Helminths (Parasitic Worms)


   Kingdom: Animalia

Phylum: Platyhelminthes (flatworms)

Dorsoventrally flattened; incomplete/no digestive tract

   Class: Trematodes (flukes)

Leaf-shaped body, oral and ventral suckers

Named for tissue they live in (definitive host)

   Class: Cestodes (tapeworms)

Long and thin, with scolex and proglottid sections

Intestinal parasites, but can invade tissues

Phylum: Nematoda (roundworms)

Cylindrical shape; complete digestive tract

Infective egg or infective larvae


Characteristics of Helminths

   Reduced digestive system

   Reduced nervous system

   Reduced locomotion

   Complex reproduction


Life Cycle of Helminths

   Monoecious (hermaphroditic)

Male and female reproductive systems in one animal


Separate male and female

   Egg → larva(e) → adult


Important Helminth Diseases

   Fluke – Lung Fluke

   Tapeworm – Taenia saginata, Echinococcus

   Nematode – Pinworm, Trichinellosis*

*    CDC pathogen


Arthropods as Vectors

   May transmit diseases (vectors)

   Kingdom: Animalia

Phylum: Arthropoda (exoskeleton, jointed legs)

   Class: Insecta (6 legs)

Lice, fleas, mosquitoes

   Class: Arachnida (8 legs)

Mites and ticks


Arthropods Vector Types

   Mechanical transmission

   Biological transmission

Microbe multiplies in vector

   Definitive host

Microbe’s sexual reproduction in vector


Important Arthropod-Vectored Diseases

   Flea – Plague

   Mosquito – Dengue, Malaria, Yellow Fever

   Tick – Ehrlichiosis, Lyme Disease, Rickettsiosis, Tularemia