Canine Schistosomiasis in North America - SLIDEBLAST.COM
Parasites 101
Canine Schistosomiasis in North America:
An Underdiagnosed Disease With an Expanding Distribution Eileen M. Johnson, DVM, PhD Oklahoma State University
H
eterobilharzia americana, a digenean trematode snail, Pseudosuccinea columella, experimentally shown to in the family Schistosomatidae, is the etiologic support development of H. americana.9,10 Both L. cubensis agent of canine schistosomiasis in the southeast- and P. columella are present in Oklahoma,11 although schisern United States.1 A few cases of canine schistosomiasis tosomiasis in indigenous dogs or raccoons has not been have been reported in Florida, Louisiana, North Carolina, reported there. P. columella, a North American lymnaeid, Texas, and, recently, Kansas.1–6 The natural definitive host has spread worldwide through the trade and transport for the fluke is the raccoon1; however, infections have been of aquatic plants.12 L. cubensis is known to be distribdetected in nutrias, bobcats, mountain lions, opossums, uted in Florida, Georgia, Louisiana, Texas, Mexico, South white-tailed deer, swamp rabbits, armadillos, coyotes, red America, and the West Indies12; it has also been found in wolves, red wolf–coyote crosses, Brazilian tapirs, minks, Oklahoma.11 A retrospective study conducted in Texas discovered a and beavers.7 higher rate of H. americana infection in dogs than the preGeographic Distribution vious literature seems to reflect, with a broader distribution The geographic distribution of H. americana is believed than along the Gulf Coast.13 Within a 4-year consecutive to be restricted to the south Atlantic and Gulf Coast states period, 127 cases were confirmed in 25 of 254 counties (Alabama, Florida, Louisiana, Georgia, North Carolina, in Texas. Distinct clusters of cases were found along the South Carolina, Virginia, Mississippi, Texas) due to the envi- Gulf Coast and associated with major urban populations. ronmental requirements of its intermediate host, the fresh- These findings indicate that canine schistosomiasis is not water snail Lymnaea cubensis8; however, H. americana a rare disease and that the distribution of the trematode infections have been reported in indigenous raccoons7 and in Texas has expanded. Another retrospective study of three companion dogs in Kansas.6 These cases are likely 22 naturally infected dogs in Texas found the infection due to introduction of the fluke with raccoons translocated in younger, larger-breed, indoor dogs that had occasional from Florida before 1983 and transmission by a freshwater access to the outdoors. Often, multiple animals in a house-
Contributed by the Companion Animal Parasite Council The Companion Animal Parasite Council (CAPC) is an independent association of veterinarians and other animal health care professionals established to create guidelines for the optimal control of internal and external parasites that threaten the health of pets and people. It brings together broad expertise in parasitology, internal medicine, public health, veterinary law, private practice, and association leadership. Initially convened in 2002, the CAPC was formed with the expressed purpose of changing the way veterinary professionals and pet owners approach parasite management. The CAPC advocates best practices for protecting pets from parasitic infections and reducing the risk for zoonotic parasite transmission. For more information, visit www.capcvet.org.
Vetlearn.com | March 2010 | Compendium: Continuing Education for Veterinarians®
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©Copyright 2010 MediMedia Animal Health. This document is for internal purposes only. Reprinting or posting on an external website without written permission from MMAH is a violation of copyright laws.
Parasites 101: Canine Schistosomiasis FIGURE 1
FIGURE 2
Heterobilharzia americana egg (magnification: 400×).
Miracidium hatching from an egg in deionized water (magnification: 400×).
