Clinical Parasitology PDF

# **Clinical Parasitology** ## **Introduction** * Parasitology is the area of biology concerned with the phenomenon of dependence of one living organism on another. * Medical Parasitology is concerned primarily with parasites of humans and their medical significance, as well as their importance i...

# **Clinical Parasitology** ## **Introduction** * Parasitology is the area of biology concerned with the phenomenon of dependence of one living organism on another. * Medical Parasitology is concerned primarily with parasites of humans and their medical significance, as well as their importance in human communities. * Parasitism is a symbiotic relationship where one organism, the parasite, lives in or on another, depending on the latter for its survival and usually at the expense of the host. ## **Host** * **Host** - in which the parasite attains sexual maturity. * *E.g., Taenia spp: humans* * **Paratenic host** - one in which the parasite does not develop further to later stages, however, the parasite remains alive and is able to infect another susceptible host. * *E.g., Taenia spp: Pigs or cattle* * **Reservoir hosts** - allow the parasite's life cycle to continue and become additional sources of human infection. * *E.g., Pigs are reservoirs of Balantidium coli* * *Field rats of Paragonimus westermani* * *Cats of Brugia malayi* * **Accidental or Incidental host** - host in which a parasite is not usually found. * *E.g., man is an accidental host for cystic echinococcosis* ## **Basic Principles In Parasitology** ### **Parasite Classification: Habitat** * **Endoparasite** - parasite living inside the body of a host * *E.g., Protozoan and helminthic parasites* * **Ectoparasite** - parasite living outside the body of a host * *E.g., Lice, ticks and mites* ### **Parasite Classification: Mode of Development** * **Parasite** - they need a host at some stage of their life cycle to complete their development and to propagate their species. * *E.g., Toxoplasma gondii* * **Accidental or Incidental parasite** - establishes itself in a host where it does not ordinarily live. * *E.g., Echinococcus granulosus* * **Permanent parasite** - remains on or in the body of the host for its entire life. * **Temporary parasite** - lives on the host only for a short period of time. * **Spurious parasite** - free-living organism that passes through the digestive tract without infecting the host. * **Aberrant parasites** - infect a host where they cannot develop further and are known as aberrant or wandering parasites. * *E.g., Toxocara canis* ## **Exposure and Infection** * **Carrier** - harbors a particular pathogen without manifesting any signs and symptoms. * **Exposure** - process of inoculating an infective agent. * **Infection** - connotes the establishment of the infective agent in the host. * **Incubation Period** - period between infection and evidence of symptoms. ## **Sources of Infection** * **Soil** * lack of sanitary toilets and the use of night soil or human excreta as fertilizer allow the eggs to come in contact with the soil and favor the development * *E.g., Hookworm* * *Ascaris lumbricoides* * *Trichuris trichiura* * *Strongyloides stercoralis* * **Water** * contaminated with cysts of amebae or flagellates, as well as cercariae of Schistosoma. * **Food** * may contain the infective stage of the parasite, as exemplified by a number of trematode and cestode infections. * **Arthropods** * mosquitoes are vectors of malaria and filarial parasites. * Triatoma bugs are carriers of Trypanosoma cruzi causing Chagas disease. * Sand flies (e.g., Phlebotomus spp.) are the natural vectors of all types of Leishmania. * **Animals** * may also harbor parasites. * cats are direct sources of Toxoplasma infection * rats may be infected with Hymenolepis nana. * **Fomites** * other sources of