Nematodes: Morphology, Life Cycle, and Medical Importance, Schemes and Mind Maps of Parasitology

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Parasites of medical importance

Helminths

Platyhelminths

Trematodes Cestodes

Nemathelminths

Nematodes

Protozoa

Nematodes (General characters) Elongated Cylindrical

Unsegmented worms

Separate sex

Parasite of humans and animals

Nematodes digestive system

The digestive system is complete

1 - Consists of mouth (anterior) 2 - Esophagus (vary in shape and structure) 3 - Intestine followed by rectum, which opens through anus

Morphology

Buccal cavity

Morphological differences between male and female nematode Male Female Length Short^ Long Width Thinner^ Thicker Posterior end Coiled or curved, has penial spicules and may have bursa for copulation Straight Ascaris

Life cycle of nematodes

• Man is the optimum host for all nematodes.
• Most nematodes pass their life cycle in one host.
• Some may need a 2 nd host; animal or arthropod.
• Eggs develop to rhabditiform larva then filariform larva
• Most nematodes live in the intestinal tract, and lay eggs (diagnostic stage) that pass with host stool (except Trichinella deposits larvae).
• Trichinella adults live in small intestine, but deposit larvae that encyst and encapsulate mainly in striated muscles.
• Some nematodes live in tissues and deposit larvae.

Example of nematodes that need one host

Ascaris

Tissue Nematodes

14

• Some Nematodes inhabits extraintestinal tissue (muscles, eye,…).
• Those are larviparous (laying larva directly).
• Larvae reach their intermediate hosts for further development inside.
• Larvae mature inside the intermediate host (usually an arthropod) to become infective filariform larvae.
• Infection is mediated through transmission of filariform larva from their intermediate hosts (vector )
• Trichinella spiralis is an intestinal and tissue Nematode

Modes of infection Ingestion of the infective stage Ascaris Enterobius (pinworm) Trichinella Dracunculus medinensis (Guinea or medina worm) Inhalation of dust containing the infective stage Ascaris Enterobius Skin penetration by the infective stage Ancylostoma (hookworm) Strongyloides Insect bite Filaria

Transmission methods

& DRINK

Nematodes classification according to habitat

Intestinal nematodes Somatic nematodes

1. Small intestine

• _Ascaris lumbricoides
• Ancylostoma duodenale
• Strongyloides stercoralis_
• Trichinella spiralis 2. Large intestine
• Enterobius vermicularis 1. Lymphatics
  • Wuchereria bancrofti 2. Muscles
  • Trichinella spirals 3. Eye
  • Loa loa 4. Skin/subcutaneous tissue - Medina worm
  • Onchocerca volvulus

Summary

• Nematodes are cylindrical worms affecting human.
• Life cycle runs in one or two hosts.
• They have male and female worms (sexually differentiated).
• Live in the intestine or other parts of the body.
• Can be transmitted through ingestion or inhalation of the infective stage, or by skin penetration or vector bite.

Differences between

platyhelminths and

nemathelminths

General characteristics of helminths

Shape Fixation Reproductive system