Regarding Covid-19 infections, there have been several reports in recent months of dogs testing positive for the virus. One very recent case involves a dog in the province of Bari, which sparked unjustified alarm and many questions among pet owners. Light is shed on the episode by a study conducted by the Department of Veterinary Medicine at the University of Bari, in collaboration with the University of Milan, the Liverpool School of Tropical Medicine, and the veterinary diagnostic laboratories Mylav and i-Vet, which demonstrated that some dogs and cats — animals living in the regions most affected by the first pandemic wave — had developed specific antibodies to this type of coronavirus.

None of the animals tested had, however, previously returned a positive result on the molecular test, so it is reasonable to conclude that these few animals had become infected before sampling and had already recovered from the infection. The majority of the seropositive pets belonged to owners with cases of Covid-19. All of this confirms once again that it is close contact with infected people that facilitates the transmission of the infection to our pets, and not the other way around. On this point, we take stock of the situation with the help of Nicola Decaro, full professor of Infectious Diseases of Animals at the University of Bari and expert consultant at Mylav.

Covid-19 and dogs

The dog at the centre of the unjustified alarm is an eighteen-month-old poodle belonging to a family who had tested positive for Covid-19. The dog did not develop any symptoms, but simply tested positive for the virus (a test carried out on dogs and humans in exactly the same way, using a simple swab) for several consecutive days, before returning a negative result. All of the swabs taken from the animal that came back positive showed very low viral titres, meaning the dog could not have been a source of contagion.

Sporadic cases of coronavirus infection in dogs have been reported in various parts of the world since the start of the pandemic. The first case was indeed recorded as early as late February 2020 in a 17-year-old Pomeranian from Hong Kong (which subsequently died for reasons entirely unrelated to the infection). A few days later, also in Hong Kong, an eighteen-month-old German shepherd also tested positive without, however, showing any symptoms, returning a negative result within a few days. Further cases were subsequently observed in the United States, Japan, Canada and the Netherlands. Only in a very small number of these cases did the infected dogs develop mild respiratory symptoms, which resolved within a few days, while the majority of infections were entirely asymptomatic.

In all reported cases, moreover, these animals became infected as a result of close and prolonged contact with positive human patients, and showed very low viral titres in their secretions and excretions (nasal swabs, oropharyngeal swabs and faeces), which were therefore considered non-infectious. Experimental infection trials have also confirmed that dogs play absolutely no epidemiological role in the pandemic. Not all subjects experimentally infected became infected, and those that did always developed asymptomatic infections characterised by a low viral load detectable only by molecular testing. Isolation attempts on cell cultures (the only method capable of demonstrating the infectivity of a biological sample) always returned negative results. Furthermore, not all subjects found to be infected produced specific antibodies.

The conclusions of the Italian study

In conclusion, both naturally occurring infection cases and experimental infection trials document a low susceptibility in dogs to the virus and a negligible, if not entirely non-existent, epidemiological role. Compared with the nearly 60 million people infected with Covid-19 worldwide, there is, to date, not a single case of transmission from a dog (or a cat) to a human. Dogs are therefore, at most, "victims" of contagion from humans, not "spreaders." Precisely for this reason, in accordance with the precautionary principle and the guidelines of all international scientific societies dealing with companion animals, dogs (and cats) living in households that have tested positive for Covid-19 must be "protected" from infection. It is therefore recommended that they be cared for by uninfected members of the household, or, in the event that the entire household has tested positive, by relatives or friends who can perhaps keep them at their own home for however long is necessary.