Cat World > Feline Parasites

Heartworm in Cats

Feline Parasites

How do cats get heartworm disease?   Life cycle of heartworms   What damage do heartworms do?   Symptoms of heartworm disease   How is heartworm diagnosed?   Treatment of heartworm disease   Do cats need a heartworm preventative?   What age should I start my cat on a preventative?   What happens if I forget to give my cat his heartworm preventative?   Reducing the risks of transmission of heartworm   Can I catch heartworm from my cat?

heartworm in cats

Also known as dirofilariasis, heartworm disease (HW) is a serious parasitic infection caused by the nematode Dirofilaria immitis which lives in the pulmonary arteries, lungs, and hearts of cats. Heartworms are a type of roundworm, with adult heartworms reaching a length of 12 to 30 cm.

Heartworms are a common parasite in dogs, although cats can also become infected and may develop disease. While cats may be more resistant to heartworm infection than dogs, cats, in particular, are extremely vulnerable to heartworm and even a small number can cause death.

The definitive host of D. Immitis is the dog, however they can infect wolves, cats, ferrets and humans. Infection in non-canine species is usually lighter, with fewer worms, however serious and life threatening consequences can develop.

There is no age or breed predilection, males have been shown to be easier to infect experimentally. Outdoor cats are at greater risk due to their increased exposure to mosquitoes.

Heartworm can be found in temperate and tropical regions of the world in particular Australia, the USA (all 50 states), Southern Europe, South America and Japan. More than 70 species of mosquito are capable of transmitting heartworm.

How do cats get heartworm disease?

Microfilaria (baby heartworms) are present in the blood of an infected animal (in most cases, a dog), when a female mosquito feeds on the blood, microfilaria are also ingested, once inside the gut of the mosquito, they undergo further development before migrating to the labium (a part of the mouth) of the mosquito. When the infected mosquito feeds on another host (in this case, your cat), the larvae move from the mouthpart and onto the skin of the cat (or dog), from there, they enter the bloodstream via the bite wound left behind by the mosquito.

Life cycle of heartworms:


  • In an infected animal, the adult heartworms produce their young, known as microfilaria, which swims around the bloodstream. Microfilaria requires an intermediate host in the form of the mosquito. When the mosquito bites an infected animal, it takes up some of these microfilaria circulating in the animal's blood. Once inside the mosquito, if the weather is warm enough, they undergo two molts (L2 and L3), which takes between 7 - 21 days depending on temperature, at this time they become infective larvae. When the mosquito feeds from a cat or dog, these infective larvae (L3) are injected into the animal.


  • Once the L3 larvae have made their way inside the cat, they molt a further two times (L4 and L5) which takes approximately 60 days. By this stage the juvenile worms are 1 - 3 cm long. Once L5 has developed, they migrate through the subcutaneous tissue, penetrating the peripheral veins and migrating to the pulmonary arteries (the blood vessels which carry deoxygenated blood from the heart to the lungs).  It takes between 4 - 6 months post infection for juvenile worms to reach the pulmonary artery. At this point in time, a large percentage of juvenile worms die in the pulmonary artery, although it is possible some can survive and develop into adult worms. Worms which do survive typically live within the  central part (lumen) of the pulmonary artery. As the heart beats, the worms move, causing damage to the endothilial lining.


  • Adult heartworms produce microfilaria (L1) which circulate the bloodstream (known as patent infection) for as long as 2 years waiting for a passing mosquito to take a blood feed and begin the cycle again.


  • Due to their resistance, cats are usually only infected with a small number of heartworms (usually between 1-3 worms), whereas in dogs numbers are generally higher. However, cats do not tolerate heartworm infection as well as dogs and even one or two heartworms can cause death.
  • Heartworms live in dogs for around 5-7 years and in cats for around 2-3 years. Cats are commonly found to have only one sex of heartworm, and it is unusual for cats to have microfilaria in their bloodstream. It is uncommon for heartworms in cats to produce microfilaria, due to the low number of worms found in cats.

What damage do heartworms do to cats?

As we have already said, heartworm actually live mostly in the pulmonary arteries causing inflammation of the arteries (arteritis).  Infected cats are at greater risk than dogs due to their smaller heart and blood vessels, as well as that, they react more severely.

