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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Cestodes

Dipylidium caninum is often referred to as the flea tapeworm because dogs and cats become infected when they ingest fleas and, less commonly, lice containing the infectious immature cestodes. The prevalence of D. caninum in shelter animals in some studies is reported to be as high as 52.7% in cats and 60% in dogs, likely reflecting the high prevalence of flea infestations and lack of care the population considered received.4,17 Although the prevalence is probably lower in well-cared-for animals in more temperate climates, D. caninum infection is almost certainly underappreciated when evaluated by fecal examination alone, as proglottids are intermittently shed and may not be present in the sample examined.1

Infection of dogs and cats with Taenia species is also frequently encountered by veterinarians. Ingesting infected prey animals is necessary to establish an infection with adults of Taenia species, as well as Echinococcus species in areas where the latter cestode occurs. Infection with Spirometra species, a primitive cestode of cats and, less commonly, dogs, is routinely diagnosed in many areas of the southeastern United States. Again, cats and dogs become infected when they ingest infected prey containing the immature cestode larvae. Although aesthetically unpleasant because of the shedding of motile proglottids into pets' environments, the common adult cestodes of dogs and cats do not cause clinical disease in their hosts.5 However, infection with Spirometra species may cause weight loss, vomiting, and diarrhea in infected animals; this primitive cestode passes eggs rather than proglottids in the feces of the dog or cat host.18

Like their nematode counterparts, some cestodes of dogs and cats can infect people. Children who accidentally ingest an infected flea from an infested environment may develop D. caninum adults in their small intestine. Infections are recognized when motile proglottids are found in the diaper or on the perianal area of the infected child.19 Although disease is usually absent or mild, and anthelmintic treatment prescribed by a pediatrician readily clears the infection,19 parents may still experience distress at the diagnosis and the source of infection. Echinococcus species infection poses a very serious potential health risk to anyone who ingests eggs from feces or a fecal-contaminated environment; Echinococcus species eggs are immediately infectious when shed.20 Spirometra species infection also presents a zoonotic risk, but people acquire infection from consuming water containing copepod intermediate hosts or consuming or coming into contact with infected prey species serving as second intermediate hosts; direct contact with Spirometra species-infected dogs or cats does not pose a public health risk.18

ZOONOTIC CONCERNS

As mentioned above, several of the gastrointestinal helminths commonly found in dogs and cats are zoonotic and may cause disease in children or adults who are exposed to or ingest the infectious stages. Infection with these parasites is usually acquired from a contaminated environment rather than directly from an infected dog or cat. For most of these parasites, time in the environment is needed for the infectious stages to develop. Preventing infection in people requires not only treating dogs and cats to eliminate the source of the parasites but also paying careful attention to basic hygiene measures. Such measures include washing hands frequently, washing fruits and vegetables carefully before consumption, promptly removing pet feces from the yard, avoiding contact with fecal-contaminated soil, covering sandboxes when not in use, discouraging dogs and cats from roaming (by enforcing leash laws and other pet confinement legislation), and supervising young children to prevent geophagia and other forms of pica. Direct contact with well-cared-for dogs and cats is not considered a major risk factor in most of these diseases.

Open communication between veterinarians and physicians is essential to prevent zoonotic disease from gastrointestinal helminths of dogs and cats. Physicians should encourage patients to seek routine veterinary care for their pets to ensure that contamination of the home environment is kept to a minimum. Similarly, veterinarians who encounter clients with signs consistent with a zoonotic parasitic disease should refer them to their physicians. When zoonotic diseases are diagnosed in people, the attending physician should ensure that all dogs and cats that might serve as a source of the infection are promptly examined by a veterinarian and treated with effective ant helmintics. Veterinarians also serve as an excellent source of management recommendations to prevent future infection of pets and to remove infectious stages from the environment, when possible.

Because dogs and cats can serve as a source of infection of zoonotic gastrointestinal helminths to people, some physicians erroneously think that other nonzoonotic helminths are also acquired from dogs and cats. The most common of these misunderstandings involves the human pinworm, Enterobius vermicularis. Pinworms are common in children, but people and nonhuman primates are the only hosts of E. vermicularis. Dogs and cats do not become infected with pinworms and cannot serve as a source of pinworm infection to children. Likewise, dogs and cats are not involved in the life cycle of and do not serve as a source of infection for the human ascarid Ascaris lumbricoides, the human hookworms Ancylostoma duodenale and Necator americanus, or the human whipworm Trichuris trichiura. The primary source of all of these parasites is other infected people.


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