Adult ascarids in the small intestine of pups and kittens can induce a mucoid enteritis, which may be associated with a mild
diarrhea. A characteristic potbelly appearance may develop in heavily infected animals. Intussusception and intestinal obstruction
due to large numbers of ascarids in the small intestine of young animals have been reported but are relatively rare. Adult
ascarids may migrate from the small intestine to the stomach where they irritate the gastric mucosa and induce vomiting. Intact,
live ascarids are often found in vomit or feces from infected animals.7 Older pups may vomit a large mass of live ascarids either spontaneously or after treatment with an ant helmintic, a phenomenon
that can cause great distress to clients. Older kittens and adult cats will often vomit one or two intact adult T. cati, which can be readily distinguished from Physaloptera species, another stout stomach worm of dogs and cats occasionally found in vomit, by the presence of prominent cervical alae
that give the anterior end of T. cati a characteristic arrowhead shape (Figures 1A & 1B).5
Figure 1A: The prominent cervical alę of Toxocara cati, a nematode of cats that is occasionally found in vomitus.
Ascarid infection in dogs and cats must be controlled not only to protect the health of the pets but also because both T. canis and T. cati can induce severe disease in people, particularly children, who consume eggs containing infective larvae from a fecal-contaminated
environment. Eggs containing infective larvae of Toxocara species are commonly found in soil samples from public areas such as parks and playgrounds, and the eggs survive and remain
infectious for many years.2 When geophagia leads to ingestion of eggs containing infective larvae, the larvae emerge and migrate aberrantly in the child,
resulting in disease syndromes. Different syndromes of toxocariasis include visceral larva migrans, in which hepatomegaly
and eosinophilia develop because of the inflammatory reaction to larvae migrating in the liver; covert toxocariasis, in which
chronic or recurrent abdominal pain and eosinophilia are associated with infection; and ocular larva migrans, in which the
larvae induce a unilateral granulomatous retinitis. Asymptomatic infections also commonly occur.8
Figure 1B: The cervical collar of Physaloptera species, a stomach worm that can infect cats and dogs.
Other ascarids are occasionally found in small animals, including Toxascaris leonina, an ascarid of dogs and cats that migrates only in the gastrointestinal tract, and Baylisascaris species, ascarids of wildlife that have occasionally been reported in domestic dogs.5
Toxascaris leonina is not known to be zoonotic. However, the finding of patent Baylisascaris species infections in dogs is particularly troubling because larvae of some Baylisascaris species migrate in the central nervous system of paratenic hosts, including people, and can cause severe neurologic disease.
A number of cases of severe Baylisascaris species-induced neurologic disease and death have been reported in children who consumed eggs containing infective larvae
from a fecal-contaminated environment.9,10