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Heartworm and Intestinal Parasites

December 12, 2021

We're all aware of the blood sucking parasites that make our pets itch and scratch, those horrible pests known as fleas, but what about those wriggling writhing parasites that take residence amongst our pets internal organs? There are a few different species of worms and intestinal parasites that like to reside in specific areas of our pets bodies, each affecting their health in different ways. It's important to know the different kinds and how to treat, but better yet prevent them from ever living in your pet.


It's all in the name, Heartworms like to take up residence in your pet's heart. Their journey there however is a long one, and it all starts with a mosquito! A mosquito will drink the blood of an infected animal, picking up microfilaria (heartworm larvae) that's been deposited into the blood stream by the adult heartworms. The infected mosquito will then transmit the microfilaria into the next animal it feeds on. This larval  stage of the worm is deposited under the animals skin, it will then mature for the next 5-6 months in the organs. Once fully matured, it will start making its journey through the organs to the heart and blood vessels of the lungs. It's here that they breed, producing more microfilaria, depositing it into the blood stream and thus enabling the cycle to start all over again!

Signs of a heartworm infection

The signs that your pet is playing host to heartworms vary between cats and dogs, but ultimately they are being affected in the same way. During the initial stages of a heartworms life cycle it is quite hard to diagnose, as few symptoms appear, months or even years can pass before symptoms begin to develop.

When symptoms do start to appear they will often resemble heart failure as the worms affect your pet by interfering with the movement of the heart valves, they can also cause turbulence of the blood and roughening in the blood vessels leading to the lungs. This means the heart has to work much harder to pump the blood, and starts to become enlarged & exhausted. Some of the earliest signs in a dog may be shortness of breath, a nagging dry cough or loss of stamina. If left untreated, the disease will progress to a point where breathing becomes more difficult and the dog will become lethargic, they will lose weight and often stop eating. However, it's not uncommon for one of the only symptoms to be a severe coughing attack, that develops into the dog coughing up large amounts of blood to the point where it becomes fatal. In cats there aren't often any clinical signs, you may be lucky enough to notice the early onset of heart failure, vague lethargy or a cough, but more often than not the first hint is sudden death, which isn't very helpful in treating heartworm. So with both cats and dogs prevention is always better than treatment!

There are many treatments/prevention options available for both cats and dogs, each with benefits of their own, so to find out what regime is best for you and your pet it's best to contact the clinic to discuss the different options. For dogs monthly tablets or spot on products are available, it is however very important that you administer the doses religiously each month as unfortunately there is no grace period in their coverage. The alternative option is an annual injection, often given at the same time as your dogs annual vaccinations, this is a prevention program highly beneficial for those of us with forgetful memories! For our feline friends, unfortunately no injectable option is available and they remain with a monthly dosage in the form of either a tablet or spot on treatment. If your pet has never been on heartworm prevention it is necessary to perform a quick blood test to ensure they haven't been infected before proceeding with a prevention program, the reason being that it will largely impact the type of treatment/prevention program that you will be able to implement if your pets test turns up positive.

Heartworm is easily spread, even to indoor pets as mosquitoes are cunning creatures, and it is unfortunately prevalent in our day and age. Suffice to say this is one nasty parasite that you don't want calling your pet home!

Intestinal Parasites

The most common intestinal parasitic worms that dogs and cats are likely to pick up are Roundworms, Hookworms, Whipworms and Tapeworms. A worm infestation mainly occurs when a dog or cat ingests worm eggs from faeces, contaminated meat or offal, or even from grass, the microscopic eggs and hookworm larvae can end up on dog’s and cat’s feet, they then lick their feet and infect themselves. However, certain species of worms are often passed through the womb or mother's milk and some adult worms are actually able to burrow through the skin.


Roundworm is a large white worm that can grow up to 10cm long, and it is probably the most common worm found in cats and dogs. They tend to take up residence in the intestines, and large infestations can produce signs of bloating around the abdomen, poor coat condition, diarrhoea with the unpleasant side affect of your pet actually vomiting up or passing live round worms through the faeces. If the roundworms migrate through the body to the lungs they can damage the lung itself, resulting in your pet developing a nasty cough.

