Horace Ochanda

Comparison of the transmission of Theileria parva between different instars of Rhipicephalus appendiculatus

The transmission of Theileria parva by nymphal and adult Rhipicephalus appendiculatus was compared by the assessment of salivary gland infections in tick batches fed on the same group of infected cattle at the same time. When larval and nymphal R. appendiculatus Muguga ticks were fed concurrently on cattle undergoing acute infection with T. parva Muguga, the resultant nymphae developed a slightly lower prevalence of infection than did the adult ticks. The abundance of infection was 5-20 times higher in the adult ticks than in the nymphae. When larval and nymphal R. appendiculatus Muguga and R. appendiculatus McIlwaine were fed to repletion on cattle infected with T. parva Boleni, a parasite causing subacute infection, resultant adult tick batches had a relatively high prevalence of infection, but infection was not detected in resultant nymphal batches. When cattle that were carriers of 2 stocks of T. parva, Marikebuni and Kiambu 5, were used as the source of infection, the infections developing in adult R. appendiculatus Muguga ticks were much higher than those developing in nymphae. The structure of salivary glands differed between nymphal ticks, adult males and adult females, and this is considered to be an important factor affecting the infection levels. The morphology of the type III acini, the target acini for sporogony, was similar, but the mean numbers of type III acini were different, with 87 in nymphae, 1346 in males and 1736 in females. This difference was correlated with the different tick instars and sexes was similar, the rate of sporogony was fastest in feeding nymphae, taking on average 2-3 days. compared to 3-4 days in females and an irregular period in the males. These results are discussed in relation to the epidemiology of T. parva.

Vector competence of 7 rhipicephalid tick stocks in transmitting 2 Theileria parva parasite stocks from Kenya and Zimbabwe

The competence of 7 different stocks of Rhipicephalus appendiculatus and R. zambeziensis to transmit 2 different stocks of Theileria parva was compared by feeding nymphae of each tick stock simultaneously on infected cattle and assessing the infections in the salivary glands of the resultant adult ticks. There were significant differences in the patterns of infection of the 2 stocks (T. parva Muguga and T. parva Boleni) in the different stocks of ticks, and these differences were shown to be reproducible. The Muguga tick stock from Kenya and the Zambia tick stock from Eastern Province had the highest infections of T. parva Muguga and T. parva Boleni respectively. The Zambia Southern Province tick stock and the Zimbabwe Mashonaland West tick stock had the lowest infections of T. parva Muguga and T. parva Boleni respectively. The difference in mean abundance of infection between the most and least efficient vector for T. parva Muguga was 63.3 while that for T. parva Boleni was 54.4 infected acini. The implications of these results for laboratory transmission of T. parva and for the epidemiology of theileriosis are discussed.

Host–parasitoid population density prediction using artificial neural networks: diamondback moth and its natural enemies

1 An integrated pest management (IPM) system incorporating the introduction and field release of Diadegma semiclausum (Hellén), a parasitoid of diamondback moth (DBM) Plutella xylostella (L.), comprising the worst insect pest of the cabbage family, has been developed in Kenya to replace the pesticides‐only approach. 2 Mathematical modelling using differential equations has been used in theoretical studies of host–parasitoid systems. Although, this method helps in gaining an understanding of the systems dynamics, it is generally less accurate when used for prediction. The artificial neural network (ANN) approach was therefore chosen to aid prediction. 3 The ANN methodology was applied to predict the population density of the DBM and D. semiclausum, its larval parasitoid. Two data sets, each from different release areas in the Kenya highlands, and both collected during a 3‐year period after the release of the parasitoid, were used in the present study. Two ANN models were developed using these data. 4 The ANN approach gave satisfactory results for DBM and for D. semiclausum. Sensitivity analysis suggested that pest populations may be naturally controlled by rainfall. 5 The ANN provides a powerful tool for predicting host–parasitoid population densities and made few assumptions on the field data. The approach allowed the use of data collected at any appropriate scale of the system, bypassing the assumptions and uncertainties that could have occurred when parameters are imported from other systems. The methodology can be explored with respect to the development of tools for monitoring and forecasting the population densities of a pest and its natural enemies. In addition, the model can be used to evaluate the relative effectiveness of the natural enemies and to investigate augmentative biological control strategies.

