EPIDEMOLOGY OF EBOLA VIRUS.CAUSE, TRANSMISION, PREVENTION.
The epidemiological investigations attempted to describe the outbreak of Ebola haemorrhagic fever (EbHF) by its distribution in time, in geography and amongst persons. Factors related to spread were also studied. These included possible modes of transmission, the incubation period, secondary attack rates and related risk factors. Serological surveys were undertaken to find evidence of prior Ebola virus disease in the area and asymptomatic infections occurring during the epidemic The cause of the epidemic (1) was searched for by attempts to find the index case and evidence of Ebola virus in some animal and insects
EVD is caused by four of five viruses classified in the genus Ebolavirus, family Filoviridae, order Mononegavirales. The four disease-causing viruses are Bundibugyo virus (BDBV), Sudan virus (SUDV), Taï Forest virus (TAFV), and one called simply, Ebola virus (EBOV, formerly Zaire Ebola virus)). Ebola virus is the sole member of the Zaire ebolavirus species, and the most dangerous of the known Ebola disease causing viruses, as well as being responsible for the largest number of outbreaks.
The virus may be acquired upon contact with blood or bodily fluids of an infected animal (commonly monkeys or fruit bats). Spread through the air has not been documented in the natural environment. Fruit bats are believed to carry and spread the virus without being affected. Once human infection occurs, the disease may spread between people as well.
Since no none cure of the diseases have been found a number of preventive measures as outline below can be followed.
Ebola viruses are contagious, with prevention predominantly involving behavior changes, proper full-body personal protective equipment, and disinfection. Techniques to avoid infection involve not contacting infected blood or secretions, including from those who are dead. This involves suspecting and diagnosing the disease early and using standard precautions for all patients in the healthcare setting. Recommended measures when caring for those who are infected include isolating them, sterilizing equipment, and wearing protective clothing including masks, gloves, gowns, and goggles. Hand washing is important but can be difficult in areas where there is not even enough water for drinking.
Due to lack of proper equipment and hygienic practices, large-scale epidemics have occurred mostly in poor, isolated areas without modern hospitals or well-educated medical staff. Traditional burial rituals, especially those requiring embalming of bodies, should be discouraged or modified. Airline crews, who fly to these areas of the world, are taught to identify Ebola and isolate anyone who has symptoms.
Quarantine, also known as enforced isolation, is usually effective in decreasing spread. Governments often quarantine areas where the disease is occurring or individuals who may be infected. In the United States, the law allows quarantine of those infected with Ebola. The lack of roads and transportation may help slow the disease in Africa. During the 2014 outbreak, Liberia closed schools.
No vaccine is currently available for humans. The most promising candidates are DNA vaccines or vaccines derived from adenoviruses, vesicular stomatitis Indiana virus (VSIV) or filovirus-like particles (VLPs) because these candidates could protect nonhuman primates from ebolavirus-induced disease. DNA vaccines, adenovirus-based vaccines, and VSIV-based vaccines have entered clinical trials.
Vaccines have protected nonhuman primates. Immunization takes six months, which impedes the counter-epidemic use of the vaccines. Searching for a quicker onset of effectiveness, in 2003, a vaccine using an adenoviral (ADV) vector carrying the Ebola spike protein was tested on crab-eating macaques. Twenty-eight days later, they were challenged with the virus and remained resistant. A vaccine based on attenuated recombinant vesicular stomatitis virus (VSV) vector carrying either the Ebola glycoprotein or the Marburg glycoprotein in 2005 protected nonhuman primates, opening clinical trials in humans. The study by October completed the first human trial, over three months giving three vaccinations safely inducing an immune response. Individuals for a year were followed, and, in 2006, a study testing a faster-acting, single-shot vaccine began; this new study was completed in 2008. Trying the vaccine on a strain of Ebola that more resembles one that infects humans is the next step.