infection include another person, his beddings and clothing, as well as the immediate environment he has contaminated. ## **Modes of Transmission** * **Foodborne** * *Taenia solium, Taenia saginata, and Diphyllobothrium latum from eating food harboring the infective larval stages* * *Entamoeba histolytica and Giardia lamblia from drinking water contaminated with cysts* * *Clonorchis, Opisthorchis, and Heterophyids through ingesting raw or improperly cooked freshwater fish containing infective larvae* ## **Life Cycle of Parasites** * **Direct Life Cycle** - when a parasite requires only single host to complete its development, it is called as direct life cycle. * *E.g., Entamoeba histolytica requires only a human host to complete its life cycle* * **Indirect Life Cycle** - when a parasite requires two or more species of host to complete its development, the life cycle is called as indirect life cycle. * *E.g., malarial parasite requires both human host and mosquito to complete its life cycle* * **Components of Parasitic Life Cycle** * **Mode of transmission** * **Infective stage** - morphologic form that invades humans. * **Diagnostic stage** - forms that can be detected via laboratory retrieval methods. * **Phases of Parasitic Life Cycle** * Parasite in or on the human body * provides an understanding of the symptomatology and pathology of the parasite * Insights about the best the method of diagnosis * Determine the selection of appropriate antiparasitic medication * Route independent of human body * provides crucial information pertinent to epidemiology, prevention, and control ## **Classification of Parasites** * Three major groups of clinically significant parasites: * **Single-celled parasites -Protozoa** * **Multicellular worms -Metazoa helminths** * **Arthropods (insects and their allies) -Animalia** ### **Protozoan** * Protozoan parasites are provided with locomotory apparatus, which include cilia, flagella, and pseudopodia. * **Sarcodina/Amoeba** (foot-like extrusion) * **Mastigophora/Flagellates** (whip-like structure) * **Ciliophora/Ciliates** (hair-like projections) * **Apicomplexa** - apical complex (structures are involved in the penetration and invasion) * **Microspora** - extrusion apparatus (polar tube) which enables them to insert infective material into the host cell. ### **Nematodes (Roundworm)** * **Intestinal** * *Ascaris lumbricoides* * *Capillaria philippinensis* * *Enterobius vermicularis* * *Hookworm* * *Strongyloides stercoralis* * *Trichuris trichiura* * *Parastrongylus cantonensis* * *Trichinella spiralis* * **Extraintestinal** * *Lymphatic filarial* ### **Cestodes (Tapeworm)** * **Pseudophyllidea** * *Diphyllobothrium latum* * *Spirometra spp* * **Cyclophyllidea** * *Dipylidium caninum* * *Echinococcus spp.* * *Hymenolepis diminuta* * *Hymenolepis nana* * *Raillietina garrisoni* * *Taenia saginata* * *Taenia solium* ### **Trematodes (Flukes)** * **Intestinal** * *Fasciolopsis buski* * *Heterophyes heterophyes* * *Metagonimus yokogawai* * *Echinostoma ilocanum* * **Liver** * *Fasciola gigantica* * *Fasciola hepatica* * *Clonorchis sinensis* * *Opisthorchis felineus* * *Opisthorchis viverrini* * **Lung** * *Paragonimus westermani* * **Blood** * *Schistosoma haematobium* * *Schistosoma japonicum* * *Schistosoma mansoni* ## **Checkpoint Quiz** 1. **Autoinfection is seen in all except:** * a. Hymenolepis nana * b. Enterobius vermicularis * c. Ascaris lumbricoides * d. Taenia solium 2. **Which type of host is defined as the one in which the parasite reaches sexual maturity?** * a. Intermediate host * b. Definitive host * c. Paratenic host * d. Reservoir host 3. **Which parasite can cause hyperinfection?** * a. Enterobius vermicularis * b. Toxoplasma gondii * c. Echinococcus granulosus * d. Strongyloides stercoralis 4. **Which of the following is NOT a characteristic of a definitive host?