Hemorrhagic Fevers - 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

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.