Sporozoa life cycle - Plasmodium 1.Oocyst forms in mosquito gut, mitosis forms sporozoites 2.Mosquito injects sporozoites, migrates into hepatocyte 3.Schizogeny (mitosis) of sporozoite results in merozoites, hepatocyte ruptures 4.Merozoites infect RBCs: a) mitosis = more merozoites to infect more RBCs (malaria) b) meiosis = gametes injested by mosquitos 5. Gametes fuse to form zygote in mosquito gut. 6. Zygote encysts in mosquito gut to form oocyst Big differences: weird, complex separate vector/host: man & skiter >1 host cell type infected: hepatocyte & RBC troph (sporozoite) is NOT the primary pathogenic form asexual stage is infective/pathogenic stage ↓

Plasmodium life cycle – see fig 20-2, pg

About helminths *Macroscopic? multicellular parasitic worms - animals *Size: 2-3mm larvae to 10meter adults (Taenia) *Classification: 3 groups in 2 phyla of the animal Kingdom (Trematodes, Cestodes, Nematodes) grouped by morphology of adult worm, larvae and egg stages. Trematodes and Cestodes are classes in the phylum Platyhelminthes (flatworms). Nematodes are their own phylum (roundworms vs annelids). *Life cycle stages: adult worm, larvae & egg - complicated by the fact that multiple larval stages can exist. Depending on the helminth, any of the 3 stages can result in pathological changes in humans – next slide *Nutrition: aerobic heterotrophic respiration ↓

Pathogenic helminth life cycle stages Helminth egg larvae adult 1. Trematode Cestode Nematode - ++

Helminth taxonomy *Helminths are separated & classified according to general morphological characteristics and the host organ they inhabit, e.g. lung flukes, intestinal tapeworms, & extra-intestinal roundworms. They are all very prolific egg-laying machines! *Phylum Trematode: flukes are flat leaf-shaped worms with oral suckers (an actual mouth, but a body cavity is lacking), and ventral suckers (acetabulum) used as anchors to help maintain their position. Reproduction is hermaphroditic except blood flukes (Schistosomes) which have 2 sexes (dioecious). The life-cycle includes a snail intermediate host in which asexual reproduction occurs. Sexual reproduction occurs in the human definitive host. Clinically significant flukes include: blood flukes (Schistosoma), liver flukes (Clonorchis, Fasciola), intestinal flukes (Fasciolopsis) and lung fluke (Paragonimus). Images 

Adult liver flukes Clonorchis: Chinese liver fluke Fasciola: sheep liver fluke

Helminth taxomony continued Phylum Cestode: tapeworms are flat, elongated, segmented (redundant), strictly hermaphroditic flatworms that inhabit the intestinal lumen. Each segment is called a “proglottid.” All proglottids combined is the “strobila.” The head or “scolex” is fitted with suckers in 1 of 2 arrangements, and maybe also hooks to attach to the lumen wall. Larval forms inhabit extra-intestinal tissues while adults are lumen dwellers. Absence of an alimentary canal (scolex is NOT a mouth) = nutrients must be absorbed through the tegument. Clinically significant intestinal genera include: Taenia, Diphyllobothrium, Hymenolepis, Echinococcus and Dipylidium. Images 

 scolex  Sections = “proglottids” Tapeworm images

Helminth taxonomy continued Phylum nematode: roundworms are cylindrical, non- segmented worms (vs Cestodes & Annelids). They inhabit intestinal and extra-intestinal sites. More advanced having 1) a complete digestive system, and 2) reproductively “dioecious” meaning that male & female organs are in separate individuals (males & females), results in true sexual reproduction. Many nematodes are soil dwellers, some being plant parasites or parasites of other insects, including other nematodes! Clinically significant genera include Ascaris (night crawler!!!), Trichinella, Trichuris (whipworm), Necator & Ancyclostoma (hookworms), Strongyloides, Enterobius (pinworm), Dranunculis, Capillaria and Trichostrongylus. Whipworm & pinworm are exclusively intestinal. The other genera have both intestinal and tissue phases. Images 

Ascaris lumbricoides Trichuris trichiura (whipworm) Nematode images

Necator Enterobius – eek!

On-line image quiz at: Read the intro. to parasitology at: Other good sites:  !!!  !!! …and there are lots more out there…