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Parasite control in pets - keeping bugs at bay!

None of us like to think of our pets having creepy crawlies in or on them - but the chances are, they have a few! If you keep ignoring a few fleas here, or a worm there, sooner or later your pet will have a full-blown infestation to deal with! So, in this blog, we’re going to take a quick spin through the more common parasites of pets… and how to kill them.

Dogs and Cats

Roundworms - Dogs and cats carry a wide variety of roundworms (a group technically called “nematodes”). The most common ones are Toxocara canis (in dogs), Toxocara cati (in cats, unsurprisingly) and Toxascaris leonina (which can live 
in either, but generally prefers cats). The adults live in the guts of dogs and cats, and are spread primarily through eggs in the faeces. The Toxascaris worms are unpleasant, living in the gut and eating your pet’s food, but Toxocara are much nastier - these worms can spread from a mother to her puppy or kitten in the milk, or directly in her womb. The eggs can also infect humans, causing a nasty disease called toxocariasis.

The symptoms of roundworm infestation in dogs usually include weight loss, diarrhoea and sometimes vomiting; generally, the more worms there are, the worse the symptoms.

Roundworms are, fortunately, fairly easy to kill - there are a wide range of effective prescription-only medications that kill the adults, many of which will also treat other parasites such as fleas, mites or lice. These are available as tablets or as spot-ons. There are also effective non-prescription drugs available from us, but in general, over the counter, herbal and homeopathic products offer only very limited protection.

Informative image: worms

Tapeworms - There are several different tapeworms that can live in dogs, although only one of these (Dipylidium caninum, the Dog Tapeworm) is (ironically) common in cats as well. These are long, flatish worms made up of a string of segments called proglottids, each of which contains both male and female organs. These segments fertilise themselves and then, when pregnant, crawl out of your pet’s anus (they look like grains of rice). There they burst, spreading their eggs (“oocysts”) in the faeces and infecting other animals (“intermediate hosts”). The eggs hatch inside their bodies, forming infective cysts which, if the animal is eaten by a dog or cat, hatch out into an adult tapeworm in the intestine.

The intermediate hosts for Dipylidium are fleas and lice. When the dog or cat scratches at a flea they’ll try to bite and kill them - if they succeed, they may become infested with the tapeworms the flea was carrying. Other species have different intermediate hosts - Taenia tapeworms are carried in cattle, sheep, rabbits, mice or rats, and infect hunting cats or dogs when they eat their prey. The dangerous Echinococcus or Hydatid Worm can form cysts (that can be huge, up to several litres) in almost any animal, including humans.

It is likely that most cats and dogs carry a few tapeworms, but small numbers of small tapeworms (i.e. before they’ve had a chance to grow too long) are unlikely to cause major problems. Symptoms are usually be similar to infestation with roundworms, although because the tapeworm segments are uncomfortable, itchy bottoms are one of the most common signs.

Tapeworms are harder to treat than roundworms, and usually we use a medicine called praziquantel to kill them. This is mixed into most worming tablets for dogs and cats, and a few prescription-only spot-ons for cats.

Informative image: small fleaFleas - the most common external parasite (or “ectoparasite”) of dogs and cats. These little wingless insects survive by sucking blood from our pets, jumping from animal to animal. However, only 5% of the fleas in a house are as adults living on our pets - the remainder are living as eggs, larvae and pupae in the carpet, the soft furnishings, and even the dust on the floor. The adult flea lays her eggs, which fall off the pet and hatch out into maggot-like larvae in the environment. These live off dust and the faeces of the adults, and then go into a chrysalis called a pupa. Here they can lie in wait for weeks, months or even years, until a warm blooded victim walks past… then they hatch out and jump on board to feed.

Fleas most commonly cause itching and scratching; however, a very heavy infestation may cause anaemia in young kittens or puppies. In addition, some dogs and cats develop an allergy to flea saliva. This Flea Allergic Dermatitis causes severe suffering - incessant itching, hair loss and skin infections.

There are a large number of products that kill fleas. However, killing the adults is only part of the solution - you need to break the cycle of infection, killing the larvae before they can infect the pet. In general, the most effective products are those that either kill the flea so fast that they cannot breed, or contain an environmental control product. Most over-the-counter products are quite limited in how efficiently they kill the fleas, but we stock plenty of powerful and safe prescription-only alternatives.

Mange Mites - there are a number of mites that can infest dogs, but the most important are probably the mange mites. The most common (and nastiest!) is Sarcoptes scabei, which burrows into the skin causing a rash and hyper-severe itching (it’s the itchiest parasite of all). It mainly infects dogs (who catch it from each other or foxes), but can also infect cats and even humans (where it’s called scabies). Cats have their own version called Notoedres cati, but it is now very rarely diagnosed in the UK. Some prescription flea spot-ons will kill mites, but most are ineffective.


We tend not to think about parasite control in rabbits; however, there are three important parasites that it’s vital to keep under control.

Fur mites - these live in the fur causing itching and dandruff. Technically called Cheyletiella, these are widely known as “walking dandruff” because that’s what they look like! They can be controlled if necessary with spot-on medicines.

Flystrike - a rabbit with a soiled bottom is home away from home to certain flies, who lay their eggs in the fur. They hatch out into maggots, but unfortunately, the maggots don’t discriminate between muck and flesh, meaning they progressively eat the poor bunny alive. Flystrike is much more common in rabbits with digestive disorders (who are more likely to be mucky in the first place) and those who have dental disease or are obese (because they can’t groom themselves so well).

Treatment of flystrike is usually too late - prevention is FAR MORE IMPORTANT. There are prescription-only insecticidal roll-ons that are safe to the rabbit but will kill any eggs that might be laid before they can hatch. Careful grooming and helping your rabbit to keep themselves clean is also important.

Encephalitozoon cuniculi - this is a protozoan parasite that is spread in urine and faeces, and is usually contracted via contaminated food or water. Once in the rabbit, the parasites may be defeated by the immune system (probably in over half of cases); if, however, the rabbit doesn’t defeat them quickly, they invade the brain and kidneys.

This causes the characteristic symptoms of a severe head tilt, hindlimb weakness or paralysis, tremors, incontinence, collapse and sometimes even seizures.

Prevention is probably better than cure, and there are products available from the practice that can be given regularly (usually every 2-3 months) to prevent the parasites from getting a hold.

If this makes you squirm… think how your pet feels! Make sure they’re protected against parasites...