Zoonotic parasitic infections contracted from dogs and cats: How frequent are they? - Veterinary Medicine
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Zoonotic parasitic infections contracted from dogs and cats: How frequent are they?
Your clients probably don't know that their lovable pets can transmit parasitic infections to them and their children, so it is up to you to educate them. Being aware of the gastrointestinal parasites with the most zoonotic potential will enable you to give clients the best advice for zoonosis prevention.


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Hookworms

Infections with the hookworms Ancylostoma braziliense and Ancylostoma caninum remain common in dogs and cats, with the highest prevalences in the southern United States, mainly in coastal areas from southern New Jersey to the Florida Keys and westward along the Gulf of Mexico to Texas. Infections in people are acquired from contact with moist or wet sand or loam soil containing filariform larvae of hookworms generated from the feces of dogs and cats, usually in unprotected sandboxes, on bathing beaches, and under houses where workers lie prone while repairing leaking water pipes. Larval invasion of skin in humans produces pruritic papules. In two or three days, these papules become serpiginous tunnels in the epidermis caused by inflammation resulting from intradermal migration of larvae (cutaneous larva migrans).7 Without treatment, migration may continue for several weeks or months before the immune system kills the larvae. Zoonotic hookworm infection may also be acquired through ingestion of the larvae in soil or in tissues of paratenic hosts. Infection in humans acquired by these latter routes, especially A. caninum, may occasionally lead to enteric localizations of zoonotic hookworms, causing eosinophilic enteritis.8 Although eosinophilic enteritis has been diagnosed with relative frequency in Australia where it was first noted, it has rarely been diagnosed in the United States.9 The eosinophilic enteritis syndrome requires clinical experience and technical sophistication to diagnose and may occur more frequently than currently recognized and documented.

Tapeworms

Dipylidium caninum. Zoonotic tapeworm infections associated with dogs and cats include the flea tapeworm, Dipylidium caninum. Infection is acquired when a person, usually a young child, accidentally ingests a flea carrying the larval stage of the tapeworm. Dipylidium caninum infection can lead to diarrhea and pruritus in infected humans. This infection rarely causes serious symptoms; however, the stress associated with seeing tapeworm segments in a child's stool or diapers can be considerable.10

Echinococcus species. Echinococcus species of dogs may infect humans with larval stages that cause cystic or tumorous growths in the liver and other visceral organs. Cystic echinococcosis, or hydatid disease, is caused by infection with larval stage Echinococcus granulosus. Cases of cystic echinococcosis acquired in the northernmost regions of North America, especially Canada and Alaska, are caused by the northern sylvatic genotype maintained in cycles involving wolves, dogs, moose, caribou, and other cervids.11 The practice of feeding the viscera of moose and caribou to working and pet dogs leads to infection in dogs and subsequent exposure to humans. Infection continues to be relatively commonly diagnosed in most Canadian provinces. A review of hospital records in Edmonton, Alberta, noted 42 cases diagnosed and treated between 1991 and 2001.12

Foci of local transmission involving a variety of domestic intermediate hosts have been described in various regions of the United States.11 Distinct foci of E. granulosus transmission were noted in the 1970s in western states including California, Utah, New Mexico, and Arizona. Epidemiologic investigations revealed that transmission was associated with unique cultural practices involving home slaughter of sheep and the access of dogs to discarded viscera of these hosts. Human populations at risk in these settings were transhumant sheep ranchers, including Basque-Americans in California, Mormons in central Utah, and Navajo and Zuni Indians in New Mexico and Arizona. Active transmission appears to have been eliminated in some of those foci; however, local hospital records indicate that an average of one to four cases continue to be diagnosed each year among Native American communities in Arizona and New Mexico.11

Echinococcus multilocularis, the cause of the alveolar form of human hydatid disease, is an emerging zoonotic parasite in the United States. The life cycle of E. multilocularis involves foxes and coyotes and their rodent prey in ecosystems generally separate from that of humans. However, there is ecologic overlap with humans because fox and coyote populations have increasingly encroached upon suburban and urban areas of many regions, and domestic dogs or cats may become infected when they eat infected wild rodents.11 Infections in domestic pets increase the risk of human exposure. Humans may acquire infection when they accidentally ingest eggs by direct or indirect fecal-oral contamination from infected definitive hosts. Human alveolar echinococcosis in North America has been mainly confined to certain Eskimo populations in northern coastal Alaska in which annual diagnostic incidence rates during the 1970s and 1980s were among the highest ever reported for this infection (7 to 98 per 100,000 population).13 A control intervention in endemic Alaskan villages initiated in 1990 involving education, improved housing, and preventive treatments of dogs has greatly reduced or eliminated transmission to humans.14 No new cases have been diagnosed in humans since that time.14

This tapeworm also occurs in a large area of central North America, and its geographic range and prevalence may be increasing. Before 1964, there were no reports of E. multilocularis in North America south of the Arctic tundra zone, but, in that year, it was reported in foxes and rodents in North Dakota.15 Subsequent surveys revealed that the cestode was enzootic in cycles involving red foxes, coyotes, and deer mice in North and South Dakota, Minnesota, Montana, Iowa, Wyoming, Nebraska, Wisconsin, and Illinois.16,17 The most recent surveys have extended the range eastward to Indiana, Michigan, and Ohio.18,19 Prevalence of infection in foxes and coyotes in the northern Great Plains (25% to 90%) is as high as in any region in the world. To date only two persons are known to have acquired their infections in the endemic region in central North America—a 54-year-old man from Manitoba, Canada, and a 60-year-old woman from Minnesota20 —however, the potential exists for a more serious public health problem as domestic dogs and cats become involved in the life cycle.

Taenia species. Coenurosis is an infection by larval forms of several related tapeworms of the genus Taenia (formerly designated Multiceps). The coenurus is a fluid-filled cyst that measures from a few millimeters to 2 cm or more in diameter. Dogs and other canids (wolves, coyotes, foxes) are the final hosts of Taenia tapeworms. Taenia serialis, the only coenurid-forming cestode currently present in North America, uses rodents or hares as intermediate hosts, and the coenuri are typically found in the intermuscular fascia and subcutaneous tissues. Humans become infected when they accidentally ingest tapeworm eggs in the feces of infected canids. The symptoms of coenurosis are due to the physical presence of the cyst and depend on the site of localization. In North America, fewer than 10 autochthonous (locally acquired) human cases have been documented; three involved the central nervous system or the eye, and the others involved intramuscular or subcutaneous localization.21


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