Elegant is the word that describes the complex and successful life cycle

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A REPRINT FROM OMPENDtUM ON ~NTlNUING UCATION .=or THE PRACTICING VETERINARIAN KEY FACTS o The complex sexual and asexual life cycle of Plalynosomum concinnum involves snails, terrestrial isopods, reptiles
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A REPRINT FROM OMPENDtUM ON ~NTlNUING UCATION .=or THE PRACTICING VETERINARIAN KEY FACTS o The complex sexual and asexual life cycle of Plalynosomum concinnum involves snails, terrestrial isopods, reptiles or amphibians, and cats. o Although the parasite is worldwide in distribution, geographic sening is a factor that limits its occurrence. o Definitive diagnosis based on finding fecal fluke eggs can be elusive. o Praziquantel is the preferred drug for treatment. o Prevention is challenging because the life cycle of the fluke capitalizes on feline predatory instincts. Platynosomum concinnum Infection in Cats Upper Keys Vererinary Clinic Islamorada, Florida Robert H. Foley, DVM Elegant is the word that describes the complex and successful life cycle of the biliary trematode of cats, Platynosomum concinnum. First described at the beginning of this century, it has been referred to as Dicrocoelium concinnum, Platynosomum planicipitus, and Platynosomum fastosum.i- 3 The adult P. concinnum is also capable of parasitizing civet cats, opossums, ferrets, and white mice. The fluke requires three other animal hosts to complete its life cycle, and these are simultaneously indigenous only in the tropical and subtropical climates ofthe world (Figure 1).1,4--9 LIFE CYCLE A cat excretes the fluke egg (Figure 2) to the soil. The egg is ingested by the snail Subulina octona or, in Hawaii, Eulota (Bradybaena) similaris. 3 6 The asexual phase of the digenetic trematode begins in the snail. In the snail's crop, in 15 minutes or less, the miracidium extrudes through the operculum of the egg. The miracidium must quickly penetrate into the connective tissue of the snail, preferably near respiratory tissue. During the next 28 days, the miracidium develops into a mother sporocyst. This sporocyst creates numerous migratory daughter sporocysts, each laden with approximately 18 cercariae. Exactly 60 days after ingestion of the fluke egg, the daughter sporocysts begin exiting through the mantle of the snail to the soil. Daughter sporocyst emergence is influenced by high humidity and increased light. 4 These factors affect snail activity and accommodate a rainy summer fluke infection season. Terrestrial isopods, such as pill, sow, or dung bugs (Figure 3), become the second intermediate hosts by ingesting the cercariae-laden daughter sporocysts. 5 Maturation to metacercariae apparently occurs in the isopod. The isopods are ingested by such lower vertebrates as lizards, frogs, or toads (see Third Intermediate HostS).5-11 Insectivorous birds may also be involved. 9 The metacercariae encyst in the gallbladder and common bile duct of the lower vertebrate, waiting for the final, definitive host to complete the life cycle. 5 The natural predatory instinct of cats ensures the completion of the P. concinnum life cycle. A cat ingests the lizard (Figure 4), consuming the en- Copyright 1994, Veterinary Learning Systems Co., Inc. All Rights Reserved. Printed in USA 1272 Small Animal The Compendium October 1994 DEFINITIVE HOST Domesticated cat with adult fluke in biliary system Cat eats lizard Egg with miracidium in soil THIRD INTERMEDIATE HOST Lower vertebrate with encysted metacercariae FIRST INTERMEDIATE HOST Snail with sporocysts Lizard eats isopod Sporocyst in soil Figure l-life cycle of Platynosomum concinnum. SECOND INTERMEDIATE HOST Isopod with metacercariae Figure 2-Platynosomum concinnum eggs, one of which has the operculum hatch open. The eggs measure 25 X 45 microns. Figure 3-Pill bugs, which are terrestrial isopods that serve as second intermediate hosts. cysted metacercariae. Within hours after ingestion, the metacercariae migrate up the major duodenal papilla of the cat and into the common bile ducc. 4 Twenty percent of cats have a minor duodenal papilla; it is possible but rare for the metacercariae to migrate into this papilla and finally into pancreatic tissue via the accessory pancreatic ducc. 2 Once in the feline biliary system, metacercariae mature into egglaying adult flukes in four to five weeks. This completes the life cycle and commences the disease process in cats. CLINICAL INFECTION In tropical and subtropical settings, the prevalence of fluke infection has been reported to be 15% to 85% of the feral cat population The variation probably reflects the imprecise nature of fecal