THE WORLD ON THE BRINK OF NEW PANDEMICS: The Mutation of Viruses Exchanged Between Animals and Humans
Photo source: health.com
If you think the story of the coronavirus epidemic has ended happily, you are mistaken. As long as animals inhabit our planet, pandemics will continue to shake our civilization. It’s important to be aware and prepared for this inevitability. Moreover, as Pulitzer Prize winner Jared Diamond demonstrated in his bestseller «Guns, Germs, and Steel», pandemics are not always detrimental to humanity. They can even spur civilizational development.
Humans and animals have been exchanging viruses for millennia, with these viruses mutating within their bodies and unleashing devastating epidemics on the world. This process cannot be stopped, but it can be studied, and attempts can be made to control it. This is precisely what scientists are currently trying to do.
BATS HAVE COMPETITION
If we set aside conspiracy theories, the coronavirus most likely came to us from wild or domestic animals. The history of epidemics suggests that nothing is surprising about this. Moreover, bats are not the only candidates as the source of the coronavirus. While these creatures are unique in many ways, being mammals capable of flight, they are not the only potential culprits.
One thousand four hundred species of bats possess a fantastic immune system. Besides rabies, they are not susceptible to any viral diseases. While this is beneficial for the bats themselves, it’s not so great for others, as their resistance to viruses makes them particularly dangerous carriers of various pathogens. However, early in the pandemic, science began to question bats’ monopoly on contagiousness.
For instance, the coronavirus could have easily reached humans from the critically endangered pangolin, an animal resembling an armadillo. Civets, mammals that live in palm trees, were also found to be carriers of SARS. The virus was also detected in cats, dogs, camels, and minks raised on farms. People who are in constant contact with these animals could have easily contracted the virus from them.
In the case of camels, some researchers proposed the theory that they might have been infected with the coronavirus by a type of bat known as a sheath-tailed bat, which resides in the Middle East. But this is just a theory; no one has even come close to describing the mechanism by which this could have happened. And where, for example, could the “corona” have come from in lions?
CORONAVIRUS IN THE WILD
Past and present epidemics remain full of mysteries. So far, scientists’ knowledge about how COVID-19 is transmitted between animals and its impact on wildlife is limited. At the start of the pandemic, the virus was detected in more than 50 animal species, but most of these were domestic animals: cats, dogs, ferrets, hamsters, and animals in zoos and farms. However, there were isolated reports of infections in wild animals as well.
In France, antibodies were found in badgers and martens. In Brazil, coatis – mammals similar to raccoons – were infected. In India, leopards were affected, and in Senegal, white rhinos. There have even been documented cases of COVID-19 transmission both from animals to humans and from humans to animals.
For instance, in Denmark and the Netherlands, workers on mink farms contracted the virus from these furry creatures, leading to the culling of millions of animals. In Hong Kong, the virus was transmitted to humans from pet hamsters, which is a previously unknown strain in the region.
Scientists are now trying to determine which animal species allow the virus to persist and evolve into new strains that could threaten human immunity by evading diagnosis and treatment.
PANDEMIC AMONG DEER
Last year, the United States launched a large-scale project aimed at understanding how viruses are transmitted from humans to wild animals. To determine how COVID-19 evolves in a host organism, scientists began by studying populations of North American deer.
Now, a team led by ecologist Kurt Vandegrift from Pennsylvania State University and veterinarian Suresh Kuchipudi from the University of Pittsburgh plans to collect and analyze more than 24,000 samples from 58 species of wild animals over the next two years. This will help to determine the threat COVID poses to wildlife, as well as to study the risk of the virus mutating into new strains that could trigger another epidemic surge in humans.
To achieve this, samples will be taken from a wide variety of animals – foxes, bears, rabbits, beavers, moose, deer, moles, coyotes, lynxes, opossums, rats, raccoons, skunks, shrews, weasels, squirrels, voles, marmots, chipmunks, porcupines, and others. However, so far, deer remain the only animals in which systematic studies of COVID-19 infections have been conducted.