** * a. It harbors the sexual stage of the parasite. * b. It allows for the parasite's reproduction. * c. It is the first host in the life cycle. * d. It supports the full development of the parasite. 5. **Which parasite is commonly associated with inhalation as a mode of transmission?** * a. Giardia lamblia * b. Enterobius vermicularis * c. Strongyloides stercoralis * d. Toxoplasma gondii 6. **What is a characteristic of the subphylum Mastigophora?** * a. It has flagella for locomotion. * b. It uses pseudopodia for movement. * c. It reproduces exclusively through spore formation. * d. It is always non-motile. 7. **Which of the following parasites is known for causing sexually transmitted infections?** * a. Cryptosporidium hominis * b. Trichomonas vaginalis * c. Toxoplasma gondii * d. Plasmodium falciparum 8. **What is the main characteristic of the class Cestoda?** * a. They are segmented and ribbon-like. * b. They have a cylindrical shape. * c. They are leaf-like and unsegmented. * d. They possess cilia for movement 9. **What kind of organism is Balantidium coli?** * a. Nematode * b. Cestode * c. Ciliate * d. Flagellate 10. **Which of the following parasites is classified under the class Trematoda?** * a. Taenia saginata * b. Schistosoma japonicum * c. Ascaris lumbricoides * d. Enterobius vermicularis ## **Protozoa: Sarcodina** * **Sarcodina (sarcos meaning flesh or body)** - It includes those parasites, which have no **permanent locomotory organs**, but move about with the aid of **temporary prolongations** of the body called **pseudopodia** (e.g. amoebae). * **Forms:** * **Infective stage** - resistant to environmental changes: nonfeeding stage * **Vegetative stage** - feeds, multiplies, and possesses pseudopods * **All have cystic stage except Entamoeba gingivalis** * **Pathogenic** * *Entamoeba histolytica* * *Entamoeba dispar* * *Entamoeba moshkovskii* * *Entamoeba hartmanni* * *Entamoeba coli* * *Entamoeba polecki* * *Endolimax nana* * *lodamoeba bütschlii* * *Entamoeba gingivalis* * *Naegleria fowleri* * *Acanthamoeba spp.* ## **Protozoa: Mastigophora** * **Many of these protozoa require a wet environment for feeding, locomotion, osmoregulation, and reproduction.** * **Reproduction** * **Flagellates and amebae** multiply by **binary fission** * **Sporozoans** reproduce by a process known as **merogony**(also called schizogony). ### **Phlyum: Sarcomastigophora** * **Sarcordina** * **Pathogenic** * *Entamoeba histolytica* * *Entamoeba dispar* * *Entamoeba moshkovskii* * *Entamoeba hartmanni* * *Entamoeba coli* * *Entamoeba polecki* * *Endolimax nana* * *lodamoeba bütschlii* * *Entamoeba gingivalis* * *Naegleria fowleri* * *Acanthamoeba spp.* * **Non-Pathogenic** * *Chilomastix mesnili* * *Dientamoeba fragilis* * *Giardia lamblia* * *Trichomonas hominis* * *Trichomonas tenax* * *Trichomonas vaginalis* * **Mastigophora** * **Atrial flagellates** * **Hemoflaggelates** * *Trypanosoma cruzi* * *Trypanosoma brucei gambiense* * *Trypanosoma brucei rhodesiense* * *Leishmania braziliensis* * *Leishmania donovani* * *Leishmania mexicana* * *Leishmania tropica* ### **Phlyum: Ciliophora** * **Ciliophora** * *Balantidium coli* ### **Phlyum: Apicomplexa** * **Hematozoa** * *Plasmodium vivax* * **Intestinal Coccidians** * *Cytoisospora belli* * *Crytosporidium parvum* * *Cyslospora cayatenensis* * *Toxoplasma gondii* * *Sarcocystis hominis* ### **Phlyum: Microspora** * **Microspora** * *Enterocytozoon bieneusi* * *Encephalitozoon spp.* * *Vittaforma cornea* * *Pleistophora spp.* * *Anncaliia vesicularis* * *Microsporidium spp.* * *Trachipleistophora hominis* ### **Metazoan** * **Includes multicellular organisms such as parasitic worms.