Infection: Ebola and Marburg Hemorrhagic Fevers

Definition
Description
Demographics
Causes and Symptoms
Diagnosis
Treatment
Prognosis
Prevention
The Future
For more information

Definition

Ebola and Marburg fevers are two forms of viral hemorrhagic fever (VHF), a devastating infection with a very high mortality rate. Both are considered emerging infectious diseases because they were unknown before the mid-1960s. Both are also considered zoonoses because humans are thought to get them from contact with the tissues or body fluids of infected animals. Once the virus infects a human, the infections can spread from person to person.

Both Ebola and Marburg fever are caused by an unusual type of virus called a filovirus. Filoviruses look like long looped threads when viewed under an electron microscope. There are four known strains of Ebola virus but only one strain of Marburg virus.

Description

Marburg virus was the first identified filovirus, named for the city in Germany where seven laboratory staff members died after working with green monkeys imported from Uganda. The monkeys were being used to develop polio vaccines. Two doctors in Marburg became infected by contact with blood drawn from the first group of patients. Later cases of Marburg virus infection resulted from tourists visiting caves in Africa where infected bats are known to roost, or from direct contact with infected humans. An outbreak in the Congo from 1998 to 2000 was spread by gold miners.

Ebola virus is named for the river valley in the Democratic Republic of the Congo (then Zaire) where the first outbreak in humans occurred in 1976. Three of the four subtypes of Ebola virus are known to cause disease in humans. The fourth, known as Ebola Reston, was identified at the U.S. Army research laboratories (USAMRIID) in Reston, Virginia, in 1989. It causes disease in monkeys but not in humans. Researchers think that tropical fruit bats are the reservoir of Ebola as well as the Marburg viruses. The bats can give the filoviruses to monkeys, humans, and other animals, but do not get sick themselves.

Both Ebola and Marburg fevers have a high mortality rate—from 23–90 percent for Marburg fever and 50–90 percent for Ebola. Humans usually get infected by direct contact with the blood, other body fluids, or tissues of infected animals or other humans. Healthcare workers and family members preparing the dead for burial have been at highest risk. Viral hemorrhagic fevers typically begin suddenly with flu-like symptoms (fever, headache, muscle and joint pains) followed rapidly by a skin rash, violent nausea and vomiting, bloody diarrhea or bleeding from the nose and other parts of the body, mental confusion, and depression. Death results from a loss of blood volume and massive organ failure. Not all viral hemorrhagic fevers are caused by filoviruses.

Demographics

In the United States, there were no documented cases of Ebola or Marburg fever as of 2008. There have been four instances in 1989 and 1990 when several animal care workers in research laboratories tested positive for infection with the Ebola Reston strain of the virus. The workers did not become sick, however. The chief concern of public health doctors in Canada and the United States is the possibility that the Marburg and Ebola viruses could be used as agents of bioterrorism.

According to the World Health Organization (WHO), viral hemorrhagic fevers are equally deadly to men and women, and to members of all races. Children appear to be less likely to become infected, but that is most likely because they have less contact with sick adults than health-care workers or adult caregivers.

The risk of someone living in North America being infected with a viral hemorrhagic fever is very low. The following groups of people are at increased risk, however:

• Those having jobs involving frequent travel to areas of the world with known outbreaks of Ebola or Marburg fever. These include the Democratic Republic of the Congo (formerly Zaire), Sudan, Angola, Gabon, and Côte d'Ivoire.
• Field biologists who travel to Africa to study fruit bats.

• Researchers who study monkeys or other primates imported from Africa.
• Doctors, nurses, and other caregivers who treat or care for people infected with Marburg or Ebola virus.

Causes and Symptoms

Both Marburg and Ebola fever are caused by filoviruses that usually enter the body through direct contact with blood, urine, vomit, or other body fluids from infected animals or people. The viruses can also be spread by reusing contaminated needles or syringes. Some researchers think it may be possible for the viruses to spread through the air as well, as some monkeys appear to have become infected by breathing dust from bat droppings.

Once inside a human body, filoviruses replicate rapidly during an incubation period of three to nine days. They target the tissues that line the inner walls of blood vessels, causing tissue destruction, problems with blood clotting, and the hemorrhaging that is characteristic of these fevers. The liver is the internal organ that is most severely damaged by these diseases.

Patients usually feel sick quite suddenly. Viral hemorrhagic fevers can be difficult to diagnose at this point because the first symptoms are similar to those of malaria, yellow fever, typhoid fever, flu, or various bacterial infections. The patient has a high fever (102°F/39°C), sore throat, severe headache, nausea, dizziness, abdominal pain, muscle aches, and general weakness. In the next stage, the patient may have a reddish skin rash resembling measles; red eyes due to hemorrhaging of the tiny blood vessels in the eyes; vomiting blood; hemorrhaging blood from the nose, mouth, ears, or anus; severe diarrhea; and abnormally low blood pressure.

Flioviruses can destroy the patient's kidneys, lymph nodes, lungs, and spleen as well as the liver. Death occurs between seven and fourteen days after the first symptoms as a result of shock and organ failure.

Diagnosis

A correct diagnosis of Ebola or Marburg fever requires the doctor to suspect that the patient has an illness more serious than typhoid or malaria. The patient's history—particularly a history of travel to Africa or an occupational history of working with animals—may be the most important clue.

