HEMORRHAGIC FEVERS

DEFINITION

Hemorrhagic fevers (pronounced heh-meh-RA-jik) are a group of diseases caused by viruses. They occur throughout the world, but are most common in tropical areas. Early symptoms include muscle aches and fevers. The disease can progress to a more serious condition and, in many cases, can be fatal. A prominent symptom in late stages is hemorrhaging (rapid or heavy bleeding) from body openings and internal organs.

DESCRIPTION

Hemorrhagic fevers are a growing concern throughout the world. They are not new diseases, but they are affecting much larger numbers of people every year.

The viruses that cause hemorrhagic fevers live in a great variety of animals, such as arthropods and mammals. Arthropods are insects, spiders, and other animals with hard external skeletons. These animals are called the natural reservoir for the disease. In many cases, these animals do not become ill when infected by the viruses. They do, however, carry the viruses in their body.

Viruses are transferred from these animals to humans by vectors. A vector is an organism that carries a disease from one animal to another. Mosquitoes are common vectors. When they bite an animal, they suck in some of its blood. If the animal is infected with a virus, the blood also contains that virus. When the vector bites a human, it leaves some of its saliva in the wound. Some of the virus may also be left behind. The human becomes infected with the virus.

Hemorrhagic fevers are often endemic. An endemic disease is one that affects many people in a given area over long periods of time. Dengue fever (pronounced DEN-gay) is an example. It affects about 100 million people annually. Most of these people live in southeast Asia. The area is very crowded. People often live in close contact with each other. The disease is transmitted easily from one person to another. In addition, the mosquito that carries dengue fever thrives in southeast Asia.

Some hemorrhagic fevers are very rare. An example is Marburg hemorrhagic fever. It was first discovered in 1967. In the next thirty years after that, fewer than forty people were diagnosed with the disease.

The rate of fatalities (deaths) varies among the different forms of hemorrhagic fever. In the case of dengue fever, the death rate is about 1 to 5 percent. At the other extreme, ebola (pronounced ee-BO-la), an African hemorrhagic fever, kills 50 to 90 percent of those infected.

The onset (beginning) of hemorrhagic fevers may be sudden or gradual. They all have one characteristic in common, however. They all have the potential to result in hemorrhaging. The seriousness of the hemorrhaging also varies. In some cases, it involves no more than tiny pinpoints of bleeding under the skin. In other cases, the patient may bleed extensively from the mouth, nose, and other body openings.

CAUSES AND SYMPTOMS

Many different kinds of hemorrhagic fevers are known. The viruses that cause these diseases are usually found in tropical locations, but some are also found in cooler climates. Typical disease vectors include rodents (mice and rats), ticks, and mosquitoes. The virus can also be passed from person to person through sexual contact or other means.

Filoviruses

Ebola (pronounced ee-BO-la) is the most famous of the filoviruses (pronounced fi-lo-VI-russ-ez). It is endemic to Africa, especially to the Republic of the Congo and to Sudan. Scientists have not discovered the natural reservoir for the filoviruses.

Symptoms of a filovirus infection appear suddenly. They include severe headache, fever, chills, muscle aches, and loss of appetite. These symptoms may be accompanied by nausea, vomiting, diarrhea, and abdominal pain. A person with the infection may become listless and disoriented. Severe bleeding occurs from the stomach and intestines, nose, throat, and vagina. Ebola is fatal in 50 to 90 percent of all cases.

Arenaviruses

Arenavirus (pronounced uh-RE-nuh-virus) infections occur most often in parts of South America and west Africa. In west Africa they cause a disease known as lassa fever. The disease is spread by rodents. The virus is transmitted when humans come in contact with the urine and saliva of rats and mice. Symptoms differ somewhat between South American and west African forms of the disease.

The first symptoms of South American arenavirus infection are fever, muscle ache, weakness, and loss of appetite. Later, patients experience dizziness, headache, back pain, and upset stomach. The face and chest become red, and the gums begin to bleed. In about 30 percent of all cases, hemorrhaging occurs. Bleeding occurs under the skin and in the mucous membranes, the moist tissues that line body openings. In late stages, the nervous system is affected. A person experiences delirium and convulsions and may go into a coma. About 10 to 30 percent of patients die of the disease.

The symptoms of lassa fever are somewhat similar to those of South American infections, but the death rate is usually much lower, about 2 percent.

Flaviviruses

The two best known diseases caused by flaviviruses (pronounced fla-vih-VI-russ-ez) are yellow fever and dengue fever.

