What are Round Worms – Toxocara Canis and Toxascaris Leonina

Your new addition to the family, little Fluffy or Fido, is absolutely perfect! He fits in with the kids, the adult cat that owns the house, he sleeps through the night and is learning his house manners. He is affectionate, happy and content – perfect in every way!

Until one day he vomits and hidden within the vomit are six-inch long, fat strings that are now wriggling around on the floor! Suddenly Fluffy or poor Fido are the anti-Christ and never again will you ever let him lick your face!

Roundworms are the most common infestation in puppies and kittens as they are passed during the embryonic development from an infected mother and through nursing. However, pets of all ages can be infected with roundworms through consuming infected soil and eating infected prey such as rats or squirrels.

There are three types of roundworms commonly seen in domestic pets Toxocara cati in cats, Toxocara canis in dogs and Toxascaris leonina that is seen in both species. Identification of the species of worm is done in a fecal flotation test where the eggs are extracted from the feces and examined under a microscope. The same medication kills all three species of worms however if you have a multiple species of pets in the house, it may help to know which pets are at risk for further infection.

Not all species of roundworms share the same lifecycle. Toxocara canis and cati are more complicated then leonina and for successful treatment, understanding their life cycle is necessary.

Stages of Round worms

Stage One eggs are passed in the feces of the host and can be detected during a fecal flotation exam. Once in the environment, eggs develop into larva within that same egg sac. This process takes a month and the roundworm larva is not infectious during this time meaning that roundworms cannot be passed through fresh feces. Roundworm eggs can lay dormant or inactive for years and survive the worst weather conditions within that microscopic egg.

Stage Two at this point Fluffy or Fido saunter through the infected soil and pick up the second stage larva on their fur. When they groom themselves soon after, they ingest the larva where it hatches in the intestinal tract before burrowing its way out of the intestines to encyst or attach onto another of the body’s tissues. If it is not Fluffy or Fido that pick up the second stage larva, the hatched worm remains encysted until the host is eaten by the appropriate species for that particular worm.

Fluffy has it worse off then Fido as well. Rarely do the cati’  encyst but instead travel directly to the lungs, reaching them within three days of infection.

Stage Three the encysted larva can remain attached for years causing few problems for the host. If the host is the appropriate species, eventually the larvae will excyst and migrate to the lungs. Here they burrow into the small airways and travel up through the lungs towards the throat. A mild infection will cause a cough where as a serious infection can cause pneumonia. Once in the upper airways, the host coughs them up where they are swallowed a second time to continue their development.

The only difference to second stage larvae development is if the host is pregnant or nursing. They then travel to the uterus and infect the fetuses or to the mammary tissue and are passed through the mother’s milk. In most cases, the babies are already infected at this point through the intrauterine cycle.

Stage Four once in the intestine, larvae mature and begin to mate within a week. If there are no interruptions to the cycle, the journey from first infection to laying new eggs takes four to five weeks.

Roundworm infection can cause their host to suffer a number of problems. Vomiting or diarrhea is not uncommon in young animals and the worms do consume the host’s food causing a nutrient deficiencies and the ‘pot bellied’’ appearance commonly associated with wormy puppies and kittens. Serious infections can cause pneumonia and can obstruct the bowel if there are enough worms in the intestinal tract.

It is usually assumed that puppies and kittens are infected and treatment can begin as young as six weeks old. Fecal testing should be performed on adult animals as part of their yearly check up and animals that hunt should be treated with a deworming agent every few months.

Your veterinarian will prescribe one a many deworming medications depending on the age and overall health of your pet. There are also monthly treatments on the market that are especially effective for limiting environmental contamination and there is some piece of mind that comes with knowing your pet is well protected. Dewormer anesthetizes the worm, allowing them to let go of the intestinal tract where they are passed through the feces or vomited up. Do not be alarmed if you see live worms in your pet’s feces after treatment, this is normal and the worms will soon die outside of their host.

Because of their multi-stage life cycle, one treatment of dewormer is not enough to eradicate the infestation. Usually three treatments are required over a course of nine weeks. In a serious infestation, your vet may request a fecal sample at the end of the course to make sure that no eggs are present.’

During treatment, traditional dewormers only kill the worms already in the intestinal tract, not the encysted larvae. Because the second stage larvae in a pregnant or nursing dog do not travel to the lungs then intestinal tract, treatment cannot prevent the pups or kittens from becoming infected. There are new generation dewormers on the market however that have proved safe for preventing this cycle of infection in unborn puppies.

Toxascaris leonina do not have as complicated of a lifecycle as they do not migrate through the body like the species specific roundworms. Treatment is the same for leonina.

If you have any concerns about your pet’s health or whether they could have a roundworm infestation, contact your veterinarian. They will prescribe medication appropriate for your pet and give you instructions on how to avoid further contamination of your household.



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