Molecular epidemiology of Theileria parva in the field.
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Molecular tools based on seminested RFLP-PCR techniques to characterize field parasites in bloodspots dried on filter paper permitted investigation of the extent and the dynamics of diversity of Theileria parva populations in the field. Parallel molecular studies explored the long-term genome stability of various isolates by probing Southern blots of EcoRI digested total genomic DNA with four different reference nucleic acid probes. Three polymorphic single copy loci encoding for antigen genes were developed for seminested PCR detection in order to apply them for a multilocus approach in population genetic studies. Seven alleles were identified for the polymorphic immunodominant molecule (PIM) locus by using restriction enzymes, and 4 alleles each for the p150 and p104 loci. A simple DNA extraction method gave good results in amplifying these loci from carrier animals using samples of blood dried on filter papers. Results from probing Southern blots of cultures taken at sequential timepoints indicate relative genome stability in T. parva in comparison to other parasitic protozoa such as Plasmodium. Comparatively homogeneous profiles in sympatric isolates from Zambia were identified using all four probes and PCR amplified products which contrasted with the variety found amongst Kenyan stocks. Preliminary characterization of T. parva field samples from the Southern Province of Zambia strongly suggest clonal expansion of one of the components of a non-Zambian trivalent vaccine used on a limited scale in the Province from 1985 until 1992. (+info)
The current epidemiological status of bovine theileriosis in eastern Zambia.
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Results of a longitudinal study conducted in the eastern province of Zambia from 1994 to 1997 indicate that it is doubtful whether a state of endemic stability of East Coast fever (ECF) can be reached in the near future. Even in endemic areas, the mortality of Theileria parva infections is still estimated above 50%. The main factors limiting progress towards endemic stability are high innate susceptibility of the Zebu cattle, the virulence of the parasite and the climate. The unimodal rainfall pattern results in restricted activity of Rhipicephalus appendiculatus instars and year-to-year variation in rainfall causes fluctuations in tick phenology and T. parva transmission. Adult tick activity invariably peaks during the rains and is associated with the highest ECF incidence. Nymphal transmission of T. parva to cattle appears to be less important. Second periods of activity of both adult and nymphal instars are pronounced only when the climate is suitable. These second waves of tick activity ensure a more continuous and efficient transmission of T. parva and also play a key role in the dynamics of prolonged outbreaks in epidemic areas. ECF control methods may have an important influence on ECF epidemiology. Immunizations as well as chemotherapy of clinical cases create a reservoir of virulent parasites in susceptible cattle, resulting in artificial endemic stability. (+info)
Spatial and temporal variation in Rhipicephalus appendiculatus size in eastern Zambia.
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The size of Rhipicephalus appendiculatus collected at different altitudes in the Eastern Province of Zambia between February 1985 and May 1986 and between October 1994 and December 1996 showed distinct variation dependent on altitude and season. The ticks were smallest during the dry season and at the start of the rains, and specimens were larger as the rainy season progressed. Second-generation adults where on average smaller than first-generation ticks. At higher altitudes, where a one-generation-per-annum phenology dominates, ticks were larger than at intermediate altitudes, where two generations per year are common. Larger size, associated with increased survival, is also favoured in low-lying, drier areas. Selective mortality of smaller adult ticks in years with a delayed rainy season appears to play an important role in the variation in size between years. (+info)
Economics of theileriosis control in Zambia.
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For an economic analysis of theileriosis control, we adopted the total economic cost (TEC) method, which calculates the sum of output losses from tick damage, theileriosis mortality and morbidity, and expenditures for treatment or prevention of the disease. At farm level, the TEC can be minimized by a specific combination of vector control and/or immunization and an acceptable level of losses. Expenditures for vector control include acaricides, construction of dipping or spraying facilities and their maintenance, and variable costs such as those for water and labour. Economics of vector control depend on the herd size and the method of application of the acaricide. Morbidity, mortality and tick damage losses are effectively reduced by correct and intensive vector control programmes. Expenditures for vector control are estimated at US$ 8. 43, 13.62 and 21.09 per animal per year for plunge dipping, hand spraying and pour-on, respectively. Immunization costs comprise production of parasite stabilates, storage and application, delivery and treatment. At US$ 9.5 per animal, immunization limits losses caused by Theileria parva, but ticks still may reduce the productivity of the animals. Expenditures for treatment after natural infection involve drugs, transport, veterinary fees and farm labour costs. Treatment has a moderate success rate, hence both morbidity and mortality remain important factors. Equally, it does not affect the vector, which may continue to reduce overall productivity of cattle. Expenditures for treatment range between US$ 9.04 and US$ 27.31 per animal. To compare different TECs in relation to different control strategies, assumptions have to be made on disease occurrence, case fatality, value and productivity of the cattle, reductions in productivity due to morbidity and number of animals under a specific control regime. Calculations based on data from Southern Province, Zambia show that large-scale immunization reduces the TEC by 90% compared to no intervention. Treatment, which is the second-best option, reduces the TEC by 60%. Appendix 1 Summary of factors influencing total economic cost (+info)
Theileriosis control modelling (experiences from Southern Province, Zambia).
