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Worms in cats and dogs

Dr N Sparks BVSc

INTRODUCTION

Worms are surely one of the most underestimated causes of illness and death in dogs and especially puppies are affected.  One of the most commonly asked questions is how often animals need to be dewormed.  Normally it should be sufficient to deworm young animals at 3 weeks, 6 weeks, and then monthly until 6 months of age.  Hereafter deworming should take place every 6 months.  Sometimes it may be necessary to deworm more frequently.  The following factors will increase the frequency of deworming:

HOOKWORM

This is by far the most dangerous worm and is responsible for deaths in puppies.  Adult worms live in the intestines of the dog where they suck blood by attaching to the lining.  This causes anaemia and death.  Most dogs are infected by larvae penetrating the skin of the animal but dogs can also be infected orally.  Puppies are commonly infected through the mother's milk or sometimes in the uterus before birth.

A microphotograph of the mouth parts of the hookworm of dogs, Ancylostoma caninum.

The life cycle of hookworm makes for some interesting reading: The adult worms produce eggs which are excreted in the animal's faeces and develop into infective larvae outside the animal.  These larvae penetrate the skin of the dog and migrate via the lymphatics and bloodvessels through the heart to the lungs and into the bronchi.  It then move up in the windpipe, get coughed up an swallowed.  Once inside the intestines, it develops into the deadly adults once again.  (BELIEVE IT OR NOT !)

The life cycle of hookworm in dogs Hookworm in the small intestine

It takes about two weeks to complete this life cycle, which means that pups can already be infested with deadly adult worms from two weeks of age.  A bitch that was infected as a pup will carry the infection and can infect as many as 4 litters through her milk.  Hookworm is normally not such a big problem in cats and infection takes place orally or through the skin.

Signs of infection:

IMPORTANCE IN HUMANS:
The larvae can penetrate the skin and migrate under the skin to cause a itchy lesion.  Children playing in the sand are especially prone to this.

ROUNDWORM

This is the most common worm in dogs and cats.  Where hookworm is difficult to see in the faeces, roundworms are easily seen and look like white earthworms.  The bitch gets infected by taking the eggs in orally which hatch into larvae.  These larvae burrow their way through the tissues of the bitch and go to the uterus where they infect the unborn puppies or to the milk glands to infect suckling pups.  They then develop into adult worms in the intestines of the pups.  The eggs are very drought resistant and can survive for years in the environment.  Other animals and insects can also carry the worms.

The life cycle of roundworm in dogs Severe roundworm infestation in a pup

Signs of infestation:

IMPORTANCE IN HUMANS:
People get infected by contamination of food and hands.  Especially children are susceptible when playing in sand or on the grass.  The eggs are taken in orally and the larvae can migrate to all organs eg.  liver, lungs and brain.

WHIPWORM

Only in dogs.  Not very common.  Eggs are taken in orally, develop into adults in the intestine and burrow into the intestinal lining. The life cycle takes about 70 to 90 days to be completed.

Signs of infection:

Whipworm doesn't affect humans.

TAPEWORM

Tapeworm is the most common worm in cats.  There are several different tapeworm species affecting dogs, cats, cattle, sheep and pigs. 

There are two groups of importance in pets:

  1. The first group has mites and fleas acting as intermediate hosts.
  2. The second group has sheep, goats, cattle and pigs acting as intermediate hosts.

Group 1

Dogs and cats are infected by ingesting fleas while licking or grooming themselves.  The eggs develop into adults within 3 weeks.  This means that your pet can be infected with adult worms 3 weeks after being dewormed.  This explains why it sometimes look as if deworming was ineffective.  Flea control is essential for control of these worms.


IMPORTANCE IN HUMANS:
Children playing with animals are prone to infection by accidently ingesting fleas.  These children will, like animals, also develop adult worms in their intestines.

The life cycle of tapeworm (Dipyllidium) Tapeworm in the small intestine

Group 2

The tapeworm forms cysts in the muscle, brain and intestines of these animals.  These cysts are ingested when uncooked animal products are fed to dogs, whereafter they develop into adults in the intestines.  To control this group it is important not to feed uncooked animal products to your dogs.

IMPORTANCE IN HUMANS:
This group is very dangerous because they can form cysts in humans and these cysts can have devastating effects as they are often located in the brain.  Luckily they are not very common in this area.

Signs of tapeworm infestation:

Acknowledgement for photo's:  Information poster on worms of pets by VIRBAC Animal Health, Private Bag X115, Halfway House 1685