Natural reservoir

For other uses, see Reservoir (disambiguation).

A natural reservoir or nidus (the latter from the Latin word for "nest") is the long-term host of a pathogen of an infectious disease.[1] Hosts often do not get the disease carried by the pathogen or it is carried as a subclinical infection and so asymptomatic and non-lethal. Once discovered, natural reservoirs elucidate the complete life cycle of infectious diseases, providing effective prevention and control.

Examples

Examples of natural reservoirs are:

Eradication efforts

Some viruses have no non-human reservoir: poliomyelitis and smallpox are prominent examples. The lack of a non-human reservoir makes these viruses good candidates for eradication efforts.

Ebola virus disease

Bushmeat being prepared for cooking in Ghana, 2013. Human consumption of equatorial animals in Africa in the form of bushmeat has been linked to the transmission of diseases to people, including ebola.[2]

The natural reservoir of some diseases remain unclear. This is the case of the Ebola virus disease.[3]

One study between 1976 and 1998, from 30,000 mammals, birds, reptiles, amphibians, and arthropods sampled from outbreak regions, no ebolavirus was detected apart from some genetic traces found in six rodents (Mus setulosus and Praomys) and one shrew (Sylvisorex ollula) collected from the Central African Republic.[4][5] Traces of EBOV were detected in the carcasses of gorillas and chimpanzees during outbreaks in 2001 and 2003, which later became the source of human infections. However, the high lethality from infection in these species makes them unlikely as a natural reservoir.[4]

However, a subsequent study, in a later outbreak, found 31.8% of the dogs closest to an outbreak contained antigens that indicate a previous active viral load.[6] Whether dogs passed the virus to humans, or both were infected by a third species is unknown.

Plants, arthropods, and birds have also been considered as possible reservoirs; however, bats are considered the most likely candidate.[7] Bats were known to reside in the cotton factory in which the index cases for the 1976 and 1979 outbreaks were employed, and they have also been implicated in Marburg virus infections in 1975 and 1980.[4] Of 24 plant species and 19 vertebrate species experimentally inoculated with EBOV, only bats became infected.[8]

The absence of clinical signs in these bats is characteristic of a reservoir species. In a 2002–2003 survey of 1,030 animals including 679 bats from Gabon and the Republic of the Congo, 13 fruit bats were found to contain EBOV RNA fragments.[9] As of 2005, three types of fruit bats (Hypsignathus monstrosus, Epomops franqueti, and Myonycteris torquata) have been identified as being in contact with EBOV. They are now suspected to represent the EBOV reservoir hosts.[10]

The existence of integrated genes of filoviruses in some genomes of small rodents, insectivorous bats, shrews, tenrecs, and marsupials indicates a history of infection with filoviruses in these groups as well.[11] However, it has to be stressed that infectious ebolaviruses have not yet been isolated from any nonhuman animal.

Bats drop partially eaten fruits and pulp, then terrestrial mammals such as gorillas and duikers feed on these fallen fruits. This chain of events forms a possible indirect means of transmission from the natural host to animal populations, which have led to research towards viral shedding in the saliva of bats. Fruit production, animal behavior, and other factors vary at different times and places that may trigger outbreaks among animal populations.[12] Transmission between natural reservoirs and humans are rare, and outbreaks are usually traceable to a single index case where an individual has handled the carcass of gorilla, chimpanzee, or duiker.[13] The virus then spreads person-to-person, especially within families, hospitals, and during some mortuary rituals where contact among individuals becomes more likely.[14]

