Applicability of a colorimetric reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for SARS-CoV-2 detection in high exposure risk setting.

OBJECTIVES: During the third wave, the growing number of COVID-19 case clusters reported countrywide in Thailand demonstrated the rapidly evolving characteristics of SARS-CoV-2, the causative agent of the COVID-19 pandemic. The rapid spread of COVID-19 infections had been extensively reported in public areas and construction camps, as well as in congested communities with poor sanitation. High demand for SARS-CoV-2 genome testing and quick reporting by an hour for case identification and isolation characterizes the COVID-19 crisis in Thailand. This situation leads to an urgent need for alternative molecular tests which are reliable, rapid, and cost-effective. METHODS: In this study, we assessed colorimetric reverse transcription loop-mediated isothermal amplification (RT-LAMP), using real-time reverse transcription-polymerase chain reaction (RT-PCR) as a reference standard, for active case finding in suspected (mostly asymptomatic) cases living in high-risk areas of Bangkok. RESULTS: The diagnostic performance of the RT-LAMP compared with real-time RT-PCR in specimens from 549 Thais were computed in a real-world field study setting. Our study demonstrated that RT-LAMP achieved robust identification of SARS-CoV-2 infection, with a diagnostic sensitivity and specificity of 91.67% and 100%, respectively. CONCLUSION: RT-LAMP is a reliable assay for SARS-CoV-2 detection and is scalable for use in the emergency response to a nationwide pandemic, despite resource limitations. The RT-LAMP real-world data derived from this field study validate its potential use in laboratory practice. RT-LAMP is a good choice as a laboratory-based SARS-CoV-2 molecular test when real-time RT-PCR is not available.

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

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.