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Effects of different tick-borne disease control strategies on cattle productivity are simulated based on a 30-year herd projection, calculated by a modified Markov Chain model. Input data can be grouped in technical, economic and epidemiological parameters. The output is a set of economic parameters such as benefit/cost ratio (BCR), net present value (NPV) of the profit, internal rate of return (IRR), total economic cost (TEC) as well as graphs showing animal production over time. Shadow prices are obtained for input and output in kind. Throughout the calculations a distinction is made between transactions in cash and transactions in kind. A case study was run for Southern Province, Zambia, to illustrate the model. Either vector control or treatment, or a combination of these, controls theileriosis at farm level after natural infection. Preventive immunization against the parasite is also possible. Although the calculations are based on a mixture of data obtained from literature, field experience, expert opinion and assumptions, the importance of theileriosis control is clearly indicated. Immunization gives better economic results than chemotherapy. Vector control can only be used as a last resort. (+info)
A community perspective on the efficacy of malaria treatment options for children in Lundazi district, Zambia.
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In 1996, Zambia's Ministry of Health made sulfadoxine-pyrimethamine (SP) available as a second-line antimalarial. SP differs from chloroquine (CQ) in ways that might affect parents' acceptance of the drug, resulting in possible delays in seeking treatment if parents perceive SP as less efficacious. A multifaceted study consisting of a rapid community ethnographic assessment to examine local attitudes and perceptions toward malaria, a 14-day in vivo drug efficacy study comparing clinical and parasitological efficacy of CQ, SP, and SP with paracetamol (PCM) in children under five, and a qualitative study examining caretakers' perceptions of drug efficacy helped to guide implementation of the new drug policy. The rapid ethnographic study indicated that the community was aware of malaria as an illness best treated with modern medicines, particularly CQ. The drug efficacy study demonstrated a 25% level of clinical failures compared to none with SP, and 30% of the children treated with CQ had either RIII or RII parasitological failures whereas none occurred in children treated with SP. Most parents perceived that their children were improving and that the drugs were working. Parents in the SP groups were most pleased and readily accepted SP as a new drug. The addition of PCM did not improve perceptions of SP efficacy, contradicting conventional wisdom regarding the need for direct antipyretic action for parents to perceive a drug as efficacious. The combined results reflected a community that was in the beginning stages of evaluating a new malaria therapy mostly unknown to them. Perceptions of efficacy of CQ were beginning to shift, indicating a readiness for accepting a new drug based on its shown biological efficacy. Parasitological and clinical failure rates reinforced the need to fully implement the changed national policy as soon as possible, and to consider a change in first-line therapy. (+info)
Zambia: the role of aid management in sustaining visionary reform.
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As part of its ongoing reform of the health sector, Zambia has developed a number of systems and structures to coordinate and manage external resources. With increasing attention being given to the potential for sector-wide approaches (SWAps) to enhance the efficiency and effectiveness of health systems in low-income countries, Zambia provides an interesting case study of how this is emerging in practice over time. The paper outlines the different coordination mechanisms and assesses them in terms of selected criteria of effectiveness, finding that the potential to meet reform objectives is currently not being met. Factors influencing the effectiveness of these mechanisms are identified as falling into categories around personalities and human interaction, the nature of reform processes, and the impact of broader context. The need to maintain dialogue in the face of external constraints and uncertainties is stressed. (+info)
Severe linear growth retardation in rural Zambian children: the influence of biological variables.
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BACKGROUND: The prevalence of stunting in preschool children in Zambia is high; stunting has detrimental effects on concurrent psychomotor development and later working capacity. OBJECTIVE: Our objective was to investigate biological variables that may contribute to linear growth retardation in preschool children in Samfya District, Zambia. DESIGN: Children aged 6-9 mo (n = 108) and 14-20 mo (n = 102) attending mother-and-child health clinics were included. With a mixed-longitudinal design, they were followed up 9 and 21 mo later. Height and weight of children and their mothers were measured. Biochemical measures (eg, serum zinc, retinol, thyrotropin, iron, and acute phase protein concentrations), malaria parasitemia, and intestinal parasitosis were assessed. RESULTS: Height-for-age z scores (HAZ) were low, indicating a high prevalence of stunting (36-79%). Ninety percent of the children were anemic, 53-71% had elevated acute phase proteins, and 80% had malaria parasitemia. Regression analyses showed that maternal height predicted the children's height at 6-9 mo (regression coefficient = 0.05; 95% CI: 0.02, 0.08). The children's height at an early age (6-9 and 14-20 mo) showed a strong relation with their height at later ages (22-30 and 34-41 mo). Serum micronutrient status did not show a significant relation with later HAZ. CONCLUSION: Unlike other studies, we did not identify specific biological factors, such as health and micronutrient status, which contribute to the retardation of linear growth. The normal zinc and iodine statuses of the children suggest that at least these factors are not causal. (+info)