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Ascarids & Hookworms ASCARIDS, HOOKWORMS AND As with other ascarids, eggs are excreted in feces and must develop BAYLISASCARIS PROCYONIS externally, typically in soil, to become infectious. When raccoons ingest infective eggs, larvae will hatch, enter the wall of the small (2 CE Hours) intestine and subsequently develop to adult worms in the small bowel. However, ingestion of eggs by other host animals, especially Learning objectives rodents and other small mammals, results in extraintestinal migration ! List the risk factors for ascarids, hookworms and Baylisascaris of larvae; an estimated 5-7 percent of larvae invade the brain. The procyonis infections. migration of helminth larvae through tissue in suboptimal hosts ! Explain how and where humans and animals can become is termed larva migrans and may affect the viscera (visceral larva infected. migrans [VLM]), the eye (ocular larva migrans [OLM]), or the ! Explain how to diagnose, treat and prevent hookworm infection. nervous system (neural larva migrans [NLM]). Raccoons may also ! Describe the life cycle of these parasites. become infected when they eat larvae that have become encapsulated ! List recommendations you can provide to pet owners about in the tissues of rodents and other animals. treatment and prevention. ! List the contraindications when prescribing medications for More than 90 species of wild and domesticated animals have been ascarids and hookworm. identifi ed as infected with B. procyonis larvae. Outbreaks of fatal central nervous system disease caused by B. procyonis have occurred Introduction on farms and in zoos and research animal colonies and have affected Happy and healthy animals are the goals of any veterinarian. It is commercial chickens, bobwhite quail, guinea pigs, commercial important to make sure that not only pets are protected from harm pheasants and domestic rabbits. Natural infections have also been but also that they do not pose a risk to others. Wildlife, our domestic recognized in dogs, rodents, porcupines, chinchillas, prairie dogs, pets and humans are all susceptible to contracting and spreading primates, woodchucks, emus, foxes and weasels. Experimental commonly found parasites. It is important to recognize, treat and infection of a variety of nonhuman primates has also been reported. prevent these infections so that they do not spread to a greater population. The prevalence of these infections varies with climatic conditions, but they are present in all parts of the United States and must be Common parasites viewed as a potential public health hazard. Ascarids (Toxocara canis, T. cati) and hookworms (Ancylostoma spp.) are common intestinal parasites of dogs and cats (referred to Zoonotic transmission and human disease here as pets). Not only can ascarids and hookworms cause disease The growing popularity of dogs and cats in the United States as in their respective hosts, they are also well-known causes of larva well as high rates of ascarid and hookworm infections have resulted migrans syndromes in humans, especially children. While ascarids in widespread contamination of the soil with infective eggs and and hookworms are most commonly diagnosed in puppies and larvae. Epidemiologic studies have implicated the presence of dogs, kittens, infections can occur in dogs and cats of all ages. Dogs can particularly puppies, in a household, and pica (dirt eating) as the also become infected with Baylisascaris procyonis, the common principal risk factors for human disease. Children’s play habits and raccoon ascarid, which can cause serious disease in other animals their attraction to pets put them at higher risk for infection than and humans.1 adults. Ascarids – Because of the occurrence of both transplacental and Humans become infected with ascarids (Toxocara spp., Baylisascaris transmammary transmission of T. canis, puppies are usually born spp.) through ingestion of infective eggs in the environment. When with or acquire ascarid infections early in life.2 Kittens do not a human ingests infective eggs, the eggs hatch and release larvae become infected in utero, but like puppies, can acquire ascarids that can migrate anywhere in the body, a condition known as (T. cati) through the queen’s milk.3 The tissue-migrating and early visceral larva migrans. The signs and symptoms seen in humans are intestinal stages of these worms may cause severe, sometimes determined by the tissues or organs damaged during larval migration. life-threatening, disease in the fi rst few weeks of life. Patent Organs commonly affected are the eye, brain, liver and lung, where intestinal infections can develop within the fi rst 2½-3 weeks of life. infections can cause permanent visual, neurologic or other tissue Left untreated, this can lead to widespread contamination of the damage. The common dog ascarid T. canis has long been recognized environment with infective eggs. as a cause of larva migrans syndromes in children. The cat ascarid T. cati can also cause disease in humans, although for reasons partly Hookworms – Both puppies and kittens acquire hookworm related to the defecation