Companion Animal Zoonoses COPYRIGHTED MATERIAL Parasitic Diseases 1 J. Scott Weese , Andrew S. Peregrine , Maureen E.C. Anderson , and Martha B. Fulford Introduction that undergoes sexual reproduction. Like other ascarids, as well as hookworms and Trichuris , A. Companion animals can harbor a wide range of lumbricoides undergoes a maturation stage in soil parasites, some of which are transmissible to and is therefore sometimes referred to as a geohel- humans. The overall burden of human diseases minth. 1 Female worms are larger than males and attributable to companion animal - associated para- can reach 40 cm in length and 6 mm in diameter. 2 sites is unknown and varies greatly between regions. The risks associated with some are often Life c ycle overstated while others are largely ignored, and the range of illness can extend from mild and self - Adult worms live within the small intestinal lumen limited to fatal. of humans and excrete massive numbers of eggs per day. As with other ascarids, eggs are not imme- Ascaris l umbricoides diately infective and must mature to infective third - stage larvae in the environment over a period Introduction of days. After embryonated eggs are ingested by a human, larvae hatch, penetrate the intestinal A. lumbricoides is a roundworm that has typically mucosa, and reach the liver via portal circulation. been considered host specifi c to humans; however, After migrating through the liver, the larvae even- there is evidence of infection of dogs and the tually reach the lungs, penetrate the airways, potential for dogs to be an uncommon source of ascend the tracheobronchial tree, and are coughed human infection. up and swallowed. They mature into adults in the small intestinal lumen and complete the life cycle. The time from ingestion of infective eggs to devel- Etiology opment of adults is approximately 8 weeks. 2 As with other intestinal nematodes, A. lumbricoides is a nonsegmented, elongated, cylindrical parasite Geographic d istribution/ e pidemiology Companion Animal Zoonoses. Edited by J. Scott Weese and A. lumbricoides is one of the most prevalent nema- Martha B. Fulford. © 2011 Blackwell Publishing Ltd. todes in humans and is most common in tropical 3 4 Companion Animal Zoonoses and subtropical regions, infecting approximately contact with dogs was not a risk factor in a study 25% of the world ’ s population. 3 – 5 Up to 80% of of adult humans in northern India.7 Whether there people can be infected in some areas. 1,4,6 – 9 The truly is a risk from dogs is unclear, but the limited regional prevalence varies depending on factors data indicate that consideration of the role of pets, such as climate, sanitation, socioeconomic status, particularly dogs, in the transmission of this pre- and human behavior. Areas with warm, humid dominantly human - associated parasite is required. climates facilitate maturation and survival of infective eggs. Poor sanitation leads to an increased risk of contamination of the environment with Animals human feces. Outdoor defecation similarly results in increased likelihood of contamination, and Clinical p resentation outdoor activities in contaminated areas that are Little is known about A. lumbricoides in dogs. While accompanied by suboptimal hand hygiene increase it was previously thought that dogs shedding the the risk of fecal – oral infection. A. lumbricoides eggs parasite represented a mechanical, not biological, can be found in the soil in public places such as vector, there is now evidence that adult worms can parks 10,11 and can survive outdoors for years in grow in the canine intestinal tract. It is not known favorable environmental conditions. 1 Infections whether this can result in disease. are more common in children. Some older studies reported the presence of ascarid eggs that could have been A. lumbricoides Diagnosis in canine feces. 12,13 More recently, convincing evi- Diagnosis is based on the detection of eggs in feces dence of the presence of A. lumbricoides in dogs using fecal fl otation and subsequent speciation of has been reported. A study of dogs in tea - growing the parasite by evaluation of micromorphological communities in northern India identifi ed A. lum- features 14 or using molecular methods such as bricoides eggs in 18 – 37% of dogs. 7 In that study, PCR - RFLP. 7 dogs were at increased risk of shedding A. lumbri- coides if one or more household members regularly defecated outdoors. Simply fi nding eggs in feces, Management particularly in an environment where dogs may No specifi c data are present, but presumably, any ingest human feces, does not necessarily indicate prophylactic or therapeutic agent that is used for that dogs are involved in the biological cycle of the treatment of Toxocara in dogs would be effective the organism. Indeed, there has been some thought against A. lumbricoides . These include milbemycin that dogs only act as mechanical vectors and that oxime, moxidectin, fenbendazole, and pyrantel. eggs passed in feces simply moved passively through the intestinal tract. However, a recent study of dogs in an area in Egypt where outdoor defecation by humans is common reported detec- Humans tion of adult A. lumbricoides in 8% of dogs. 14 Clinical p resentation Furthermore, viable eggs were detected, suggest- ing that dogs can truly be infected and could Various presentations can occur, but most infec- potentially play a role in the life cycle of this tions are asymptomatic. 