Seroepidemiological studies of coronavirus and influenza A virus infections in companion animals

Coronaviruses and influenza A viruses are notorious for crossing host species barriers and their potential emergence upon zoonotic introduction poses a substantial threat to public health. In addition to animal health implications, the close contact between companion animals and humans also has potential risks of zoonotic virus infection. High-quality serological assays are key to understand the prevalence of and immunity to virus infections. In this thesis, we focused on the development of robust and specific serological assays that can serve as a toolkit for rapid diagnosis of CoVs and IAVs infections. This will give more insight and knowledge on the occurrence of different CoVs and IAVs infections in companion animals and their association with clinical diseases. In Chapter 2, we set out to detect CoV infection in cats through profiling of antibody presence in cat serum samples. Recombinant CoV spike S1 proteins of different animal and human CoVs were used as antigens for screening of cat sera for the presence of antibodies against the respective proteins. Positive samples were further tested by virus neutralization assays. This investigation intends to extend our knowledge of CoV epidemiology, potential reservoirs, and cross-species transmission. Chapter 3 describes the development and validation of an S1-protein-based ELISA method for the detection of specific antibodies against ECoV. With this method, we are able to provide a consolidated diagnostic test to confirm ECoV outbreaks, as a complement to qRT-PCR analysis of equine feces samples. In addition, this method will be used for future estimation of ECoV prevalence and incidence in various equine (sub) populations. In Chapter 4, we performed a survey to follow and study the spread of SARS-CoV-2 in companion animals. A set of serological assays including ELISA and virus neutralization were developed and validated and next used to conduct the first seroprevalence study in the Netherlands. This will provide information regarding the potential risk of animal infections for public health in the later stages of the pandemic, especially when SARS-CoV-2 transmission between humans is greatly reduced and virus reservoir in animals could become more important. Except for studies of CoVs, in Chapter 5, we also developed a pipeline of serological assays which allow broad to specific analysis of IAV-specific antibody responses in cats and dogs. In this pipeline, serum samples were tested first with HA- and HA1-specific ELISAs and subsequently analyzed by nanoparticle-based, virus-free HI assays. We also demonstrated the value of using comprehensive serological assays to analyze IAV antibodies. Finally, in Chapter 6, the main findings presented in this thesis are discussed and summarized, along with yet unpublished observations