Avian immune responses to Mycobacterium avium: the wildfowl example

Immunological responses of wildfowl (Order Anseriformes: ducks, geese, swans and screamers) to mycobacteria have been investigated as part of studies to develop a vaccine and diagnostic assay for avian tuberculosis. 10(9) killed Mycobacterium vaccae protected the Cairinini (perching ducks) from avian tuberculosis (p<0.02) but did not achieve statistically significant protection in the other taxonomic tribes. The Cairinini includes the threatened, yet highly susceptible, white-winged duck (Cairina scutulata).Together, loss of cell-mediated responses to common mycobacterial antigens, increased responsiveness to the species specific antigens of M. avium, and increased antibody production are reminiscent of the T(H1) to T(H2) shift seen in mammalian mycobacterial infections. It is speculated that excessive exposure to environmental mycobacteria prior to vaccination is detrimental and common antigens play an important role in wildfowl immunity to mycobacteria. A new vaccination trial using killed M. vaccae is being undertaken. Antibody responses are a useful ante mortem diagnostic indicator in most taxonomic tribes with the exception of the primitive Dendrocygnini (whistling ducks).