Rodent Borne Hantavirus Pulmonary Syndrome (HPS) in Yosemite National Park

Hantavirus Infections

Deaths from Hantavirus Infections in the United States since 1993 – Image courtesy of the US CDC

A recent outbreak of hantavirus infections among campers in the Yosemite area has left three dead out of a total of eight cases, as health officials work to contact others who may have been exposed to the disease. What is Hantavirus anyway, and how does it affect the human body?

Hantavirus, and Hantavirus Pulmonary Syndrome

Hantavirus is carried in rodent feces, urine and saliva which dries out and mixes with dust, and is inhaled by humans, particularly in small, confined spaces with poor ventilation. Hantavirus infections may develop into Hantavirus Pulmonary Syndrome (HPS), which can be fatal. Hantaviruses are negative RNA viruses from the Bunyviridae family, and can infect people through contact with hantavirus infected rodents, or their urine and droppings. The Sin Nombre hantavirus was first recognized in 1993, and is one of several New World hantaviruses circulating in the US.

Yosemite Hantavirus Outbreak

The recent deaths of three people in Yosemite National Park, where at least 10,000 people stayed in rodent-infested huts during the summer of 2012,  may be self limiting. Most of the victims are believed to have contracted the virus while staying in tent-style cabins during the summer of 2012 in a popular camping area called Curry Village. Park officials closed 91 tent-cabins on finding deer mice which burrow through holes to nest in the double walls of the cabins.


Park authorities notified 22,000 visitors to Yosemite, who rented the tent cabins from June through August, that they may have been exposed to hantavirus, and experts continue to investigate the outbreak. The number of cases could rise, as visitors exposed to the virus become ill over time.

Hantavirus and Medical Care

Hantavirus symptoms can be severe or mild, but there is a standard battery of tests performed by medical personnel when hatavirus infection is suspected.

  • Symptoms: The early symptoms of hantavirus disease are similar to the flu: chills, fever and muscle aches – although people with hantavirus may improve for a short time, within 1-2 days breathing becomes labored, and the disease takes hold rapidly. Later, more severe, symptoms include: dry cough, general ill feeling, headache, nausea and vomiting, and shortness of breath.
  • Examinations and Tests: When a doctor examines the patient, he or she may find acute respiratory distress syndrome (ARDS), kidney failure, low blood pressure, and low blood oxygen levels causing the skin to turn blue (cyanosis). The doctor will most likely order the following tests: blood tests to confirm hantavirus, full blood count, complete metabolic indicators, kidney and liver function tests, and a chest X-ray.

Click to Read Page Two: Hantavirus Treatment and Prognosis

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  • Decoded Science

    Reader Question: “How does the mouse get the virus?”

  • No One

    From other deer mice. The transmission cycle is species-specific; deer mice transmit Sin Nombre virus to other deer mice. Long-tailed pygmy rice rats (South America) transmit Andes hantavirus to other rice rats. There are many other rodent (and some shrews and moles) species that host hantaviruses. In each virus:rodent relationship, there is no pathology in the rodent and they do not clear the virus. Humans, on the other hand, get an aggressive inflammatory response by the immune system that causes the disease. The viruses do very little in terms of pathology in humans.

  • Michael

    The imponderable question – deer mice are latent carriers of hantavirus which is present in their colonies. The manner by which they acquire the virus is unknown. Rodents are major killers of humans cf. the rat borne bubonic plague of the European 13th century [killing 300 million people] which is memorised in the ‘atishoo, atisho we all fall down, ring a ring a rosy’ nursery rhyme.
    The deer mouse (Peromyscus maniculatus) is the main carrier of hantavirus in the western United States. All wild rodents should be avoided. We all live within 2 metres of some type of rodent. Deer mice live in rural areas. Deer mice pass the virus to each other and some of the population is usually infected, but deer mice do not become ill or have any symptoms. In Washington State, 14% of 1,100 tested deer mice were found to be infected with Sin Nombre virus.
    Infected deer mice are ubiquitous, so, human cases of hantavirus pulmonary syndrome may occur anywhere.