THE IMPORTANCE OF EPIDEMOLOGY IN THE CONTROL OF EBOLA VIRUS
The importance of epidemology in the control of ebola virus cannot be over emphaised as Ebola virus is one of at least 30 known viruses capable of causing viral hemorrhagic fever syndrome. The genus Ebolavirus is currently classified into 5 separate species: Sudan ebolavirus, Zaire ebolavirus, Tai Forest (Ivory Coast) ebolavirus, Reston ebolavirus, and Bundibugyo ebolavirus.
At present, no specific anti-Ebolavirus agents are available but due to the epidemiology carried out on the virus agents that have been studied for the treatment or prevention of Ebola virus disease include the following:
• Ribavirin (possesses no demonstrable anti-Ebolavirus activity in vitro and has failed to protect Ebolavirus -infected primates)
• Nucleoside analogue inhibitors of S-adenosylhomocysteine hydrolase (SAH)
• Interferon beta
• Horse- or goat-derived immune globulins
• Human-derived convalescent immune globulin preparations
• Recombinant human interferon alfa-2
• Recombinant human monoclonal antibody against the envelope glycoprotein (GP) of Ebola virus
• DNA vaccines expressing either envelope GP or nucleocapsid protein (NP) genes of Ebola virus
• Activated protein C
• Recombinant inhibitor of factor VIIa/tissue factor
In those patients who do recover, recovery often requires months, and delays may be expected before full resumption of normal activities. Weight gain and return of strength are slow. Ebola virus continues to be present for many weeks after resolution of the clinical illness.
1. Van der Groen, G. et al. (1978) Results of Ebola antibody surveys in various population groups, (cite symposium publication).
2. Germain, M. (1978) Collection of Mammals and Arthropods (Zaire), (cite symposium publication).
3. Piot, P. et al. (1978) Clinical aspects of Ebola virus infection in Yambuku area, Zaire, 1976, (cite symposium publication).
4. Wulff, H., Lange, J.V. (1975) Indirect immunofluorescence for diagnosis of Lassa Fever, Bull. WHO, 523 429-436.
5. Lebrun, A.J. (1963) Jungle yellow fever and its control in Gemena, Belgian Congo, Am. J. Trop. Med. Hyg., 12, 398-407.
6. Monath, T.P., Cassals, J. (1975) Diagnosis of Lassa fever and the isolation and management of patients, Bull. WHO, 52, 707-715.
7. Hornick, R.B., Woodward, T.E. (1971) Typhoid fever, in Harrison’s Principles and Practice of Medicine, edited by M.W. Wintrobe, G.W. Thorn, R.D. Adams, I.L. Bennett, K.J. Isselbacher, R.G. Petersdorf, McGraw Hill Book Company, New York, Sixth edition, 810-815.
8. Report of an International Commission (1978) Ebola Haemorrhagic fever in Zaire, 1976, Bull. WHO, 56, (in press).
9. Martini, G.A. (1971) Marburg Virus Disease, Clinical Syndrome, in Marburg Virus Disease, edited by G.A. Martini and R. Siegert, Springer-Verlag, Heidelberg- New York, 1-9.
10. Stojkovic, L.J. et al. (1971) Two cases of Corcopithecus Monkeys associated haemorrhagic fever, in Marburg Virus Disease, edited by G.A. Martini and R. Siegert, Springer-Verlag, Heidelberg – New York, 24-33.
11. Hennessen, W. &1971) Epidemiology of “Marburg Virus” disease, in Marburg Virus Disease, edited by G.A. Martini and R. Siegert, Springer-Verlag, Heidelberg – New York, 161-165.
12. Henderson, B.E. et al. (1971) Epidemiological studies in Uganda relating to the Marburg Agent, in Marburg Virus Disease, edited by G.A. Martini and R. Siegert, Springer-Verlag, Heidelberg – Yea York, 166-176.
13. Gear, J.S.S. et al. (1975) Outbreak of Marburg Virus disease in Johannesburg, Brit. Med. Journ., 4, 489-493.
14. Francis, D.P. et al. (1978) The Epidemiology of Ebola virus infection in the Sudan, (cite symposium publication).