See also

References

  1. ↑ Aguirre, A. Alonso; Ostfeld, Richard; Daszak, Peter. New Directions in Conservation Medicine: Applied Cases of Ecological Health. Oxford University Press; 28 June 2012. ISBN 9780199731473. p. 196.
  2. ↑ 25 people in Bakaklion, Cameroon killed due to eating of ape
  3. ↑ Biek, R, Walsh PD, Leroy EM, and Real LA (27 Oct 2006). "Recent Common Ancestry of Ebola Zaire Virus Found in a Bat Reservoir". PLoS Pathogens. Retrieved 11 Feb 2013.
  4. 1 2 3 Pourrut, X.; Kumulungui, B.; Wittmann, T.; Moussavou, G.; Délicat, A.; Yaba, P.; Nkoghe, D.; Gonzalez, J. P.; Leroy, E. M. (2005). "The natural history of Ebola virus in Africa". Microbes and infection / Institut Pasteur 7 (7–8): 1005–1014. doi:10.1016/j.micinf.2005.04.006. PMID 16002313.
  5. ↑ Morvan, J.; Deubel, V.; Gounon, P.; Nakouné, E.; Barrière, P.; Murri, S.; Perpète, O.; Selekon, B.; Coudrier, D.; Gautier-Hion, A.; Colyn, M.; Volehkov, V. (1999). "Identification of Ebola virus sequences present as RNA or DNA in organs of terrestrial small mammals of the Central African Republic". Microbes and Infection 1 (14): 1193–1201. doi:10.1016/S1286-4579(99)00242-7. PMID 10580275.
  6. ↑ Allela L, Boury O, Pouillot R, Délicat A, Yaba P, Kumulungui B, Rouquet P, Gonzalez JP, Leroy EM (2005). "Ebola virus antibody prevalence in dogs and human risk". Emerging Infect. Dis. 11 (3): 385–90. doi:10.3201/eid1103.040981. PMC 3298261. PMID 15757552.
  7. ↑ "Fruit bats may carry Ebola virus". BBC News. 2005-12-11. Retrieved 2008-02-25.
  8. ↑ Swanepoel, R. L.; Leman, P. A.; Burt, F. J.; Zachariades, N. A.; Braack, L. E.; Ksiazek, T. G.; Rollin, P. E.; Zaki, S. R.; Peters, C. J. (Oct 1996). "Experimental inoculation of plants and animals with Ebola virus". Emerging Infectious Diseases 2 (4): 321–325. doi:10.3201/eid0204.960407. ISSN 1080-6040. PMC 2639914. PMID 8969248.
  9. ↑ Leroy, E. M.; Kumulungui, B.; Pourrut, X.; Rouquet, P.; Hassanin, A.; Yaba, P.; Délicat, A.; Paweska, J. T.; Gonzalez, J. P.; Swanepoel, R. (2005). "Fruit bats as reservoirs of Ebola virus". Nature 438 (7068): 575–576. Bibcode:2005Natur.438..575L. doi:10.1038/438575a. PMID 16319873.
  10. ↑ Pourrut, X.; Délicat, A.; Rollin, P. E.; Ksiazek, T. G.; Gonzalez, J.‐P.; Leroy, E. M. (2007). "Spatial and temporal patterns of Zaire ebolavirus antibody prevalence in the possible reservoir bat species". The Journal of Infectious Diseases. Suppl 2 (s2): S176–S183. doi:10.1086/520541. PMID 17940947.
  11. ↑ Taylor, D.; Leach, R.; Bruenn, J. (2010). "Filoviruses are ancient and integrated into mammalian genomes". BMC Evolutionary Biology 10: 193. doi:10.1186/1471-2148-10-193. PMC 2906475. PMID 20569424.
  12. ↑ Gonzalez, J. P.; Pourrut, X.; Leroy, E. (2007). "Ebolavirus and other filoviruses". Current topics in microbiology and immunology. Current Topics in Microbiology and Immunology 315: 363–387. doi:10.1007/978-3-540-70962-6_15. ISBN 978-3-540-70961-9. PMID 17848072.
  13. ↑ Peterson, A. T.; Bauer, J. T.; Mills, J. N. (2004). "Ecologic and Geographic Distribution of Filovirus Disease". Emerging Infectious Diseases 10 (1): 40–47. doi:10.3201/eid1001.030125. PMC 3322747. PMID 15078595.
  14. ↑ Questions and Answers about Ebola Hemorrhagic Fever. Centers for Disease Control and Prevention. 2009-03-25. Retrieved 2009-05-31.
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