The Ebola Virus Infection
By [http://ezinearticles.com/?expert=Roda_Joanna_Abaya]Roda Joanna Abaya
Ebola Hemorrhagic Fever infection (EHF) caused by the fatal and still mysterious Ebola Virus has became a worldwide concern since its discovery in 1976. The Ebola outbreaks in the African continent have alarmed scientists, medical experts, and the government and volunteer organizations so that teams have been deployed to monitor and control the situation. The main concern of this paper is to present vital information that will establish the fact that Ebola virus infection can be transmitted by direct contact with infected animals. Bulk of this paper is an analysis of the nature of Ebola virus and its transmission from animals to human beings contained in the first four sections. A section was also provided for the information on the Ebola outbreaks and reported occurrence, arranged chronologically using CDC and WHO recent reports and fact sheets. The last two sections were designated for the EHF symptoms, diagnosis and laboratory tests information. A section was also provided for recent update on the Ebola virus infection.
Ebola virus is a member of Filoviridae, a family of RNA virus. Ebola was named after the river in the Republic Congo, Ebola, where it was discovered. It is one of the 18 known viruses that cause viral hemorrhagic fever syndrome (J. King). As backgrounder, RNA viruses like the Ebola virus are considered as zoonoses, meaning they are animal-borne, that cause damage to the microvasculature leading to an increased vascular permeability. The family Filoviridae is has the largest genome of the order Mononegavirales. Filo (in Filoviridae) is Latin word for worm (E. Burton). Members of this family appear to be thread-like and look like worms when seen under a microscope (Oldstone 134). Other descriptions of its form include that of pigtails, snakes, that of a “shepherd’s crook” and form a “U” shape when bended (www.geocites.com). Studies made on the virions revealed that they are composed of helical nucleocapsid and are of 80nm diameter (CDC, 2000). Ebola virus and its co-member Mamburg virus were re-classified from Rhabdoviridae family to Filoviridae (CDC).
Ebola virus has three subtypes: the Ebola-Zaire, the Ebola-Sudan, Ebola-Ivory Coast and Ebola-Reston all of which were named after the rivers from which they were discovered (WHO, 2004). Zaire was said to be the most lethal of the four strains of Ebola. It was the first recorded strain of Ebola to have affected humans which was recorded in October 1976. Zaire causes 80%-90% fatality rate on its human victims (E. Burton). Ebola Sudan, compared to Zaire is less fatal with only 50%-60% fatality rate. Ebola Tai or the Ebola Ivory Coast was discovered in 1994 which was found to have infected and killed chimpanzees (L. Garette). The last subtype seems to have an Asian origin since it was identified and discovered from the batch of monkeys shipped from the Philippines (geocites.com). The laboratory experiment done in Reston, Virginia revealed that the said strain can be transmitted by air and has not yet been proven to be fatal not dangerous to humans ( Peterson, et. al).
Since the Ebola virus was first discovered, scientists and health workers immediately isolated the infected hosts. The isolation was promptly made for the purpose of searching for the possible cure of Ebola Hemorrhagic Fever. When it was fist discovered in a cotton factory, everything in the factory, including bat droppings were collected and brought in laboratories for studies. The insects and every living thing contained in the factory were also captured for study. This step was however disadvantageous as to the experts’ search for the answer to a vital question: where is the virus’ reservoir?
Based on the origin of the infected mammals, the scientists thought that it could have been a resident of the African rainforests and in the West Pacific area. The scientists’ theory was that it was not the non-human primates or the humans who are the source of the infection as they appear to be just being only infected as a result of transmission from the real reservoir.
Bats, which were also captured from the cotton factory, were found to have also been infected by the virus. The laboratory tests however revealed that bats, unlike humans and primates victims do not die of the infection. Studies at this point as to the natural reservoir of the Ebola virus were so far in vain. As with human infection, studies revealed that it was due to the transmission of the virus by direct contact with infected gorillas, chimpanzees, monkeys, forest antelope and porcupines found dead in the rainforest.
The well-known disease caused by Ebola virus is the Ebola Hemorrhagic Fever (EHF), which according to experts is often fatal in both human and non-human primate victims according to Centers for Disease Control and Prevention. The World Health Organization reported a 50%-90% fatality rate on victims. In the Ebola Hemorrhagic Fever Fact Sheet No.103 released by the World Health Organization on May 2004, the following information was provided relative to the transmission of Ebola:
a. The Ebola virus can be transmitted by direct contact with the blood, secretions, organs or other bodily fluids of infected persons.
b. Direct contact with the dead bodies of infected persons can also be a possible means of Ebola transmission.
c. Handling of infected animals, both dead and alive can also transmit the virus. The said case was true and was actually documented on the Reston strain where researchers who handled the infected monkeys were also infected.
d. Inadequate precautions while treating infected individuals can also be a means of Ebola transmission. WHO says that those health workers who have frequent and direct contact with the patients have the possibility of being also infected. Unhygienic hospital practices such as the use of unsterilized syringes can also spread the virus.
African-derived Filovirus infections are said to have been transmitted through the body fluids of the host such as blood and saliva (King, 2007). “The results of tests and studies on non-human primates revealed that EBO-Z (Ebola Zaire) and EBO-S (Ebola Sudan) were possibly transmitted through the mucous membranes, conjunctiva, pharynx and gastrointestinal surfaces, small breaks in the skin, and, at least experimentally, by aerosol,” says King. King also mentioned in his discussion the case of infected patients who were found to have Ebola virus in 100% of their oral secretions. For this, the author believes that oral secretions can also be a means of the viral transmission.
