanta virus disease has been reported in every western state, and in many eastern states.

Hanta virus is carried by rodents, particularly deer mice, and is present in their urine and feces. The Hanta virus does not cause disease in the carrier animal, but it does in man. Humans are thought to become infected when they are exposed to contaminated dust from the nests or droppings of mice.

The disease is not, however, passed between humans. Contaminated dust is often encountered when cleaning long-vacated dwellings, sheds, or other enclosed areas.

The federal Centers for Disease Control and Prevention (CDC) reported that rodents carrying Hanta virus have been found in at least twenty national parks and that it is possible that the virus is in all of the parks.

Epidemiologists at the CDC suspect that campers and hikers may have a higher chance of contracting the disease than most people. This is due to the fact that they pitch tents on the forest floor and lay their sleeping bags down in musty cabins. So far, however, out of the more than 110 cases that have been reported in the United States, only two of them were directly linked to camping or hiking.

The initial symptoms of Hanta virus disease closely resemble influenza. The disease begins abruptly with fever, chills, muscle aches (myalgia), headache, nausea and vomiting, and malaise. A dry cough may be present. The fever may be higher in younger people than in older people.

For a very short period, the infected person feels somewhat better, but this is followed within a day or two by an increased respiratory rate caused by a seepage of fluid into the lungs. The initial shortness of breath is subtle and the patient may be unaware of it, but progression is rapid. The patient bleeds internally, and ultimately develops respiratory failure.

An effective treatment for Hanta virus is not yet available. Even with intensive therapy, over 50% of the diagnosed cases have been fatal.

• fever
• chills
• muscle aches (myalgia)
• headache
• general ill feeling
• malaise
• dry cough
• increased respiratory rate (tachypnea)
• shortness of breath
• respiratory failure
• history of exposure to mice droppings, nest, or contaminated dust

The physical examination may show signs of:

• hypoxia (decreased saturation of oxygen in the blood)
• hypotension (decreased blood pressure)
• adult respiratory distress syndrome (ARDS)

Tests include:

• CBC (elevated white blood count)
• platelet count (less than 150,000 and decreasing)
• X-ray of the chest (may show interstitial infiltrates or diffuse infiltrates involving both lungs)
• liver enzymes (LDH is elevated)
• serum albumin (decreased)
• hematocrit (increased, showing hemoconcentration)
• serological testing for Hanta virus

Because the breathing problems progress rapidly and there is a high death rate, treatment must occur in the hospital, often with admission to an intensive care unit.

Oxygen therapy is used, and regulated by close monitoring of the blood gases. Respiratory support with a breathing tube (endotracheal tube) and ventilator becomes necessary in severe cases.

IV ribavirin therapy is experimental and is under evaluation for its effectiveness.

Hanta virus is a serious infection with a death rate (even with aggressive treatment) exceeding 50%.

• cardiorespiratory failure
• death

Call your health care provider if you have had any exposure to mouse urine or feces (excreta), or dust that may have been contaminated with mouse excreta, and you have developed influenza-like symptoms.

Avoid exposure to mouse or rodent urine and feces. When hiking and camping, pitch tents in areas without rodent droppings, avoid rodent dens, drink disinfected water, and sleep on a ground cover and pad.

If you must work in an area where contact is possible, follow these recommendations from the Centers for Disease Control (CDC):

1. When opening an unused cabin, shed, or other building, open all the doors and windows, exit the building, and allow the space to air out for 30 minutes.
2. Return to the building and spray the surfaces, carpet, and other areas with a disinfectant. Leave the building for an additional 30 minutes.
3. Spray mouse nests and droppings with a 10% solution of chlorinebleach or equivalent disinfectant, allow to sit 30 minutes, and using rubber gloves place the materials in plastic bags, seal, and dispose of the bags in the trash or incinerator. Dispose of gloves and cleaning materials in the same manner.
4. Wash all potentially contaminated hard surfaces with a bleach or disinfectant solution. Vacuuming should be avoided until the area has been thoroughly decontaminated and then should only be done (the first few times) with adequate ventilation. Surgical masks may provide some protection.