that swim for a short period of time in search of a suitable snail. Mother and daughter sporocysts and cercariae develop asexually in the hepatopancreas of infected snails. Cercariae are then shed from the snail to reinitiate the life cycle. Eggs can be detected in the feces of definitive hosts approximately 68 days after exposure to infective cercariae.10
Courtesy of Dr. Jill Brunker, Oklahoma State University, CVHS, Small Animal Clinic
FIGURE 3
A
B
Diagnosis and Treatment
Eggs that have been hematogenously Gastroendoscopic photographs. (A) Healthy small intestine. (B) Small intestine of a disseminated to visceral organs or the dog infected with H. americana, demonstrating the thickened, corrugated appearance of the intestinal wall provoke a severe granuluminal surface of the intestinal wall. lomatous reaction (FIGURES 3 and 4) responsible for most of the clinical hold were affected.14 Cases have also recently been identi- signs and pathology.15 Initially, a papular vesicular rash fied in Alabama, Georgia, North Carolina, and Tennessee.a and coughing may be noted. Chronic diarrhea, characterized as mucoid to hemorrhagic, develops and progressively Life Cycle becomes more severe. Fever, anorexia, hypersalivation, Dogs and wildlife are exposed to H. americana while wad- lethargy, and weight loss may also be noted.2–6,14 Anemia, ing or swimming in freshwater areas such as marshes, mud dehydration, hyperglobulinemia, hypoalbuminemia, hyperflats, and canals.10 Cercariae discharged from infected snails calcemia associated with elevated parathyroid hormone– penetrate the host’s skin. The immature schistosomes (schis- related protein levels, and eosinophilia are common tosomula) first migrate through the body to the lungs, where clinicopathologic findings in infected dogs.2–6,14 Elevated they are associated with hemorrhage. They are then carried serum alkaline phosphatase, aspartate aminotransferase, to the liver, where they develop into adult male and female and alanine aminotransferase activities may also be eviflukes. The adults move into the mesenteric veins, mate, dent.5 Eggs are not likely to float with centrifugal flotation16; and deposit nonoperculated, spineless eggs (FIGURE 1). The examination of direct saline smears and sedimentation eggs penetrate venules to enter the intestinal wall and are of feces facilitate the detection of H. americana eggs. A shed into the intestinal lumen. If the eggs reach fresh water, miracidia hatching technique that involves resuspending they rapidly hatch, releasing ciliated miracidia (FIGURE 2) eggs sedimented in saline with deionized water can be employed to verify egg identification.16 An antigen capture a Personal communications: Byron Blagburn, MS, PhD, Auburn ELISA for schistosome circulating anodic antigen5,b and a University; Dana Ambrose MS, University of Georgia; Anne Zajac, DVM, PhD, Virginia Tech; and Sharon Patton, MS, PhD, University of Tennessee; October 2009.
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b Available from North Carolina State University College of Veterinary Medicine by request.
Compendium: Continuing Education for Veterinarians® | March 2010 | Vetlearn.com
Parasites 101: Canine Schistosomiasis FIGURE 4
Key Points • Canine schistosomiasis is a debilitating and often fatal parasitic disease of dogs in the southeastern United States. • Clinical signs and clinicopathogic findings are nonspecific and often mimic other diseases. • Clinical signs may include anorexia, lethargy, weight loss, and chronic mucoid to hemorrhagic diarrhea.
Section of small intestine from a dog showing a histiocytic inflammatory reaction to two H. americana eggs in the lamina propria of an intestinal villus (hematoxylin–eosin stain; magnification: 100×).
polymerase chain reaction assay for H. americana are also available for diagnosis.17,c Infections in dogs have been treated with high-dose praziquantel (25 mg/kg PO bid or tid for 2 to 3 days) or fenbendazole (40 mg/kg PO sid for 10 days).5 Treatment may result in complete cure or resolution of clinical signs, or it may be ineffective. The protracted course of the disease, poor response to treatment, and diagnostic challenges often lead to euthanasia. Many of the clinical signs and the hypercalcemia associated with elevated parathyroid hormone–related protein levels detected in some cases of canine schistosomiasis are more commonly associated with tumors, endocrine disorders, and other infectious granulomatous diseases.3 Some infections are secondary findings in animals with neoplasms.14 Expensive and invasive procedures may be required to rule out these conditions. Therefore, the definitive diagnosis of schistosomiasis is often delayed, as is initiation of appropriate therapy.
Conclusion Increased awareness of canine schistosomiasis and implementation of appropriate diagnostic parasitology tests in dogs with chronic diarrhea, especially in the southeastern United States, should improve early detection of H. americana infections and could improve therapeutic outcomes. The limited number of reported cases in dogs is incongruent with the high prevalence reported in the natural host (raccoon) and the broad range of naturally infected hosts.7 Geographic distribution of the snail intermediate hosts seems to be expanding.11,12 These factors suggest that canine infections with H. americana are often not detected because c Available from Texas A&M University, College of Veterinary Medicine, Gastrointestinal Laboratory; www.cvm.tamu.edu/gilab/assays/ Heterobilharzia%20americana.shtml.