36% of the 360 deer tested were infected. Three distinct lines of the virus were found, indicating three independent episodes of herd infection. Further studies in the United States and Canada confirmed the high prevalence of the virus among more than 30 million white-tailed deer living east of the Rocky Mountains and among 4 million mule deer residing to the west. In one population in Iowa, 82% of the animals were found to be infected.
HUMANS AND ANIMALS: WHO INFECTED WHOM?
Genetic studies suggest that the virus was transmitted to deer from humans, and this transmission continues… However, scientists are still unsure exactly how this happens. Various theories have been proposed – from feeding deer by hand to contact with discarded masks and wastewater – but none have been confirmed. Vandegrift, for example, initially blamed mice, but research showed that mice are not an intermediate host for the virus.
The second mystery is the speed at which the virus spreads among deer. Unlike humans, they don’t gather in restaurants and theaters, and unlike farm animals, they inhabit vast areas, making their contact with each other relatively infrequent. Much about the spread of COVID in the wild remains a genuine puzzle to scientists. The only clear thing is that the threat to humans from this is not diminishing.
Somehow, the virus, after mutating in deer, is transmitted back to humans. Two cases of COVID infection «of deer origin» have already been reported in Massachusetts, one in North Carolina, and another in Canada. However, it is still being determined how the virus jumps from deer to humans. Only in the last case was there evidence of actual contact between a human and a deer.
Currently, these contacts are not very dangerous – the strain of the virus in deer is similar to the one circulating among humans. However, as Vandegrift points out, animals have their coronaviruses, which could recombine with SARS-CoV-2. Therefore, in about 30 years, as these viruses continue to live and evolve in deer, they could become a severe threat to humanity.
BIRD FLU IN CATTLE: PREPARING FOR A NEW PANDEMIC!
Unfortunately, COVID is not the only virus being exchanged between humans and animals. In the United States, scientists are sounding the alarm about bird flu. For humans, it poses a danger by affecting the nervous system, liver, kidneys, and blood-forming organs, with potential consciousness disorders. Symptoms include high fever, difficulty breathing, and muscle pain.
Currently, the number of bird flu cases among cattle is rapidly increasing across America. So far, bird flu has been spreading among cows in a form that is relatively safe for humans. However, immunologist Scott Hensley from the University of Pennsylvania in Philadelphia warns that even one unpredictable factor could drastically change the situation.
Highly pathogenic avian influenza H5N1 has now been detected in 145 cattle herds. Four agricultural workers have already been infected, leading virologists to be less than optimistic about containing the outbreak. Many more cases of transmission from cows to humans likely exist, but the vast majority go unrecorded.
However, there is some relatively good news: it is known how bird flu infects cows – through insufficiently clean milking equipment. Close and regular contact between humans and cows could trigger airborne transmission, easily sparking a pandemic. The only way to prevent it is through vaccination.
VACCINATION: ANOTHER SURGE IN DEMAND?
In May of this year, the World Health Organization published a list of vaccines effective against H5N1, which is circulating among cattle. In preparation for a potential epidemic, the European Commission and the U.S. Department of Health have already begun mass procuring these vaccines. Workers on fur and poultry farms should receive special attention during vaccination.
The main issue with vaccination is the time factor. The currently available vaccines are based on inactivated virus strains grown in chicken eggs. They are inexpensive, but their production is quite time-consuming. However, scientists are already developing next-generation vaccines using mRNA technology. These vaccines will be more expensive but faster to produce and more effective. The new vaccine is already being tested on ferrets.
Researchers are also exploring the possibility of vaccinating cattle. The main challenge here is that the virus finds refuge in the mammary glands and epithelial cells of the udder, where it is difficult to elicit a protective immune response.
Moreover, there is concern that vaccines could mask symptoms in still-infectious animals, increasing the risk to humans. Interestingly, before the outbreak in the U.S., researchers did not even suspect that cattle could be infected with bird flu.
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