Username (email) Password
vetask
vetask vetask
topleft | home | about vetask | your pet healthcare questions answered | register | topleft

Toxocara spp in Dogs

Toxocariasis is the term used to indicate infection with Toxocara roundworms. Toxocara canis and Toxascaris leonina are important roundworms in the dog belonging to the group of parasites known as ascarids. If these worms infect humans they may cause serious problems.

Up to 40% of adult dogs and 70% of puppies may be infected with Toxocara canis or Toxascaris leonina. In adult dogs they are often carried in the absence of any clinical signs, although they may cause problems in puppies. They are large, buff coloured worms about 10-18 cm in length which live in the dog's intestine as adults.

THE LIFE CYCLE

The life-cycle of the Toxocara roundworm is interesting and quite complex.

Toxocara roundworms have two main ways of infecting dogs:

1: Adult worms living in the intestine produce eggs which are shed in the faeces of infected dogs. Once shed the eggs take about 2 weeks to develop into the infective stage if the weather is warm or much longer in the cold, (the process is temperature dependent). These infective eggs are then eaten by an animal.

2: Toxocara may also form dormant cysts in the muscle of infected animals. Here it waits until the animal is killed or dies and the infected muscle tissue is eaten by a carnivore.

Once the worm eggs or dormant cysts are ingested by an animal the eggs will hatch or the larvae of the cysts will reactivate inside the intestines. The resulting first stage larvae will then penetrate the small intestine and enter the blood stream in which they are carried to various organs.

What happens next depends upon what type of animal has been infected:

In adult dogs the larvae migrate in the blood to organs such as the muscles where they form cysts in the tissues. Larvae in the body tissues remain dormant unless a bitch becomes pregnant in which case they will reactivate to cross the placenta or go into the milk to infect the pups. Reactivation of dormant larvae occurs about 6 weeks into pregnancy.

In puppies the main route for the larvae is to go from the intestine to the liver then on to the lungs. From here they work their way up the bronchi to the pharynx and are then swallowed by the dog to enter the intestines again, where they develop into adult worms. The life-cycle takes around 4 weeks to complete in puppies.

If eggs are swallowed by animals other than dogs the larvae migrate to the muscles of that animal where they form dormant cysts and wait for the muscle tissue to be eaten by a dog so they can complete their life-cycle.

The process of the worm migrating through the body tissues is known as visceral larval migrans and this is a natural part of the life-cycle of this worm. Visceral larval migrans may occur in species other than dogs if they happen to ingest Toxocara eggs. The larvae need to get back to a dog to complete their life-cycle. They attempt to do this by migrating to the muscles and residing there as a dormant form. Here they are likely to be eaten with the muscle tissue by a dog when the animal dies.

TOXOCARIASIS IN DOGS

Up to 40% of adult dogs may have toxocariasis. Many adult dogs will have been infected as puppies. Routes of infection also include the ingestion of transport hosts such as mice which carry the encysted larvae in their tissues. Adult dogs may have dormant larval cysts in their body which will reactivate if a bitch becomes pregnant. A bitch may also become re-infected by eating her pup's faeces.

Around 70% of puppies will be infected with T.canis. These puppies may become infected before birth from their mothers (as the worms may cross the placenta). They may also be infected via the mother's milk or from contact with the mother's faeces. In the puppy, the worm will begin to migrate through the body tissues via the blood. The lungs and the liver are included in the route of migration and the worm eventually finds its way back to the intestines to start shedding eggs and begin the life-cycle once more.

Puppies infected with Toxocara may show no signs of clinical disease. However some puppies will show clinical signs especially if there is a high worm burden. Infected puppies may fail to gain weight or become lethargic. They may develop a pot bellied appearance, so they look fat in the middle but skinny elsewhere. As the larvae migrate they may cause respiratory problems in the pup such as coughing or pneumonia. The puppies may show signs of gastrointestinal upset with vomiting or diarrhoea. (If Toxocara worms are vomited they may look a bit like elastic bands because they are often coiled and similar in colour.) If severely affected the puppies may become weak, emaciated and die. Adult dogs are generally more resilient to infection and show few clinical signs.

ZOONOTIC POTENTIAL

People may become infected with Toxocara if they somehow ingest the eggs which are shed in dog faeces. Children are particularly susceptible to toxocariasis because they are more likely than adults to ingest worm eggs while playing either with animals or on contaminated soil.

In humans the migration of Toxocara around the body (visceral larval migrans) may cause respiratory problems and fever. Problems also arise in cases where the worms do not migrate properly through the body to the muscles but "get lost" and end up in nervous tissue (such as the brain or spinal cord) or the eye. Toxocara canis has been implicated in problems such as epilepsy, eye tumours and blindness; it is presently unclear whether T.leonina is involved as well. In the eye the microscopic larvae can cause inflammation and a permanent scar may form. Around 100 people in the UK every year suffer permanent partial loss of vision due to this problem.

Puppies may be the main cause of human infection because adult dogs may develop some kind of immunity to these worms. Puppies start to shed worms at about 3 weeks of age with maximal shedding at around 6 to 12 weeks of age. Pregnant bitches are also a risk because the hormonal changes of pregnancy reactivate the worms so that they may infect the next generation of puppies.

