Ascaridoidea

PARASITES NEMATODES

General Appearance

Toxocara cati - Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine

Toxoscaris leonina - Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine

Toxocara canis - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

Toxoscaris leonina - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

• Non-bursate
• Big fleshy worms; typically 5-40cm long (depending on age, sex and species)
• Three lips around the mouth
• A single-bulbed pharynx

General Life-Cycle

• Adult females in small intestine lay eggs
• Eggs have a thick protective shell
• Some also have a sticky outer albuminoid coat
• Eggs passed in faeces
• L1 → infective L2 inside the egg
• Infection is by ingestion of the embryonated egg (egg in which a larva has formed)
• Eggs can remain viable in humid environment for up to 5 years
• After hatching in the intestine, the larvae of most species (but not all) undergo hepato-tracheal migration:
  • egg hatches in intestine → larva penetrates intestinal mucosa → hepatic portal blood → liver → venous blood → heart → lung capillaries → alveoli → ascends trachea → swallowed → small intestine (where the adults develop)

NOTE: there are important variations on this theme; for example, the migratory larvae of some species can cross the placenta or enter the mammary glands (examples of vertical transmission); while some species will utilise paratenic or intermediate hosts.

Ascaridida

Occlusion of pancreatic ducts sometimes happens Pancreas - parasitic

In Peritoneal Cavity Parasitic - Pathology

• Parascaris equorum in rhinitis and lungs
• Ascarid larvae in myositis