Close this window to return to IVIS www.ivis.org Proceeding of the LAVC Latin American Veterinary Conference Oct. 25-27, 2010 Lima, Peru Next LAVC Conference: Oct. 24-26, 2011 Lima, Peru Reprinted in the IVIS website with the permission of the LAVC http://www.ivis.org/
Customized Approach to Parasite Control: risk assessment and routine deworming of pets Susan E. Little, DVM, PhD, Dipl. EVPC Center for Veterinary Health Sciences Oklahoma State University, Stillwater, OK, USA Introduction Despite the advent of highly effective, easily administered broad-spectrum parasite control products for both dogs and cats, infection with intestinal parasites remains a common finding in most veterinary practices. Many of the common intestinal parasites of pets not only induce disease in pets, they may also pose a risk of infection to people. Correct performance of fecal flotation using centrifugation and examination of the slide by a trained technician skilled at identifying parasites is essential to detecting the presence of intestinal parasites in our patients. Wellness programs should include measures to actively seek to identify these infections when they occur through routine fecal examination performed under best practice guidelines, as well as proactively manage both dogs and cats to prevent infection with common intestinal parasites. This presentation will review the most commonly encountered zoonotic intestinal parasites of pets and describe a method of risk assessment that allows identification of lifestyle factors that can contribute to parasite infection. Measures which can be taken to mitigate that risk will also be discussed. I. Common and important intestinal parasites in pet dogs The most common and important zoonotic intestinal parasites of dogs that fecal flotation is effective for diagnosing are listed in Table 1. Infection rates with each of these parasites vary widely among individual dogs according to age, lifestyle, and a variety of other factors that influence both immune status and exposure rate. Surveys of dogs in animal shelters, pet dogs, and/or symptomatic dogs presenting with diarrhea continue to show that infections with these parasites commonly occur (Table 1). Table 1. Common and important intestinal parasites of dogs. Scientific Disease Zoonotic Reported Parasite name(s) caused agent? prevalence 0.7% 1 Ascarids Toxocara canis mucoid diarrhea, vomiting, yes 14.5% 1 malnutrition, ill-thrift Toxascaris leonina considered minor no Baylisascaris spp. neurologic disease (larvae) yes ND Hookworms Ancylostoma caninum anemia, diarrhea, pruritus yes 19.2% 1 Ancylstoma braziliense pruritus yes ND 1.0% 1 Uncinaria stenocephala considered minor yes
Whipworms Trichuris vulpis diarrhea, mucoid or bloody no* 14.3% 1 Giardia Giardia sp. mucoid diarrhea possible 15.6% 2 *despite occasional reports in the medical literature of human infections with T. vulpis, the consensus opinion is that T. vulpis should not be considered a zoonotic parasite at this time (CAPC Guidelines, 2010) 1 shelter dogs determined to be positive by sugar centrifugation as summarized in Blagburn et al., 1996 2 symptomatic pet dogs determined to be positive by IDEXX SNAP Giardia Test as summarized in Carlin et al., 2006 ND = not done (prevalence from large surveys not reported) Ascarids in Dogs Ascarids known to infect dogs include Toxocara canis, Toxascaris leonina, and Baylisascaris spp. Infection with each of these parasites follows ingestion of a larvated egg from a fecal contaminated environment or, in the case of T. canis and Baylisascaris spp., ingestion of larvae in the muscle tissues of transport hosts. Ascarid eggs are long-lived in the environment and can persist to cause infections in animals for years. In the case of T. canis, infections commonly occur in pups in utero when larvae in the tissues of the dam are activated late in pregnancy to cross the placenta and begin migrating in the fetal pups. In this way, entire litters are born already harboring larval ascarids on their way to the small intestine of the puppies. Pups with heavy T. canis infections may develop malnutrition, a pot-bellied appearance, and overall ill-thrift. Neonatal pups infected with massive