Recovery of Ebola virus from non-fatal human case in cote d'lovoir and the outbreak of Ebolo haemorrhagic fever in and around the aly kikwit (Zaire) have raised eye brows of all concerned about health threat to humans because of this virus. Ebolo virus infection was first recognised in 1976 when two outbreaks occured first in sudan in july and second in Zaire in the month of september claiming hundreds of deaths. Another outbreak occured in 1979 in Africa when sudan subtype had infected 34 persons.
In 1996, people Mayibout (Gabon) village found dead chimpanzee lying in the undergrowth near their home. They skinned, cooked and ate it. All these persons had fallen ill within a week of this incident and by the end of week, about 13 were dead. Thus deadliest disease of recent times had emerged from the forest of Africa. In the fast moving world there is potential for the spread of this disease to every hook and corner of the world.
Viral Characters
Ebolo virus belong to family filoviridae, genus Filovirus having two sutypes sudan and Zaire. As it is kept in WHO risk group" 4" of pathogens so it requires maximum containment facilities for laboratort work. Being pleomorphic it may be long filamentous or branched forms, "U" or "6" shaped. It may have circular forms. It is 900nm to 14000nm long. During infectivity it is 970nm long and 80nm in diameter. It is ss Rna with helical nucleocapsid. It has lipid envelope derived from plasma membrane of host cell. There are peplomers (10nm) projecting from the surface of envelope. Virus can be killed by ultra violet rays, gamma irradiation, beta propiolactone, hypochlorite and phenolic disinfectants.
Pathogenesis
It is presumed that Ebola virus enters the host through broken skin and mucous membrane to initiate the infection. Incubation period is 4 to 10 days. How does it cause haemorrhagic shock, is not clear. However, increased vascular endothelial permeability related to decreased capacity of endothelial cells to secrete prostacyclin (PGI2)is probably the reason for haemorrhage.
It occurs abruptly with non specific symptoms like fever increased frontal headache, malaise, myalgia, bradycardia , conjunctivitis , maculopapular rash with desquamation in those who survive. After two to three days there can be pharyngitis , severe nausea, vomiting , breathlessness and malena even. Manifestation of bleeding may be as petechiae , ecchymoses , uncontrolled bleeding especially from venepuncture sites. There may be abortion in pregnant ladies, increased post-partum haemorrhage, Visceral haemorrhage effusion and death occurs six to nine days after the onset of clinical disease . Convalescence is quiet slow and takes usually up to five weaks
Laboratory Diagnosis
Direct
viral antigen can be demonstrated by immunofluorescence technique (IF). This is done by preparing thick impression smears from frozen liver specimen fixed in acetone and then stain them by either direct or indirect methods. Virus sub-types and strain specific monoclonal antibodies can be used for IF. The virus can be demonstrated by electron microscopy from body fluid tissue or cell culture supernatant fluid.
Culture of vero clone E6 is most sensitive and useful for the propagation of the virus. The cytopathogenesis effect can be studied using vero cells and BGM cell line. About 80 to 90% cell monolayer destruction occurs by 7 to 8 days after virus inoculation. Solid phase indirect enzyme immunoassay is also useful in the detection of Ebola virus antigen.
Another useful method for detection of Ebola antigen is post-embedment immunoelectron microscopic examination of MA-104 infected cells. This method along with standard transmission electron microscopy (TEM) may provide reasonably good results especially in acute Ebola infection.
Animal Inoculation
Guinea pig is the ideal animal used for isolation of virus especially if the sample is contaminated with bacteria.
Serology
Useful serological tests include indirect immunoflurescence assay (titre 1:256 and above is taken as positive), radio-immunoassay (titre 1:20 and more is positive), ELISA etc. To confirm the serological specificity Western Blot can be used.
Latest techniques
Diagnostic probes like cDNA or RNA is the addition to the diagnostic tests. Also inclusion is the polymerase chain reaction in this category
Treatment
No antiviral treatment is available till date. Many antiviral tried so far (ribavirus, plasma obtained from Ebola patients) are not proved useful. Human interferon may be of some use in treating Ebola patients. What seems to be important is prevention of shock, cerebral edema, renal failure, bacterial super infection, hypoxia and hypertension.
Control
1. It requires evaluation and treatment of infection immediately.
2. Patient should be placed in an isolation facility ideally under negative pressure.
3. Personal protective equipment, i.e. face shield, surgical mask glassed with side shields, leg and shoe covering should be worn by care giver to prevent droplet contact.
4. Caretakers should also use barrier precautions to prevent skin or mucous membrane exposure to blood, other body fluids, secretions and excretions.
5. Laboratory testing should be kept to minimum. Clinical specimens should be obtained using strict precaution, placed in a plastic bag, then transported in clearly labelled durable leak proof container directly to the specimen handling area of the laboratory.
6. If patient dies, handling of body should be as minimum as possible. The dead body should be wrapped in sealed, leak proof material (not embalmed) and buried or cremated in a sealed casket.
7. Person with percutaneous or mucocutaneous exposure to blood or body fluids, secretions or excretions from a patient should immediately wash the affected skin surface with soap and water. Mucous membrane must be irrigated with adequate amount of water or eye wash solution.