“Several animal species have been predicted to be susceptible to SARS-CoV-2,” said Suresh V. Kuchipudi, interim director of the Animal Diagnostic Laboratory at the Huck Institutes of Life Sciences. But the risk remains unknown for many animals in different parts of the world, he says. “Therefore, there is an urgent need to monitor SARS-CoV-2 exposure of high-risk animals in different parts of the world.”
In June, India introduced Ancovax, the first COVID-19 vaccine for animals. The development came a year after the nation reported that the virus had infected eight Asiatic lions, two of which died. While 30 COVID-19 vaccines for humans have been approved for general or emergency use around the world, Ancovax is only the third vaccine for animals. The first, called Carnivac-Cov, was registered by Russia in March last year, followed four months later by another vaccine developed by Zoetis, a US pharmaceutical company.
Christina Lood, a spokesperson for Zoetis, says the company has donated more than 26,000 doses of its animal vaccine to more than 200 zoos — in addition to 20 conservatories, reserves and other animal organizations in more than a dozen countries, including Canada, Chile and the US. vaccine, she adds, has been administered to more than 300 mammalian species to date.
“At least 75 percent of emerging infectious diseases are of animal origin, including COVID-19,” says Lood. “Now more than ever, we all see the important link between animal health and human health.”
The dangers of COVID-19 infections in animals
Cases of the virus in animals have been reported in several countries around the world. Since March of this year, 29 species of animals have been infected. These include companion animals such as dogs, cats, ferrets and hamsters; farm animals such as minks; wildlife such as the white-tailed deer, the mule deer, and the black-tailed marmoset; and animals in zoos and sanctuaries, including hyenas, hippos, and manatees. Despite the widespread infection, the U.S. Centers for Diseases Control and Prevention (CDC) noted that “we don’t yet know all the animals that could become infected,” adding that more studies and surveillance are needed to understand how the virus has spread between human and animal.
Leyi Wang, a veterinary virologist at the Veterinary Diagnostic Laboratory, University of Illinois, says captive and companion animals are most often infected by humans. It goes both ways, he says, citing a recent study in Hong Kong that showed the virus spread from hamsters to humans.
Wang’s main concern is the possibility that humans or pets could pass the virus back to wildlife, creating an uncontrollable reservoir of the disease, especially given the difficulty of vaccinating non-captive wild animals. Such spillbacks have previously occurred with diseases such as plague, yellow fever and rabies.
It is challenging and expensive to develop and implement vaccines for animals, and in demand because the broader health risk to animals is not well known to the public. People tend to only think about their pets.
In the past, other human respiratory viruses have proved fatal to endangered great apes such as chimpanzees and gorillas. Fearing that COVID-19 could have the same effect, primatologists have been working to protect primates during the pandemic. Meanwhile, virus reservoirs have already been created among other animals, Wang says. “Deer from more than 20 US states tested SARS-CoV-2 positive,” Wang said, citing a study that confirmed both human-to-deer transmission and deer-to-deer transmission. It remains unclear how many animal species are susceptible to the disease as a result of interacting with infected deer, Wang says.
In April, the CDC expressed concern about new coronavirus variants mutating in wildlife, and urged health authorities to monitor the spread of the infection in animals as a threat to humans. The WHO has made similar recommendations.
Challenges for Vaccine Development
Zoetis started development activities for its COVID-19 vaccine in February 2020, when the first known infection of a dog occurred in Hong Kong. The pharmaceutical giant completed the first development work and research on dogs and cats and shared their findings at the World One Health Congress in the fall of 2020. A few months later, after a troop of eight gorillas contracted the virus at the San Diego Zoo. Safari Park, Zoetis has donated its experimental vaccine for emergency use in the great ape population.
Zoetis has uniquely formulated its COVID-19 vaccine for animals. It uses the same antigen as human vaccines, but contains a different type of carrier protein for inducing a strong immune response. “The unique combination of antigen and carrier ensures safety and efficacy for the species in which a vaccine is used,” says Lood.
But developing and implementing vaccines for animals is challenging and expensive, and in demand because the broader health risk to animals is not well known to the public. People tend to only think about their pets. “When it became clear that the risk of serious diseases for pets such as cats and dogs was low, demand for those vaccines declined before they became commercially available,” said William Karesh, executive vice president of health and policy at EcoHealth Alliance. He adds that in affected commercial mink farms, the usefulness of a vaccine could justify the cost in some cases.
While scientists have made huge strides in creating vaccines for animals, Kuchipudi believes the need for COVID-19 vaccines for animals “needs to be evaluated based on many factors, including the susceptibility of the specific animal species, the health implications and the costs”.
Not every scientist feels the need for vaccines for animals. Joel Baines, a professor of virology at Cornell University’s Baker Institute for Animal Health, says that while domestic cats are most susceptible to COVID-19, they usually suffer from mild infections. Big cats in zoos are vulnerable, but they can be isolated or kept away from people. He says mink farms are a relatively small industry and ensuring that human handlers are COVID negative can contain such outbreaks.
Baines also suggests that human vaccines could likely work in animals, as they were tested on animals during early clinical trials and induced immune responses. “However, these vaccines should be used as a priority in humans and it would be unethical to use a vaccine intended for humans to vaccinate an animal if vaccine doses are restrictive at all,” he says.
William Karesh, chairman of the World Animal Health Organization Working Group on Wildlife Diseases, says the best way to protect animals is to reduce their exposure to infected people.
William Karesh
In the absence of enough vaccines, Karesh says the best way to protect animals is to protect unvaccinated people — reducing their exposure to infected people by isolating them if necessary. “People who work with or spend time with wildlife should follow available guidelines, including self-testing and wearing personal protective equipment to avoid accidentally contaminating wildlife,” he says.
The link between animal and human health
While there is a need for animal vaccines in response to virus outbreaks, the best approach is to try to prevent the outbreaks in the first place, explains K. Srinath Reddy, president of the Public Health Foundation of India. He says the incidence of zoonotic diseases has increased over the past six decades, as human actions such as increased deforestation, wildlife trade and the consumption of animal meat have opened an ecological window for the transmission of disease between humans and animals. Such actions are breaking down the natural barriers between humans and forest-dwelling viruses, while building conveyor belts for the transmission of zoonotic diseases such as COVID-19.
Many studies suggest that the source of COVID-19 was infected live animals sold in a wet market in Wuhan, China. Live dogs, rats, porcupines, badgers, hares, foxes, hedgehogs, marmots and Chinese muntjac (small deer) were sold and the virus was found in stalls, animal cages, carts and water drains, according to a study published in July.
This research strongly suggests that COVID-19 is a zoonotic disease, one that spreads from animals to humans because of our close relationship with them in agriculture, as companions and in the natural environment. Half of the infectious diseases that affect humans come from animals, but the study of zoonotic diseases has historically been underfunded, even though they may reduce the likelihood and cost of future pandemics.
“We need to invest in vaccines,” Reddy says, “but that cannot replace an environmentally sound approach to contain zoonoses.”
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