Viral hemorrhagic fevers (VHFs) are caused by viruses from four distinct families and range in severity from relatively mild to life-threatening. When they do occur, they’re often found in people who’ve recently traveled internationally. Although all begin with fever and muscle aches, some viral hemorrhagic fevers progress to more serious problems, including severe internal and external bleeding (hemorrhage), widespread tissue death (necrosis), and shock. No current treatment can cure viral hemorrhagic fevers. Immunizations exist for only two of the many viral hemorrhagic fevers. Until additional vaccines are developed, the best approach is prevention.
The VHF designation includes a broad range of diseases. Signs and symptoms can vary widely, even among members of the same viral family. But VHFs do have some common characteristics, especially in their effects on your vascular system — the network of arteries, veins and capillaries that circulates blood throughout your body.
Hemorrhagic fevers make blood vessels more permeable — that is, more likely to leak — causing bleeding that can range from relatively minor to massive. Bleeding may occur under your skin, in internal organs, and from your mouth, eyes, ears and rectum. People with severe bleeding may experience potentially lethal signs and symptoms such as shock and coma, but rarely die of blood loss.
In general, signs and symptoms of most VHFs begin two days to two weeks after you’ve been exposed to the virus. Typically, VHFs begin with fever and muscle aches; many cause vomiting and diarrhea; and all create problems in a number of organ systems, especially your liver, lymphatic system, lungs and sometimes your kidneys.
Problems more specific to diseases within each of the four families of viruses that cause viral hemorrhagic fevers are listed below.
This viral family includes Lassa fever, Argentine hemorrhagic fever, Bolivian hemorrhagic fever, Brazilian hemorrhagic fever and Venezuelan hemorrhagic fever. If you’ve been exposed to one of these illnesses, you’re likely to experience some of the following signs and symptoms:
- Fever, which may be constant or intermittent
- Pain behind your chest wall and in your back
- A sore and inflamed throat with white patches on your tonsils
- Abdominal pain
- Conjunctivitis, an inflammation of the transparent membrane (conjunctiva) that covers your eyelids and part of your eyeballs
- Bleeding from your gums or in your stomach, small intestine and other internal organs
- Facial swelling
- Temporary or permanent hearing loss
- Fluid around your lungs (pleural effusion)
- Encephalitis, a life-threatening inflammation of the brain
Included in this group of VHFs are Rift Valley fever, Crimean-Congo hemorrhagic fever, hemorrhagic fever with renal syndrome, and hantavirus pulmonary syndrome. Depending on the type of virus involved, signs and symptoms of bunyaviruses may include:
- Severe muscle aches
- Sore throat
- In the case of Crimean-Congo hemorrhagic fever, sore eyes and sensitivity to light (photophobia); mood swings and agitation; bleeding into the skin and from the gums, rectum and kidneys; and eventual pulmonary failure
- In the case of hantavirus pulmonary syndrome, shortness of breath and difficulty breathing, possibly leading to respiratory failure
This viral family consists of the Ebola virus and Marburg viruses, which are among the most virulent of all known diseases.
Signs and symptoms appear within two days to two weeks of infection and initially include those common to other VHFs: fever, intense weakness, muscle pain, vomiting and diarrhea. As the disease progresses, some people also develop:
- A distinctive, hemorrhagic rash, often appearing around the fifth day
- Bleeding from the nose, mouth, eyes, ears and rectum
Depending on the strain, Ebola and Marburg viruses are fatal in 50 to 90 percent of infected people and are almost always fatal in pregnant women.
Yellow fever. Yellowing of the skin and eyes (jaundice) is the hallmark sign of yellow fever. Other common signs and symptoms include fever, headache, muscle aches, facial flushing and sensitivity to light.
Dengue fever. Signs and symptoms of dengue fever vary with age. Infants and young children usually develop a rash and severe, flu-like symptoms, whereas older children and adults may experience a high fever, severe headache, eye pain, muscle aches and rash. In the hemorrhagic form, an extremely high fever may be accompanied by bleeding, convulsions and circulatory failure.
