Asymptomatic animal handlers at a private zoo in South Africa transmitted the Delta variant of Covid-19 to captive lions, who were placed in quarantine and developed symptoms like breathing problem, runny nose and dry cough, according to a recent study by a team of scientists from the University of Pretoria.
The research report, published recently in the journal ‘Viruses’, also urged members of the public to be aware of the possibility of infecting their pet cats and dogs if they have Covid-19.
The team was led by Professor Marietjie Venter, Head of the Zoonotic, Arbo-and Respiratory Virus Programme at the university's Department of Medical Virology; and Professor Katja Koeppel, Associate Professor of Wildlife Health at the Faculty of Veterinary Science. They conducted a study on three sick lions at the zoo during South Africa’s third wave of the Covid-19 pandemic late in 2021.
“The team of transdisciplinary scientists found that reverse zoonotic transmission of Covid-19 from asymptomatic animal handlers at a private zoo in Gauteng (province) posed a risk to big cats kept in captivity,” the university said in a statement.
“Transmission of the Delta variant to these animals could result in more severe disease. The animals tested PCR positive for up to seven weeks after becoming sick.
“This extended period of potential virus shedding poses a risk of infection to animals in close proximity and possibly humans. The animals were therefore placed in quarantine until they tested negative,” the scientists said.
Koeppel said the lions had breathing problem as well as runny nose and a dry cough for up to 15 days.
“A persistent cough was seen between five and 15 days, with two lions experiencing difficulty in breathing. One lioness developed pneumonia that did not respond to antibiotics,” she added.
The staff and lions were monitored in the weeks that followed for the presence of SARS-CoV-2 and, within 15 to 25 days, all three lions made a full recovery.
“(Further) tests showed that SARS-CoV-2 could have been circulating among staff during the time that the lions got sick, and suggests that those with direct contact with the animals were likely responsible for the reverse zoonotic transmission,” Venter said.
A year earlier, two pumas at the zoo also tested positive for Covid-19.
Genome sequencing was conducted on the humans and three lions, and tests revealed that each of the infections was a Delta variant.
The two pumas and three lions presented with respiratory illness that was similar to Covid-19 in humans.
The animals did not respond to antibiotic treatment but recovered after treatment with anti-inflammatory drugs and supportive care.
“Detection of viral RNA in the upper respiratory tract and the faeces, coupled with the fact that the pumas and lions had symptoms, reveal that this virus is able to infect these animals via a natural infection route,” Venter said.
The scientists said the timeline of infections of the lions from a Covid-positive human is difficult to estimate as all staff members were asymptomatic during the outbreak.
They said that reverse zoonotic transmission of SARS-CoV-2 from asymptomatic animal handlers pose a risk to large felines kept in captivity.
The scientists stressed that precautions such as vaccinating staff, wearing masks when entering cages and preparing food, infection control through use of disinfectants, and distance barriers for members of the public should be put in place at zoos.
“This is to protect potentially endangered species from getting infected and dying,” the scientists said.
“These measures are also important because of the risk of new variants emerging if the virus establishes itself in other animal reservoirs; these variants could be transmitted back to humans,” they said.