numbers of larvae in utero may die acutely at 2-3 days of age due to the damage caused by migration of the larvae through the lungs as they make their way to the small intestine. Infections with T. canis, by far the most common of the three, are most commonly seen in dogs less than 6 months of age although prevalence rates greater than 10% have been reported for dogs 6 months to 7 years of age, and infections occur in older dogs as well (Blagburn et al., 1996). In addition to causing disease in dogs, T. canis is an important zoonotic pathogen. Upon consumption of larvated ascarid eggs from the environment, people, particularly children, may develop visceral or ocular larva migrans. A particularly severe form of visceral larva migrans is caused by Baylisascaris spp., the larvae of which are neurotropic and tend to migrate in the CNS, causing damage and inciting inflammation (Gavin et al., 2005). Hookworms in Dogs Hookworms reported from dogs include Ancylostoma caninum, the common hookworm of dogs, A. braziliense, which is associated with sandy environs, and Uncinaria stenocephala, a relatively apathogenic hookworm occasionally reported from dogs and cats. Infection with hookworms occurs following ingestion of larvae from a contaminated environment or, in the case of neonatal pups, in the milk of the dam. Skin penetration, with subsequent dermal migration of larvae and pruritus, can also occur upon direct contact with active, motile larvae in the environment. Whether infection occurs by ingestion or skin penetration, the larvae make their way to the small intestine, where they begin developing to adults. Immature and adult hookworms in the small intestine feed on blood from bite wounds they create on the intestinal mucosa, and anemia due to blood loss can result when infection levels are high. Ancylostoma
caninum is a voracious and wasteful blood feeder; anemia is commonly seen in pups heavily infected with this species although not commonly with A. braziliense or U. stenocephala. Unlike with T. canis, where infections rates decrease somewhat but do not disappear entirely in adult dogs, the likelihood of infection with hookworms appears to remain relatively constant throughout the life of a dog (Blagburn et al., 1996). The presence of an infection is most likely dependent on acquisition of larvae from a contaminated environment. Dogs with hookworm infections shed eggs into the environment. Under proper environmental conditions of warmth and humidity, larvae hatch and develop to the infectious third-stage. Larvae of A. caninum and A. braziliense readily penetrate the skin of hosts other than dogs, including people, migrate in the skin, and induce inflammation and the resultant sinuous erythematous track lesions known as cutaneous larva migrans. Adults of A. caninum also have been recovered via endoscopy from the intestine of human patients with eosinophilic enteritis and severe abdominal pain (Croese et al., 1994). Canine Whipworms Trichuris vulpis, the canine whipworm, infects dogs upon ingestion of larvated eggs from a fecal contaminated environment. Like those of ascarids, the eggs of T. vulpis are long-lived; once deposited in the environment, a source of infection is all but assured for many years. Although many T. vulpis infections are asymptomatic in otherwise healthy dogs, a large burden of whipworms in the large intestine of a dog can result in bloody diarrhea. Trichuris vulpis has a long prepatent period and perinatal infections from the dam to the pups are not known to occur. Although T. vulpis infections do occur in dogs less than 6 months of age, the rate of both infection and clinical disease is much higher in older dogs. As stated in the current CAPC Guidelines (2010), reports in the medical literature of human infections with T. vulpis lack sufficient validation to consider T. vulpis a zoonotic parasite at this time. II. Common and important intestinal parasites in pet cats The most common and important zoonotic intestinal parasites of cats that fecal flotation is effective for diagnosing are listed in Table 2. As with dogs, infection rates with each of these parasites vary according to age, lifestyle, and other factors that impact exposure