Reservoirs

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This page collects observations, interpretations, and consequences for action about the reservoirs of SARS-CoV2 in general. Please observe the structure of the page, when you add your content. Please use references where possible. Remember to find the relevant page. For example, if your observation is about transmission routes, please use that page, instead of posting your content here.

What is already known[edit]

  • Exposure to wild animals is associated with the first cases of COVID19 disease in humans[1].
  • Humans developed clinical symptoms in December 2019 attributed to SARS-CoV-2 infection after visiting a live animal market in Wuhan, China, which suggested animals from the live market as main source of COVID19 disease[2].
  • Later it was suggested that other animals also played a role in transmission, because 13 patients of the first patient cluster involving 41 patients did not visit the live animal market, which would imply that other animals than only those present on the live animal market play a role in the transmission[3].
  • The causative virus for COVID19 disease; SARS-CoV-2, clusters genetically in lineage B of Sarbecovirus with 2 bat-derived SARS-CoV strains, suggestive for bats as virus reservoir [4], [5].
  • However, no clear evidence is available to date on the animal reservoir(s) of SARS-CoV-2.
  • The virus has now established itself well in the human population, humans get infected easily and spread the virus[4].
  • On the role of animals in transmission: SARS-CoV-2 turns out to be very effective in being transmitted between humans, and as far as is known to date, human to human interactions contribute much more to the risk of getting infected than human to animal contact [6].
  • Several types of coronaviruses can infect animals and can be transmitted to other animals and people. There is no evidence that animals pose a risk of infection to humans[7].

Animals as reservoirs or transmitters[edit]

  • Viruses do occur abundantly in humans and in animals, and humans and animals have many viruses in common. However, because viruses need to enter body cells in order to multiply, they need to adapt themselves very precisely to particular hosts, and even are adapted to very specific proteins present on the surface of specific host tissues, such as lungs, to survive. That means that although viruses constantly mutate and change, only seldom such a change would allow a virus to infect another tissue, or even other host. Viruses often need a very specific protein, that can attach to a tissue cell, to enter it and start multiplying. These tissue proteins vary widely between tissues and between animal species, including humans. Generally, viruses do not easily “jump” from animals to humans to multiply abundantly, cause disease and form a new pathogen for humans.
  • However, in the last decades there are several examples in which viruses did jump from animals to humans causing disease.
  • As example, previous outbreaks of coronaviruses in humans involved direct exposure to civet cats (SARS) and camels (MERS), that carry viruses that are genetically very similar to SARS-CoV-1 or MERS-CoV, respectively. Small mutations of the viruses in these animals made these viruses successful in infecting human tissues, multiply, and cause disease.
  • However, experience from MERS and SARS has shown that humans in fact were infected by an intermediate animal host. So, although in the case of SARS humans were infected by civet cats and in the case of MERS by infected camels as intermediate animal hosts, civet cats and camels in their turn appeared to be infected by bats as the primary virus reservoir. Therefore, distinction must be made between primary animal species in which coronaviruses normally circulate and the animal species in which the coronavirus variant emerges that transmitted the virus to humans: as secondary, intermediate host between the primary animal reservoir and humans. The transmission route of the SARS-CoV-2 to humans may therefore also involve intermediate animal hosts[8] .

Bats[edit]

Observations[edit]

  • Bats do harbour many viruses, including coronaviruses. Bats are implicated in many virus diseases, including severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), porcine epidemic diarrhea (PED) and severe acute diarrhea syndrome (SADS) [9]. Similarity of SARS-CoV-2 to bat SARS-like CoVs has been demonstrated particularly for virus RaTG13 sampled from a Rhinolophus affinis bat, which suggests that bats can serve as reservoir hosts for SARS-CoV-2 [10]. Other reports showed that 2019-nCoV is 96% identical at the whole-genome level to a bat coronavirus[11]. However, it is not known if bats are the primary reservoir and if they infected other animals more in contact with humans that caused the virus to so efficiently enter humans as a new host species. Although the bat SARS-like CoV uses the same cell entry receptor—angiotensin converting enzyme II (ACE2)—as virus SARS-CoV-2 found in humans [12], recently it was described that the Receptor Binding Domain (RBD) of coronaviruses isolated from Guangdong pangolin has more identical amino acids at the five critical residues of the RBD (97,4 % amino acid similarity in the RBD), than the bat-derived cornonaviruys RaTG13 that only shares one amino acid with SARSCoV-2 (89.2% amino acid similarity in the RBD)[13]. This RBD protein is crucial for the virus to attach to host cell proteins.

