A polar bear looking at the camera over a patch of grass and seeding plants with a cave behind (Credit: Lincoln Park Zoo)
Siku, a polar bear at Lincoln Park Zoo, developed allergies to various substances including human hair dander (Credit: Lincoln Park Zoo)
It may be that zoo animals are so well cared for they develop allergies as a side effect.
In 2018, staff at Lincoln Park Zoo in Chicago began to notice something unusual about a male polar bear named Siku. He was losing hair, revealing patches of black skin underneath. Evidently itchy, he was scratching and rubbing himself against his enclosure. Kathryn Gamble, the zoo's director of veterinary medicine, had a hunch what was wrong: allergies.
But what would a polar bear be allergic to? Gamble and her colleagues anaesthetized Siku and conducted a skin test, injecting small amounts of various allergy-provoking substances into his skin. Siku's skin reacted against house mites, as well as elm, mulberry and red cedar pollen. Oddly enough, "one of the things that he initially showed a very strong response to on his skin was actually human hair dander", Gamble recalls.
We often think that allergies only afflict people, but a broad range of other animals can also develop them. That includes pet dogs and cats – in which experts say allergies are on the rise – but also everything from rhinoceroses, bats, dolphins to chimpanzees and rhesus monkeys. Lincoln Park Zoo staff say they have seen allergy-afflicted black leopards, fennec foxes, saki monkeys, Japanese macaques and black bears.
Fortunately for itchy animals living in captivity like Siku, animal allergies are treatable, just like in humans. But these cases may also tell us something deeper about how and why allergies develop.
Scientists speculate that animals get allergies for similar reasons as people in many Western countries – especially those living in cities – who are currently experiencing a rise in allergies.
Some experts blame the fact that pets, as well as farm and zoo animals, are increasingly being raised in manmade environments where they're less exposed to the parasites, microbes and other pathogens that they evolved with, causing their immune system to go awry.
"In dogs and cats, the numbers definitely have gone up, as the numbers in people have gone up," says Annette Petersen, a veterinary dermatologist at Michigan State University. "I wouldn't be surprised if more zoo animals [are getting] allergies too," she adds – although no research has yet looked into whether or not this is the case.
Allergy symptoms can vary across animals. Humans and other primates that inhale allergy-causing substances through the nose often develop hay fever-type symptoms, with discharge, sneezing and weepy eyes. But most animals absorb allergy-provoking substances through the skin and develop skin conditions, says Andrew Rosenberg, a veterinary dermatologist and director of medical operations at the Animal Dermatology Group, a US-based veterinary company.
Experts say allergies in dogs are on the rise too, with flea and environmental allergies more common than food allergies (Credit: Getty Images)
Experts say allergies in dogs are on the rise too, with flea and environmental allergies more common than food allergies (Credit: Getty Images)
The cats Rosenberg sees will often scratch their face and neck, tear out hair, or develop pink plaques or crusted pimples on their bodies. Allergic dogs will lick itchy paws and scratch at armpits and groin areas – and tend to develop ear infections. Horses can break out in hives. Occasionally, Rosenberg also sees allergic zoo animals – like the itchy female rhinoceros and her calf from New York's Bronx Zoo that developed severe rashes, bloody ulcerations and weeping infections.
Put simply, allergies occur when the immune system – which is supposed to protect us from harmful parasites, bacteria or viruses – mistakenly produces an exaggerated response to harmless substances, like peanuts or pollen.
It's unclear what exactly is causing the current rise in allergies among people. While some experts used to solely blame the fact that humans are increasingly growing up in cleaner, more hygienic environments where they're less exposed to microbes than in the wild, research is now pointing to a wider set of factors that also involves the loss of important microbes and parasites that live in and on our bodies, says Andrea Graham, a parasitologist at Princeton University.
Frequent cleaning and soaps likely contributes to our reduced exposure to these organisms, alongside the use of antibiotic drugs and ointments, greater distancing from domesticated animals and parasite-free food, Graham says. (People can take some steps to help reduce the likelihood of allergies, however – read more about the habits that help prevent allergies here**).**
The loss of certain parasites and microbes in our guts may be particularly consequential; scientists believe that these used to play an important role in our biology by suppressing and modulating our immune system in order to avoid being attacked by it, says Graham. Now, without these organisms to rein in and train our immune response, our immune system is more likely to go into overdrive, including against harmless pathogens, she adds.
