Ron Hines DVM PhD 8/28/07

Introduction
Fleas are the most important external parasites of pets in the United States. In northern climates they are especially troublesome from July through October. In the southern half of this Country or in pets kept in a heated environment they are a problem all year long. Fleas are one of the most common reasons pets are brought to my animal hospital. Often, owners have no idea that fleas are the root of their pet’s problems. Ear infections, personality changes, anemia, tapeworms and hair loss are a few of the problems traceable to fleas.
Fleabites are not in themselves painful or itchy. It is the saliva that the fleas secrete to maintain the pet’s blood flow that causes irritation and itching (pruritis). This itching varies from pet to pet and is directly related to the number of fleas that are present on your pet. Fleabites leave a small, firm reddish pimple at the site of the bite. For reasons that I did not know ,fleas tend to congregate on the rump and dorsal base of a pet’s tail. A biologist who read this article, W. Baker, suggests that this is because at this location the pet has problems destroying them and because it is close to a source of moisture - their anus. Another common place to find fleas is surrounding the neck. Rather than look for the fleas themselves, I often look for tell-tail pepper-like granules on the pet’s skin. This material is the pet’s blood that has passed through the digestive system of the flea. If you are uncertain if this material is “flea dirt” or just dirt, wet one of these granules on a white paper towel or facial tissue with a drop of water. If the granule “bleeds” that is if the rust color spreads over the paper then fleas are present on your pet. Fleas jump on and off pets so none may be present when you make your exam. If one pet in your family has fleas, then they all do. No pets are immune to fleas. I have found the common cat flea on dogs, cats, rabbits, squirrels, ferrets, raccoons and opossums as well as lions and tigers. When they jump onto a human being, they usually jump off relatively quickly.

Flea Biology
Adult fleas are about 1/16 to 1/8-inch long, dark reddish-brown, wingless and hard-bodied. They are amazingly difficult to crush between fingers. Fleas are flattened from side to side. They have three pairs of legs. The most rear set are enlarged enabling fleas to jump amazingly far. It is said that fleas can jump 12 inches. That would be equivalent to a human being jumping over 400 feet! The flea’s narrow shape allows it to move rapidly through the animals fur. Fleas have mouthparts that pierce the skin and then siphon out blood. Cat, dog, human and rat fleas differ in the placement and length of the spines on their bodies. Flea eggs are laid on the pet’s body. They are smooth, oval and white. The flea larvae that hatch from these eggs are about 4 millimeters long. They are grub-like, slender, and off-white in color. These larva fall from the pet and live in cracks and niches on floors where they feed on dead organic matter or out of doors in sandy, shaded soils. Flea larva do not suck blood. They do actively avoid light. After a time, these larva develop into pupae – the non-motile developing fleas that are enclosed in silken capsules covered with particles of the debris in which the larval fleas lived. The time it takes a flea to complete this life cycle is extremely variable. It can be as short as two weeks or as long as eight month. The length of a flea’s life cycle is dependent on room temperature as well as a natural staggering of hatching time. Fleas lay about five hundred eggs in their lifetime. At any one time, about five percent of the fleas associated with a pet are adults on the pet. The rest are about evenly divided between eggs, larva and pupa. So you are dealing with a lot more fleas than meet the eye. Fleas position themselves motionless on the ground or in bedding. When an object cuts off light shining on the flea it hops. If it lands on a pet it is satisfied. If it lands on a person I usually leaves without biting. Certain people are more susceptible to flea bites than others. We do not know why.
A rather unique characteristic of fleas is that a large portion of them will remain dormant in their cocoons until vibrations, body warmth, and carbon dioxide emanating from pets or people cause them to hatch. This is why new occupants of apartments that appear free of fleas can suddenly be attacked by hoards of these parasites a day or two later. Adult fleas in this resting stage can live for up to one year. Once they have left their cocoons they can only survive about a week without feeding on a pet.
Fleas encountered in the United States are the cat flea, Ctenocephalides felis, the dog flea, Ctenocephalides canis, the northern rat flea, Nosopsyllus fasciatus, the oriental rat flea, Xenopsylla cheopis, the human flea, Pulex irritans and the rabbit flea, Cediopsylla simplex. Of these, the cat flea is the most common and does not confine itself to cats. These fleas are the carrier of the most common tapeworm of dogs and cats, Dipylidium caninum. I have read that this tapeworm can infest people if they should accidentally consume a flea but I have never encountered this.

