Diseases

Currently, there are no readily available tests to diagnose HPS or even hantavirus infection in the early stage of the infection or disease mainly because the early symptoms are so nonspecific and the disease of HPS so infrequent. There has been no pressing need or use for a test. However, if the more severe HPS disease develops, the disease is presumptively diagnosed by the patient's association with an area where rodents proliferate or areas where HPS is known to occur (for example, the Four Corners area and more recently the Yosemite National Park recreational area, especially certain tent-cabins rented to the public). Sequential chest X-rays may show worsening changes and fluid buildup. Definitive diagnosis is usually done by the CDC labs using special immunological tests that can distinguish hantavirus from Ebola, Marburg, and other viruses.

In North America, there is no evidence that hantavirus is contagious. In South America, an estimated 16-35 days was the contagious period for a few patients who investigators considered to have exhibited person-to-person transfer.

Hantavirus is not contagious from person to person. The virus is transferred from rodents to humans. Although outbreaks seem like there is person-to-person transfer, outbreaks are usually noted among groups of people exposed to the same infected rodent population; but those with hantavirus infections do not transfer them to other uninfected individuals. While this is the situation in North America, there are reports that in 1996, mild infections with hantaviruses were transmissible in an outbreak in Argentina. However, to date, there has been no reported person-to-person transfer of the virus in the United States. Small outbreaks are reported each year; for example, Texas had its first individual diagnosed with hantavirus in 2015.

There are no vaccines available to protect against any hantavirus types. The CDC recommends elimination or reduction of contact with any rodents (for example, at home, worksites, campsites, barns, sheds) by reducing rodent access. Sealing up gaps and holes, placing traps, and keeping areas as clean and food free as possible will help. If a person must come in contact with rodents or areas where they live, precautions such as gloves and masks may reduce the chances for infection.Do not attempt to use a vacuum or use a broom to remove rodent urine or feces; this action may increase the risk of HPS by generating an aerosol. The risk of HPS can be reduced by inactivating hantaviruses in the environment by using a household detergent and 1½ cups of bleach per gallon of water to wipe or spray the potentially infected area and while minimizing contact by wearing gloves and a mask. Similar precautions should be taken when rodents are caught in traps.

The major complication of HPS is death from respiratory failure. Those who survive may take a few weeks to fully recover. Those patients who survive do not have chronic infections nor do they experience other chronic problems or complications.

The symptoms and signs of HPS are usually grouped into early and late stages. Early HPS signs and symptoms begin about one to five weeks after the person contacts hantavirus associated with rodent urine, feces, or saliva. The early symptoms last about four to 10 days and include the following:

• Fatigue
• Fever
• Muscle aches (especially large muscles in the legs, back, and hips)

Almost every infected person develops these symptoms. Other symptoms that may occur in about half of infected patients include abdominal pain (with nausea, vomiting, and diarrhea), headaches, chills, and dizziness.Late symptoms of HPS symptoms occur about four to 10 days after the early symptoms and include coughing, chest pain, and shortness of breath that can become severe.

The major risk factor for HPS is association with rodents, their saliva, urine, or feces or with dust, dirt, or surfaces contaminated with such items, either by direct contact or by aerosol. Barns, sheds, homes, or buildings easily entered by rodents are potential places for hantaviruses to come in contact with humans. Rural areas that have forests and fields that can support a large rodent population are areas that increase the risk of exposure to HPS. Camping and hiking in areas known to have a high rodent population and occupying areas where rodents may seek shelter increase one's risk. Those who work in areas that may be shelter for rodents (for example, crawl spaces, vacated buildings, construction sites) may also have increased risk of HPS. The risk is higher in people who work in areas known to have produced HPS infections.

As stated above, the cause of HPS is infection of the patient by hantavirus. Currently, about 14 subtypes of hantaviruses have been identified. Many subtypes have been named (for example, Sin Nombre, Black Creek hantavirus, and New York hantavirus); some investigators simply lump them under the term of "New World hantaviruses." The Sin Nombre subtype has caused the majority of current HPS disease. The virus apparently damages cells that compose blood vessel capillaries, causing them to leak fluids. This fluid leak, if it is profound in the lungs, causes the pulmonary syndrome that can lead to death.Hantaviruses live their lifecycle in rodents but apparently do no harm; the viruses multiply and are shed in the rodent's urine, feces, and saliva. A recent study in California suggested about 15% of all deer mice examined tested positive for hantavirus. Although the deer mouse has been the source of most HPS infections, many other rodents may carry a different hantavirus subtype virus (for example, the white-footed mouse, the cotton rat, and the rice rat).

