The most deadly killers on this earth are too small to see with the naked eye. These microscopic predators are viruses. In my report, I will answer many basic questions concerning one of the fastest killing viruses, the Ebola virus. Questions such as “How does it infect its victims? “, “How are Ebola victims treated? “, “How are Ebola outbreaks controlled? ” and many others related to this deadly virus. GENERAL INFORMATION The Ebola virus is a member of the negative stranded RNA viruses known as filoviruses. There are four different strains of the Ebola virus – Zaire (EBOZ), Sudan (EBOS), Tai (EBOT) and Reston (EBOR).
They are very similar except for small serological differences and gene sequence differences. The Reston Strain is the only one which does not affect humans. The Ebola virus was named after the Ebola river in Zaire, Africa after its first outbreak in 1976. STRUCTURE When magnified by an electron microscope, the ebola virus resembles long filaments and are threadlike in shape. It usually is found in the form of a “U- shape”. There are many 7nm spikes which are 10nm apart from each other visible on the surface of the virus. The average length and diameter of the virus is 920nm and 80nm.
The virons are highly variable in length (polymorphic), some attaining lengths as long as 14000nm. The Ebola virus consists of a helical nucleocapsid, which is a protein coat and the nucleic acid it encloses, and a host cell membrane, which is a lipoprotein unit that surrounds the virus and derived form the host cell’s membrane. The virus is composed of 7 polypeptides, a nucleoprotein, a glycoprotein, a polymerase and 4 other undesignated proteins. These proteins are synthesized by mRNA that are transcribed by the RNA of the virus.
The genome consists of a single strand of negative RNA, which is noninfectious itself. The order of it is as follows: 3′ untranslated region, nucleoprotein, viral structured protein, VP35, VP40 glycoprotein, VP30, VP24, polymerase(L), 5′ untranslated region. HOW IT INFECTS Once the virus enters the body, it travels through the blood stream and is replicated in many organs. The mechanism used to penetrate the membranes of cells and enter the cell is still unknown. Once the virus is inside a cell, the RNA is transcribed and replicated.
The RNA is transcribed, producing mRNA which are used to produce the virus’ proteins. The RNA is replicated in the cytoplasm and is mediated by the synthesis of an antisense positive RNA strand which serves as a template for producing additional Ebola genomes. As the infection progresses, the cytoplasm develops “prominent inclusion bodies” which means that it will contain the viral nucleocapsid that will become highly ordered. The virus then assembles and buds off from the host cell, while obtaining its lipoprotein coat from the outer membrane.
This destruction of the host cell occurs rapidly, while producing large numbers of viruses budding from it. WHAT IT INFECTS The Ebola virus mainly attacks cells of the lymphatic organs, liver, kidney, ovaries, testes, and the cells of the reticuloendothelial system. The massive destruction of the liver is the trademark of Ebola. The victim looses vast amounts of blood especially in mucosa, abdomen, pericardium and the vagina. Capillary leakage and bleeding leads to a massive loss in intravascular volume. In fatal cases, shock and acute respiratory disorder can also be seen along with the bleeding.
Numerous victims are delirious due to high fevers and many die of intractable shock. SYMPTOMS During the onset of Ebola, the host will experience weakness, fever, muscle pain, headache and sore throat. As the infection progresses, vomiting (usually black), limited kidney and liver function, chest and abdominal pain, rash and diarrhoea begin. External bleeding from skin and injection sites and internal bleeding from organs occur due to failure of blood to clot. TRANSMISSION How “patient zero” (first to be infected) acquires natural infection is still a mystery.
After the first person is infected, further spread of Ebola to other humans (secondary transmission) is due to direct contact with bodily fluids such as blood, secretions and excretions. It is also spread through contact with the patients skin which carries the virus. Spread can be accomplish either by person to person transmission, needle transmission or through sexual contact. Person to person transmission occurs when people have direct contact with Ebola patients and do not have suitable protection. Family members and doctors who contract the virus usually obtain it from this type of transmission.
Needle transmission occurs when needles, which have been used on Ebola patients, are reused. This happens frequently in developing countries such as Zaire and Sudan because the heath care is underfinanced. A lucky person who has recovered from the Ebola virus can also infect another person though sexual contact. This is because the person may still carry the virus in his/her genital. A fourth method of transmission is airborne transmission. This type is not proven 100% although there have been several experiments done to prove that this type of transmission is highly possible.