Controlling Fleas
Controlling fleas on pets used to be a very complex and often ineffective endeavor. Until rather recently, we relied on toxic pesticides applied to the pet as well as to it’s home. Then, about fifteen years ago, insect growth hormone inhibitors became available that interrupted the flea’s life cycle. Some of these (methoprene, Precor) were applied to the pet itself either topically or orally. Others were sprayed on the pet’s environment. Most recently, two monthly-use compounds imidacloprid (Advantage) and fipronil/methoprene (Frontline) have become available. Both these products are remarkable in their efficiency in eliminating fleas. Hopefully, fleas will not become resistant to them. Fleas are tough, adaptable critters. It is doubtful that they will not find was to survive any compound eventually.

Advantage
Imidacloprid is an insecticide that paralyzes the central nervous system of the flea causing it to die. Because the nervous system of fleas and pets and humans are very different, imidacloprid is very safe when used as directed. It is sold by the Bayer Corporation as a topical solution containing benzyl alcohol and propylene carbonate under the trade name, Advantage. It can be safely administered at one drop per pound body weight on all pet species. Advantage mixes with the natural oils in your pet’s skin and hair and penetrates deep within the hair follicles and oil glands of the skin. It does not enter the pet’s body or circulate in the blood stream. The effect of this chemical kills fleas from thirty to fifty days after a single application to the nape of the neck. Because it is not water soluble, pets having received Advantage can be lightly bathed without loosing the chemical’s effect. Imidacloprid kills fleas very quickly – almost all fleas are dead within twelve hours after application. New fleas that hop on your pet die within two hours so the premises is quickly sterilized of fleas. Advantage is safe to use on ferrets, rabbits, and guinea pigs at one drop per pound.

Frontline
The combination of one of a new group of insecticides the arylheterocycles, called Fipronil and the insect growth hormone inhibitor, (S)-methoprene. It is marketed as Frontline by the Merial Corporation. It is slightly less effective against fleas than Advantage. It does, however, repel ticks, which Advantage does not do. Promotional information from the manufacturer claims that Frontline kills 100% of fleas on your pet within 48 hours after application to the nape of the neck. The average time it takes a flea to die on a Frontline-treated pet is 18 hours. Simple contact with the ingredients kills these parasites, which do not need to bite your pet to die. These drugs collect in the oil of the hair follicles from which it is slowly released. Like Advantage, Frontline interferes with the flea and ticks nervous system. Fleas tend to run around rapidly on a Frontline-treated pet before they die. I have no experience using Frontline on species other than dogs and cats. You can purchase Frontline from me.

ProMeris

The Fort Dodge Animal Health company recently introduced a new treatment for fleas on cats. It is called Promeris. Its active ingredient is metaflumizone. I have had clients tell me that some of the older products such as Frontline and Advantage are not as effective as they once were.

Pyrethrins
For safety on newborn pets and exotic species, no compounds are as safe as pyrethrins. It is usually sold in combination with a synergist, pipronyl butoxide. Its problem is that it has very little residual action and is rapidly broken down. Synthetic forms of the compound include permethrin, allethrin and resmethrin, which have more residual action. Pyrethrin is an extract of the flowers of certain chrysanthemum plants grown especially in Kenya in East Africa.. They kill fleas, ticks and lice by interfering with their nervous system. They have a reputation of being very safe. I have used the puppy/kitten formula on a wide variety of pets including snakes. Permethrin should NOT be used on kittens cats or rabbits.

Insect growth regulators
Insect growth regulators and insect development inhibitors are often added to flea-control products. These insect growth regulators include methoprene (Precor), diflubenzuron, , lufenuron, fenoxycarb and pyriproxyfen (Nylar). These products attach the immature stages of fleas only by preventing their maturation into adults. Insect development inhibitors prevent the formation of the flea’s outer skeleton composed of chitin. Since they do not kill adult fleas they are usually added to some ingredient that does. They are often sold as foggers and sprays. None are effective against ticks.

Organophosphates & Carbamates
These are the more old-fashioned insecticides used the world over. They include chlorpyrifos (Dursban), carbamates/carbaryls (Sevin dust), diazanon, malathion, fenthion and dichlorovos (DDVP-vapona). They must all be used with caution in environments where pets and humans are present. With the advent of Advantage and Frontline there is really no legitimate use for these chemicals for fleas. They do, however, still make good yard sprays for ticks if you follow the directions accurately. All the toxicity problems I have seen in pets were due to misuse of these compounds. Cats, greyhounds and whippets are particularly susceptible to overdose with these compounds.

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