After a tiger and a domestic cat contracted the new coronavirus, experts evaluate the transmission of the disease between humans and other species.
A tigress who lives at the Bronx Zoo in New York, United States, tested positive for Covid-19. Additionally, six other large cats are under suspicion of infection with the new coronavirus. Authorities believe the animals were infected by an asymptomatic zoo worker, but intend to conduct further research to understand how the contamination may have occurred.
It is not so clear whether human-to-animal transmission actually occurred for one reason: most viruses are “specialists”, that is, they affect a single species. However, sometimes mutations in the genetic material of these microorganisms allow them to “jump” from one species to another – and that is exactly what researchers believe has happened to Sars-CoV-2.
“The new coronavirus (SARS-CoV-2) that emerged from Wuhan in November isn’t actually ‘new’. The virus evolved over a long period, probably millions of years, in other species where it still exists,” explains Steve Wylie, a professor at Murdoch University in Australia, in a text published on The Conversation. “We know the virus has close relatives in Chinese rufous horseshoe bats, intermediate horseshoe bats, and pangolins – which are considered a delicacy in China.”
Often, for these microorganisms to be able to affect humans, a vector is necessary, that is, people need to come into contact with the animals that are the original hosts of the microorganism. According to experts, globalization and the consumption of meat, milk, eggs and other products of animal origin contribute to viruses jumping from one species to another, as occurred with the new coronavirus.
“As we push back the boundaries of the last wild places on Earth – felling the bush for farms and plantations – viruses from wildlife interact with crops, farm animals and people,” writes Wylie. “Human beings are also heating up the climate. This allows certain species to expand their geographic range in areas previously too cold to be inhabited. As a result, many viruses are finding new hosts for the first time.”
Experts believe it was precisely this contact between humans and animals that caused the tigers to become infected at the Bronx Zoo. While some researchers are trying to help the animals recover from the infection, others are concerned about the health of another group: primates.
“Great apes share about 98% of human DNA, and they also share susceptibility to several human pathogens,” said Lesley Elizabeth Craig, a professor at the University of Stirling in the UK, in an article on The Conversation. “During the Ebola virus epidemic between 1994 and 2003 in Central Africa, wildlife surveys were carried out in two areas of Gabon, before and after the outbreak. Between the two surveys, gorilla and chimpanzee populations in the areas shrank by 90-98%.”
The researcher believes that, although no case of Covid-19 has been reported in great apes, the history of disease transmission between these animals and humans is enough to cause concern. “We must assume that transmission is likely and strict measures are needed to prevent it,” said Craig.
Another subject that has made headlines in recent weeks and has worried dog and cat owners worldwide is the infection of a domestic cat in Belgium. According to the country’s authorities, the animal showed symptoms of the disease after living with the owner, who tested positive for the new coronavirus a few days earlier.
A few days after the case became popular, a team from the Harbin Veterinary Research Institute in China discovered that cats are highly susceptible to Covid-19. According to the study, published by the researchers in BioRxiv, felines can transmit the disease to each other through respiratory droplets. On the other hand, species of dogs, chickens, pigs and ducks tested were considered unlikely to contract the infection.
With all this in mind, the World Small Animal Veterinary Association (WSAVA) clinicians point out in a statement that “there is currently no evidence that pets can be a source of infection for people.” The cases observed in pets until then occurred in the opposite way: owners contaminated by Sars-CoV-2 ended up infecting their pets.
The recommendation for those who are sick is to avoid contact with animals, and always wash your hands before and after interacting with pets. “If you are sick with COVID-19, avoid contact with your pet, including petting, snuggling, being kissed or licked, and sharing food,” advises WSAVA. “If you must care for your pet or be around animals while you are sick, wash your hands before and after you interact with pets.”