Life cycle of Babesia argentina (Lignières, 1903) (Sporozoa : Piroplasmidea) in the tick vector Boophilus microplus (Canestrini)

Abstract

Babesia argeutina, a protozoan parasite causing tick fever of cattle in Australia, is transmitted by Boophilus microplus. Its development in this invertebrate vector is very similar to that recorded by Riek (1964) for Babesia bigemina. Many of the parasites occurring in the bovine erythrocytes are destroyed on ingestion but the early development in the lumen of the gut is uncertain. By about 36 hr, blunt, cigar-shaped forms, 7.2–1 3.8 µ by 2.6–5.6 µ, invade the epithelial cells of the gut and subsequent development is by means of multiple fission. This leads, by about 96 hr, to the production of mature vermicules which measure about 15.8 µ by 3.0 µ, with a range of 14.3–16.9 µ by 2.8–3.5 µ. At about this time vermicules enter the mature ova of the tick, and a further cycle of multiple fission in the gut cells of the developing larva gives rise to vermicules similar to those produced in the adult tick. The final cycle takes place in the salivary glands of the larva, and the forms infective to the vertebrate host appear 2–3 days and longer after larval attachment. Multiplication in this cycle is also by multiple fission and gives rise to comparatively small numbers of infective forms measuring about 1.5 µ by 1.0 µ. Not all ticks develop an infection even after engorging on blood with a high parasite density. Certain 'strains' of Boophilus microplus seem to be more susceptible to infection than others. Heavy mortalities occurred in many ticks after ingesting blood with a parasite density of 5% or higher.