Nematodes that cause PGE are not normally a problem for intensively reared poultry but are important with free-range birds, ornamental & game birds, especially pheasants and grouse. In developing countries, village chickens are prone to various nematode and parasitic diseases.
What are the main nematodes that affect birds to cause PGE in the UK, and what types of birds are affected?
Trichostrongylus tenuis - grouse
Syngamus trachea - wide host range: rooks, crows, poultry, game birds; causes gapes in pheasant poults
Heterakis gallinae - causes "black head" in turkeys
Trichostrongylus tenuis nematode is a strongyle worm that affects grouse. Where in the grouse is it found?
Intestine & caeca. See photo.
What is the pathogenesis of Trichostrongylus tenuis in grouse? Why is it so devastating for grouse populations?
L3 accumulate on heather tips → hungry, weak grouse following tough winter in spring eat heather & L3 → accumulate heavy worm burdens
Infestation by the worm contributes to cyclical crashes that occur already due to poor condition of grouse following long, cold winter
How can grouse affected by Trichostrongylus tenuis be treated?
Why is Syngamus trachea considered an atypical strongyloid? Give three reasons.
1. Y-shaped adult - smaller male permanently attached to female
2. Strongyle egg has operculum at each end (see photo)
3. Infective larva (L3) develops
Where does Syngamus trachea target in the bird? (Hint: name of worm)
What condition does it cause in birds?
Since it's in the trachea, it causes respiratory distress aka "gapes", especially in young birds.
Birds can become infected by Syngamus trachea in several ways, by ingesting different stages of the worm. What are these different stages?
1) eating larvated egg - remember L3 develops inside
2) eating larva that’s hatched out of egg
3) eating earthworm (transport host) that had previously swallowed an egg or larva
How do pheasant poults, in particular, come down with respiratory gapes caused by Syngamus trachea?
- droppings on ground
- soil contaminatd with Syngamus trachea eggs
- earthworms infected
- these become reservoir of infection
- eggs and earthworms eaten by poults reared on earth-floored pens in woodland
How does Heterakis gallinae cause blackhead in turkeys?
It's a vector for Histomonas meleagridis, the protozoan parasite that causes blackhead in turkeys; they skin becomes cyanotic.
Why is Heterakis gallinae considered an atypical ascarid?
1. It doesn't undergo hepatic-tracheal migration but rather stays within the wall of the caecum
2. It's only 1.5 cm long
NB It does still have the three buccal lips
What is unique about Heterakis gallinae's morphology that helps it with mating?
It has a pre-cloacal sucker that replaces the bursa. The sucker is used to anchor it to the female while mating.
It's relatively slender and has a pointed tail. See photo.
What is the role of the earthworm in Heterakis gallinae's life cycle?
It helps as a transport host