Seroprevalence of Anti-SARS-CoV-2 Antibodies in Cats during Five Waves of COVID-19 Epidemic in Thailand and Correlation with Human Outbreaks

Abstract

Human-to-animal SARS-CoV-2 transmission was observed, including a veterinarian contracting COVID-19 through close contact with an infected cat, suggesting an atypical zoonotic transmission. This study investigated the prevalence of SARS-CoV-2 antibodies in cats during human outbreaks and elucidated the correlation between cat infections and human epidemics. A total of 1107 cat serum samples were collected and screened for SARS-CoV-2 antibodies using a modified indirect ELISA human SARS-CoV-2 antibody detection kit. The samples were confirmed using a cPass™ neutralization test. The SARS-CoV-2 seropositivity rate was 22.67% (199/878), mirroring the trend observed in concomitant human case numbers. The waves of the epidemic and the provinces did not significantly impact ELISA-positive cats. Notably, Chon Buri exhibited a strong positive correlation (r = 0.99, p = 0.009) between positive cat sera and reported human case numbers. Additionally, the cPass™ neutralization test revealed a 3.99% (35/878) seropositivity rate. There were significant differences in numbers and proportions of positive cat sera between epidemic waves. In Samut Sakhon, a positive correlation (r = 1, p = 0.042) was noted between the proportion of positive cat sera and human prevalence. The findings emphasize the need for ongoing surveillance to comprehend SARS-CoV-2 dynamics in both human and feline populations.

Keywords: COVID-19; SARS-CoV-2; Thai; cat; correlation; indirect ELISA; seroprevalence; surrogate viral neutralization assay.

Figure 1

Map of Thailand showing the studied provinces and highlighting the distribution of SARS-CoV-2-positive cat sera detected by cPass™ (% true seropositivity) and the percentages of SARS-CoV-2-positive cat sera detected by indirect ELISA (green).

Figure 2

Number of reported human cases in relation to the epidemic’s waves in 5 provinces.

Figure 3

Numbers of ELISA-positive cat serum samples in relation to waves of the epidemic (A) and province (C) and proportions of ELISA-positive cat sera separated in relation to waves of the epidemic (B) and province (D).

Figure 4

Correlation between number of reported human cases and number of indirect ELISA-positive cat serum samples in four locations: Bangkok–Pathum Thani; r = 0.77, p = 0.23 (A), Chon Buri; r = 0.99, p = 0.009 (B), Samut Sakhon; r = 0.98, p = 0.12 (C) and Phuket; r = 0.89, p = 0.11 (D) and correlation between number of reported human cases and the proportion of indirect ELISA-positive cat sera in four locations: Bangkok–Pathum Thani; r = 0.31, p = 0.69 (E), Chon Buri; r = 0.89, p = 0.11 (F), Samut Sakhon; r = 0.61, p = 0.58 (G) and Phuket; r = 0.064, p = 0.94 (H).

Figure 5

Number of true positive cat serum samples (cPass™) in relation to waves of the epidemic (A) and province (C) and the percentages of true positive cat serum samples (cPass™) separated in relation to waves of the epidemic (B) and province (D).

Figure 6

Statistical analyses of the prevalence of reported human cases and number of true positive cat sera (cPass™) in four locations: Bangkok–Pathum Thani; ρ = 0.63, p = 0.37 (A), Chon Buri; r = 0.59, p = 0.41 (B), Samut Sakhon; r = 0.94, p = 0.22 (C), and Phuket; r = 0.61, p = 0.39 (D), and of the prevalence of reported human cases and percentages of true positive cat sera (cPass™) in four locations: Bangkok–Pathum Thani; r = 0.70, p = 0.30 (E), Chon Buri; r = 0.87, p = 0.13 (F), Samut Sakhon; r = 1, p = 0.042 (G), and Phuket; ρ =0.74, p = 0.26 (H).