Cestodes in Dogs and Cats: A Practical Guide PDF

CLINICAL PATHOLOGY I – Lecture Cestodes: The Tapeworms Kingdom: Animalia Phylum: Platyhelmiths Class: Cestode Subclass: Eucestoda=true tapeworm Order: Cyclophyllidean Subclass: Cotyloda=psuedotapeworms Order: Diphyllobothriidean I. Overview of Cestode...

CLINICAL PATHOLOGY I – Lecture Cestodes: The Tapeworms Kingdom: Animalia Phylum: Platyhelmiths Class: Cestode Subclass: Eucestoda=true tapeworm Order: Cyclophyllidean Subclass: Cotyloda=psuedotapeworms Order: Diphyllobothriidean I. Overview of Cestodes  Flatworms that lack a body cavity  Always indirect life cycle A. Cyclophyllidean: “True” tapeworms; scolex contains suckers, and may be “armed” (contain hooklets) or “unarmed” (no hooklets); genital pores are laterally located on the proglottid; require one IH. ** =Zoonotic 1. Dipylidium caninum** 2. Taenia spp.  T. pisiformis (dogs and other canids)  T. hydatigena (dogs and other canids)  T. ovis (dogs and other canids)  T. taeniaeformis (cats and other felids) 3. Echinococcus spp.**  E. granulosis (dogs and other canids)  E. multilocularis (dogs, cats, wild canids and felids) B. Cotyloda :“Pseudo tapeworms”; scolex contains two bothria (slit-like organs of attachment); genital pores are centrally located on proglottid; require two IHs. ** =Zoonotic 1. Diphyllobothrium latum** 2. Spirometra spp.** II. Cestode Life Cycle and Anatomy A. Cestode Life Cycle 1. Indirect = Requires IH 2. Adults attached by scolex to mucosa of small intestine 3. Proglottids containing ova infective to IH pass in feces; ova are infective to IH upon passage. 4. Ova ingested by and mature in IH 5. IH must be eaten by DH to complete life cycle – oral transmission only B. Adult Cestode 1. In small intestine 2. Contains NO digestive organs -- absorbs food/nutrients through specialized tegument 3. Extremely variable in size: From Diphyllobothrium latum (30 ft) to Echinococcus granulosis (6 mm) 12/3/2024 1  C. Cestode Anatomy 1. Scolex = “Head”  “Holdfast”  Attaches to intestinal wall via hooks and/or suckers  Located at anterior end of organism 2. Proglottids = “Segments”  Flattened  Absorb nutrients from bowel of DH  Separate from strobila when mature and pass intermittently  Hermaphroditic : Contain both male and female reproductive organs  Most distal segments are more mature and gravid  Very commonly seen by clients D. Ova 1. Contained within proglottids that pass with feces 2. Contain 1st stage larva (oncosphere or hexacanth embryo) infective to IH upon passage (this is different in pseudotapeworms) 3. Ingested by IH E. Larvae 1. 1st Stage Larva  Infective immediately upon passage to IH  Oncosphere is 1st stage larva which develops to 2nd stage larva in body cavities or tissues of IH 2. 2nd Stage Larva  Infective to DH  Cysticercus or cysticercoid: Refers to 2nd stage larva  Cysticercus in mammalian IH; e.g., Taenia and Echinococcus  Cysticercoid in arthropod IH; e.g., Dipylidium  Clear, fluid-filled sac (containing scolex) is infective to DH  Commonly known as “bladderworm” 3. “Bladderworm”  Develops in IH likely to be eaten by DH  Once ingested, “bladder” digested away and scolex imbeds in mucosa of DH's small intestine 12/3/2024 2 III. Cyclophyllidean: “True” tapeworms A. Dipylidium caninum: The “flea tapeworm” 1. Adults in small intestine of DH mature and release gravid proglottids 2. Ovum of tapeworm ingested by larval flea (Ctenocephalides spp.) or biting louse which serve as IH 3. Cysticercoid forms in flea (or louse) 4. Dog or cat ingests flea (or louse) while grooming 5. Prepatent period = 4 weeks 6. Dx: “Cucumber seed” segments on perineal area 7. Proglottids have double pores at lateral midpoint 8. Ova frequently remain inside segments and are not easily found 9. Tx: Must tx for fleas at same time as treating for tapeworms 10. ZOONOTIC if human ingests infested flea