(January 13th, 2012) A team of researchers from Spain and the USA has reported the first instance of a filovirus in Europe. Fortunately, the virus doesn’t seem to be as fatal as its family members, Marburgvirus and Ebolavirus, at least not to us humans; bats are not so lucky...
Filoviruses represent one of the deadliest pathogens known to men. In humans and non-human primates, they cause hemorrhagic fever, which, in the worst of all cases, can lead to death. Therefore, according to the WHO's guidelines, filoviruses are filed into Risk Group 4, meaning that it's “a pathogen that usually causes serious human or animal disease and that (it) can be readily transmitted from one individual to another, directly or indirectly. Effective treatment and preventive measures are not usually available”.
To the family Filoviridae belong two very prominent members: Marburgvirus (MARV) and Ebolavirus (EBOVs); up until now, these two fiends have only been reported in sub-Saharan Africa, where bats have been identified as reservoirs and vectors for transmission, and the Philippines.
Although endemic to non-European countries, Europe has not been immune to filoviruses either. Actually, MARV was discovered in 1967 in Marburg, Germany, as the cause of a hemorrhagic fever outbreak in a research facility, where workers had been exposed to MARV-infected tissues from monkeys imported from Uganda. In total, 31 people contracted the disease and seven died. After that, MARV disappeared from Europe until 2008, when a woman died less than two weeks after she returned from Uganda, where she had visited some caves.
Now, an international team led by Gustavo Palacios (Columbia University, USA) and Ana Negredo from the National Center of Microbiology, (ISCIII) in Madrid, Spain has made another disturbing discovery, once again in a cave. Bat carcasses in Asturias, Northern Spain carried a novel, European filovirus. Originally, the scientists were intrigued by a “massive die-off” of Schreiber's bats (Miniopterus schreibersii) in caves in France, Spain and Portugal, which occurred in 2002. For now, the new virus is named Lloviu virus (LLOV), after the site, Cueva de Lloviu, at which the bats were found.
For their PLoS Pathogens paper, Negredo et al. analysed 34 bat corpses from the Asturian cave. Examination of internal organs showed evidence of an immune response consistent with viral pneumonia: “interstitial lung infiltrates (were) comprised of lymphocytes and macrophages, and (there was a) depletion of lymphocytes and lymphoid follicles in spleen”. Lung and spleen samples analysed by a PCR-based approach pinpointed to DNA sequences specific for filoviruses. Their findings were unexpected: they detected a new virus, and not just any virus, a filovirus with high (73.7%) similarity to the Zaire ebolavirus.
It is still unclear, whether LLOV was ultimately responsible for the death of the bats. However, unlike MARV and EBOVs that do not cause disease in bats, LLOV was exclusively found in dead specimens. There was no evidence of LLOV in healthy bats: “rectal and throat swabs [...] obtained from 1,295 healthy bats representing 29 different species (including M. schreibersii from distinct geographic locations in Spain)” revealed that not a single healthy one carried LLOV. All this strongly suggests that the virus may be harmful to the health of bats.
The discovery of LLOV is significant for several reasons. As the first case of a naturally occurring filovirus in Europe, it is a reminder of how little we know about emerging infectious diseases. The dead bats from Spain were not the only ones, similar die-offs have also been detected across parts of Western Europe and it will be interesting to determine whether LLOV is present in these locations, too.
Research is critical in order to find out how widespread LLOV is - being migratory animals, bats could have already spread the virus to numerous places, near and far. Additionally, it will be important to determine whether LLOV really has something to do with the deaths of the bats. Bats are important players in the ecosystem; they are involved in plant pollination, seed transportation and controlling insect populations, so pathogens affecting their population may end up having a significant ecological impact.
Last but not least, what about a potential threat from LLOV to humans? It is worthy to note that Cueva de Lloviu is a popular tourist destination BUT, so far, no human infections have been reported. So, besides the Philippine-domiciled Reston ebolavirus (REBOV), LLOV might be the second reported filovirus that is, luckily, not pathogenic for us.
Jacqueline Loo
Photo: Fotolia/Alex Ciopata