Some factors controlling the stimulation of sporogony of Theileria parva in its tick vector Rhipicephalus appendiculatus

Young A. S., Leitch B. L. and Mutugi J. J. 1984. Some factors controlling the stimulation of sporogony of Theileria parva in its tick vector, Rhipicephalus appendiculatus. International Journal for Parasitology14: 97–102. The effect of various temperature treatments on the sporogony cycle of Theileria parva in the salivary glands of unfed adult Rhipicephalus appendiculatus ticks of various ages was investigated. It was found that ticks incubated at 28 or 37°C would develop sporozoites infective to cattle but never in such large numbers as in ticks fed on rabbits. Heat stimulation of sporogony was possible for isolates of T. parva with minimal laboratory handling. The age of the ticks incubated at 28 or 37°C was important since sporozoites could only be induced at the earliest on day 27 or 28 p.repl. (post-repletion) and at the latest by day 41 p.repl. The age of ticks fed on rabbits was not as important for the production of sporozoites.     

Salivary gland of the tick vector of east coast fever. IV. Cell type selectivity and host cell responses to Theileria parva

Responses of cells in the tick salivary gland to parasitism by Theileria parva were studied by electron microscopy. The gland is composed of three distinct types of acini (I, II, III) which together include ten or more different cell types. Of some 30 infected cells observed in the present study, all were E-cells of acinus III. The parasite thus exhibits a high degree of selectivity for acinus and cell type. The glandular cell invaded undergoes massive hypertrophy and accumulates glycogen deposits in its cytoplasm which may serve as an energy source for the growing intracellular parasite. As synthesis of its secretory material declines the product is packaged in progressively smaller secretory granules. The extensive arrays of endoplasmic reticulum are dismantled and eliminated in autophagic vacuoles. Excess secretory granules are also broken down by crinophagy. After 4 days, sporogony is completed and the host cell contains 30,000–50,000 sporozoites in an electron-lucent cytoplasm largely devoid of cytomembranes and secretory granules. Mitochondria are still present and normal in appearance. The loss of basophilia and secretory granules observed heretofore by light microscopy have been attributed to ingestion and destruction of host organelles by the parasite. The pallid appearance of the cytoplasm has been interpreted as a sign of impending degeneration of the host cell. In electron micrographs no ingestion of organelles by the parasite or degenerative changes were found. The host cell clearly remains viable and metabolically active throughout sporogony. The striking changes in its ultrastructure result from active elimination of organelles and inclusions by the host cell itself in response to parasitism.     

Salivary gland of the tick vector (R. appendiculatus) of East Coast fever. I. Ultrastructure of the type III acinus

The brown ear tick Rhiplcephalus appendiculatus is the vector for East Coast fever, a disease that seriously limits livestock production in East Africa. The sporozoites of the infectious agent Theileria parva develop in the tick salivary gland. This paper describes the organization of the type III acinus of the gland and establishes unambiguous ultrastructural criteria for identification of the three secretory cell types: the d-cell, e-cell and f-cell. These observations are basic to exploration of possible cell-type specificity of the invading theileria and other aspects of host-parasite relations.     

East Coast fever: quantitative studies of Theileria parva in cattle

A series of experiments is described in which infective material obtained by grinding adult Rhipicephalus appendiculatus ticks containing mature Theileria parva parasites was titrated in East Coast fever-susceptible cattle. The reactions of the cattle to the various inocula, and the rate of multiplication of macroschizonts in their lymph nodes, were studied. In the final experiment, conclusive evidence was produced to support the observations of previous workers that the prepatent period, time to onset of febrile response, and time to death of the animals was dose-dependent, whereas the production of intraerythrocytic piroplasms was totally time-dependent. Furthermore, the effective rate of multiplication of macroschizonts was shown for the first time to be dose-dependent. It was not possible to detect macroschizonts before the fifth day after inoculation, and an occult phase of the parasite's life cycle, between the infective particle and the uninuclear macroschizont, is postulated. The discrepancies between the results of the present work and those of previous workers are discussed.     

East coast fever: 60Co-irradiation of Theileria parva in its tick vector, Rhipicephalus appendiculatus

Three experiments were carried out in which Theileria parva was irradiated in its tick vector, Rhipicephalus appendiculatus. In the first experiment, infected unfed adult ticks were irradiated at doubling doses from 4 to 32 krad. Some of the ticks were then fed for 4, 5, 6, 7 and 8 days on rabbits, and the parasites in their salivary glands examined. Five male and 5 female ticks from each irradiation dose were put onto each of a pair of susceptible cattle, whose reactions were recorded. Increasing doses of irradiation resulted in progressive destruction of the parasites. All cattle receiving ticks irradiated at doses up to and including 16 krad died of East Coast fever (ECF), and one of the cattle receiving ticks irradiated at 32 krad died.In the second experiment, recently engorged nymphs were irradiated at 1, 2 or 4 krad, and moulting nymphs at doses of 2, 4, 8, 12, 16 or 32 krad. The salivary glands of the resultant adult ticks were examined after the ticks had fed for 4, 5, 6, 7 or 8 days on rabbits. Engorged nymphs irradiated at 4 krad failed to moult, whilst moulting nymphs irradiated at 32 krad moulted but failed to attach to rabbits. Doses of irradiation survived by the ticks had no apparent morphological effect on the parasites they contained.In the third experiment, infected unfed adult ticks were irradiated at 0, 5, 10, 15, 20 25 30, 35, 40, 45, 50 or 60 krad. The ticks were fed on rabbits for 5, 6 or 7 days. Some of them were then examined morphologically, whilst others were ground in MEM/BPA and aliquots of the supernatant used to inoculate groups of 5 cattle. The reaction of these cattle, together with the morphological examination of the parasites, suggested that increasing doses of irradiation destroyed increasing numbers of parasites.     

