Hantavirus Pulmonary Syndrome (HPS)

What is hantavirus pulmonary syndrome?

Hantavirus pulmonary syndrome (HPS) is a potentially deadly respiratory illness caused by certain types of hantaviruses, which are viruses found in the saliva, urine, and droppings of some rodents.

Although hantaviruses are found worldwide, the first outbreak in the United States was identified in 1993. Most cases of HPS have been reported in the southwestern region, in the "four corners" states of New Mexico, Arizona, Colorado, and Utah. However, 31 states have reported cases of the infection.

HPS tends to occur in desert areas in seasons of above-average rainfall. Although HPS can develop throughout the year, most cases have occurred in the spring and summer.

What causes HPS?

In the U.S., most cases of HPS are caused by one strain of hantavirus primarily carried by the deer mouse. People can become infected 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.

No cases of person-to-person spread have been reported in the U.S. HPS has not been spread to people from farm animals, pets, or insects. However, your pet may bring an infected rodent into contact with you.

What are the symptoms?

HPS causes people who are generally healthy to suddenly become very sick. About 2 weeks (possibly a range from 1 to 5 weeks) after being infected with the virus, the person develops a fever and muscle aches. Other symptoms of HPS may include a headache, chills, nausea and vomiting, abdominal pain, and shortness of breath.

Within a few days, these symptoms may become worse and may be accompanied by coughing and severe shortness of breath. Breathing becomes rapid and more difficult as the lungs fill with fluid (pulmonary edema). After people become short of breath, they may die within hours. Most deaths caused by HPS occur within 1 to 2 days of when severe shortness of breath first began.

During the initial outbreak of the virus in 1993, about 70% of people who developed HPS died.¹ Today, the death rate has fallen to 36%, perhaps because of improved treatment with fluids and other supportive care early in the course of the illness.²

How is HPS diagnosed?

A careful medical history, physical exam, and other tests (such as a complete blood count and oxygen saturation test) may suggest HPS. These other tests may provide helpful information in the early stages of HPS or when there are breathing problems caused by HPS. However, for you to be accurately diagnosed with HPS, tests must show that the virus is or has been in your blood or tissues along with having symptoms of the condition.

How can it be treated?

When symptoms of HPS develop, immediate intensive treatment is needed. Treatment is mainly supportive and includes using assisted mechanical breathing (mechanical ventilation) and maintaining fluid and electrolyte balance and blood pressure.

Can HPS be prevented?

The best way to prevent infection with hantaviruses is to avoid contact with rodents and their droppings. If you live in an area where hantaviruses have been found, and you believe your home may have a rodent infestation, set metal traps to catch rodents, and close all possible rodent entries into your home. Clear possible rodent bedding sites from around your house, and keep garbage in tightly covered containers. For more information, see the U.S. Centers for Disease Control (CDC) Web site at http://www.cdc.gov/ncidod/diseases/hanta/hps/index.htm.

Use extreme caution when cleaning rodent-infested areas. If you have an area that is heavily infested with rodents, call a professional exterminator to remove them.

Frequently Asked Questions

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.³

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.

The first symptoms of hantavirus pulmonary syndrome (HPS) may resemble those of other common illnesses. HPS symptoms usually begin from 1 to 5 weeks after exposure to the virus and usually last 3 to 5 days (prodromal phase). Symptoms that almost always occur in the early stages of HPS are:

• Sudden fever.
• Muscle pain (myalgia), especially in the thighs, hips, and back, and sometimes in the shoulders.
• Fatigue.

In the early stages of HPS, about one-half of the people also develop:

• Headache.
• Chills.
• Nausea and vomiting.
• Diarrhea.
• Abdominal pain.
• General feeling of being ill (malaise).
• Dizziness and lightheadedness.

Other, less common symptoms of HPS that may occur include:

• Joint pain.
• Chest pain.
• Sweating.

About 4 to 10 days after the initial symptoms appear, late symptoms usually develop, including:

• Shortness of breath.
• Coughing.
• Rapid heartbeat and rapid breathing, indicating fluid buildup in the lungs (pulmonary edema).

Once these symptoms develop, a person's condition rapidly deteriorates, and hospitalization within 24 hours often is needed. Even people with mild cases of the infection need to be treated in a hospital.

HPS may be mistaken for other conditions with similar symptoms, such as the flu or pneumonia.