Analysis and Interpretation[edit]

  • Bats associated with COVID-19 are horshoe bats, a distinct group of bats but many people in China now want to expell all bats species. This is dangerous and even counterproductive as it risks further disrupting ecosystems and other viruses emerging from bats. Bats have important biologial role: they kill insects, acting as a biological pesticide and contribute to pollination and seed dispersal for many important plants [14].

Consequences for action[edit]

  • The concept of live (or "'wet") markets in Asia and Africa where all kinds of often illegal and poached wildlife is transported, traded, and slaughtered must be stopped.
  • The recent action in China making eating wild animals illegal[15], the banning in the Chinese city of Shenzen of eating cats and dogs[16], and the banning of eating pangolin and bats in Ghana in Africa [17] is a start but must be followed by a wider adoption and enforcement of stopping wild life trade and wet markets, which will require appropriate level of penalties to be effective.
  • Also disruption of ecosystems must be stopped as a general preventive measure, and be included in national policies that must more vigorously control existing and new companies involved in land use and deforestation.
  • Protect the bats and their habitats.
  • Ban all trade and consumption of bats.

Malayan pangolins[edit]

Observations[edit]

  • Malayan pangolins ( Manis javanica ) are among the most illegally trafficked mammals: traditional Chinese medicine utilises their scales, and the animals are also used as a food source. Most pangolin species now are regarded as critically endangered on the International Union for Conservation of Nature Red List of Threatened Species. [18][19].

Analysis and interpretation[edit]

  • In Malayan pangolins ( Manis javanica ) that were illegally imported into Guangdong province a coronavirus (CoV) has been found that was similar to SARS-CoV-2. However, no pangolin CoV has yet been identified that is sufficiently similar to SARS-CoV-2 across its entire genome to support direct human infection. The study suggested that another intermediate animal host is involved. As for the bats, it is not clear yet if pangolins are the primary reservoir and if they infected other animals more in contact with humans that caused the virus to so efficiently enter humans as a new host species[20]. However, two sublineages of the SARS-CoV-2-related coronavirus were identified in Malayan pangolins seized in anti-smuggling operations in southern China, of which one showed 97,4% homology with the human receptor-binding domain (RBD). The RBD protein is used by the virus to attach to host cell proteins such as to the human ACE2 protein present in lung epithelial tissue. [21]. This supports the hypothesis that humans present on the wet market in Wuhan contracted the virus from live pangolins illegally traded there.

Consequences for action[edit]

  • see under "Bats".
  • Protect the pangolins and their habitats.
  • Ban all trade and consumption of pangolins.

Tigers[edit]

Observations[edit]

  • End of March 2020 SARS-CoV-2 was found in a Malayan tiger at the Bronx zoo in New York. Samples from this tiger were taken and tested after several tigers and lions in the zoo developed coughing and wheezing. Public health officials believe these large cats became sick after being exposed to a zoo employee who was actively shedding virus. Only one tiger was tested from the ill lions and tigers as it requires putting the animals under general anesthesia to sample them [22],[23].

Analysis and interpretation[edit]

  • There is no reasons to fear cats nor tigers as important sources of infection for humans, human-to-human transmission remains the most important source to contract an infection. However, normal hygienic precaution must be taken in contact with all Felidae (cats and cat-alikes) avoiding close contact[24].

