Ebola Virus

Ebola Virus:

Introduction:

Ebola is a virus of the family Filoviridae that is responsible for a severe and often fatal viral hemorrhagic fever; outbreaks in primates such as gorillas and chimpanzees as well as humans have been recorded. The disease is characterized by extreme fever, rash, and profuse hemorrhaging. In humans, fatality rates range from 50 to 90 percent.

History:

The virus takes its name from the Ebola River in the northern Congo basin of central Africa, where it first emerged in 1976. Outbreaks that year in Zaire (now Congo [Kinshasa]) and The Sudan resulted in hundreds of deaths, as did another outbreak in Zaire in 1995. Ebola is closely related to the Marburg virus, which was discovered in 1967, and the two are the only members of the Filoviridae that cause epidemic human disease. A third related agent, called Ebola Reston, caused an epidemic in laboratory monkeys in Reston, Virginia, but apparently is not fatal to humans.

Signs and symptoms:

EVD/EHF is clinically indistinguishable from Marburg virus disease (MVD), and it can also easily be confused with many other diseases prevalent in Equatorial Africa, such as other viral hemorrhagic fevers, falciparum malaria, typhoid fever, shigellosis, rickettsial diseases, cholera, gram-negative septicemia or EHEC enteritis. The most detailed studies on the frequency, onset, and duration of EVD clinical signs and symptoms were performed during the 1995 outbreak in Kikwit, Zaire (EBOV) and the 2007-2008 outbreak in Bundibugyo, Uganda (BDBV). The mean incubation period, best calculated currently for EVD outbreaks due to EBOV infection, is 12.7 days (standard deviation = 4.3 days), but can be as long as 25 days. EVD begins with a sudden onset of an influenza-like stage characterized by general malaise, fever with chills, arthralgia and myalgia, and chest pain. Nausea is accompanied by abdominal pain, anorexia, diarrhea, and vomiting. Respiratory tract involvement is characterized by pharyngitis with sore throat, cough, dyspnea, and hiccups.

The central nervous system is affected as judged by the development of severe headaches, agitation, confusion, fatigue, depression, seizures, and sometimes coma. The circulatory system is also frequently involved, with the most prominent signs being edema and conjunctivitis. Hemorrhagic symptoms are infrequent (fewer than 10% of cases for most serotypes), (the reason why Ebola hemorrhagic fever (EHF) is a misnomer) and include hematemesis, hemoptysis, melena, and bleeding from mucous membranes (gastroinestinal tract, nose, vagina and gingiva).

Cutaneous presentation may include: maculopapular rash, petechiae, purpura, ecchymoses, and hematomas (especially around needle injection sites). Development of hemorrhagic symptoms is generally indicative of a negative prognosis. However, contrary to popular belief, hemorrhage does not lead to hypovolemia and is not the cause of death (total blood loss is low except during labor). Instead, death occurs due to multiple organ dysfunction syndrome (MODS) due to fluid redistribution, hypotension, disseminated intravascular coagulation, and focal tissue necroses


Causes:

EVD is caused by four of five viruses classified in the genus Ebolavirus, family Filoviridae, order Mononegavirales: Bundibugyo virus (BDBV), Ebola virus (EBOV), Sudan virus (SUDV), and Taï Forest virus (TAFV). The fifth virus, Reston virus (RESTV), is thought to be apathogenic for humans and therefore not discussed here.

Prevention:

Ebola viruses are highly infectious as well as contagious.
As an outbreak of ebola progresses, bodily fluids from diarrhea, vomiting, and bleeding represent a hazard. Due to lack of proper equipment and hygienic practices, large-scale epidemics occur mostly in poor, isolated areas without modern hospitals or well-educated medical staff. Many areas where the infectious reservoir exists have just these characteristics. In such environments, all that can be done is to immediately cease all needle-sharing or use without adequate sterilization procedures, isolate patients, and observe strict barrier nursing procedures with the use of a medical-rated disposable face mask, gloves, goggles, and a gown at all times, strictly enforced for all medical personnel and visitors.The aim of all of these techniques is to avoid any person’s contact with the blood or secretions of any patient, including those who are deceased.

Vaccines have successfully protected nonhuman primates; however, the six months needed to complete immunization made it impractical in an epidemic. To resolve this, in 2003, a vaccine using an adenoviral (ADV) vector carrying the Ebola spike protein was tested on crab-eating macaques. The monkeys were challenged with the virus 28 days later, and remained resistant. In 2005, a vaccine based on attenuated recombinant vesicular stomatitis virus (VSV) vector carrying either the Ebola glycoprotein or Marburg glycoprotein successfully protected nonhuman primates, opening clinical trials in humans. By October, the study completed the first human trial; giving three vaccinations over three months showing capability of safely inducing an immune response. Individuals were followed for a year, and in 2006, a study testing a faster-acting, single-shot vaccine began. This study was completed in 2008.

There are currently no Food and Drug Administration-approved vaccines for the prevention of EVD. Many candidate vaccines have been developed and tested in various animal models. Of those, the most promising ones are DNA vaccinesor are based on adenoviruses, vesicular stomatitis Indiana virus (VSIV) or filovirus-like particles (VLPs) as all of these candidates could protect nonhuman primates from ebolavirus-induced disease. DNA vaccines, adenovirus-based vaccines, and VSIV-based vaccines have entered clinical trials.

Contrary to popular belief, ebolaviruses are not transmitted by aerosol during natural EVD outbreaks. Due to the absence of an approved vaccine, prevention of EVD therefore relies predominantly on behavior modification, proper personal protective equipment, and sterilization/disinfection.
In 6 December 2011 the development of a successful vaccine against Ebola for mice were reported. Unlike the predecessors it can be freeze-dried and thus stored for long periods in wait for an outbreak. The research will be presented in Proceedings of National Academy of Sciences.