Hantavirus pulmonary syndrome (HPS) quickly progresses (within 4 to 7 days) from fever and muscle aches to severe breathing difficulty with fluid buildup in the lungs (pulmonary edema) and heart problems.

• Once severe respiratory symptoms develop, hospitalization within 24 hours often is needed.
• During the initial outbreak of the virus in 1993, about 70% of people who developed HPS died.¹ Today, the death rate has fallen to 40%, perhaps because of improved treatment with fluids and other supportive care early in the course of the illness.¹

The likelihood of death is greatest for people who develop shock and whose blood develops too much acid (acidosis).

In people who survive, recovery occurs fairly quickly. For most people, breathing tubes can be removed after 2 to 4 days, although they may continue to receive oxygen for as long as they are in the hospital. These people are usually able to leave the hospital after 7 days.

It is not yet known whether HPS has any long-term effects on the lungs in people who survive the illness.

The risks of developing hantavirus pulmonary syndrome (HPS) are increased if you breathe in tiny airborne particles formed when rodents urinate or if you come into direct contact with infected rodent urine, saliva, or droppings. Bites from infected rodents also may increase your risk of developing HPS, although this is a rare method of infection.

People who live in or visit rural areas, especially in the western United States, have an increased risk of coming into contact with rodents infected with hantaviruses, because the deer mouse (Peromyscus maniculatus) is common in these areas. Other areas of the U.S. also have rodents that may carry hantaviruses.

Hantavirus infection also may be more likely to occur if you:

• Live in a home, cabin, or other dwelling where rodents have nested or are nesting.
• Clean barns and other outbuildings where rodents have nested.
• Disturb rodent burrows while hiking or camping.
• Plant or harvest field crops.
• Live in or visit areas in which the rodent population has increased.

Hantavirus pulmonary syndrome (HPS) is a life-threatening condition. Call 911 or seek immediate medical treatment if you have the following symptoms:

• Fever
• Muscle aches, especially in the thighs, hips, back, and sometimes the shoulders
• Severe difficulty breathing

Immediate treatment may be needed to support your breathing and prevent shock.

Watchful Waiting

Because early hantavirus pulmonary syndrome (HPS) symptoms are similar to those of the flu, it is important to seek medical attention if your symptoms get worse over a short period of time.

However, if you know you may have come in contact with rodents or their urine, saliva, or droppings within the past 1 to 5 weeks, watchful waiting is not appropriate. Contact a health professional immediately if you have a fever, muscle aches, and difficulty breathing.

Who To See

The following health professionals can do an initial evaluation for hantavirus pulmonary syndrome (HPS):

• Internist
• Family medicine doctor
• Emergency department doctor
• Infectious disease specialist

The following health professionals can provide treatment for HPS:

• Critical care specialist
• Pulmonologist
• Infectious disease specialist

To prepare for your appointment, see the topic Making the Most of Your Appointment

A careful medical history, physical exam, and other tests are necessary to diagnose hantavirus pulmonary syndrome (HPS). These other tests may provide helpful information in the early stages of HPS or when there are breathing problems caused by HPS. However, some test results may be normal during the early course of HPS and may not become abnormal until severe illness occurs.

The following tests may help determine whether HPS is causing your symptoms:

• Complete blood count (CBC). A complete blood count (CBC) may be done to determine whether the white blood cell count is increasing, indicating that an infection may be present, or the platelet count is decreasing (thrombocytopenia). A CBC also may be done to check for a rising hematocrit level.
• Oxygen saturation.Pulse oximetry or arterial blood gas (ABG) tests may be done to determine whether the amount of oxygen in the blood is adequate. ABG tests also may identify increased levels of acid in the blood (acidosis).
• Chest X-ray. A chest X-ray may be done if the amount of oxygen in the blood (as determined by ABG or pulse oximetry) is less than 90%, especially if you are having difficulty breathing. An X-ray also may be done if you have signs of pulmonary edema.

Other tests that may be done include:

• An enzyme-linked immunosorbent assay (ELISA), to detect antibodies in the blood to hantaviruses. If this test is positive, it may indicate that you are currently infected or were infected in the recent past.
• Prothrombin time (PT) and partial thromboplastin time (PTT), to determine how long it takes the blood to clot.
• Tests to help confirm or rule out other causes of the infection, such as viral influenza (flu) or infectious mononucleosis (mono).

If your condition gets worse and you are admitted to an intensive care unit (ICU), more tests will be done to identify the cause of your symptoms.