The term hantavirus represents several groups of RNA-containing viruses (that are members of the virus family of Bunyaviridae) that are carried by rodents and can cause severe respiratory infections termed hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS).HPS is found mainly in the Americas (Canada, U.S., Argentina, Brazil, Chile, Panama, and others) while HFRS is found mainly in Russia, China, and Korea but may be found in Scandinavia and Western Europe and occasionally in other areas. Like HPS, HFRS results from hantaviruses that are transmitted by rodent urine, droppings, or saliva (rodent bite), by direct contact with the animals, or by aerosolized dust contaminated with rodent urine or feces to human skin breaks or to mucous membranes of the mouth, nose, or eyes. The vast majority of HPS and HFRS infections are not transferred from person to person.The goal of this article is to discuss HPS; however, much of what is presented about HPS applies to HFRS -- the main difference is that the predominant symptoms in the late stages of disease vary somewhat between the two diseases (lung fluid and shortness of breath in HPS and low blood pressure, fever, and kidney failure in HFRS).HPS is a disease caused by hantavirus that results in human lungs filling with fluid (pulmonary edema) and causing death in about 38% of all infected patients.

The first recognized outbreak of HPS was noted in 1993 in the "Four Corners" area of the U.S. where the states of Arizona, New Mexico, Colorado, and Utah meet. Two otherwise healthy young people, a Navajo Indian and his fiancee, suddenly became short of breath and died. This unusual situation triggered a review of deaths in the four states that resulted in identification of five other young people who recently died with similar breathing problems. During the next few weeks, additional people were found being treated in the same geographic area with similar pulmonary syndromes. Tissues from affected patients were sent to the CDC, where researchers searched for causes and found a link among the patients: infection with a previously unknown type of hantavirus. Since other known hantaviruses (in Asia and Europe) were known to be transmitted to people by rodents, the researchers started trapping rodents from June to August 1993 to determine if the virus was associated with the animals. In November 1993, a rodent (a deer mouse) trapped by CDC researchers in a house where a person who developed the pulmonary syndrome lived yielded the previously unknown virus. In addition, army researchers soon isolated the same virus from an infected patient who also had exposures to mice. This new hantavirus was first termed Muerto Canyon virus, then Sin Nombre virus (SNV), and eventually simply hantavirus. The disease caused by this virus was termed hantavirus pulmonary syndrome (HPS). Further investigations suggested that other people had died from this infection in the past when autopsy tissue was found to contain the virus. When Navajo Indian medical traditions were studied, the Navajo medical culture apparently recognized the disease and had associated it with mice. The outbreak in 1993 probably occurred because environmental factors led to favorable survival and proliferation of mice. The mouse population was about tenfold greater in 1993 than in 1992 in the Four Corners area.A large more recent outbreak of HPS occurred at Yosemite National Park, Calif., in 2012. The outbreak was linked to deer mouse dropping contamination in campsites (tent-cabins) used by tourists. At least three deaths occurred, and seven other infected people recovered. Public-health officials sent notices out to over 230,000 park visitors to warn them of potential exposure to hantaviruses by mid-September 2012. A map of the location of those people who were diagnosed with hantavirus infections is available at http://www.cdc.gov/hantavirus/outbreaks/yosemite/map.html.

According to the CDC, in North America, the incubation period (time from initial exposure to the virus and development of the first symptoms) is estimated to be between one to five weeks after initial exposure to infected rodent urine, droppings, or saliva. In South American outbreaks, researchers estimate that the incubation period varies from about 12-27 days.

The prognosis of HPS is fair to poor because currently, about 62% of patients recover, while about 38% will die. The prognosis may be better if the patient is diagnosed early and given support in an intensive-care unit in a hospital. However, the early diagnosis of HPS is difficult; some patients did not know they had been exposed to rodents that carried hantavirus.

At this time, there is no definitive treatment for HPS other than early recognition of HPS and subsequent medical support (usually consisting of symptomatic medical treatment and respiratory support or mechanical ventilation). The CDC suggests that early treatment in an intensive-care unit may allow the patient to survive severe HPS. Experimentally, physicians have administered the antiviral medication ribavirin (Rebetol, Copegus), but there are no clear data currently that establish that the drug is effective against HPS; however, its use against HFRS early in the disease suggests ribavirin can decrease illness and deaths. There is no vaccine available to protect against any hantaviruses to date.

Unfortunately, hantavirus infections can lead to hantavirus pulmonary syndrome (HPS). Hantavirus infections according to the CDC have a mortality rate of about 38%. Consequently, most patients diagnosed with hantavirus are usually cared for in the intensive-care unit by specialists trained in critical care and usually in consultation with an infectious-disease specialist. Because the lungs are the most compromised organ in these infections, a lung specialist (pulmonologist) is also usually consulted. In addition, specialists from the CDC are often involved to help locate the outbreak source and to help health-care personnel at the outbreak site prevent further infections.

Centers for Disease Control and PreventionViral Special Pathogens Branch1600 Clifton RoadAtlanta, GA 30333