Eukaryotic Pathogens: Helminthes
What 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 crab
Definitive host: human
Fluke (Trematode) Flatworm
Humans as Definitive Host: Lung Fluke (A Trematode)
Intermediate hosts: snail,
then crayfish or crab
Definitive host: human
Lung fluke: Paragonimus westermanii
Figure 12.26
Shistosomiasis or Blood Fluke
(Shistosoma)
Blood fluke
Flatworm (Platyhelminthes)
Intermediate host: snail
Definitive host: human
Beef/Pork Tapeworms (Cestode in Platyhelminthes)
Intermediate host: pig or cow
Definitive host: human
Figure 12.27
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
Nematodes: Eggs Infective for Humans
Figure 12.29
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
Making a Table to Study and Associate Characteristics
Species
Helminth
Group and
Subgroup
Disease
Name
Disease
description
Hosts
Reproduction
Sketch
Arthropods as Vectors
• 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)
Figure 12.31, 32
Arthropods as Vectors
Figure 12.33