Faculty of Allied Medical Sciences Parasitology (MLPR-201) fall 2013/2014

Dr. Hamdy Badie M. El-Wakil Prof. of Parasitology & Public Health. Faculty of Allied Medical Sciences. Pharos University In Alexandria,Egypt

General characters,  By the end of this lecture students should understand helminthes types and General characters, classifications, mode of transmission to humans, life cycles, pathogenicity, clinical importance and clinical features.

Medical helminthology is the study of parasitic worms (helminthes) which parasitize man. These worms belong to two phyla: 1- Platyhelminthes (Flat-worms). 2- Nemathelminthes (round – worms ). Medical Helminthology

- The helminthes are worms, some of which are parasitic to humans. They are multi-cellular, bilaterally, symmetrical elongated, flat or rounded animals. These parasite, belong to one of three groups: Trematodes (Flukes), cestodes (tape worms) or nematodes (roundworms). It is estimates that at least 70% of the world’s population is infected with a parasitic helminth. The mode of transmission to humans varies from species to species, and includes ingestion of larvae in raw or under cooked pork, beef, or fish and ingestion of helminth eggs in faeces, by insect bites, or by direct skin penetration. Helminthic diseases are endemic in regions of the world where community sanitary conditions are poor, and human faeces is usued as fertilizer.

 The mode of transmission to humans varies from species to species, and includes ingestion of larvae in raw or under cooked pork, beef, or fish and ingestion of helminth eggs in faeces, by insect bites, or by direct skin penetration. Helminthic diseases are endemic in regions of the world where community sanitary conditions are poor, and human faeces is usued as fertilizer.

1- Phylum : Platyhelminthes General characters: 1- Bilaterally symmetrical and triploblastic (i.e. the body is built up of three embryonic, ectoderm mesoderm and endoderm). 2- Flatenned dorse ventrally. 3- Without body cavity (i.e. absence of coelomic or haemocoelic cavities). 4- Alimentary canal incomplete or lacking, and anus absent. 5- Excretory system is provided with flame cells. 6- usually hermaphrodite.

(a) Class: Trematoda (Flukes) General characters: 1- Body unsegmented, oval or leaf shaped. 2- They possess two suckers, one oral anterior in position and surrounding the mouth and the other the ventral lying on the ventral surface. 3- Body covered by thick cuticle which may be spiniferous or tuberculated. 4- The intestine is simple and branching into 2 intestinal caeca which may unite.

Trematodes infest various organs of the human host (for example, intestinal veins, urinary bladder, liver, or lung). All parasitic trematodes use fresh water snails as an intermediate host. Trematodes infest various organs of the human host (for example, intestinal veins, urinary bladder, liver, or lung). All parasitic trematodes use fresh water snails as an intermediate host.

Class : Trematoda (Flukes) Cestoidea (Tape worms) Family :  Fasciolidae - Fasciola spp. (Fasciolopsis)  Diphyllobotriidae - Diphyllobothrium latum (Broad fish tape worm) (Diphyllobothriasis)  Heterophyidae - Heterophyes heterophyes (Hetrophyiasis)  Troglotrematiolae - Paragoninus westermani (Lung fluke) (Paragohimiasis)  Taeniidae - Taenia spp. (Taeniasis) - Echinococcus granulosus (Dog tape worm) (Echinococcosis)(Hydatidosis) Opisthorchidae - Clonorchis sinensis (Chinese or Oriantal liver fluke) (Clonorchiasis)  Hymeaolepidiidae Hymenolepis spp.  Schistosomatidae - Schistosoma spp. (Blood fluke) (Schistosomiasis)  Dilepidiidae - Dipylidium spp. (Doge tape worm) Phylum : Platyhelminthes : (Flat – worms)

Developmental events in the life cycle of a typical fluke being when the adult fluke, which is hermaphroditic, produces eggs in the human (the definitive host). The eggs are then excreted into the environment. Inside of eggs the first larval stage (the miracidium) develops. These larvae seek out and infect suitable snail species, which are the first intermediate host. In the snail, asexual reproduction occurs, during which several intermediate developmental forms can be distinguished, including Sporocyst, Redia (an early larval stage) and eventually large numbers of the final larval stage called Cercaria, which leave the snail and seek out a second intermediate host (a fish or crustacean, depending on the species of fluks). In this second intermediate host the cercaria form cysts called metacercaria that can remain viable indefinitely. Finally, if the infected raw or undercooked fish or crustacean is eaten by a human, the metacercaria excysts, and the fluke invades tissues such as the lung or the liver and beings producing eggs, thus completing the life cycle.

The life cycle of schistosomes is similar to that of the hermaphroditic flukes. One difference is that schistosomes have only one intermediate host, the snail. Another difference is that schistosomiasis is not acquired by ingestion of contaminated food, but rather from schistosome cercaria directly penetrating the skin of swimmers in contaminated rivers and lakes. After dissemination and development in the human host, the adult schistosomes take up residence in various abdominal veins, depending on the species, they are therefore called “blood flukes”. Also, incontrast to the “typical” hermaphroditic flukes described above, the schistosomes have separate, distinctive sexes. A remarkable anatomical features on the ventral surface of the large male is the long groove or schist in which the smaller female resides and continuously mates with the male. This mating takes place in the human liver. Fertilized eggs penetrate the human host’s vascular walls, and enter the intestine or bladder, emerging from the body in faeces or urine. In fresh water, the organisms infect snails in which they multibly, producing cercaria (the final, free-swimming larval stage), which are released into the fresh water to complete the cycle.

Trematode (Flat) worms Schistosoma species (Blood flukes) Life cycle for all species

Human eats watercress with encysted metacercariae Fasciola hepatica (Sheep Liver fluke)

Heterophyes heterophyes Morphology

What are the general characters of Platyhelminthes and Trematoda ? Schistosoma species (Blood flukes) Draw the life cycle of: Schistosoma species (Blood flukes) Fasciola hepatica And Fasciola hepatica

 Group of students will be selected for an assignment topic,one of the parasites that are studied in your course.  The following points should be covered in your assignment sheets: ( 1) Classification Position: (2) Name of the parasite; (3)Description ( Morphological Characters in vivo): (4) Definitive (Final) Host: (5) Intermediate Host: (6) Mode Of Infection: (7) Infective Stage:-. (8) Habitat:- (9) Diagnostic Stage:- (10) Disease:- (11) life cycle

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