Viral hemorrhagic (hem-uh-RAJ-ik) fevers are infectious diseases that can cause severe, life-threatening illness. They can damage the walls of tiny blood vessels, making them leak, and can hamper the blood's ability to clot. The resulting internal bleeding is usually not life-threatening, but the diseases can be.

Some viral hemorrhagic fevers include:

• Dengue
• Ebola
• Lassa
• Marburg
• Yellow fever

These diseases most commonly occur in tropical areas. In the United States, people who get them usually have recently traveled to one of those areas.

There's no cure for viral hemorrhagic fevers. There are vaccines for only a few types. Until additional vaccines are developed, the best approach is prevention.

Signs and symptoms of viral hemorrhagic fevers vary by disease. In general, early signs and symptoms can include:

• Fever
• Fatigue, weakness or general feeling of being unwell
• Dizziness
• Muscle, bone or joint aches
• Nausea and vomiting
• Diarrhea

Symptoms that can become life-threatening

More-severe symptoms include:

• Bleeding under the skin, in internal organs, or from the mouth, eyes or ears
• Nervous system malfunctions
• Coma
• Delirium
• Kidney failure
• Respiratory failure
• Liver failure

When to see a doctor

The best time to see a doctor is before you travel to a developing country to ensure that you've received any available vaccinations and pre-travel advice for staying healthy.

If you develop signs and symptoms once you return home, talk to a doctor, preferably one trained in international medicine or infectious diseases. Tell your doctor where you've traveled.

Viral hemorrhagic fevers are spread by contact with infected animals or insects. The viruses that cause viral hemorrhagic fevers live in a variety of animal and insect hosts. Most commonly the hosts include mosquitoes, ticks, rodents or bats.

Some viral hemorrhagic fevers can also be spread from person to person.

How is it transmitted?

Some viral hemorrhagic fevers are spread by mosquito or tick bites. Others are spread by contact with infected body fluids, such as blood, saliva or semen. A few varieties can be inhaled from infected rat feces or urine.

If you travel to an area where a particular hemorrhagic fever is common, you can be infected there but not develop symptoms until after you return home. Depending on the type of virus, it can take from two to 21 days for symptoms to develop.

Living in or traveling to an area where a particular viral hemorrhagic fever is common will increase your risk of becoming infected with that particular virus. Other factors that can increase your risk include:

• Working with infected people
• Slaughtering or eating infected animals
• Sharing needles to use intravenous drugs
• Having unprotected sex
• Working outdoors or in rat-infested buildings
• Being exposed to infected blood or other body fluids

Viral hemorrhagic fevers can cause:

• Septic shock
• Multiorgan failure
• Death

Preventing viral hemorrhagic fevers is challenging. If you live in, work in or travel to areas where these diseases are common, protect yourself from infection by using appropriate protective barriers when working with blood or body fluids. For example, wear gloves and eye and face shields. Precautions also include careful handling, disinfection and disposal of lab specimens and waste.

Get vaccinated

The yellow fever vaccine is generally considered safe and effective. However, in rare cases, serious side effects can occur. The yellow fever vaccine isn't recommended for children younger than 9 months of age; pregnant women, especially during the first trimester; or people with compromised immune systems.

There's also an Ebola vaccination that protects against one type of Ebola. Check with the Centers for Disease Control and Prevention about the status of the countries you're visiting — some require certificates of vaccination for entry.

Avoid mosquitoes and ticks

Do your best to avoid these insects, especially when traveling in areas where there are outbreaks of viral hemorrhagic fevers. Wear light-colored long pants and long-sleeved shirts or, better yet, permethrin-coated clothing. Don't apply permethrin directly to the skin.

Avoid being outside, if possible, at dusk and dawn when mosquitoes are most active, and apply mosquito repellent with a 20% to 25% concentration of DEET to your skin and clothing. If you're staying in tented camps or in hotels, use bed nets and mosquito coils.

Guard against rodents

If you live where there are outbreaks of viral hemorrhagic fevers, take steps to keep rodents out of your home:

• Keep pet food covered and stored in rodent-proof containers.
• Store trash in rodent-proof containers, and clean the containers often.
• Dispose of garbage regularly.
• Make sure doors and windows have tightfitting screens.
• Keep woodpiles, stacks of bricks and other materials at least 100 feet from your house.
• Mow your grass closely and keep brush trimmed to within 100 feet of your house.

Diagnosing specific viral hemorrhagic fevers in the first few days of illness can be difficult because the early signs and symptoms — high fever, muscle aches, headaches and extreme fatigue — are common to many other diseases.

To help with diagnosis, tell your doctor about your medical and travel history and your exposure to rodents or mosquitoes. Include the countries you visited and the dates, as well as any contact you might have had with possible infection sources.

Lab tests, usually using a blood sample, are needed to confirm a diagnosis. Because viral hemorrhagic fevers are particularly infectious and contagious, these tests are usually performed in specially designated labs using strict precautions.

There's no cure for viral hemorrhagic fevers. Vaccinations exist for only a few types. The best approach is prevention. Supportive care is the mainstay of treatment.

Medications

While no specific treatment exists for most viral hemorrhagic fevers, the antiviral drug ribavirin (Rebetol, Virazole) might shorten the course of some infections and prevent complications in some people. Other medications are being developed.

Therapy

Supportive care is essential. To prevent dehydration, you might need fluids to help maintain your balance of electrolytes — minerals that are critical to nerve and muscle function.

Surgical and other procedures

Some people might benefit from kidney dialysis, which removes wastes from your blood when your kidneys fail.