FELINE INFECTIOUS DISEASES: GENETIC CHARACTERIZATION OF EMERGING AND ZOONOTIC PATHOGENS

Cats are one of the most common companion animals worldwide. Emerging viruses have been reported in cats worldwide in the last decades. Feline emerging viruses, including domestic cat hepadnavirus (DCH), may play an important role in cat diseases and evaluation of their presence, genetic characterization and pathogenicity is required to investigate the impact on feline health. Owing to their close and direct contact with humans, it is also important to understand the role of cats in the epidemiology of emerging viruses that represent a threat to humans, such as the pandemic severe acute respiratory coronavirus 2 (SARS-CoV-2). Besides viruses, antimicrobial resistant bacteria have become one of the major threats to public health and, according to the One Health concept, the presence of multidrug-resistant bacteria should also be monitored in cats. Therefore, the aims of this PhD thesis were i) to evaluate the presence, genetic characterization and impact of the novel DCH on feline health (studies I-II) ii) to investigate the role of cats in SARS-CoV-2 epidemiology (studies III-V), and iii) to study the faecal carriage of antimicrobial-resistant (AMR) Escherichia coli in cats (studies VI-VII). Starting with DCH, we investigated the presence of the virus in cats and its potential pathogenicity by analysis of cats with and without biochemical alterations suggestive of liver disease (study I) and cats with and without cavitary effusion (study II). Phylogeny showed that DCH sequences from study II clustered with the prototypic Australian strain but were not included in the clade with other Italian DCH sequences, showing the circulation of two different groups of DCH in Italy. Moreover, DCH was detect in both animals with and without biochemical changes associated with liver disease and in cats with cavitary effusions suggesting that DCH may not be a significant feline pathogen but further studies are needed to confirm these findings. To investigate the role of cats in the current coronavirus disease 2019 (COVID-19) pandemic, in study III we evaluated the presence of SARS-CoV-2 RNA and anti-SARS-CoV-2 antibodies in stray cats from colonies located in an Italian area highly affected by the COVID-19 pandemic. Results suggested that stray cats may not have a significant role in the spreading of SARS-CoV-2 in an area highly affected by the COVID-19 pandemic. In study IV we investigated whether cats and dogs living in close contact with COVID-19-positive patients may act as passive mechanical carriers of SARS-CoV-2 via contamination of hair or paws. The results showed that pets do not likely play an epidemiological role in the indirect transmission of SARS-CoV-2 to humans, even if in contact with COVID-19 positive owners. In study V we studied the diagnostic performances of three different commercially available immunoassays for the detection of SARS-CoV-2 antibodies in pets, in comparison with the gold standard virus neutralization test. Our results showed that assay validation is a fundamental step for epidemiological surveillance in pets and surrogate virus neutralization test may be an effective method that does not require a biosafety level-3 laboratory for predicting serum neutralization antibodies in cats and dogs. In studies VI and VII we investigated the faecal carriage of ESBL-/AmpC- and carbapenemase-producing E. coli in cats. ESBL-/AmpC- or carbapenemase-producing E. coli were detected in both stray and domestic cats, and their presence was associated with unhealthy status, previous antimicrobial therapy and hospitalization. Our results suggested that cats may have a role as potential carriers of ESBL/AmpC/carbapenemase-producing E. coli highlighting the need of antimicrobial stewardship in veterinary medicine. In conclusion, the results of this thesis allowed the preliminary evaluation of the pathogenic role of DCH in cats and further studies with a larger sample size will be necessary to confirm our results. Despite cats may not play an important epidemiological role in the spread of SARS-CoV-2, continuous monitoring of SARS-CoV-2 infection in cats may be suggested given the emergence of new viral variants. Ultimately, the role of cats as carriers of ESBL/AmpC/carbapenemase-producing E. coli needs to be further explored with a One Health approach in order to understand the risk of transmission to humans.