1,2 Large worm burdens can human parasite. It has also been suggested that result in malnutrition, nonspecifi c gastrointestinal the dog ’ s coat could be a source of exposure since signs, or, in rare cases, intestinal obstruction. 2 the eggs are “ sticky ” and highly tolerant of envi- Obstruction of the bile duct can result in cholangi- ronmental effects, and could potentially adhere tis, biliary colic, or pancreatitis.2 Chronic infections and mature to the infective stage on the animal. 14 can produce insidious disease, with growth retar- A study of young Nigerian children indicated dation and negative effects on cognitive function that children whose families owned dogs were 3.5 in children. 5 During larval migration, acute pulmo- times as likely to be shedding A. lumbricoides com- nary signs (Loeffl er ’ s syndrome), fever, and marked pared with non - dog - owning families. 15 In contrast, eosinophilia can occur. 2 There is also increasing Parasitic Diseases 5 concern about the broad effects of ascarid infection therefore shedding levels, by routine antiparasitic on the immune system, something that may be chemoprophylaxis). Decreasing the numbers of particularly important with concurrent infections free - roaming dogs and prompt removal of feces, such as malaria or for the development of allergic particularly from public areas such as parks, would diseases, 16,17 though more research needs to be per- presumably help achieve that goal. General hygiene formed in this area. practices are the key to reducing inadvertent inges- tion of infective larvae by humans, including good attention to hand hygiene and proper washing of Diagnosis food. Eggs are usually easily detectable in stool because Prophylactic use of albendazole, mebendazole, of the large numbers that are shed by adult worms. or pyrantel pamoate in humans can be practical Rarely, adult worms will be passed in stool or and affordable in endemic areas, particularly in vomitus. 2 Adult worms may also be identifi ed ultra- school - age children. 2,20 Based on the commonness sonographically as an incidental fi nding or during of the parasite in humans in some regions and the investigation of gastrointestinal complaints. very rare incidence of patent infections in dogs, prophylactic treatment of dogs directed specifi cally against A. lumbricoides is not indicated. However, Management routine deworming targeted against other round- A single dose of albendazole, mebendazole, or worms will be effective against this parasite. pyrantel pamoate has high cure rates (88 – 95%). 18 Three days of mebendazole or a single dose of ivermectin has also been recommended in people Baylisascaris p rocyonis over 2 years of age. 2 Nitazoxanide is also effec- tive. 19 Retesting of stool 2 weeks after treatment has Introduction been recommended. 2 Most drugs are only effective against adult parasites, so repeated treatment may B. procyonis is a large nematode that is highly prev- be needed. alent in healthy raccoons in many regions.21 Human infections are very rare but can be devastating. Neural larva migrans is the most common form of Prevention this rare disease, but visceral (VLM) and ocular larva migrans (OLM) can also develop. Prevention of zoonotic transmission of A. lumbri- Dogs can shed B. procyonis in feces and can also coides , should it occur, involves basic measures to theoretically be a source of human exposure through reduce the incidence of exposure of dogs, to reduce transporting infective eggs into the household on contamination of the environment by dog feces, their hair coat. While objective evidence of a risk and to prevent fecal – oral exposure in humans. from pets is minimal, the severity of disease in Evidence - based data are not available for any of humans indicates that basic measures should be these areas, but reasonable recommendations can taken to reduce the risk of exposure to this parasite. be made. Reducing exposure involves decreasing the chance that dogs will ingest infective A. lumbri- Etiology coides eggs, which are predominantly found in human feces. Reducing “ promiscuous defecation ” B. procyonis belongs to the order Ascaridida, along by humans, something that is common in some with Toxocora canis and T. cati . 21 The North American developing regions, 14 is a means of achieving this raccoon ( Procyon lotor ) is the defi nitive host, and B. and involves both education and improved procyonis is often termed the “ raccoon round- infrastructure. worm. ” An unusual aspect of B. procyonis is its Reducing contamination of the environment by ability to infect a wide range of animal species, dogs is as discussed for similar organisms like causing neural larva migrans in over 100 avian and Toxocara canis (e.g., reducing worm burdens, and mammalian species.