DNA measurements and ploidy determination of developmental stages in the life cycles of Theileria annulata and T. parva.

The relative DNA levels of different developmental stages of Theileria annulata and T. parva in the cow and the tick were measured by the cytophotometric DNA technique using the fluorochrome Hoechst 33258 as a staining dye. The results revealed that sporozoites, merozoites, gamonts, and gametes were haploid, whereas multinucleated intralymphocytic schizonts were polyploid. No difference was observed between T. parva and T. annulata in these stages. For both Theileria species, the DNA measurements revealed that fusion of gametes occurred in the gut of the final host, thus providing evidence of sexual reproduction. However, differences were observed between the two parasites in the tick. Whereas T. parva zygotes underwent a two-step meiotic division, a comparable reduction division could not be unequivocally detected in T. annulata. Differences could also be detected in the further development of kinetes, indicating that Theileria species are not characterized by only one life cycle, which is specific for this genus.

DNA measurements reveal differences in the life cycles of Babesia bigemina and B. canis, two typical members of the genus Babesia.

The relative DNA levels of different developmental stages of Babesia bigemina and B. canis were measured by cytophotometry using the fluorochrome Hoechst 33258 as a staining dye. The DNA measurements provided direct proof of sexual reproduction, i.e., fusion of gametes resulting in the formation of zygotes followed by a meiotic division. Both Babesia species are considered to be typical members of the genus Babesia; however, the DNA measurements revealed important differences in the life cycle of these parasites, indicating that Babesia species are not characterized by a life cycle, which is specific for this genus.

The development of Babesia (Theileria) equi (Laveran, 1901) in the gut and the haemolymph of the vector ticks, Hyalomma species.

The development of the piroplasm Babesia equi was studied by light microscopy in the gut and the haemolymph of three different Hyalomma species during and after the nymphs had engorged on parasitaemic horses. The stock of B. equi used was isolated from a horse imported from Turkmenistan (CIS) in 1991. The existence of gamogony was identified by the occurrence of gamonts and gametes in the gut contents of the nymphs at between 3 and 4 days after infestation of the nymphs, before the ticks dropped off the experimentally infected horses. Zygotes and kinetes were observed in the intestinal cells from day 4 until day 7 after infestation i.e. 2 days prior to engorgement until repletion of the nymphs. Simultaneously, kinetes could also be seen in the haemolymph of engorged nymphs. The morphology and the sequence of the developmental stages of B. equi identified in the gut and the haemolymph of the vector ticks were identical in all three Hyalomma species. They resembled typical developmental stages of bovine Theileria species. Because of the close similarity of the developmental cycle of B. equi in Hyalomma species to the life cycle of Theileria species and due to the differences to the other Babesia species, a discussion about classifying B. equi into the family of Theileriidae now seems to be justified.

New findings in the development of Babesia (Theileria) equi (Laveran, 1901) in the salivary glands of the vector ticks, Hyalomma species.

The development of the piroplasm Babesia equi was studied by light microscopy in the salivary glands of three different Hyalomma species during and after the engorgement of nymphs on experimentally infected horses and after adults had fed on a vertebrate host following ecdysis. The stock of B. equi used was isolated from a horse imported from Turkmenistan (CIS) in 1991. The findings, being identical in all three Hyalomma species, differ with regard to the chronological order of the development stages in several respects from the results of previous studies based upon light or electron microscopy. A first sporogony phase of B. equi was found to develop in the salivary glands of the engorged nymphs before the ticks moulted to adults. Beginning at day 6 postinfestation (p. infest.) of the nymphs, spindle-shaped sporozoites appeared to be formed by both rapid sequential fission of a multinucleated complex and a process of radial budding from multiple fission bodies. Sporozoites isolated from the salivary glands of the engorged nymphs proved to be infectious when they were injected into a susceptible horse. After the nymphs had moulted, a second sporogony phase similar to the first one observed in the salivary glands of engorged nymphs could also be initiated in the salivary glands of adults when they were attached to a vertebrate host. Sporozoites produced in the salivary glands of adults were equally infectious for horses. Thus, two completely separate sporogony phases in B. equi seem to develop successively in the salivary glands of Hyalomma species during a transstadial transmission.