INTRODUCTION
Tick toxicosis has been a research focus for almost 80 years and during this time, several excellent reviews on this subject have been written that cover the history of toxicosis research as well as its aetiology and pathology (Gregson, 1943, 1973; Stampa, 1959; Neitz, 1962; Murnaghan & O'Rouke, 1978; Gothe, Kunze & Hoogstraal, 1979; Gothe, 1984, 1999; Wikel, 1984; Gothe & Neitz, 1991; Sonenshine, 1993; Masina & Broady, 1999). A comprehensive monograph on tick toxicoses of all forms has also been published (Gothe, 1999).
FUNCTIONAL SIGNIFICANCE OF TICK TOXINS
While arthropods such as spiders and scorpions are notoriously venomous organisms that utilize their toxins for protection as well as predation, the advantages for ticks being toxic is unclear. It has been suggested that tick paralysis may be a vestigial function conserved in ticks, when ticks evolved a parasitic lifestyle (Stone et al., 1989). Paralysis toxins have been attributed to functional significance during feeding of the tick, in that host mobility and grooming is impaired. This might be relevant, as tick paralysis sets in at the later stages of tick engorgement, when the tick is most liable to be killed by grooming practices. Paralysis would also affect the respiratory system leading to elevated breathing rates and an increase in carbon dioxide expiration. This together with pheromone secretion could attract ticks to the paralysed animal, which accelerates the finding and feeding of ticks.