TWiV 173: Going to bat for flu research

On episode #173 of the podcast This Week in Virology, the TWiVites discuss seroevidence for human infection with avian influenza H5N1, and the discovery of a new influenza virus in Guatemalan bats.

You can find TWiV #173 at

TWiV 44: No hysteria

twiv_aa_2001Hosts: Vincent Racaniello, Dick Despommier, Alan Dove, and Jennifer Drahos

In episode #44 of the podcast “This Week in Virology”, Vincent, Dick, Alan, and Jennifer Drahos consider Marburg virus in Egyptian fruit bats, bacterial citrus pathogen found in shipping facility, canine parvovirus in Michigan, Relenza-resistant influenza virus, new HIV from gorillas, and public engagement on H1N1 immunization program.

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Click the arrow above to play, or right-click to download TWiV #44 (54 MB .mp3, 78 minutes)

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Links for this episode:
Isolation of Marburg virus from Egyptian fruit bats
Inspectors find bacterial citrus pathogen in California
Parvovirus killing hundreds of dogs in Michigan
Relenza-resistant H1N1 identified in Australia (press and journal article)
New HIV from gorilla
CDC wants public comment on H1N1 vaccination
Original antigenic sin (article 1 and article 2)
Dr. Stanley Plotkin on Meet the Scientist (thanks Peter!)
audioBoo (iPhone app – thanks Jim!)
Audio clips (first and second) from the podcast No Agenda (thanks peripatetic apoplectic!)

Weekly Science Picks
Jennifer Piled Higher and Deeper (PhD Comics)
Vincent Giant Microbes (thanks Stephen!)
Dick Virology in the 21st Century
Alan Annals of the Former World by John McPhee

Send your virology questions and comments (email or mp3 file) to or leave voicemail at Skype: twivpodcast

Marburg virus in Egyptian fruit bats

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

Ebola in pigs – Nipah redux?

10816_loresEbola virus infection was reported in Phillipine pigs in 2008. This past week it was revealed that the virus was apparently transmitted from Phillipine pigs to a pig farmer. Why do these events bring Nipah virus to mind?

The Ebola virus that was found in 4 of 6,000 pigs in the Phillipines last year is the Reston strain. This isolate was first identified in Reston, VA, in 1989, in monkeys in a primate facility that had been shipped from the Phillipines. It infected at least 20 lab workers, but did not cause severe disease. In contrast, African strains of Ebola, such as Zaire and Sudan, are associated with high fatality rates.

It is not known how Ebola-Reston infected the Phillipine pigs. There is evidence that the reservoir for African Ebola strains is the fruit bat (or flying fox). It is possible that the virus is transmitted to primates in Africa through contaminated fruit (upon which the bats urinate or defecate while feeding) or bat meat. A recent article in Microbe Magazine explores bats as reservoirs of viruses.

Yes, there are similar fruit bats in the Phillipines. And they have been implicated previously in the transmission of other virus diseases. For example, Nipah virus, a member of the Paramyxoviridae, was first identified as the agent of respiratory illness and encephalitis in Malaysian pig farmers in 1999. This outbreak lead to 105 human deaths; one million pigs were slaughtered to stop the spread of infection. It is believed that fruit bats infected the pigs by contaminating them with urine, feces, or fruit. The pigs, in turn, infected their handlers, who are in close contact with them each day.

Given the Nipah virus scenario, it is not difficult to imagine the spread of Ebola-Reston from fruit bats, to pigs, and then to pig farmers. The pig farms are here to stay, and they only grow larger – increasing the contact between pigs and mobile wild animals. The conclusion is inescapable – more frequent contact between pigs and wild animals, more  future infection of pigs with Ebola.

Dr. Pierre Rollin of the Centers for Disease Control and Prevention has said that “This virus is very stable, not like flu or HIV”. He indicated that there is no change of the virus when it travels from primates to humans. Limited genetic change is typical of a dead-end zoonotic infection: one example is the identical genome sequence of the NYC 1999 West Nile virus isolate with that of a virus from a goose in Israel. Since then, West Nile virus has undergone enormous variation as it has spread across the United States. This is typical of RNA viruses, whose genomes undergo extensive mutation. I seriously doubt that Ebola is genetically ‘very stable’ as implied by Dr. Rollin’s statement above. Rather, we have not yet seen extensive circulation in humans which would lead to a more diverse sequence pool.

I also find curious the statement by Dr. Thomas G. Ksiazek, from the University of Texas Medical School in Galveston, that “It’s probably a rare event that pigs get infected”. Perhaps so far it has been rare. But the rapid growth of farming is leading to more overlap between bat habitats and pig farms. It seems likely that farm animals will be taking more frequent dips in the zoonotic pool, with dire consequences.