• Clinicopathologic findings may include anemia, hyperglobulinemia, hypoalbuminemia, hypercalcemia, elevated serum parathyroid hormone–related protein levels, and elevated serum alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase activities. • Abdominal radiography may detect enlargement of the liver, spleen, and lymph nodes and thickening of the intestinal wall. • Heterobilharzia americana eggs do not float in standard fecal flotation solutions. • Fecal sedimentation and direct saline smears are the tests of choice for detection of eggs. • A polymerase chain reaction assay and an antigen capture ELISA are available for the diagnosis of canine schistosomiasis.
routine parasitologic examinations do not include the fecal sedimentation technique or because owners choose euthanasia after exhaustive diagnostic testing fails to determine the etiology of clinical disease. References
1. Malek EA. Heterobilharzia infection in the dog and other mammals in Louisiana. J Parasitol 1961;47:619-623. 2. Slaughter JB Jr, Billups LH, Acor GK. Canine heterobilharziasis. Compend Contin Educ Pract Vet 1988;10:606-612. 3. Rohrer CR, Phillips LA, Ford SL, Ginn PE. Hypercalcemia in a dog: a challenging case. JAAHA 2000;36:20-25. 4. Fradkin JM, Braniecki AM, Craig TM, et al. Elevated parathyroid hormone–related protein and hypercalcemia in two dogs with schistosomiasis. JAAHA 2001;37:349355. 5. Flowers JR, Hammerberg B, Woo SL, et al. Heterobilharzia americana infection in a dog. JAVMA 2002;220:193-196. 6. Wilson N, Johnson EM, Brunker J, Ritchey J. Heterobilharziasis in a dog [abstract]. Proc 52nd AAVP 2007:93. 7. McKown RD, Veatch JK, Fox LB. New locality record for Heterobilharzia americana. J Wildl Dis 1991;27:156-160. 8. Malek EA. Experimental infection of several lymnaeid snails with Heterobilharzia americana. J Parasitol 1967;53:700-702. 9. Malek EA, Short RB, Teehan WH, Jama A. Differential susceptibility of snail hosts to Heterobilharzia americana from Texas and Louisiana. J Parasitol 1987;73:872-873. 10. Lee H. Life history of Heterobilharzia americana Price 1929, a schistosome of raccoon and other mammals in southeastern United States. J Parasitol 1962;48:728739. 11. Cheriuyot HC, Jordan HE. Potential for the spread of Fasciola hepatica in cattle in Oklahoma. JAVMA 1990;196:1090-1094.
Vetlearn.com | March 2010 | Compendium: Continuing Education for Veterinarians®
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Parasites 101: Canine Schistosomiasis 12. Madsen H, Frandsen F. The spread of freshwater snails including those of medical and veterinary importance. Acta Tropica 1989;46:139-146. 13. Snowden K, White S, Barbara L, Craig T. Distribution and characterization of Heterobilharzia americana infections in the dog in Texas [abstract]. Proc WAAVP 2009:99. 14. Fabrick C, Bugbee A, Fosgate G. Clinical features and outcome of Heterobilharzia americana infection in dogs. J Vet Intern Med 2010;24:140-144. 15. Bartsch RC, Ward BC. Visceral lesions in raccoons naturally infected with Heterobilharzia americana. Vet Pathol 1976;13:241-249. 16. Goff WL, Ronald NC. Miracidia hatching technique for diagnosis of canine schistosomiasis. JAVMA 1980;177:699-700. 17. Bishop MA, Suchodolski JS, Steiner JM. Development of a PCR test for the detection of Heterobilharzia americana DNA in dog feces. J Vet Intern Med 2008;22:804805.
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Compendium: Continuing Education for Veterinarians® | March 2010 | Vetlearn.com
©Copyright 2010 MediMedia Animal Health. This document is for internal purposes only. Reprinting or posting on an external website without written permission from MMAH is a violation of copyright laws.