Consequences for action[edit]

  • See under Bats: protect habitats and ban all trade and consumption of tigers or tiger-derived products such as for traditional Chinese medicine.
  • See under pets: normal hygienic precautions

Mink[edit]

Observations[edit]

  • On 26 April, dutch media reported that SARS-CoV2 had infected mink farms in a southern province of the country. As far as is known, mink hardly contribute to the spread of coronavirus, according to RIVM and the Ministry of Agriculture. The ministry advises to avoid walking or cycling in close vicinity (400 meter radius) of the infected farms [25]
    • The minks showed various symptoms including respiratory problems. Investigations have been launched to determine the source of the infections. Because some employees had symptoms of the coronavirus at both companies, it is assumed that people are infected with animals. According to the RIVM, based on current knowledge about COVID-19, the mink companies do not pose a risk of further spread to humans. [26]

Analysis and Interpretation[edit]

  • This alert is very fresh, and updates are expected in the coming days.
  • There is evidence that ferrets are highly susceptible for Coronavirus.[27] It seems wise, therefore, that authorities recommend to avoid walking and cycling in proximity of the farms as further investigations are ongoing to assess the risks.

Consequences for Action[edit]

Pets[edit]

Observations[edit]

  • SARS-CoV-2 has been detected in dogs with evidence of only a limited (abortive) virus replication, but evidence of the possibility of more productive infection has been found in cats [28],[29]. This, with the finding of the virus in one tiger, suggests that cats can be productively infected, however, there is no evidence that cats are important in spreading of the virus; humans are still considered the most important source of contracting an infection.

People ask "Can my Dog or Cat be infected?" and "Can my pet infect me?"

  • On March 27, 2020, in Belgium a cat was reported to be infected by coronavirus by the faculty for veterinary medicine in Luik. The owner was infected with the coronavirus. The cat became ill one week after the owner was ill. However, no further evidence of further spread or other cases in cats were reported. [30].
  • On March 31, 2020, a Chinese study reported on susceptibility of ferrets and animals in close contact with humans to SARS-CoV-2. They report that "SARS-CoV-2 replicates poorly in dogs, pigs, chickens, and ducks, but efficiently in ferrets and cats. It was found that the virus transmits in cats via respiratory droplets". [31].

Analysis and interpretation[edit]

  • From the isolated report on the infected dog in HongKong from an infected owner[32], it can be speculated that the dog was infected by its owner rather than vice versa. However, even this would not be a cause for grave concern because there is no evidence that the virus rapidly multiplies in dogs, but suggests that an abortive infection took place and that the virus does not effectively infect dogs.

Consequences for action[edit]

  • With the evidence that cats may pose a risk of infection to humans, extra precautions are warranted for people living with or handling cats.
  • Further study is needed to understand to what extent cats can infect other cats or humans and if humans can infect cats. With this information, caution is needed when dealing with cats both in veterinary practice and in homes where people live with cats.

Questions about live animal markets[edit]

Observations[edit]

  • Live or so-called 'wet' animal markets are common in Asia, but also in Africa. There are "classical" live markets with mammals (sheep and goats, cattle, pigs), birds (poultry, geese, ducks) but also markets with wildlife, bushmeat (monkeys, snakes, reptiles, etc), and, mostly in Asia, also markets with mostly seafood. Many of the consumers who buy there appreciate buying living animals considering them "fresh" and "healthy" when killed on the market, or taken home and killed there for consumption[33],[34].
  • The biggest risk for spread of unknown viruses comes from wildlife species that are legally or illegally traded on such wet markets. For instance Malayan pangolins ( Manis javanica ) are the most illegally trafficked mammals: they are used as both a food source and their scales are utilized in traditional Chinese medicine. Based on available data from the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and data from UNODC’s World WISE database, illegal trade in pangolins between 1999 and 2017 involved an estimated 192,576 pangolins, far exceeding levels of legal trade in this period. This illegal trade involved all eight species and is based on 1,557 seizures that have taken place in Asian and African range States and non-range States. The majority of these seizures took place in 2006 or later and these analyses can, therefore, be considered an evaluation of pangolin trafficking in the last decade. [35][36].

Analysis and Interpretation[edit]

Are Fish, crustaceans, shellfish, amphibians related to spreading of COVID19 disease?

  • The Wuhan live market with seafood present was suspected, but no evidence of animal sources for SARS-CoV-2 among fish, crustaceans, shellfish, amphibians have been published to date. Other animal species (see Bats and Pangolins) are considered more important in the epidemiology of SARS-CoV-2[37].

