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Theileria parva piroplasm infection of mouse erythrocytes was detected, following intraperitoneal inoculation of mice with irradiated cultures of T. parva-infected bovine lymphoid cells. Infection could not be transmitted to cattle using Rhipicephalus appendiculatus ticks.

Adult Rhipicephalus appendiculatus ticks, infected as nymphs by feeding them on an African buffalo harbouring Theileria lawrencei, were applied to the ears of rabbits. Equal numbers of the feeding ticks were removed daily from rabbits and either dissected and processed so that parasites in their salivary glands could be examined morphologically and classified, or ground in Eagle's Minimal Essential Medium, to harvest parasites from the ticks in the resultant supernatant fluid. The infectivity of the supernatant fluid was tested by inoculation of aliquots into groups of susceptible cattle. It was found that supernatant fluids produced from day 0 to day 2 fed ticks were uninfective to cattle but those produced from 3 to 9 days were infective. The most infective supernatant fluid was produced from 6 day fed ticks. The reactions resulting in cattle were correlated with the number and morphology of parasites in sections of salivary glands and it was found that mature parasites coincided with infectivity of the supernatant fluid to cattle. From the reactions in cattle inoculated with supernatant fluids from 5 and 6 day fed ticks it was concluded that this method of harvesting parasites was efficient. Examination of the salivary glands of a representative sample of a T. lawrencei infected tick batch is a potential means of screening material for T. lawrencei stabilates.

A comparison was made between the development of Theileria mutans (Aitong) in adult Amblyomma variegatum ticks and the development of T. parva (Muguga) in adult Rhipicephalus appendiculatus ticks. Both batches of ticks dropped as engorged nymphs from cattle whose intraerythrocytic parasitemias were approximately 40%, and it was thus possible to make a direct comparison of the infection rates produced in their tick hosts in this experiment by the 2 species of Theileria. Ticks of the 2 batches were fed in ear bags on rabbits, and equal numbers of male and female ticks were removed daily for 5 days. The salivary glands were dissected out from these ticks, and from unfed ones in each batch, processed, and examined for Theileria parasites, which were categorized according to their morphological maturity. The A. variegatum ticks had a lower rate of infection with Theileria. Fewer parasites were observed in the ticks, and they took longer to mature. When the development of the 2 species of Theileria was compared, the major difference appeared to be that T. mutans had large Babesia-like infective particles.

A serological comparison between British Theileria mutans and Japanese T sergenti using the indirect fluorescent antibody test, showed that the two parasites were indistinguishable. On the basis of this and previous findings it is suggested that the British parasite is identical with the Japanese one and that its name should therefore be changed to T sergenti.