SINGAPORE - None of the animals at Singapore's zoo or wildlife parks has been vaccinated against Covid-19 and there are currently no plans to do so, said the Mandai Wildlife Group.
Responding to queries from The Straits Times, it said on Tuesday (Nov 9) evening that more understanding of the safety and efficacy of vaccination for animals is needed.
"We are checking in with our global zoo counterparts who have started trialling vaccinations for some of their high-profile animals," it added.
This comes after four Asiatic lions at the Night Safari tested positive for Covid-19 last Saturday.
The four lions, along with one African lion at the Singapore Zoo, exhibited mild signs of Covid-19, including coughing, sneezing and lethargy. Test results for the African lion are pending.
Dr Sonja Luz, vice-president of conservation, research and veterinary at Mandai Wildlife Group, said on Tuesday that the Asiatic lion exhibit along the tram route at the Night Safari has been closed since Sunday, while the African lions exhibit at the Singapore Zoo has been closed since Tuesday.
Since September, 48 animals at the Oakland Zoo in California, including lions, bears and ferrets, have been inoculated with an experimental vaccine for animals by veterinary pharmaceutical company Zoetis.
In January, apes living in the San Diego Zoo were inoculated with the same vaccine after a Covid-19 cluster was detected among a troop of gorillas living there.
In March, Russia registered a Covid-19 vaccine for animals, with tests showing that the jab could generate antibodies against the virus in dogs, cats, foxes and minks.
Known as Carnivac-Cov, the vaccine was said to be able to protect vulnerable species and thwart viral mutations.
Dr Luz said the lions remain "bright, alert and are eating well". She noted there is evidence showing that animals in general do not fall seriously ill from the virus.
"We expect that the lions will make full recovery with minor supportive treatment. However, anti-inflammatory (drugs) and antibiotics may be prescribed if further treatment is needed," she added.
"The animal care teams are keeping a close watch on all higher-risk species, including primates and carnivores, under their care. No other animals across the four wildlife parks currently present clinical signs of the virus."
Professor Dale Fisher, a senior consultant at the National University Hospital's Division of Infectious Diseases, said that if an animal has close exposure with humans and has the same ACE2 receptor as humans on its respiratory lining, it can also get infected.
The Sars-Cov-2 virus, which causes Covid-19, binds with the ACE2 receptor to infect host cells. He noted that this happened commonly in minks and resulted in millions being culled.
Professor Wang Linfa from the Duke-NUS Emerging Infectious Diseases programme said ACE2 is a "highly conserved protein among different mammals".
He noted that more than 10 mammals, other than humans, have been infected by the virus.
Prof Fisher added that pets that were infected by humans generally only had mild disease, and getting infected does not pose a major threat to the animals, or create a major source of spread.
"The animals are more like innocent bystanders and the transmission chain generally stops," he said.
Prof Wang said while humans can infect their pets, such as cats and dogs, the virus does not replicate efficiently in them. Hence the risk for infected pets passing the virus to other humans remains low.
According to the World Organisation for Animal Health, there is currently no evidence showing that animals play a role in spreading the virus to humans.
Therefore, the risk of humans contracting the Sars-CoV-2 virus from animals is very low.
Prof Fisher said that while it is possible for the virus to spread from animals to humans, it is generally not common.
"We think the whole pandemic started with a spillover event - that is an animal somehow infected a person and after this initial seeding, human-to-human transmission took off," he added.
Therefore, animal-to-human transmission could seed a small cluster, but it is not the main driver of transmission, which is human to human, said Prof Fisher.
Dr Han Zi Yang, a vetinary consultant at VetTrust Singapore, told ST the clinic is not aware of any cases of pets in Singapore being infected with Covid-19.
"Pet owners should not be overly worried at this stage and should continue to adopt the same set of good hygiene measures in pet care. This involves regular handwashing before and after handling their pet, their food and supplies, and avoid sharing food with them," he added.
Those suspected or confirmed to have Covid-19 should isolate themselves and seek help from family and friends to take care of their pets during their period of recovery. If the pet is a suspected or confirmed case, consult a vet immediately, he advised.
Dr Luz said that since the onset of Covid-19 in 2020, safety measures have been put in place to reduce the likelihood of asymptomatic animal carers passing the disease to susceptible species.
Current precautions being taken include requiring staff to wash their hands before and after interacting with any animal, donning face masks and gloves when working closely with an animal, as well as minimising or avoiding direct contact with these animals unless required.
The great apes, such as orangutans and chimpanzees, will continue to undergo temperature checks twice a day as part of added preventive measures.
Animal care staff will be required to do antigen rapid testing weekly to reduce the likelihood of asymptomatic transmission from human to animal.
ST has contacted Mandai Wildlife Group to find how the infections occurred and if additional precautions will be taken to protect visitors.