orld renowned for its spectacular landscapes and unmatched beauty, the American Southwest, and in particular the Four Corners area of the Colorado Plateau is undeniably unique. Still, uniqueness comes in many forms, some not so awe-inspiring, some even deadly. Unfortunately, this area is also one of the few places to find one of the world's most deadly viruses.

   Hantaviruses actually exist in most regions around the world. As a genus of the family Bunyviridae, hantaviruses are illness-causing vectors in a category called Zoonoses, that is they transmit diseases from nature to man. They are not new. In fact, an epidemic condition from hantaviruses has existed in Sweden since 1934. They are agents for two kinds of acute and severe illnesses, one affecting the kidneys and the other the lungs. Worldwide, the kidney-related disease form is much more common, but it is the lung or pulmonary form that is the deadliest.

  In May 1993, a cluster of deaths from a mysterious respiratory illness occurred in the Four Corners area of the United States, causing not only widely disseminated fear in the Southwest, but a flurry of research by the Centers for Disease Control (cdc) to identify the cause. "Four Corners Virus", "Muerto (Dead) Canyon" and "Sin Nombre (Without Name) Virus" were all names given to what would ultimately be identified as a hantavirus strain in June ‘93. Causing a severe form of respiratory distress, the illness was termed Hantavirus Pulmonary Syndrome or "hps", and caused 32 deaths (60% mortality) in 53 cases that year.

   Pulmonary hantaviruses are transmitted by rodents (in whom they generally cause no disease), primarily deer and pinyon mice, with the virus being "shed" in the rodent's saliva, urine and feces. Humans usually become infected after inhaling aerosolized droplets of urine or particulates contaminated with rodent excrete, but a remote risk does exist from a rodent bite.

  In July 1998, a professional Grand Canyon river guide developed a case of hps. His reported exposure was the camp on the left bank at river mile 19.5 (just upstream from North Canyon). While he lay sleeping under an overturned paddle raft to stay out of the rain, a mouse ran across his face. His reaction apparently startled the mouse which then urinated, and the guide accidentally aspirated several urine droplets. He became very ill a few weeks later. He was hospitalized and tests confirmed Hantavirus. Fortunately, he completely recovered. Unfortunately, Grand Canyon researchers later confirmed Hantavirus in the reported area with 4 of 42 mice as positive carriers.

   The potential seriousness of this development is tremendous and should not be underestimated. There are nearly 27,000 annual river runners and 120,000 backcountry hikers. Multitudes of mice exist, and are extremely prevalent at all the popular camps, especially along the river corridor. How long has the Hantavirus been there? Is it prevalent only in isolated rodent populations in certain areas? Is it spreading? There are many unanswered questions. Research is continuing, but for now be on the lookout, and take appropriate precautions.

Hantavirus Pulmonary Syndrome

• 1993: Serious (potentially fatal) viral lung infection outbreak occurs in U.S. Southwest transmitted from mice. Ultimately identified as Hantavirus.

• Acquired from inhaling viral particles from mice urine (rarely acquired through bite). Dust from droppings in mice nests, dens or burrows may be contaminated with virus and transmit infection if inhaled.

• Responsible for 6 fatalities in Arizona since 1993.

• July '98—First and only case reported in Grand Canyon involved a professional river guide.

• August '98—Researchers in Grand Canyon find 4 of 42 mice at Colorado River Mile 19.5 (left bank camp) in Grand Canyon positive for Hantavirus.

Signs and Symptoms

1. "Flu-like" symptoms beginning 1–6 weeks after exposure, i.e. fever, muscle/body aches, dry cough, and sometimes abdominal cramping and vomiting. These symptoms last 2–15 days.

2. Life-threatening respiratory distress or respiratory failure (Adult Respiratory Distress Syndrome or "ards") may evolve rapidly within 24–48 hours following above flu-like symptoms. Lungs fill with fluid and become inflamed causing progressive difficulty with breathing or "respiratory distress", characterized by:

• Rapid, shallow respirations.

• Use of accessory muscles to assist breathing (e.g. neck and rib muscles appear to pull or retract in, as if sucking on a straw) during inhalation.

• Skin color (especially lips and fingertips) may become gray, bluish or mottled.

Treatment

1. If strongly suspected, evacuate immediately to see a doctor. Let them know that you suspect you have been exposed to Hantavirus and insist on tests. The symptoms look a lot like pneumonia and the treatment for that is exactly what you don't want for Hantavirus. For people going home to areas outside the Southwest, they need to tell their doctors what they suspect, because doctors outside the area will not think to test for the virus and may not know the procedures.

2. No antibiotic therapy exists.

3. Hospitalization is required, usually in critical care for advanced life support measures.

4. Survival rate for ards with Hantavirus is 44%.

Hantavirus Precautions for River Runners and Backpackers

1. Avoid contact with rodents, rodent burrows or den sites (commonly found under rocks, vegetation, logs etc.).

2. If possible, sleep in enclosed tent or on the boat rather than directly on ground, avoiding areas near rodent den sites.

3. Do not enter or use cabins or enclosed structures that are or could be rodent-infested.

4. Keep all food and trash in rodent-proof containers to avoid attracting them to campsite.

Tom Myers, M.D.
Grand Canyon National Park