Strongylida and Their Life Cycle

Study Notes

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

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 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.

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.

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.

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.