and susceptibility rates of individual cats. Data on infections in cats are quite limited compared to that in dogs, and both clients and some veterinarians have the erroneous impression that parasitism is relatively uncommon in pet cats. However, more recently acquired data is demonstrating that infections with these parasites commonly occur in pet cats. Appropriate fecal examination techniques (i.e. active centrifugation with an adequate sample size) must be used to identify these infections; when centrifugation is not performed, many infections are missed. Table 2. Common and important intestinal parasites of cats. Scientific Disease Zoonotic Reported Parasite name(s) caused agent? Prevalence* Ascarids Toxocara cati mucoid diarrhea, vomiting, yes 3.46%-28.2% 1 malnutrition, ill-thrift Toxascaris leonina considered minor no Hookworms Ancylostoma tubaeforme anemia, diarrhea yes 0.75%-10.2% 1
Ancylstoma braziliense pruritus yes Uncinaria stenocephala considered minor, rare in cats yes Giardia Giardia sp. mucoid diarrhea possible 0.58-7.3% 2 *prevalence estimates vary widely in cats largely because inappropriate testing methods, such as inadequate sample size of failure to use centrifugation, are often employed and result in failure to detect infections 1 pet and shelter cats as summarized in De Santis et al., 2006 2 pet and shelter cats as reported in De Santis-Kerr et al., 2006 and Spain et al., 2001 Ascarids, Hookworms, and Giardia in Cats Cats may be infected with a number of intestinal parasites, including ascarids (Toxocara cati, Toxascaris leonina), hookworms (Ancylstoma tubaeforme, A. braziliense, or rarely Uncinaria stenocephala), and Giardia spp. Cats acquire ascarids by ingestion of larvated eggs or ingestion of larvae in the muscle tissues of transport hosts; with continued exposure the risk of infection and re-infection remains high throughout the life of a cat. Transplacental transmission of T. cati is not known to occur, but kittens may infected from the dam transmammarily. Like T. canis, T. cati is considered a zoonotic pathogen capable of inducing visceral and ocular larva migrans. A recent study of fecal examination results from samples submitted from over 250,000 pet cats across the United States showed that ascarid infection is very common in even well-cared-for pet cats, with 5.5% of pet cats shedding T. cati nationally; in some areas, such as the Midwestern US, infection rates are as high as 10.6% (Johnson and Little, unpublished data). Cats acquire hookworm infections most commonly via ingestion of larvae from a contaminated environment. In areas where high humidity and warmer temperature allow better survival of hookworm larvae, the infection rate in pet cats is higher (Johnson and Little, unpublished data). Giardia infections develop upon ingestion of cysts, usually in contaminated water, feed, or an environment contaminated with feces of infected pets. As with dogs, although feline infections with Giardia sp. may be asymptomatic, this parasite can induce moderate to severe diarrhea (CAPC Guidelines, 2010). III. Risk factors for parasitic infections in pets Although dogs and cats remain susceptible to parasitic infection throughout their life, differences in lifestyle and contact with infectious stages in the environment results in differences in subsequent risk of infection. For example, parasites are much more commonly identified in young animals that are allowed to roam and in animals that do not receive monthly parasite control products on a routine basis. Although intestinal parasites are usually controlled in well managed dogs maintained year-round on parasite control products, cats are less likely to receive preventives and the rate of infection in pet cats, particularly with Toxocara cati, is surprisingly high. Questions that can be posed to clients to attempt to gage the risk of infection in a given pet are provided in Appendix 1. IV. Risk factors for parasitic infections in people Infection with zoonotic parasites remains common. A recent study showed that 13.9% of the US population has antibodies to Toxocara spp. (Won et al., 2008). Risk of infection was associated with certain demographic groups and factors such as poverty and lack of education. Indeed, human toxocariasis is now considered, along with toxoplasmosis and strongyloidiasis, a neglected infection of poverty in the USA (Hotez, 2008). This problem is compounded by the
