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