Hantavirus pulmonary syndrome is an infectious disease characterized by flu-like symptoms that progress rapidly to potentially life-threatening breathing problems.

Several types of hantavirus can cause hantavirus pulmonary syndrome. They are carried by several types of rodents, particularly the deer mouse. You become infected primarily by breathing air infected with hantaviruses that are shed in rodent urine and droppings.

Because treatment options are limited, the best protection against hantavirus pulmonary syndrome is to avoid rodents and their habitats.

Hantavirus pulmonary syndrome advances through two distinct stages, with the first signs and symptoms appearing between one and five weeks after exposure to a hantavirus.

The early stage
Signs and symptoms such as fever, fatigue and chills are early indicators of a hantavirus infection. Within several days, nausea, vomiting, abdominal pains and headaches may develop. In its early stages, hantavirus infection is difficult to distinguish from influenza, pneumonia or other viral conditions.

Signs and symptoms of early-stage infection include:

• Fatigue
• Fever
• Chills
• Muscle aches, especially in large muscle groups, such as your thighs, hips and back
• Bubbling or rattling sounds in your lungs (rales)
• Abnormally fast breathing (tachypnea)
• Abnormally fast heartbeat (tachycardia)
• Headaches
• Dizziness
• Nausea
• Vomiting
• Diarrhea
• Abdominal pain

The cardiopulmonary stage
A cough often indicates that the hantavirus infection has progressed into the cardiopulmonary stage, in which the capillaries of your lungs begin to weaken and leak fluid. Shortness of breath and respiratory troubles can follow.

Symptoms or signs of the cardiopulmonary stage include:

• A cough that produces secretions
• Reduction of oxygen (hypoxia or hypoxemia) and a buildup of carbon dioxide (hypercarbia) and acid (acidemia) in your blood
• Shortness of breath
• Respiratory insufficiency (shock) or failure
• Buildup of fluid in your lungs (pulmonary edema)
• Acute respiratory distress syndrome (ARDS), in which your lungs' ability to transfer oxygen to your blood is severely impaired
• Multiorgan failure
• Low blood pressure (hypotension)
• Slower or faster than normal heartbeat (arrhythmia)

When to see a doctor
If you've been around rodents or rodent droppings and have symptoms of fever, chills, muscle aches or any difficulties breathing, seek immediate medical attention. Be sure to tell your doctor you have had exposure to rodents or their droppings.

Each type of hantavirus has a preferred rodent carrier. The deer mouse is the primary carrier of the Sin Nombre virus, which is responsible for most cases of hantavirus pulmonary syndrome in North America. Other hantavirus carriers include the white-tailed mouse, cotton rat and rice rat.

Inhalation: The main route of transmission
Hantaviruses are transmitted to people primarily through the "aerosolization" of viruses shed in infected rodents' droppings, urine or saliva. Aerosolization occurs when a virus is kicked up into the air, making it easy for you to inhale. For example, a broom used to clean up mouse droppings in an attic may nudge into the air tiny particles of feces containing hantaviruses, which you can then easily inhale.

After you inhale hantaviruses, they reach your lungs and begin to invade tiny blood vessels called capillaries, eventually causing them to leak. Your lungs then flood with fluid, which can trigger any of the respiratory problems associated with hantavirus pulmonary syndrome.

Other routes of transmission
Although rare, there are other methods of hantavirus transmission. You can become infected after receiving a rodent bite or after eating food containing rodent excrement. Person to person transmission of this disease is rare.

Hantavirus pulmonary syndrome has been reported in many U.S. states, but it's most common in rural areas of the western United States during the spring and summer months. Hantavirus pulmonary syndrome also occurs in South America and Canada. Other hantaviruses occur in Asia, where they cause kidney disorders rather than lung problems.

Certain groups of people — such as hunters or construction workers — are more likely to be exposed to rodents who carry hantaviruses. The chance of developing the syndrome is greater for people who work, live or play in spaces where rodents live.

Factors and activities that increase the risk of developing hantavirus illness include:

• Opening and cleaning previously unused buildings or sheds
• Housecleaning, particularly in attics or other low-traffic areas
• Having a home or work space infested with rodents
• Having a job that involves exposure to rodents, such as construction, utility work and pest control
• Camping, hiking or hunting

You may start by first seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, your doctor may recommend urgent medical care.

If you're having severe difficulty breathing, call for emergency help or have someone take you to the emergency room.

Because appointments can be brief, and because there's often a lot of ground to cover, it's important to be well prepared for your appointment. Here's some information to help you get ready for your appointment, and what to expect from your doctor.

