The Ecology and Pathology of Trichostrongylus tenuis (Nematoda), a Parasite of Red Grouse Lagopus lagopus scoticus.

Author Watson, H.
Citation Watson, H. (1988). The Ecology and Pathology of Trichostrongylus tenuis (Nematoda), a Parasite of Red Grouse Lagopus lagopus scoticus. Unpublished Ph.D. thesis. University of Leeds, Leeds.

Abstract

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 populations.  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  0-30oC, 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 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.

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