You, Your Pets, and Parasites

For many animal caregivers, pets are an important part of the household environment. As humans and pets co-inhabit, your family is more likely to be exposed to internal and external parasites. Consequently, quality family health may be determined by actions taken to maintain your pet’s well being.

“Because our pets live in an environment with many other animals they will be constantly exposed to parasites,” notes Dr. Thomas Craig, professor of Pathobiology at Texas A&M University College of Veterinary Medicine & Biomedical Sciences. “The local prevalence of parasites depends on the local environment.”

“Dogs are infected by some parasites while still in the uterus, from an activation of larvae in the mother’s tissues. Both cats and dogs also transmit parasites in the milk. For some species, parasites enter the body by penetrating the skin or when the pet ingests microscopic worm eggs, or cysts in the environment. Cats generally have fewer worms but tend to have several species of worms acquired by eating the prey they catch and devour,” explains Craig. “In central Texas the most common internal parasites of dogs are hookworms and heartworms with a lesser number being infected with roundworms, whipworms, tapeworms, and coccidia.”

“Dogs may be infected with parasites when bitten by ticks, fleas or mosquitoes and, additionally, by eating ticks, fleas, bugs or beetles and other animals that have tissue forms of parasites.” Dr. Craig says that the transmission to cats is by the same means as for dogs, but cats spend less time resting on the soil and spend more time eating other creatures in the environment.

Internal parasites are not easy to visually detect in dogs and cats. “About the only internal parasite the pet owner typically sees are tapeworm segments which resemble a grain of rice in size. They are seen in fecal material or moving on the hair.” Dr. Craig says occasionally a worm will be vomited and the animal may have clinical signs such as coughing, white mucous membranes, tires easily or a bloody stool — all may indicate parasites. However, other things can cause these same signs so most infections are not obvious to the average person.

Your veterinarian should be able to run fecal and blood samples from your pet to determine if there are internal parasites. These should be part of your pet’s annual checkup.

“External pet pests, such as fleas, generally are of little significance to human health but infect pets with other parasites such as the bacteria causing cat scratch fever, which occurs in humans, from a cat bite, scratch or contamination of a wound by flea feces. The most common tape worm of cats and dogs is acquired by eating fleas and occasionally occurs in young children.” Craig notes that if flea infested pets have been in an environment but no longer are present, then fleas will gladly feed on humans.

“As pets get older they become resistant to some types of parasites but not others. Therefore, parasite control will be required throughout the life of the pet. Continuing prophylactic treatment is especially important with heartworms which can be transmitted by mosquitoes every month of the year, depending on the climate.”

“Humans become infected by parasites of pets by walking barefoot or gardening without gloves in soil where a dog has defecated weeks earlier or by eating eggs or cysts deposited by a cat or dog in the environment for up to two years previously.” Humans also share parasites transmitted by ticks and other invertebrates and these can be transmitted by bites or by eating bugs, states Craig.

There are health tips that can help protect family members. “Wear shoes and gloves in the garden, clean up the cat’s litter box daily, pick up poop! Cook or peel raw vegetables from the garden, wash your hands after handling the pet or anything that has been in contact with the pet.”

Craig notes that prompt disposal of fecal material and wearing protective clothing is important. “One hundred years ago hookworm infection was common in the human population, but use of toilets and regular wearing of shoes has eliminated the infection. Screens keep out malarial mosquitoes, and the common roundworm and whipworm of humans are largely controlled by toilets and personal hygiene. If it worked in humans could it work in pets?”

Pet Talk is a service of the College of Veterinary Medicine & Biomedical Sciences, Texas A&M University. Stories can be viewed on the Web at Suggestions for future topics may be directed to

Angela G. Clendenin
Director, Communications & Public Relations
Ofc – (979) 862-2675
Cell – (979) 739-5718

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