diagnosis and the local variation in the snail-isopod-lower vertebrate population necessary for a high fluke bur- den. A typical patient with asymptomatic parasitism is a young, hungry, 6- to 24-month-old, feral cat of either gender. The cat feeds on native fauna, such as lizards and birds. The fluke egg is usually an incidental finding on fecal examination. Cats with small fluke burdens (less than 125 adult flukes) are often clinically asymptomatic. There is no correlation between fluke parasitism and feline immunodeficiency virus status or feline leukemia virus status. In my practice, house cats diagnosed with P. concinnum infection are usually older than two years of age and have a history of hunting lizards. Overt clinical cases of P. concinnum parasirism typically occur in adult outdoor or indoor-outdoor cats. Cats present with a panorama of clinical signs. The severity of the signs is proportional to the number of adult flukes and the duration of parasitism. Clinical signs may be as vague as lethargy, anorexia, unthrifty haircoat, or slight weight loss. More extreme signs in- The Compendium October 1994 Small Animal 1273 Third Intermediate Hosts Reptiles Anolis cristatellus Anolis equestris Anolis sagrei Anolis carolinensis Eumeces inexpectadus Hemidactylus frenatus Lygosoma metallicum Amphibians Eleutherodactylus ricordi Bufo marinus Bufo terrestrus c1ude vomiting, mucoid diarrhea, and a change in the character ofthe stools. Extreme parasite burdens can cause anemia, hepatomegaly, abdominal ascites, and jaundice8-10 (Figure 5). In cats with total biliary occlusion, jaundice is accompanied by clay-colored stools that lack bile. DIAGNOSIS Definitive diagnosis is accomplished by detecting operculated fluke eggs in the feces (Figure 2). A low number of eggs is often present, and daily output by flukes varies. The eggs are too dense to float in sugar or zinc sulfate solution; it is advisable to use direct examination or the formalin ether sedimentation technique (see the box). This technique demonstrates eight times as many eggs as does direct fecal examination. 12 Serial fecal examinations may be necessary because all flotation techniques only identify positive feces in 25% ofparasitized cats. 13 I use corn oil as a cholagogue to increase the number of fluke eggs in the feces of a parasitized cat. The patient is given corn oil (2 mllkg) orally. The corn oil, like egg yolk or magnesium sulfate, acts as a cholagogue and contracts the gallbladder. For the technique to succeed, the patient must have a patent biliary system. The feces are reexamined 2 to 24 hours after the corn oil is administered. A substantial number of eggs sequestered in the gallbladder or biliary system are usually discovered in the feces by direct fecal examination or formalin ether flotation. The hematologic changes that are evident with P. concinnum infection are best summed up by stating that no disease level is pathognomonic for parasitism. Compared with normal feline values, hematologic values may change. The biliary fluke induces circulating eosinophilia beginning three weeks after infection. Eosinophilia is proportional to the number of adult flukes, peaks at 8 to 18 weeks, and persists for months. s. 8 A practitioner can expect a 50% to 100% increase in the number of eosinophils relative to normal feline values in the practice. Figure 4-The tropical lizard Anolis carolinensis, a third intermediate host. A 10% to 20% increase in serum alanine transaminase and aspartate transaminase is expected in the first four to five months of parasitism. The enzymes eventually return to normal. Serum alkaline phosphatase is usually unaffected and is normal even if hepatomegaly or jaundice is present All liver enzymes increase when cholangiocarcinoma accompanies the parasitism. In rare cases, pancreatic enzymes may be elevated. 2 ls Total serum bilirubin values depend on the degree of biliary tract inflammation, hyperplasia, and resultant bile stasis. Total biliary values as high as 20 mg/dl are possible.1 6 Bilirubinuria accompanies jaundice (Figure 5). In early cases of parasitism, before severe periductal fibrosis occurs, there are no signs ofane mia, hypoalbuminemia, altered blood ammonia, or altered renal function. Ultrasonographic examination of a parasitized cat might demonstrate distention of the gallbladder and/or common bile duct. Hepatomegaly and distention of the hepatic biliary tree may be evident. Radiography might demonstrate hepatomegaly, which is usually palpable. 