fact that veterinary care may be less commonly obtained for pets of certain demographic groups, limiting the ability of the veterinary profession to implement effective intervention strategies. Individuals of all socioeconomic levels also differ in their risk of acquiring a given parasite from an infected dog or cat based on various age and lifestyle factors. This elevated risk can make parasite control more imperative in certain situations, particularly when pets are in contact with children, immunosuppressed individuals, or older people. Measures for preventing infection endorsed by national and international organizations, such as the CDC, CAPC, ESCCAP, and CEPHA, focus on pet owner education and routine deworming of dogs and cats. These recommendations are summarized in Table 3. Table 3. Recommendations for preventing infection with zoonotic parasites. Companion Animal Parasite Council, 2010. www.capcvet.org Parasite control guided by veterinarians Prescribe control programs to local parasite prevalence and individual pet lifestyle factors Adapt prevention recommendations to address emerging parasite threats Conduct physical examinations at least every 6-12 months or as deemed advisable by your veterinarian Conduct annual heartworm testing in dogs; test adult cats prior to placing on preventive and thereafter as indicated by history and physical findings Conduct fecal examinations 2-4 times during the first year of life and 1-2 times a year in adults depending on patient health and lifestyle factors Every pet, all year long Administer year-round broad spectrum parasite control with efficacy against heartworm, intestinal parasites with zoonotic potential, fleas, and ticks Administer anthelmintic treatment to puppies and kittens starting at 2 weeks of age repeating every 2 weeks until regular broad spectrum parasite control begins Maintain pregnant and nursing dams on broad spectrum control products Healthy lifestyle, healthy pets, healthy people Feed pets cooked or prepared food (not raw diets) and provide fresh, potable water Cover sandboxes when not in use and protect garden areas from fecal contamination Pick up feces immediately whenever walking dog in a public area; remove feces from backyard at least weekly, preferably daily Keep dogs and cats under control; do not allow roaming Practice good personal hygiene, particularly important for children and others at increased risk If less than optimal control is practiced Deworm puppies and kittens starting at 2 weeks of age, repeating every 2 weeks until 2 months of age, and then monthly until the pet is 6 months old Conduct fecal examinations 2-4 times a year in adult pets depending on patient health and lifestyle factors and treat with appropriate parasiticides
Appendix 1. Pet lifestyle and parasite risk assessment questions. Feline Questions 1. *How old is [your cat]? When/where did you find [your cat]?* 2. *Is [your cat] on monthly internal parasite control? How do you remember to give it each month?* 3. *What do you do for flea and tick control for [your cat]? When did you last give it?* 4. Where does [your cat] stay during the day? At night? Does [your cat] sleep with you or your children? Does [your cat] ever go outside at all? Did [your cat] get out in the last year? 5. Where do you live? a. apartment b. condo or duplex c. single family home urban, suburban, rural 6. Do you have other pets? Do you ever see other cats or dogs outside in your neighborhood? Wildlife? 7. Do you have a litter box? How many and where do you keep it? How often do you change it? 8. Does [your cat] participate in any of these activities? a. play/nap time outdoors b. play/nap time on screen porch, deck, patio, or windowsill c. play time with other pets d. play time with other animals that don t live with you e. boarding at a kennel f. ingestion of grass outdoors g. ingestion of house plant leaves; dig up soil in houseplants 9. Do you know if [your cat] ever hunts? Does [your cat] bring prey home or catch and play with insects that occasionally get in the house? 