EBOLA VIRAL DISEASE AND EBOLA VIRUS: A REVIEW

V. C. Sangar*, L. Samant and Dr. A. S. Chowdhary
Haffkine Institute for Training, Research and Testing, Mumbai, INDIA

ABSTRACT

Ebola virus disease (EVD) is a severe, often fatal illness with a death rate of up to 90%. EVD formerly known as “Ebola haemorrhagic fever (EHF)”. Till now due to 36 EVD outbreaks 4140 number of cases reported while 2,510 lost their lives during outbreaks. EVD is caused due to ebola virus which is linear, single-stranded, negative-sense RNA molecule and belongs to the family Filoviridae. Mode of transmission of Ebola into the human population is through close contact with the blood, secretions, organs or other bodily fluids of infected animals. The incubation period I defined as “the time interval from infection with the virus to onset of symptoms”.

The incubation period for ebola virus is 2-21 days. EV infection can be diagnosed by Enzyme-linked Immunosorbent Assay (ELISA), antigen detection tests, serum neutralization test, reverse-transcriptase polymerase chain reaction (RT-PCR) and virus isolation by using viro cell line. No effective antiviral drug and no specific licensed vaccines are available in international market for EV. EV outbreak was limited in African countries but globalization has made everyone vulnerable to this outbreak and therefore an urgent solution & investment in its cure is required.

To overcome this lack of awareness and knowledge part about ebola virus this review article in planned.

Keywords:
Ebola virus (EV), Ebola viral disease (EVD), Ebolavirus species, clinical features and treatments.

Ebola virus disease (EVD) is a severe, often fatal illness with a death rate of up to 90%. EVD formerly known as “Ebola haemorrhagic fever (EHF)”. In this article, the concise overview of the outbreaks of ebola viral disease (EVD) history, structure of ebola virus, mode of transmission, clinical features, diagnosis, treatments and preventive measures are given below-

OUTBREAK OF EBOLA VIRUS DISEASE (EVD)
Ebola virus disease (EVD) affects humans and nonhumans primates like chimpanzees, gorillas and monkeys. Till now 36, EVD outbreaks recorded. From 36 outbreaks, 4140 number of cases reported while 2,510 lost their lives during outbreaks. The first EVD outbreak was appeared in 1976 in Nzara, Sudan and in Yambuku, Democratic Republic of Congo. The latter was in a village situated near the Ebola River, from which the disease takes its name 1. Table 1 shows the chronology of previous ebola virus disease outbreaks from 1st September 1976 to 6th August 2014. The World Health Organization, in partnership with the Ministries of Health in Guinea, Sierra Leone, Liberia, and Nigeria announced a cumulative total of 1,779 suspect and confirmed cases of Ebola virus disease (EVD) and 961 deaths, as of August 6, 2014. Of the 1,779 clinical cases, 1,134 cases have been laboratory confirmed for Ebola virus infection 2. Table 2 shows number of incident and death cases reported during ebola virus disease outbreaks from 1st September 1976 to 6th August 2014.

TABLE. 1: SHOWS THE CHRONOLOGY OF PREVIOUS EBOLA VIRUS DISEASE OUTBREAKS FROM 1ST SEPTEMBER 1976 TO 6TH AUGUST 2014.

TABLE. 2: SHOWS NUMBER OF INCIDENT AND DEATH CASES REPORTED DURING EBOLA VIRUS DISEASE OUTBREAKS FROM 1ST SEPTEMBER 1976 TO 6TH AUGUST 2014.

EBOLA VIRUS (EV)
Ebola virus disease (EVD) is sever haemorrhagic fever caused due to EV. According to the International Committee on Taxonomy of Viruses, ebola virus belongs to the family Filoviridae. Filovirus particles are ~80 nm in diameter and found in the form of twisted filaments 3. This Ebola virus (EV) genome is 19kb long and 4.2×106 Da with seven open reading frames encoding structural proteins including the virion envelope glycoprotein (GP), nucleoprotein (NP), and matrix proteins VP24 and VP40; nonstructural proteins, including VP30 and VP35; and the viral polymerase 4. The GP open reading frame of Ebola virus gives rise to two gene products namely, a soluble 60-70 kDa protein (sGP) and a full-length 150-170 kDa protein (GP) that inserts into the viral membrane through transcriptional editing 5. It is linear, single-stranded, negative-sense RNA molecule. The EV virion is pleomorphic, producing ‘U’-shaped, ‘6’-shaped or circular forms but the predominant forms of the virion most frequently seen by electron microscope are long tubular structures 6.

Ebola virus comprises of 5 distinct species namely- 1) Bundibugyo ebolavirus (BDBV), 2) Zaire ebolavirus (EBOV), 3) Reston ebolavirus (RESTV), 4) Sudan ebolavirus (SUDV) and 5) Taï Forest ebolavirus (TAFV). Out of these 5 species, BDBV, EBOV, and SUDV are associated with large EVD outbreaks in Africa. The RESTV can infect humans but no illness or death in humans has been reported till date. This species predominantly found in Philippines and the People’s Republic of China 1. Table 3 shows death rates as per 5 ebola virus species from 1st September 1976 to 6th August 2014.

