Ebola virus disease is truly a mysterious disease. It appears from nowhere, causes outbreaks and then disappears. For example, there were virtually no cases from 1980 to 1993, and then subsequently there have been outbreaks most years, albeit often in different locations.
Ebola virus disease brings the most frightening of infectious disease syndromes to mind. Ebola virus disease is the kind of thing that horror writers dream about. The nonfiction book The Hot Zone by Richard Preston and the 1995 movie Outbreak, patterned after Ebola virus disease, are equally terrifying. Just imagine victims bleeding from their eyes, ears and nose and, at autopsy, the pathologist finding necrotic organs.
The first recognized outbreaks of Ebola virus disease occurred in 1976 in the Sudan and in Zaire (now the Democratic Republic of the Congo). Since then, there have been multiple outbreaks in central Africa, the largest of which occurred in 2000-2001 and involved 425 people. Outbreaks of Ebola virus disease have occurred primarily in remote villages near tropical rainforests. Historically, the disease has occurred most often in the Democratic Republic of the Congo and also Uganda, South Sudan and Gabon. Since 1976, there have been about 2,200 reported cases with 1,500 deaths.
The disease is caused by members of a family of filoviruses called ebolavirus, and there are five distinct species: Bundibugyo ebolavirus, Tai Forest ebolavirus, Reston ebolavirus,Sudan ebolavirus and Zaire ebolavirus. All but Reston are restricted to Africa and is found in primates in the Philippines and appears not to be a human pathogen. The Zaire species is the most lethal, with a case fatality rate of up to 90%, and is the cause of the current outbreak that began in Guinea in February.
This outbreak is the first-ever to occur this far west in Africa. As of early May, there have been 236 reported clinical cases with 158 deaths in Guinea. Some cases have occurred in neighboring Liberia. As with previous outbreaks, health care workers have been unfortunate victims of the epidemic, with at least 16 deaths.
Bats are likely the main reservoir
Fruit bats are probably the main reservoirs of the virus. They become infected without becoming ill, and the virus can be found in their saliva. Primates are the major victims of the disease. Primates (chimpanzees, gorillas, monkeys) and rarely other animals in the jungle such as forest antelope and porcupines periodically become ill with Ebola virus disease. The populace must be warned to avoid dead or sick animals.
Humans become infected by skin or mucous membrane contact with these infected animals and probably also by contact with fruit bats. Meat of bats as well as of the other animals is often consumed in many parts of the world and may be another mode of transmission. The consumption of bat meat, a popular meal, should be forbidden, considering they are thought to be the natural host of the general ebolavirus.
Transmission between humans occurs via contact with blood, secretions or other bodily fluids, which are highly contaminated with virus in infected patients. Presence of virus in blood and secretions means the patient is literally covered by virus, and exposure is easy. Therefore, health care workers and family members caring for sick individuals have been at high risk for infection. Historically, infection also has been spread in health care facilities by contaminated needles or syringes.
Burials also have served as a means of ebolavirus spread. Burial preparation of the cadaver has resulted in disease, and ritual close contact with the deceased is common, leading to additional infections. Authorities have advised against contact with the deceased at burials, where bodies are traditionally washed by hand, but they should be banned.
Infection is by direct contact with skin (presumably through small abrasions) or mucous membranes. Aerosolization of the pathogen does not seem to be involved as a mechanism of natural infection. But if it is ever weaponized and transmitted by aerosol, Ebola virus is classified as a Category A biological weapon.
Symptoms of infection
After an incubation period of 2 to 21 days, the patient develops a typical viral illness with fever, weakness, sore throat, headache and myalgias. This is followed by vomiting and diarrhea. There is a maculopapular rash. The severe illness then occurs with a coagulopathy and, in some, bleeding from multiple sites, including the gastrointestinal tract and mucous membranes. Multi-organ damage and necrosis then ensue with renal and hepatic failure, or in the lucky ones, defervescence and improvement ensue with survival. For those who survive, virus has been found in semen for up to 9 weeks. Therapy is supportive only, as there is no specific treatment for the disease.
No vaccine is available for prevention. The only real approach to an outbreak is to contain it until it ends. Early recognition of cases is critical with prompt institution of appropriate isolation with barrier care and use of personal protective gear by caregivers.
One of the fortunate aspects of Ebola virus disease is that patients are not contagious until becoming ill, and then are usually so sick that they do not move about. Therefore, wide exposure is unusual.
The professionals currently dealing with the epidemic come from the countries involved, from Médecins Sans Frontières (Doctors Without Borders), CDC, WHO, and other agencies are experienced and know what they are doing. The current epidemic will end as the others have in the past. As recommended by WHO, the outbreak will be declared over when no cases occur during 42 days — which is double the maximum incubation period of 21 days for ebolavirus.
And then Ebola virus disease will emerge again at some other time in some other place.
Baize S. N Engl J Med. 2014;doi:10.1056/NEJMoa1404505.
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Donald Kaye, MD, is a professor of medicine at Drexel University College of Medicine, associate editor of the International Society for Infectious Diseases’ ProMED-mail, section editor of news for Clinical Infectious Diseases and is an Infectious Disease News Editorial Board member.
Disclosure: Kaye reports no relevant financial disclosures.