Zoonotic Diseases at the Zoo: How Big Cats Became Infected with SARS-CoV-2 at the Bronx Zoo
Written by Erica Wang
Edited by Justin Gambill
March 21, 2022
Edited by Justin Gambill
March 21, 2022
Unsurprisingly, human-to-human transmission of SARS-CoV-2 is at the forefront of research and public concern. It is believed that the virus originated from horseshoe bats [1,2] and then spread to humans. How easily could Covid-19 spread back to other non-human animals? This question was partially answered in March of 2020, when four tigers and three lions became infected with SARS-CoV-2 at the Bronx Zoo in New York [3]. Previously, there have been instances of infected domestic dogs, cats, and farmed mink [4-6], but these big cats were the first nondomestic animals to test positive for the virus. Analysis of the specific mutations in the SAR-CoV-2 viral DNA sequence showed that the tigers had been infected by their keepers.
On March 27, 2020, a Malayan tiger at the Bronx Zoo began coughing and wheezing. A few days later, three other tigers (one Malayan and two Amur) and three African lions developed similar respiratory symptoms. Investigators conducted thorough physical exams and collected respiratory tract and fecal samples to diagnose them. Common feline pathogenic infections were ruled out and they all tested positive for SARS-CoV-2 by reverse transcription polymerase chain reaction, or RT-PCR. PCR is a technique used to amplify a genetic sample in order to detect genetic components from certain organisms, such as the SARS-CoV-2 virus. During this time period, the zoo had mostly been closed to the public. That left the possible transmission to a small group of zoo staff that had close contact with the big cats.
During this timeline, two tiger keepers and two lion keepers reported having mild Covid-19 symptoms. The four keepers were tested and showed evidence of current or prior infection of SARS-CoV-2. Upon closer genetic analysis, the strains between the tigers and one of the tiger keepers were similar enough to conclude that the tigers had been infected by their keeper. Additionally, the lions were infected by a separate strain from that of the tigers. An asymptomatic personnel might have exposed the lions to the virus. The tigers and lions were housed in separate buildings in different parts of the zoo. They did not share any equipment, so the lions were not infected by the tigers nor the tiger keepers.
What makes a species more vulnerable to SARS-CoV-2? Some preliminary research suggests that felines are more vulnerable because they have an ACE2 receptor on their cells that is similar to the ACE2 receptors in human cells [7]. ACE2 is the receptor responsible for binding to the SARS-CoV-2 spike 1 protein which allows the virus to infect its host. The discovery of the transmission between keepers to the big cats spurred the use of personal protective equipment protocols for susceptible species at the Bronx Zoo and other wildlife organizations, which had not been outlined before, except in primates. Cases like these reinforce the need for more diligence when it comes to zoonotic diseases, especially as humans continue to interact with wildlife through recreation and resource management.
References
- McAloose D, Laverack M, Wang L, Killian ML, Caserta LC, Yuan F, Mitchell PK, Queen K, Mauldin MR, Cronk BD, Bartlett, SL, Sykes JM, Zec S, Stokol T, Ingerman K, Delaney MA, Fredrickson R, Ivanˇic’ M, Jenkins-Moore M, Mozingo K, Franzen K, Bergeson NH, Goodman L, Wang H, Fang Y, Olmstead C, McCann C, Thomas P, Goodrich E, Elvinger F, Smith DC, Tong S, Slavinski S, Calle PP, Terio K, Torchetti MK, Diel DG. 2020. From people to Panthera: natural SARS-CoV-2 infection in tigers and lions at the Bronx Zoo. mBio 11: e02220-20. https:// doi.org/10.1128/mBio.02220-20.
- Zhou P, Yang XL, Wang XG, Hu B, Zhang L, Zhang W, Si HR, Zhu Y, Li B, Huang CL, Chen HD, Chen J, Luo Y, Guo H, Jiang RD, Liu MQ, Chen Y, Shen XR, Wang X, Zheng XS, Zhao K, Chen QJ, Deng F, Liu LL, Yan B, Zhan FX, Wang YY, Xiao GF, Shi ZL. 2020. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 579: 270-273. https://doi.org/10.1038/s41586-020-2012-7.
- Andersen KG, Rambaut A, Lipkin WI, Holmes EC, Garry RF. 2020. The proximal origin of SARS-CoV-2. Nat Med 26: 450-452. https://doi.org/10 .1038/s41591-020-0820-9.
- Sit THC, Brackman CJ, Ip SM, Tam KWS, Law PYT, To EMW, Yu VYT, Sims LD, Tsang DNC, Chu DKW, Perera RAPM, Poon LLM, Peiris M. 2020. Infection of dogs with SARS-CoV-2. Nature https://doi.org/10.1038/ s41586-020-2334-5.
- Newman A, Smith D, Ghai RR, Wallace RM, Torchetti MK, Loiacono C, Murrell LS, Carpenter A, Moroff S, Rooney JA, Barton Behravesh C. 2020. First reported cases of SARS-CoV-2 infection in companion animals - New York, March-April 2020. MMWR Morb Mortal Wkly Rep 69: 710 –713.https://doi.org/10.15585/mmwr.mm6923e3.
- Oreshkova N, Moelnaar RJ, Vreman S, Harders F, Munnink BBO, Hakze- van der Honing RW, Gerhards N, Tolsma P, Bouwstra R, Sikkema RS, Tacken MGJ, de Rooij MMT, Weesendorp E, Engelsma MY, Bruschke CJ, Smit LA, Koopman M, van der Poel WH, Stegeman A. 2020. SARS-CoV-2 infection in farmed minks, the Netherlands, April and May 2020. Euro Surveill 25: 2001005. https://doi.org/10.2807/1560-7917.ES.2020.25.23 .2001005.
- Luan J, Lu Y, Jin X, Zhang L. 2020. Spike protein recognition of mam- malian ACE2 predicts the host range and an optimized ACE2 for SARS- CoV-2 infection. Biochem Biophys Res Commun 526: 165-169. https:// doi.org/10.1016/j.bbrc.2020.03.047.