B. Taenia spp. 1. Adult segments are rectangular and ~ size of rice 2. Proglottids have single pore at lateral midpoint 3. Ova are passed in proglottids 4. Ova are emptied from proglottid as it moves about on fecal mass C. Taenia pisiformis 1. Adults in small intestine of dog (DH) mature and release gravid proglottids 2. Proglottids release eggs eaten by grazing rabbit (IH) 3. Cysticercus (“bladderworm”) develops in rabbit’s tissues 4. Dog eats raw or undercooked rabbit and becomes infested 5. Prepatent period = 8 weeks D. Taenia hydatigena and Taenia ovis 1. Infective ova pass in feces of canine DH 2. Ova ingested by appropriate IH  T. hydatigena: Sheep  T. ovis: Sheep 3. DH consumes raw tissue of infested IH 4. Life cycle completed in DH 5. Prepatent period ~ 8 weeks E. Taenia taeniaeformis 1. Similar to T. pisiformis, etc. except involves cats (DH) and mice (IH) 2. VERY common in cats allowed to hunt 3. Recurrent infestations are typical 4. Prepatent period = 4 to 6 weeks F. Echinococcus spp. (ZOONOTIC and REPORTABLE) 1. Adults are tiny, 1.2 - 7 mm in length  Composed of scolex and three proglottids 12/3/2024 3   Proglottids: #1 immature, #2 mature, and #3 is gravid 2. 1st stage larva develops into hydatid cyst (2nd stage larva) in IH's bocy. [Hydatid cyst is analogous to“bladderworm”] G. Echinococcus granulosis 1. Adults in small intestine of dog (and other wild canids); do not cause significant disease in DH 2. Proglottid passed and oncosphere ingested by IH a. Typically sheep or other ruminants; sometimes swine, horses, and even kangaroosAnd sometimes by people. 3. ZOONOTIC 4. Prepatent period = 4 to 8 weeks 5. Larvae form hydatid cysts in various tissues of IH  Liver  Lungs  Kidneys  Spleen  Bone  Brain 6. Disease is “hydatidosis” 7. In people, cysts can be very large (grapefruit-sized) and cause terrible disease due to space-occupying properties 8. Life cycle complete when IH is consumed by DH; i.e., sheep eaten by dog H. Echinococcus multilocularis 1. Adults in small intestine of dogs, foxes, coyotes, wolves, and cats; do not cause significant disease in DH 2. Life cycle same as E. granulosis except IHs are mice and occasionally people 3. ZOONOTIC 4. Prepatent period = 4 to 8 weeks 5. “Alveolar hydatidosis” 6. Larvae produce alveolar hydatid cysts that continuously grow and infiltrate tissues of the liver, lung, brain, kidney, spleen, bone and other organs (like malignant neoplasm) 7. Alveolar hydatid infestations typically prove fatal in few years I. Echinococcus spp. other information 1. Diagnosis  Cannot differentiate ova from Taenia spp. -- must identify adult worms  May collect adults via purgative 2. Wildlife & Echinococcus spp.  Sylvatic cycles exist with moose/wolves/sled dogs/people  Dogs infested by scavenging wild game, shed infective oncospheres in their feces  People infested via poor hygiene after handling dog feces – WASH YOUR HANDS 3. Public Health Concerns of Echinococcus spp.  Humans can serve as IH 12/3/2024 4   Hydatid cysts are space-occupying lesions which can be fatal to people  Do not feed raw meat to pets  Do not let cats or dogs hunt IV. Cotyloda “Pseudotapeworms” A. Diphyllobothrium latum** 1. Zoonotic potential 2. Requires two IHs  1st is copepod (small crustaceans found in saltwater and freshwater)  2nd is fish 3. DH (dogs, cats and humans) infested via raw fish 4. Prepatent period ~ 6 weeks 5. Dx  Identification of characteristic operculated egg  Identification of proglottid via medial pore B. Spirometra spp.