TREATMENT

All dogs should be regularly treated for worms. Since dogs may carry Toxocara without showing any signs of infection it is best to assume your dog has them and treat accordingly. This is especially true of young puppies and breeding bitches who will very often be infected and shedding eggs. There are many products available which will treat Ascarids such as Toxocara in dogs. A drug called fenbendazole is the active ingredient in the preparations I usually recommend for this purpose. My favourite product for adult dogs is Drontal Plus which should be given at the correct dose every three months; this product treats all the worms normally found in dogs in the UK. For puppies I would recommend Drontal Puppy Suspension which should be given orally to the puppy on its own or mixed in the feed. Puppies should be wormed every two weeks until 12 weeks old, beginning at two weeks of age. For breeding bitches I like Panacur Favourites which should be given daily at the recommended dose for your dog from day 40 of pregnancy to 2 days post whelping. This helps prevent transplacental infection of the puppies. It is also recommended that bitches should be wormed about 25 days post whelping when she is likely to be shedding Toxocara eggs in her faeces.

PREVENTION

To prevent anyone in your family catching toxocariasis it is wise to treat your pet for worms regularly as discussed above. Many owners only worm their dog every 6 to 12 months but I would suggest an interval of around every three months. Worm puppies every two weeks until they are 12 weeks old then every month until they are 6 months old when they can begin the adult regime. Wash your hands well with soap and water after touching your dog or cleaning up faeces etc. Do not allow children to play in soil which may be contaminated; parks or other areas frequented by dogs are likely to have soil contaminated with Toxocara eggs.

There are approximately 6 million dogs in the UK producing around 1000 tons of faeces daily. A large proportion of this waste is likely to be contaminated with Toxocara. Since the eggs shed in dog faeces take around 2 or 3 weeks to mature to an infective stage, clearing away dog excreta will help to avoid the problem of toxocariasis. If eggs are allowed to get into the ground they are very difficult to destroy and may remain infective for up to three years. It is every dog owner's duty to clean up after their dog if it fouls in public areas.

© Samantha Coe. All rights reserved. Further information, news and pet-related healthcare articles are available at vetbase.co.uk

Questions Answered

roundworms (cat) (02-Mar-07 10:26PM)

Sally asks: We have tried lots of treatments but still she carries on getting them both sides are really big could she get pregnant even after being done? ... view

dog skin problem (na) (12-Feb-07 07:10PM)

Edward asks: Hi. My dog has been scratching himself lots, his skin is pink in colour. He scratches his nose just below his eyes until it draws blood, and has made his armpits ... view

Fur loss (rabbit) (01-Feb-07 04:12PM)

Rose-hannah asks: What causes a male rabbit to lose his fur? Patches of skin are showing and fur is becoming very thin as if the rabbit is going bald? ... view

Buying a non hip-scored pup (dog) (04-Feb-07 12:08PM)

Anna asks: We have been searching for a Spanish Water dog for some time now, and I have recently been in contact with a breeder who will have a litter available in March. ... view

Bleeding from the nose in lungworm (dog) (08-Feb-07 04:15PM)

Coleen asks: My friend's dog has been bleeding from the nose & the vet has treated him for lungworm. Could you tell me what this is? ... view

Odd humping and aggressiveness (cat) (05-Jun-07 12:40AM)

Sarah asks: Salem is usually very sweet but lately he is attacking one of our other cats Rainman and he has been aggressively humping another one of our cats. What is going on? ... view

Diabetes insipidus (dog) (09-Feb-07 09:14PM)

Potts asks: Please could you tell me if diabetes insipidus can be caused by long term use of prednoleucotropin (PLT) tablets? ... view

Worm symptoms after already being wormed (cat) (06-Sep-07 06:44AM)

cm asks: Our cat has just been treated with a worming and flea treatment and he still has some undesirable symptoms. He smells bad and is still dragging his bottom on the ground ... view

My kitten can't control his bowels (cat) (17-Sep-07 12:39PM)

Rob asks: I have a british blue kitten, 15 weeks old & although he is litter trained, he can't seem to control his bowels. His rear seems to be constantly leaking but he ... view

update re breathing problems in cat (cat) (18-Mar-07 04:07PM)

Shari asks: Hello Sam Many thanks for your reply, just after posting the question I did manage to contact the emergency vet who was very good and saw us at the surgery. Carra was ... view

back end pain (na) (06-Jun-07 06:59PM)

Al asks: My 10 yr. old stonezu seemed very off one day. The next day he was yelping when you picked him up or put him down. I brought him to the vet ... view

after care of pyometra (dog) (07-Apr-07 02:59AM)

Abril asks: Hello my dog Seven is one year 5 months old. This past Monday she had an emergency spay because of pyometra, she's been in the hospital all week; today is Friday ... view

Itching head and chewing paws (dog) (31-Jan-07 09:11AM)

Gary asks: My dog has been itching and scratching herself to the extent of her bleeding. I have given her Frontline thinking it was fleas, but this has not done the trick. I ... view

feeding (dog) (22-Oct-07 01:37PM)

