HELMINTHOLOGY INTRODUCTION Medical Parasitology includes the study of

HELMINTHOLOGY INTRODUCTION

Medical Parasitology includes the study of 3 major groups of parasites: Helminths Protozoa Simply called Worms called One-celled organisms Medical Helminthology Medical Protozoology Arthropods I like to present my self as insects and my allies Medical Arthropodology Medical Parasitology

Helminths (Worms) Platyhelminths (Flat worms) Trematodes (Flukes) Cestodes (Tape worms) Nematodes (Round worms)

Helminths of medical importance Trematodes Liver & Lung Fasciola hepatica Paragonimus westermani Intestinal Fasciolopsis buski Heterophyes heterophyes Blood Schistosoma haematobium Schistosoma mansoni Schistosoma japonicum Nematodes Cestodes Intestinal Diphyllobothrium latum Taenia saginata Taenia solium Hymenolepis nana Hymenolepis diminuta Dipilidium caninum Ascaris lumbricoides Enterobius vermicularis Hookworms Trichuris trichiura Extra-intestinal - Taenia solium (Cysticercosis Cellulosae) - Echinococcus spp. (Hydatidosis) - Sparganosis (? ) Blood Filarial worms

General characteristics of Platyhelminths q Dorso-ventrally flattened worms with bilateral symmetry. q No body cavity. q If present, the alimentary canal is blind ending (caecum). q Mostly hermaphrodites. q Generally complex life cycles with intermediate host(s). q Includes two classes: Trematoda (flukes) and Cestoda (tape-worms)

1 TREMATODES

General characteristics of Trematodes o Flat, unsegmented and covered with a cuticle. o Leaf-like (except Schistosoma females). o Ranging from few millimeters to several cm. o Having generally 2 muscular suckers (organs of fixation) o Alimentary canal: intestinal caeca (blind, without anus) o Excretion by flame cells and collecting tubules o Hermaphrodites (except Schistosoma).

Trematodes’ general life cycle Life cycle stages: • Egg: usually diagnostic stage. • Miracidium: hatches from egg. • Cercaria: infective in Schistosoma. • Metacercaria: infective stage in other species. • Adult worms: in DH and RH. Trematodes’ life cycles involve: § Snail: intermediate host (IH) in which asexual generations occur. § Some, involve a 2 nd IH.

Trematodes’ life cycle stages ADULT • Adults lay eggs that pass out of the body in the feces, urine, or sputum. Eggs need water & snails to continue their cycle. • Eggs hatch giving miracidia that find their way to the snail. • Miracidia sporocysts rediae daughter rediae cercariae • Cercariae leave the snail to water and (i) enter the body of the final host or (ii) develop into encysted metacercariae on water plants or inside an intermediate host.

Geographical distribution World distribution of parasitic flukes is limited by the presence of their snail intermediate hosts. Larvae from snails infect a human by penetrating the skin (schistosomes) or by being eaten as encysted larvae (other trematodes) the intensity of human infection is related to the rate of exposure to infective larvae (by contact with contaminated water & consumption of contaminated food).

Side-by-side adult trematodes comparison Schistosoma

Side-by-side trematodes’ eggs comparison

Platyhelminths Helminths (Worms) Platyhelminths (Flat worms) 1 Trematodes covered (Flukes) 2 Cestodes (Tape worms) Nematodes next (Round worms)

Cestodes of of medical importance Helminths medical importance Trematodes Liver & Lung Fasciola hepatica Paragonimus westermani Intestina l Fasciolopsis buski Heterophyes heterophyes Blood Schistosoma haematobium Schistosoma mansoni Schistosoma japonicum Cestodes Intestinal Nematodes Intestinal Diphyllobothrium latum Taenia saginata Taenia solium Hymenolepis nana Hymenolepis diminuta Ascaris lumbricoides Enterobius vermicularis Hookworms Trichuris trichiura Extraintestinal - Taenia solium (Cysticercosis Cellulosae) - Echinococcus spp. (Hydatidosis) Blood Filarial worms

General characteristics of Cestodes q Flattened dorso-ventrally. Ribbon like and range in length from few mm to several meters (depending on the species). q Have no body cavity or alimentary canal (absorb nutrients through the tegument). q q All Cestodes are parasitic (small intestine) Have a complex (indirect) life cycle requiring one or more intermediate (I. M) hosts. q q Are hermaphrodites.