habits of cats, it does so less frequently. The infections (A. caninum, A. braziliense, and A. tubaeforme) through raccoon ascarid B. procyonis is increasingly being recognized as a ingestion of or skin penetration by infective larvae, or from infective cause of human disease.10 larvae passed in their dam’s milk (A. caninum).2 Hookworms suck large amounts of blood from their hosts, and while infected animals Humans can become infected with hookworms through ingestion 7 may look healthy in the fi rst week of life, they can develop a rapidly of infective larvae or through direct penetration of the skin. When severe, often fatal, anemia.4 Patent intestinal infections can occur infective larvae penetrate the skin, they undergo a prolonged as early as 2 weeks (dogs) to 3 weeks (cats) of age, leading to migration that causes a condition known as cutaneous larva migrans. environmental contamination with infective larvae.5,6 These larval migrations are characterized by the appearance of progressive, intensely pruritic, linear eruptive lesions, which are Baylisascaris procyonis, a ubiquitous roundworm infection of usually more extensive with A. braziliense infections. A. caninum raccoons (Procyon lotor), is increasingly being recognized as a larvae may also penetrate into deeper tissues and induce symptoms cause of severe human disease. B. procyonis has a widespread of visceral larva migrans, or migrate to the intestine and induce an geographic distribution, with infection rates as high as 70 percent eosinophilic enteritis.11,12 in adult raccoons and exceeding 90 percent in juvenile raccoons. Although relatively few human cases of baylisascariasis have been reported, several factors suggest that the likelihood of exposure and 1 infection may be greater than is currently recognized. Raccoons Life cycle (intestinal hookworm infection) have a widespread geographic distribution, and infection with B. procyonisis is common in raccoon populations, with typically high prevalence rates observed. An infected raccoon can harbor numerous adult worms and may excrete large numbers of eggs. A single adult female worm may produce an estimated 115,000 to 877,000 eggs per day, and an infected raccoon can shed as many as 45 million eggs daily. In light of the relatively low infectious dose of B. procyonis (estimated to be less than 5,000 eggs) and the viability of the eggs in the environment for months to years, the infection potential is not insubstantial. Raccoons have increasingly become peridomestic animals living in close proximity to human residences and are among the fastest growing wildlife populations nationwide. These animals benefi t from feeding on abundant pet food left accessible, either accidentally or intentionally, and their populations can thrive under such conditions. In one suburban area near the residence of a recent patient in northern California, the raccoon population was measured at 30 animals per quarter-acre. Areas frequented by raccoons and used for defecation were found in close proximity to human dwellings, and B. procyonis eggs are routinely recovered from these areas. Children, particularly toddlers, may be at particular risk of Eggs are passed in the stool q, and under favorable conditions exposure. (moisture, warmth, shade), larvae hatch in one to two days. The released rhabditiform larvae grow in the feces and/or the soil, and Although baylisascariasis may indeed be underdiagnosed, after 5 to 10 days (and two molts) they become fi lariform (third- asymptomatic human infection may be the typical response, and the stage) larvae that are infective e. These infective larvae can survive limited number of cases reported may indicate that an unrecognized three to four weeks in favorable environmental conditions. On immune defect is necessary for severe infection to occur. The contact with the human host, the larvae penetrate the skin and are prevalence of asymptomatic infection in human populations has yet carried through the blood vessels to the heart and then to the lungs. to be determined. They penetrate into the pulmonary alveoli, ascend the bronchial tree In an era of increasing concern about bioterrorism, certain to the pharynx and are swallowed r. The larvae reach the small characteristics of B. procyonis make it a feasible bioterrorist agent. intestine, where they reside and mature into adults. Adult worms live The organism is ubiquitous in raccoon populations and therefore in the lumen of the small intestine, where they attach to the intestinal easy to acquire. Enormous numbers of eggs can be readily obtained, wall with resultant blood loss by the host t. Most adult worms are and these eggs can survive in an infectious form for prolonged eliminated in one to two years, but the longevity may reach several periods of time. As with other ascarids, the eggs can remain viable years. in a dilute (0.5 percent-2 percent) formalin solution for an indefi nite Some A. duodenale larvae, following penetration of the host skin, period of time, and animal studies suggest that B. procyonis has a can become dormant (in the intestine or muscle).
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