Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is the cause of Coronavirus Disease 2019 (COVID-19) and responsible for the current pandemic. Recent SARS-CoV-2 susceptibility studies in cats show that the virus can replicate in these companion animals and transmit to other cats. Here, we present an in-depth study of SARS-CoV-2 infection, disease and transmission in domestic cats. Cats were challenged with SARS-CoV-2 via intranasal and oral routes. One day post challenge (DPC), two sentinel cats were introduced. Animals were monitored for clinical signs, clinicopathological abnormalities and viral shedding. Postmortem examinations were performed at 4, 7 and 21 DPC. Viral RNA was not detected in blood but transiently in nasal, oropharyngeal and rectal swabs and bronchoalveolar lavage fluid as well as various tissues. Tracheobronchoadenitis of submucosal glands with the presence of viral RNA and antigen was observed in airways of the infected cats. Serology showed that both, principals and sentinels, developed antibodies to SARS-CoV-2. All animals were clinically asymptomatic during the course of the study and capable of transmitting SARS-CoV-2 to sentinels. The results of this study are critical for understanding the clinical course of SARS-CoV-2 in a naturally susceptible host species, and for risk assessment.

The arterivirus family (order Nidovirales) of single-stranded, positive-sense RNA viruses includes porcine respiratory and reproductive syndrome virus and equine arteritis virus (EAV). Their replicative enzymes are translated from their genomic RNA, while their seven structural proteins are encoded by a set of small, partially overlapping genes in the genomic 39-proximal region. The latter are expressed via synthesis of a set of subgenomic mRNAs that, in general, are functionally monocistronic (except for a bicistronic mRNA encoding the E and GP2 proteins). ORF5, which encodes the major glycoprotein GP5, has been used extensively for phylogenetic analyses. However, an in-depth computational analysis now reveals the arterivirus-wide conservation of an additional AUG-initiated ORF, here termed ORF5a, that overlaps the 59 end of ORF5. The pattern of substitutions across sequence alignments indicated that ORF5a is subject to functional constraints at the amino acid level, while an analysis of substitutions at synonymous sites in ORF5 revealed a greatly reduced frequency of substitution in the portion of ORF5 that is overlapped by ORF5a. The 43-64 aa ORF5a protein and GP5 are probably expressed from the same subgenomic mRNA, via a translation initiation mechanism involving leaky ribosomal scanning. Inactivation of ORF5a expression by reverse genetics yielded a severely crippled EAV mutant, which displayed lower titres and a tiny plaque phenotype. These defects, which could be partially complemented in ORF5a-expressing cells, indicate that the novel protein, which may be the eighth structural protein of arteriviruses, is expressed and important for arterivirus infection. INTRODUCTIONArteriviruses are enveloped viruses (approx. 60 nm diameter) with a 13-16 kb positive-sense RNA genome. The family Arteriviridae (Snijder & Meulenberg, 1998; currently comprises four members: equine arteritis virus (EAV, the family prototype), lactate dehydrogenase-elevating virus (LDV) of mice, porcine reproductive and respiratory syndrome virus (PRRSV) and simian haemorrhagic fever virus (SHFV). The consequences of arterivirus infection can range from an asymptomatic, persistent or acute infection to abortion or lethal haemorrhagic fever (Maclachlan et al., 2007). Three of the four arteriviruses (EAV, LDV and SHFV) were first isolated and characterized approximately 50 years ago.In the late 1980s, two distantly related PRRSV genotypes, European (PRRSV-EU) and North American (PRRSV-NA), sharing a genome-wide mean nucleotide identity of only~63 % (Allende et al., 1999; Suárez et al., 1996), emerged simultaneously on both sides of the Atlantic (Collins et al., 1992;Wensvoort et al., 1991). Since then, the virus has been causing worldwide epidemics of a previously unknown reproductive and respiratory disease and has become one of the most economically important swine diseases. Recently, a large outbreak of highly virulent PRRSV affected the Asian swine industry, causing considerable economic losses (Zhou & Yang, 2010).The unification of the ...

In this review, we mainly focus on zoonotic encephalitides caused by arthropod-borne viruses (arboviruses) of the families Flaviviridae (genus Flavivirus) and Togaviridae (genus Alphavirus) that are important in both humans and domestic animals. Specifically, we will focus on alphaviruses (Eastern equine encephalitis virus, Western equine encephalitis virus, Venezuelan equine encephalitis virus) and flaviviruses (Japanese encephalitis virus and West Nile virus). Most of these viruses were originally found in tropical regions such as Africa and South America or in some regions in Asia. However, they have dispersed widely and currently cause diseases around the world. Global warming, increasing urbanization and population size in tropical regions, faster transportation and rapid spread of arthropod vectors contribute in continuous spreading of arboviruses into new geographic areas causing reemerging or resurging diseases. Most of the reemerging arboviruses also have emerged as zoonotic disease agents and created major public health issues and disease epidemics.

The emergence of SARS-CoV-2 has resulted in an ongoing global pandemic with significant morbidity, mortality, and economic consequences. The susceptibility of different animal species to SARS-CoV-2 is of concern due to the potential for interspecies transmission, and the requirement for pre-clinical animal models to develop effective countermeasures. In the current study, we determined the ability of SARS-CoV-2 to (i) replicate in porcine cell lines, (ii) establish infection in domestic pigs via experimental oral/intranasal/intratracheal inoculation, and (iii) transmit to co-housed naïve sentinel pigs. SARS-CoV-2 was able to replicate in two different porcine cell lines with cytopathic effects. Interestingly, none of the SARS-CoV-2-inoculated pigs showed evidence of clinical signs, viral replication or SARS-CoV-2-specific antibody responses. Moreover, none of the sentinel pigs displayed markers of SARS-CoV-2 infection. These data indicate that although different porcine cell lines are permissive to SARS-CoV-2, five-week old pigs are not susceptible to infection via oral/ intranasal/intratracheal challenge. Pigs are therefore unlikely to be significant carriers of SARS-CoV-2 and are not a suitable pre-clinical animal model to study SARS-CoV-2 pathogenesis or efficacy of respective vaccines or therapeutics.

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