General morphology of cestodes Cestodes’ bodies are composed of: a scolex, a neck and a strobila (segmented into immature, mature & gravid proglottids). 1. Scolex: with organs of attachment 2. Neck (underneath scolex): form the germinative portion. 3. Immature segments: undeveloped reproductive organs. 4. Mature segments: mature male & female reproductive organs. 5. Gravid segments: eggs are stored in the uterus. Eggs

Classification of medically important cestodes Order/ Pseudophyllidea Order/ Cyclophyllidea • Diphyllobothrium latum • Taenia saginata • Taenia solium • Hymenolepis nana • Hymenolepis diminuta • Echinococcus spp.

Habitat of medically important cestodes Intestinal • Diphyllobothrium latum • Taenia saginata • Taenia solium • Hymenolepis nana • Hymenolepis diminuta • Dipilidium caninum Extra-intestinal • Taenia solium (Cysticercosis Cellulosae) • Echinococcus spp. (Hydatidosis)

Man and Cestodes Man may be infected with adult tapeworms being the definitive host, Or may be infected with their larval stages being the intermediate host.

Intestinal Cestodes’ Infections

Intestinal cestodes’ general life cycle involves: • A DH & one or more IH, except for the one-host cycle of H. nana. • Once passed in stool of DH and RH, the Eggs and gravid segments of: (i) D. latum, embryonate in water liberating coracidia that if ingested by cyclops become procercoid larvae. These, when ingested by a fish become plerocercoid infective larvae. (ii) Taenia spp. , if ingested by cattle or pigs, liberate Oncospheres that invade intestinal wall & develop into Cysticerci in striated muscle. These infect persons eating non or undercooked meat. While cysticercosis occurs by ingesting T. solium eggs. (iii) Hymenolepis spp. , if ingested by insects develop into Cysticercoid larvae that infect humans when accidentally ingested. H. nana eggs may hatch in Man’s intestine causing autoinfection

Epidemiology D. latum (fish tapeworm) Diphyllobothriasis is common in temperate & subarctic regions, where freshwater fish are eaten raw or under-cooked, as in Scandinavia, Russia, the Great Lakes, Japan, central Europe, Chile, etc. . q T. saginata (beef tapeworm) taeniasis saginata; is cosmopolitan (worldwide). q T. solium (pork tapeworm) taeniasis solium and cysticercosis; are cosmopolitan where pork is eaten. q H. nana (dwarf tapeworm) nana hymenolepiasis; the most common of all Man cestode infections. Occurs worldwide, but more commonly in warm climates and among children. Autoinfection may also occur if eggs hatch in the intestine. q H. dimnuta (rat tapeworm) diminuta hymenolepiasis; infects rats allover the world and rarely infects Man. q

Extra-intestinal Cestodes’ Infections

Extra-intestinal cestodes’ infections Cysticercosis: is the infection of human tissues (brain, heart, eye, lung, subcutaneous tissues etc. ) by Cysticercus cellulosae, the larval stage of T. solium. Man infection occurs by ingestion of T. solium eggs in contaminated food or drink, & by autoinfection. q Hydatidosis: infection of human tissues by Echinococcus tapeworms larval stage. Dogs & wild canids are DH harboring adults in small intestine. Cattle, sheep, pigs …, & humans are IH harboring larvae in different organs (liver, lung, heart, brain …). q E. granulosus (dog tapeworm): causes in man the cystic or unilocular form (more frequent). Ø E. multilocularis: causes in man the alveolar or multilocular form (less frequent). Ø