H.
D.
SRIVASTAVA
405
bursa of the male, into the lumen of the trachea and bronchi. In their appear-
ance, the eggs differ from those of other strongyles in the presence of a thicken-
ed operculum at either end. From the trachea they are coughed up into the
mouth and swallowed and are eventually voided with the droppings. Under
suitable conditions of temperature and moisture, the eggs usually hatch
in seven to ten days. The larva undergoes two moults inside the egg-
shell and the third stage larva is infective. It is, however, not necessary
for the larva to hatch and an infection may result by the ingestion
of the egg containing fully developed larva. Although the intercolation
of an invertebrate intermediate host, such as earth-worms, snails and
slugs in the life-cycle of this parasite, is not necessary, they often
act as reservoirs for the larvæ and serve as facultative hosts. When
larvæ and mature eggs are ingested along with soil by earth-worms,
they migrate from the gut to their muscular parts and remain alive
there for over three years. The earth-worm thus plays an important rôle in
the collection of larvæ from the soil, in carrying over the infection from season
to season and in transferring them to the final host. On being swallowed by
the final host, the larvæ quickly migrate to the lungs where they undergo a
further moult and sex differentiation and pairing take place. After pairing,
the worms leave the smaller air-passages and work their way into the larger
windpipes. Sexual maturity is attained in 10 days after the worms reach
the trachea. The entire life-cycle is completed within a month or so.
Chicks, turkey poults and young pheasants are particularly susceptible
to ' gapes' and may die in large numbers. However, chickens invariably
develop a very definite immunity against this parasite when eight or nine
weeks' old, and, once this age immunity has developed, any worms which may
be present die or are expelled and a re-infection is impossible. The turkey
on the other hand does not develop any age immunity and may remain infected
throughout life. Turkeys do not show any symptoms, unless very heavily
infested, and hence may serve as carriers for the parasite. The ' gape ' disease
in young birds is probably mainly due to the mechanical blockage of the
trachea, which is brought about by the presence of the parasite, local
oedema of the mucosa and the formation of nodule at the seat of
attachment and the accumulation of mucus. The migration of the larvæ
through the lungs does not appear to have any serious effect. Though the
worms are blood suckers, the actual loss of blood is probably negligible.
The symptoms are mainly those of suffocation. There is a peculiar cough
or sneeze, the bird tosses its head, the neck is stretched forward with open
beak in an attempt to take in more air. The death is usually due to
suffocation, though progressive emaciation is undoubtedly a contributory
factor.
In the absence of any satisfactory treatment, the practice of mechanically
dislodging the worm with or without the aid of chemicals is widespread. A
loop of horse hair is introduced into the trachea, twisted to entangle the
worms and then withdrawn. The tip of a feather moistened with clove oil
or turpentine is also often used in dislodging the parasite. In cases of