Salivary gland of the tick vector (R. appendiculatus) of East Coast fever. II. Cellular basis for fluid secretion in the type III acinus

Fluid balance is a major physiological problem for hematophagous ticks. To maintain osmotic balance they must conserve water for prolonged periods while seeking a mammalian host, and they must eliminate a very large volume of excess fluid taken in during a relatively short period of feeding. This is accomplished in part by modification of the salivary gland during 7–10 days of feeding to secrete a copious saliva which is pumped into the bovine host. This function has previously been attributed to certain interstitial epithelial cells of the type III acinus which differentiate in the course of feeding into cells reminiscent of those of the avian salt gland. The ultrastructural changes in the type III acinus during the blood-meal were studied. In addition to the differentiation of the interstitial cells, this paper describes a remarkable sequence of changes in external form and internal organization of the e-cells. This results in their transformation from typical protein-secreting glandular cells to transport cells having myriad basolateral processes interdigitating with those of the ablumenal interstitial cells to form a basal labyrinth comparable to that of other fluid-transporting epithelia. The findings are discussed in relation to various postulated mechanisms for fluid and electrolyte transport.     

East Coast fever: the infectivity for cattle of infective particles of Theileria parva harvested in various substrates

Cunningham M.P., Brown C.G.D., Burridge M.J., Joyner L.P. and Purnell R.E. 1973. East Coast fever : the infectivity for cattle of infective particles of theileria parva harvested in various substrates. International Journal for Parasitology3: 335–338. Female Rhipicephalus appendiculatus ticks infected with Theileria parva were pre-fed on rabbits for 4 days before being removed and restrained on ‘plasticine’. They were then fed for 2-h periods on capillary tubes containing various substrates, the contents of which were subsequently inoculated into East Coast fever-susceptible cattle. Using this technique, precolostral calf serum and Eagle's Minimum Essential Medium, with the addition of Bovine Albumin Powder, were selected as substrates suitable for further laboratory investigation on East Coast fever as they were acceptable to the ticks and supported the viability of the parasites.     

Theileria parva: variation in the infection rate of the vector tick, Rhipicephalus appendiculatus

The variation in Theileria parva infection rates of experimental batches of adult Rhipicephalus appendiculatus ticks, used during the course of several years, was examined. It was found that considerable variation occurred, but that this could not always be correlated with the piroplasm parasitaemia in the cattle on which the ticks engorged as nymphs. Statistical analysis showed that the infection rate of ticks fed on cattle with a parasitaemia of 41–50 per cent was significantly higher than that of ticks fed on cattle with lower parasitaemias. A number of experiments were then carried out in which one or several factors of this aspect of the host-parasite relationship remained constant whilst others were altered. None of these factors was seen to play a major part in the variation. Finally, randomly selected groups of 10 ticks which had dropped engorged as nymphs from the same animal on the same day were examined. The variation observed even in these groups was so great that it was concluded that the infection rate could depend on a factor such as the juxtaposition of possibly-infected gut epithelial cells and developing salivary glands during the nymphal moult.     

The genome of Theileria parva: some structural properties

The DNA of the protozoan Theileria parva, the causal agent of the bovine East Coast Fever, has been prepared at least 99% pure from the intra-erythrocytic form of the parasite. Its buoyant density was found to be 1.696 g/cm3 and its calculated G + C content was 36.7%. Fragmentation of T. parva by the restriction enzyme EcoRI provides some evidence of the presence of repetitive DNA sequences.     

East Coast Fever of Cattle: 60Co Irradiation of Infective Particles of Theileria parva

SYNOPSIS. Infective particles (IPs) of Theileria parva , the causative organism of East Coast Fever of cattle, were harvested from the tick vector, Rhipicephalus appendiculatus , using an in vitro feeding technic. In a ranging experiment, pairs of cattle were inoculated with aliquots of suspensions of IPs irradiated at doses of 4–137.6 krad. Doses of irradiation in excess of 8 krad appeared to destroy the parasite. In the 2nd and 3rd experiments, groups of 5 cattle were inoculated with aliquots of suspensions containing low and high concentrations of IPs respectively, irradiated at doses of 4–32 krad. In the 2nd experiment, doses of irradiation in excess of 10 krad appeared to destroy the parasite. In the 3rd experiment, at least 1 animal became infected when inoculated with an aliquot of a suspension irradiated at 16 krad. In all experiments, it appeared that increasing doses of irradiation destroyed increasing numbers of IPs. There was no conclusive evidence that IPs which survived irradiation were attenuated, and it appears that vaccination of cattle against ECF is unlikely to be achieved by inoculation of irradiated IPs using the methods described.