The Ebola virus, a member of the viral family Filoviridae, has been known to cause fatal viral hemorrhagic disease in humans and other homid-like primates (chimpanzees and gorillas). Filoviruses have been described as enveloped, non-segmented and negative-stranded RNA viruses divided into two distinct genera: Marburgviruses and Ebolaviruses. Following the biological convention of naming the viruses according to where they are first discovered, Ebolaviruses have been subdivided into four species: Ebola Zaire (ZEBOV), Ebola Ivory Coast (ICEBOV), Ebola Sudan (SEBOV) and Ebola Reston (REBOV) (Hensley, et. al., 2005). Since the virus’ discovery thirty years ago, scientists have learned a great deal about this mysterious and elusive killer. Ebola has managed to keep many of its secrets away from the grasp of researchers further adding to the virus’ mystique. After the tragic events of September 11, 2001, the fear arose that Ebola and other deadly pathogens could be developed and used as bioterroristic weapons agents. The questions that scientists have left to answer are how did this virus emerge, the possibility of the existence of a reservoir host and the reasons for the cyclic emergence of outbreaks. One way to do this is for scientists to retrace the steps of where and when Ebola first made its deadly appearance.
Ever since the Ebola virus was identified as the causative agent of the viral hemorrhagic fever outbreaks in Zaire, Sudan and Ivory Coast, scientists have tried to find Ebola’s reservoir host. They knew that since many of the endemic monkeys and apes were also dying from the same disease that infected humans, monkeys had been ruled out as the reservoir host. Scientists hypothesized that the reservoir host had to be a mammalian species or an arthropod that was able to harbor the virus for a period of time without becoming infected with the disease. A recent survey of small vertebrates during the 2001 and 2003 Gabon outbreaks found evidence of asymptomatic infections of Ebola Zaire in three species of fruit bats: Hypsignathus monstrosus, Epomops franqueti and Myonycteris torquata. All three of these species were found in African regions where human Ebola outbreaks have occurred (Leroy, et.al, 2005). Spleen and liver tissue samples taken from these bats found Ebola Zaire RNA and serum antibody levels in some animals. This data helped to support earlier findings that demonstrated replication and circulation of high titers of Ebola in experimentally infected fruit and insectivorous bats in the absence of illness. It also demonstrated that there was the presence of Ebola Zaire specific Ig-G antibodies in at least 5% of the bat species. These findings supported the theory that bats could be the reservoir host for Ebola. These bats came from both epidemic and non-epidemic regions at the time of the outbreaks, an indication that the virus was circulating in both these areas. In addition there happened to be a 1% decrease in prevalence in all regions during the period of outbreaks, inferring that Ebola Zaire was present in forested countries of Central Africa and would wax and wane. Reasons for these changes could be attributed to possible die-offs in the bat population due to disease or reduced reproduction in sick animals (Groseth, et.al, 2007). Mortality among the great apes from Ebola infection was increased during dry seasons when fruit sources in the forest were scarce, fostering contact among other animals as they competed for food. Immune function among the bat population also changed during these periods in correlation to the food shortage or pregnancy, which can favor viral reproduction. In addition to aggressive behavior among the apes, the instance of viral infections increased. These factors taken together all contributed to the episodic nature of Ebola outbreaks. It is possible that other bat or animal species may play a role in serving as reservoir hosts to Ebola infection. Insight into the behavioral ecology of these particular bat species could be of tremendous help in protecting the great apes from Ebola viral infection. Human infection from Ebola by direct contact with the bats can be countered with education, as the local population living in the outbreak regions has used these animals as food. (Leroy, et.al, 2005).
