Improved toxin/antitoxin assays for studies on the Australian paralysis tick Ixodes holocyclus

Sensitive biological assays of toxin/antitoxin potency have been developed to assist in research on characterization of salivary toxins of the Australian paralysis tick Ixodes holocyclus and on immunity to tick paralysis. The toxin assay utilizes suckling mice (4-5 g); a quantitative paralysis index is applied over a range of doses. The antitoxin assay is based on an in vitro/in vivo neutralization test which required a sensitive toxin assay and methods of standardization of toxin preparations. This assay permits the monitoring of blood antibody levels in animals during the course of development and loss of immunity and is assisting a study into the feasibility of producing an anti-paralysis vaccine. The method also allows standardization of commercial tick paralysis antiserum. The methods and applications are described and comparisons made with previous assays. Sample data are examined statistically by regression and variance analyses; parallelism of dosage-response lines is tested and relative toxicities (toxin) or potencies (antiserum) calculated.