The four possible modes of roundworm infection include: larvae passed from mother to puppy via the womb, or from kittens and puppies feeding off an infected animals milk, the ingestion of infected meat and finally they can be picked up from the soil and faeces.


There are two species of Hookworm that can affect dogs and cats in Australia; Ancylostoma spp and Uncinaria spp, as adults they are relatively tiny, approximately 16mm long and are very thin, it is in large numbers that these parasites can cause illness and potentially even death. They attach themselves to the intestines and live quite comfortably in dogs, cats and even humans, by feeding off the blood and the intestinal wall. This can lead to your pet becoming anaemic and underweight, they will often lose their appetite and develop a poor coat. Occasionally bloody diarrhoea can also be seen.

Hookworm eggs (ova) can be directly ingested by mouth from the ground or food that's been contaminated by faecal matter. Hatched larvae is able to directly penetrate the skin, but they are also often ingested by the animal eating another hookworm infested animal, such as rodents. The ova are also able to be transmitted via a mothers milk or placenta to her off-spring, as it is often young animals that are most heavily affected this is a serious concern. That is why it's important to maintain proper worming schedules during and after pregnancy.


Whipworms reside in the cecum, which the area where the small and large intestine meet. It is an intestinal parasite that is mainly transmitted through the ingestion of whipworm eggs, this is commonly done by swallowing infected faeces or soil. It's important to note that whipworms can live in the environment for up to five years! Pets with light infestations may not present with any clinical signs, it's not until the infestation becomes heavier and they start to cause inflammation to the lining of the large intestine that your pet may present with watery, mucous, or bloody diarrhoea.

Whipworm tends to be more difficult to diagnose than other intestinal parasites and for this reason a parasite prevention program is preferable.

Whipworm, Roundworm and Hookworm can all be prevented by the use of the same product, a tablet given or spot-on applied monthly (these products often double as flea and heartworm prevention as well), these products however require another tablet given to prevent tapeworm infections. Alternatively an all intestinal wormer can be given every three months, which covers whipworm, roundworm, hookworm and tapeworm prevention. If you would like further information on the products and regimes available please contact the clinic.


Tapeworms are long and flat in appearance and attach themselves to the intestines. The body of a tapeworm is made up of multiple parts, each segment having it's own reproductive organs, forming an egg sac. It is these sacs that often lead to a diagnosis, they resemble small grains of rice, and are found in the faeces, around the anus or even where your pet sleeps. There are two types of tapeworms, each needing both a main host (your pet) and an intermediate host (in-between host) for their life cycles; Dipylidium caninum uses fleas as it's intermediate host, where as Taenia and Echinococcus more commonly known as hydatids, uses small rodents (mice and rats), rabbits, large animals (kangaroos, sheep, cows etc) and even humans as its intermediate host.

The health risks associated with tapeworms towards your pet as the main host are minimal, mostly they'll give your pet an itchy rear end, the greater risks are posed towards the secondary hosts, most commonly their human counterparts. So stopping the cycle in your pet serves a greater purpose to your health! It is ingestion of the tapeworm eggs that leads to an infection, which in foraging or grazing animals is easy to do, but unsatisfactory hygiene practices in pet owners can easily lead to the accidental ingestion of tapeworm eggs. Hydatids are the most detrimental to our health, with ingestion of the eggs leading to cysts forming on the liver and other organs, of which if they burst can cause a serious peritonitis, respiratory distress or anaphylaxis. These cysts can only be removed via surgery, so a tapewormer tablet given a few times a year (quarterly) prevents a lot of heartache for both you and your pet!

If you have any concerns or questions about your pet's parasites, please do not hesitate to contact our Mornington Veterinary Clinic clinic on 5975 3811 to speak to one of our staff, they will be only too happy to assist you.

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