What you can do

• Be aware of any pre- or post-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance.
• Write down any symptoms you're experiencing. It will help your doctor to have as many details as possible about when your symptoms first appeared and how they may have changed or worsened over time. Did you initially think you had the flu? Why do you now suspect it may be something else? Thinking about these questions in advance will help your doctor quickly understand your concerns.
• Write down key personal information, including recent "spring cleaning" or similar activities. Your doctor will want to know about any rarely or seasonally opened rooms or buildings that you've recently entered or cleaned. If you know you've been exposed to rodents or rodent droppings, be prepared to give your doctor a timeframe in which that occurred.
• Make a list of all medications, vitamins and supplements that you're taking.
• Take a family member or friend along. Hantavirus pulmonary syndrome can be a medical emergency. Take someone who can soak up all the information your doctor provides and who can stay with you if you need immediate treatment.
• Write down questions to ask your doctor.

Prepare a list of questions so that you can make the most of your time with your doctor. For hantavirus pulmonary syndrome, some basic questions to ask your doctor include:

• What is likely causing my symptoms or condition?
• Other than the most likely cause, what are possible causes for my symptoms or condition?
• What kinds of tests do I need?
• What treatment do you recommend?
• Am I at risk of long-term complications?
• Am I contagious? Is there anything I should do to reduce the risk to my family?
• What can I do to prevent a recurrence of this illness?
• Should I see a specialist? What will that cost, and will my insurance cover seeing a specialist?
• Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

• What are your symptoms?
• When did you first begin experiencing symptoms?
• How severe are your symptoms? Do they seem to be getting worse?
• Have your symptoms included flu-like discomfort, such as fever, muscle aches and fatigue?
• Have you had any gastrointestinal symptoms, such as diarrhea or vomiting?
• Have you noticed your heart beating faster than normal?
• Are you having difficulty breathing? Is it getting worse?
• Do you know if you've been exposed to rodents or rodent droppings?
• Have you recently entered or cleaned a building, room, attic or other space that previously had been closed up for an extended period?
• Have you recently traveled, including hunting or camping trips? Where?
• Do you come into contact with rodents or other animals as part of your work?
• Is anyone else in your life having similar symptoms?
• Are you being treated for any other medical conditions?

Blood tests are the main method for diagnosing hantavirus pulmonary syndrome. These are laboratory tests that analyze samples of your blood for the presence of certain antibodies that your body produces as a defense against disease-causing agents (pathogens). For people with hantavirus infection, antibodies of the IgM and IgG classes are nearly always present in the blood by the time signs and symptoms appear.

Because hantavirus pulmonary syndrome can resemble many other illnesses, your doctor may order further laboratory tests — such as cultures, urinary antigen tests or other blood tests — to rule out other conditions. For example, symptoms of hantavirus pulmonary syndrome can resemble influenza, Legionnaires' disease, pneumonic plague and Q fever.

Specific treatment options for hantavirus pulmonary syndrome are limited. But the prognosis improves with early recognition, immediate hospitalization and adequate support for breathing.

Two hantavirus treatment options are:

• Supportive therapy. People with severe cases need immediate treatment in an intensive care unit. Assisted respiration, whether through intubation or mechanical ventilation, can help with breathing and ward off pulmonary edema. Intubation involves placing a breathing tube through your nose, mouth or trachea to help keep your airways open and functioning.
• Blood oxygenation. In extremely severe cases of pulmonary distress, you'll need a method called extracorporeal membrane oxygenation to help ensure you retain a sufficient supply of oxygen. This involves continuously pumping your blood through a machine that removes carbon dioxide and adds oxygen. The resulting oxygenated blood is then returned to your body.

The antiviral medication called ribavirin effectively reduces the risk of complications from a type of hantavirus found in China. In the U.S. and Canada, studies of ribavirin in people in the cardiopulmonary stage of hantavirus infection showed no benefit. Researchers are evaluating whether ribavirin treatment might be beneficial if started before cardiopulmonary symptoms develop.

Minimize or eliminate contact with rodents to help prevent exposure to the hantavirus. Although only certain rodent species are known to carry hantavirus, it's best to minimize contact with all rodents, because others may carry pathogens that cause various illnesses.

Take these steps to help prevent hantavirus infection:

• Keep dwellings clean and rodent-free.
• Avoid contact with all rodents — including urban rats — and their droppings.
• Disinfect dead rodents before handling and disposing of them.
• Neutralize rodent droppings or urine with household disinfectants before sweeping or vacuuming.
• Take special precautions, such as wearing a respirator, when cleaning buildings with heavy rodent infestations.