The time between the invasion of Ebola and the appearance of its symptoms (incubation period) is 2-21 days. HOW IT IS DIAGNOSED Diagnosing the Ebola virus may take up to 10 days. The methods used to detect the virus are very slow, compared to how rapid Ebola can kill its victims. Blood or tissue samples are sent to a high- containment laboratory designed for working with infected substances and are tested for specific antigens, antibodies or the viruses genetic material itself. Recently, a skin test has been developed which can detect infections much faster.
A skin biopsy specimen is fixed in a chemical called Formaline, which kills the virus, and is then safely transported to a lab. It is processed with chemicals and if the dead Ebola virus is present, the specimen will turn bright red. TREATMENT No treatment, vaccine, or antiviral therapy exists. Roughly ninety percent of all Ebola’s victims die. The patient can only receive intensive supportive care and hope that they can be one of the fortunate ten percent who survive. In November of 1995, Russian scientist claimed that they had discovered a cure for Ebola.
It uses an antibody called Immunoglobulin G (IgG). They immunized horses with it and challenged them with live Ebola Zaire viruses. The scientists took their blood and used it as antiserum. With the antiserum, they have developed Ebola immune sheep, goat, pigs and monkeys. USAMRIID (USA Medical Research Institute for Infections Disease) received some equine Immunoglobulin and had some successes but fell short of the great claims of the Russians. This discovery does give grounds for optimism that an effective cure for Ebola can be found. CONTROL OF THE OUTBREAK.
To control an outbreak of Ebola, you must prevent further spread of the virus. The CDC (Center for Disease and Control) usually sends a team of medical scientists to the area of the outbreak where they provide advice and assistance to prevent additional cases. To limit the spread, they collect specimens, study the course of the virus, and look for others who may have been in contact with the virus. If anyone has been exposed to the virus, they are put under close surveillance and are sprayed with chemicals. The patients are isolated to interrupt person to person spread at the hospitals.
This is called the “barrier technique”. 1) All hospital personnel in contact with the patient must wear protective gear such as gowns, masks, gloves, and goggles. 2) Visitors are not allowed. 3) Disposable materials and wastes are removed or burned after use. 4) Reusable materials, such as syringes and needles are sterilized. 5) All surfaces are cleaned with sanitizing solution. 6) Fatal cases are buried or cremated. The outbreak is officially over when two maximum incubation periods (42 days) have passed without any new cases. PAST OUTBREAKS In the past, there has been 4 major outbreaks.
The first occurred in 1976 in Zaire, Africa where there were 280 fatalities out of 318 cases. The second also occurred in 1976, but in a nearby country, Sudan, Africa where 150 additional victims out of 250 cases died. In total, there were 340 deaths out of the 568 who were infected, a death rate of almost 60%. A smaller outbreak arose in 1979, also in Sudan. There were only 34 cases and 22 fatalities. Tiny outbreaks have occurred periodically in Africa up until 1995. In 1995, after 16 years of hiding, the fourth appearance of Ebola emerged and devastated Africa once again.
This time it was in Kikwit, Zaire. The first patient was discovered on January the 6th and the outbreak was officially over on August the 24th (see chart for death distribution of each month during its peak – 212 deaths). There was a total of 315 cases and 244 deaths, a 77% fatality rate. THE ANIMAL RESOVOIR The animal species which carries the Ebola virus has not been found. Since outbreaks begin when man comes in contact with the animal resovoir, scientist have made several attempts during the 1970 outbreaks to find it, but have been unsuccessful.
The 1995 outbreak gave scientist a perfect opportunity to search for the source once again. After locating “patient zero”, a charcoal- maker named Gaspard Menga, they decided to search the jungle where he probably came in contact with Ebola. They collected over 18,000 animals and 30,000 insects. These include mosquitoes, hard ticks, rodents, birds, bats, cats, small bush antelope, snakes, lizards and a few monkeys. After collecting, the specimens are tested for antibodies of Ebola or Ebola itself. The scientist will continue searching until the end of the year, hoping that they will find the animal resovoir.