Controlling canine and feline gastrointestinal helminths - Veterinary Medicine
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Controlling canine and feline gastrointestinal helminths
Nearly all of our canine and feline patients, especially pups and kittens, will present with a helminth infection at some point. Some of these infections also have zoonotic potential, but fortunately most are easily treated and prevented.


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Hookworms

Infection with the hookworms Ancylostoma caninum and Ancylostoma tubaeforme is also commonly diagnosed in dogs and cats, respectively. Infection with A. caninum is common throughout the United States, with 19.2% of dogs found to be shedding eggs, and is even more common (> 35% prevalence) in the southeastern United States, where warm, humid climates support the development and survival of infectious larvae in contaminated environments.1 Dogs become infected with A. caninum upon skin penetration by or ingestion of infectious third-stage larvae from a contaminated environment. Larvae that penetrate the skin migrate in the bloodstream to the lungs, cross the pulmonary parenchyma to migrate up the respiratory tree, and are then swallowed to develop in the small intestine. Ingested larvae may penetrate the oral mucosa and migrate through the lungs, or they may pass directly to the small intestine and begin development to the adult stage.5

Some of the larvae that migrate to the lungs remain in circulation and develop into quiescent forms in the musculature of dogs. If a dog is an intact female, these quiescent larvae will become active late in pregnancy, migrate to the mammary glands, and be transmitted to nursing pups. Such transmammary infections can result in large numbers of larvae being passed directly to neonatal pups. These quiescent larvae may also be reactivated in adult dogs in the absence of pregnancy or lactation, migrating to the small intestine to reestablish a patent infection even in the absence of exposure to infectious stages in a contaminated environment.7 Referred to as larval leak, this phenomenon can be frustrating to both veterinarians and clients attempting to clear a dog of infection. Ancylostoma tubaeforme follows a similar life history pattern as A. caninum does except transmammary transmission has not been demonstrated.7

Ancylostoma caninum infection in pups and young dogs causes an acute anemia because of the blood loss induced by the feeding worms in the small intestine. This anemia is most severe, and may be fatal, in neonatal pups that acquire large numbers of larvae by transmammary transmission. Because the developing hookworms begin feeding on the small intestinal mucosa as early as eight days after infection, but the worms themselves do not begin producing eggs until two or three weeks after infection, pups that receive large numbers of larvae can become moribund and die even though their fecal examination results are negative. Anemic pups less than 3 weeks old should be presumptively dewormed for A. caninum regardless of the results of any fecal examination. Adult dogs may also be infected with A. caninum, but because adult dogs are larger and have greater iron reserves, disease is generally less acute. In a contaminated environment, larvae can penetrate the skin and may cause dermatitis.7 Disease in cats due to A. tubaeforme is similar to, but generally less severe than, that caused by A. caninum in dogs.

People can become infected with A. caninum when they contact the infectious larvae in a contaminated environment. Larval penetration of the skin of the aberrant human host results in cutaneous larva migrans, a pruritic dermatitis associated with tortuous tracts of erythema characteristically arising on the hands, feet, or other areas of the body that have contacted soil containing A. caninum larvae. Intestinal infection of people with adults of A. caninum has been reported as a cause of eosinophilic enteritis and abdominal pain in affected individuals.11 The related hookworm Ancylostoma braziliense, which infects both dogs and cats, is another well-known cause of cutaneous larva migrans in people; this parasite is considered to be more common in sandy, coastal areas and warm climates. Uncinaria stenocephala is another canine and feline hookworm found throughout the United States. However, the northern hookworm, so named because of the ability of the larval stages to survive lower temperatures than Ancylostoma species, is not thought to cause severe disease in infected animals or zoonotic infections.5

Whipworms

Trichuris vulpis, the whipworm of dogs, is a common parasite in older pups and adult dogs. In some surveys, up to 10% of dogs are shedding whipworm eggs in their feces.12,13 The eggs are persistent in the environment and remain infectious for many years. No reasonable, effective means of removing or killing eggs in a contaminated yard exists, although completely removing the topsoil or paving the contaminated area, when possible, may be effective.5

Dogs acquire T. vulpis infection by ingesting eggs containing infective larvae from a contaminated environment. The larvae then emerge from the eggs, penetrate the glandular epithelium of the cecum, and develop to adults. Adult worms embed their anterior ends into the cecal or colonic mucosa, disrupting the integrity of the epithelium and causing a watery diarrhea that may contain blood. Disease may be chronic, and elimination of infection can be difficult.7 Although most cases of whipworms in people are due to infection with the human whipworm, Trichuris trichiura, zoonotic gastrointestinal T. vulpis infections are occasionally reported.14-16


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