Marburg virus in Egyptian fruit bats

5 August 2009

marburg-antigens-bat-tissuesMarburg virus has been isolated from Egyptian fruit bats (Rousettus aegyptiacus) living in Kitaka Cave, Uganda, demonstrating that bats are a natural reservoir of the virus.

Marburg virus, the founding member of the Filoviridae, is an enveloped virus with a negative-strand RNA genome. Other members of the filovirus family are the five species of ebolavirus. Filoviruses are indigenous to Africa, but the animal reservoir for the virus has not been definitively identified. The first outbreaks of Marburg hemorrhagic fever took place in laboratories in Marburg, Frankfurt, and Belgrade in 1967. The virus was believed to originate from African green monkeys that were being used for laboratory research. However, these monkeys were trapped in regions of Uganda where fruit bats are common. Other evidence suggests that bats are the natural reservoir of filoviruses. For example, two patients who developed Marburg hemorrhagic fever in 1980 and 1987 in Kenya had been in a cave inhabited by bats before they became ill. In January 2009 the first US case of Marburg hemorrhagic fever was reported in Colorado. The patient had traveled to Uganda in December 2007 and visited a python cave that houses thousands of bats.

The study was undertaken to understand why miners working in Kitaka Cave in July and September 2007 developed Marburg hemorrhagic fever. The authors captured 611 bats and found Marburg viral RNA in 31. Given the population of 100,000 bats in Kitaka Cave, at least 5,000 are likely to harbor the virus. Antibodies to Marburg virus were also detected in bat sera, and infectious virus was recovered from 4 animals, all of which were healthy.

Filovirus antigens were detected in tissues of naturally infected bats for the first time. Viral antigens were detected by immunohistochemistry in the livers of two bats from which infectious Marburg virus was isolated in cell culture (illustrated). Viral antigens were also detected in the spleen of one bat, in the cytoplasm of mononuclear cells.

Nucleotide sequence analysis revealted that in the Kitaka Cave outbreak the two miners did not infect each other, but were infected separately by two independent introductions of virus from bats to humans. Furthermore, remarkable diversity – up to 21% between virus lineages – was observed in viral RNAs from the bat colony. This diversity suggests that the virus remains for long periods in its reservoir host, and also infects large numbers of bats. R. aegyptiacus bats migrate  over 300 miles to other colonies each season, providing a pool of millions of bathosts for Marburg virus.

These findings have clear implications for public health: the large numbers of bats that harbor Marburg virus have the potential to initiate epidemics of hemorrhagic disease in humans. There are many other caves throughout Africa that harbor similar colonies of bats. Given the high case fatality ratio of filovirus hemorrhagic fever – approaching 90% – it is clear that bat-infested caves should be avoided by miners and spelunkers.

Towner, J., Amman, B., Sealy, T., Carroll, S., Comer, J., Kemp, A., Swanepoel, R., Paddock, C., Balinandi, S., Khristova, M., Formenty, P., Albarino, C., Miller, D., Reed, Z., Kayiwa, J., Mills, J., Cannon, D., Greer, P., Byaruhanga, E., Farnon, E., Atimnedi, P., Okware, S., Katongole-Mbidde, E., Downing, R., Tappero, J., Zaki, S., Ksiazek, T., Nichol, S., & Rollin, P. (2009). Isolation of Genetically Diverse Marburg Viruses from Egyptian Fruit Bats PLoS Pathogens, 5 (7) DOI: 10.1371/journal.ppat.1000536

  • Everett197281

    Is that odd then, that if bats are the natural reservoir that only 5% have the virus? Given bats living habits, it seems (at least intuitively) that it should be a lot higher-unless something was passing it from one bat to the next. Is another vector still possible here?

    Additionally, the histo slides of hepatic tissue seem to indicate that at least in bats, the virus is attracted to the liver (and controlled). So, what is it about human endothelium that makes for a better home? Do filoviruses directly attack human liver as well?–(I know multi organ system failure sets in at some point-but that is typically a fatal symptom, not a causal one.)

    Is there something that were not understanding about bats immune system? Aside of white nose disease, it seems astoundingly robust.

  • thor183

    So, I more or less get the pathogenic lifecycle of viruses. What about non-pathogenic lifecycles. For instance, how does the lifecycle of Marburg in these bats, a natural resevoir for it, differ from say humans where it is lethal? My impressions is that the virus thrives in its natural host environment and so must have an effective lifecycle in it. Does it differ from that in humans?

    Do you think there is any merit to the idea that natural hosting is an evolved symbiotic defensive mechanism wherein the host species derives a defense against potential enemy species via a lethal species transition in the virus? A sort of differential-immunity selective strategy.

    If I'm making any sense here.

  • http://www.virology.ws profvrr

    The whole question of how viruses exist without damaging their hosts
    is one of the greatest unexplored areas in virology. Most (but not
    all) of these interactions involve viruses in wild animals and receive
    very little study. It may very well be that such virus-host
    interactions are beneficial for both. For example, see TWiV #46 in
    which we discussed a virus that infects a fungus of a plant, which
    allows the plant to grow at high temperatures.

  • http://www.virology.ws profvrr

    The whole question of how viruses exist without damaging their hosts
    is one of the greatest unexplored areas in virology. Most (but not
    all) of these interactions involve viruses in wild animals and receive
    very little study. It may very well be that such virus-host
    interactions are beneficial for both. For example, see TWiV #46 in
    which we discussed a virus that infects a fungus of a plant, which
    allows the plant to grow at high temperatures.

  • Pingback: Killers on the loose: the deadly viruses that threaten human survival « News in Briefs

  • Pingback: Killers on the loose: the deadly viruses that threaten human survival | Politics News and Discussion

  • Pingback: Flus.us » Blog Archive » Killers on the loose: the deadly viruses that threaten human survival » Flus.us

  • Pingback: Killers on the loose: the deadly viruses that threaten human survival - Government Tenders, Government News and Information - Government Online

  • Pingback: Influenza A viruses in bats