Confirmed cases of Ebola HF have been reported in the Democratic Republic of the Congo, Gabon, Sudan, the Ivory Coast, and Uganda (www.webmd.com). Ebola has been found to be the cause of well-documented outbreaks of severe human hemorrhagic fever, with 88% mortality rates in the areas of Yambuku, Democratic Republic of the Congo (King, 2007). Yambuku is a small village in Northern Zaire from which Ebola outbreak began in 1976 (CDC 5-8). It was in a small village run by Belgian nuns where the outbreak began recording 318 infected individuals (Garrett 100-105). Gabon was struck next, with several occurrences between 1994 and 1996 with about 57% fatalities according to the CDC report. There were also cases of infection found in Liberia, in England and in the Philippines although there were no reports of fatalities.
According to Pennsylvania Department of Health, victim of Ebola Hemorrhagic Fever may generally experience sore throat, muscle aches and weakness. At the early stage of the disease, the patient may present with fever and severe constitutional signs and symptoms (King, 2007). Documented cases also include symptoms such as maculopapular rashes that are easily recognized on white skin. At the development stage of the infection, infected patients experience an inflammation of the throat medically termed as Diarrhea Pharyngitis and also inflammation of the mucous membranes in the eyes referred to as Conjunctivitis, aside from vomiting and abdominal pains. At the late stage of the disease, hippocratic facies occur (Leroy, E.M., et. al). As a result of the inability of blood clotting, internal bleeding occurs. Bleeding starts from injection sites, on the mucous membranes, into the gastrointestinal tracts, on the skin and internal organs. Myocarditis and pulmonary edema also are seen in the later stages of the disease (Pennsylvania Department of Health).
Because some of the early symptoms of EHF are similar to symptoms of other diseases such as malaria and typhoid fever, medical experts agree that EHF diagnosis is somewhat difficult. For this reason, specialists need to conduct several laboratory tests to a person suspected on having infected by EHF to ensure results. Such laboratory tests include blood film examination and stool culture. Other comprehensive tests include the following:
a. ELISA (Antigen-capture enzyme-linked immunosorbent assay) Testing-a serologic testing that is done after few days of the onset of symptoms. Follow up tests are also done using immunoglobulin M-capture ELISA, that is conducted using EBO-Z viral antigens. Such antigens are taken from cells that are infected by Vero E6 (A. Takada, 1988). Also done as ELISA test is the immunoglobulin G (IgG) that uses detergent-extracted Ebola antigens. PCR (polymerase chain reaction) and virus isolation are done on diseased patients. The above tests, according to CDC are however considered high-risk procedures and are done only on high-containment laboratories.
b. Indirect immunofluorescence test – it is the most common test done on EHF patients which lack specificity. For this reason, other tests such as the ELISA tests were consequently developed.
c. Electron microscopy – the purpose of this test is mainly to identify filoviruses in tissue of patients. However, limitations of the results of this testing method have been reconsidered when human outbreaks in other areas occurred.
d. Immunohistochemical test – it is a more specific testing method used by medical experts for diagnosis and surveillance. This test is done on skin of diseased patients after formalin has been applied.
EHF has been one of the biggest fear of humans especially in Africa where it the several initial outbreaks occurred. However, recent reports said EHF is not only harmful and fatal to humans but also to primates, especially to gorillas. In the report releases by the National Geographic News on December 07, 2006, the virus has been “marching steadily across western and central Africa, wiping out more than 90 percent of the gorillas in its path and threatening the species with extinction” (K. Ravilious). The report made by a team of researchers and scientists monitoring the spread of Ebola virus on gorilla population, the team estimated that there were about 5,000 gorillas killed by the virus since 1995 in Lossi Sanctuary alone (Science Journal). What remains hidden to scientists is the natural reservoir of the Ebola virus, although there have been hypothesis that points to fruit bats, which were also tested for the infection but did not die out of it.
Researches on possible cure for EHF are a continuing effort. In 2003, the National Institute of Allergy and Infectious Disease (NIAID) released official reports of its human trial of the vaccine designed to prevent Ebola virus infection. The report said that the experimental vaccine, a type called a DNA vaccine, “is similar to other investigational vaccines that hold promise for controlling such diseases as AIDS, influenza, malaria and hepatitis” (NIAID, 2003). The experiment was conducted at the NIH Clinical Center in Bethesda, on 27 volunteers, ages 18-44. Volunteers injected with the trial vaccine thrice in two months are expected not to be exposed with Ebola virus.
Prior to the NIAID vaccine trial, group of scientists from Emory and the Centers for Disease Control and Prevention (CDC) has discovered valuable information relative to the Ebola virus lethal effects (H. Korschun). The scientists reported that “a mouse strain of Ebola virus adapted from a human strain induces a strong T-cell immune response” (Emory Report, April 23, 2001). Such finding is contrary to the previous hypothesis that infected patients die of the Ebola virus due to a virus-caused suppression of the immune system. The researchers’ conclusion was that Ebola virus has rapid fatal response in the experimented mice that even with the presence of T-cells, the immune response of infected host cannot cope up with the fatal virus.
Using vital information from CDC and WHO reports and fact sheets, we were able to analyze the nature of the killer Ebola virus, how it is transmitted to animals and to humans how it replicates and consequently damages the system of the infected patient. Having information on the Ebola outbreaks, from its discovery to the most recent reported case, we were able to have the idea that Ebola virus is unlike malaria and typhoid fever viruses although similar symptoms are being experienced by patients. The uniqueness of the virus lies on the fact that not only humans are being infected but also non-human primates like monkeys and gorillas. Although the natural reservoir of the virus remains unknown, experiments and trials of Ebola vaccine offer hope for the world especially the African continent which has been severely affected. The researches and experiments continue and the world hopes to find favorable results in the near future.
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