> To: virology at net.bio.net> From: fmzerbini at UCDAVIS.EDU (Francisco Muril Zerbini)
> Subject: Re: ebola info
> On 28 Feb 1995, Mathew Roberts wrote:
>> > I'm a senior Microbiology student at Colo. State Univ. I've
read "The > > Hot Zone," and was wondering how much is known about
Ebola, and if there
> I have a suggestion to make. There have been so many messages on
Ebola > lately, could someone with more knowledge on this subject
(and time to > spare) make a mini-FAQ on Ebola and related viruses ?
Herewith a contribution. Excerpted from ebola.html at
http://www.bocklabs.wisc.edu/ed/, and
http://www.uct.ac.za/microbiology/ebola.html
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.
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. 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 humandisease and primate
infection suggests that a vaccine inducing a strong cell- mediated
response will be necessary for virus clearance and adequate
protection. Neutralizing antibodies are not observed in convalescent
patients nor do they occur in primates inoculated with killed
vaccine. A vaccine expressing the glycoprotein in vaccinia is being
prepared for laboratory evaluation.
Alison Jacobson, 1994
_____________________________________________________
| Ed Rybicki, PhD | (ed at molbiol.uct.ac.za) |
| Dept Microbiology | University of Cape Town |
| Private Bag, Rondebosch | 7700, South Africa |
| fax: xx27-21-650 4023 | tel: xx27-21-650 3265 |
| URL: http://www.uct.ac.za/microbiology |
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