Spillover infection
Spillover infection, also known as pathogen spillover and spillover event, occurs when a reservoir population with a high pathogen prevalence comes into contact with a novel host population. The pathogen is transmitted from the reservoir population and may or may not be transmitted within the host population.[1] Due to climate change and land use expansion, the risk of viral spillover is predicted to significantly increase.[2][3]
Spillover zoonoses
Spillover is a common event; in fact, more than two-thirds of human viruses are
If the history of mutual adaptation is long enough, permanent host-microbe associations can be established resulting in co-evolution, and even permanent integration of the microbe genome with the human genome, as is the case of endogenous viruses.
During the late 20th century, zoonotic spillover increased as the environmental impact of agriculture promoted increased land use and deforestation, changing wildlife habitat. As species shift their geographic range in response to climate change, the risk of zoonotic spillover is predicted to substantially increase, particularly in tropical regions that are experiencing rapid warming.[8] As forested areas of land are cleared for human use, there is increased proximity and interaction between wild animals and humans thereby increasing the potential for exposure.[9]
Intraspecies spillover
Commercially bred
Disease | Reservoir |
---|---|
Hepatitis E | Wild Boar[10] |
Ebola | Fruit Bats[11] |
HIV/AIDS | Chimpanzee[12] |
COVID-19 | Bats[28] |
Causes of spillover
Zoonotic spillover is a relatively uncommon but incredibly dangerous natural phenomenon—as is evidenced by the Ebola epidemic and Coronavirus pandemic. For zoonotic spillover to occur, several important factors have to occur in tandem.[1] Such factors include altered ecological niches, epidemiological susceptibility, and the natural behavior of pathogens and novel host or spillover host species.[29] By suggesting that the natural behavior of pathogens and host species impacts zoonotic spillover, simple Darwinian theories are being referenced. As with all species, a pathogen's main goal is to survive. When a stressor puts pressure on the survival of the pathogenic species, it will have to adapt to said stressor in order to survive.[30] For example, the ecological niche of the novel host may be subject to a lack of food which leads to a decrease in the novel host population. In order for a virus to replicate, it must invade a eukaryotic organism.[31] When the novel eukaryotic organism is not available for the virus to infect, it must jump to another host.[30] In order for the virus to make the jump to the spillover host, the spillover host must be epidemiologically susceptible to this virus. Although it is not well understood what makes one spillover host "better" than another host, it is known that the susceptibility has to do with the shedding rate of the virus, how well the virus survives and moves while not within a host, the genotypic similarities between the novel and spillover hosts, and the behavior of the spillover host that leads to contact with a high dose of the virus.[1]
See also
- Cross-species transmission
- Reverse zoonosis
- Epidemic
- Infection
- Outbreak
- List of Legionellosis outbreaks
- 1993 Four Corners hantavirus outbreak
- Severe acute respiratory syndrome coronavirus 2
References
- ^ PMID 22966141.
- PMID 17507975.
- ^ Ebola. (2014). National Center for Emerging and Zoonotic Infectious Diseases, Division of High-Consequence Pathogens and Pathology, Department of Health & Human Services, CDC.
- S2CID 3937352.
- ^ ISSN 1387-3547.
- S2CID 84926310.
- PMID 26246556.
- PMID 18648661.
- PMID 25165632.
- ^ PMID 27983488.
- ^ PMID 36048780.
- ^ a b "About HIV/AIDS | HIV Basics | HIV/AIDS | CDC". www.cdc.gov. 2022-06-30. Retrieved 2022-12-08.
- PMID 26246556.
- PMID 18648661.
- PMID 25165632.
- PMID 28560161.
- PMID 34202101.
- PMID 34460063.
- PMID 34774124.
The current weight of evidence suggests that SARS-CoV-2, or its progenitor, probably emerged in humans from a zoonotic source in Wuhan, China, where it was first identified in 2019. Although evidence on the origins of SARS-CoV-2 are inconclusive, bats have been suggested to be the most probable evolutionary source for the virus."
- S2CID 257015965.
The pandemic of Coronavirus disease (COVID-19) has highlighted bats as reservoirs of coronaviruses that cause severe respiratory diseases in humans and, frequently, in other animals. However, despite the spillover events of SARS-CoV and MERS-CoV, the implication of bats as natural reservoirs of the ancient virus of SARS-CoV-2 is, to date, unconfirmed, as only closely related SARS-like viruses have been detected by genomic sequencing and little is known about the mechanisms of host switch from bats to humans.
- PMID 32582786.
- ^ S2CID 231138544.
- PMID 33172935.
- PMID 33864026.
- PMID 33547281.
- S2CID 256875846.
It is almost certain that the virus originated in bats and crossed species to humans either directly or indirectly via intermediary hosts.
- S2CID 252818019.
The increasing scientific evidence concerning the origins of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is most consistent with a zoonotic origin and a spillover pathway from wildlife to people via wildlife farming and the wildlife trade.
- PMID 28811483.
- ^ PMID 36310377.
- PMC 7149683