By Dr. Daniel Eubanks
The spring/summer season is upon us and with it comes one of the most dreaded nuisances — fleas! It is amazing how much annoyance can be created by such a little critter. But one peek at a flea under the microscope will reveal how they are capable of causing so much misery for both the pet and the owner.
They are 10 percent mouthparts and 90 percent egg-laying machine. They bite, suck blood, mate, lay eggs and then repeat this process until death do us part. One female flea can literally lay thousands of eggs per month.
There is only one flea that parasitizes our pets – Ctenocephalides felis. Both dogs and cats are usually infested by the same flea species. There are no “cat fleas,” “dog fleas” or “sand fleas”. Just fleas!
Adult fleas feed and mate on the host, either canine or feline. Female fleas usually leave the host and lay their eggs wherever they fall — in grass, carpeting or bedding. They may also lay eggs directly on the host, most of which fall off of the pet into the environment.
In either case, most eggs finally come to hatch in the environment, not on the host.
Eggs hatch into larvae which feed on organic debris (crumbs, skin scale, etc.) for about three weeks, then spin a cocoon and pupate. The new generation flea soon emerges and hops back onto a host.
This entire life cycle can take from five weeks to one year or more depending on environmental conditions and availability of a host.
Eradicating fleas is a challenge for several reasons. They are hearty, resilient pests and require bona fide insecticides to kill them. They are elusive in that their entire life cycle is not spent in one place. And lastly because one active ingredient isn’t capable of killing all four stages of the life cycle — egg, larva, pupa, and adult.
There is a huge consumer market for flea control products. Manufacturers provide a myriad of applications, thus constituting the “giant flea market.”
There are the old-stand-by products such as powders, sprays and dips. There are shampoos, collars and mousses. More recently, “spot-on” and even oral preparations have become available.
Each of these seemingly vastly different applications is merely a vehicle by which an active ingredient can be delivered to the host and make contact with the parasite. It’s the active ingredient that ultimately delivers the knockout punch, not the vehicle. So selecting the vehicle that is the easiest, most convenient method of delivering the proper active ingredient at an effective concentration to the appropriate location without toxicity to the patient is the challenge.
Active ingredients are of several types. Adulticides are the true insecticides that paralyze and kill adult fleas, whether on the pet or in the environment. They usually have no effect on the egg or the larva.
IGRs are insect-growth regulators. These mimic juvenile hormone in the larva and prevent the larva from molting into the pupa, thus interrupting the life cycle. An example is methoprene (Precor*).
Another ingredient is a chemical that prevents flea eggs from ever hatching in the first place. It is administered orally to the pet, is ingested by the flea while taking a blood meal, and is incorporated into the flea egg. These eggs never hatch into larvae. An example is lufenuron (Program*).
Both methoprene and lufenuron are useful because they break the flea life cycle and have a very wide margin of safety from toxicity to the host. However, neither one kills the primary problem — the adult flea.
A pet with an infestation of adult fleas should be treated with an adulticidal pesticide. There are a number of popular preparations available now called “spot-ons.” These are very small amounts of a concentrated liquid applied to a “spot on” the skin behind the neck once a month. These products kill adult fleas on the pet very effectively and conveniently.
Very young, geriatric or convalescing pets might better be treated with an adulticidal shampoo, spray or dip containing pyrethrin. This naturally occurring insecticide is derived from the chrysanthemum plant. It is very safe and effective, though short-lived due to its lack of residual activity.
Collars and powders are less effective applications. Both have offensive odors and powders make the pet unpleasant to handle afterwards. They’re also not color coordinated. Have you ever seen, smelled and cuddled a black cat after applying a white flea powder? Not pleasant!
Adult fleas in the environment can be treated with foggers and/or premise sprays containing one of many adulticides. Flea larvae can be treated at the same time with the same application by including methoprene.
Care must be taken not to use cumulative pesticides on the patient — that is, more than one of the same type of insecticide. An example would be using a spot-on product and a flea collar concurrently. One could, however, use a spot-on adulticide with the oral drug lufenuron to prevent flea eggs from hatching.
The important message is that effective flea control requires killing the adult flea on the pet and eliminating all stages of the life cycle in the environment. Caution should be exercised in using an appropriate active ingredient carried by an effective vehicle, considering the age and physical status of the patient and selecting products from reputable, responsible manufacturers. All of these products have the potential for causing side effects or adverse reactions, but careful, informed selections are almost always safe and effective in achieving flea control.