** * **Phylum:** * **Nemathelminthes (roundworms):** elongated and cylindrical in shape, with bilateral symmetry * **Platyhelminthes (Flatworms):** * **Class** *(tapeworms)*: segmented, with a ribbon-like appearance * **Class** *(flukes)*: leaf-like and unsegmented ## **Nematodes (Roundworm)** * **Intestinal** * *Ascaris lumbricoides* * *Capillaria philippinensis* * *Enterobius vermicularis* * *Hookworm* * *Strongyloides stercoralis* * *Trichuris trichiura* * *Parastrongylus cantonensis* * *Trichinella spiralis* * **Extraintestinal** * *Lymphatic filarial* ## **Cestodes (Tapeworm)** * **Pseudophyllidea** * *Diphyllobothrium latum* * *Spirometra spp.* * **Cyclophyllidea** * *Dipylidium caninum* * *Echinococcus spp.* * *Hymenolepis diminuta* * *Hymenolepis nana* * *Raillietina garrisoni* * *Taenia saginata* * *Taenia solium* ## **Trematodes (Flukes)** * **Intestinal** * *Fasciolopsis buski* * *Heterophyes heterophyes* * *Metagonimus yokogawai* * *Echinostoma ilocanum* * **Liver** * *Fasciola gigantica* * *Fasciola hepatica* * *Clonorchis sinensis* * *Opisthorchis felineus* * *Opisthorchis viverrini* * **Lung** * *Paragonimus westermani* * **Blood** * *Schistosoma haematobium* * *Schistosoma japonicum* * *Schistosoma mansoni* ## **Protozoa: Ciliophora** * **Ciliates**, parasites that move by means of hairlike cytoplasmic extensions called cilia. * **Balantidum coli** is the largest protozoan parasite affecting humans and is the only ciliate known to cause human disease. Natural host: pigs. * **Morphology** * **Cilia** – hair-like structures that facilitate movement. * **Cytostome** – oral apparatus. * **Cytopyge** – excretes waste. * **Contractile Vacuole** - bean-shaped: regulation of cellular functions and activities; round: reproductive processes. * **Contractile Vacuole** - helps in osmoregulation. ## **Protozoa: Apicomplexa** * **Protozoan parasites characterized by the production of spore like oocysts containing sporozoites were known as Sporozoan** - They live intracellularly, at least during part of their life cycle. Obligate intracellular parasite. * **At some stages in their life cycle, they possess a structure called the apical complex, by means of which they attach to and penetrate host cells** ### **Plasmodium spp. Life Cycle** * **Intermediate host:** Mosquito * **Definitive Host:** Humans * **Infective stage:** Sporozoite * **Diagnostic stage:** * **Ring** * **Trophozoite** * **Schizont** * **Gametocytes** ## **Protozoa: Mastigophora** * **Flagellates** belong to the phylum Protozoa and are members of the subphylum Mastigophora * **Morphology** * **Flagella** – whiplike structures * **All flagellate life cycles** consist of the trophozoite form. Some has no one cyst stage. * **Finlike structure** connected to the outer edge of some flagellates, assists in movement (Trichomonas spp. & Trypanosoma spp.) * **Axostyle** – rodlike support structure ### **Classification of Flagellates** * **Intestinal Flagellates** * *Giardia duodenalis* * *Chilomastix mesnili* * *Dientamoeba fragilis* * *Enteromonas hominis* * *Retortamonas intestinalis* * *Pentatrichomonas hominis* * *Trichomonas tenax* * **Extraintestinal Flagellates** * *Trichomonas vaginalis* * *Trypanosoma cruzi* * *Trypanosoma brucei gambiense* * *Trypanosoma brucei rhodesiense* * *Leishmania braziliensis* * *Leishmania donovani* * *Leishmania mexicana* * *Leishmania tropica* ## **Nematodes (Roundworms)** * **General Characteristics:** * elongated and cylindrical in shape, with bilateral symmetry. * complete digestive tract and a muscular pharynx. * provided with separate sexes, although some may be parthenogenetic (may or may not require male; E.g., Strongyloides stercoralis) * **Male:** small, curved posterior tail, with spicule. * **Female:** large, pointed posterior. * **Types of female worms:** * lay immature/unembryonated eggs * lay embryonated/mature eggs * lay larva not eggs. * **Sensory organs:** * **Amphids:** anterior sensory organs * **Phasmids:** posterior sensory organs * **Aphasmids:** no sensory organs. * **Examples:** * *Trichuris trichiura* * *Trichinella spiralis* * *Capillaria philippinensis* ### **Soil-transmitted helminths:** * *Hookworm* * *Ascaris lumbricoides* * *Trichuris trichiura* * *Strongyloides stercoralis* ### **Unholy three:** * *Hookworm* * *Ascaris lumbricoides* * *Trichuris trichiura* ### **Heart-Lung Migration** * *Ascaris lumbricoides* * *Strongyloides stercoralis* * *Hookworm* ## **Nematodes** * **Intestinal** * *Small Intestine:* * *Capillaria philippinensis* * *Ascaris lumbricoides* * *Strongyloides stercoralis* * *Hookworm* * *Large intestine:* * *Trichuris trichiura* * *Enterobius vermicularis* * *Trichinella spiralis* * *Parastrongylus cantonensis* * **Extraintestinal:** * *Lymphatic filarial* ## **Modes of Transmission** * **Ingestion of embryonated ova** * *Ascaris lumbricoides* * *Trichuris trichiura* * *Enterobius vermicularis* * **Ingestion of food** * *Fish: Capillaria philippinensis* * *Pork: Trichinella spiralis* * *Snail: Parastrongylus cantonensis* * **Skin penetration** * *Hookworm* * *Strongyloides stercoralis* * **Bite of vectors** * *Lymphatic filaria* ## **Cestodes (Tapeworm)** * **General Characteristics:** * **Dorso-ventrally flattened with bilateral symmetry.** * **Cestodes are segmented,** with a ribbon-like appearance. * **Do not have a digestive tract & circulatory system.** * **Adult tapeworms are hermaphroditic.** * **Location:** * **Adults found in the intestines of the definitive host.** * **Larval stage is encysted in the tissues of the intermediate host.** ### **Morphology:** * **Scolex** - an anterior structure which is the main organ of attachment of the worm to the definitive host. * *Rostellum* - protrusible structure (armed or unarmed) * *Acetabula* - suckers * *Neck* - considered the region of growth, because segmentation or strobilization originates from it. * **Strobila** - chains of segments * **Immature segments** - nearest to the neck. * **Mature segments** * **Gravid segments** - most distal, filled with eggs; can be detached (apolysis). ## **Trematodes (Flukes)** * **General characteristics:** * **Bilaterally symmetrical,** flat leaf-like and unsegmented. * **Well-developed reproductive organ**. * **Have incomplete digestive tract & do not have a circulatory system**. * **They are all hermaphroditic (except Schistosoma spp.)** * **Mode of transmission:** Ingestion of raw/uncooked 2nd intermediate host. (except Schistosoma spp.) ### **Morphology:** * **Adult trematodes are equipped with an oral sucker, and a ventral sucker called an acetabulum or gonotyl** * A third sucker called a genital sucker or gonotyl is observed only among the heterophyids. * **General Life Cycle** * **Ova** * **Miracidium** (1st intermediate host) * **Sporocyst** * **Redia** * **Cercaria** (2nd intermediate host) * **Metacercaria** * **Definitive host** * **Adult** * **All trematodes have operculated eggs (except Schistosoma spp). They can be embryonated or unembryonated** ### **Ova** * **Mature/Embryonated Ova** * *Schistosoma spp.* * *Heterophyes* * *Opisthorchis spp.* * *Clonorchis sinensis* * *Echinostoma ilocanum* * *Fasciola spp.* * *Fasciolopsis buski* * **Immature/ Unembryonated Ova** * *Schistosoma mansoni* * *Schistosoma haematobium* * **All trematodes require two intermediate hosts in their life cycle. (except Schistosoma spp.)** * *First intermediate host is always a snail.* * *Second intermediate host may be a fish, crustacean, another snail, or fresh water plants.* ## **Checkpoint Quiz** 1. **The cestode morphologic form characterized by a segmented appearance that houses male and female reproductive structures is referred to as a(an):** * a. Scolex * b. Proglottid * c. Egg * d. Cyst 2. **Characteristics of the cestodes include all the following except:** * a. They are hermaphroditic. * b. They generally require intermediate host(s). * c. Their laboratory diagnosis consists of finding larvae in feces. * d. Their anatomic regions include the scolex, neck, and strobila. 