No abstract

The maintenance of Theileria parva parva infection in an endemic area of Kenya on the shore of Lake Victoria was studied in the field and laboratory. High prevalences of antibodies against T. parva and T. mutans and intra-erythrocytic piroplasms were detected in local zebu (Bos indicus) cattle. The mean infection rate of Theileria parasites in the tick, Rhipicephalus appendiculatus, in field collections was 1.1%. Most of the infection was attributed to T. parva parva by application of field ticks to susceptible cattle. Five cattle, all about 1.5 years old, were purchased from local owners and transported to the laboratory. All five had oscillating antibody titres against T. parva and T. mutans and had patent theilerial infections during the subsequent 13 months. Uninfected R. appendiculatus nymphs were applied to cattle at 0, 3, 6, 9 and 13 months after transport to Muguga, and 18 out of 23 batches transmitted T. parva parva infection to cattle when 100 resultant R. appendiculatus adults were applied. Infection rates in the tick batches were usually low, with 1 salivary gland acinus infected/tick. Hence, a frequent carrier state of naturally infected cattle has been demonstrated for T. parva parva for the first time, and it is likely that this carrier state is of great importance in maintenance of T. parva parva infection in the field.

Experiments were carried out to determine the susceptibility of mammalian cells to infection with different species of Theileria in vitro. Sporozoites of Theileria parva (parva), Theileria parva (lawrencei) and Theileria taurotragi were isolated from Rhipicephalus appendiculatus ticks by grinding infected ticks in medium, filtering the suspension and concentrating by centrifugation. The sporozoites were used in attempts to infect in vitro peripheral blood leucocytes harvested from 16 different mammalian species which included 12 species of Bovidae from 6 different sub-families. The technique was shown to be both sensitive and reproducible. The sporozoites of T. parva (parva) infected and transformed cells from 2 species of the sub-family Bovinae, the two cattle types and African buffalo. Theileria parva (lawrencei) infected and transformed cells from the two cattle types, African buffalo and Defassa waterbuck. Theileria taurotragi sporozoites infected in vitro cells from 11 different species of Bovidae which were members of 6 sub-families; Bovinae, Tragelaphinae, Reduncinae, Alcelaphinae, Antilopinae and Caprinae. Transformed lymphoblastoid cell lines were established from 7 of the species infected. Sporozoite attachment and infection was not observed with non-susceptible bovid host cells, nor were any of the non-bovid leucocytes infected by the parasites. The host range observed in this study corresponded to the known host range in vivo.

SUMMARYThe moulting behaviour of nymphal Rhipicephalus appendiculatus from the laboratory colony and 3 field strains from Kenya was greatly influenced by constant temperatures between 18 and 37 °C but was not significantly different for the 4 tick strains. Six batches of R. appendiculatus (Muguga laboratory) nymphs which had engorged on cattle parasitaemic with 4 stocks of Theileria parva (Kiambu 4, Kiambu 5, Muguga and Mbita 4) isolated in Kenya were incubated at constant temperatures between 18 and 37 °C during their pre-moult and post-moult periods. The Theileria infections in the salivary glands of the resultant adult ticks were assessed by staining with Feulgen's stain. Two stocks (Muguga and Kiambu 5) developed their highest infections in ticks incubated at 28 °C while the other two (Kiambu 4 and Mbita 4) developed their highest infections at 23 °C. Constant temperatures of 18, 33 and 37 ° C were detrimental to the development of salivary gland infections. Temperature influenced the rate of development and numbers of the earlier Theileria stages in the ticks. Engorged nymphal ticks incubated for 4 days at 37 °C during their pre-moult period developed lower infections than ticks exposed at 4 °C for 4 days.

The characteristics of intra-lymphocytic Theileria isolated from African buffalo and from cattle that were infected with buffalo-derived parasites were evaluated using anti-schizont monoclonal antibodies (mAbs) and DNA probes. Antigenic differences were revealed by the reactivities of 27 mAbs with the buffalo-derived parasites isolated from different animals. Antigenic diversity was also seen with Theileria-infected lymphoblastoid cell isolates taken from the lymph nodes and lambda gt11, showed specific hybridization to parasite DNA in Southern blots of restriction enzyme-digested, lymphoblastoid cells infected with buffalo-derived theilerial parasites. Genotypic differences between the buffalo-derived parasites were revealed by the restriction fragment length polymorphisms seen with hybridization of those probes to DNA from cloned and uncloned Theileria-infected cell lines. The evaluation of theilerial parasites derived from buffalo and from cattle which underwent typical T. p. lawrencei reactions, after being infected with buffalo-derived theilerial parasites, did not show any specific phenotypic or genotypic characteristics of these parasites that would distinguish them from T. p. parva and T. p. bovis parasites. The validity of these subspecies distinctions is discussed.