Scientists conducting these previous studies had a reason to feel a sense of excitement for having finally been able to draw a correlation between a possible reservoir host in regions were outbreaks were more prevalent. However in a recent study, that theory could very well be blown out of the water with the possible discovery of a new strain of an Ebola-like filovirus discovered in Europe. A massive die-off of Schreiber’s bats in caves in France, Spain and Portugal in 2002 prompted scientists to study the carcasses of these bats to try and determine the cause. After analyses of the body fluids and organ tissues taken from these animals it was discovered that the bats had become infected with a possible new strain of Ebola Virus like filovirus, typed Lloviu after the site of the detection, Cueva del Lloviu in Spain. Unlike in the case of Marburg and Ebola where circulation of the virus had been deemed asymptomatic in bats, the Lloviu virus seemed to be pathogenic to them. The bat die-offs in Spain were reported to destroy several bat colonies in less than ten days. It had similarities to an outbreak of ‘white nose syndrome’, a lethal fungal infection that was responsible for recent declines in the North American bat population. Any sudden die-off of a bat population should raise some concern from an ecological standpoint because bats are useful in insect control, plant pollination and seed dissemination. With this recent finding scientists still have not come up with a relationship between the mortality of the bats and the discovery of a novel Ebola-like Lloviu virus in Europe. (Negredo, et. al., 2011)
Human and animal mortality is not always a reliable method of determining the presence of a virus in a region. However, the evidence of the presence of the Ebola virus in bats as well as seasonal changes in the areas the virus was found during outbreaks have enabled scientists to stay on the hunt. With this latest discovery, with the different geographical niches Filoviruses have been found, a look into the diversity of Filoviruses should be an issue to consider.
References
Groseth, A., Feldmann, H., and Strong, J.E., (August, 2007). The ecology of Ebola virus Trends in Microbiology, 15(9), 408-416. Downloaded from Science Direct database on December 18, 2012.
Leroy, E.M., Kumulungui, B., Pourrut, X., Rouquet, P., Hassanin, A., Yaba, P., Delicat, A., Paruseska, J.T., Gonzalez, J., and Swanespoel, R., (2005). Fruit bats as reservoirs of Ebola virus, Nature, 438(7068), 575-576. Downloaded from Academic Search Premier on December 18, 2012.
Negredo, A., Palacios, G., Vazquez-Moron, S., Gonzalez, F., Dopazo, H., et. al. (2011) Discovery of an Ebolavirus-like Filovirus in Europe. PLoS Pathogens 7(10), 1-8 doi:10.1371/journal.ppat.1002304.
Hensley, L.E., Jones, S.M., Feldmann, H., Jahrling, P.B., and Geisbert, T.W. (2005). Ebola and Marburg viruses: pathogenesis and development of countermeasures. Current Molecular Medicine, 5, 761-772. Downloaded from Google Scholar database on December 18, 2012.
Ever since the Ebola virus was identified as the causative agent of the viral hemorrhagic fever outbreaks in Zaire, Sudan and Ivory Coast, scientists have tried to find Ebola’s reservoir host. They knew that since many of the endemic monkeys and apes were also dying from the same disease that infected humans, monkeys had been ruled out as the reservoir host. Scientists hypothesized that the reservoir host had to be a mammalian species or an arthropod that was able to harbor the virus for a period of time without becoming infected with the disease. A recent survey of small vertebrates during the 2001 and 2003 Gabon outbreaks found evidence of asymptomatic infections of Ebola Zaire in three species of fruit bats: Hypsignathus monstrosus, Epomops franqueti and Myonycteris torquata. All three of these species were found in African regions where human Ebola outbreaks have occurred (Leroy, et.al, 2005). Spleen and liver tissue samples taken from these bats found Ebola Zaire RNA and serum antibody levels in some animals. This data helped to support earlier findings that demonstrated replication and circulation of high titers of Ebola in experimentally infected fruit and insectivorous bats in the absence of illness. It also demonstrated that there was the presence of Ebola Zaire specific Ig-G antibodies in at least 5% of the bat species. These findings supported the theory that bats could be the reservoir host for Ebola. These bats came from both epidemic and non-epidemic regions at the time of the outbreaks, an indication that the virus was circulating in both these areas. In addition there happened to be a 1% decrease in prevalence in all regions during the period of outbreaks, inferring that Ebola Zaire was present in forested countries of Central Africa and would wax and wane. Reasons for these changes could be attributed to possible die-offs in the bat population due to disease or reduced reproduction in sick animals (Groseth, et.al, 2007). Mortality among the great apes from Ebola infection was increased during dry seasons when fruit sources in the forest were scarce, fostering contact among other animals as they competed for food. Immune function among the bat population also changed during these periods in correlation to the food shortage or pregnancy, which can favor viral reproduction. In addition to aggressive behavior among the apes, the instance of viral infections increased. These factors taken together all contributed to the episodic nature of Ebola outbreaks. It is possible that other bat or animal species may play a role in serving as reservoir hosts to Ebola infection. Insight into the behavioral ecology of these particular bat species could be of tremendous help in protecting the great apes from Ebola viral infection. Human infection from Ebola by direct contact with the bats can be countered with education, as the local population living in the outbreak regions has used these animals as food. (Leroy, et.al, 2005).
