Coronaviruses are RNA viruses that infect both animals and humans. The current 2019 coronavirus disease (COVID-19) pandemic, caused by the severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2), has claimed more than 4 million lives worldwide.
This virus has been described as a zoonotic virus and could have come from bats with an unknown intermediate host. Scientists have suggested some potential intermediate hosts such as pangolins, rodents, and bats. However, the transmission dynamics associated with the virus jumping between species, including humans, are not clear.
Determination of far-reaching species that can be infected with SARS-CoV-2
Several studies have been conducted to identify the wide range of species that can be infected with SARS-CoV-2. Researchers have determined the affinity of the angiotensin converting enzyme 2 (ACE2) from different animal species for the SARS-CoV-2 spike protein (S). Previous research has shown that susceptibility to infection varies from species to species. Due to the high affinity of the virus to the ACE2 ortholog, cats and members of the Felidae family were found to be more susceptible to SARS-CoV-2. However, it has been found that dogs are less susceptible to the virus because of the lower expression of ACE2 in the airway cells.
Previous studies have reported that various viruses in the Coronaviridae family can infect domestic and wild cats. These viruses are classified as feline coronaviruses (FCoVs). These studies have shown that cats infected with the coronavirus can develop mild bowel disease (feline enteric coronavirus; FECV) or viruses can mutate and produce feline infectious peritonitis virus (FIPV). FIPV is more contagious and can cause serious illness that can be fatal.
The importance of investigating clinical signs of SARS-CoV-2 infection in cats
As a rule, domestic cats have a close relationship with their owners. Cats in the zoo or wildlife center are also very attached to their caretaker. Therefore, an increasing number of reports of SARS-CoV-2 infection in cats has created the need to understand the clinical implications of SARS-CoV-2 infection in cats.
A new systematic review has now been published in Animals magazine, focusing on clinical symptoms in cats diagnosed with SARS-CoV-2 worldwide.
Distribution of reported cases of SARS-CoV-2 in domestic and wild cats worldwide. Red circles indicate cases in domestic cats that were reported by country. The virus has been detected in these animals on at least three different continents (America, Europe and Asia). Yellow triangles mark cases in captive wild cats that have been reported in the Americas, Europe and Africa.
Scientists who conducted this review implemented various search strategies to obtain research on felidae diagnosed with SARS-CoV-2 infection from the existing databases and found 19 articles and 65 detailed reports from official sources.
The World Organization for Animal Health (OIE) website was the main official source of information. The authors found evidence of 76 domestic cats in the USA with confirmed SARS-CoV-2 infection. However, in these cases only 22 documented relevant pieces of information on the occurrence or absence of clinical symptoms.
A global distribution pattern was observed in felids infected with SARS-CoV-2. However, most of the cases were reported in America and Europe. Such an observation coincides with the fact that these regions were massively affected by the COVID-19 infection. Limited studies of felid infection from other severely affected areas such as India and Brazil are available.
Clinical symptoms of SARS-CoV-2 infection in cats
Both domestic and wild cats are said to be infected with SARS-CoV-2. The following section describes the clinical symptoms associated with the disease.
Domestic cats
The cats were asymptomatic in 54% of the cases. They were identified because their owners were diagnosed with COVID-19. Out of curiosity, the researchers examined the cats for the disease and, interestingly, found that they were COVID-19 positive.
In the remaining 46% of cases, the cats showed clinical symptoms related to COVID-19 infection. Of these infected felids, 26 survived and six died as a result of the infection.
One of the reports showed that cats developed shortness of breath and tachypnea. They were also diagnosed with hypertrophic cardiomyopathy and Mycoplasma haemofelis infection.
One of the cats that died from the disease showed clinical symptoms such as nasal discharge and neurological symptoms such as headache. The autopsy symptoms indicated that the cat developed bacterial meningoencephalitis.
The cats infected with COVID-19 were also diagnosed with anemia, thrombocytopenia, and hypertrophic cardiomyopathy. An ultrasound scan showed a broncho-interstitial pattern in the lungs.
In addition, tissue analysis in the infected cats showed signs of severe pulmonary edema, bleeding and congestion. Some of the other symptoms such as vomiting, mouth ulcers, and diarrhea have also been reported.
Wild cats
Several cases of SARS-CoV-2 infections in wild cats have been reported worldwide. Scientists have shown that members of the genus Panthera (e.g. tigers, lions and snow leopards) and the genus Puma (e.g. Puma concolor) are infected with the virus.
SARS-CoV-2 infection in wild cats has been linked to human-to-animal transmission, although the staff responsible for caring for these animals have been COVID-19 positive and may have transmitted the disease to the animals.
All animals that tested positive for SARS-CoV-2 (except for one asymptomatic tiger) showed clinical signs such as coughing and wheezing. In addition to respiratory symptoms, other symptoms such as loss of appetite and lethargy have been reported.
Felid species reported with SARS-CoV-2 infection. SARS-CoV-2 infection has been reported in members of two subfamilies, Pantherinae and Felinae, belonging to the Felidae family. Despite the obvious morphological differences between pantherids and cats, the virus is able to infect members of these two dissimilar families and cause very similar clinical symptoms.
Conclusions
Experimental studies have shown that cats previously infected with SARS-CoV-2 can be re-infected with the virus. However, infected cats could not transmit the infection to another healthy cat.
Histopathological studies showed that SARS-CoV-2 infection could cause lesions of the nasal and tracheal mucosa and the lung parenchyma. This may be due to the fact that virus replication takes place in these tissues. The histopathological lesions showed purulent lymphoplasmacytic rhinitis of the turbinates and lymphoplasmacytic tracheitis and alveolar histiocytosis.
The authors conclude: “Given the current complex situation created by the COVID-19 pandemic and the emergence of viruses with zoonotic potential, it is of the utmost importance to put in place both national and international surveillance systems to monitor the development and the occurrence of SARS-CoV-2 and other pathogens of public health concern in animals and its possible “spillover” on humans and the possible “spill-back” – leading to public health concerns – emphasizing, that all efforts on the concept and implementation of “One Health / One Medicine” in order to understand how aspects affecting the environment, animals and humans could contribute significantly to epidemic control in the near future. “