The viruses that cause Ebola and Marburg fever can be detected in blood and tissue samples, but these must be carefully collected and sent to the Centers for Disease Control and Prevention (CDC) or another laboratory equipped to handle samples that are considered a level 4 bio-hazard (the highest possible rating). The best tests for detecting filoviruses are the enzyme-linked immunosorbent assay or ELISA test, and the reverse transcriptase polymerase chain reaction or [RT-]PCR test.

Treatment

There is no specific treatment for viral hemorrhagic fevers. Patients must be taken to a hospital for supportive care, which consists of fluid replacements, replacing blood loss, monitoring the patient's blood pressure, and prescribing medications to treat any bacterial infections that may develop in addition to the viral infection.

Patients diagnosed with Ebola or Marburg fever must be kept in strict isolation from other patients, and the doctors and nurses who care for them must wear goggles, face shields, and gowns as well as rubber gloves at all times. Any object that has been in contact with the patient's body fluids must be completely disinfected with chlorine bleach.

Prognosis

The prognosis for surviving Ebola virus is poor. The disease has a mortality rate as high as 90 percent. Patients who live for two weeks after symptoms appear have a chance of making a slow recovery that takes months.

Marburg hemorrhagic fever has a mortality rate between 23 and 90 percent. As with Ebola fever, survivors may take months to regain their strength. The after-effects of both diseases may include hair loss, eye problems, hepatitis, weakness, headaches, and (in men) inflammation of the testicles.

Prevention

The best way to avoid infection with a filovirus is to avoid traveling to parts of the world with known outbreaks of viral hemorrhagic fever. People should also avoid all contact with the remains of dead monkeys or other primates in these areas.

In the event of an outbreak, those who die from Ebola or Marburg fever must be buried as quickly as possible by specially trained workers in order to lower the risk of the infection spreading farther.

The Future

Researchers are presently working on developing a vaccine for humans against Ebola and Marburg fever. Vaccines that are 99 percent effective in monkeys have already been developed. However, early trials of a vaccine for humans were not successful. As of 2008, a newer vaccine for use in humans had entered clinical trials and seemed to be effective. Further study is needed before it can be approved for use.

Some doctors are concerned that Ebola and Marburg viruses could be used as weapons of bioterrorism. The filoviruses are classified by the CDC as Category A agents (the highest category) along with smallpox and anthrax. Category A agents are disease agents that have high fatality rates and could be spread across a large population. There are, however, two factors that could limit the use of filoviruses by bioterrorists. One is that Ebola and Marburg viruses are not easily spread among humans through the air. There is only one known case of a person being infected by airborne droplets coughed up by an Ebola patient. The other limitation on the use of these viruses in bioterrorism is that they infect everyone in a small community very rapidly but then die out before reaching larger human groups. In any case, the possibility of these viruses being used by terrorists is a major motivation for speeding the development of safe and effective vaccines against them.

WORDS TO KNOW

Bioterrorism : The use of disease agents to frighten or attack civilians.

Emerging infectious disease (EID) : A disease that has become more widespread around the world in the last twenty years and is expected to become more common in the future.

Filovirus : The category of viruses that includes Ebola and Marburg viruses. Filoviruses look like long pieces of thread under a microscope.

Reservoir : The term used by biologists for the natural host species of a disease organism. Bats are thought to be the reservoir of viral hemorrhagic fevers.

Zoonosis (plural, zoonoses) : A disease that animals can transmit to humans.

SEE ALSO Anthrax; Smallpox; West Nile virus infection

For more information

BOOKS

Grady, Denise. Deadly Invaders: Virus Outbreaks around the World, from Marburg Fever to Avian Flu. Boston: Kingfisher, 2006.

Preston, Richard. The Hot Zone. New York: Anchor Books, 1995.

Willett, Edward. Ebola Virus. Berkeley Heights, NJ: Enslow Publishing, 2003.

PERIODICALS

Altman, Lawrence K. “Test of an Experimental Ebola Vaccine Begins.” New York Times, November 19, 2003. Available online at http://query.nytimes.com/gst/fullpage.html?res=9B01E3D71F38F93AA25752C1A9659C8B63&sec=&spon=&pagewanted=all (accessed September 22, 2008).

Altman, Lawrence K., and Judith Miller. “Scientists Report Progress in Ebola Treatment.” New York Times, December 12, 2003. Available online at http://query.nytimes.com/gst/fullpage.html?res=9F06E4DD143CF931A25751C1A9659C8B63&sec=&spon=&pagewanted=all (accessed September 22, 2008).

WEB SITES

Centers for Disease Control and Prevention (CDC). Questions and Answers about Ebola Hemorrhagic Fever. Available online at http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/ebola/qa.htm (updated November 18, 2005; accessed September 22, 2008).

Centers for Disease Control and Prevention (CDC). Questions and Answers about Marburg Hemorrhagic Fever. Available online at http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/marburg/qa.htm (updated October 19, 2007; accessed September 22, 2008).

Mayo Clinic. Ebola Virus and Marburg Virus. Available online at http://www.mayoclinic.com/health/ebola-virus/DS00996 (updated June 21, 2007; accessed September 22, 2008).