Treatment for hantavirus pulmonary syndrome (HPS) consists of supporting you through the illness, usually in an intensive care unit. Treatment may include:

• Using a mechanical ventilator to help you breathe. This includes monitoring the amount of oxygen in your blood and adjusting the treatment as needed to maintain the proper amount of oxygen in your blood.
• Monitoring the pressure and blood flow in your heart and lungs by placing a thin tube (Swan-Ganz catheter) inside your heart and lungs.
• Using intravenous (IV) fluids and medications to maintain your blood pressure and prevent shock.

What To Think About

If you think you have hantavirus pulmonary syndrome (HPS), you should seek immediate medical care to evaluate whether emergency medical treatment is needed to support your breathing and to prevent shock.

During the initial outbreak of the virus in 1993, about 70% of people who developed HPS died.¹ Today, the death rate has fallen to 36%, perhaps because of improved treatment with fluids and other supportive care early in the course of the illness.²

New treatments to improve the chance of survival are being studied.

The best way to prevent infection with hantaviruses is to avoid contact with rodents and their droppings. The majority of cases of hantavirus pulmonary syndrome (HPS) have occurred in the southwestern region of the United States.

You can reduce your exposure to rodents that may carry hantaviruses by:

• Reducing rodents indoors and outdoors.
• Cleaning up rodent-infested areas.

Special precautions for hikers and campers also may be needed to avoid contact with infected rodents.

Home treatment for hantavirus pulmonary syndrome (HPS) focuses on avoiding exposure to rodents and getting immediate medical attention if you become ill after exposure. If you have symptoms such as a fever and muscle pain and there is a possibility that you have been exposed to rodents or their urine or droppings, you need to call a health professional immediately.

You can decrease your chances of getting HPS by:

• Reducing rodents indoors and outdoors.
• Cleaning up rodent-infested areas.
• Taking precautions when hiking and camping.

There is no known medication that effectively reduces the risk of dying from hantavirus pulmonary syndrome (HPS) or shortens the length of illness in people who have HPS.

People who see a health professional for symptoms of fever and muscles aches and are suspected to have HPS should be given broad-spectrum antibiotics until it is known for sure whether HPS is the cause of the illness.

Studies have not yet proved the benefits of using intravenous (IV) ribavirin to treat suspected cases of HPS, and this treatment is not recommended.

There is no surgical treatment for hantavirus pulmonary syndrome (HPS).

There is no other treatment for hantavirus pulmonary syndrome (HPS) at this time.

Organization

Citations

1. Yates TL, et al., (2002). The ecology and evolutionary history of an emergent disease: Hantavirus pulmonary syndrome. Bioscience, 52(11): 989–999.

2. National Center for Infectious Diseases, Centers for Disease Control and Prevention (2005). Case information: Hantavirus pulmonary syndrome case count and descriptive statistics. All About Hantavirus. Available online: http://www.cdc.gov/ncidod/diseases/hanta/hps/noframes/caseinfo.htm.

3. Howard MJ, et al. (1999). Hantavirus pulmonary syndrome in pregnancy. Clinical Infectious Diseases, 29(6): 1538–1544.

Other Works Consulted

• Committee on Infectious Diseases, American Academy of Pediatrics (2003). Hantavirus pulmonary syndrome. In LK Pickering et al., eds., Red Book: 2003 Report of the Committee on Infectious Diseases, 26th ed., pp. 301–304. Elk Grove Village, IL: American Academy of Pediatrics.

• Khan AS, Ksiazek TG (2000). Diseases caused by hantaviruses. In GT Strickland, ed., Hunter's Tropical Medicine and Emerging Infectious Diseases, 8th ed., pp. 288–293.

• Mackenzie J, Plant A (2004). Hantavirus pulmonary syndrome. In DL Heyman, ed., Control of Communicable Diseases Manual, 18th ed., pp. 243–245. Washington, DC: American Public Health Association.

• National Center for Infectious Diseases, Centers for Disease Control and Prevention (2005). Technical information for health care providers, public health professionals, educators, and others. All About Hantavirus. Available online: http://www.cdc.gov/ncidod/diseases/hanta/hps/noframes/phys/printtechsection.htm.

• Peters CJ (2005). California encephalitis, hantavirus pulmonary syndrome, and Bunyavirid hemorrhagic fevers. In GL Mandell et al., eds, Principles and Practice of Infectious Diseases, 6th ed., pp. 2086–2090. Philadelphia: Elsevier Churchill Livingstone.