Browsing by Author "Branagan, D."
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Item The developmental Periods of the Ixodid Tick Rhipicephalus Appendiculatus Neum. under Laboratory Conditions(1973) Branagan, D.; East African Veterinary Research Organization, Muguga, P.O. Kabete, KenyaA study, begun in 1966 at Edinburgh University, and completed during the ensuing 30 months at Muguga, Kenya, of the developmental periods of Rhipicephalus appendiculatus Neum. under controlled temperature and humidity was carried out to provide basic background information for an intensified FAO/EAVRO programme of East Coast fever research. Quantitative data are given on the preoviposition, pre-eclosion and, for larvae and nymphs, premoulting periods at three constant temperatures, 25, 21 and 18°C. The rate of development at all stages was accelerated by raising the temperature and retarded by lowering it. A “pre-immobilization period” which precedes the entry of engorged larvae and nymphs to the true moulting process also appeared to be temperature dependent. Development became very prolonged as temperatures fell below 18°C, being negligible at 15°C and having apparently ceased altogether at 9°C. Continuous exposure for more than two or three days to temperatures of 4°C and below were lethal to all engorged instars. Humidity (controlled at levels between 18 and 87% r.h.) had no influence on the rate of development. It is concluded that within limits of tolerable aridity, developmental periods would be completed within the times dictated by temperature regardless of the level of humidity or changes in the level of humidity. No suggestion of any diapause mechanism was discerned.Item A Note on the Survival of Unfed Adult Rhipicephalus Simus Simus Koch,1844(1968) Branagan, D.; Bailey, K. P.; East African Veterinary Research OrganizationOne-third of a batch of unfed adults of Rhipicephalus simus simus Koch survived for 32 months in the laboratory in Kenya and a few subsequently produced normal progeny after they had engorged on a rabbit. The probable importance of the species in the transmission of various human and animal diseases is briefly discussed in relation to the apparent preference of the immature stages for small animals as hosts. This is thought to make it unlikely that R. s. simus is an important field vector of either East Coast fever or anaplasmosis, although its ability to transmit the causal agents (Theileria parva and Ana plasma marginale) is well established [cf. RAE B 26 26; 46 121; 57 262]. On the other hand, it has been suggested that small mammals are important in the maintenance of rickettsial infections [cf. 51 150], and the production of a syndrome typical of tick typhus {caused by Rickettsia conori] following inoculation into a human volunteer of a strain of rickettsiae isolated from Rhipicephalus s. simus has been recorded [48 130]. It is considered that this tick may be a more important vector of rickettsial infections than has hitherto been realised.Item Preliminary Observations on a Theilerial Species Pathogenic to Cattle Isolated from Buffalo (Syncerus Caffer) in Tanzania(1973) Young, A.S.; Branagan, D.; Brown, C.G.D.; Burridge, M.J.; Cunningham, M.P.; Purnell, R.E.; East African Veterinary Research Organization, Muguga, P.O. Kabete, KenyaA theilerial species, pathogenic to cattle, and resembling Theileria lawrencei, was isolated from two buffalo captured in the Serengeti National Park, Tanzania. When nymphal Rhicephalus appendiculatus ticks were fed on the buffalo, on four out of six occasions the resultant adults were shown to be capable of causing highly pathogenic T. lawrencei-type infections in cattle. Aspects of the life cycle of the parasite in both ticks and cattle were studied. Its development in the tick was apparently similar to that of T. parva, and, in cattle, only differed from T. parva by causing the host’s death when relatively few lymphocytes were infected with macroschizonts and when neither microschizonts nor piroplasms were detectable. The parasite was designated T. lawrencei (Serengeti).Item The use of Parasympathomimetic Drugs to Stimulate Salivation in the Tick Rhipicephalus Appendiculatus, and the Transmission of Theileria Parva using Saliva Obtained by this Method from Infected Ticks(1969) Purnell, R.E.; Branagan, D.; Radley, D.E.; East African Veterinary Research Organisation, P.O Box 32, Kikuyu, Kenya.Various parasympathomimetic drugs were injected per anus into female R. appendiculatus, previously fed for 5 days on rabbits, in attempts to induce the ticks to salivate. Pilocarpine nitrate and arecoline hydrobromide gave the best results and these drugs were therefore injected into ticks of various weight ranges and at various concentrations of the drug and the diluent, saline. The drugs were most effective at a concentration of 10% in 6 % sodium chloride solution. If ticks salivated, the amount of saliva they produced could be positively correlated with their weight. Sections of salivary glands from 5-day-fed female ticks in the corresponding weight ranges were examined for infection with T. parva. There appeared to be an inverse relationship between the infection rate of the ticks, and the number of infected acini observed, with increase in their weight. It was established that the greatest numbers of infective particles of T. parva should be obtained by the injection of 1 ul of 10% pilocarpine nitrate in 6 % sodium chloride solution into ticks weighing between and 13.0 mg. Twenty-five infected ticks in this weight range were injected, and the resultant saliva added to concentrated autologous leucocytes in phosphate-buffered saline before injection into a steer. The animal underwent a typical East Coast fever reaction and died, thus indicating that infective particles had been harvested by our methods.
