Study of the seroprevalence of SARS-CoV-2 antibodies in domestic cats

The idea that coronavirus disease 2019 (COVID-19) is a zoonotic disease is very popular. The theory that the initial case was due to the transmission of a bat in a wet market in Wuhan gained media attention in the early months of the pandemic. While other theories have drawn more attention as it cannot be denied that the disease has shown several zoonotic events since then. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and variants have been identified in mink, several rodents and several zoo animals, including pumas, gorillas and snow leopards. In an article published in Emerging infectious diseases, researchers at the Hanover University of Veterinary Medicine studied the spread of the disease in domestic cats in Europe.

To study: SARS-CoV-2 – Specific antibodies in domestic cats during the first wave of COVID-19, Europe. Image Credit: TanyaPhOtOgraf / Shutterstock

The study

Many vaccines and treatments for the disease target spike protein for SARS-CoV-2. It is essential for the pathogenicity of the organism. The spike protein is a trimer with many copies that cover the surface of the virus and is made up of two subunits. S1 contains a receptor binding domain (RBD) which can bind to several receptors, including angiotensin converting enzyme 2 (ACE2), to allow entry of viral cells. The N-terminal domain of the S2 subunit is responsible for membrane fusion.

The researchers collected more than 2,000 samples in total from cats in Europe. Between April and June 2020, 1,136 samples were collected in Germany, 331 in the United Kingdom, 333 in Italy and 360 in Spain. About 1,800 of them contained information about the cat’s age, with an average age of 11. Twenty-five pre-pandemic cat serum samples and 25 cat samples were confirmed positive for the feline coronavirus.

Scientists used a plaque reduction virus neutralization (VNT) test to measure seroconversion by analyzing the rate of virus neutralization. They developed an indirect ELISA to detect RBD antibodies by replacing the anti-human IgG conjugate with an anti-cat IgG conjugate to further validate these results. The performance of this ELISA was evaluated using Pearson’s correlation, and the VNT was analyzed using Gaussian distribution analyzes.

In total, the seroprevalence of SARS-CoV-2 was around 4.2% in Germany, 3.3% in the United Kingdom, 4.2% in Italy and 6.4% in Spain. The two tests revealed similar results, with the VNT showing a total of 96 positive samples and the ELISA showing 92 positive samples. Gaussian distribution analyzes showed a strong correlation between the sensitivities of the new tests. Both controls showed negative results for all samples in both tests, confirming the specificity of the tests.

ELISA showed higher sensitivity and specificity than VNT. Still, VNT has been shown to be better at detecting low titer positive samples – possibly because it can detect a wider range of viruses –neutralizing antibodies. In contrast, ELISA can only detect anti-RBD antibodies.

While most COVID-19 infections in felines appear to have a mild or asymptomatic course, and there is little evidence of a common cat-to-human infection, the disease is likely to develop. is first transmitted to cats through a human-caused zoonotic event. Further investigation of the transmission of COVID-19 in animals and zoonotic events is important, as animal populations could constitute a reservoir for the disease. In other animals, such as mink, the spread of the disease between humans and mink is quite common, and there is some evidence that the disease could infect other primates as well.

Conclusion

The authors point out that their tests show very similar results and suggest that further testing for WT SARS-CoV-2 in felines be performed using their homemade ELISA, as there is no need for a live virus, thus avoiding the requirement for a biosafety level 3 laboratory. In addition, they suggest that to prevent cross infection between humans and domestic cats, infected people should maintain a social distance from their cats, wear masks when ‘they are in the same room and usually avoid close contact. The researchers admit that because all samples were sent to veterinary diagnostic laboratories for conditions other than COVID-19, they may not fully represent the European feline population.

However, this study provides valuable information on the spread of SAS-CoV-2 among feline populations and provides tools for further investigation. The same concept used for their ELISA could also be adapted to study the spread in other animals, which might be more susceptible to cross-infection with humans. As vaccination rates in the US and UK stagnate, it looks like the disease is likely to last much longer than expected. Understanding the zoonotic effects and the spread among pets could be extremely important in minimizing future outbreaks.