The ecology and pathology of Trichostrongylus tenuis (nematoda), a parasite of red grouse( Lagopus Lagopus scoticus)

Trichostrongylus tenuis is a nematode that lives in the
caeca of wild red grouse. It causes disease in red grouse
and can cause fluctuations in grouse pop ulations. The aim
of the work described in this thesis was to study aspects
of the ecology of the infective-stage larvae of T.tenuis,
and also certain aspects of the pathology and immunology of
red grouse and chickens infected with this nematode.
The survival of the infective-stage larvae of T.tenuis
was found to decrease as temperature increased, at
temperatures between 0-30 C? and larvae were susceptible to
freezing and desiccation. The lipid reserves of the
infective-stage larvae declined as temperature increased
and this decline was correlated to a decline in infectivity
in the domestic chicken. The occurrence of infective-stage
larvae on heather tips at caecal dropping sites was
monitored on a moor; most larvae were found during the
summer months but very few larvae were recovered in the
winter. The number of larvae recovered from the heather
showed a good correlation with the actual worm burdens
recorded in young grouse when related to food intake.
Examination of the heather leaflets by scanning electron
microscopy showed that each leaflet consists of a leaf roll
and the infective-stage larvae of T.tenuis migrate into the
humid microenvironment' provided by these leaf rolls.
Scanning electron microscopy showed that the adult
nematodes burrowed into the mucosa as well as lying on its
surface and that the caecal mucosa of heavily infected
grouse became disrupted in areas of nematode activity. The
caecal mucosa of lightly infected grouse exhibited little
damage and the caecal mucosa of grouse treated with an
anthelmintic and shot 5-6 months later was similar to that
of lightly infected birds. Some of the nematodes from
these treated birds were covered in rosette-shaped cells
which have been tentatively identified as adherent
lymphocytes. The cuticle of adult T.tenuis was
superficially annulated but did not possess cuticular
ridges, as described in some other trichostrongyle
nematodes.
Primary and challenge infections with T.tenuis were
established in the domestic chicken and these reached
patency but nematodes were expelled in blood-stained balls
of mucus and all adult nematodes had been expelled from the
birds 30 days after dosing with infective-stage. Following
trickle doses of larvae,,there was a rise and then a fall in
nematode egg output but larvae administered later in the
trickle infection appeared to fail to establish. Light and
scanning electron microscopy showed haemorrhagic lesions
and blood spots on the caecal mucosa of infected chickens
and nematodes were found to burrow beneath mucus secreted
on the mucosal surface. There were significant increases
in the proportions of circulating leucocytes in infected
chickens, but only on certain days of infection. No
antibodies to T.tenuis were detected in the blood of
infected chickens. There was a decrease in the length of
the caeca of infected chickens during the period when the
Ill
nematodes were being expelled from the caeca. Nematode egg
output continued to rise during an infection in young red
grouse and there was no expulsion of nematodes from these
infected birds.
Infective-stage larvae that had been attenuated by cobalt
60 irradiation stimulated some degree of resistance to
challenge infection in the domestic chicken but not in the
red grouse. It was concluded that immunization with
irradiated larvae would be of little use in the control of
T.tenuis in red grouse.