San Diego Natural History Museum--Your Nature ConnectionSDNHM Field Guide



Lyme Disease

The Natural History of Disease


In 1993 the nation was riveted by news of an epidemic of unknown origin that rapidly killed healthy young people on an Indian Reservation in the Four Corners area of the southwest. Epidemiologists converged on the area and amazingly were able to isolate the virus in a matter of months. The story of their success is truly dramatic and relied on cooperation among investigating agencies, years of basic research on hantaviruses from other countries, and the continuing development of modern molecular virologic tests.

Early investigation in the Four Corners area pegged the viral disease as coming from rodents. During an intensive trapping program, 1700 rodents were collected from areas of possible human contact and the deer mouse (Peromyscus maniculatus) was found to be the main host animal. Tests showed 30% of the animals were infected with hantavirus. Several other rodents tested positive but in lesser numbers. Since then hantavirus has been discovered in every western state except Washington, and in many eastern states.

The Centers for Disease Control and Prevention (CDC) reports that hantavirus- carrying mice have been reported in 20 national parks, and that it's possible the virus is in all the parks. This puts campers and hikers at high risk, because they pitch tents on the forest floor and sleep in musty cabins. However, of the 110-plus cases reported, only 2 have been linked to camping or hiking. Hantavirus has also been found in deer mice living in out local deserts.


Hantavirus is carried by rodents, particularly deer mice, in their urine and feces. The carrier does not suffer from the disease but humans do. Humans are thought to become infected when they are exposed to contaminated dust from the nests or droppings of mice. Contaminated dust is frequently encountered when working in or cleaning long-vacated cabins, sheds, or other enclosed areas. Infection is not passed between humans.

Hantavirus cycle


The early symptoms of hantavirus resemble influenza with the rapid onset of a fever, chills, muscle aches, headache, nausea, vomiting, and malaise. A dry cough may be present. Young people may have a higher fever than older people. Symptoms progress to an increased respiratory rate, with seepage of fluid into the lungs. The initial shortness of breath progresses rapidly. The patient bleeds internally and ultimately develops respiratory failure.


There is no effective treatment available and, even with intensive therapy, over 50% of the diagnosed cases have been fatal. Because the breathing problems progress rapidly, treatment must be in a hospital.


Avoid exposure to mouse or rodent urine and feces. Pitch tents in areas without rodent droppings and avoid rodent dens. Drink disinfected water and sleep on a ground cover and pad. Do not feed wild animals or leave food where they can get it.

If you are cleaning an area where rodents are living use, appropriate precautions listed below. For more complete directions or if area requires professional cleaning consult the CDC website listed below.

  • Put latex gloves on before cleaning up.
  • Don't stir up the dust by sweeping, dusting, or vacuuming.
  • Instead, thoroughly wet the contaminated area with a detergent or bleach solution to deactivate the virus.
  • Once everything is wet, take up contaminated materials with a damp towel, then mop or sponge the area with disinfectant.
  • Spray dead rodents with disinfectant and double bag along with all the cleaning materials, and burn or bury them. If that is not possible, contact the Environmental Health Department for correct disposal methods.
  • Disinfect gloves before taking them off. After taking the gloves off, throroughly wash hands with soap and warm water.
  • Open up and air out cabins and outbuildings before cleaning.

Inform yourself

All about Hantavirus—Centers for Disease Control and Prevention. Provides extensive directions for cleaning enclosed areas and avoiding contamination, as well as a compelling account of the epidemiologic story.
Hantavirus— Medical Encyclopedia

Information for this page comes from the Centers for Disease Control and Prevention

Illustration of the Hantavirus cycle
and the banner microbe, Borrelia burgdorferi, the bacterium causing Lyme disease,
from the American Museum of Natural History Epidemic! exhibition

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