Kyasanur Forest disease and Omsk hemorrhagic fever. Both conditions are biphasic diseases, meaning that the initial signs and symptoms are followed by a brief period of recovery before they reappear. No matter when they occur, signs and symptoms of these two diseases generally include:
- Fever, which may be constant or intermittent
- Pain behind your eyes
- Pain in your arms and legs
- A rash on the soft palate of your mouth
- Swollen glands in your neck
- Bleeding in your eyes
- Bleeding in your gastrointestinal tract
Most of the viruses associated with VHFs are zoonotic, which means they reside in an animal or insect host and are dependent on that host for their survival. In general, humans acquire the virus when they come into contact with an infected host, but in some cases, person-to-person transmission can occur after the initial infection. Human epidemics occur sporadically, usually because of a combination of climatic, ecological and social factors.
Lassa fever, a common arenavirus, is endemic in West Africa, where as many as 500,000 cases occur each year. It may spread in the following ways:
Wild rodents. The multimammate rat is the main source of Lassa virus infection. You can acquire the virus from direct contact with infected rat droppings or urine, from touching surfaces or objects or eating food contaminated with these excretions, or possibly by inhaling airborne particles that contain the virus (airborne or aerosol transmission).
Person-to-person contact. You can contract the virus if you come in contact with the blood, throat secretions or urine of an infected person, especially during the acute fever stage of the illness.
Sexual contact. Because the virus can be transmitted in semen long after infection, experts recommend that men who have recovered from Lassa fever refrain from sexual activity for at least three months.
Contaminated needles and syringes. This form of transmission is most likely to occur through an accidental needle stick or in a hospital in a developing nation where equipment may be used on more than one person.
Argentine, Bolivian, Brazilian and Venezuelan hemorrhagic fevers are less pervasive arenavirus illnesses, occurring only in South America. These particular arenavirus illnesses are carried by rodents.
The diseases in this group spread by contact with an infected insect or animal:
Mosquitoes. Rift Valley fever primarily affects animals, especially sheep, cattle, camels and goats, but it can also cause severe disease in humans. It’s spread by a number of mosquito species, some of which transmit the virus to their offspring. Noninfected mosquitoes acquire the virus when they feed on sick animals and then pass it on to their next victim, perpetuating the cycle of infection. Humans contract the virus through a mosquito bite or through contact with the blood, organs, body fluids and possibly the raw milk of infected animals.
Ticks. Crimean-Congo hemorrhagic fever, a severe VHF that’s often fatal, is endemic in many countries in Africa, Europe and Asia. It’s spread by ticks, some of which transmit the virus to their offspring via eggs. More often, ticks acquire the virus when they feed on infected animals, especially cattle, sheep and goats. Humans may become infected from a tick bite or from direct contact with the blood or tissues of sick livestock, especially during the first week after the animal has been exposed to the virus.
Rodents. The hantaviruses that are responsible for hantavirus pulmonary syndrome are typically spread by rodents and occur in the United States, Canada and South America. In most cases, you contract the virus when you breathe the aerosolized droppings of infected rodents. The risk is especially high for farm workers, campers and other people who spend time outdoors in endemic areas, but you can also be exposed to the virus when rodents invade your home during cold weather or nest near your house.
The natural reservoir of these diseases isn’t known, but once a person is infected, the virus can be transmitted in several ways:
Person-to-person contact. You can become infected if you’re exposed to the blood, body fluids or organs of someone who’s severely ill with Ebola or Marburg virus. Most at risk are health care workers and family members caring for a sick relative.
Contaminated needles and syringes. This form of transmission is most likely to occur in a hospital when equipment is reused or through an accidental needle stick.
Sexual contact. The Ebola virus and Marburg virus can be transmitted through semen, even when the affected person is no longer sick. For that reason, experts recommend refraining from sexual activity for at least three months after recovery.
