HELMINTHS

Helminth Helminths Helminthology: Study of parasitic worms and their effect on their hosts

A division of parasites living inside their host. Parasitic, worm-like organisms that live & feed off living hosts, receiving nutrition & protection Disrupt hosts' nutrient absorption, causing weakness & disease Those inside the digestive tract: intestinal parasites They can live inside humans as well as other animals.

The Flatworms (Platyhelminthes) Includes 2 phyla: The Flatworms (Platyhelminthes) Cestodes (or Tapeworms), Trematodes (or Flukes). The Roundworms (Nemathelminthes)

1. FLATWORMS Adult worms have flattened bodies Have a HEAD Bilaterally symmetrical bodies Specialized organ systems (nervous, excretory & reproductive) Have a digestive tract with a single opening through which food enters and waste leaves. Some absorb nutrients via their outer covering.

1a. TAPEWORMS In the intestines of animals incl. humans Can grow upto 30 feet Flat, segmented body has of 3 parts: A scolex with hooks / suckers to attach the worm to intestinal lining, Necklike germinal center where new segments are formed, Segments (Proglottids) - Egg-making machines

Hermaphrodite: Each segment has both male & female reproductive organs Fertilization occurs within the segment. The larger & older segments are packed with fertilized eggs Finally, shed in the feces. Life cycle: Larval Form: Develop in muscle, brain, eye, liver, or heart tissue. They displace surrounding tissue, causing serious damage. Adult Form

The SCOLEX or head, of Taenia solium

Taenia saginata – Beef tapeworm Humans parasitized by the adult form Cattle carry Taenia saginata larvae Encysted in their muscle as Cysticerci. Humans get this by eating undercooked infected meat Larvae hatch in human intestine Develop into tapeworm in their intestines. Proglottids containing eggs, excreted in their feces. If this is on a grazing land, cattle might get infected, eggs hatch in cow’s intestine, larvae penetrate the intestinal wall and encyst in cow muscle

Echinococcus granulosus Grazing animals & humans carry larval form. Dogs carry adult form – relatively harmless Larvae damage muscles of liver & lungs.

1b. TREMATODES / FLUKES Flattened bodies, but NOT segmented. Small, but deadly. Size: From a few mm to a few cm Have a ventral SUCKER to attach firmly to the host. Larval & Adult forms Humans carry adult forms in lung, liver & blood vessels Aquatic animals & plants carry larvae: Intermediate hosts Snails / Clams Fish / Aquatic plant.

Paragonimus westermani - Lung fluke Adult fluke develops in human lung. Fever and cough producing blood-tinged sputum. Hermaphrodite – Produces eggs Hatch in water bodies & release free-swimming larvae: MIRACIDIA Penetrates snail and multiplies: REDIA Develops into a free-swimming form: CERCARIA Penetrates crabs / crayfish, forms cysts: METACERCERIAE Human consumption of undercooked crabs, etc  Larvae hatch from cysts, burrow through intestine and mature in the lung

2. ROUNDWORMS Cylindrically shaped bodies Bilaterally symmetrical, tapered at both ends Have a complete digestive, reproductive & nervous system Separate male and female individuals Larval & Adult forms

Trichinella spiralis Causative agent of Trichinosis Larvae form cysts in animal muscles Meat-eating animals ingest these cysts Larvae hatch in the small intestine Develop into adult worms Produce more larvae Some larvae, into blood via intestinal wall Reach muscle and form cysts.

WHIPWORM – Trichuris trichiura (a roundworm) causing Trichuriasis

Hook Worms, attached to intestinal mucosa

Wuchereria bancrofti (a roundworm that causes elephantiasis)

Diseases caused in humans Ascariasis Dracunculiasis Elephantiasis Lymphatic filariasis Onchocerciasis Schistosomiasis Trichuriasis