16 Liver biopsy and necropsy findings exhibit consistent hepatic disease. Inflammation and edematous hyperplasia of the bile ducts with infiltration of eosinophils and plasma cells are present. Also apparent is an increase in the size and tortuosiry of the common, cystic, and hepatic ducts (Figure 6). The bile is thickened and may be inspissated within the gallbladder. The liver may be enlarged and yellow. Viscera are jaundiced in proportion to the serum bilirubin level. Trematodes and eggs may be seen anywhere in the biliary system. Pancreatic atrophy is evident in cases in which the fluke has migrated into the minor duodenal papilla and accessory pancreatic duct. 2 ls The flukes are easily visible and readily identifiable (Figure 7). Specimen flukes must be allowed to die in 1274 Small Animal The Compendium October 1994 Formalin Ether Sedimentation Technique 1. Suspend one gram of feces in 25 milliliters of 0.9% saline solution. 2. Filter through fine mesh (e.g., a tea strainer or gauze). 3. Centrifuge filtrate for five minutes at 1500 rpm, and discard supernatant. 4. Suspend centrifuged pellet in seven milliliters of 10% buffered formalin for 10 minutes. 5. Layer three milliliters ofcold ether on the suspension, and shake well for 60 seconds. 6. Centrifuge mixtute for three minutes at 1500 rpm, and discard supernatant. 7. Resuspend pellet in 0.9% saline solution, and examine for eggs. The number is equivalent to eggs per gram. Figure 5-A three-year-old, jaundiced cat with a total serum bilirubin of 8.4 mg/dl. a 0.9% saline solution. Direct placement in 10% formalin hopelessly crenates the flukes 2 (Figure 8). Older cats that have been parasitized for extended periods present with emaciation, cachexia, and liver cirrhosis. Chronic cholangiohepatitis is replaced by periductal fibrosis that affects connective tissue. An affected cat can have hundreds of adult flukes in the biliary system. I have seen four cases of cholangiocarcinoma in parasitized cats (Figure 9). The cats were middle-aged (6 to 11 years old) and had gross hepatomegaly and elevated serum alanine transaminase, aspartate transaminase, and alkaline phosphatase levels. All of the patients were markedly icteric and had total bilirubin levels exceeding 8 mg/dl. The four cases represent less than 2% of all parasitized cats seen. Feral cats usually have a short life span and are seldom examined when ill; the true incidence of carcinoma may be much higher. In humans, the liver fluke Opisthorchis induces hepatic carcinoma in 55% of the individuals that it parasitizes. I? The adult flukes stimulate minimal immune response, which is detected by the presence of humoral antibodies in the bile. 14 The flukes do not suppress the function of T or B lymphocyres. 9 Immune suppression is not a primary ailment but can be secondary to debilitation. TREATMENT AND PREVENTION The cesticidal drug praziquantel is the only effective agent available for treating patients with P concinnum. The drug is administered parenterally at 20 mg/kg (four times the recommended dose level of 5 mg/kg for cats).18 Extralabel use with client consent is necessary. As a precaution, treated cats should be Figure 6-A parasitized liver with hyperplastic and tortuous common, cystic, and hepatic bile ducts. observed. The action of praziquantel on flukes is unknown. The drug is excreted in the bile; perhaps trematodes, like cestodes, lose their abiliry to resist digestion by the host. After treatment, fluke eggs may be evident in the feces for as long as nine weeks because of incomplete killing of the trematode or the sequestering of eggs in the biliary system. 18 Ideally, praziquantel therapy is repeated at 12-week intervals. I have also used a three-day oral praziquantel regimen. Using the canine dose rate (10 mg/kg), a cat is treated for three days. The results compare favorably and should involve a reversal ofsigns in mildly to moderately ill cats. Vomiting subsides, appetite returns, weight is restored, and jaundice resolves. The cat returns to normal activity, which often includes more lizard hunting. Supportive treatment of parasitized cats must be tailored to the signs of the verminous cholangiohepatitis. The attending veterinarian must address nutritional needs and concomitant bacterial, viral, or parasitic infection. Associated bacterial infections, such as with Yersinia, may be worse than the effects of the trematode. 