As kitten season marches on, shelters across the country are pulling out their Strongid and their Nemex and are vigorously deworming kittens. It is common knowledge that all young animals have worms, and that frequent deworming is necessary. But why is that? This week we will be diving into the specifics of the large roundworms of puppies and kittens, also known as ascarids. Ascarids are some of the largest, hardiest and most common worms seen in our domestic animals. Cats and dogs each have their own, unique ascarid known as Toxocara cati and Toxocara canis respectively. They can also both be infected with a less common ascarid called Toxascaris leonina. Ascarids are commonly 10 – 15cm and are easily seen in the feces of infected animals.
Adult ascarids live in the intestinal tract of dogs and cats and their eggs are shed in feces. The eggs themselves have a thick, sticky, tough outer shell which protects them from the environment. This is why the eggs tend to get stuck in fur or carpet, and are hard to destroy. The eggs in the feces take 2 weeks of growing in the environment before they are infectious, which is why prompt cleaning is so important in a shelter. Eggs are eaten by the animal when they eat anything which has been contaminated with feces, groom themselves, etc. Eggs can also be eaten by other animals such as rodents, who are then infective to dogs or cats if consumed.
The eggs hatch in the stomach of the animal, but do not take a direct route to the intestines. The baby worms migrate through the body, passing through the liver and lungs in their way to the small intestine. Occasionally larvae are lost on their way to the gut, and become trapped in other tissues such as kidneys or muscle, where they do not develop and become dormant cysts. In a pregnant dog these cysts are activated in the last trimester, and the worms migrate across the placenta to infect the puppies. Thus, puppies are born with worms already growing inside. Similarly in cats, the worms migrate to the mammary glands and are shed in the milk to the newborn kittens.
Normally, infection takes a month or two from the time an adult animal eats the egg until the worms are fully developed. In puppies it can be much sooner, due to the prenatal infection (3 weeks), which is why early deworming of puppies is so important. Relative to a puppy’s intestinal size, even a small number of 10cm worms can cause serious gastrointestinal upset or even death. Kittens, on the other hand, take longer to develop adult worms because they are infected after birth, but should still be dewormed on a similar schedule as puppies.
Only pyrantel pamoate (Strongid, Nemex) is labeled for use in puppies and kittens as early as two weeks of age. Because this drugs is inexpensive and relatively safe, it is usually the go-to for shelters. Puppies and kittens should be dewormed every two (2) weeks until at least 12-16 weeks of age, by which time they are hopefully adopted. Many other products are effective against ascarids, but toxicity and off-label usage is a concern.
Remember, keeping a clean environment will go a long way to preventing reinfection of young animals! Killing ascarid eggs is very challenging and they can stay viable in the environment for extended periods. Thoroughly clean surfaces to mechanically remove eggs, then use diluted bleach to strip away the protein layer of the eggs, leaving them vulnerable to desiccation. Play yards and outdoor spaces are impossible to clean and heavily contaminated spaces may require a fresh layer of dirt or gravel placed on top. This is just another good reason why play yards are not for puppies!
I hope you’ve enjoyed this information about ascarids in puppies and kittens. Stay tuned until next week for more parasitology fun!