Canine Schistosomiasis in North America:
An Underdiagnosed Disease With an Expanding Distribution Eileen M. Johnson, DVM, PhD Oklahoma State University
H
eterobilharzia americana, a digenean trematode snail, Pseudosuccinea columella, experimentally shown to in the family Schistosomatidae, is the etiologic support development of H. americana.9,10 Both L. cubensis agent of canine schistosomiasis in the southeast- and P. columella are present in Oklahoma,11 although schisern United States.1 A few cases of canine schistosomiasis tosomiasis in indigenous dogs or raccoons has not been have been reported in Florida, Louisiana, North Carolina, reported there. P. columella, a North American lymnaeid, Texas, and, recently, Kansas.1–6 The natural definitive host has spread worldwide through the trade and transport for the fluke is the raccoon1; however, infections have been of aquatic plants.12 L. cubensis is known to be distribdetected in nutrias, bobcats, mountain lions, opossums, uted in Florida, Georgia, Louisiana, Texas, Mexico, South white-tailed deer, swamp rabbits, armadillos, coyotes, red America, and the West Indies12; it has also been found in wolves, red wolf–coyote crosses, Brazilian tapirs, minks, Oklahoma.11 A retrospective study conducted in Texas discovered a and beavers.7 higher rate of H. americana infection in dogs than the preGeographic Distribution vious literature seems to reflect, with a broader distribution The geographic distribution of H. americana is believed than along the Gulf Coast.13 Within a 4-year consecutive to be restricted to the south Atlantic and Gulf Coast states period, 127 cases were confirmed in 25 of 254 counties (Alabama, Florida, Louisiana, Georgia, North Carolina, in Texas. Distinct clusters of cases were found along the South Carolina, Virginia, Mississippi, Texas) due to the envi- Gulf Coast and associated with major urban populations. ronmental requirements of its intermediate host, the fresh- These findings indicate that canine schistosomiasis is not water snail Lymnaea cubensis8; however, H. americana a rare disease and that the distribution of the trematode infections have been reported in indigenous raccoons7 and in Texas has expanded. Another retrospective study of three companion dogs in Kansas.6 These cases are likely 22 naturally infected dogs in Texas found the infection due to introduction of the fluke with raccoons translocated in younger, larger-breed, indoor dogs that had occasional from Florida before 1983 and transmission by a freshwater access to the outdoors. Often, multiple animals in a house-
Contributed by the Companion Animal Parasite Council The Companion Animal Parasite Council (CAPC) is an independent association of veterinarians and other animal health care professionals established to create guidelines for the optimal control of internal and external parasites that threaten the health of pets and people. It brings together broad expertise in parasitology, internal medicine, public health, veterinary law, private practice, and association leadership. Initially convened in 2002, the CAPC was formed with the expressed purpose of changing the way veterinary professionals and pet owners approach parasite management. The CAPC advocates best practices for protecting pets from parasitic infections and reducing the risk for zoonotic parasite transmission. For more information, visit www.capcvet.org.
Vetlearn.com | March 2010 | Compendium: Continuing Education for Veterinarians®
E1
©Copyright 2010 MediMedia Animal Health. This document is for internal purposes only. Reprinting or posting on an external website without written permission from MMAH is a violation of copyright laws.
Parasites 101: Canine Schistosomiasis FIGURE 1
FIGURE 2
Heterobilharzia americana egg (magnification: 400×).
Miracidium hatching from an egg in deionized water (magnification: 400×).
