The human-animal bond was built on parasite control

A client walks into the clinic with their dog. Their jeans appear black. Not denim black, moving black. Fleas. Thousands of moving fleas.

Back in the 1980s, we used to joke that the fleas carried the dog into the exam room, not the other way around. But honestly, it wasn’t really funny. It was exhausting, disgusting, and emotionally draining for the patient, client, and veterinary team. We saw flea infestations severe enough to cause life-threatening anemia in puppies and kittens. These patients presented lethargic, pale, and close to death. We removed the fleas, transfused and stabilized the patients, and then sent them right back into the same heavily contaminated environment because long-term flea control was nonexistent.

What is striking to me now is how dramatically parasiticides have changed over the course of my career. Veterinarians today simply don’t encounter the kinds of severe parasite burdens that used to be routine in practice, and that is a good thing. It speaks to how effective modern parasiticides have become and how much they have changed daily life for pets, owners, and veterinarians alike.

Fleas gone, but so is the house

I can remember when clients told me they had to rip the carpet out of their homes because they couldn’t get flea infestations under control. I would explain to owners that they needed to vacuum constantly, wash every piece of bedding, and immediately throw the vacuum cleaner bag away. Even as a veterinarian, not much makes my skin crawl, but there was a lot that made my skin crawl back then.

When it came to the patient’s treatment plan, we had what we jokingly called the “Vet-Kem tower” in our waiting room, shelves stacked with flea shampoos, dips, sprays, collars, and foggers, basically an entire flea-control survival kit. I would spend 30 or 40 minutes walking owners through the process of treating not only the pet, but the entire environment. Treat the dog, cat, house, and yard. Wash all the bedding, vacuum constantly, and bomb the house.Before setting off the flea fogger bombs, we had to remind owners to cover the fish tanks, remove the bird, put away the food, and be sure to turn off the pilot lights. (Congratulations. We solved your flea problem, but your house burned down.)

If that conversation wasn’t exhausting enough, right as the client was about to leave, staring at me with a completely defeated look on their face, I’d have to say, “Oh, and one more thing. You’re going to need to come back in 2 weeks and buy all of this again because your flea problem will probably be just as bad.” It was a full-time job for pet owners, and sometimes it felt like the Wild West.

The reality was that parasites dictated how people lived with their pets. They ruled where pets slept, how close families wanted them in the home, and, whether pets could fully become family members at all.

The era of “blunt instruments”

Parasiticides in the 1980s were like blunt instruments. We had products, but many were difficult to use, inconsistently effective, toxic, or completely dependent on perfect owner compliance.

Heartworm prevention is a perfect example. We started with diethylcarbamazine citrate (DEC), which had to be administered every single day. Filaribits (diethylcarbamazine) and later Filaribits Plus (diethylcarbamazine and oxibendazole) followed. At the time, those products felt revolutionary because suddenly we could target multiple parasites at one time. But there was almost no room for error. If owners missed several doses and the dog had harboring heartworms that hadn’t yet been detected, there was concern for potentially dangerous effects when restarting prevention. Now we weren’t just managing parasites, we were managing compliance anxiety as well.

At the same time, flea and tick products could create problems. We relied heavily on organophosphates and pyrethrins, and owners frequently misused products. Owners came in with very sick dogs and explained that they had treated the fleas with Sevin Dust. The problem was that Sevin Dust was to treat the yard, not the dog. Another product was Adam’s Flea-Off, which came in giant containers. I’d jokingly tell owners that they should keep a spray bottle next to the La-Z-Boy recliner and hose the dog down every time he ran through the living room. Not exactly precision medicine, but that was normal veterinary medicine at the time.

When the treatment was almost worse than the disease

Veterinarians weren’t just battling parasites back then; we were battling the limitations of medicine itself. Caparsolate was one of the early adulticide treatments for heartworm disease, and it was an arsenic-derived compound administered intravenously. If extravasation occurred, it could cause severe tissue necrosis at the injection site. It was horrible, but we used it because we had no better options. The same was true for generalized demodicosis before modern isoxazolines transformed treatment. Dogs would arrive nearly hairless with deep pyoderma and severe discomfort. Owners often tried home remedies before finally seeking veterinary care.

