In the United States, most cases of hantavirus pulmonary syndrome (HPS) are caused by one strain of hantavirus primarily carried by the deer mouse (Peromyscus maniculatus). These rodents appear healthy but shed the virus in their saliva, urine, and droppings. Deer mice are found in rural, semirural, and suburban areas, but not usually in cities.

How the virus is spread

Experts believe that most people become infected with hantaviruses by:

• Breathing in tiny airborne particles formed when rodents urinate.
• Coming into direct contact with infected rodent urine, saliva, or droppings.
• Being exposed to dust particles contaminated with the virus.
• Being bitten by a rodent infected with the virus (a rare source of infection).

There is no evidence that pregnant women infected with hantavirus can spread the virus to their babies before or after birth or through breast-feeding.

Ticks, fleas, mosquitoes, and other biting insects are not known to carry or spread hantaviruses. In the U.S., cats and dogs are not known to be carriers of hantavirus. Guinea pigs, hamsters, gerbils, and other similar pets also are not known to carry hantaviruses.

Contagious and incubation periods

In most cases, the incubation period-the time between infection with the hantavirus and development of symptoms of the infection-is believed to be 1 to 5 weeks.

A person who has HPS usually cannot spread the infection to another person. Spread of hantavirus infection from one person to another has never been documented in North America, but there has been one report in South America (Argentina) of an outbreak of HPS that was spread by person-to-person contact.

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