MARBURGVIRUS, EGYPTIAN FRUIT BAT - UGANDA
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A ProMED-mail post
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[1]
Date: Fri 31 Jul 2009
Source: Reuters News [edited]
<
http://www.reuters.com/article/latestCr ... SN31432759>
Marburg virus found in fruit bats in Uganda
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Thousands of bats in a cave in Uganda are
infected with a marburgvirus, a cousin of
ebolavirus [i.e., viruses classified in
the Ebolavirus and Marburgvirus genera of the
family _Filoviridae_], researchers said on Friday
[31 Jul 2009], strengthening the theory the
mammals are natural carriers of the deadly
viruses. A study by Pierre Rollin and colleagues
at the Special Pathogens Branch at the U.S.
Centers for Disease Control and Prevention (CDC)
[and at other laboratories in South Africa,
Switzerland and Uganda -- see part 2 below] found
live virus in 5 percent of the bats tested in the
cave, where miners were infected with a marburgvirus in 2007.
"Our finding of active virus infection in
approximately 5 percent of _R. aegyptiacus_ bats
and their population exceeding 100 000 in Kitaka
cave in Uganda suggests there are likely over
5000 marburgvirus-infected bats in this cave,
which is only one of many such cave populations
throughout Africa," they wrote in their report in
the Public Library of Science journal PLoS
Pathogens [see part 2 below]. "Clearly, these
bats could serve as a major source of virus with
potential to initiate human epidemics, and the
implications for public health are striking."
Researchers have long suspected bats were the
natural reservoirs of ebolaviruses and
marburgviruses -- both lethal viruses in the same
family [the family _Filoviridae_]. Ebolaviruses
can kill between 50 percent and 90 percent of
patients, while Marburg is a bit less deadly. A
natural reservoir is an animal that carries and
transmits an infection without becoming ill.
Rollin's team sampled the blood of bats in the
giant cave, where one miner died from Marburg in
2007. The virus samples from the sick miners and
from the bats were close genetic matches, they
reported. "These data indicate common Egyptian
fruit bats can represent a major natural
reservoir and source of marburgviruses with
potential for spillover into humans," they wrote.
[Byline: Paul Simao]
--
Communicated by:
Powell Gammill
<
pgammill@cox.net>
*******
[2]
Date: 31 Jul 2009
Source: PLoS Pathogens [edited]
<
http://www.plospathogens.org/article/in ... at.1000536>
[The publication referred to in the preceding Reuters report is the following:
Towner JS, Amman BR, Sealy TK, Carroll SAR, Comer
JA, et al. (2009) PLoS Pathog 5(7): e1000536.
doi:10.1371/journal.ppat.1000536. Full article available at the above URL]
Isolation of Genetically Diverse Marburg Viruses from Egyptian Fruit Bats
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ABSTRACT: In July and September 2007, miners
working in Kitaka Cave, Uganda, were diagnosed
with Marburg hemorrhagic fever. The likely source
of infection in the cave was Egyptian fruit bats
(_Rousettus aegyptiacus_) based on detection of
marburgvirus RNA in 31/611 (5.1 percent) bats,
virus-specific antibody in bat sera, and
isolation of genetically diverse virus from bat
tissues. The virus isolates were collected 9
months apart, demonstrating long-term virus
circulation. The bat colony was estimated to be
more than 100 000 animals using mark and
re-capture methods, predicting the presence of
more than 5000 virus-infected bats. The
genetically diverse virus genome sequences from
bats and miners closely matched. These data
indicate common Egyptian fruit bats can represent
a major natural reservoir and source of
marburgvirus with potential for spillover into humans.
AUTHORS SUMMARY: [Members of the genus
Marburgvirus] are similar to their close
relatives in the Ebolavirus genus, can cause
large outbreaks of hemorrhagic fever (HF) in
rural Africa with case fatalities approaching 90
percent. For decades, a long-standing enigma has
been the identity of the natural reservoir of
this deadly virus. In this report, we identify
the cave-dwelling Egyptian fruit bat (_Rousettus
aegyptiacus_) as a natural host of marburgviruses
based on multiple lines of evidence which
include, for the 1st time ever, the isolation of
virus directly from wild-caught and apparently
healthy bats. The species _R. aegyptiacus_ is
common throughout Africa with distribution into
the eastern Mediterranean and Middle East. Our
finding of active virus infection in
approximately 5 percent of _R. aegyptiacus_ bats
and their population exceeding 100 000 in Kitaka
cave in Uganda suggests there are likely more
than 5000 marburgvirusinfected bats in this
cave, which is only one of many such cave
populations throughout Africa. Clearly, these
bats could serve as a major source of virus with
potential to initiate human epidemics, and the
implications for public health are striking.
Additionally, we found highly divergent (21
percent) genome sequences among viruses
circulating in these bat populations, a level of
diversity that would result from a long-term
association with a suitable reservoir host of large population size.
[The authors contend that although the source of
filoviruses in nature has not been definitively
identified, the cumulative evidence suggests that
bats are involved. The infected monkeys consigned
from Uganda to Europe in 1967, which resulted in
the 1st recognized outbreaks of Marburg
hemorrhagic fever, were caught on the shores of
Lake Victoria and on islands where fruit bats are
prevalent. In 1996, it was shown that
experimentally infected fruit bats were capable
of supporting replication of ebolavirus without developing overt disease.
