Ebola Virus

Ebola virus, a member of the Filoviridae, burst from obscurity with spectacular
outbreaks of severe, haemorrhagic fever. It was first associated with an
outbreak of 318 cases and a case-fatality rate of 90% in Zaire and caused 150
deaths among 250 cases in Sudan. Smaller outbreaks continue to appear
periodically, particularly in East, Central and southern Africa. In 1989, a
haemorrhagic disease was recognized among cynomolgus macaques imported into the

United States from the Philippines. Strains of Ebola virus were isolated from
these monkeys. Serologic studies in the Philippines and elsewhere in Southeast

Asia indicated that Ebola virus is a prevalent cause of infection among macaques
(Manson 1989). These threadlike polymorphic viruses are highly variable in
length apparently owing to concatemerization. However, the average length of an
infectious virion appears to be 920 nm. The virions are 80 nm in diameter with a
helical nucleocapsid, a membrane made of 10 nm projections, and host cell
membrane. They contain a unique single-stranded molecule of noninfectious
(negative sense ) RNA. The virus is composed of 7 polypeptides, a nucleoprotein,
a glycoprotein, a polymerase and 4 other undesignated proteins. Proteins are
produced from polyadenylated monocistronic mRNA species transcribed from virus

RNA. The replication in and destruction of the host cell is rapid and produces a
large number of viruses budding from the cell membrane. Epidemics have resulted
from person to person transmission, nosocomial spread or laboratory infections.

The mode of primary infection and the natural ecology of these viruses are
unknown. Association with bats has been implicated directly in at least 2
episodes when individuals entered the same bat-filled cave in Eastern Kenya.

Ebola infections in Sudan in 1976 and 1979 occurred in workers of a cotton
factory containing thousands of bats in the roof. However, in all instances,
study of antibody in bats failed to detect evidence of infection, and no virus
was isolated form bat tissue. The index case in 1976 was never identified, but
this large outbreak resulted in 280 deaths of 318 infections. The outbreak was
primarily the result of person to person spread and transmission by contaminated
needles in outpatient and inpatient departments of a hospital and subsequent
person to person spread in surrounding villages. In serosurveys in Zaire,
antibody prevalence to Ebola virus has been 3 to 7%. The incubation period for
needle- transmitted Ebola virus is 5 to 7 days and that for person to person
transmitted disease is 6 to 12 days. The virus spreads through the blood and is
replicated in many organs. The histopathologic change is focal necrosis in these
organs, including the liver, lymphatic organs, kidneys, ovaries and testes. The
central lesions appear to be those affecting the vascular endothelium and the
platelets. The resulting manifestations are bleeding, especially in the mucosa,
abdomen, pericardium and vagina. Capillary leakage appears to lead to loss of
intravascular volume, bleeding, shock and the acute respiratory disorder seen in
fatal cases. Patients die of intractable shock. Those with severe illness often
have sustained high fevers and are delirious, combative and difficult to
control. EBOLA SEROLOGY The serologic method used in the discovery of Ebola was
the direct immunofluorescent assay. The test is performed on a monolayer of
infected and uninfected cells fixed on a microscopic slide. IgG- or IgM-specific
immunoglobulin assays are performed. These tests may then be confirmed by using
western blot or radioimmunoprecipitation. Virus isolation is also a highly
useful diagnostic method, and is performed on suitably preserved serum, blood or
tissue specimens stored at -70oC or freshly collected. TREATMENT OF EBOLA No
specific antiviral therapy presently exists against Ebola virus, nor does
interferon have any effect. Past recommendations for isolation of the patient in
a plastic isolator have given way to the more moderate recommendation of strict
barrier isolation with body fluid precautions. This presents no excess risk to
the hospital personnel and allows substantially better patient care, as shown in

Table 2. The major factor in nosocomial transmission is the combination of the
unawareness of the possibility of the disease by a worker who is also
inattentive to the requirements of effective barrier nursing. after diagnosis,
the risk of nosocomial transmission is small. PREVENTION AND CONTROL OF EBOLA

The basic method of prevention and control is the interruption of person to
person spread of the virus. However, in rural areas, this may be difficult
because families are often reluctant to admit members to the hospital because of
limited resources and the culturally unacceptable separation of sick or dying
patients from the care of their family. Experience with human disease and
primate infection suggests that a vaccine inducing a strong cell- mediated
response will be necessary for virus clearance