10. Do you take [your cat] on trips or vacations with you? Has [your cat] been out of state in the last 3 years? Where? Canine Questions 1. *How old is [your dog]? When/where did you find [your dog]?* 2. *Is [your dog] on monthly internal parasite control? How do you remember to give it each month?* 3. *What do you do for flea and tick control for [your dog]? When did you last give it?* 4. Where does [your dog] stay during the day? At night? Does [your dog] sleep with you or your children? Does [your dog] ever get outside unsupervised? In the last year? 5. Where do you live? a. apartment b. condo or duplex c. single family home urban, suburban, rural 6. Do you have other pets? Do you ever see other dogs or cats outside in your neighborhood? Wildlife? 7. Where does [your dog] usually go to go? Are you with [your dog] or do you let him go on his own? 8. Does [your dog] participate in any of these activities? a. leash walks around the neighborhood b. unsupervised free play outside
c. play groups with friend s dogs d. obedience class or dog day care e. play time at a dog park f. boarding at a kennel g. hiking, fishing, swimming, or hunting with family 9. Do you know if [your dog] ever hunts or has access to prey? Does [your dog] eat grass, chew sticks, drink from puddles, or catch and play with insects that occasionally get in the house? 10. Do you take your dog on trips or vacations with you? Has [your dog] been out of state in the last 3 years? Where? *For established patients, summarize information in record to confirm. Selected References (additional detailed references available upon request) Blagburn BL, Lindsay DS, Vaughan JL, et al., 1996. Prevalence of canine parasites based on fecal floatation. Comp Cont Ed Pract Vet 18:483-509. Carlin EP, Bowman DD, Scarlett JM, et al., 2006. Prevalence of Giardia in symptomatic dogs and cats throughout the United States as determined by the IDEXX SNAP Giardia test. Vet Ther 7(3):199-206. Croese J, Loukas A, Opdebeeck J, Fairley S, Prociv P. 1994. Human enteric infection with canine hookworms. Ann Intern Med 120(5):369-74. Companion Animal Parasite Council Guidelines, Ascarids, Hookworms, Whipworms, Giardia, Coccida. http://www.capcvet.org. Accessed January 4, 2010. Dunn JJ, Columbus ST, Aldeen WE, Davis M, Carroll KC. 2002. Trichuris vulpis recovered from a patient with chronic diarrhea and five dogs. J Clin Microbiol 40(7):2703-4. Gavin PJ, Kazacos KR, Shulman ST. 2005. Baylisascariasis. Clin Microbiol Rev 18(4):703-18. Bowman DD, 1999. Georgis Parasitology for Veterinarians. (7th ed) Philadelphia:WB Saunders Co., p186 De Santis AC, Raghaven M, Caldanero RJ, Glickman NW, Moore GE, Lewis HB, Schantz PM, Glickman LT, 2006. Estimated prevalence of nematode parasitism among pet cats in the United States. J Am Vet Med Assco 228:885-892 De Santis-Kerr AC, Raghaven M, Glickman NW, Caldanero RJ, Moore GE, Lewis HB, Schantz PM, Glickman LT, 2006. Prevalence and risk factors for Giardia and coccidia species of pet cats in 2003-2004. J Feline Med Surg 8(5):292-301 Dryden MW, Payne PA, Ridley R, Smith V, 2005. Comparison of common fecal floatation techniques for the recovery of parasite eggs and oocysts. Vet Ther 6(1):15-28 Hotez PJ, 2008. Neglected infections of poverty. PLOS Neglected Tropical Diseases. 2(6): 1-11. Jordan HE, Mullins ST, Stebbins ME, 1993. Endoparasitism in dogs: 21, 583 cases (1981-1990). J Am Vet Med Assoc 203: 547-549 Little SE, Johnson EM, Lewis D, Jaklitsch RP, Payton ME, Blagburn BL, Bowman DD, Moroff S, Tams T, Rich L, Aucoin D. 2009. Prevalence of intestinal parasites in pet dogs in the United States. Vet Parasitol. 166(1-2):144-52. Nolan TJ, Smith G, 1995. Time series analysis of the prevalence of endoparasitic infections in cats and dogs presented to a veterinary teaching hospital. Vet Parasitol, 59: 87-96. Spain CV, Scarlett JM, Wade SE, McDonough P, 2001. Prevalence of enteric zoonotic agents in cats less than 1 year old in central New York State. J Vet Intern Med, 15(1):33-8. Won KY, Kruszon-Moran D, Schantz PM, Jones JL, 2008. Seroprevalence and risk factors for zoonotic Toxocara spp. infection. Am J Trop Med Hyg. 79(4): 552-7.