"If someone in the household is infected, susceptible pets should be tested"

Since the beginning of the covid-19 crisis, the scientific community has detected, although to a lesser extent, the spread of the virus in some animal species such as tigers, cats and minks, all of them in captivity. Cats and mustelids, the group of animals to which minks and ferrets belong, have been especially susceptible.

In fact, until January 2021 the virus has been detected in about 400 mink farms in eight European States: 290 farms in Denmark, 69 in the Netherlands, 21 in Greece, 13 in Sweden, three in Spain, two in Lithuania, and one in France and Italy.

For this reason, the European Commission requested a report to a group of experts from the European Food Safety Authority (EFSA, for its acronym in English) and the European Center for Disease Prevention and Control (ECDC, for its acronym in English) to determine strategies to monitor and control the spread of the disease on these farms.

For Alessandro Broglia (Monza, Italy, 1975), a veterinarian who works as a scientific expert in the Animal and Plant Health Unit of EFSA and one of the authors of the work published last week, priority is given to surveillance activities in these establishments in which thousands live of animals with close human contact.

What is the main risk for animals and humans of mustelids and other animals such as cats becoming infected with the virus?

SARS-CoV-2 infection in mink and other susceptible animals that are raised intensively or in close contact with infecting humans could pose a significant risk to both human and animal health, as our scientific report shows. Add to this the fact that cases of reverse transmission have been documented, that is, from animals to humans working on mink farms. Therefore, at present, all mink farms should be considered at risk, as the exposure of humans to SARS-CoV-2 is very high. Once introduced, the virus spreads efficiently within the farm and, in areas with a high density of these farms, it is likely to spread to others.

Could the danger be increased with variants of the virus associated with mink?

With a mink-related variant of the virus, antibodies generated by vaccines or by natural infection with other variants may be less protective. However, it is important to note that the study's findings are based on limited data and the impact on the risk of reinfection, the efficacy of the vaccine or the benefit of treatments needs to be further studied.

What then do they propose as a preventive measure?

We recommend, above all, to closely monitor the appearance of new virus variants in mink and farm workers. As for cats, the report confirms that they may be included in the monitoring plans designed for these establishments, since they are one of the species that has been shown to be susceptible and capable of continuing to transmit the disease. Ferrets, raccoon dogs and certain bats can also be added.

What symptoms can these animals present and what impact has the virus had on them?

Both the American mink and the ferret are highly susceptible to SARS-CoV-2, and the clinical signs in mink resemble those seen in humans and appear only in part from infected animals. They are often nonspecific such as increased mortality, mild respiratory signs, and a slight decrease in food intake. The replication of the virus occurs mainly in the respiratory tract with minimal involvement of the digestive tract.

Since only a proportion of infected animals show clinical signs, EFSA considers that the follow-up strategy based on passive surveillance is not sufficient and recommends also adopting an active follow-up approach, based on early detection of infected animals.

So far, what has been the strategy followed by the different countries where positive cases were detected in mink farms?

Each country has taken different measures to respond to this situation, but you have to go back and start over; first, by detecting the disease in animals. For this, a good follow-up strategy is key. Our scientific report is, in fact, focused on proposing monitoring strategies that will help prevent and control the spread of SARS-CoV-2.

However, so far, a part of the infected farms has been detected through passive monitoring, that is, the worker observed and reported clinical signs or abnormalities in the production parameters (feed consumption, mortality, etc. ). Another part was detected after a suspicion arose due to an epidemiological link to SARS-CoV-2 in workers and owners. Finally, active monitoring was carried out (active sampling and tests on 812 animals) to detect the rest of the infected farms.

According to your report, how can the spread of the virus be controlled when there are thousands of individuals in these establishments?

Once introduced, SARS-CoV-2 spreads efficiently within the farm and, in areas with a high density of mink farms, it is likely to spread to others. That is why early detection of the disease and prevention are key. This is the reason why we advise to carry out strict weekly tests of the farm staff and all the people in contact with the animals and members of your household. It is the most important part of monitoring. More studies should be conducted on farms with a personnel history with SARS-CoV-2.

What kinds of tests and measurements need to be done?

It depends on the objectives of the monitoring strategy. For early detection, EFSA experts recommend frequent and strict PCR testing of both animals and people in contact with them. In the event that positive animals are detected, a genetic sequencing analysis should be performed to identify the origin and source of the virus and thus monitor the evolution of the virus and the possible appearance of new variants. To control the level of exposure of animals to SARS-CoV-2, that is, to verify whether the animal population has ever been exposed to the virus, an evaluation can be carried out by taking blood samples and analyzing them with serological tests.

Could this strategy work for other groups of animals such as pets that live with people at home?

Yes, it is also a monitoring option for pets, especially mustelids, such as ferrets. Every time a suspicious animal (with clinical signs) or a case of SARS-CoV-2 is detected in people in contact with it, this pet should be evaluated by PCR to confirm or exclude infection.

And in these cases, how should the owners proceed? Do they go directly to the vet?

Yes, domestic ferrets, as well as hunting ones, are cared for by veterinarians. These can be part of the surveillance of the disease and take swabs and blood samples in case of suspicion, such as the presence of respiratory signs or diarrhea, death or a doubtful or confirmed case of Covid-19 in the owner or in home. If someone in the household is infected, all owned ferrets and other susceptible pets, such as cats or dogs, should be tested.