Some of these parasites are dangerous for your and your dog’s and cat’s health, with the most important being fleas, ticks, flies, and mosquitoes.
Veterinarians prescribe parasite control solutions, as a measure of precaution, monthly or every three months. But, are these harmful to our dogs, families, homes, and environment? Well, yes, they can be.
Important note: Most anti-parasite substances are toxic to humans if used/applied improperly.
Here’s a list of the most common ingredients used in spot-on solutions, to prevent or treat flea or tick infestations and information on how toxic or harmful they are.
Fipronil Based-Solutions
Fipronil was among the first ingredients used to kill fleas, lice, and ticks and as a pesticide, mainly for preventing Triatoma infestans infections, a blood-sucking bug that spreads Chagas disease in humans in some Latin countries. It is still widely used for dogs and cats.
Fipronil-based solutions are applied topically, on the dog’s and cat’s upper torso. After the skin absorbs the substance, it goes into the bloodstream, from where it reaches body fat, the brain, and the liver. Here, it is metabolized into fipronil sulfone.
Insects bite animals and ingest the fipronil when they come in contact with the animal’s blood. The fipronil blocks GABA-gated chloride channels in insects’ central nervous systems, leading to their death.
A single application effectively kills ticks, fleas, and lice and keeps the animals safe from reinfesting for up to 4 weeks.
Fipronil sulfone metabolite is responsible for the fipronil-induced toxicity. It is highly toxic to fish and other aquatic invertebrates. Water may be contaminated by bathing animals treated with these products.
Homes can also be contaminated by direct contact with the animal’s treated skin and by residual waste coming from the animal’s body. This is an important aspect, especially for families with children. They can accidentally ingest fipronil by touching areas where fipronil residues are found or by touching the areas treated on the animal.
Although the danger of human exposure to these substances is reduced, the health problems they can cause are not negligible.
Recent studies have shown that it has a potentially toxic effect on mammals and humans and can interact with certain administered drugs. Also, it may cause behavioral and cognitive changes to animals it is applied to.
Fipronil acute toxicity manifests in humans with intense sweating, nausea, vomiting, dizziness, abdominal pain, and even seizures. In dogs and cats, fipronil causes signs of neurotoxicity.
In vivo and in vitro studies have shown that fipronil causes cellular oxidative stress in mice and rats, which damages lipids, DNA, and proteins.
Chronic toxicity may lead to thyroid impairment and tumors in lab animals. Due to extensive recent research, fipronil is classified as a “Group C – possible human carcinogen”.
Pyrethrins
Pyrethrins and their synthetic derivates, the pyrethroids are synthesized from chrysanthemum flowers. Pyrethroids were created to resist sunlight better than pyrethrins.
They’re widely used due to reduced environmental damage and are less toxic than other insecticides to fish, animals, and humans.
They mainly alter nerve function in insects, causing subsequent paralysis and death, although the specific mechanism of activity is uncertain.
They’re used in households against ticks, fleas, and lice in pets and farm animals, and for treating clothes, furniture, and crops against harmful insects.
Pyrethrins and pyrethroids must be applied in greater quantity and more often than other insecticides because they degrade quickly. They’re usually diluted with water and applied by spraying directly onto surfaces and animals.
According to the product’s label, they can be applied directly to humans, in small quantities, against scabies and pediculosis. Intoxication may occur if the recommended dosage is exceeded.
Unlike other insecticides used in pets, pyrethrins and pyrethroids can cause toxicity by inhalation, apart from direct skin contact and ingestion.
High levels can cause acute intoxication symptoms, such as nausea, dizziness, muscle twitching, headache, mental status alterations, convulsions, and even loss of consciousness.
Dogs are more resistant to pyrethroid-induced toxicity and exhibit only nervous symptoms, but cats are more sensitive.
Intoxicated cats can exhibit drooling and vomiting, tremors, signs of hyperexcitability, seizures, weakness, and difficulty breathing, which can progress to death if untreated (treatment should come as soon as possible).
Cats can accidentally ingest the product when licking the treated areas, by direct skin contact when entering areas treated against insects, or, as I’ve commonly discovered, by inappropriate flea treatments designed for dogs only, which have been applied to cats.
In mice and rats, research has shown that pyrethrins and pyrethroids can cause a decrease in sperm motility, sperm count, and lactating issues, and in men, a reduction in semen quality.
Studies have shown that pyrethrins and pyrethroids can cause infertility by decreasing the ovarian reserve in women. This means that women who currently use or have been in close contact with these substances may have trouble getting pregnant.
