PARIS- A new strain of the Ebola virus has been isolated
from the blood of a Swiss zoologist who had performed an autopsy on a chimpanzee
which had been infected by the same virus in the wild, according to a team
of researchers from The Pasteur Institute here. The strain has been dubbed
'Ebola Tai' after the forest in which the chimpanzees were found..
The discovery means that five different strains of the Ebola family of
viruses have now been identified (Ebola Zaire, Sudan, Reston, Marburg and
Tai), but this is the first time that infection of a human has been linked
to naturally infected monkeys anywhere on the African continent. At the
same time, it is still not clear how the chimpanzee may have contacted the
new Ebola virus strain in the first place, notes Bernard Le Guenno, MD,
of the Pasteur Institute.
The troop of wild chimpanzees to which the infected animal belonged had
been severely decimated over the past few years following episodes of severe
hemorrhaging similar to what has been observed recently in patients in Zaire
who were infected by another strain of the Ebola virus.
The female zoologist who performed the autopsy on 24 November in Cote
d'Ivoire, West Africa in November of last year developed typical symptoms
of Dengue syndrome, including high fever, headache, etc. and was hospitalized
two days later. Her fever failed to respond to standard anti-malarial drugs
and she went on to develop diarrhea and a pruritic rash over the next few
days. She was then evacuated to a hospital in Switzerland where she recovered
without sequelae. The dedicated researcher has now returned to Ivory Coast
to continue her work.
Examination of blood samples taken from the affected zoologist showed
that antibodies to other viruses known to cause hemorrhagic fever, such
as Dengue, yellow fever, as well as for the three other Ebola virus strains
were absent.
However, immunofluorescence assays showed that samples of the patient's
serum contained large cytoplasmic inclusions which appeared to be viral
antigens recognized by the woman's antibodies. Under the electron microscope,
the viral particles seemed to be from the same family of "filoviruses"
to which the other three strains of the Ebola virus belong. A battery of
immunological tests confirmed that the French team had indeed discovered
a new strain of the Ebola virus, Dr. Le Guenno pointed out.
When the Pasteur investigators examined tissue taken from the dead chimpanzee
they found that the animal's spleen and the liver showed large areas of
necrotic tissue resembling what had previously been found in autopsies of
patients who had succumbed to other Ebola virus outbreaks in Sudan and Zaire.
Finally, immunohistochemical staining of the affected animal tissue showed
that it contained the new strain of the virus , he noted.
The discovery of the new Ebola virus raises new questions as to where
it and other strains of the virus originated and to what extent and under
what conditions it can be transmitted to human beings, said Dr. David Simpson,
Queen's University, Belfast in an editorial Dr. Guenno's article in the
Lancet medical journal.
The fact that it is lethal for chimpanzees suggests that they are not
the originating source and may have picked up the infection from other sources,
such as other monkeys or rodents that they sometimes feed on, he suggested.
In addition, Dr. Le Guenno noted that none of the close coworkers of
the infected zoologist were affected by the virus, indicating that the improved
nursing practices successfully developed to prevent infection of hospital
staff by AIDS patients in Ivory Coast, may also have reduced their risk
of infection by the Ebola virus. No one has died of Ebola virus infection
in Ivory Coast.
" Our study also indicates that although the risk of infection after
exposure to infected tissue may be high, the transmissibility from human
patients seems to be low, outside hemorrhagic episodes," Dr. Le Guenno
concluded.
The discovery of the new strain of virus may help solve one of the persistent
mysteries surrounding Ebola, that of its original ecologic niche. Virus
hunters from the World Health Organization are currently searching the Tai
forest area for the source of this virus.
For more information, see The Lancet, Vol. 345, May 20, Le Guenno et
al., pp. 1271-124.