Heartworm associated respiratory disease (HARD) is a term used to describe respiratory disease caused by heartworms. The following can occur during infection leading to damage of the arteries and the lungs.

Damage to the pulmonary arteries:

  • The juvenile worms cause changes to the walls of the pulmonary arteries (which go from the heart to the lungs) by causing an acute inflammatory response. Denuding (stripping) of the endothilium (cells which line the walls of the arteries).  Macrophages, granulocytes (both types of blood cells) and platelets arrive at the site of endothilial damage, adhering to the exposed layer, there is a proliferation of the myointimal cells (smooth muscle cells of the vessel), producing lesions. As a result of these changes, the arteries become narrower, with pulmonary hypertension developing. 
  • A large percentage of juvenile worms die within the pulmonary artery upon arrival, as they die and break up they are carried into the smaller pulmonary arterioles and capillary beds where they cause inflammation and can block blood flow which leads to fibrosis (thickening and scarring).

Lung damage:

  • This can develop secondary to vascular changes due to plasma (the clear portion of blood) and inflammatory cells leaking from the small vessel walls into the lung parenchyma (the functional parts of the lungs responsible for gas exchange).

Pulmonary embolism:

  • A dead adult heartworm can break up and lodge in the pulmonary arteries causing a partial or complete blockage and inciting an inflammatory response. This may be due (in part) to a bacterium known as Wolbachia which symbiotically lives in the heartworm. When the heartworm dies, the bacterium are released which may result in the inflammatory response and embolism many cats develop.

In addition to HARD, heartworms can cause the following disorders.

Anaphylactic shock:

  • The death of a single heartworm can lead to anaphylactic shock in cats which is a medical emergency.

Aberrant migration:

  • In some cases, juvenile heartworms can migrate to other sites such as the eyes, spinal cord, an artery in the leg and brain.

Caval syndrome  (or Vena Cava Syndrome)

  • This is caused when heartworms move from the pulmonary artery to the vena cava which is a large vessel that carries deoxygenated blood to the right-hand side of the heart from the lower body. When heartworms obstruct this vessel, life-threatening consequences occur. Red blood cells are destroyed as they flow through the mass of worms. Liver and kidney dysfunction occur along with reduced cardiac output and in some cases disseminated intravascular coagulation, a rare condition in which systemic coagulation develops forming blood clots throughout the body. There is a high mortality rate with this condition.

Kidney disease:

  • Circulating microfilaria in the blood stream may contribute to the formation of immune complexes (antigen-antibody bound complexes) which is believed to be due to exposure to the bacterium present in the worms. When the kidneys filter the blood containing these immune complexes, the tiny filtering units (known as nephrons) can become damaged.

Right sided heart failure:

  • Narrowing of the pulmonary arteries due to inflammation and vascular lesions leads to pulmonary hypertension which requires the heart to work harder, this can result in heart failure.

What are the symptoms of heartworms in cats?

Some cats may display no symptoms of heartworm at all, while others develop serious and life threatening complications. Some cats will die suddenly having displayed no clinical signs.

Heartworm disease can manifest in many different forms with a wide range of symptoms. It is not uncommon for heartworm to initially be diagnosed as asthma or bronchitis due to the similar symptoms between the diseases.

Symptoms of heartworm may be acute (sudden onset), which is life-threatening, or chronic. They typically occur in one of two stages:

  1. During the initial migration of the immature heartworms to the pulmonary arteries.
  2. When an adult heartworm dies.



Abherrant migration:

Symptoms of abherrant migration can vary depending on the location. But may include:

  • Limping
  • Paralysis
  • Seizures
  • Blindness
  • Sudden death

How are heartworms diagnosed?

Diagnosis of heartworms in cats is often difficult and not always 100% reliable therefore diagnosis usually requires a combination of tests. Your veterinarian will perform a physical examination and listen to the heart and lungs. Increased lung sounds may be heard during examination.

Antibody test: This blood test detects antibodies made by the cat, to adult heartworm antigen. This may give false positive results if the cat has had a prior heartworm infection which has cleared up. Also, it is possible for the cat to have had microfilaria in the blood and removed them without them developing into adult worms. Up to 25% of cats with adult heartworm infection are antibody-negative.