Terry asks: Is it safe to feed my GSD raw chicken wings, he is 16 months old and is 37 kg? ... view

Itching head and chewing paws (na) (09-Feb-07 09:10PM)

Jakki asks: Both dogs keep itching and it is driving me mad one black lab and other a boxer have been treated and also bedding and surrounding areas but can't find anything. ... view

Ronin lethargic, off food, very quiet. (dog) (04-Feb-07 11:01AM)

Colin asks: For the past 2 days he's been lethargic and now he's off his food, yawning a lot and seems very quiet. Could this be a worm problem or something more serious? ... view

Cat skin problem (na) (01-Feb-07 01:42PM)

Emma asks: My cat who is 8 months old has been continually scratching. I assumed it was fleas and recently got him a flea collar. However since he has had the collar his ... view

Swollen glands, sick and weight loss. (dog) (10-Feb-07 10:59PM)

Helen asks: My dog has had gastroenteritis two weeks ago which was treated by our local vet and she appeared to be over it. She has however not regained the weight she lost ... view

All the dog's limbs (na) (09-Feb-07 08:57PM)

Janice asks: I have a large 8 month old dog, a cross breed newfoundland sheep dog, welsh mountain, who is having problems with his legs. The back one, trouble standing, keeps having to ... view

right leg swollen (na) (17-Mar-07 02:15PM)

Ben asks: Dakota's leg is swollen and black and blue he can't stand, sit or lay without severe pain. We took him to the vet and had many tests done only to be ... view

Your Questions Answered

Injured Wild Owl 30-Nov-07

Kelly asks: I found an owl this morning, very small but adult. It flew into a power line. It's still alive. ... view

swollen hind leg 20-Nov-07

Zshai asks: I have a 6-day-old bunny who has a swollen hind leg. I saw her mama step on her but ... view

Sick syrian hamster 08-Nov-07

Sara asks: Hi. My syrian hamster is 2 and half yrs. old. The last 24 hrs I have noticed a big ... view

lack of sleep 07-Nov-07

Bill asks: We have a 14 month old Yorkshire terrier, which goes to bed at around 6.30pm, because I have MS ... view

wet tail 06-Nov-07

Evelyn asks: Can a young hamster be successfully treated for wet tail and what would it roughly cost? ... view

Alfie 06-Nov-07

Elaine asks: Hi Sam Thank you. Alfie has no feeding time he just has food in his bowl when he wants it ... view

Guarding problem 05-Nov-07

Elaine asks: Alfie is a terrible guarder and will take your hand off if you try and retrieve an object he ... view

White Gums and Dark Stool 02-Nov-07

Leslie asks: My 8 week old American Bulldog has really white gums, around the eyes is also white. She has dark ... view

Dog's Health 01-Nov-07

William asks: My dog is around 11 years old, possibly older (we received her as she was taken from a bad ... view

behaviour 31-Oct-07

Debby asks: Hi Max is very lively of course but he seems to get very excited and bites the children, not ... view

Blood in dog's stools 31-Oct-07

Lee asks: Hi. We recently got a 3 year old Labrador from a friend. From what we can see she has ... view

upset stomach 30-Oct-07

kat asks: About three days ago my dog started acting like she was sick; diarrhoea and vomiting along with excessive sneezing ... view

Blood in Poo 28-Oct-07

Mandy asks: Treacle is now 9 wks old and had her first vaccination two days ago. I have noticed that at ... view

neutering 27-Oct-07

ashen1956 asks: 3 days ago Molly-Mae gave birth to 5 kittens. How long should I wait before having her neutered and ... view

Ordering Insulin Online 26-Oct-07

Purdie asks: Purdie is diabetic and I'm keen to find a way of reducing the cost of the treatment. Currently ... view

Fleas and skin problem 26-Oct-07

Joanne asks: I have two cats, a neutered tom and his sister. They are 6 and a half yrs. old. They ... view

My cat has a hole in its stomach! 23-Oct-07

Sarah asks: My cat has a hole the size of a dime in its stomach. He doesn't seem to be ... view

labrador vomiting bile and nearly passing out 22-Oct-07

Paul asks: Hi there - our five year old male labrador is generally in very good health - excellent appetite, plenty ... view

Guinea pig fits 22-Oct-07

Renate asks: My guinea pig is acting strange. I've only had him around a week and he's running as if spooked ... view

feeding 22-Oct-07

Terry asks: Is it safe to feed my GSD raw chicken wings, he is 16 months old and is 37 kg? ... view


© vetask.com Springing Dragon Limited 2012 | Terms and Conditions and Privacy Policy | All Rights Reserved | All Trademarks observed | No responsibility taken for links to external sites or any content beyond our control | Views expressed by contributors or forum users not endorsed by vetask.com. Disclaimer: The content of this website is based upon the opinions of the authors and contributors, unless otherwise stated. Individual articles, extracts, and any links to external sites are based upon the opinions of the respective author(s). The purpose of this site is the sharing of knowledge and information and you are encouraged to make informed healthcare decisions for animals in your care based upon your research and in consultation with your vet.