Yellow fever occurs in tropical areas of the Americas and Africa. It is transmitted from monkeys to humans by mosquitoes. Some people experience only a mild form of the disease. They may not even realize that they

An ebola virus, which causes severe bleeding and is fatal in 50 to 90 percent of cases. (© 1996

CDC/CMPS

. Reproduced by permission of

Custom Medical Stock Photo

.)

have been infected. In more serious cases, a patient experiences fever, weakness, low back pain, muscle pain, nausea, and vomiting. After about a week, these symptoms nearly disappear. Then they come back stronger than before. They develop into delirium (a form of madness), seizures, numbness, and coma. Bleeding occurs under the skin and in the mucous membranes. Blood also appears in stools and vomit.

Bunyaviruses

Bunyaviruses (pronounced BUN-yuh-vi-russ-ez) cause a number of hemorrhagic fevers, including Rift Valley fever and Crimean-Congo hemorrhagic fever. Rift Valley fever occurs in southern Africa and the Nile delta. The disease is transferred from wild and domestic animals to humans by

A city truck in Rio de Janeiro sprays insecticide to fight against an outbreak of dengue fever which is transmitted by mosquitos. (Reproduced by permission of

AP/Wide World Photos

)

bites of infected animals or through mosquito bites. The death rate is less than 3 percent.

Crimean-Congo hemorrhagic fever is found throughout much of Africa, Asia, and the Middle East. It is found in rabbits, birds, ticks, and domestic animals. Humans contract the disease after being bitten by an infected animal or by infected ticks. Death rates range from 10 to 50 percent. The symptoms of both Rift Valley and Crimean-Congo fevers are similar to those of other hemorrhagic fevers.

DIAGNOSIS

The symptoms of hemorrhagic fevers are similar to those of other diseases. Diagnosis depends on blood tests that show the presence of the virus.

TREATMENT

There are few drugs for the treatment of viral infections. Ribavirin (pronounced RI-buh-vih-rin) is one such drug. It is sometimes used to treat lassa fever and other hemorrhagic fevers. Treatment of these diseases is generally aimed at making patients more comfortable. Patients are often given fluids to replace those lost by vomiting and diarrhea. They may be given antibiotics to protect against other infections. Vitamin K is sometimes given to help stop bleeding. Blood transfusions may also be used to restore blood lost during hemorrhaging.

In many parts of the world, patients with hemorrhagic fevers receive no treatment at all. There are not enough medical or financial resources to treat everyone with the disease. People are left to recover or die on their own.

PROGNOSIS

The prognosis for various forms of hemorrhagic fever vary widely. The death rate for ebola can be as high as 90 percent. For some forms of dengue fever, it can be as low as 1 percent.

Some types of hemorrhagic fever can cause permanent disability. For example, about 10 percent of those who develop Rift Valley fever will suffer eye damage. They may become permanently blind. About 25 percent of patients with South American hemorrhagic fever become permanently deaf.

Proper treatment is very important. It can reduce the death rate dramatically. In some forms of dengue fever, lack of treatment results in a death rate of 40 to 50 percent. With adequate treatment, the death rate drops to less than 2 percent.

PREVENTION

The best way to prevent hemorrhagic fevers is to eliminate the vectors that carry the diseases. For example, efforts have been made to wipe out mosquito or rodent populations in some areas. These efforts are sometimes successful in big cities in developed nations. They are less successful in large rural areas in developing nations. In these cases, the best hope may be personal protection. People should use mosquito netting, insect repellents, and other devices to protect themselves against vectors.

Vaccines have also been developed against some hemorrhagic fevers, including yellow fever, Argentinean hemorrhagic fever, and Crimean-Congo fever. People who plan to travel in areas where these diseases occur should

Medical workers take extra precautions at the quarantined site of an ebola outbreak in Gozon, on the Ivory Coast. (Reproduced by permission of

AP/Wide World Photos

)

be vaccinated against them. The vaccines are costly, however, and many local populations cannot afford them.

FOR MORE INFORMATION

Books

Garrett, Laurie. The Coming Plague: Newly Emerging Diseases in a World Out of Balance. New York: Farrar, Strauss, and Giroux, 1994.

Henig, Robin Marantz. A Dancing Matrix: How Science Confronts Emerging Viruses. New York: Vintage Books, 1994.

Regis, Edward. Virus Ground Zero: Stalking the Killer Viruses With the Centers for Disease Control. New York: Pocket Books, 1996.

Ryan, Frank. Virus X: Tracking the New Killer Plagues Out of the Present and into the Future. Boston: Little Brown & Company, 1997.

Periodicals

LeGuenno, Bernard, "Emerging Viruses," Scientific American (October 1995): pp. 56+.

Web sites

Outbreak (An on-line information service about emerging diseases) http://www.outbreak.org (accessed October 25, 1999).

National Center for Infectious Diseases. Viral Hemorrhagic Fever. http://www.cdc.gov/ncidod/diseases/virlfvr/virlfvr.htm (accessed October 25, 1999).