Antigen test: Detects the presence of heartworm antigen in the blood. This relies on the cat being infected with an adult female heartworm, so may give false negatives if the cat is infected with male only or immature heartworms.

Echocardiogram (ultrasound reading of the heart): To detect the presence of heartworms in the pulmonary artery branches as well as look for caval syndrome and assess the heart and arteries.

Radiography (X-ray): May detect enlarged pulmonary arteries possibly with ill-defined margins and an enlarged right-hand side of the heart and lung changes.

Microfilarial tests: This tests for the presence of microfilaria in the blood. Unlike dogs, less than 20% of infected cats will have microfilaria in the blood. This may be due to several reasons. As cats often only have one or two heartworms, they may male only or female only, which would rule out mating of worms producing microfilaria. Also, the cat's immune system may be attacking and destroying any microfilaria present. Therefore a negative blood test will not rule out the presence of heartworms. Cats with heartworm but no microfilaria in the blood are known to have occult dirofilariasis.

How are heartworms treated in cats?

There are no approved adulticide (medications to kill adult heartworms) treatments for cats. Adulticides are themselves dangerous. A single dead worm can be fatal in cats as it can break away and cause a blockage of the pulmonary artery (pulmonary embolism). Heartworms in cats have a shorter lifespan than those in dogs, therefore it is preferable to manage symptoms and use a wait and see approach.

If there are no clinical symptoms your vet may decide not to treat the cat and wait for it to clear the parasite in its own time. As already noted, heartworms live for around 2-3 years in cats. If this is the chosen method, your veterinarian will want to monitor your cat every 6-12 months for signs of complications.

Reduce inflammation: If the cat is displaying symptoms of heartworm disease supportive therapy may be recommended. Corticosteroids (Prednisone) may be given to the cat to reduce the inflammatory response in the lungs, bronchi and pulmonary arteries.

Supportive care: Cats with severe symptoms may require additional supportive therapy such as a bronchodilator to open the airways, oxygen therapy, and intravenous fluids.

Adulticide treatment: This may be recommended for cats with clinical signs who are not responding to supportive care. Caparsolate or Immiticide are the drugs used and kills the adult worms in cats. Neither has been approved for use in cats and treatment does carry risks. A dead and decomposing worm can break up into smaller fragments in the circulatory system and lodge in the pulmonary (lung) artery, resulting in a pulmonary embolism (blockage of the artery). Around 1/3rd of cats receiving treatment will face life-threatening complications as a result of the dying worms. Confinement and activity restriction will be necessary for a few weeks after treatment. Either way, if you choose to let nature take its course and hope that the worm lives out its lifespan within the cat, or if you use an adulticide, there are risks. These must be weighed up by your veterinarian before a decision is made. Surgical removal of the worms has been used in some cases.

Antibiotics: When treading cats for heartworm, your veterinarian may prescribe the antibiotic doxycycline before adulticide treatment. This symbiotic parasite is needed by the heartworm for a number of functions including maturation, reproduction and infectivity. Administration of doxycycline can enhance the effectiveness of adulticide therapy as well as reducing the immune response to the death of the worms.

Antithrombotic agents: Such as aspirin can help by reducing vascular lesions as well as reducing pulmonary vasoconstriction and minimising post-adulticidal pulmonary embolism. Aspirin is highly toxic to cats and must be administered under close veterinary supervision.

Surgical removal of adult worms: Some cats who are not responding supportive care and too unwell to receive adulticide treatment may instead have surgery to remove the worms.  Your cat will receive a general anesthetic and a catheter is inserted into the jugular vein in the neck, and the worms are carefully removed. If the worm is accidentally dissected during removal a severe and life-threatening shock like response can develop. An ultrasound will be performed before surgery to determine the location and number of worms present.

If your veterinarian has decided on a wait and see approach, follow up xrays will be required every 6-12 months to evaluate the lungs.

Do cats need heartworm preventative?

All cats should receive heartworm preventative. One study by the American Heartworm Society showed that 25% of cats who tested positive for heartworm were indoor cats, but only 5% of cat guardians regularly administer a heartworm preventitive.