Scientists conducting these previous studies had a reason to feel a sense of excitement for having finally been able to draw a correlation between a possible reservoir host in regions were outbreaks were more prevalent. However in a recent study, that theory could very well be blown out of the water with the possible discovery of a new strain of an Ebola-like filovirus discovered in Europe. A massive die-off of Schreiber’s bats in caves in France, Spain and Portugal in 2002 prompted scientists to study the carcasses of these bats to try and determine the cause. After analyses of the body fluids and organ tissues taken from these animals it was discovered that the bats had become infected with a possible new strain of Ebola Virus like filovirus, typed Lloviu after the site of the detection, Cueva del Lloviu in Spain. Unlike in the case of Marburg and Ebola where circulation of the virus had been deemed asymptomatic in bats, the Lloviu virus seemed to be pathogenic to them. The bat die-offs in Spain were reported to destroy several bat colonies in less than ten days. It had similarities to an outbreak of ‘white nose syndrome’, a lethal fungal infection that was responsible for recent declines in the North American bat population. Any sudden die-off of a bat population should raise some concern from an ecological standpoint because bats are useful in insect control, plant pollination and seed dissemination. With this recent finding scientists still have not come up with a relationship between the mortality of the bats and the discovery of a novel Ebola-like Lloviu virus in Europe. (Negredo, et. al., 2011)
Human and animal mortality is not always a reliable method of determining the presence of a virus in a region. However, the evidence of the presence of the Ebola virus in bats as well as seasonal changes in the areas the virus was found during outbreaks have enabled scientists to stay on the hunt. With this latest discovery, with the different geographical niches Filoviruses have been found, a look into the diversity of Filoviruses should be an issue to consider.
References
Groseth, A., Feldmann, H., and Strong, J.E., (August, 2007). The ecology of Ebola virus Trends in Microbiology, 15(9), 408-416. Downloaded from Science Direct database on December 18, 2012.
Leroy, E.M., Kumulungui, B., Pourrut, X., Rouquet, P., Hassanin, A., Yaba, P., Delicat, A., Paruseska, J.T., Gonzalez, J., and Swanespoel, R., (2005). Fruit bats as reservoirs of Ebola virus, Nature, 438(7068), 575-576. Downloaded from Academic Search Premier on December 18, 2012.
Negredo, A., Palacios, G., Vazquez-Moron, S., Gonzalez, F., Dopazo, H., et. al. (2011) Discovery of an Ebolavirus-like Filovirus in Europe. PLoS Pathogens 7(10), 1-8 doi:10.1371/journal.ppat.1002304.
Hensley, L.E., Jones, S.M., Feldmann, H., Jahrling, P.B., and Geisbert, T.W. (2005). Ebola and Marburg viruses: pathogenesis and development of countermeasures. Current Molecular Medicine, 5, 761-772. Downloaded from Google Scholar database on December 18, 2012.
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