Contact with nonhuman primates. In a few instances, researchers have contracted Marburg virus after handling monkeys infected with the disease.
In most cases, insects are responsible for the spread of this family of viruses:
Mosquitoes. Yellow fever and dengue hemorrhagic fever are virulent forms of flaviviruses, and both are spread by a particularly efficient species of mosquito: Aedes aegypti. The mosquitoes thrive in and near human habitations where they breed in even the cleanest water. Although most cases of yellow fever and dengue fever occur in South America, Asia and parts of Africa, isolated cases have been reported in the United States. The Aedes aegypti mosquito is now found in a large portion of the United States, and in some Caribbean and European countries, increasing the possibility of epidemics in these areas.
Ticks. Kyasanur Forest disease and Omsk hemorrhagic fever are far more obscure and isolated illnesses — Omsk hemorrhagic fever, for example, occurs only in parts of western Siberia where it mainly affects muskrat trappers. Although ticks spread both diseases, you can also contract Omsk hemorrhagic fever by handling infected muskrats or by drinking water that contains the virus.
Your chance of contracting most VHFs is low. Some are confined to isolated pockets in remote areas where the risk of transmission is slight. And because each virus is usually associated with a specific host species, it’s normally restricted to the area where that species lives.
Yet taken together, the viruses that cause VHFs occur over most of the world. And some VHFs, especially Lassa, yellow and dengue hemorrhagic fevers, pose a real threat to people traveling to or living in regions where these diseases are widespread, primarily sub-Saharan Africa and South America.
In general, your risk of contracting any disease abroad depends on your itinerary and activities, the length of your stay and the rate of transmission of a particular disease at the time. If you’re visiting a region for a short time, staying in westernized hotels and taking guided tours, your risk is less than it is if you’re traveling for months and living in a tent. Still, you’re at risk of epidemic diseases such as dengue fever even in the best of circumstances, although your risk is likely lower if there are no outbreaks of the disease during your visit.
In the United States, you’re more likely to contract a hantavirus if your region has a large rodent population known to carry the virus. The risk increases if you live in the country or suburbs, you work outdoors, or you spend time in rodent-infested buildings.
On the other hand, hospital workers treating people with VHFs as well as researchers and laboratory personnel who deal with the viruses are at high risk of infection. In Africa, health care workers frequently contract Ebola from patients, and a number of cases of laboratory-acquired infection have been documented worldwide.
Although complications of VHFs vary, some problems occur with many of the viruses. They include:
Uveitis. This serious eye inflammation affects the uvea, the layer just beneath the white of your eye (sclera). Uveitis causes redness, pain and sensitivity to light, but when treated promptly and appropriately, it doesn’t usually cause long-term complications.
Blindness. Rift Valley fever infections result in blindness for about one in five people affected.
Pericarditis. This is swelling and irritation of the pericardium, the thin, membranous sac that surrounds your heart. Pericarditis usually causes sharp, stabbing chest pain, shortness of breath and an overall feeling of weakness or fatigue. Mild cases may go away on their own, but severe pericarditis can lead to life-threatening conditions such as cardiac tamponade, which puts pressure on your heart and interferes with its ability to pump blood efficiently.
Encephalitis. This severe, potentially life-threatening brain inflammation is a possible complication of VHFs. Severe encephalitis can cause respiratory arrest, marked mental impairment, coma and death.
Orchitis. This acute inflammation of the testicles causes swelling and pain and usually occurs as a result of a viral infection. In some cases, orchitis can lead to infertility.
Hearing problems. As many as one-third of those who recover from Lassa fever will have deficits in their hearing, and possibly deafness.
Spontaneous abortion. Loss of an unborn child is a frequent complication in pregnant women who develop VHFs.
Hair loss. Many people who recover from VHFs experience temporary or permanent hair loss.