There are several products on the market which can be used to prevent heartworm. These are administered monthly and either come in tablet, chewable or topical form.  Many also treat a number of other parasites including intestinal worms and/or cat fleas. These products work by killing the microfilaria and migrating immature worms. These products do NOT kill adult heartworms and are a preventative only. Cats should be tested for heartworm prior to going on preventative medication.

Ivermectin not only kills microfilaria but also stops adult worms reproducing and shortens the lifespan of the worms. This has two plusses, it prevents the microfiliara maturing into adult heartworms and also reduces the risks of transmission to other animals.

Active ingredient Brand/product Minimum age
Ivermectin Heartgard 6 weeks
Milbemycin Interceptor 6 weeks/over 500g
Selamectin Revolution 6 weeks
Imidacloprid and Moxidectin Advantage Multi/Advocate 9 weeks

What age should I start my kitten on heartworm preventative medication?

The American Heartworm Society recommends kittens from eight weeks of age start heartworm preventative medications. It is not necessary to test a kitten due to the 6 - 7 months prepatent period.

What happens if I forget to give my cat preventative medication for heartworm?

  • If you have missed a month or less, administer medication as directed. Your veterinarian may recommend heartworm testing 6-7 months later.
  • If you have missed more than one month, administer medication as directed. Inform your veterinarian of the missed doses as he may decide to prescribe doxycycline for a month.
  • If you have missed more than 6 - 7 months of heartworm preventative medication, your veterinarian will want to test for heartworm.

Other ways to reduce the transmission of heartworm in cats:

Keep cats indoors reduces their exposure to mosquitoes although doesn't completely eliminate the risk. More than 25% of heartworm positive cats in the United States are indoor only cats. All it takes is one mosquito.

Don't leave standing water around your home or garden, as these can be a breeding ground for mosquitoes.

Ensure doors and windows are adequately screened.

When adopting or fostering cats, dogs or ferrets, check that they have been tested for heartworm. Of course, this is not possible which again shows just how important it is for cats to be on preventative medication.

Speak to your veterinarian about periodic testing of cats and dogs in the household for heartworm.

Not a preventative, but it is recommended you have your cat tested for heartworm yearly. No preventative medication is 100% so annual testing is important so that if he has developed heartworm disease, he can be treated appropriately.

Can I catch heartworm from my cat?

You can not catch heartworm directly from your cat, but it is possible to become infected via a mosquito bite. Heartworm infections in humans are extremely rare and almost all cases the larvae are unable to develop into adult heartworms. Other pets in the household can also become infected the same way.

Also see:

Roundworm   Tapeworm   Hookworm

Cat Ear Mites - Symptoms and Treatment

Ear mites in catsEar mites are a common spider-like external parasite which causes significant discomfort to the cat. Although the name would suggest otherwise, ear mites can live on any part of the body although they generally live in the ear canal of cats. They are the most common cause of otitis externa (inflammation of the outer ear canal) in cats.

Read more...

Removing Fleas From Newborn Kittens

Signs of fleas   Tackling an outbreak   Treating kittens   Treating the mother   Treating the environment   Fleas and tapeworm

Removing fleas from newborn kittens

Fleas on very young kittens can be fatal as they can cause anemia (low red blood cell count). Most flea products are toxic to very young kittens and can not be used. This article will give advice on how to treat kittens for fleas as well as a summary of common flea products and the age they can be safely used on kittens.

How do you know if your pet has fleas?

Scratching and biting the skin is a good indicator your cat has fleas, although cats scratch and bite for reasons other than fleas. Upon close inspection of the fur and skin, you can usually see fleas on your cat, they are small dark brown insects. It is easier to see fleas if you have a light coloured cat. You may also notice flea droppings on your cat's bedding. If you are unsure, stand your cat on a white piece of paper, rough up his fur a little and then lightly spray the paper with a demister. If you have very small brown specks which leave red stains on the paper then that is a sure sign your cat has fleas.

It is safe to assume that if the mother has fleas, the kittens will have them also.

Tackling a flea outbreak

Below is a percentage of the flea population in the environment:

  • 5% of adult fleas live on your cat.
  • 10% are pupae
  • 35% are larvae
  • 50% are eggs

Killing fleas on your cat  will not solve the problem as most of the flea life cycle is spent off the animal. You need to focus your attention in three areas:

  1. Kill adult fleas on the cat.
  2. Kill adult fleas, eggs, and larvae in the home.
  3. Killing adult fleas, eggs and larvae in outdoor areas.

