Strongylida and Their Life Cycle

Strongylida

• Strongylida, also known as 'strongyles', are a large group of parasitic nematodes.
• They are of significant parasitological importance.

Morphology

• Strongyles are typically 0.5-3.0cm long (males ~1cm, females ~2cm).
• Males have a copulatory bursa (fan-like structure strengthened by chitinous rods) at the posterior end.
• Leaf crowns may be present at the anterior end.
• Eggs are thin-shelled, oval, and unembryonated when passed out.

Life Cycle

• Life cycle can be direct or indirect.
• Some strongyles (e.g., Ancylostoma) penetrate the skin, leading to hepatic-tracheal migration.
• Others (e.g., other strongyles) use the oral route.
• L3 (third-stage larvae) are the infective stage.
• L1 and L2 feed on materials in feces.
• L3 do not feed and depend on food granules accumulated during L1 and L2 phases.
• L3 can be found in soil and grasses.
• L3 gains entry into the host through ingestion.

Ancylostoma spp.

• Includes Ancylostoma caninum, Ancylostoma ceylanicum, and Ancylostoma braziliense, affecting cats and dogs.
• Commonly known as hookworms due to the hook-like posture of the anterior ends.
• Possess large buccal capsules with teeth.
• Their primary pathological consequence is blood sucking, leading to acute or chronic hemorrhagic anemia (in larvae and adult worms).
• Dogs and cats infected with Ancylostoma can transmit the infection to humans via contact with contaminated soil.

Strongylus vulgaris

• A strongyle affecting horses.
• Characterized by a leaf crown surrounding the mouth opening and a large buccal capsule with two rounded teeth.
• Larvae migrate on the endothelium, causing arteritis, thrombosis, and infarction in the intestines.
• Resultant damage and inflammation cause colic.
• Adult worms are tissue feeders in the cecum and colon, leading to hemorrhage.

Syngamus trachea

• A tracheal worm affecting poultry.
• Male and female worms are permanently joined in a Y-shape.
• Can act as paratenic hosts (earthworms are an example).
• Cause haemorrhagic tracheitis, characterized by excess mucous production.

Routes of Infection

• Skin penetration by L3: L3 stage larvae penetrating the skin then undergoing tracheal migration.
• Ingestion of L3: L3 larvae are ingested.
• Transmammary infection: L3 can be passed in milk.

General Notes:

• The time of larvation of eggs depend on factors like temperature, oxygen density, and humidity.