Prospective cohort; Ecological
Study population and setting
The study focuses on fifteen dogs and seven cats from households with known COVID-19 cases that were quarantined and tested by the Hong Kong Agriculture, Fisheries, and Conservation Department in Hong Kong, China, as of March 27, 2020.
Summary of Main Findings
Two dogs out of the fifteen tested positive for SARS-CoV-2: a 17-year-old male Pomeranian with pre-existing diseases and a 2.5-year-old male German Shepherd in good health. The owner of the Pomeranian developed symptoms of COVID-19 on February 12, 2020 and was diagnosed on February 24, 2020; a female domestic helper developed fever on February 16, 2020. Five consecutive nasal swabs from the Pomeranian tested positive for SARS-CoV-2 genetic material between February 25 and March 9, 2020; all rectal and fecal samples tested negative. The owner of the German Shepherd developed symptoms on March 10, 2020 and was diagnosed with COVID-19 on March 17, 2020. Oral and nasal swabs from the dog tested positive for SARS-CoV-2 genetic material on March 18 and 19, 2020; rectal swabs from March 18, 2020 also tested positive, although with lower viral load than oral and nasal swabs. A second dog from the same household tested negative on five occasions between March 18 and 30, 2020. Both positive dogs showed no clinical signs of infection but produced measurable antibody titers, on March 3, 2020 for the Pomeranian and March 23,2020 for the German Shepherd. Sequencing of viral genetic material from both dogs showed that the viruses in both dogs were identical to those from their respective owners, but the viral clusters in the two households were distinct from one another.
Compared to other studies focused on testing community dogs, the study focused only on dogs from COVID-19 patients to ascertain whether human-to-dog transmission can occur. The sequencing of the virus in the human cases and in the infected dogs was important for confirming human-to-dog transmission (rather than independent infection from a community source).
With the very small sample size, it is difficult to determine the frequency of human-to-dog transmission of SARS-CoV-2, the possibility of dog-to-dog transmission, and the absence of clinical signs in infected dogs. The focus in this study on dogs from COVID-19 patients certainly overestimates the frequency of human-to-dog transmission relative to the larger population of dogs.
The evidence presented in this study demonstrating occasional human-to-dog transmission of SARS-CoV-2 confirms anecdotal reports of dogs becoming infected with SARS-CoV-2, and experimental transmission studies confirming that dogs are susceptible to SARS-CoV-2 infection, although to a lesser degree than cats.
This review was posted on: 17 June 2020