If you live in a multi-cat household or have dogs, it is important to treat all animals simultaneously.

Treat the kitten

  • The best and safest method to manually remove fleas from your cat with a flea comb. Have a bowl of water with a couple of drops of liquid detergent nearby. As you comb the fleas off the kitten, place the flea in the water and swish it around so that it drowns.
  • Dilute 5 parts water to 1 part Avon's Skin So Soft bath oil and gently sponge or spray onto the kitten's coat. Once dampened, manually remove fleas with a flea comb. Once again, ensure the kitten is in a warm room so he doesn't become chilled, which can be life-threatening in young kittens.
  • Another method is to remove the fleas with a flea comb and then stick them to some tape.

Do not use flea medications (including topical/spot on products, flea collars, dips or shampoos) on young kittens unless you have been told to do so by your veterinarian.

Keep a very close eye for fleas on kittens, as a heavy infestation can kill. If in any doubt whatsoever, seek veterinary attention immediately.

Treat the mother

If you treat the kitten but not the mother then the kitten will quickly become infected again. Check with your veterinarian for products which are safe to use on nursing queens.

Treat the environment

No flea treatment is complete until you have treated the environment.

To treat the house and environment you can either hire the services of a professional pest controller or buy a product from your local supermarket. Most DIY products come in the form of an aerosol "bomb". Prior to letting the bomb off you and your pets should temporarily vacate the premises. Be aware that flea bombs are toxic to other animals, so all pets (including fish) need to be removed prior to bombing.

IGR's: (insect growth regulators) disrupt the cycle of the flea. They prevent eggs from hatching, kill larvae and prevent adult fleas from reproducing. These most often come in as a  bomb/spray.

A pest controller should be able to spray your house and garden for fleas. It is important to specify that you have cat(s) living in the house, so they can use a suitable spray which is safe for pets.

Wash rugs, cat bedding etc., in the hottest possible cycle.

Frequent vacuuming will also remove fleas and their eggs. One useful tip is to put a flea collar in your vacuum cleaner bag. When vacuuming, pay extra attention to corners, skirting boards, under furniture and any other nooks and crannies. Also vacuum furniture, curtains etc. This is where the larvae love to hang out, eating dust and debris, so it is vital that you thoroughly vacuum. Once you have vacuumed, clean out the bag and dispose of carefully. Ensure that every time you vacuum, you empty it out to prevent any fleas escaping.

Fleas and tapeworm

Cats become infected with tapeworm via fleas, and an appropriate tapeworm treatment will also be necessary.

Below is a guideline on common flea products and what age they can be used on kittens. Always check with your veterinarian before treating kittens for fleas.