Estimation of heritability of susceptibility to infection with Theileria parva in the tick Rhipicephalus appendiculatus

Heritability of susceptibility to infection with Theileria parva was estimated from full sib families of Rhipicephalus appendiculatus ticks. Male and female ticks of 2 stocks were mated singly. Nineteen full sib families of the Muguga stock and 17 full sib families of the Kiambu stock were obtained. Nymphae of these families were fed on cattle infected with T. parva so that the ticks became replete on days 16 and 17 after infection when the blood was parasitaemic with intraerythrocytic piroplasms. The T. parva infections were assessed in the resultant adult ticks of each full sib group and the abundance of infection, the number of salivary gland acini infected/tick, was found to be the most useful parameter for analysis. Estimates of heritability of the susceptibility to infection with T. parva for the Kiambu and the Muguga tick stocks were 0.24 and 0.26 respectively. Using only the data from ticks which fed on day 16, the heritability estimates were 0.39 for the Kiambu stock and 0.59 for the Muguga stock. These results indicate that tick lines of high or low susceptibility for T. parva infection could be produced through selection.

The effect of temperature on the rate of transmission of Theileria parva parva infection to cattle by its tick vector, Rhipicephalus appendiculatus

A steer was infected with Theileria parva parva Kilae stabilate; nymphal Rhipicephalus appendiculatus ticks were applied to its ears so that they completed repletion when the steer had a high piroplasm parasitaemia. The engorged nymphs were subsequently incubated at 28 degrees C for 26-29 days to complete moulting, when the adult ticks were divided into two groups; one was incubated at 18 degrees C for 20 days and the other at 18 degrees C for 14 days and then at 37 degrees C for 6 days. Groups of ticks incubated at 37 and 18 degrees C were triturated and each resultant supernatant fluid inoculated into a steer. Both steers became infected, but the 37 degrees C supernatant group showed a much shorter pre-patent period to schizonts. Groups of ticks incubated at 37 or 18 degrees C were applied to pairs of cattle for 24, 48 and 72 h and then removed. There was a more rapid transmission of theileriosis to cattle by ticks kept at high ambient temperatures compared to those kept at low ambient temperatures. All cattle on which ticks treated at 37 degrees C were applied developed acute and fatal T. parva infection irrespective of the duration of tick application, while only 1 animal receiving ticks treated at 18 degrees C and fed for 72 h developed infection. The pre-patent period for macroschizonts was very short in all the groups receiving ticks incubated at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Survival of Theileria parva in its nymphal tick vector, Rhipicephalus appendiculatus, under laboratory and quasi natural conditions

Groups of nymphal Rhipicephalus appendiculatus Muguga, having a mean of 1 or 9 Theileria parva Muguga-infected salivary gland acini per tick, were kept under quasi-natural conditions at an altitude of 1950 m or 20 degrees C at a relative humidity of 85% in the laboratory and their survival and infection prevalence and abundance determined over time. Theileria parva infections for both categories of ticks survived in the nymphal ticks for 50 or 26 weeks post salivary gland infection under quasi-natural or laboratory conditions respectively. There was a distinct decline in infections in the more heavily infected nymphae under both conditions of exposure, reflecting an apparent density dependence in parasite survival. Nymphal ticks having an average infection level of 1 infected salivary gland acinus per tick, survived for up to 69 or 65 weeks post-repletion under quasi-natural or the laboratory conditions respectively. Nymphae having an average infection level of 9 infected salivary gland acini per tick survived for a similar duration under each of the 2 conditions. The infection level of 9 infected salivary gland acini per tick did not seem to significantly affect the survival of the tick vector compared to those having an average of 1 infected salivary gland acinus per tick.

Evaluation of an antigen-ELISA in the diagnosis of bovine cysticercosis in Kenyan cattle

A monoclonal antibody-based antigen-ELISA (Ag-ELISA) was studied in Kenyan cattle with the objective of evaluating its reliability in diagnosing bovine cysticercosis. A total of 55 cattle divided into artificially (n = 30) and naturally (n = 25) infested animals, were utilized. Total dissection was used as a gold standard of validity at autopsy. In natural infestations, the assay identified 16 cases as true seropositives, 2 cases as false seropositives, 3 cases as true seronegatives and 4 cases as false seronegatives. While in artificial infestations, the assay identified 9 cases as true seropositives, 14 cases as true seronegatives and 7 cases as false seronegatives. There weren’t any false seropositive cases identified with artificial infestations. The assay showed good precision level and kappa level in quantifying the relative quality of the amount of agreement in natural (n = 25; k = 0.482; p > 0.05) and artificial (n = 24; k = 0.374; p > 0.05) infestations. The study showed that, besides other advantages, the Ag-ELISA with its sensitivity of 60.00–80.00%, specificity of 60.00–100%, predictive value of 88.89–100%, apparent prevalence of 37.50–72.00% and accuracy of 75.00–76.00% may be recommended for use in combination with other control measures, viz chemotherapy, post-mortem diagnosis and or vaccination.