Diagnosing specific VHFs in the first few days of illness can be difficult. All infected people initially exhibit the same signs and symptoms: fever, muscle aches, headache and extreme fatigue. What’s more, these signs and symptoms frequently occur with many diseases that are far more common than are VHFs.
To reach an accurate diagnosis, your doctor is likely to ask about your medical and travel history and any exposure to rodents or mosquitoes. Be sure to describe international trips in detail, including the countries you visited and the dates, as well as any contact you may have had with possible sources of infection.
Laboratory tests, usually using a sample of your blood, are needed to confirm a diagnosis of viral hemorrhagic fever. Because VHF viruses are particularly virulent and contagious, these tests are usually performed in specially designated laboratories using strict precautions.
No specific treatment exists for most VHFs, although the antiviral drug ribavirin may help shorten the course of infection and prevent complications in certain arenaviruses and bunyaviruses. Whether bleeding complications should be treated with therapies such as clotting factors, platelets and heparin remains a matter of debate.
Supportive care is essential for every person with VHF, no matter what type of virus is involved. This is likely to include measures to:
- Provide adequate fluids and maintain the balance of electrolytes — substances such as sodium, potassium, chloride and calcium, which control the movement of nutrients into cells
- Aid breathing with a mechanical ventilator, if necessary
- If needed, provide kidney dialysis, an artificial way of removing excess fluids and wastes from your body when your kidneys stop working
- Provide therapy for secondary infections and other complications
The best approach to prevention of viral hemorrhagic fevers is to take precautions to protect yourself from infection:
Get vaccinated. Vaccines exist for yellow fever and Argentine hemorrhagic fever. If you’re traveling to areas where these diseases are endemic, consider being vaccinated. The yellow fever vaccine is generally considered safe and effective, although in rare cases, serious side effects can occur. Check with the CDC about the status of the countries you’re visiting — some require certificates of vaccination for entry. The yellow fever vaccine isn’t recommended for children under 9 months of age or for pregnant women, especially during the first trimester.
Be sure you’re mosquito-proof. Take common-sense precautions to protect yourself and your family from mosquitoes, such as wearing light-colored long pants and long-sleeved shirts or better yet, permethrin-coated clothing. Don’t apply permethrin directly to the skin. Avoid unnecessary activities at dusk and dawn when mosquitoes are most active and apply mosquito repellent with a 20 to 25 percent concentration of DEET to your skin and clothing. DEET is a powerful insecticide; use it with care. Apply it in moderation and don’t use it on the hands of young children or on infants under 2 months of age. Oil of lemon eucalyptus and other more natural products, including oils of geranium, cedar and lemongrass, may offer protection similar to low concentrations of DEET. If you’re staying in tented camps or local hotels, use bed nets and mosquito coils.
Avoid high-risk areas. Before you travel, obtain a consular information sheet from the Office of Overseas Citizens Services, which provides information on health and security issues. If there’s an outbreak or epidemic of infectious disease in an area you’re planning to visit, consider revising your itinerary.
Rodent control in and around your home is the primary way to prevent hantavirus infection. These measures can help:
- Keep pet food covered and stored in rodent-proof containers, and don’t leave food out overnight.
- Store trash in rodent-proof containers, and clean the containers often.
- Dispose of garbage on a regular basis.
- Make sure doors and windows have tightfitting screens.
- If you use traps inside or outside, be sure to keep children away from them.
- Place woodpiles and stacks of bricks and other materials at least 100 feet (about 30 meters) from your house.
- Mow your grass closely and keep brush trimmed to within 100 feet (about 30 meters) from your house.
- If you find evidence of rodent infestation in your home, don’t sweep or vacuum the area. Instead, make sure you wet the entire area with a household disinfectant, or with a solution of 1.5 cups of bleach to 1 gallon of water (about .37 liters of bleach to 4 liters of water). The CDC has more advice on cleaning up a rodent infestation on the Web.