3. **Which of the following are key distinguishing factors in differentiating an infection between T. saginata and T. solium?** * a. Egg morphology and number of uterine branches in proglottid * b. Presence of hooklets on scolex and egg morphology * c. Presence of hooklets and number of uterine branches in proglottid * d. Egg morphology and presence of suckers on scolex 4. **Which of the following is characteristic of an H. diminuta egg?** * a. Spherical, with radial striations * b. Ellipsoid, with terminal polar plugs * c. Oval, with thin shell and polar filaments * d. Oval, with polar thickenings and no filaments 5. **A primary differential feature between an H. nana egg and H. diminuta egg is which of the following?** * a. A flattened side for H. diminuta egg * b. A thick shell for H. nana egg * c. Polar filaments in H. nana egg * d. Radial striations in H. diminuta egg 6. **A unique characteristic of Dipylidium caninum is which of the following?** * a. Lack of suckers on the scolex * b. Formation of egg packets * c. Proglottid resemblance to Taenia solium * d. Alternation of female and male proglottids 7. **The egg of D. latum is unique among the cestodes in that it contains which of the following?** * a. An operculum and terminal knob * b. Radial striations and oncosphere * c. An operculum and lateral spine * d. A ciliated rhabditiform larva 8. **The primary pathology associated with a D. latum infection is which of the following?** * a. Eosinophilic pneumonitis * b. Vitamin D deficiency * c. Vitamin B12 deficiency * d. Fat malabsorption 9. **In order, what is the developmental stage of pseudophyllidean?** * a. Procercoid-Plerocercoid-Coracidium * b. Coracidium-Procercoid-Plerocercoid * c. Coracidium-Plerocercoid-Procercoid * d. Plerocercoid-Procercoid-Coracidium 10. **All of the following contain hooklets in their rostellum, except:** * a. D. caninum * b. E. granulosus * c. H. diminuta * d. T. solium ## **Metazoa: Trematodes (Flukes)** * **General characteristics:** * **Bilaterally symmetrical,** flat leaf-like and unsegmented. * **Well-developed reproductive organ.** * **Have incomplete digestive tract & do not have a circulatory system.** * **They are all hermaphroditic (except Schistosoma spp.)** * **Mode of transmission:** Ingestion of raw/uncooked 2nd intermediate host. (except Schistosoma spp.) ### **Morphology:** * **Adult trematodes are equipped with an oral sucker, and a ventral sucker called an acetabulum or gonotyl.** * **A third sucker called a genital sucker or gonotyl** is observed only among the heterophyids. * **General Life Cycle** * **Ova** * **Miracidium** (1st intermediate host) * **Sporocyst** * **Redia** * **Cercaria** (2nd intermediate host) * **Metacercaria** * **Definitive host** * **Adult** * **All trematodes have operculated eggs (except Schistosoma spp). They can be embryonated or unembryonated.** ### **Ova** * **Mature/Embryonated Ova** * *Schistosoma spp.* * *Heterophyes* * *Opisthorchis spp.* * *Clonorchis sinensis* * *Echinostoma ilocanum* * *Fasciola spp* * *Fasciolopsis buski* * **Immature/Unembryonated Ova** * *Schistosoma mansoni* * *Schistosoma haematobium* * **All trematodes require two intermediate hosts in their life cycle. (except Schistosoma spp.)** * *First intermediate host is always a snail.* * *Second intermediate host may be a fish, crustacean, another snail, or fresh water plants.