5. Ebola virus species

Ebola haemorrhagic disease is caused by Ebola virus which is an RNA virus in nature. It is a virus that belongs to mononegavirales order, Filoviridae and the genus Ebola. There exist five species of this virus which include the following [22, 23].


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

permitting the virus to evade the immune system as they show very high homology with immunosuppressive protein found in oncogenic retroviruses [27]. There is also an RNAdependent RNA polymerase known as the L protein which catalyzes transcription. The mor-

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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

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.

phology of Ebola virus is shown in Figure 1.

7. Transmission and transmission dynamics

needles are possible means of transmission [30].


## 6. Ebola virus morphology

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, glycoprotein [28].

permitting the virus to evade the immune system as they show very high homology with immunosuppressive protein found in oncogenic retroviruses [27]. There is also an RNAdependent RNA polymerase known as the L protein which catalyzes transcription. The morphology of Ebola virus is shown in Figure 1.
