Roger Ruppanner

An epidemiologic systems analysis model for African trypanosomiasis

Abstract Systems analysis and simulation modelling were applied to describe the quantitative epidemiology of trypanosomiasis. With the aid of a causal loop diagram, and based on mechanistic decomposition of the components of the trypanosomiasis-tsetse complex, a Forrester flow diagram was developed. Interactions between factors in the system and variables required in the model were estimated from existing data. Appropriate differential equations were set up to describe the dynamics of the model based on mass action theory. Simulation involved integrating birth and death rates, infection and population dynamics as they relate to the carrying capacity of the land, and fluctuations in temperature and rainfall. Both deterministic and stochastic aspects were considered. The model was computerized using a continuous systems modelling program and integration time intervals of one day. Simulations were run using various initial conditions as provided by data from southwestern Ethiopia. The performance of the model was satisfactory when compared with an independent set of data. The procedure enhanced our understanding of the dynamics of the trypanosomiasis-tsetse complex; it could thus be used as a guide to evaluating different programs to control trypanosomiasis in Ethiopia and in other African countries.

Application of a linear programming model to the control of African trypanosomiasis

Abstract A linear programming (LP) model was designed to evaluate trypanosomiasis control activities in south-western Ethiopia. The objectives included maximizing net benefits, utilization of unskilled labor, and resettlement of reclaimed land, and decreasing the prevalence of trypanosomiasis from 20% to less than 5% at the end of 5 years, subject to epidemiological, ecological and economic constraints. The model was a multiperiod specification with 127 equations and 81 activities for the project period of 5 years. The optimal solution required reclamation of 5221 km 2 of tsetse infested land and used treatment of cattle at maximal levels. At the end of the project period, the prevalance decreased to 2% with net benefits of E

Evaluation of trypanosomiasis control alternatives using an epidemiologic simulation model

1.281 million. LP provided a potentially optimal means of resource allocation in the short run and a means of identifying those restrictive resources which could be vital to long range planning.

The benefit—cost analysis of alternative strategies for the control of bovine trypanosomiasis in Ethiopia

Abstract The effect of various disease-vector control alternatives on the prevalence of trypanosomiasis in southwest Ethiopia was examined with the aid of an epidemiologic model. The alternatives considered included vegetation clearing by manual labor, game elimination, insecticidal spraying from airplanes coupled with settlement, use of sterile male Glossina , avoidance of tsetse infested areas, increasing the resistance of the cattle population, therapy, and combinations of the above methods. First, the currently estimated endemic prevalence of trypanosomiasis (27.3%) in the simulated area of Ethiopia was established and maintained over a 10 year period. Then, various control alternatives were introduced and the simulation was run for an additional 10 years to observe the effect of these control alternatives on the prevalence. The combined use of vegetation clearing, insecticides, therapy, and settlement (or resettlement) was the most effective and feasible method of trypanosomiasis control for the simulated situation.

Epidemic and endemic characteristics of trypanosomiasis in cattle: A simulation model

Abstract A benefit—cost analysis of trypanosomiasis control programs for an area of 1500 km2 in southwest Ethiopia, for a project span of 15 years at a discount rate of 10%, was conducted to determine cost effective and benefit maximizing alternatives. The trypanosomiasis control scenarios considered were: (a) reduction of tsetse flies by use of insecticides sprayed from knapsacks, (b) game reduction, (c) no control program. Information on costs was obtained from existing data. A Leslie type model was utilized to simulate the cattle population dynamics in southwest Ethiopia for trypanosomiasis controlled versus uncontrolled situations. From these results costs and benefits of control were quantified. The benefit—cost analysis using net present values (NPV) and benefit/cost (B/C) ratio as decision criteria of project feasibility and efficiency, indicated that insecticide application was preferable to game reduction. Estimates of present value costs were E

Estimating the probability of effective transmission of trypanosomes using the poisson distribution

630.17 per km2 per year while the present value benefits were E

Determination of risk groups to African trypanosomiasis using discriminant analysis

720.24 per km2 per year. The B/C ratio was 1.14 and net present value of the project was E

Q fever vaccination of sheep: challenge of immunity in ewes.

2.03 million. Sensitivity analysis and implications of the results are discussed.

Enzyme immunoassay for surveillance of Q fever

Abstract A simulation model was utilized to analyze the infection characteristics of trypanosomiasis in Ethiopian cattle. Epidemic and endemic conditions, the threshold phenomenon, proportional distribution of single, multiple and super infections were examined. The results indicate that at the endemic level the prevalence of trypanosomiasis was 0.27 and the incidence varied from 0.007 to 0.01. A large proportion of the infections were of the single type; multiple and surper infections were rare. The importance of such information lies in its usefulness in evaluating control alternatives.

Q fever (Coxiella burnetii) investigations in dairy cattle: challenge of immunity after vaccination.

Abstract The trypanosome infection rate in cattle is determined by the probability of effective transmission (PET) of trypanosome from Glossina spp. to susceptible cattle. The PET in turn is a function of the rate of contact between cattle and Glossina spp. and was calculated using a Poisson probability distribution. Seven parameters determined the final form of the PET. These were: probability of at least one contact with Glossina spp. (PTC), probability that Glossina spp. will feed on the host (PFF), proportion of Glossina spp. which are non-tenerals (PNT), proportion of infected Glossina spp. (PTI), proportion of infected Glossina spp. which are infectious (PMTI), proportion of successful transmissions of the infective agent in inoculum of infectious Glossina spp. (PII), and finally, the probability for the presence of a susceptible host animal (PC). The product of these proportions provided an estimate of effective transmission of trypanosomes from infectious Glossina to susceptible cattle. The probability of this event varied between (0.0007 and 0.0009) or 7–9 infections per 10 000 susceptible cattle per year at a steady state.