Viral Hemorrhagic Fevers

What are viral hemorrhagic fevers?

Viral hemorrhagic fevers (VHF) is a term that refers to a group of illnesses caused by several distinct families of viruses. While some types of hemorrhagic fever viruses cause illnesses that are relatively mild, many of these cause severe, life-threatening diseases with no known cures. Perhaps the most well-known of this group of diseases is the Ebola virus, made famous by the movie Outbreak.

Hemorrhagic fever viruses are caused by viruses of four distinct families:

• Arenaviruses

• Filoviruses

• Bunyaviruses

• Flaviviruses

These viruses share the following common features:

• The viruses are geographically restricted to the areas where the host species live.

• Their survival depends on an animal or insect host, called the natural reservoir.

• Humans are not the natural reservoir for any of these viruses; they only become infected when coming into contact with an infected host. However, with some of these viruses, humans can transmit the virus to one another after the accidental transmission from the host.

• They are all ribonucleic acid (RNA) viruses, covered in a fatty (lipid) coating.

• With a few exceptions, there is no known cure or drug treatment for these diseases.

• Human outbreaks or cases of these diseases occur sporadically and irregularly, making outbreaks difficult to predict.

What are the natural reservoirs of viral hemorrhagic fevers?

For the most part, rodents and arthropods are the reservoirs for these viruses. Some examples of the rodents involved include the multimammate rat, cotton rat, deer mouse, house mouse, and other field rodents. Arthropod ticks and mosquitoes are vectors for some of the illnesses. However, the hosts of viruses, such as the Ebola and Marburg, remain unknown. Transmission of the viruses carried by rodents typically occur when humans come in contact with body excretions, urine, feces, or saliva of an infected rodent. Anthrodod vectors spread viruses when an infected mosquito or tick bites a human. Viruses can also be spread when a person crushes an infected tick.  

Where have cases of viral hemorrhagic fever occurred?

The viruses that cause these illnesses are distributed globally. However, since each virus is generally associated with one or more particular host species, the virus and its ensuing disease are usually seen where the host species lives. For some species, this is a limited geographic area; however, in other cases, a particular species, such as the common rat, may be distributed worldwide.

While people usually become infected only in areas where the host lives, occasionally the host is exported from its natural habitat, causing an outbreak in a different area. Occasionally, an infected person travels from an area where the virus occurs naturally, and if it is the type of virus that can be transmitted by person-to-person contact, others then contract the disease (as was the case with the Ebola hemorrhagic fever). With more and more people traveling each year, outbreaks of these diseases are becoming a greater threat to areas where the diseases have not been seen before.

Travelers are advised to take appropriate precautions to prevent infection. These include:

• Liberal use of insect repellent

• Wearing long sleeves and pants

• Using bednets in areas where outbreaks are occurring

• Avoiding contact with livestock in areas where outbreaks are occurring

Consult your health care provider for more information.

What are the symptoms of viral hemorrhagic fever diseases?

The specific symptoms of viral hemorrhagic fever diseases vary by the specific disease, and each individual may experience symptoms differently. Various organs in the body can be affected. Symptoms often include:

• Marked fever

• Fatigue

• Dizziness

• Muscle aches

• Loss of strength

• Exhaustion

Patients with severe cases often show signs of bleeding under the skin, in internal organs, or from body orifices, such as the mouth, eyes, or ears. While bleeding may occur from many sites around the body, blood loss is rarely the cause of death. Severely ill patients may also experience shock, seizures, nervous system failure, coma, and delirium. Some forms of the viral hemorrhagic fever disease are associated with kidney failure.

The symptoms of viral hemorrhagic fever may resemble other medical conditions or problems. Always consult your doctor for a diagnosis.

What is the treatment for viral hemorrhagic fever?

While patients receive supportive treatment, generally there is no known cure or treatment for these illnesses. The antiviral drug, ribavirin, has been effective in treating some people with Lassa Fever and hemorrhagic fever with renal syndrome.

How can viral hemorrhagic fever diseases be prevented?

Because no vaccines exist that can prevent these diseases (with the exception of yellow fever and Argentine hemorrhagic fever), efforts are concentrated on avoiding contact with host species.

Disease prevention efforts on hemorrhagic fever viruses carried by rodents include:

• Controlling rodent populations

• Preventing rodents from entering or living in homes or workplaces

• Learning about safe cleanup of rodent nests and droppings

For hemorrhagic fever viruses spread by arthropod vectors, prevention efforts focus on:

• Community-wide insect and arthropod control

• Use of insect repellent, proper clothing, bed nets, window screens, and other insect barriers to avoid being bitten