Scientists also believe that early childhood exposure to microbes and parasites is especially important for training the immune system to correctly discriminate between harmful and harmless substances and mount an appropriate response. "Early life is really important for getting the tuning of your immune system right," Graham says.
Some of the best evidence for this theory comes from studies of Amish populations in the US. One 2016 study compared Amish children in Indiana state, who use traditional farming practices and are exposed to lots of microbes through interactions with farm animals and house dust, with children from Hutterite communities in South Dakota, who use highly industrialised farming practices and live in households less exposed to dust and animals. Though both populations were genetically very similar, "the rate of allergies was about four times higher in the Hutterites who had taken on modern industrial farming", says Andrew Flies, an immunologist at the University of Tasmania's Menzies Institute for Medical Research.
Rhinoceroses in captivity have also been found to have developed allergies, including severe rashes, bloody ulcerations and weeping infections (Credit: Getty Images)
Rhinoceroses in captivity have also been found to have developed allergies, including severe rashes, bloody ulcerations and weeping infections (Credit: Getty Images)
Flies, Petersen, Graham and Rosenberg all suspect that animals kept in households, farms and zoos might develop allergies for similar reasons. They typically get dewormed and vaccinated to prevent infections, and are generally less exposed to the bacteria and parasites they evolved with compared to their relatives in the wild, Graham says.
For zoo animals, Petersen says, "the food they're eating is parasite-free and probably not heavily bacterially contaminated". Compare that to a bacteria-smothered cadaver a lion would eat in the Serengeti, probably together with the prey's microbe- and parasite-containing guts.
In other words, it may be that animals are so well cared for in zoos they develop allergies as a side effect.
While no-one has yet published a specific study looking into this, Flies and others suspect that allergies are much more common in these more human environments than in the wilderness. In the wild, allergies might affect the survival of animals – for instance if allergic animals scratch themselves and develop infections, Flies says. Petersen recalls a lion with allergies she once treated who had developed a bad ear infection. "If he can't hear well in the wild – if the ears are plugged with pus and stuff from the infection – that would obviously be a major disadvantage," she says. For these reasons, allergies may have disappeared from wild populations.
But that theory is tough to prove. Animals in the wild may well have allergies, Gamble says – but we would be less likely to spot them.
What may have contributed to Siku's allergies, Gamble adds, is the fact that he had been moved to Chicago two years before he started developing them. Often, "if a person moves to a new environment where they're exposed to pollens that their bodies have never seen before, they have a response to it," she says.
Other factors may also be contributing to allergies in animals. Rosenberg says that in his clinic in the northeastern US, where he's seen rising cases of pet allergies, this may be linked to climate change, which is causing higher pollen counts and longer allergy seasons. "It's my impression that we're seeing more common allergies and we're seeing more severe allergies than ever before," he says.
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As awareness around animal allergies is growing, so is knowledge on how to treat them. Rosenberg was able to treat the allergic rhinoceroses with an approach similar to allergy shots in people, injecting them with small doses of the allergy-provoking substances and gradually dialling up the dose to teach their immune systems that they don't represent a threat and to lessen their response.
After treatment of allergy-provoking substances mixed into organic honey, Siku became much less reactive to these substances (Credit: Lincoln Park Zoo)
After treatment of allergy-provoking substances mixed into organic honey, Siku became much less reactive to these substances (Credit: Lincoln Park Zoo)
Siku the polar bear received a similar treatment, receiving a combination of allergy-provoking substances mixed into organic honey – the licking of which helped the substances get absorbed through the soft tissues in his mouth. Honey has the added benefit of containing some local pollen itself, Gamble adds. And sure enough, during another allergy test 36 months after the treatment, Siku was much less reactive to the substances he had previously been allergic to – including human hair dander.
For a long time, studies of animals have been used to better understand health conditions in people, but allergies are a rare case where lessons learned in humans may help animals, Flies says.
One lesson is the value of being exposed to a rich community of microorganisms. As many people turn to yoghurts and other probiotics for their health benefits, including a reduction in allergies, perhaps researchers can find ways to do the same for zoo animals, farm animals and pets at risk of developing allergies, says Graham.
"I'm hopeful that more and more people will study it because I do think we're still battling against this idea that 'clean' is always healthier."
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