You never read about it: a chimpanzee with a fig allergy or a deer with hay fever. Weird actually. Some cats and dogs are allergic to certain foods or substances in the house or in the city. Why shouldn’t wild animals be allergic to substances that occur naturally in their environment?
Jooske IJzer, veterinary pathologist at the Dutch Wildlife Health Center of Utrecht University, thinks it’s a nice question. “I myself have never had a case on my cutting table, or under the microscope, where I knew for sure: this is an allergy,” she says, “but that doesn’t mean it doesn’t happen.”
In fact, Iron sees no reason why it couldn’t. “Wild mammals have the same immune system as we do. So that might as well get out of hand once in a while.”
But in wild animals, allergies will quickly pick out, she notes. There is often a strong genetic component to it. “A deer with hay fever will be less able to breathe, run less well, be more vulnerable to predators and spend less time eating. On average, such a deer will then have fewer offspring.”
Yzer explains how she investigates a wild animal that is brought into the DWHC dead. “We carefully examine the animal from the outside. Then you could see irritated mucous membranes or red skin, for example,” she says. “But they can also indicate a parasitic infection.” To investigate this further, she looks at wafer-thin tissue samples – sections – under the microscope. “Then you can see which immune cells are involved in an immune response. But here too we see an overlap between allergy and infection.”
Let’s turn the question around: why people and their pets can be allergic. First of all, because the disorder does not select itself so quickly in them. Natural selection has lost control of humans and their pets in recent centuries, thanks to the availability of good food, medicine and housing and the absence of predators. “But evolution generally takes place over hundreds of generations,” notes IJzer, “while in the past two or three generations we have seen significant changes in humans when it comes to allergies.”
Why have people and their pets become so much more allergic in recent decades? The number of people with eczema has increased by a factor of 2 to 3 in industrialized countries over the past 20 years increased; 10 to 40 percent of Europeans are now allergic to something, and that will probably be half by 2025. The explanations for this increase vary. One of them is the hygiene hypothesis , which states that we have started to live too ‘clean’, as a result of which our immune system is insufficiently trained. But that hypothesis is increasingly under pressure.
In addition, there is some evidence that climate change and changes in our diet are fueling allergies in both humans and their pets. And because they often live in the same environment, they appear to share many allergies – especially in urban areas. All these factors are less relevant for wild animals.
“But again, I cannot rule out the possibility that wild animals do have allergies,” concludes IJzer. “We know they can have individual food preferences. Maybe they have something to do with allergies. In general, animals avoid foods that they do not respond well to – although in nature there is often not much to choose from.”