The death of tigers, lions and cheetahs in various zoos around the worlddue to avian influenza, has sparked new alarm among infectious disease experts and those responsible for facilities hosting protected species. This wave of highly pathogenic infections, also known as HPAI (Highly Pathogenic Avian Influenza)goes well beyond the perimeter of chicken coops and farms: now it also dangerously targets large mammalsincluding felines.
The latest outbreak, involving some facilities in the United States, recorded the deaths of a cheetah, a mountain lion, an Indian goose and a kookaburra al Wildlife World Zoo in Phoenix. Other temporary closures were then added in various parks, such as the San Francisco Zoo, forced to stop access to the aviaries after the discovery of a wild red-shouldered buzzard positive for the virus. In Seattle, a rare red-breasted goose died at the Woodland Park Zoo, prompting management to take extraordinary safety measures. Similar incidents occurred last summer in Vietnam, where 47 tigers, three lions and a panther they died in rapid succession, presumably following contact with infected birds.
A real danger for biodiversity in captivity
Bird flu has already caused the death of over 280 million birds on a global scale, but recent reports of contagion among big cats in zoos confirm that the virus is no longer limited only to birds. Connor Bamford, virologist at Queen’s University Belfasttold The Guardian that the effects on tigers, lions and cheetahs in captivity they could have “serious implications” on the survival of already threatened species. Structures such as zoos sometimes represent the last hope of conservation for animals that are almost extinct in the wild, and such an aggressive virus risks compromising the research and protection work carried out over the years.
The greatest fear is that, with the arrival or passage of infected migratory wild birds, the enclosures hosting mammals and birds can become ideal grounds for interspecific transmission. In many cases, just a single wild animal carrying the virus enters the area to start a chain of infections. Several US states, including Louisiana, Missouri and Kansashave recently recorded an increase in cases of avian influenza; in Iowathe authorities spoke of a “sudden leap” after almost a year of respite.
Biosafety measures and containment protocols
Given the possibilities of infection for big cats, It is essential to minimize contact between wild animals and species housed in zoos. According to the Ed Hutchinsonvirologist at the University of Glasgow, visitors to some zoos in Europe will have already noticed the use of temporary barriers, protection nets or the complete closure of some bird enclosures. In this way, an attempt is made to prevent the access of potentially infected migratory birds.
Rowland Kaoan epidemiologist at the University of Edinburgh, highlights how the often high density of animals in zoos, combined with biosecurity protocols that are not always homogeneous, make these structures particularly vulnerable. Each park adopts different strategies for animal health and well-being, and the opportunities for contact with wildlife can vary greatly depending on the geographical location and the architecture of the spaces. All this makes it difficult to establish a single containment line valid for everyone.
In some geographical areas, such as United Kingdom and theEuropean Union, vaccines against avian influenza are already authorized and can be administered to animals in captivity, especially those specimens that are particularly at risk. In the United StatesInstead, such vaccinations are not permitted by lawpartly out of fear that resistant strains may emerge or that epidemic surveillance will be reduced. However, faced with a scenario where the virus seems to be constantly evolving and capable of affecting even large mammals, many experts argue that the policy of bans could prove counterproductive in the long term.
Ian Brownvirologist at the Pirbright Institute in Surrey, believes that it is however possible to act immediately on another prevention lever: improve the hygiene, cleanliness and protection of enclosures. «Some zoos – explains Brown – have already made the decision to keep flamingos in their internal structures during the most critical phases of viral spread, thus reducing the risk of contact with migratory wild birds».
A globalized virus: from Antarctica to American farms
The H5N1 avian influenza strain, in its most aggressive variant, it has been circulating on a global scale for several years. Already in 2020, researchers had observed how the virus had spread unabated in Africa, Eurasia and the Americas, even arriving in Antarctica in late 2023with a catastrophic toll of millions of dead wild animals. In the United States, its ability to adapt it also led to the virus spreading to livestock farmswith serious consequences for animal health and, potentially, for humans. Some episodes reported by the American authorities show how the consumption of infected raw milk can transmit infection to domestic catswhile at least two farm workers in California have tested positive for the virus in recent weeks.
This scenario confirms a stark reality: avian influenza, once thought to be a problem confined mainly to poultry and other bird species, it is now a global health issue which concerns a wide range of animals, from aquatic mammals to large cats, from rodents to primates. And now that the disease has lethally affected rare and precious animals for conservation, the need for preventive interventions and safety measures in wildlife parks becomes even more urgent.
