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Following previous reports of Covid-19 infection in two dogs in Hong Kong earlier in February and March,1-4 further test results have been released by the Government of the Hong Kong Special Administrative Region (GHKSAR), changing the serology interpretation previously reported (VR, 28 March 2020, vol 186, pp 388–389).3, 5
Despite several positive RT-PCR results suggesting a true infection in a Pomeranian dog, the dog had initially tested negative for antibodies specific to Covid-19 on a blood sample taken on 3 March 2020. Further serological testing of this sample at the WHO reference laboratory at the University of Hong Kong (HKU) was reported positive in late March.5
Antibody formation can take 14 days or more before it can be detected and this lag could explain why antibodies were not identified initially. However, a weak infection where antibodies do not develop is sometimes seen with other coronavirus infections in people.
This latest report of seroconversion means the dog created antibodies against the virus, suggesting that the weak infection would have caused an immune response from the dog and further supports a true infection caused by human-to-animal transmission. Similarities in gene sequencing (performed by the Agriculture, Fisheries and Conservation Department [AFCD] of Hong Kong and the School of Public Health of HKU) from the infected pet owner and the dog additionally supported human-to-animal transmission.
The consensus remains at this time that there is no evidence that infected pets are a source of infection for people or other pets
As mentioned in my previous letter, no virus was isolated during culture testing, implying an inability of the virus to grow in an ideal medium. The consensus remains at this time that there is no evidence that infected pets are a source of infection for people or other pets.
As of 25 March the AFCD had conducted tests on 17 dogs and eight cats, of which only two dogs had tested positive. Both dogs later tested negative on RT-PCR, indicating they were free of infection.
On 31 March, a third case, this time in a cat, was reported in Hong Kong by the GHKSAR . The cat had tested positive to Covid-19 on RT-PCR from oral, nasal and faecal samples but did not show any clinical signs of disease.6
Positive viral SARS-CoV-2 genes were also recently found in vomit and faeces from a cat tested at the University of Liège in Belgium, but more information is needed before any conclusions can be made.
A report from a veterinary diagnostic company said that thousands of samples from cats and dogs had been tested and all had been negative to date.7
The rapidly evolving nature of Covid-19 means significant further research is required to increase our understanding of this novel disease.
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