Brand name/active ingredient Type Parasites treated Dosage frequency Age/pregnant etc
Revolution (Selamectin) Spot on Fleas (adult, larvae and eggs), intestinal worms (except tapeworm), heartworm, ear mites. Monthly 6 weeks old. Can be used on pregnant and lactating females.
Activyl (Indoxacarb) Spot on Fleas (adult, larvae and eggs), ticks and ear mites. Monthly 8 weeks old. Can not be used on pregnant or lactating females.
Advantage (Imidacloprid) Spot on Fleas (adult fleas and larvae). Monthly 8 weeks old. Can be used on pregnant and lactating females.
Advocate/Advantage Multi (Imidacloprid and Moxidectin) Spot on Fleas (adult), roundworms, hookworms, heartworm, ear mites. Monthly 9 weeks old. Safe use on pregnant and lactating females has not been established.
Capstar (Nitenpyram) Tablet Adult fleas. As needed. Can be given daily. 4 weeks old. Can be used on pregnant and lactating females.
Comfortis (Spinosad) Tablet Adult fleas. Monthly 14 weeks old. Safe use on pregnant and lactating females has not been established.
Fidos Fre-Itch Rinse (Pyrethrins,  Piperonyl butoxide,  N-Octyl ) Rinse Fleas (adults) and ticks. 1-2 weeks. For continuous tick prevention use every 3 days. Check with your veterinarian. No information available.
Frontline Plus (Fipronil and S-methoprene) Spot on Fleas (adults, larvae, pupae and eggs), intestinal worms, heartworm and flea allergy dermatitis. Monthly 8 weeks old. Can be used on pregnant and lactating females.
Frontline Spray (Fipronil) Spray Fleas (adult), ticks and ear mites (ear mites are off label). No more than every 30 days. 8 weeks old. Can be used on pregnant and lactating females.
Frontline Spot on Fleas (adult) Monthly. 8 weeks old. Can be used on pregnant and lactating females.
Program (Lufenuron) Oral liquid Fleas (doesn't kill adult fleas, but prevents the development of flea eggs and larvae). Monthly 6 weeks old. Can be used on pregnant and lactating females.
Program (Lufenuron) Tablet Fleas (doesn't kill adult fleas, but prevents the development of flea eggs and larvae). Monthly 4 weeks old. Can be used on pregnant and lactating females.
Program (Lufenuron) Injection Fleas (doesn't kill adult fleas, but prevents the development of flea eggs and larvae). 6 months 6 weeks old. Can be used on pregnant and lactating females.
Revolution (Selamectin) Spot on Fleas (adult, larvae and eggs), intestinal worms (except tapeworm), heartworm, ear mites. Monthly 6 weeks old. Can be used on pregnant and lactating females.
Seresto (Imidacloprid and Flumethrin) Collar Fleas (adults and larvae) and ticks. 8 months 10 weeks old. Safety hasn't been established on pregnant or lactating females.
Vectra (Dinotefuran, Pyriproxyfen) Spot on Fleas (adults, pupae, larvae and eggs). Monthly 8 weeks old. Do not use on senior, debilitated, pregnant or lactating cats.

Related articles:

Teething in kittens   Kitten care   Quick guide to Cat Flea Products   Quick Guide to Cat Worming Products

Flea Treatment For Cats - Types Of Flea Control

Feline Parasites
Today we are swamped with a vast array of different types of flea products to use on our cats. It can be somewhat confusing for the cat owner to choose which product should be used on their cat. We will attempt to look at the different products available, what they do and their efficiency. It should be noted that no flea control method will work if you don't treat your house and garden at the same time. Only 5% of fleas actually live on your cat, the rest of the flea population is in the environment. Both your cat and home (including cat bedding etc) should be treated on the same day.

Flea collars:

There are many different types of flea collar on the market. Some are insecticide only and work by killing adult fleas on the cat. Other flea collars contain IGR's to kill the eggs and larvae.

Flea collars often only kill fleas on the cat's head and neck, but fleas further down the body survive.

Some cats can develop a rash from the chemicals in the flea collar. This is known as "flea collar dermatitis or flea collar rash".

One handy use for flea collars is to put a flea collar into your vacuum cleaner bag so that any fleas that are vacuumed up from the environment will be killed. a

Flea powders, shampoos, and dips:

Flea shampoos are an effective way to kill fleas on your cat. The downside is that many cats can be difficult to bathe. Also, flea shampoos  and dips will only kill the fleas on your cat at the time, and won't help prevent re-infestation. Therefore re-infestation will occur if your cat is exposed to fleas remaining in the environment or on other pets.

Shampoos and dips also need to be repeated often.

Flea combs:

Flea combFlea combs aren't overly effective, only removing 10 - 50% of fleas on your cat. If you wish to use this method place a small bowl of water with some detergent in it close by and drop the fleas into the bowl. This will drown the fleas. Placing a small amount of petroleum jelly onto the teeth of the comb will help the fleas stick to it. These can be useful when removing fleas on newborn kittens as flea products are not safe to use on very young kittens.

Oral suspensions:

Program oral suspensionProgram® and Sentinel® is given to cats via an oral suspension once a month. The product is added to the cat's food and is absorbed into the bloodstream. When a flea bites a cat treated with Program it ingests the active ingredient (lufenuron), which is passed to her eggs and prevents them from hatching. As this product only prevents eggs from hatching, an appropriate adulticide will also be needed to kill adult fleas. Seek advice from your veterinarian before using more than one product on your cat. It is also extremely important to speak to your veterinarian if you are considering treating a pregnant or nursing cat. They will be able to recommend the safest treatment for your cat.