Imidacloprid
Imidacloprid is a neonicotinoid substance similar to nicotine, that acts on the insects’ central nervous system. Its uses include topic spot-on dog and cat solutions, usually combined with other antiparasitic substances to increase efficiency, because it is more active against fleas than other parasites that affect domestic animals.
It is more toxic to insects than to mammals and fish.
For about 20 years from 1999, it was the most widely used insecticide in the world for pest control in agriculture. But, because it was lethal to honey bees, it was banned for outdoor use.
Imidacloprid is toxic by inhalation and aerosols are more toxic than dust containing it. It is corrosive to the skin and eye, which can be irreversibly damaged.
After ingestion, humans can suffer from nausea, dizziness, vomiting, disorientation, diarrhea, and fever. High doses can cause severe cardiac toxicity. Animals may experience lethargy, vomiting, diarrhea, hypersalivation, tremors, seizures, and even coma.
Chronic exposure can lead to liver damage in laboratory rodents and reduced bone growth in puppies.
There isn’t enough research on the effects of long-term exposure to imidacloprid in humans. It is classified as a ”Group E substance, no evidence of carcinogenicity”.
Moxidectin
Moxidectin is used in pets as a spot-on solution associated with imidacloprid and as oral and injectable formulations, against fleas, ear mites, notoedric mange, gastrointestinal nematodes, and prevention of heartworm disease.
In human medicine, it is used for treating the tropical disease called “river blindness” or onchocerciasis. This is caused by a microscopical worm and transmitted by blackflies which causes skin conditions and even blindness.
Moxidectin toxicity in humans can be caused by accidental ingestion or overdose or by direct skin contact. Clinical signs include dizziness, fatigue, diarrhea, increased heart rate, liver enzymes increase, and transient CNS-related clinical signs (piloerection, abnormal gait).
Dogs treated with high doses of moxidectin exhibited salivation, tremors, and ataxia.
Cats can withstand up to 10 times the recommended dose. They may exhibit transient CNS-related clinical signs such as salivation, vomiting, ataxia, generalized tremors, dilated pupils, nystagmus, and abnormal respiration.
Up to this point, no studies have shown long-term carcinogenicity effects of moxidectin.
Fluralaner
Fluralaner is a new-generation systemic drug used for treating fleas and tick infections in cats and dogs and in vitro, tested against bed bugs. It was approved by the US FDA in 2014. Fluralaner inhibits GABA-chloride channels in insects.
It is administered orally as chewing tablets at 12-week intervals. It is very well tolerated and the effect sets in after the first hours after it is administered.
It can be administered topically along with moxidectin in cats every 2 months against fleas, ticks, and heartworms.
However, individual neurological toxicity signs can occur in some dogs treated with fluralaner, which include ataxia, tremors, dysphagia, and muscle twitching.
Cats tolerate fluralaner very well, without any particular toxicosis signs.
In humans, fluralaner is still undergoing studies, but oral and dermal acute toxicity is low.
Selamectin
Selamectin is a topical substance used against fleas, heartworms, ear mites, scabies, notoedric mange, nasal mites, cordylobiolosis, and certain ticks in dogs and cats.
Cats and dogs treated with selamectin didn’t exhibit signs of toxicity or reproductive problems.
Cats that accidentally swallowed selamectin by licking the treated areas exhibited excessive salivating and vomiting.
Selamectin exposure can be considered an important health risk to pet owners. The highest potential for human exposure is the first 24 hours after application because the selamectin concentration is the highest. Residues that can be easily transferred to the skin were observed after 4 weeks post-application.
Up until now, no studies can prove selamectin’s effects on human health.
How To Avoid Exposure
Parasite control solutions may contain other ingredients that are not human-friendly, besides the main substance that kills bugs. To keep yourself and your family safe from these chemicals, there are a few rules you have to follow.
1. Avoid touching & petting
If your pet has recently been treated for parasite control, avoid touching and petting it, until the treated areas are completely dry. If you have children, limit their access to the areas where the animal stays. Pets can contaminate the area with harmful chemicals by aerosols or by skin contact.
2. Don’t share
Your pet shouldn’t be allowed to share your bed or couch, at least 48 hours after it’s been treated.
Residual debris and hair impregnated with these substances may end up on your sheets or furniture and you may contaminate by close skin contact or inhalation.
3. Clean your home thoroughly
A couple of days after applying parasite control solutions on the animal, beware of ticks that may fall off the animal and which it can eat. These can contain toxic chemicals that your animal may ingest. It’s best to vacuum the areas where the animal has access to, to ensure proper removal of insects and debris.
4. Wash your hands more often
After petting the dog or cat which was treated with parasite control solutions, be careful to wash your hands thoroughly. Children are more susceptible to contamination because they don’t wash their hands as often as adults do after petting the animal or after playing around the house.
