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Eukaryotic Pathogens: HelminthesWhat types of eukaryotic organisms are pathogenic, and how do they differ from bacteria?
Helminthes (The Worms)
• Specializations of Animal Parasites
• Flatworms (Platyhelminthes)
• Flukes and tapeworms
• Roundworms (Aschelminthes/Nemtodes)
• Egg infective: pinworm, ascaris
• Larvae infective: hookworm, trichinella
Eukaryotic pathogens are mostly parasitic and are difficult to target selectively with drugs since their cells are so similar to human cells.
The Helminths
Table 12.1
Pathogenic Helminths (Worms)
• Pathogenic helminthes belong to:
• Flatworms (Phylum Platyhelminthes)• Roundworms (Phylum Nematoda/Aschelminthes)
Pathogenic Helminths (Worms)
• Pathogenic helminthes belong to:
• Flatworms (Phylum Platyhelminthes)• Roundworms (Phylum Nematoda/Aschelminthes)
•As parasites, they have:•Little or no digestive system•A very simple nervous system•Little or no means of locomotion•A complex reproductive system, sometimes with multiple
hosts (definitive and intermediate)
Pathogenic Helminths (Worms)
• Pathogenic helminthes belong to:
• Flatworms (Phylum Platyhelminthes)• Paragonimus westermanii - paragonimiasis (lung fluke)• Shistosoma - shistosomiasis (blood fluke)• Taenia sp. - beef/pork tapeworm
• Roundworms (Phylum Nematoda/Aschelminthes)• Enterobium vermicularis -pinworm/threadworm infection• Ascaris- ascariasis• Necator americanus - hookworm infection
Flatworm Characteristics
General Characteristics• Flattened shape• Incomplete gut• Same individual makes both sperm and eggs (monoecious)
Divided into two groups:
Flukes (Trematoda)• Suckers on ventral surface
Tapeworms (Cestodes)• Barbed scolex “head”• Proglottid segments
Lung fluke(Paragonimus westermanii)
Intermediate hosts: snail, then crayfish or crabDefinitive host: human
Fluke (Trematode) Flatworm
Humans as Definitive Host: Lung Fluke (A Trematode)
Figure 12.26Lung fluke: Paragonimus westermanii
Intermediate hosts: snail, then crayfish or crabDefinitive host: human
Shistosomiasis or Blood Fluke(Shistosoma)
Blood flukeFlatworm (Platyhelminthes)
Intermediate host: snailDefinitive host: human
Beef/Pork Tapeworms (Cestode in Platyhelminthes)
Figure 12.27
Intermediate host: pig or cowDefinitive host: human
Humans as Intermediate Host: Tapeworm
Figure 12.28
Pathogenic Helminths (Worms)
• Pathogenic helminthes belong to:
• Flatworms (Phylum Platyhelminthes)• Paragonimus westermanii - paragonimiasis (lung fluke)• Shistosoma - shistosomiasis (blood fluke)• Taenia sp. - beef/pork tapeworm
• Roundworms (Phylum Nematoda/Aschelminthes)• Enterobium vermicularis -pinworm/threadworm infection• Ascaris- ascariasis• Necator americanus - hookworm infection
Roundworm Characteristics
General characteristics• Cylindrical shape• Tapered ends• Complete gut• Different individuals for difft genders (dioecious)
Divided into two groups:
Egg infective roundworms
Larva infective roundworms
Aschelminthes (Nematodes): Roundworms
Figure 12.29
Nematodes: Eggs Infective for Humans
Pinworm/Threadworm(Enterobius vermicularis)
Egg infective roundworm
Ascaris worm(Ascaris sp.)
egg infective roundworm
Hookworm(Necator americanus)
larva infective roundworm
Trichinosis(Trichinella spiralis)
larva infective roundworm
Nematodes: Larvae Infective for Humans
Figure 25.26
Species Helminth Group and Subgroup
Disease Name
Disease description Reproduction
Hosts Sketch
Making a Table to Study and Associate Characteristics
• Kingdom: Animalia
• Phylum: Arthropoda (exoskeleton, jointed legs)
• Class: Insecta (6 legs)
• Lice, fleas, mosquitoes
• Class: Arachnida (8 legs)
• Mites and ticks
• May transmit diseases (vectors)
Arthropods as Vectors
Figure 12.31, 32
Arthropods as Vectors
Figure 12.33