Flea Control Problems:

When holistic fails, go for the lesser evil

It is an odd thing to be thinking of fleas in the winter. It may seem an odd thing to be thinking of fleas at all! Yet not if you are a vet –'; not that I spend my nights awake worrying about the jumping critters and what they may do, but it is my job to consider alternative treatments.

Usually I entertain subjects of seemingly deeper meaning than flea control, posing ethical or philosophical questions and exploring possible answers. There is rather little philosophy in fleas and flea treatments: they are blood-sucking critters that love to live on our pets. Nova Scotia seems to be a nice place for them to live. Our humid climate provides the best conditions for flea reproduction, and as a result I spend significant time in my practice dealing with flea problems.

If it is of any comfort for those dealing with fleas on their pets, fleas may have a beneficial effect in puppies: by triggering allergy-like symptoms, they help the immune system learn to cope with actual allergies.

The flea we have in Nova Scotia is a cat flea called Stenocephalus cati. This flea is very versatile, living in cats, dogs, mice, rats, and if given the chance, humans. So do not blame the cat … again (after all, it was rats, not cats, who carried the fleas which spread the bubonic plague!).

Evolution is a process whereby living creatures find solutions to survival problems. Fleas have evolved a reproductive strategy that makes it difficult to control them – it is almost as if they were preparing for our attempts at such control. They feed on blood from the animal and then lay their eggs, tons of them. Their bites cause itching in the animal, so the animal scratches and off come the eggs, right onto the bed, carpet … everywhere. But we find flea eggs mostly on and around the areas where the dog or cat sleeps (which too often is your own bed). Warmth and humidity are the two ingredients that allow the eggs to mature, so we have the perfect combination of conditions for most eggs to mature, allowing the larvae to hatch.

Since the flea eats blood, it poops out a blood-rich material that dries up due to the heat generated by the animal. As the pet scratches, this 'flea dirt' falls off, and flea dirt is what the larvae eat. So, the flea has beautifully resolved the problem of how to feed its young. From the larvae stage, the flea goes on to form a cocoon, and as soon as it senses the presence of a warm-blooded animal, this cocoon turns into a jumping adult – which jumps onto the animal and starts the cycle again.

Fleas have been around for as long as there have been warm-blooded animals, so we are not going to get rid of them any time soon. Cold winters used to provide a climatic barrier, but our winters are becoming less cold, overall, and more humid. Humidity protects flea eggs from extremes of temperature. By contrast, there is hardly a flea in the dry prairies, but we are seeing fleas in Nova Scotia year 'round.

We have multiple strategies for flea control, but the main strategy is prevention. A healthy, well-nourished animal is less likely to catch anything or at the least, will suffer less from the effects of invaders. Many plants have insect-repelling substances, so if the animal likes to eat fresh greens, this may help a little. Strategically placing insect repelling plants such as Artemisia Vulgaris (also known as Wormwood) around a dog's bed may help to repel fleas. Garlic is also well-known insect repellent, and yeast appears to have insect repelling properties as well.

All of these things may help but in my experience, when fleas really decide to take over, garlic, yeast, DE (Diatomaceous Earth, tiny sharp crystals that mechanically kill the flea but may also scratch the cornea of the animal being treated – I wouldn't use it), and other natural products are practically useless. I've experimented in my own home and with willing participants, trying out different combinations of plants. Many of these turn out to be toxic, and I've found it difficult to control the dosing, while achieving only a rather mediocre effect at best. After much agonizing over this failure to come up with an effective all-natural flea control strategy, I researched the chemicals on the market. There are some topical treatments available, and some that are given internally. They all are very effective at controlling fleas but one in particular, Lufenuron (sold under the trade names Sentinel or Program) seems to be the least toxic of all.

Lufenuron is an insecticide that prevents the flea larvae from hatching, so that essentially they die of starvation. No amount of Lufenuron has shown to be toxic (at least in an acute form), which is to say that no amount of the chemical seems to cause toxic effects on the body and it is excreted unaltered. On ingestion, lufenuron does not touch the internal organs. When the flea bites the dog or cat, it receives a dose of the drug through the animal's skin, and excretes it in its poop, which is then passed on to its larvae – as described above. The larvae in turn cannot develop the necessary tooth, comprised of a protein called quitin, in order to hatch from the egg.

A problem I see with lufenuron is that it may affect other insects that depend on quitin for survival. The product needs to be given year 'round to prevent all possible larvae from surviving and its extensive use may negatively affect the environment. Still, on balance, lufenuron is the lesser evil among choices available.

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