Introduction
Ebola virus which causes Ebola hemorrhagic fever, was first recognized in 1976 in Zaire, now Democratic Republic of Congo, and Sudan. It is named after the river Ebola in Zaire. The virus has five known subtypes named after the location where they were first identified and caused disease: Ebola Sudan, Ebola-Bundibugyo, Ebola-Zaire, Ebola-Ivory Coast and Ebola-Reston. (CDC.gov) Ebola-Reston is the newest subtype and was identified in research macaques imported from Philippines to Virginia in 2004 and later in Texas in 2006. It was discovered that the research animals in both cases were from the same site in the Philippines where guinea pigs were also found to have been infected with the same strain. (CDC.gov) While Ebola-Ivory Coast and Ebola-Reston do infect humans, symptoms as manifested by infection with other subtypes is not seen nor have any human deaths been reported. (Lee and Saphire, 2009) Ebola-Zaire and Ebola-Sudan are the most lethal with mortality rates upwards of 90% and 61% respectively. (CDC.gov)
Ebola virus is classified as a Class A bioterrorism agent and one that must be handled bio- safety level 4 labs. Research of Ebola virus requires trained professionals and facilities with rigorous levels of control to access. (CDC.gov) Like other viruses, the survival and spread of Ebola is dependent upon the host organism. At this time, the natural reservoir is not known which complicates containment and prevention of acquisition of Ebola. There are hypotheses that a non-primate is the host organism. Recent research points to fruit bats as the possible host carriers as the virus and viral antibodies are found in them though they do not exhibit any symptoms. Research continues in attempting to discover the natural reservoir so transmission prevention mechanisms may be implemented. The virus is not known to be native to continents other than Africa and Philippines in Asia. (CDC.gov) Ebola virus poses a considerable public health concern due to recent emergence of new subtype, high mortality rate associated with it, concern of possible misuse of the virus and lack of antiviral or vaccines. (Sarwar, 2011)
Pathophysiology
Ebola virus belongs to the Filoviridae family of viruses which also includes the very similar Marburg virus. It is an enveloped virus and is characterized by a long filamentous structure which can present as straight, branched, circular or folded strand with a uniform diameter of approximately 80 nm but variable in length. It specifically targets, endothelial cells, liver cells, neutrophils and macrophages. Infected cells produce large amount of cytokines which solicits a huge response from the immune system and disrupts normal behavior of liver, kidneys, respiratory system, skin and blood. (Hammer, 2012)
“Ebola virus is a non-segmented negative strand RNA genome containing 7 structural and regulatory genes. The Ebola genome contains four virion structural proteins and three membrane associated proteins.” (CDC.gov)The viral non structural secretory glycoprotein, sGP, is produced in large quantities early in infection. This glycoprotein binds to neutrophil receptor and inhibits its activation and the body’s innate immune response at large. A non secretory envelope glycoprotein, GP, binds to endothelial cells but not to neutrophils. “It is known to destroy endothelial cells which is associated with disseminated intravascular coagulation. This may contribute to the hemorrhagic manifestations of Ebola.” (Lee and Cook, 2013) The receptor of host cell on which the glycoprotein attaches to is still being researched. The virus enters the host cells through endocytosis where it replicates and synthesizes its proteins. It exits the cell with host cell membrane including its proteins enveloped around it. (Lee and Cook, 2013)
Ebola virus is classified as zoonotic as transmission of it can be from animals to humans. It can also be passed from human to human and is contracted through direct contact with bodily fluids of infected person. Endemic level of infection in mid to late 70s was seen both in Sudan and Zaire due to lack of sanitation of reusable needles and improper barrier techniques. Still today, in poor African countries where clinical sites are unsanitary or where sanitary hospital practices are not used, Ebola is often transmitted from patients to their caregivers. Many cultures have
burial rituals which include cleansing of the dead body prior to burial. The bodies of people who have died of Ebola are still contagious and many family members unknowingly acquire the virus through this process. (Sarwar, 2011) Many of the large Ebola endemics were contained only after implementing strict quarantine and preventing family members from performing these rituals thus limiting their exposure to the virus. In some African countries, “bush meat” is considered a delicacy. Eating or butchering infected animals can spread the virus. (WHO.int)
Clinical Manifestations
The incubation period for Ebola virus is 2 to 21 days. The infected person is not considered contagious during the early stages of incubation period but as the illness progresses, bodily fluids are considered extremely bio-hazardous. Virus isolation and antigen-capture enzyme-linked immunosorbent assay testing can be used to diagnose Ebola. (CDC.gov)
The onset of symptoms is sudden and usually confused with other common viral infections such as flu. They include fever with or without chills, soar throat, severe headaches, chills and joint and muscle aches. (CDC.gov) Over time, symptoms become severe and include red eyes, nausea and vomiting, raised rash and bleeding from mucous membranes. Blood fills the intestines, bladder, spilling out from nose, eyes and mouth. The terminally ill may manifest rapid breathing, hypotension and coma. (mayoclinic.com) Medical Management
There is currently no antiviral drugs proven effective for treatment of Ebola. Supportive care is usually given to infected people in hospital settings. This includes maintaining adequate blood pressure, replacing blood loss, providing fluids and treating any other infections that may develop. Heparin injections are also part of treatment plan in attempt to restore the anticoagulation factor in blood. Care must be provided with strict isolation barriers to prevent spread of virus. Death comes soon after infection, typically within 7-10 days, due to multiple organ failure and virus induced septic shock. (mayoclinic.com)
There have been total 1800 reported infections of Ebola, 1300 of which resulted in death. For those who survive this disease, recovery can be slow taking months to regain strength. People may experience hair loss, headaches, fatigue, liver inflammation and sensory changes. (WHO.int) The virus remains in the body weeks after clinical symptoms may subside. Sexual transmission can occur as the virus has been detected in semen 7 weeks into recovery from Ebola. (Sarwar, 2011)
There is much research going into developing a vaccine for Ebola. Some clinical studies have shown vaccines to be effective for rats and macaques. This point to subjects being vaccinated against virus and developing both a cell-mediated response and a humoral antibody response. (Emedicine) “Antibodies that are in survivor sera appear to preferentially recognize sGP over GP . Hence, sGP could play a role in the evasion of humoral immune response by absorbing elicited antibodies.” (Lee and Saphire, 2009)
Conclusion
Bibliography
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