Coronaviruses (CoVs) are enveloped, positive-sense, single-stranded RNA viruses. SARS-CoV-2 is a betacoronavirus, a genus that includes several coronaviruses (SARS-CoV, MERS-CoV, bat SARS-like CoV, and others) isolated from humans, bats, camels, and other animals.

Although current evidence suggests that SARS-CoV-2 emerged from an animal source, that source has yet to be identified. The pandemic is driven by person to person transmission through respiratory droplets from coughing, sneezing, and talking. Genetic sequence data reveal that SARS-CoV-2 is genetically closely related to other coronaviruses circulating in Rhinolophus bat (horseshoe bat) populations. To date, there is not enough scientific evidence to identify the source of SARS-CoV-2 or to explain the original route of transmission to humans (which may involve an intermediate host).

Several animal species have tested positive for SARS-CoV-2, mostly as a result of close contact with humans infected with SARS-CoV-2. In addition, preliminary findings from experimental infection studies suggest that poultry and pigs are not susceptible to SARS-CoV-2 infection. The list of animal species for which information on natural or experimental infection is available is presented in Table 1.

Table 1. Summary of findings in animals to date

Information on the routes of transmission of SARS-CoV-2 among animals is limited. However, as for other respiratory viruses, it appears to be transmitted to animals and between animals by direct contact (e.g. droplets). SARS-CoV-2 has been found in secretions from the respiratory tract and in faeces.

In laboratory settings, the incubation period in animals appears to be similar to the one seen in humans (i.e. between 2 and 14 days, with a mean duration of 5 days). However, more studies are required to solidly estimate the mean duration of incubation and the infectious periods.

The main source of the virus is respiratory droplets and respiratory secretions, although it is possible to isolate SARS-CoV-2 from faeces of infected animals.

In laboratory settings, infected animals showed presence of the virus in the respiratory tract and, in some cases, lesions in the trachea and lungs, associated with dyspnoea and cough.

There have been sporadic reports of companion animals and captive wild animals infected with SARS-CoV-2. With regard to production animals, to date, SARS-CoV-2 has only affected mink farms in the Netherlands, with high morbidity and low mortality.

Knowledge about clinical disease manifestations in animals is limited. Current evidence suggests clinical signs may include, but are not limited to, coughing, sneezing, respiratory distress, nasal discharge, ocular discharge, vomiting or diarrhoea, fever, and lethargy. As in humans, asymptomatic infections occur.

More studies are needed to systematically categorise the lesions resulting from infection with SARS-CoV-2 in animals.

In transgenic mice expressing the human version of the SARS-CoV-2 ACE2 receptor, the typical histopathology outcome was interstitial pneumonia with significant inflammatory cell infiltration around the bronchioles and blood vessels, and viral antigens were detected in bronchial epithelial cells and alveolar epithelial cells. These pathological findings were not seen in wild type mice infected with SARS-CoV-2. In golden Syrian hamsters, histopathological changes were reported in the respiratory tract and spleen. Rhesus macaques infected with SARS-CoV-2 presented lesions similar to those seen in humans. Juvenile cats infected with SARS-CoV-2 presented massive lesions in the nasal and tracheal mucosa epithelia, and lungs. SARS-CoV-2 can replicate in the upper respiratory tract of ferrets without causing severe disease and only resulting in pathological findings such as severe lymphoplasmacytic perivasculitis and vasculitis, increased numbers of type II pneumocytes, macrophages, and neutrophils in the alveolar septa and alveolar lumen, and mild peribronchitis in the lungs.

All other causes for respiratory or digestive illness should be excluded before a tentative diagnosis for infection with SARS-CoV-2 is made. Existence of an epidemiological link with a confirmed infection, in humans or other animals should be considered when narrowing down the list of differential diagnoses.

Laboratory confirmatory tests are necessary for a final diagnosis.

Samples

Depending on the type of test, samples may include single or combinations of oropharyngeal, nasal, and rectal swabs, and blood. Faecal samples may be used in situations where direct sampling is not possible due to risks to the animal or testing staff. Tests should be validated for the purpose, species and matrix to be analysed.

Procedures

Agent identification

• Reverse-transcription polymerase chain reaction (RT-PCR);
  
• Reverse transcription loop-mediated isothermal amplification (RT-LAMP);
  
• Other molecular tests developed for use in humans;
  
• Virus isolation;
  
• Virus genome sequencing.
  

Detection of immune response:

• ELISA antibody test;
  
• Virus neutralisation test (VNT);
  
• Several other tests for antibody detection.