Cromie, Ruth Louise; (1991) Development of an avian tuberculosis vaccine for wildfowl. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Wildfowl and Wetlands Trust maintain a large and comprehensive collection of captive wildfowl at Slimbridge in Gloucestershire, Avian tuberculosis caused by Mycobacterium avium, has been enzootic since 1948 and is now the main cause of death, accounting for over a third of post fledgling mortalities. There is a grave risk of spreading infection to the enormous number of wild birds that use the grounds. The introductory chapters review the disease in both wild and captive wild birds. The particular susceptibility of the rarest duck in the world: the White-winged Wood Duck Cairina scutulata, and the effect of the disease on its captive breeding programme, are discussed. The disease situation at Slimbridge is assessed in an epizootiological study which is carried out on adult post mortem data of the years 1980-1989. This study shows both genetic and environmental factors greatly influencing incidence of the disease. However, it also suggests that there are definite levels of immunity to M.avium in some groups and individuals. The main experiments in the thesis investigate the possibility of immunoprophylaxis in the form of a vaccine as a possible method of controlling the disease. Past attempts at vaccination are reviewed, as is the current knowledge of the wildfowl immune system. Conditions for the immunological tests used to assess immune responses throughout the vaccine studies had to be optimised. These tests included: wildfowl lymphocyte transformation test (LTT) which has been made to work in the presence of antigen for the first time; a method for skin testing, previously not done in wildfowl; and an enzyme linked immunosorbence assay (ELISA). The main study chapters report the use of intradermal BCG and M.vaccae as potential vaccines. Studies with Mallard Anas platyrhynchos platyrhynchos indicate killed M.vaccae administered at one day old as an immunopotentiating agent. Studies with Mandarin ducks Aix galericulata confirm the optimum age for vaccination to be one day old. An optimum dose of this vaccine has been elucidated in studies using Gadwall Anas strepera and Hawaiian Geese or Nenes Branta sandvicensis. No protection was afforded to White-winged Wood Ducks when vaccinated with killed M.vaccae in adult life. A bacteriological study of strains of M.avium isolated from tuberculous birds at post mortem is also reported. Strains were isolated from birds from both Slimbridge and Arundel Wildfowl and Wetlands Trust centres, and also from several wild birds. These strains were subjected to lipid and DNA analysis, and studies were made of their protein patterns using SDS-polyacrylamide gel electrophoresis. The current vaccination programme at Slimbridge and The Wildfowl and Wetlands Trust centre at Llanelli, South Wales, is discussed. Results from tuberculous birds in the vaccine trials indicate the potential for the development of a diagnostic test.

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