Fleas in Dogs and Cats

By Nancy Otten, Animal Health Technologist

How do dogs and cats get fleas?

They get fleas either directly or indirectly from other cats and dogs.  Pets can pick up fleas from being in close contact with other animals that have fleas.  They can also pick them up from their environment or, more specifically, the environment that flea-ridden animals hang out in.  Here is how that works.  The flea doesn’t complete its whole life cycle on the animal.  After feeding on the animal’s blood, the flea will lay eggs within 36 to 48 hours.  These eggs will drop off of the animal and will settle down into the environment.  Inside a house this will mean that they will settle into the carpet, between the couch cushions, and underneath the refrigerator.  Outdoors, the eggs will collect in areas where animals like to hang out like under that nice, shady tree or under the porch.  These eggs will hatch in anywhere from one to ten days, depending on the temperature and humidity (the warmer the temperature and the higher the humidity, the faster they will hatch.)  They live as larvae for five to eleven days where they feed on flea dirt (flea feces which consists largely of digested blood) and pet dander (small scales from pet hair.)  They then pupate and live in these cocoons from 5 to 140 days, depending on whether or not conditions are right.  They will wait to emerge as adult fleas until they receive the appropriate cues which are movement or vibration, carbon dioxide, and heat.  When they perceive these things, they know that there is an animal nearby so will emerge from their cocoon ready to jump onto your unsuspecting pet. 

How do I know if my pet has fleas?

Some cats and dogs get very itchy when they are being bitten by fleas but not all animals do.  In fact, most animals have very limited itching due to flea bites.  This means that you can’t discount fleas if your pet isn’t scratching a lot.  A very simple way to determine if your pet has fleas is to use a flea comb (a comb with very tightly spaced teeth.)  Drag the comb across your pet, especially along the back near the base of the tail.  It is unlikely that you will catch an actual flea this way but you may collect evidence of their existence.  It is important to be careful when doing this so that you do not lose the debris that you collect in the teeth of the comb.  Shake this debris out onto a wet piece of white paper.  If, after about 30 seconds, the black debris turns reddish brown on the white paper, the debris is flea dirt (feces.)  This means that your pet has fleas.

Can fleas cause problems for my pet?

Fleas can cause significant problems for your pet.  A heavily infested animal, over time, can lose a substantial amount of blood.  This is especially true in very young or debilitated animals.  70 fleas can consume 1 mL of blood per day which could kill a puppy or kitten in 50 days.  Double the number of fleas and the young animal can be dead in a month.  They lose so many red blood cells to the fleas that they become anemic and die.  Flea allergies are also a problem.  Some animals develop an allergy to the flea’s saliva.  When these animals are bitten they experience severe itchiness and they scratch and chew at themselves so much that they actually do damage.  There is also a link between fleas and tapeworms.  Dipylidium caninum, a type of tapeworm that infects dogs and cats, must complete a stage of its lifecycle within the flea in order to survive.  Because of this, flea and tapeworm problems often go hand in hand.   

How do I rid my pet of fleas?

There are so many flea products on the market that choosing one may seem like an overwhelming task.  I hope that this will clarify things.  There are many different brands of shampoos, mousses, sprays and powders that you can apply to your pets to rid them of fleas.  They may kill the fleas on your pet at that point in time, and may provide short-term relief, but within a day your pet may be covered in fleas again.  This is because these products have no residual effect; they kill the adult fleas present on your pet but won’t kill the ones they will subsequently pick up from the environment.  Flea collars are somewhat effective but won’t be adequate if your pet has a heavy flea infestation.  Also, flea collars may cause skin irritation.  Because of these shortcomings, shampoos, mousses, sprays, powders and collars are pretty much obsolete.  Advantage and Revolution are products that are applied to the skin at the back of your pet’s neck.  The oily liquid is absorbed into the hair follicles and oil producing glands and naturally spreads over the animal’s body.  These products are adulticides which means that they kill the fleas in their adult stage.  Revolution not only kills fleas but also kills ticks, heartworm, ear mites, and the mites that cause mange.  Their residual effect is about 4 weeks so these products need to be reapplied monthly.  Program comes in three forms:  a chewable tablet for dogs, an edible liquid for cats and an injectible form for cats.  These products do not kill the adult fleas but act as a sort of flea birth control.  The flea who consumes blood from an animal that has been treated with program will lay eggs that never hatch.  You eventually rid the environment of fleas because the fleas feeding on your pet will die naturally and all of the eggs that they have laid will never hatch.  The flea population in your pet’s environment will just fade away.  Sentinel is a product that will also kill fleas.  It is a combination of Program and Interceptor, a product that kills heartworm, roundworm, hookworm and whipworm.  Sentinel and the tablet and liquid forms of Program, also have a residual effect of 4 weeks so must be given monthly.  The injectible form of Program lasts for 6 months.  Capstar is a tablet given orally.  It will kill the fleas on your dog within 4 hours and on your cat within 6 hours.  It has no residual effect, however, so in order to keep your pet free of fleas you would have to give a tablet daily.  Due to this inconvenience, Capstar is best used when bringing a flea-infested animal into a flea-free environment (like when you bring a new pet home.) 

Advantage, Revolution, Program, Sentinel and Capstar are all products that are sold through your veterinarian.  Beware of products sold in pet stores that intentionally have similar names and packaging to these products.  They may be cheaper but they do not contain the new, safe pesticides contained in the products sold by your veterinarian.  For example, pet store products that work under the same principle as Advantage and Revolution (oil placed on the back of the pet’s neck) are less expensive.  However, they are toxic to cats and are not water fast.  It may appear that they are the same products but they are definitely inferior.     

How do I rid my house of fleas?

Because of the great effectiveness of products like Program and Advantage, it may only be necessary to treat your home in the case of severe infestations.  If necessary, you can purchase premise sprays and fogs from hardware stores, pet stores and veterinary clinics.