Hong Kong is sticking to a strict ‘zero Covid’ strategy… which is not just about humans. Authorities decided to cull nearly 2,000 hamsters after some of them tested positive for Covid-19. The cull was ordered on Tuesday after cases emerged at a pet store. Hong Kong Health Minister Sophia Chan said she was protecting public health after an employee and a customer who handled hamsters tested positive. According to the local government, the animals were imported from the Netherlands. The rule is simple: any buyer of hamsters after December 22 is requested to bring them back in order to eliminate them. The measure is radical and awakens the fear of contamination of humans via animals. This is not new: certain species (monkeys, felines, mink, etc.) can, as we know, be infected with Covid-19 because they have the ACE2 receptor, the entry point for the virus into cells.
But in reality, what is the risk of an animal reservoir for the epidemic? “There is a ‘potential’ risk that there is an animal reservoir for Covid-19. Several animals susceptible to the virus have been the subject of natural contamination”, cautiously declares to L’Express Jeanne Brugère-Picoux, honorary professor of the National Veterinary School of Alfort and member of the National Academy of Medicine. Among the pets likely to be contaminated by the virus, there are dogs and especially cats, most often infected by their owner. “These are sporadic cases,” adds the specialist. Generally, felids are more susceptible to the virus. “Often the cat is sick and suffers from pneumopathy”, adds Hervé Fleury, virologist, professor emeritus at the CNRS and the University of Bordeaux. In April 2020, cases of Covid-19 were detected for the first time in tigers and lions at a zoo in the Bronx, United States. These felines had been contaminated by their caregivers.
If humans can transmit the virus to an animal, is the reverse possible? “This has only been observed in mink farms”, tempers Jeanne Brugère-Picoux. This particular case first occurs in the Netherlands, the first country to announce in June 2020 the contamination of mink farms by SARS-CoV-2. Two million mink are culled. In Denmark, farmed mink transmit mutant strains to humans, causing a political crisis. On November 4, 2020, the authorities decided to slaughter 17 million mink. The objective: “to stem the spread of a mutant strain of SARS-CoV-2 which risked compromising the vaccine protection of the human population conferred by the anti-COVID-19 vaccines then available”, according to a bi-academic report (National Academy of Medicine and French Veterinary Academy) published last summer.“Minks are very sensitive to the virus. They have the particularity of sneezing like humans so they disperse the disease more,” explains the expert.
Risky spread among pests
In the case of Denmark, the concentration of animals in an enclosed space increased the risk of contamination among humans in contact with these farmed minks. Especially since this animal has the particularity of having a respiratory system very close to that of humans. This example shows that the population is not immune to a new variant coming from the fauna. If contamination by domestic animals remains hypothetical, it is above all wildlife that can present a potential reservoir risk. This is the case “for example, of the American mink and the raccoon dog (a time envisaged by the WHO as being able to be at the origin of the epidemic in China) which are very sensitive to the Covid-19 virus. 19. These are very prolific species and are classified in the category of pests in France”, continues Jeanne Brugère-Picoux. Work carried out in 2021 – relating to white-tailed deer – confirmed the circulation of the Covid-19 virus in certain wild animals. Note that the white-tailed deer is a very abundant and sometimes widespread species near urban areas in the United States.
The American study published in November reports that more than 80% of deer, tested between December 2020 and January 2021 in several areas of the state of Iowa, are positive for SARS-CoV-2. “It’s extraordinary to see how contaminated they are. There are places where they are 70% positive in serology. With the sequencing of viruses in deer, the researchers found all the variants that we know” , comments Hervé Fleury. The question that will therefore arise in the future is the following: will animals close to us – which can create areas of concentration of the virus – be able to infect humans? And is there a risk of recombination of the virus within the animal population? If this scenario is not yet confirmed by any publication, the virologist believes that the transmission of the virus to humans by animals will “inevitably happen”. “One of the scenarios would be the contamination of non-vaccinated hunters who will be in contact with deer in Ohio”, advances Hervé Fleury.
“I think they should be vaccinated”
Behind the specialist’s projection, there is the risk that a resurgence of the pandemic is always possible if the virus continues to circulate in the animal world. To avoid such a scenario, is the elimination of contaminated animals the best solution? “I don’t want to kill animals, that’s what I’ve been saying for ten years about avian flu. I think they should be vaccinated. In Europe, we eliminated rabies by vaccinating foxes” , replies the professor. According to him, the vaccination of the animals is a hypothesis which it will be necessary to be concerned about. American zoos have already taken the plunge by vaccinating great apes and certain felines. In the meantime, the watchword is as follows: increase surveillance: “It is obvious that sensitive species must be monitored and any isolated viruses sequenced to monitor this hypothetical risk of emergence of a variant of animal origin. “, concludes Jeanne Brugère-Picoux. A luxury that will undoubtedly be reserved for rich countries.
Furthermore, recent experiments have shown that certain worrying Beta (ex-B.1.351 South African) and Gamma (ex-Brazilian P.1) variants are capable of infecting laboratory rats and mice. A study, led by Michael Diamond and colleagues at Washington University in Saint Louis, Missouri, also showed that the Omicron variant (B.1.1.529) causes attenuated lung infection in laboratory mice and hamsters. Hong Kong researchers conducted a surveillance study of SARS-CoV-2 infection in 217 rats between February 3 and May 12, 2021. They did not detect SARS-CoV-2 RNA in any of the rats studied, but did identify a brown rat (Rattus norvegicus) with anti-SARS-CoV-2 antibodies, suggesting that it had been exposed to a virus antigenically similar to SARS-CoV-2. At this stage, the possibility that city rats are exposed to SARS-CoV-2 cannot therefore be excluded. For Elliott Miot and colleagues at the University of Hong Kong, “the discovery of potential exposure to SARS-CoV-2 in a sewer rat underscores the need for sustained surveillance of rodent populations to rapidly detect spillover events and then put in place timely interventions (e.g. disinfestation using traps and pesticides) to prevent the potential establishment of new animal reservoirs”.