19 I administer a copious amount of 0.9% saline solution for rehydration and, if there is ob- 1276 Small Animal The Compendium October 1994 Figure 7-A Platynosomum concinnum adult that was allowed to die in 0.9% saline solution. The fluke measures 140 X 540 microns. Figure a-an extremely distorted formalin-fixed adult fluke that measures 120 X 320 microns. structive cholangitis, dexamethasone (l mg/kg) parenterally twice daily. The antiinflammatory agent usually restores patency to the bile duct, alleviating the jaundice by eliminating bile through the feces. Preventing infection in an attempt to maintain a healthy cat is a challenge. Avoidance of lower vertebrate hosts is essential and is more easily accomplished in house cats. Outdoor cats are thus more likely to be reinfected and progress to irreversible liver disease. CONCLUSION Platynosomum concinnum is a parasite of tropical and subtropical climates worldwide. A cat living in or traveling through such climates could become parasitized by ingesting an infected invertebrate host. The modern mobility of companion cats explains the occasional reports of infections outside the tropics It also places all veterinarians on alert for these elusive trematodes in feline patients that travel. The primary source of infection in cats is the ubiquitous tropical lizard. Frogs also may be a source. The Bufo toad (Bufo marinus) has been incriminated as a potential fluke source I doubt this hypothesis. In nature, the Bufo species are well protected by their cutaneously excreted bufotoxin. Unlike dogs, cats evidently shun interaction with Bufo toads. Definitive diagnosis of P. concinnum infection is accomplished by finding operculated fluke eggs in feces. Serial fecal examinations and additional clinical pathologic evaluation may be needed in occultly parasitized or severely ill animals. Praziquantel at extralabel doses is the preferred treatment agent. Preventing parasitism in companion cats means housing cats indoors and avoiding contact with third intermediate hosts, such as during vacations to Florida or the Caribbean. Outdoor or feral cats that live in the subtropics may require quarterly treatment with praziquantel. Figure 9-Cholangiocarcinoma with locally invasive epithelial cells. Also evident are scattered eggs and a trematode in the bile ducts. (xgo) In cats with evidence of eosinophilia, hepatomegaly, and jaundice, veterinarians should consider the possibility of fluke infection. Close inspection of cats with liver carcinoma may demonstrate underlying P. concinnum parasitism. About the Author Dr. Foley, who is a Diplomate of the American Board of Veterinary Practitioners, is the chief of staff at the Upper Keys Veterinary Clinic in Islamorada, Florida. REFERENCES 1. Braun M: Dicrocoelum aus der gallenblase der Ziberh Karze. Cent Bakt ParasitoI30:700, Purvis GB: Species of Platynosomum in felines. Vet Rec 11: , Kossak W: Neue Distomen. Cent Bakt Parasitol56: 114, Malonado ]F: The life history and biology of Platynosomum fastosum Kossak, 1910 (Trematoda:Dicrocoeliidae). Puerto Rico J Publ Health Trop Med21: 17-39, Eckerlin RP, Leigh WH: Platynosomum fastosum Kossak, The Compendium October 1994 Small Animal (Trematoda:Dicrocoeliidae) in Sourh Florida. ] ParasitoI48(Suppl):49, Ash LR: Helminth parasites of dogs and cats in Hawaii. ] Parasitol 48:63-{)5, Palumbo NE, Perri SF, Loo B, et a1: Cat liver fluke, Platynosomum concinnum in Hawaii. Am] Vet Res 35:1455, Taylor 0, Perri SF: Experimental infection of cats wirh the liver fluke Platynosomum concinnum. Am] Vet Res 38:51-54, Young CN, Miyahara AY, Chung G: The prevalence of feline liver flukes in the city and county of Honolulu. ]AAHA 13: , Bielsa LM, Gteiner EC: Liver flukes (Platynosomum concinnum) in cats.]aaha 21: , Learn G, Walker IE: The occurrence of Platynosomum fastosum in domestic cats in the Bahamas. Vet Rec 75:46-47, Palumbo NE, Taylor 0, Perri SF: Evaluation of fecal technics for rhe diagnosis of cat liver fluke infection. Lab Anim Sci 26: , Rernasabaparhy A, Prarhap K: The liver fluke Platynosomum fastosum in domestic cats. Vet Rec 88:62-{)5, Taylor 0, Siddiqui W: Parasite-host relationship between the liver fluke Platynosomum concinnum syn. fastosum and rhe domestic cat, Felis carus.] Parasitol61 (Suppl):64, Simon AM: Liver fluke (Platynosomum fastosum) in cats. Fwrida Vet]6:15-17, Jenkins CJ, Lewis DO, Brock KA, et a1: Extrahepatic biliary obstruction associated with Platynosomum concinnum in a cat. Compend Contin Educ Pract Vet 10(5):628-{)32, Koomirochana C, Sonakul 0, Chiuda K, et a1: Opisrhorchiasis: A study of 154 autopsy cases. Southeast Asian] Trop Med Public Health 9:60-64, Evans JW, Green PE: Preliminary evaluation of four anrhelmintics against rhe cat liver fluke Platynosomum concinnum. Aust Vet]54: , O'Sullivan BM, Rosenfeld LE, Green PE: Concurrent infection with Yersinia pseudotuberculosis and Platynosomumfastosum in a cat. Aust Vet] 52: , Greve JH, Leonard PO: Hepatic flukes (Platynosomum concinnum) in a cat from Illinois. ]A VMA 149: , Barriga 00, Caputo C, Weisbrode S, et al: Liver flukes (Platynosomum concinnum) in an Ohio cat. ]A VMA 179: , 1981.
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