You are presented with a paragraph from a COVID-19 literature. Classify the topics of this piece of text by choosing from the following categories:

- Epidemic Forecasting: The content relates to predictions about the spread of COVID-19.
- Treatment: The paragraph discusses therapeutic methods or medication for COVID-19.
- Prevention: The content covers measures to prevent the spread of COVID-19.
- Mechanism: The paragraph explains the biological mechanisms of the virus.
- Case Report: The content is a report of a COVID-19 case.
- Transmission: The paragraph discusses how COVID-19 is transmitted.
- Diagnosis: The content is about diagnosing COVID-19 in individuals.

Your classification should be provided as an element within a JSON array. The array should be formatted with topics enclosed in double quotes and separated by commas, following the JSON format, for example: ["Topic1", "Topic2", ...]. Include all applicable topics within the array. Your output should be a valid JSON array, and no additional text should be included in your response.

Article:

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the zoonotic causative agent of coronavirus disease 2019 (COVID-19) that has caused a pandemic situation with millions of infected humans worldwide. Among domestic animals, there have been limited studies regarding the transmissibility and exposure to the infection in natural conditions. Some animals are exposed and/or susceptible to SARS-CoV-2 infection, such as cats, ferrets and dogs. By contrast, there is no information about the susceptibility of ruminants to SARS-CoV-2. This study tested the antibody response in 90 ovine pre-pandemic serum samples and 336 sheep serum samples from the pandemic period (June 2020 to March 2021). In both cases, the animals were in close contact with a veterinary student community composed of more than 700 members. None of the serum samples analyzed was seroreactive based on an enzyme-linked immunosorbent assay (ELISA) using the receptor-binding domain (RBD) of the spike antigen. In this sense, no statistical difference was observed compared to the pre-pandemic sheep. Our results suggest that it seems unlikely that sheep could play a relevant role in the epidemiology of SARS-CoV-2 infection. This is the first study to report the absence of evidence of sheep exposure to SARS-CoV-2 in natural conditions.
["Transmission"]