No one is more vulnerable to fleas and ticks than our furry little friends. Their warm, fuzzy bodies make ideal hosts for the parasites, and they tend to spend time in grassy outdoor spaces, where they often come in contact with these disease-carrying critters. To protect them, many owners give their cats and dogs tick and flea medication. But a recent study shows this common practice could be inadvertently harming other insect populations.
The study, which was published by Oxford University Press USA in February, examines a relatively new class of antiparasitic drugs called Isoxazolines. These drugs are prescribed by veterinarians and orally administered to pets who then become protected against a whole host of parasitic assailants, including fleas, ticks, scabies, and ear mites.
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They work by attacking receptors in invertebrate species that paralyse and kill them, while having no impact on vertebrate species like cats and dogs. The problem is that the antiparasitics could be working on more than just parasites, finds the study. This is in addition to a growing body of evidence that suggests the increased use of Isoxazolines is negatively impacting the environment, including by potentially contaminating surface waters.
After oral consumption, the drugs are eliminated via fecal matter, urine, and even hair shedding.
To determine if non-parasitic insects are being harmed by the drugs, the study focussed on the main mode of excretion of Isoxazolines: fecal matter. As such, the study analysed the drugs’ impact on dung-feeding insects such dung beetles, flies, and certain species of butterflies.
The fecal matter of 20 dogs and 20 cats owned by veterinary students were analysed during and after being administered Isoxazoline drugs over a three-month period. After examining the waste, it was found that the drugs continued to be excreted long after being administered—up to 204 days for certain strains of Isoxazolines.
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Meanwhile, the study also found that concentrations of the drugs in the fecal matter were high enough to kill anywhere from eight to 92 per cent of dung-feeding insects, depending on the strain of Isoxazoline administered. “All situations result in a likelihood of high proportion of potentially exposed nontarget insects (98%–100%) if they consume feces from treated animals,” reads the study.
Dung-feeding insects play an important role in maintaining natural ecosystems. These small but mighty creatures improve soil conditions by breaking down waste, recycling nutrients, and reducing parasitic worm breeding habitats. One study even found that dung beetles can improve plant growth by up to 17 per cent.
Zooming out, Isoxazolines represent one of the many human-driven factors putting pressure on vital insect populations, alongside climate change, insecticides, habitat disruption, and invasive species. A 2019 study found that 40 per cent of insect species are in decline and, according to the United Nations, insect species are going extinct eight times faster than mammals, birds, and reptiles.
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