ebola info

RYBICKI, ED ED at molbiol.uct.ac.za
Wed Mar 1 03:22:39 EST 1995


> 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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