The most common one I remember? Motor oil.

Pet owners poured motor oil all over their dogs, trying to kill mites. Before I could even begin treating the mites, I first had to try to save a dog covered in motor oil.

Mitaban dips worked better than many previous therapies for demodectic mange, but they were labor-intensive, unpleasant, and carried toxicity concerns of its own. Nobody enjoyed those treatments, not the dog, not the owner, and definitely not the veterinary staff. Sometimes owners simply reached a breaking point. They would look at the cost of treatment, the severity of the disease, and the long road ahead and decide they couldn’t continue.

Too often, those conversations ended with euthanasia.

The stake in the ground

In 1995, Program arrived, and I still think of that moment as the stake in the ground. That was when veterinary medicine truly changed direction. Program interrupted the flea life cycle itself, and suddenly, we weren’t simply reacting to infestations anymore; we were finally beginning to control them. Products like Frontline followed, and everything accelerated from there. For the first time, parasite control became focused on long-term prevention rather than reaction. As pets became cleaner and healthier, they were able to live more closely with their human families.

How parasiticides built the modern human-animal bond

Modern parasiticides changed the way humans live with animals. Before effective parasite prevention, pets occupied a very different place in the household. Dogs and cats came inside, but people still viewed them as animals that belonged partly outdoors because parasites were simply accepted as part of pet ownership.

People worried about fleas in beds and ticks crawling across pillows in the middle of the night. They worried about tapeworm segments showing up on furniture and about zoonotic disease risks to their children and families. Those concerns create emotional distance, whether people consciously recognize it or not. We didn’t hear about dogs sleeping under the covers or cats curled up on pillows the way you do today. People loved their pets, absolutely, but the level of physical intimacy we now consider normal was far less common because parasite exposure was part of everyday life.

Modern parasiticides arrived and quietly changed everything. Pets and homes became cleaner, and flea infestations became less common. Tick control improved dramatically, and heartworm prevention became safer and easier. Parasiticides opened the door for the modern human-animal bond we now take for granted. Pets sleep in our beds, travel with us, sit on our couches, and become deeply integrated into family identity. They appear on holiday cards, have birthday parties, and are treated like children. If we were still relying on the parasite products we had available in the 1980s, pets would not be considered family members in the way they are today. That may sound dramatic, but it’s true. The modern human-animal bond exists because parasites lost the game.

The danger of success

Ironically, one of the greatest successes of modern parasite prevention may also create one of our greatest future risks. Success creates amnesia.

Veterinarians in practice today have never seen the parasite burdens that once defined everyday clinical medicine. Parasites never disappeared; veterinary professionals simply became very good at controlling them. If we stop respecting that reality, we could absolutely move backward.

Hookworm resistance is one of the best examples. Much of the problem traces back to the greyhound racing industry, particularly in Florida, where dogs raced on sandy tracks that created the perfect environment for hookworms to thrive. The dogs were repeatedly and aggressively dewormed, often without appropriate veterinary oversight, which helped drive the resistance. Then, greyhound racing declined, and retired racing dogs were adopted throughout the country. Unfortunately, resistant hookworms traveled with them. What started as a localized issue has now spread broadly into the general dog population, and today, 74% of resistant hookworm cases are no longer associated with greyhounds, and that should concern every veterinarian.¹

One of the biggest drivers of resistance is inconsistent compliance, exactly the challenge we continue battling every day in practice. When preventives are skipped, delayed, or administered inconsistently, parasites are repeatedly exposed to sublethal levels of medication. Over time, that creates ideal conditions for resistance to develop. Resistance doesn’t usually emerge through one catastrophic mistake, as it develops quietly through thousands of small ones. Unlike earlier eras of parasiticides, there may not always be another breakthrough product waiting around the corner. We’ve already stressed many of these molecules heavily over time, and there are limited new classes currently on the horizon. That means veterinarians play a critical role in preserving the long-term sustainability of the tools we still have available. More resistance equates to more parasites, and more parasites equate to sicker pets.