References[edit]

  1. https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820%2930183-5
  2. https://www.thelancet.com/action/showPdf?pii=S0140-6736%2820%2930183-5
  3. https://sciencespeaksblog.org/2020/01/25/wuhan-coronavirus-2019-ncov-qa-6-an-evidence-based-hypothesis/
  4. 4.0 4.1 ECDC Rapid Risk Assessment SARS-CoV-2, 14 February 2020. https://www.ecdc.europa.eu/sites/default/files/documents/SARS-CoV-2-risk-assessment-14-february-2020.pdf.pdf
  5. Zhu N, Zhang D, Wang W, Li X, Yang B, Song J, et al. A Novel Coronavirus from Patients with Pneumonia in China, 2019. New England Journal of Medicine. 2020
  6. https://www.oie.int/en/scientific-expertise/specific-information-and-recommendations/questions-and-answers-on-2019novel-coronavirus/
  7. ECDC Questions and Answers on Coronavirus 2020. https://www.ecdc.europa.eu/en/novel-coronavirus-china/questions-answers
  8. https://www.oie.int/fileadmin/Home/eng/Our_scientific_expertise/docs/pdf/COV-19/COVID19_21Feb.pdf
  9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6356540/
  10. http://virological.org/t/the-proximal-origin-of-sars-cov-2/398
  11. https://www.nature.com/articles/s41586-020-2012-7.pdf
  12. https://www.nature.com/articles/s41586-020-2012-7.pdf
  13. https://www.nature.com/articles/s41586-020-2169-0_reference.pdf
  14. https://science.sciencemag.org/content/367/6485/1436.1/tab-pdf
  15. https://edition.cnn.com/2020/03/05/asia/china-coronavirus-wildlife-consumption-ban-intl-hnk/index.html
  16. https://www.bbc.com/news/world-asia-china-52131940
  17. https://www.pulse.com.gh/news/world/gabon-bans-eating-of-pangolin-and-bats-amid-pandemic/5lxnj3m
  18. https://cites.org/sites/default/files/eng/com/sc/69/E-SC69-57-A.pdf
  19. https://www.nature.com/articles/s41586-020-2169-0_reference.pdf
  20. http://virological.org/t/the-proximal-origin-of-sars-cov-2/398
  21. https://www.nature.com/articles/s41586-020-2169-0_reference.pdf
  22. https://www.aphis.usda.gov/aphis/newsroom/news/sa_by_date/sa-2020/ny-zoo-covid-19
  23. https://eu.usatoday.com/story/news/nation/2020/04/05/bronx-zoo-tiger-tests-positive-covid-19/2952027001/
  24. https://www.oie.int/en/scientific-expertise/specific-information-and-recommendations/questions-and-answers-on-2019novel-coronavirus/
  25. Niels Klaassen. Nu ook corona bij nertsen: welke rol spelen dieren bij de verspreiding? 26 apr 2020. AD. Laatste update: 16:00
  26. Ministry of Agriculture website. 26 April 2020. COVID-19 geconstateerd op twee nertsenbedrijven Nieuwsbericht
  27. Shi, J., Wen, Z., Zhong, G., Yang, H., Wang, C., Huang, B., ... & Zhao, Y. (2020). Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS–coronavirus 2. Science.
  28. https://www.cnbc.com/2020/02/28/a-dog-in-hong-kong-tests-positive-for-the-coronavirus-who-confirms.html
  29. https://www.biorxiv.org/content/10.1101/2020.03.30.015347v1
  30. https://www.vrt.be/vrtnws/nl/2020/03/27/kat-besmet-met-coronavirus-is-alleenstaand-geval-wat-nu-met-u/
  31. https://www.biorxiv.org/content/10.1101/2020.03.30.015347v1
  32. https://www.cnbc.com/2020/02/28/a-dog-in-hong-kong-tests-positive-for-the-coronavirus-who-confirms.html
  33. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6467964/
  34. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7017878/
  35. https://cites.org/sites/default/files/eng/com/sc/69/E-SC69-57-A.pdf
  36. https://www.nature.com/articles/s41586-020-2169-0_reference.pdf
  37. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7054940/