7. Transmission and transmission dynamics

iii. Reston Ebola virus (RESTV): It was discovered in 1989 during an outbreak of simian haemorrhagic fever virus (SHFV) in Reston USA which infected non-human primates. It

iv. Côte d'Ivoire Ebola virus: Also referred to as Taï Forest Ebola virus (TAFV), it was first

v. Bundibugyo Ebola virus (BDBV): This virus species was discovered in 2007 in Uganda following the outbreak in Bundibugyo District which recorded 39 deaths with a mortality

The genus Ebola are negative-sense, single stranded RNA viruses which are non-segmented belonging to the Filoviridae family. The negative-sense RNA genome is approximately 19 kb in size but varies among the various Ebola species and it is encapsulated in a lipid membrane used for the formation of new particles on the surfaces of their host cells [24, 25]. The core of the virus constitutes the genomic RNA surrounded by nucleoproteins (NP). The Ebola genome consists of seven genes that codes viral proteins (VPs) each of which differs in function [26]. Among these proteins, VP24 which constitutes the main matrix protein is the most abundant virion protein. VP30 is involved in the activation of RNA transcription while VP35 is involved in viral RNA synthesis. VP35 is also attributed to be responsible for varying degrees of virulence among different strains of Ebola virus. VP40 is also a matrix protein of the negative stranded RNA and its roles is to assemble the lipid envelop of the virus by linking the nucleocapsid to the surrounding membrane. The virus also contains a transmembrane glycoprotein (GP) which is responsible for the formation of virion spikes which facilitates viral entry into cells. A section of this glycoprotein (GP1 and GP2) are responsible for immunosuppression

Figure 1. Morphological representation of the Ebola virus showing the various proteins: VP, virion protein; and GP,

has also been identified in Pennsylvania, Texas and Siena, Italy.

rate of 34%.

glycoprotein [28].

6. Ebola virus morphology

132 Current Topics in Tropical Emerging Diseases and Travel Medicine

discovered in chimpanzees from the Taï Forest in Ivory Coast in 1994

Ebola haemorrhagic fever is a zoonotic borne disease believed to be transmitted from rodents and bats as primary reservoirs. It has been noticed that bats are usually present at the sites of several outbreaks in large numbers and Ebola virus antibodies have been found in fruit bats [29] though the virus has not been isolated from these animals. It is believed that this infection is asymptomatic in bats and can be transmitted to chimpanzees, gorillas, monkeys, other mammals and humans. These transmissions may be due to direct contact with the reservoir species (Figure 2). In humans, transmission from infected persons to health humans is through direct contact with body fluids or secretions such as saliva, stool, urine, semen, and blood [30]. The virus has been shown to persist for up to 7 weeks in semen after recovery of infected individuals from the illness suggesting sexual intercourse as probable means of transmission. Also, contact of broken skin or mucous membranes with items such as clothing, bed linen, or used needles are possible means of transmission [30].

Health workers are another category of persons exposed to the infection following their care for Ebola infected patients as contact with used equipment, gloves and other clinical materials can promote transmission. Health workers or other individuals can become infected if they get in contact with dead bodies of infected subjects. In all, it has been concluded that Ebola transmission is only by means of contact as there has been no evidence of transmission from

Figure 2. Transmission of Ebola virus. Source: http://www.cdc.gov/vhf/ebolaresources/virus-ecology/.html.


increase in nitric oxide production which leads to damage of the vascular system altering the blood pressure [39]. Also, these hypotensive shock may also result from platelet-derived agents such as thrombin following the damaged of endothelial cells. Theses clotting factors

Ebola Virus Disease: Progress So Far in the Management of the Disease

http://dx.doi.org/10.5772/intechopen.79053

135

One of the possible mechanisms the virus is able to persist in the body is through its ability to evade the immune system by destroying immune cells such as lymphocytes, natural killer

Once an individual gets infected with Ebola virus, it can persist in the body for a few days with no clinical manifestation. Thus, the incubation period ranges from 2 to 21 days with an average between 4 and 10 days. After this incubation period, an acute infection emerges which starts to portray clinical manifestations. The illness commences with symptoms of flu-like syndrome which includes a sudden onset of high fever, chills and myalgia. This early infection can affect the gastrointestinal system causing anorexia, vomiting, nausea, diarrhoea, abdominal pain, as well as the respiratory system causing cough, chest pain and dyspnea. Also, the vascular system can be affected leading to hypotension, oedema as well as neurologic system causing headache and coma [42, 43]. Though the periodical manifestation of Ebola virus varies among individuals, generally, these clinical features can be categorized into four phases as suggested

Phase 1 - Influenza-like syndrome: The onset of the infection commences with non-specific signs or symptoms such as high fever, nausea, headache, sore throat, arthralgia, and myalgia. Phase 2 - Acute phase: A persistent acute fever emerges along with headache and intense fatigue within 1–6 days which is not responsive to antibiotics or antimalarial drugs. This is usually followed by gastrointestinal obstructions such as abdominal pain, diarrhoea, vomiting, etc.

Phase 3 - Pseudo-remission: After the acute phase, a false recovery phase emerges by days 7–8 where the patient feels better showing some signs of recovery such as gain of appetite. In some

Phase 4 - Aggravation phase: By day 9, the health status gets worsen in most individuals presenting respiratory disorders such as cough, dyspnea, hiccups, throat and chest pain as well as cardiovascular distress and hypovolemic shock. Also, rask may develop on the skin as

During the infection, laboratory investigations show high levels of aminotransferase, and marked lymphocytopenia, and thrombocytopenia in patients' blood [45]. More so, bleeding usually occurs in the gastrointestinal tract and may be expressed as petechiae, melena, conjunctival haemorrhage, easy bruising, haematuria, or intraperitoneal bleeding. Also, mucous membrane bleeding as well as excessive clot formation and failure of venipuncture sites are evident during infection. Progression of these symptoms over a period of time may lead to dehydration, confusion, stupor, hypotension and failure of multiple organs culminating to

patients, this phase may eventually lead to total recovery and survival of the disease.

can disseminate into various organs causing intravascular coagulation [40].

cells, phagocytes as well as impairment of the action of dendritic cells [41].

9. Clinical manifestation

by Suresh and Dashrath [44].

well as petechiae.

Table 1. Risk of Ebola virus transmission and its association with the level of contact.

human to human via the respiratory route [31]. The type of contact among individuals can influence the risk of transmission of Ebola virus disease as shown in Table 1 [32].
