Serological and Molecular Surveillance for SARS-CoV-2 Infection in Captive Tigers (Panthera tigris), Thailand

SIMPLE SUMMARY: SARS-CoV-2 can infect a variety of domestic and wild animals worldwide. Therefore, tigers are a susceptible species and potential viral reservoirs. It is important to investigate COVID-19 disease exposure in these endangered animals. This study tested for SARS-CoV-2 neutralizing antibodies in 62 serum samples from captive tigers in Ratchaburi province, western Thailand during 2020–2021. In addition, nine swab samples were also collected from tigers with a history of exposure to COVID-19 patients; however, SARS-CoV-2 RNA was not detected in any of the swab samples. SARS-CoV-2 neutralizing antibodies against the Delta variant were found in samples collected from four zoo tigers in November 2021 when that variant was circulating widely in Thailand. In addition, cross-neutralization against Wuhan Hu-1 could be observed in all of the seropositive tiger serum samples while a low-level tier of neutralizing antibodies against the Omicron BA.2 subvariant could be found in only one seropositive tiger. The source of SARS-CoV-2 infection in these tigers most likely came from close contact with the infected animal caretakers who engaged in activities such as tiger petting and feeding. To the authors’ knowledge, this is the first case of natural SARS-CoV-2 infection in captive tigers during the COVID-19 outbreak in Thailand. We suggest that continuous surveillance of SARS-CoV-2 infection in captive tigers should be performed to prevent and control outbreaks of COVID-19 zoonotic disease. ABSTRACT: Coronavirus disease (COVID-19) is an emerging infectious disease caused by SARS-CoV-2. Given the emergence of SARS-CoV-2 variants, continuous surveillance of SARS-CoV-2 in animals is important. To monitor SARS-CoV-2 infection in wildlife in Thailand, we collected 62 blood samples and nine nasal- and rectal-swab samples from captive tigers (Panthera tigris) in Ratchaburi province in Thailand during 2020–2021. A plaque reduction neutralization test (PRNT) was employed to detect SARS-CoV-2 neutralizing antibodies. A real-time RT-PCR assay was performed to detect SARS-CoV-2 RNA. Our findings demonstrated that four captive tigers (6.5%, 4/62) had SARS-CoV-2 neutralizing antibodies against Wuhan Hu-1 and the Delta variant, while no SARS-CoV-2 RNA genome could be detected in all swab samples. Moreover, a low-level titer of neutralizing antibodies against the Omicron BA.2 subvariant could be found in only one seropositive tiger. The source of SARS-CoV-2 infection in these tigers most likely came from close contact with the infected animals’ caretakers who engaged in activities such as tiger petting and feeding. In summary, we described the first case of natural SARS-CoV-2 infection in captive tigers during the COVID-19 outbreak in Thailand and provided seroepidemiological-based evidence of human-to-animal transmission. Our findings highlight the need for continuous surveillance of COVID-19 among the captive tiger population and emphasize the need to adopt a One Health approach for preventing and controlling outbreaks of COVID-19 zoonotic disease.