Spot on treatments:

Topical flea controlTopical adulticide. There are several effective products on the market which are administered via
liquid form to the cat's shoulders. These are available through your veterinarian or online pet product store.  These products are very effective for killing adult fleas on your cat. The active ingredient varies from product to product. Application is generally once a month.

When applying a flea product to a cat it is important to follow the instructions on the packet.   Cats are extremely sensitive to chemicals and if you are using one than one product your cat may be exposed to too many toxins, resulting in sickness or death.

Some of the most effective and popular topical flea control products used on cats (and dogs) include Advantage, Revolution and Frontline.

Revolution also kills worms (except tapeworm), so makes life a bit easier for pet owners,  Advantage cat flea control also kills flea larvae in the pet's environment too.


Capstar can be given to kill current adult flea infestations on your cat. One tablet can kill fleas for 24 hours and repeat treatment can be given daily if necessary.  Comfortis can also protect your cat from ticks and treat flea allergy dermatitis.

Capstar can be given to kittens from 4 weeks of age and Comfortis can be given to kittens from 14 weeks old.


Program now comes in an injectable form. This is administered subcutaneously (under the skin) once every six months.

  • Comfortis (fleas, ticks and flea allergy dermatitis), administered once a month.
  • Capstar (fleas). Kills adult fleas on your cat for 24 hours. Can be used in conjunction with topical flea products (see below).
Topical solutions
  • Revolution (fleas, ear mites, intestinal worms-except tapeworm, heartworm)
  • Advantage (fleas)
  • Program (fleas)
  • Frontline Plus (fleas, ticks, ear mites-off label and flea allergy dermatitis)
  • Activyl (fleas, ticks and ear mites)
  • Advocate (fleas, mange, ear mites, heartworm, intestinal worms)
  • Frontline (fleas and ticks)
  • Advantage (fleas)
  • Program (fleas)

When can kittens be treated for fleas?

Flea infestations in kittens can quickly become life threatening due to their tiny size. Below is a chart of the above medications and the safe age they can be given to kittens. You can also remove fleas with a flea comb.

Product Minimum age
Revolution 6 weeks
Frontline Plus 8 weeks
Frontline spray 2 days
Advocate 9 weeks and over 1kg (2.2 lbs)
Advantage 8 weeks
Program 6 weeks
Activyl 8 weeks
Comfortis 14 weeks
Capstar 4 weeks

Is it safe to use cat flea collar with a spot on flea treatment?

You should not use more than one flea product on your cat as both products combined may result in a toxic level of exposure to your cat, which is life threatening. ALWAYS consult with your veterinarian before using more than one flea control method on your cat.

My cat has been treated but still has fleas:

More and more people are raising concerns about the effectiveness of flea products, I personally have experienced this with my own cats. It is believed that fleas may be developing a resistance many popular brands of product, reducing their effectiveness. If you are experiencing this problem with your own cat, speak to your veterinarian as there are a number of newer products on the market which may help. I have a cat who suffers terribly from flea allergy dermatitis and as of today have switched him to Comfortis. I will provide an update in a few weeks on how he is.

A second possible cause is your cat is becoming quickly re-infested either because the home hasn't been adequately decontaminated (remember it is only adult fleas which live on your cat, the rest of the flea life cycle is spent in the environment such as bedding, in crevices, carpets etc). Vacuum your home, paying attention to under furniture and along skirting boards, wash all cat bedding and dry in the sun or a tumble dryer. You can also use Frontline spray on your cat's bedding. A flea bomb or a pest controller should also be used to kill fleas in the environment.

Finally, remember to treat all cats and dogs for fleas at the same time.

Remember to treat your cats regularly:

You can set up a reminder for your cat's anti-parasitic treatment (fleas, worms etc) using either a free downloadable app, or an email service, which can be found on Merck or on Frontline site.


  • Never use a dog flea product on your cat.
  • Always follow the manufacturers instructions, some products may need to be administered more frequently if you are treating more than one parasite (usually ticks).
  • For more information on flea control products, see your veterinarian.
  • Always check a product is suitable to use on pregnant or lactating females and young kittens.

Related articles:

Flea control tips   Flea allergy dermatitis

Last updated 5th December, 2016.