Significantly, diverse genetic lineages of
marburgvirus were detected in Egyptian fruit
bats, _Rousettus aegyptiacus_, and 2 species of
insectivorous bat in the mine, and the outbreak
ceased when the mine flooded, but no live virus
was isolated from bats. In 2002, ebolavirus RNA
was detected in forest-dwelling species of fruit
bat in Gabon during an investigation which
followed outbreaks of EHF and in 2005 nucleic
acid of Marburg virus was detected in _R.
aegyptiacus_ bats in the same country in the
absence of a corresponding outbreak of disease].
On both occasions it again proved impossible to
isolate live virus. In July 2007, a small
outbreak of Marburg haemorrhagic fever occurred
in workers mining lead and gold in Kitaka Cave
near Ibanda village in western Uganda. Large
numbers of _R. aegyptiacus_and insectivorous
_Hipposideros_ species bats were present in this
mine. Ecological investigations were conducted in
August 2007 and May 2008, and the findings are presented here.
It can be concluded that there was no evidence of
vertical transmission of infection in _R.
aegyptiacus_, but that juveniles are exposed to
virus at a stage of their development possibly
determined by factors such as waning maternal
immunity or seasonal occurrence of infection in
external hosts such as arthropods. Limited tests
on arthropod parasites of bats in the present
study were negative for evidence of Marburg virus
infection, and the same was true for larger
numbers of parasitic and cave-associated
arthropods tested in the investigations in the
DRC in 1999. It seems more likely that there is
horizontal transmission of infection among
susceptible bats, as has been proposed for Hendra
virus and Nipah virus. However, no Marburg virus
RNA was detected in oral swabs taken from bats,
including those with virus RNA-positive liver and
spleen samples, suggesting that transmission via
masticated fruit spats as suggested for Nipah
virus, is an unlikely route for marburgviruses.
Transmission via bat urine or feces would be
another possible mechanism. It is notable that
ebolavirus was found to be shed in the feces of
experimentally infected fruit bats for up to 3
weeks, but limited immunohistochemical analyses
of formalin-fixed kidneys of our RT-PCR positive
bats have thus far been negative, tentatively
suggesting that transmission via urine may be
less likely than through feces. However, it would
be premature to rule out transmission through
urine, feces or saliva given the limited number
of bats tested to date, and the lesser
sensitivity of immunohistochemical methods
relative to RT-PCR. The determination of virus
transmission mechanisms will be best addressed in
the future through experimental infection of R. aegyptiacus bats.
In CONCLUDING REMARKS the authors state that the
generation and perpetuation of such diverse
genetic lineages of virus, with greater or equal
to 21 percent nucleotide differences, imply the
need for a long association of the virus with its
reservoir host, plus the need for a large host
population with constant recruitment of naive
individuals. The estimated population of 112 000
_R. aegyptiacus_ bats in Kitaka mine could
probably produce up to 100 000 offspring with 2
breeding seasons a year. Moreover the species is
widely distributed in Africa, with many large
colonies in proximity in East Africa alone,
including the Kitum Cave complex on Mount Elgon,
and numerous caves in western Uganda. It has been
observed in South Africa that large proportions
of the bats within _R. aegyptiacus_ colonies
migrate greater or equal to 300 miles to other
colonies on a seasonal basis. Hence the potential
pool of vertebrate hosts for marburgviruses may
extend to tens of millions of bats across a large
geographic range. Although diverse Marburg virus
lineages were found to co-circulate at single
geographic locations in Kitaka mine in Uganda and
Goroumbwa Mine in the DRC, it is noteworthy that
very closely related lineages have also been
found at widely separated geographic locations,
in some instances over 2000 km apart. For
example, marburgvirus sequences found in bats in
Gabon are closely related to isolates from
Zimbabwe, Uganda and DRC. Isolates of the Ravn
lineage have been found in Kenya, DRC and Uganda.
In fact, an isolation-by-distance analysis of the
data presented here (Mantel test) found no
correlation between genetic and geographic
distances. The geospatial separation of the
closely related marburgvirus lineages is most
consistent with mobility of their natural host, a
dynamic easily accomplished by the enormous meta-
population of _R. aegyptiacus_ present in Africa.
Longitudinal studies of naturally infected _R.
aegyptiacus_ colonies would provide valuable
insights into the dynamics of immune status, as
well as the shedding, transmission and
persistence of marburgviruses in bat populations,
and help to determine if the proportions of
infected individuals relative to age are periodic
or stochastic. The studies should be supplemented
by experimental infections to observe the
dynamics of infection within individual bats.
Given the detection of infectious ebolaviruses in
privileged sites, such as testes, up to 3 months
after onset of symptoms in human infections,
careful examination of multiple tissues from infected bats is also warranted.
Images of the Egyptian fruit bat (_Rousettus aegyptiacus_) can be viewed at:
<
http://www.arkive.org/egyptian-fruit-ba ... size=large>
- Mod.CP]
A map showing the location of Uganda in Africa is
available at:
<
http://www.infoplease.com/atlas/country/uganda.html> - CopyEd.EJP]
