Have you ever wondered if humans can get worms from dogs and cats? You don’t have to wonder any longer, the answer is ‘yes’. In this overview we look at which worms can be transmitted between pets and humans, what diseases they cause and how to prevent this potential health risk.
Firstly when a disease or parasite can be transmitted from animals to humans it is called a zoonosis. It is often a concern when a pet is diagnosed with intestinal worms whether the family is at risk of contracting the parasite. The concern is valid but the good news is that it is easily managed with education, proper precautions and a well organised deworming program for your pets.
There are two main categories of worms that can infect people, round worms and tapeworms. For both these worm types humans can act as either definitive (or final) hosts, intermediate hosts or paratenic hosts. The definitive host is the host when the worms are adults in the intestinal system and when they shed eggs. The intermediate host occurs when the eggs are ingested and form cysts in various organs and tissues of the body. A paratenic host is one that is not necessary for the life cycle of the worm but is similar to an intermediate host in that it is a temporary host where the worm does not develop further in its life cycle until such time it can find a suitable permanent host where it can complete its life cycle. Certain larva can also penetrate and migrate through the skin. All hosts are infected by larva which are the immature parasite that come from eggs.
Zoonotic round worms:
The way that the parasite enters the body is when a human ingests or eats the eggs of the worm. The source of these eggs can be from contaminated soil, playgrounds, geophagia (eating soil) or direct contact with dogs. Not washing hands properly after working or playing in soil and having soil stuck under the nails and then touching and eating food, can lead to humans getting the eggs in through their mouths. Proper personal hygiene therefore can prevent such infections.
Once the eggs have entered the body, the larvae hatch from it and the immature stages of these round worms cause damage by burrowing through the intestinal wall and into the internal organs of the body called visceral larva migrans. Further to this the larvae also targets the eyes of humans, which is called ocular larva migrans. Some of the burrowing larva land up in the bloodstream the blood stream and cause clumps of damaged cells called disseminated granulomas in various tissues and organs in the body including the eyes, lungs, liver, brain and heart. Most of these go clinically unnoticed but sometimes you can get loss of vision (ocular larva migrans), fever, nausea, abdominal pain, muscle pain and respiratory signs (coughing, shortness of breath, wheezing). If any of these signs occur, immediately seek the advice of a medical practitioner.
One of the most important and common worms in dogs and cats is hookworm. It is a frequent cause for ill thrift and diarrhoea in puppies and kittens. The infection usually occurs through the skin (percutaneous) from direct contact with contaminated ground (beaches, sand boxes, garden soil etc.). The immature stages of this worm or larvae burrow into the skin but lack certain enzymes to break through the deeper layers of the skin resulting in an infection which is isolated to the surface of the skin. This is called cutaneous larva migrans. The larvae cause progressive skin lesions characterised by tingling initially which progresses to intense itching and redness of the skin with lines appearing in the skin. These lesions often occur in the feet, between the toes, hands, knees and on the buttocks. It is recommended to seek the advice of your medical practitioner as lack of treatment may result in the infection continuing for several weeks before your immune system is able to kill the larvae.
Hookworm infection can also happen when the larvae are ingested and localise in the intestinal tract of humans, causing inflammation of the intestines (enteritis).
Whipworms: Trichuris vulpis (rare)
Although rare, humans may become infected by whipworms originating from dogs. Humans act as definitive or final hosts in the case of this worm.
Zoonotic tapeworm infections associated with dogs and cats include the flea tapeworm, Dipylidium caninum. Infection occurs when someone accidently eats or swallows a flea carrying the larva of this worm. This is more often a problem in young children. This infection can cause diarrhea and anal itching in infected humans.
Taenia species is another Typeworm. Humans act as paratenic or intermediate hosts for Taenia tapeworms. Infection by the larvae, following accidental ingestion causes wide spread cyst formation in the muscles, organs and tissues. These fluid filled cysts can range from a few millimeters in size to more than two centimeters in size. The symptoms of this kind of infection are due to the physical presence of the cyst and depend on the site of localisation. Cysts found in muscle and tissues that are not essential go unnoticed, but rarely these larva may migrate to the brain and eye causing severe symptoms. This infection is often difficult to diagnose and treat.
Echinococcus granulosus - Hydatid disease (important)
Infection with this Tapeworm is through direct contact with infected dogs (not washing hands after being in contact with the infected dog) or indirectly through contaminated water or unwashed fresh produce. Humans act as intermediate hosts. Once ingested the larvae penetrate the intestinal tract and migrate to mainly the liver and lungs forming multiple cysts (fluid filled sacks). The symptoms depend on where the cysts form. If it is in the liver you will find symptoms of liver disease which may be quite unspecific like an animal losing appetite, losing weight, and becoming sluggish. If it is in the lungs you may notice shortness of breath, or coughing. If a large cyst bursts it can cause an emergency and even lead to death.
Prevention of zoonotic worm infections
A regular and up to date deworming program is one of the best ways to prevent your pets and family from getting infected with worms. Puppies and kittens are extremely susceptible to worm infections. The mother should be dewormed prior to having a litter and all the babies should be dewormed at weaning before they are sent off to their new homes. With each puppy/kitten vaccinations they should be dewormed. From then on all animals should be dewormed every three to six months. This is dependent on their exposure to potentially contaminated areas as well as other animals. Should you walk your dogs frequently, allowing them to interact with other dogs in the park or running off the lead unattended, they should be dewormed every three months. The same applies to cats, the more cats they potentially come into contact with and the more roaming they are allowed to do, the more frequently they should be dewormed. Apart from tablets given by mouth there are also spot-ons available for deworming cats. This makes the process of deworming a cat a bit easier. If between these periods you are concerned about your pet being infected with worms, you can ask the veterinarian to check for worms by performing a stool exam called a faecal flotation and prescribing a suitable treatment.
Controlling fleas on your animals, as well as in their environment, is an important preventative measure for worm infections. There are a variety of top spot, shampoo and tablet flea treatments and with so many options one can find the one that will most suit your lifestyle and environment. The majority of the tablet and shampoo flea treatments do not have a long lasting or residual effect and only kill fleas which are on your pet at the time. It does not have any impact on the fleas in the environment or the thousands of flea eggs which are waiting to hatch. The top spots tend to last for up to four weeks.
The courteous and correct thing to do is to clean up after your pets when taking your dogs for a walk or to the park. Stools should be picked up and disposed of correctly.
All sand boxes and pits should be covered and regularly cleaned. Do not allow children to play in areas contaminated by animal waste.
It is essential that your children are taught to wash their hands after playing outside or handling animals. This promotes good hygiene and prevents the transmission of disease, including worms.
Do not feed your pets raw meat or organs as these may be a source of Tapeworms.
It is always a good idea to deworm yourself and your family on a yearly basis especially when you have young children. Should you be concerned about any risk or illness you think may be associated with worms, you should contact your medical professional for information and treatment.
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