H. D.
SRIVASTAVA
403
birds in various parts of the world. They are usually found in the distal two-
thirds of the caeca but occasionally may be evenly scattered in the caecal con-
tent. The number of these parasites in a single host may vary from one to
over two thousand. Their life-cycle is direct like that of the large intestinal
round-worms and does not involve any extra-intestinal migration (Plate
XXXV, fig. 1). The eggs develop in the open and under optimum conditions
(33° C.) reach the infective stage in five days. If the eggs containing the
infective larvæ are ingested by a suitable bird, they hatch in its intestine
and within 24 hours the worms migrate into the caeca and immediately invade
the caecal mucosa. During the first two days, few larvæ are found in the lumen
of the caeca but after the second day they begin to reappear in the lumen ;
their close association with the tissues, however, persists, though in a much
less pronounced form, till the fifth day. The worms attain maturity and
the female starts laying eggs after 24 days or more. It is only during the
first four days of the parasitic life that the worm invades the epithelium of
the glandular crypts.
Opinions regarding the pathogenicity of the caecum worm vary a good
deal. Some consider that, far from being harmful in any way to the host,
its presence is necessary for the efficient functioning of the caeca. Others
think that, though the worms are not beneficial to the host, they are also not
harmful. Still others consider that these parasites are responsible for typhli-
tis, resulting in diarrhœa, loss of condition and even death. Nodule forma-
tion and thickening of the caecal wall have also been attributed to these para-
sites. However, the chief economic importance of these parasites is associated
with their rôle as a vector of the organism (Histomonas meleagridis) of blackhead
(Infectious enterohepatitis) in turkeys and fowls. This disease frequently
occurs in fowls without causing noticeable symptoms and the caecum worm
carries it from the fowl to turkeys. Otherwise, except when present in very
large number, these parasites do little harm to the host. In heavy infesta-
tions, they may produce per se typical helminthic typhlitis, which is caused
by the young worms ' growing out of' the glands invaded during the early
phases of life-cycle.
Treatment of these parasites is difficult because of their inaccessibility at
the blind ends of the caeca. Most of the drugs administered per os fail to
reach them. The only drug which is moderately effective against these
worms is the Blackleaf 40, which has already been discussed in connection
with the treatment of ascaridiasis. Ordinarily, no treatment is necessary but,
if required, the best results are obtained by forcing the medicine through a
syringe into the cloaca and rectum. Normally the caeca are filled from the
large intestine through reversed peristalsis, the caecal valves acting as flood
gates, forcing the fluid into the caeca. 0.1 c. c. oil of chenopodium and
5 c. c. of cotton seed oil or other blend oil are administered by means of a small
enema syringe, while the bird is lying on its side. Control measures against
these parasites are the same as for the large intestinal round-worms.
The crop thread-worms or Capillarids are extremely fine nematodes in-
habiting the upper digestive tract, that is, anterior to the intestine, of the