that swim for a short period of time in search of a suitable snail. Mother and daughter sporocysts and cercariae develop asexually in the hepatopancreas of infected snails. Cercariae are then shed from the snail to reinitiate the life cycle. Eggs can be detected in the feces of definitive hosts approximately 68 days after exposure to infective cercariae.10
Courtesy of Dr. Jill Brunker, Oklahoma State University, CVHS, Small Animal Clinic
FIGURE 3
A
B
Diagnosis and Treatment
Eggs that have been hematogenously Gastroendoscopic photographs. (A) Healthy small intestine. (B) Small intestine of a disseminated to visceral organs or the dog infected with H. americana, demonstrating the thickened, corrugated appearance of the intestinal wall provoke a severe granuluminal surface of the intestinal wall. lomatous reaction (FIGURES 3 and 4) responsible for most of the clinical hold were affected.14 Cases have also recently been identi- signs and pathology.15 Initially, a papular vesicular rash fied in Alabama, Georgia, North Carolina, and Tennessee.a and coughing may be noted. Chronic diarrhea, characterized as mucoid to hemorrhagic, develops and progressively Life Cycle becomes more severe. Fever, anorexia, hypersalivation, Dogs and wildlife are exposed to H. americana while wad- lethargy, and weight loss may also be noted.2–6,14 Anemia, ing or swimming in freshwater areas such as marshes, mud dehydration, hyperglobulinemia, hypoalbuminemia, hyperflats, and canals.10 Cercariae discharged from infected snails calcemia associated with elevated parathyroid hormone– penetrate the host’s skin. The immature schistosomes (schis- related protein levels, and eosinophilia are common tosomula) first migrate through the body to the lungs, where clinicopathologic findings in infected dogs.2–6,14 Elevated they are associated with hemorrhage. They are then carried serum alkaline phosphatase, aspartate aminotransferase, to the liver, where they develop into adult male and female and alanine aminotransferase activities may also be eviflukes. The adults move into the mesenteric veins, mate, dent.5 Eggs are not likely to float with centrifugal flotation16; and deposit nonoperculated, spineless eggs (FIGURE 1). The examination of direct saline smears and sedimentation eggs penetrate venules to enter the intestinal wall and are of feces facilitate the detection of H. americana eggs. A shed into the intestinal lumen. If the eggs reach fresh water, miracidia hatching technique that involves resuspending they rapidly hatch, releasing ciliated miracidia (FIGURE 2) eggs sedimented in saline with deionized water can be employed to verify egg identification.16 An antigen capture a Personal communications: Byron Blagburn, MS, PhD, Auburn ELISA for schistosome circulating anodic antigen5,b and a University; Dana Ambrose MS, University of Georgia; Anne Zajac, DVM, PhD, Virginia Tech; and Sharon Patton, MS, PhD, University of Tennessee; October 2009.
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b Available from North Carolina State University College of Veterinary Medicine by request.
Compendium: Continuing Education for Veterinarians® | March 2010 | Vetlearn.com
Parasites 101: Canine Schistosomiasis FIGURE 4
Key Points • Canine schistosomiasis is a debilitating and often fatal parasitic disease of dogs in the southeastern United States. • Clinical signs and clinicopathogic findings are nonspecific and often mimic other diseases. • Clinical signs may include anorexia, lethargy, weight loss, and chronic mucoid to hemorrhagic diarrhea.
Section of small intestine from a dog showing a histiocytic inflammatory reaction to two H. americana eggs in the lamina propria of an intestinal villus (hematoxylin–eosin stain; magnification: 100×).
polymerase chain reaction assay for H. americana are also available for diagnosis.17,c Infections in dogs have been treated with high-dose praziquantel (25 mg/kg PO bid or tid for 2 to 3 days) or fenbendazole (40 mg/kg PO sid for 10 days).5 Treatment may result in complete cure or resolution of clinical signs, or it may be ineffective. The protracted course of the disease, poor response to treatment, and diagnostic challenges often lead to euthanasia. Many of the clinical signs and the hypercalcemia associated with elevated parathyroid hormone–related protein levels detected in some cases of canine schistosomiasis are more commonly associated with tumors, endocrine disorders, and other infectious granulomatous diseases.3 Some infections are secondary findings in animals with neoplasms.14 Expensive and invasive procedures may be required to rule out these conditions. Therefore, the definitive diagnosis of schistosomiasis is often delayed, as is initiation of appropriate therapy.
Conclusion Increased awareness of canine schistosomiasis and implementation of appropriate diagnostic parasitology tests in dogs with chronic diarrhea, especially in the southeastern United States, should improve early detection of H. americana infections and could improve therapeutic outcomes. The limited number of reported cases in dogs is incongruent with the high prevalence reported in the natural host (raccoon) and the broad range of naturally infected hosts.7 Geographic distribution of the snail intermediate hosts seems to be expanding.11,12 These factors suggest that canine infections with H. americana are often not detected because c Available from Texas A&M University, College of Veterinary Medicine, Gastrointestinal Laboratory; www.cvm.tamu.edu/gilab/assays/ Heterobilharzia%20americana.shtml.