Sicker pets ultimately equate to a fracture in the human-animal bond.

Parasite control is public health

This conversation also extends far beyond pet comfort. Parasite control is public health, and we are seeing a dramatic expansion of tick populations across the US due to wildlife movement and environmental changes. Deer populations are larger than they’ve ever been in many regions, and ticks are moving right alongside them. Tick-borne zoonotic diseases like ehrlichiosis and Lyme disease continue expanding geographically, and now we’re seeing the rapid spread of the Asian longhorn tick. Dogs are sentinels and bring ticks into homes long before owners realize they have an environmental exposure problem. Up to 10% of infected dogs become clinically ill from Lyme disease, compared to 90% of humans.^2,3 That’s the human-animal bond again. If we protect the dog and cat, we help protect the family, too.

What we risk forgetting

Thanks to modern parasiticides, veterinarians in practice today rarely must witness the suffering that once defined our profession. They don’t see the flea anemia cases, the flea bombs, the toxic flea dips, the carpets ripped out of living rooms, and the arsenic heartworm treatments. Much of that world has faded into memory, and that is wonderful.

However, it also creates a challenge for veterinarians because when clients don’t see parasites anymore, they stop fearing them. Prevention starts feeling optional instead of essential, and that is where veterinary teams can struggle.

Adding to this, the success and high quality of modern products can work against us. When a client sees a flea or 2 on a pet while using a preventative, they may assume the product has failed. In reality, they often don’t realize just how effective these medications truly are. There is very little understanding of how these products work, what “control” means, and how much worse things would be without them.

If we don’t genuinely believe in the value of parasite prevention ourselves, clients can feel that immediately. The entire veterinary team must understand the “why” behind the recommendation and communicate it consistently. One voice and message. What’s our message on fleas? About ticks? About heartworm prevention? When every team member communicates the same consistent message, it has a tremendous effect on client behavior.

We sometimes make the mistake of assuming cost is the main barrier. Cost becomes the issue when value hasn’t been established. If clients truly understand what parasites used to do, what they still can do, and why prevention matters for both the pet and the family, those conversations become very different. Clients are not simply paying for a product. They’re paying for protection, prevention, and peace of mind. That’s why veterinarians can’t be afraid to make strong recommendations.

Clients are paying for our expertise and our judgment. They’re not asking us to behave like a retail store and present 15 different options with no guidance. They want us to tell them what we believe is best for their pet and explain why it matters. That matters now more than ever because parasites are still here and resistance is still developing. Tick-borne diseases are expanding geographically. The risks never disappeared—we just became very good at controlling them.

Biscuit, my 2-year-old Boston Terrier, lives a completely different life from the dogs I treated early in my career. She lives indoors, sleeps comfortably, receives modern medicine, and enjoys a level of close daily companionship that would have been much harder for families to comfortably maintain decades ago.

Looking back now, the modern human-animal bond did not simply emerge naturally on its own.

It was built.

References

1. Leutenegger CM, Lozoya CE, Tereski J, Savard C, Ogeer J, Lallier R. Emergence of Ancylostoma caninum parasites with the benzimidazole resistance F167Y polymorphism in the US dog population. Int J Parasitol Drugs Drug Resist. 2023;21:131-140. doi:10.1016/j.ijpddr.2023.01.001
2. American Veterinary Medical Association. Lyme disease in dogs. AVMA. Accessed June 9, 2026. https://www.avma.org/resources-tools/pet-owners/petcare/lyme-disease-dogs
3. The Ohio State University College of Veterinary Medicine. Lyme disease fact sheet. Published January 23, 2020. Accessed June 9, 2026. https://vet.osu.edu/sites/default/files/documents/Lyme%20Disease%20Fact%20Sheet%2020200123.pdf