TABLE. 3: SHOWS DEATH RATES AS PER 5 EBOLA VIRUS SPECIES FROM 1ST SEPTEMBER 1976 TO 6TH AUGUST 2014.
MODE OF TRANSMISSION

Mode of transmission of Ebola into the human population is through close contact with the all bodily fluids of infected animals and persons 7. In Africa, infection has been documented through the handling of infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest 8,9. Ebola able to spreads in the community through human-to-human transmission, with infection resulting from direct contact like broken skin or mucous membranes with the blood, secretions, organs or other bodily fluids of infected people and indirect contact with environments contaminated with such fluids 6. Sexual contact is also major route of transmission for ebola virus. Men who have recovered from the EVD can transmit the virus through their semen for up to 7 weeks after recovery from illness. Ebola virus was isolated from semen 61 days after onset of illness in a man who was infected in a laboratory 1,10. Till date, it is hard to extrapolate the health effects of the virus to all population groups such as immunocompromised persons, persons with underlying medical conditions, pregnant women and children.

CLINICAL FEATURES
The incubation period I defined as “the time interval from infection with the virus to onset of symptoms”. The incubation period for ebola virus is 2-21 days 1. The clinical features can be divided into four main parts as follows- (1) In this phase, patients suffering from ebola virus display influenza–like syndrome symptoms like high fever, headache, arthralgia, myalgia, sore throat, and malaise with nausea; (2) In acute phase, patients do not respond to antibiotics and display headache, intense fatigue, diarrhoea, abdominal pain, anorexia and vomiting like symptoms; (3) In pseudo-remission phase, patients may recover during this phase and survive from the disease on day 7-8 and in (4) aggravation stage the health status gets worse and patient might lost his life due to clinical manifestations like – respiratory disorders (dyspnea, throat and chest pain, cough, hiccups); symptoms of haemorrhagic diathesis (bloody diarrhoea, haematemesis, conjunctival injection, gingival bleeding, nosebleeds and bleeding at the site of injection consistent with disseminated intravascular coagulation); skin manifestations (petaechiae, purpura; neuro-psychiatric manifestations (prostration, delirium, confusion, coma); cardio-vascular distress fluids 6.

DIAGNOSIS
Early laboratory confirmation of suspected clinical haemorrhagic fever cases is essential to implement appropriate control measures. Ebola virus infections can be diagnosed definitively in a laboratory through several types of tests like Enzyme-linked Immunosorbent Assay (ELISA), antigen detection tests, serum neutralization test, reverse-transcriptase polymerase chain reaction (RT-PCR) and virus isolation by using viro cell line 6. Other diseases that should be ruled out before a diagnosis of EVD can be made include: malaria, typhoid fever, shigellosis, cholera, leptospirosis, plague, rickettsiosis, relapsing fever, meningitis, hepatitis and other viral haemorrhagic fevers 1. In INDIA, to diagnose this ebola disease laboratory capacity strengthened at the National Institute of Virology, Pune and National Centre for Disease Control (CDC), Delhi 11.

TREATMENT
Till writing this article no effective antiviral drug and no specific licensed vaccines are available in international market. However, several clinical trials are going on to prevent or treat ebola virus infection 6. Severely ill patients require intensive supportive care in hospitals. During infection, they are frequently feel dehydrated as a result they need intravenous fluids or oral rehydration with solutions that contain electrolytes. However, in some cases of EVD they will recover after the appropriate medical care. To prevent further spread of the virus, suspected people with EVD or confirmed with EVD should be isolated from other patients and treated by health workers using strict infection control precautions 12.

PREVENTIVE MEASURES
There are few simple ways by which Ebola transmission can be controlled if outbreak takes place:-
• Routine cleaning of animal farms of pig or monkey with sodium hypochlorite as disinfectant or other detergents should be effective in inactivating the virus.
• After EV outbreak is suspected, the premises should be quarantined immediately. Any way of animal to human transmission should be avoided. Restricting or banning the movement of animals from infected farms to other areas can reduce the spread of the disease. Gloves and other appropriate protective clothing should be worn when handling sick animals or their tissues and when slaughtering animals.
• Reducing the risk of wildlife-to-human transmission from contact with infected fruit bats or monkeys / apes and the consumption of their raw meat. Animals should be handled with gloves and other appropriate protective clothing. Animal products such as meat should be thoroughly cooked before consumption or one can avoid eating meat for that particular time of disease progression in world 6.
• Reducing the risk of human-to-human transmission can be achieved by avoiding Close physical contact with Ebola patients. Gloves and appropriate personal protective equipment should be worn when taking care of ill patients at home. Regular hand washing is required after visiting patients in hospital, as well as after taking care of patients at home.
• Samples taken from suspected human and animal Ebola cases for diagnosis should be handled by well and properly trained staff and processed in suitably equipped laboratories and should be handled with utmost care 1.

CONCLUSION
Globalization has made everyone vulnerable to this outbreak and therefore an urgent solution & investment in its cure is required.

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