Fleas in dogs and cats: treatment, prevention and home control

Summary

What are fleas?

The flea most commonly found on both dogs and cats is the cat flea, Ctenocephalides felis.

Adult fleas live on the animal, feed on blood and lay eggs in the coat. Those eggs quickly fall into the surrounding environment, including bedding, carpet, furniture and cracks in flooring. The immature stages then develop away from the pet before newly emerged adult fleas jump onto an available host.

This means pets do not need direct contact with another flea-infested animal to pick up fleas. They can acquire newly emerged fleas from contaminated environments as well as from other animals.

How do dogs and cats get fleas?

Dogs and cats can pick up fleas from other infested animals or from the environment. Direct contact is not required in every case.

Adult fleas live on animals and lay eggs in the coat, but those eggs quickly fall into the surrounding environment. They may end up in places such as pet bedding, carpets, sofas, floorboard cracks, under furniture, kennels, shaded soil and other areas where animals spend time. The eggs develop into larvae and pupae, and newly emerged adult fleas can then jump onto a passing dog or cat.

Pets may therefore pick up fleas:

• from another dog, cat or other infested animal
• in a home where fleas or flea pupae are already present
• from shared bedding, carpets or furniture
• in shaded outdoor areas where infested animals regularly rest
• from environments visited by wildlife, feral cats or other flea-carrying animals.

Fleas can even be introduced into a household by people or other animals, so indoor-only pets are not completely protected from infestation.

One flea-infested pet can also start a household infestation, because flea eggs drop from the animal into the home and later develop into new adult fleas that infest other pets.

Understanding the flea life cycle

Fleas develop through four stages:

1. Egg
2. Larva
3. Pupa
4. Adult flea

Adult fleas live mainly on the pet; eggs, larvae and pupae develop mostly in the environment.

The larvae feed and eventually develop into pupae enclosed within protective cocoons. The adult flea later emerges when conditions such as warmth, movement and carbon dioxide signal that a potential host is nearby.

This lifecycle is why simply killing the adult fleas you can see may not immediately solve the problem. Eggs, larvae and pupae may still be developing elsewhere in the home.

How do I know if my dog or cat has fleas?

Signs can include:

• scratching, licking, chewing or biting at the skin
• hair loss
• red or irritated skin
• small scabs or crusts
• restlessness
• visible fleas moving through the coat
• flea dirt – tiny dark specks in the fur.

Dogs with flea allergy dermatitis often develop itching and skin lesions around the lower back, tail base and hindquarters. Cats may develop crusted bumps, overgrooming, hair loss or intense itching around the head, neck, back or tail base.

Importantly, you may not actually see fleas, particularly in cats that groom frequently or in pets that are very sensitive to flea bites.

How to check for flea dirt

Use a fine-toothed flea comb and collect any dark specks from the coat onto a damp white tissue or paper towel.

If the specks dissolve into a reddish-brown stain, they may be flea dirt, which contains digested blood.

Why can one flea cause so much itching?

Some dogs and cats develop flea allergy dermatitis (FAD), an allergic reaction to proteins in flea saliva.

For these pets, even a small number of flea bites can trigger intense itching and inflammation. Repeated scratching, licking and chewing may then lead to hair loss, raw skin, hot spots and secondary bacterial or yeast infections.

This means a pet can have severe flea-related skin disease even when you cannot find large numbers of fleas.

If your pet is intensely itchy, develops sores or hair loss, or continues scratching after flea treatment begins, speak to your veterinarian.

How do I get rid of fleas?

Successful flea control has three parts:

1. Treat every pet in the household

Monthly oral flea preventatives can help control and prevent flea infestations when used consistently according to the label. These products do not necessarily stop a flea from jumping onto your dog; instead, they kill fleas quickly enough to help prevent them reproducing and maintaining an infestation. If fleas are already present in the home, you may still see newly emerged fleas for several weeks while immature stages continue to develop in the environment.

Depending on the product, flea preventatives may be given orally or applied topically, and some products also protect against ticks or other parasites. Your veterinarian can recommend an appropriate product and schedule.

Use an effective flea-control product that is suitable for the species, age, weight and health status of the individual pet.

Important safety warning for cats

Never use a flea treatment intended for dogs on a cat unless your veterinarian has specifically confirmed it is safe.

Some dog flea products containing permethrin can be highly toxic to cats.

2. Treat all pets consistently

If one pet has fleas, assume the other dogs and cats in the household may also be exposed.

All pets need appropriate flea control because untreated animals can allow the lifecycle to continue.

This does not mean using the same product on every animal. Products must be suitable for the individual species and pet.

3. Deal with the home environment

Most of the flea population in an established infestation may be present in the environment as eggs, larvae and pupae rather than as adult fleas on the pet.

Useful measures include:

• vacuuming carpets, rugs, furniture and areas where pets sleep
• washing pet bedding regularly in hot water where the material allows
• paying particular attention to cracks, edges and sheltered areas where immature fleas may develop
• continuing effective flea treatment on all household pets.

Environmental insecticides may sometimes be recommended for a heavy infestation, but they should be used strictly according to label directions and veterinary or professional pest-control advice. Keep pets, children, food and aquatic animals away from treated areas as directed.

Why do fleas seem to keep coming back?

Seeing new fleas after starting treatment does not necessarily mean the flea product has failed.

Flea pupae can remain protected in their cocoons in the environment before emerging as adults. As a result, newly emerged fleas may continue appearing for weeks after treatment begins.

Eliminating an established infestation can take two to three months, even when an effective flea preventative is being used, because of the immature stages already present in the environment.

Continue treatment according to the product instructions rather than stopping as soon as adult fleas disappear.

Do fleas only need treatment in summer?

No. Summer warmth and humidity can accelerate flea development, but fleas can survive year-round, particularly inside heated homes and in warmer Australian climates.

For this reason, Australian veterinary guidance generally recommends consistent year-round flea prevention rather than waiting until fleas appear in summer.

Summer is when flea populations can surge, but prevention should continue throughout the year.

Can fleas cause other health problems?