History: An outbreak of unexplained illness occurred in May 1993 in the "Four Corners," an area of the Southwest US shared by New Mexico, Arizona, Colorado, and Utah. A number of previously healthy young adults suddenly developed acute respiratory symptoms; about half soon died. The New Mexico Department of Health, the Arizona Department of Health Services, the Colorado Department of Health, the Utah Department of Health, the Indian Health Service and CDC, with the assistance of the Navajo Nation Division of Health, rapidly mounted an intensive investigation. Researchers soon suspected that they were dealing with a form of hantavirus, which is transmitted by rodents. Researchers then investigated the possible rodent connection, trapping rodents in the affected area, doing tissue studies both of rodents and hantavirus victims, until the virus and its principal carrier—the deer mouse—were positively identified. Why the Four Corners area? Simply because there was a "bumper crop" of rodents there, due to heavy rains during the spring of 1993, which produced an extra-plentiful supply of the foods that rodents eat. Early on, it was also established that person-to-person spread was unlikely. It was also determined that this "new" hantavirus had actually been present, but unrecognized, at least as early as 1959. Since the 1993 outbreak, hantavirus pulmonary syndrome (HPS) has been identified in over half of the states of the U.S.

Transmission: When exposed to rodents (deer mouse, white-footed mouse, cotton rat and rice rat) Transmission occurs via rodent saliva/dry droppings. The virus is "aerosolized" and breathed in. (This is how the virus is transmitted.) Transmission does not occur from other people, other animals or insects. Dogs may bring rodents into the house which are effected, but dogs, chickens, hamsters, sheep, goats and llamas and alpacas (and many other animals) may get the virus but are not carriers. That is, they cannot spread the virus and infect other animals. You can also become infected by touching the mouth or nose after handling contaminated materials. A rodent's bite can also spread the virus.

The Transmitters:
The deer mouse (Peromyscus maniculatus) is a deceptively cute animal, with big eyes and big ears. Its head and body are normally about 2 - 3 inches long, and the tail adds another 2 - 3 inches in length. You may see it in a variety of colors, from gray to reddish brown, depending on its age. The underbelly is always white and the tail has sharply defined white sides. The deer mouse is found almost everywhere in North America. Usually, the deer mouse likes woodlands, but also turns up in desert areas.

The cotton rat (Sigmodon hispidus), which you'll find in the southeastern United States (and way down into Central and South America), has a bigger body than the deer mouse—head and body about 5 - 7 inches, and another 3 - 4 inches for the tail. The hair is longer and coarser, of a grayish brown color, even grayish black. The cotton rat prefers overgrown areas with shrubs and tall grasses.


The rice rat (Oryzomys palustris) is slightly smaller than the cotton rat, having a head and body 5 - 6 inches long, plus a very long, 4- to 7-inch tail. Rice rats sport short, soft, grayish brown fur on top, and gray or tawny underbellies. Their feet are whitish. As you might expect from the name, this rat likes marshy areas and is semi-aquatic. It's found in the Southeastern United States and into Central America.

The white-footed mouse (Peromyscus leucopus) is hard to distinguish from the deer mouse. The head and body together are about four inches long. You should note that its tail is normally shorter than its body (about 2 - 4 inches long). Topside, its fur ranges from pale brown to reddish brown, while its underside and feet are white. The white-footed mouse is found through southern New England, the Mid-Atlantic and Southern states, the Midwest and into the western states and Mexico. It prefers wooded and brushy areas, although sometimes it will live in more open ground.

Sometimes, the "country mouse" becomes a "city mouse". Both the deer mouse and the cotton rat are usually in rural areas, but can also be found in cities when conditions are right, such as easy availability of food, water and shelter.

Other rodents may also carry hantavirus. It appears that other rodents carrying strains of hantavirus that cause HPS are yet to be identified. In addition, yet other rodent species play host to other types of hantaviruses that cause a different type of infection, hemorrhagic fever with renal syndrome, or HFRS. See " hantavirus" for more information. It is wise, therefore, to avoid close contact with rodents in general.

Killing the virus: Hantavirus is not spread from person to person. Being near a person who has hantavirus pulmonary syndrome cannot infect you. The virus, which is able to survive in the environment (for example, in contaminated dirt and dust), can be killed by most household disinfectants, such as bleach or alcohol. The virus is most active when the temperature is between 45 and 72 degrees Fahrenheit.

Symptoms Symptoms of hantavirus pulmonary syndrome usually appear within 2 weeks of infection but can appear as early as 3 days to as late as 6 weeks after infection. The primary symptom of this disease is difficulty in breathing, which is caused by fluid build-up in the lungs and quickly progresses to an inability to breathe.

First symptoms are general and flu-like: fever (101-104 F); headache; abdominal, joint, and lower back pain; sometimes nausea and vomiting. However, the primary symptom of this disease is difficulty in breathing, which is caused by fluid build-up in the lungs and quickly progresses to an inability to breathe.

If any combination of the symptoms described above especially difficulty in Breathing appear after direct or indirect exposure to rodents, contact your doctor or public health clinic immediately and be sure to mention your exposure to rodents.

At the present time, there is no specific treatment for the hantavirus infection. However, we do know that if the infected individuals are recognized early and are taken to an intensive care unit, some patients may do better. In intensive care, patients are intubated and given oxygen therapy to help them through the period of severe respiratory distress. The earlier the patient is brought in to intensive care, the better. If a patient is experiencing full distress, it is less likely the treatment will be effective. Therefore if you have been around rodents and have symptoms of fever, deep muscle aches and severe shortness of breath, see your doctor immediately. Be sure to tell your doctor that you have been around rodents—this will alert your physician to look closely for any rodent-carried disease such as HPS.


To minimize the risk for hantavirus infection, follow these precautions:

• Before occupying abandoned or unused cabins, open them up to air out.
  
• Inspect for rodents and do not use cabins if you find signs of rodent infestation. If you sleep outdoors, check potential campsites for rodent droppings and burrows.
  
• Do not disturb rodents, burrows, or dens.
  
• Avoid sleeping near woodpiles or garbage areas that may be frequented by Rodents.
  
• Avoid sleeping on bare ground; use a mat or elevated cot if they are available.
  
• Store foods in rodent-proof containers and promptly discard, bury, or burn all garbage.
  

LINKS: American Veterinary Medical Association
Hantavirus Veterinary Article from Journal of the American Veterinary Medical Association Jan. 15, 2003