Experimental evaluation of inactivated and live attenuated vaccines against Mycoplasma mycoides subsp. mycoides

The current control method for contagious bovine pleuropneumonia (CBPP) in Africa is vaccination with a live, attenuated strain of Mycoplasma mycoides subsp. mycoides (Mmm). However, this method is not very efficient and often causes serious adverse reactions. Several studies have attempted to induce protection using inactivated mycoplasma, but with widely contradictory results. Therefore, we compared the protective capacity of the live T1/44 vaccine with two inactivated preparations of Mmm strain Afadé, inoculated with an adjuvant. Protection was measured after a challenge with Afadé. The protection levels were 31%, 80.8% and 74.1% for the formalin-inactivated, heat-inactivated and live attenuated preparations, respectively. These findings indicate that low doses of heat-inactivated Mmm can offer protection to a level similar to the current live attenuated (T1/44) vaccine formulation.

Comparison of the survival of Theileria parva-infected adult Rhipicephalus appendiculatus (Acari: Ixodidae) and their infection under simulated climate conditions in the laboratory and in the field

Five groups of adult Rhipicephalus appendiculatus Neumann, with an average of 98 Theileria parva-infected salivary gland acini per tick, were exposed to four different temperature conditions in the laboratory or to quasi-natural conditions in Kenya. The survival of the infected ticks and T. parva parasites in their salivary glands were determined over time. Ticks kept under quasi-natural conditions survived up to 86 weeks. This period was longer than that of ticks exposed to any of the four laboratory conditions, except the diurnal temperature rhythm of 13–23 °C and 85% relative humidity (RH) to which it was comparable. Theileria parva survived for 82 weeks in ticks exposed to quasi-natural conditions, a period which was much longer than that of the parasites in ticks maintained under any of the laboratory conditions. Survival of the infected ticks and their infections seemed to be adversely affected by higher temperatures in the laboratory or drought in the field. There was an apparent density-dependent influence in parasite survival, with a dramatic fall in infection occurring in the more highly infected ticks before stabilizing at lower levels.RésuméResume: Cinq groupes de Rhipicephalus appendiculatus Neumann adultes avec un taux moyen d’infestation de leurs glandes salivaires de 98% par Theileria parva, ont été exposés à quatre conditions de température différentes au laboratoire et à des conditions presque naturelles. La survie des tiques et de leurs parasites a été suivie dans le temps. Les tiques maintenues en conditions naturelles ont survécu près de 86 semaines. Cette durée de survie est supérieure à celles observées dans les autres conditions de laboratoire, à l’exception des tiques maintenues à un rythme de températures de 13–23°C et une humidité relative de 85%. Theileria parva a survécu près de 82 semaines dans les tiques maintenues en conditions naturelles, une durée de survie supérieure à celles des parasites maintenues en conditions de laboratoire. La survie des tiques et de leurs parasites semble être altérée par les températures élevées du laboratoire et par la sécheresse des conditions naturelles. Il semble que la survie du parasite est fortement influencée par la densité, avec une chute drastique de l’infection sur les tiques fortement infestées, suivie d’une stabilisation aux faibles valeurs.

Survival of Theileria parva-infected adult Rhipicephalus appendiculatus under laboratory and quasi-natural conditions

Adult Rhipicephalus appendiculatus Muguga, having high or low intensities of Theileria parva Muguga infection in their salivary glands, were exposed to 20 °C and 85% relative humidity in the laboratory or quasi-natural conditions. Survival of the ticks and T. parva infections in their salivary glands was then monitored over a two year period. Ticks, having an average infection level of 2 infected acini per female, survived for up to 70 or 106 weeks after moulting under the laboratory or quasi-natural conditions respectively. Those having an infection level of 26 infected acini per female, survived for a similar duration except that those under quasi-natural conditions survived for a slightly shorter duration (102 weeks). Similarly, T. parva parasites survived for much longer periods under quasi-natural conditions than under the laboratory conditions. They survived for up to 38 or 78 weeks post salivary gland infection under the laboratory or quasi-natural conditions respectively in both categories of infection levels. There was apparently a density dependent relationship in T. parva survival, with a dramatic fall in infection occurring in ticks with high levels of infection between weeks 10 and 18 or weeks 38 and 46 post salivary gland infection in those exposed to laboratory or quasi-natural conditions before levelling off.