* # **Miscellaneous Cestodes** * **Echinococcus multilocularis** * Causes alveolar hydatid disease (fatal form) * Most lethal of all helminthic diseases * Affects the liver as a slow-growing, destructive tumor, often with abdominal pain and biliary obstruction * Untreated infections have a high fatality rate. * **Taenia asciatica** * Limited to Asia and is seen mostly in the Republic of Korea, China, Taiwan, Indonesia, and Thailand. * **Taenia multiceps** * Causes coenurosis (infection with larval stage) in humans * Commonly affects the brain, eyes, and subcutaneous tissues * Present as nodules in various areas, hence, should be distinguished from other tissue cestodes. * **Raillietina garrisoni** * Intermediate host: Ants or beettles * Armed rostellum 2 alternating circular rows 90-140 hammer-shaped hooks * Most cases are asymptomatic * Motile proglottids in the stool typically prompts clinical attention. * **Spirometra spp.** * **Mode of transmission:** * Drinking water contaminated with infected copepods (sparganosis) * Consuming the flesh of an undercooked second intermediate or paratenic host * Migrating spargana cause various symptoms. * Human serves as paratenic host. ## **Checkpoint Quiz** 1. **The cestode morphologic form characterized by a segmented appearance that houses male and female reproductive structures is referred to as a(an):** * a. Scolex * b. Proglottid * c. Egg * d. Cyst 2. **Characteristics of the cestodes include all the following except:** * a. They are hermaphroditic. * b. They generally require intermediate host(s). * c. Their laboratory diagnosis consists of finding larvae in feces. * d. Their anatomic regions include the scolex, neck, and strobila. 3. **Which of the following are key distinguishing factors in differentiating an infection between T. saginata and T. solium?** * a. Egg morphology and number of uterine branches in proglottid * b. Presence of hooklets on scolex and egg morphology * c. Presence of hooklets and number of uterine branches in proglottid * d. Egg morphology and presence of suckers on scolex 4. **Which of the following is characteristic of an H. diminuta egg?** * a. Spherical, with radial striations * b. Ellipsoid, with terminal polar plugs * c. Oval, with thin shell and polar filaments * d. Oval, with polar thickenings and no filaments 5. **A primary differential feature between an H. nana egg and H. diminuta egg is which of the following?** * a. A flattened side for H. diminuta egg * b. A thick shell for H. nana egg * c. Polar filaments in H. nana egg * d. Radial striations in H. diminuta egg 6. **A unique characteristic of Dipylidium caninum is which of the following?** * a. Lack of suckers on the scolex * b. Formation of egg packets * c. Proglottid resemblance to Taenia solium * d. Alternation of female and male proglottids 7. **The egg of D. latum is unique among the cestodes in that it contains which of the following?** * a. An operculum and terminal knob * b. Radial striations and oncosphere * c. An operculum and lateral spine * d. A ciliated rhabditiform larva 8. **The primary pathology associated with a D. latum infection is which of the following?** * a. Eosinophilic pneumonitis * b. Vitamin D deficiency * c. Vitamin B12 deficiency * d. Fat malabsorption 9. **In order, what is the developmental stage of pseudophyllidean?** * a. Procercoid-Plerocercoid-Coracidium * b. Coracidium-Procercoid-Plerocercoid * c. Coracidium-Plerocercoid-Procercoid * d. Plerocercoid-Procercoid-Coracidium 10. **All of the following contain hooklets in their rostellum, except:** * a. D. caninum * b. E. granulosus * c. H. diminuta * d. T. solium ## **Metazoa: Trematodes (Flukes)** * **General characteristics:** * **Bilaterally symmetrical,** flat leaf-like and unsegmented. * **Well-developed reproductive organ.** * **Have incomplete digestive tract & do not have a circulatory system.** * **They are all hermaphroditic (except Schistosoma spp.)** * **Mode of transmission:** Ingestion of raw/uncooked 2nd intermediate host. (except Schistosoma spp.) ### **Morphology:** * **Adult trematodes are equipped with an oral sucker, and a ventral sucker called an ace