** 1. Zoonotic potential 2. Requires two IHs  1st is copepod  2nd varies; i.e., amphibian, reptile, bird, mammal including humans 3. DH (dogs and cats) infested via ingestion 2nd IH 4. Prepatent period 2 to 4 weeks 5. Mature proglottids separate along longitudinal axis, hence name “zipper” tapeworm 6. Dx o Large operculated ovum o Proglottids have medial pore V. Signs and symptoms, diagnosis, and treatment of Cestodes A. Clinical Sign of Cestodes 1. Owners often observe proglottids around rectum and/or on bedding 2. Signs usually minimal  Occasional “scooting”  Licking anal area  Unthriftiness  Mild diarrhea B. Ovum Identification 1. Can differentiate Dipylidium ova from Taenia/Echinococcus 2. Cannot differentiate Taenia ova from Echinococcus ova 3. Diphyllobothrium latum and Spirometra spp. easily differentiated from cyclophyllideans C. Proglottid Identification 1. May need to rehydrate to examine 12/3/2024 5  2. What’s the procedure for doing this? 3. What are we looking to find? D. Cestode Tx 1. Requires very specific meds  Praziquantel  Epsiprantel 2. NOT  Ivermectin  Fenbendazole (although this drug will eliminate most species of Taenia) E. Economic Importance Cysticerci or hydatid cysts in sheep and cattle will cause lesions (often in liver – hepatic lesions), meat inspectors will condemn entire carcass F. Prevention of Cestodes in Pets 1. Eliminate fleas 2. Don’t permit pets to hunt 3. Don’t feed raw meat to pets 4. Don’t feed raw fish to pets G. Prevention of Zoonotic Cestodes in Humans 1. Don’t eat fleas 2. Don’t permit pets to hunt 3. Don’t feed raw meat to pets 4. Don’t eat raw fish 5. Wash your hands Cestode Terminology 1. Scolex: Aka “holdfast”; the attachment end of a tapeworm, considered to be the anterior end. 12/3/2024 6  2. Strobila: The chain of proglottids that make up the bulk of the body of a tapeworm. 3. Proglottid: One of the segments that comprise the strobila. 4. Oncosphere: Aka “hexacanth embryo”; the first stage larva containing 6 hooklets that is infective to the IH; can be spelled “onchosphere”. 5. Hexacanth embryo: Aka “oncosphere” (see above). 6. Cysticercus: The cyst-like larval stage of cestodes that form in the tissues of the mammalian IH; this stage is infective to the DH; commonly referred to as a “bladderworm”’; plural is “cysticerci”. 7. Cysticercoid: The cyst-like larval stage of cestodes that form in an arthropod IH. 8. Hydatid cyst: The cyst-like larval stage of Echinococcus granulosis that forms in the tissues of the IH; this stage is infective to the DH. (This is analogous to the cysticercus of Taenia spp.) 9. Alveolar hydatid cyst: Cyst-like larval stage of Echinococcus multilocularis that forms in the tissues of the IH; named “alveolar” due to its form of asexual reproduction within the IH. 10. Hydatidosis: Disease caused by the presence of hydatid cysts. 11. Gravid: Pregnant; containing developing young. 12. Sylvatic: Involving animals of the forest; found in the woods. 13. Cyclophyllidean: “True” tapeworms; scolex bears suckers, and may be “armed” (contain hooklets) or “unarmed” (no hooklets); genital pores are laterally located on the proglottid; require one IH. 14. Cotyloda “Pseudo tapeworms”; scolex bears two bothria (slit-like organs of attachment); genital pores are centrally located on proglottid; require two IHs. Quick look at DH and IH 1. Dipylidium caninum** o DH includes dog, cat and human o IH is flea; occasionally dog louse 2. Taenia pisiformis o DH is dog (can be found in other canids) o IH is wild lagomorph 3. Taenia hydatigena o DH is dog (can be found in other canids) o IH is sheep 4. Taenia ovis o DH is dog (can be found in other canids) o IH is sheep 5. Taenia taeniaeformis o DH is cat (can be found in other felids) o His include mice and rats 12/3/2024 7  6. Echinococcus granulosis** o DH is dog (and other wild canids) o IH are ruminants (sheep, cattle, moose, caribou and others) and humans 7. Echinococcus multilocularis** o DH are dogs and cats o IHs are rodents and humans 8. Diphyllobothrium latum** o DH are dogs, cats, and humans o IHs  Copepod  Fish 9. Spirometra spp.** o DH are dogs and cats o IHs  Copepod  Amphibians, reptiles, birds, various mammals including humans 12/3/2024 8