A recent study investigated whether planet Earth’s only venomous primate could help us understand why so many people are allergic to cats. The researchers believe that cat allergies might be the result of an ancient defense mechanism.
In the United States, cat allergies affect an estimated 12.1% of people over the age of 6 years. Symptoms include itchy eyes, a runny nose, coughing, sneezing, and wheezing.
Most commonly, the allergic reaction to cats is a response to a protein called FEL D1. All cats produce FEL D1 in their saliva and release it from certain glands. They spread this protein all over their body as they lick themselves.
New research by scientists from the University of Queensland in Australia might help explain why this allergy is so prevalent in humans. Their work focuses on one of nature’s most unusual mammals — the slow loris.
“Slow lorises are the only known primates with venom, and they’ve been virtually unstudied,” explains one of the authors, Dr. Bryan Fry, who works at the Cikananga Wildlife Center in Indonesia.
He continues, “Despite being a mystery to science, they’re commonly smuggled from the wild and sold in the pet trade, so our rescue center research was the perfect opportunity to do some good in a bad situation.”
When slow lorises fight each other, they raise their arms and lick venom-producing brachial glands on their upper arms. In doing this, they mix the venom with saliva, and if the opportunity arises, they use their incisors to inject this cocktail into their enemy.
The venom prevents the bite wound from healing, which can lead to tissue death, blood poisoning, and infections.
In humans, it causes an altogether different response, as Dr. Fry explains, “when humans are bitten, the victim will display symptoms as if they’re going into allergic shock.” Symptoms include a burning or tingling sensation, difficulty breathing, pain, and, in the worst cases, near fatal anaphylactic shock.
The slow loris excretions have a distinct odor due to their combination of more than 200 aromatic molecules. Although scientists have described these chemicals, they know little about the protein content of the venom.
Taking advantage of their unique access to these rare primates, the researchers decided to investigate slow loris venom in more detail, and they analyzed the DNA sequence of the protein in it. They published their findings in the journal Toxins.
Surprisingly, as Dr. Bryan explains, they found that it is “virtually identical to the allergenic protein on cats.”
This close similarity, the authors believe, could not have happened by accident. Knowing that the slow loris uses this chemical as a defense, they wonder whether FEL D1 might have evolved to help protect cats from predators.
The authors explain that the similarities between slow loris venom and FEL D1 are “reflective not only of shared molecular evolutionary history but suggestive of similar functionality.”
“This ability to trigger allergy as a weapon mightn’t be something restricted to slow lorises but may have separately evolved in cats at the same time. This is a fascinating hypothesis that we are looking to test in future research.”
– Dr. Bryan Fry
As human cat allergies are so common, Dr. Fry believes that it would be a “remarkable coincidence if this wasn’t an evolved defensive weapon, like the same protein used by slow lorises.”
Only a small number of mammals are venomous, including the platypus and vampire bat. As evolution has not equipped many mammals with this type of weaponry, scientists know very little about its evolution. This study adds a new piece of information to the otherwise sparse section of science devoted to the evolution of venom in mammals.