• Clinicopathologic findings may include anemia, hyperglobulinemia, hypoalbuminemia, hypercalcemia, elevated serum parathyroid hormone–related protein levels, and elevated serum alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase activities. • Abdominal radiography may detect enlargement of the liver, spleen, and lymph nodes and thickening of the intestinal wall. • Heterobilharzia americana eggs do not float in standard fecal flotation solutions. • Fecal sedimentation and direct saline smears are the tests of choice for detection of eggs. • A polymerase chain reaction assay and an antigen capture ELISA are available for the diagnosis of canine schistosomiasis.
routine parasitologic examinations do not include the fecal sedimentation technique or because owners choose euthanasia after exhaustive diagnostic testing fails to determine the etiology of clinical disease. References
1. Malek EA. Heterobilharzia infection in the dog and other mammals in Louisiana. J Parasitol 1961;47:619-623. 2. Slaughter JB Jr, Billups LH, Acor GK. Canine heterobilharziasis. Compend Contin Educ Pract Vet 1988;10:606-612. 3. Rohrer CR, Phillips LA, Ford SL, Ginn PE. Hypercalcemia in a dog: a challenging case. JAAHA 2000;36:20-25. 4. Fradkin JM, Braniecki AM, Craig TM, et al. Elevated parathyroid hormone–related protein and hypercalcemia in two dogs with schistosomiasis. JAAHA 2001;37:349355. 5. Flowers JR, Hammerberg B, Woo SL, et al. Heterobilharzia americana infection in a dog. JAVMA 2002;220:193-196. 6. Wilson N, Johnson EM, Brunker J, Ritchey J. Heterobilharziasis in a dog [abstract]. Proc 52nd AAVP 2007:93. 7. McKown RD, Veatch JK, Fox LB. New locality record for Heterobilharzia americana. J Wildl Dis 1991;27:156-160. 8. Malek EA. Experimental infection of several lymnaeid snails with Heterobilharzia americana. J Parasitol 1967;53:700-702. 9. Malek EA, Short RB, Teehan WH, Jama A. Differential susceptibility of snail hosts to Heterobilharzia americana from Texas and Louisiana. J Parasitol 1987;73:872-873. 10. Lee H. Life history of Heterobilharzia americana Price 1929, a schistosome of raccoon and other mammals in southeastern United States. J Parasitol 1962;48:728739. 11. Cheriuyot HC, Jordan HE. Potential for the spread of Fasciola hepatica in cattle in Oklahoma. JAVMA 1990;196:1090-1094.
Vetlearn.com | March 2010 | Compendium: Continuing Education for Veterinarians®
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Parasites 101: Canine Schistosomiasis 12. Madsen H, Frandsen F. The spread of freshwater snails including those of medical and veterinary importance. Acta Tropica 1989;46:139-146. 13. Snowden K, White S, Barbara L, Craig T. Distribution and characterization of Heterobilharzia americana infections in the dog in Texas [abstract]. Proc WAAVP 2009:99. 14. Fabrick C, Bugbee A, Fosgate G. Clinical features and outcome of Heterobilharzia americana infection in dogs. J Vet Intern Med 2010;24:140-144. 15. Bartsch RC, Ward BC. Visceral lesions in raccoons naturally infected with Heterobilharzia americana. Vet Pathol 1976;13:241-249. 16. Goff WL, Ronald NC. Miracidia hatching technique for diagnosis of canine schistosomiasis. JAVMA 1980;177:699-700. 17. Bishop MA, Suchodolski JS, Steiner JM. Development of a PCR test for the detection of Heterobilharzia americana DNA in dog feces. J Vet Intern Med 2008;22:804805.
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Compendium: Continuing Education for Veterinarians® | March 2010 | Vetlearn.com
©Copyright 2010 MediMedia Animal Health. This document is for internal purposes only. Reprinting or posting on an external website without written permission from MMAH is a violation of copyright laws.
