Mathematical modelling and control of African animal trypanosomosis with interacting populations in West Africa-Could biting flies be important in main taining the disease endemicity?

Paul Olalekan Odeniran,Akindele Akano Onifade,Simon Alderton,Susan Christina Welburn,Ewan Thomas Macleod,Isaiah Oluwafemi Ademola,Simon Clegg

doi:10.1371/journal.pone.0242435

Abstract

African animal trypanosomosis (AAT) is transmitted cyclically by tsetse flies and mechanically by biting flies (tabanids and stomoxyines) in West Africa. AAT caused by Trypanosoma congolense, T. vivax and T. brucei brucei is a major threat to the cattle industry. A mathematical model involving three vertebrate hosts (cattle, small ruminants and wildlife) and three vector flies (Tsetse flies, tabanids and stomoxyines) was described to identify elimination strategies. The basic reproduction number (R0) was obtained with respect to the growth rate of infected wildlife (reservoir hosts) present around the susceptible population using a next generation matrix technique. With the aid of suitable Lyapunov functions, stability analyses of disease-free and endemic equilibria were established. Simulation of the predictive model was presented by solving the system of ordinary differential equations to explore the behaviour of the model. An operational area in southwest Nigeria was simulated using generated pertinent data. The R0 < 1 in the formulated model indicates the elimination of AAT. The comprehensive use of insecticide treated targets and insecticide treated cattle (ITT/ITC) affected the feeding tsetse and other biting flies resulting in R0 < 1. The insecticide type, application timing and method, expertise and environmental conditions could affect the model stability. In areas with abundant biting flies and no tsetse flies, T. vivax showed R0 > 1 when infected wildlife hosts were present. High tsetse populations revealed R0 <1 for T. vivax when ITT and ITC were administered, either individually or together. Elimination of the transmitting vectors of AAT could cost a total of US$ 1,056,990 in southwest Nigeria. Hence, AAT in West Africa can only be controlled by strategically applying insecticides targeting all transmitting vectors, appropriate use of trypanocides, and institutionalising an appropriate barrier between the domestic and sylvatic areas.

Highlights

African animal trypanosomosis is a major constraint to sustainable livestock development in sub-Saharan Africa [1]
We evaluated the probability of the model in the preliminary report conducted in southwest Nigeria and explained the reality of its elimination
The growth can be narrowed if there is a problem with the balance such as problems of trypanocidal and insecticidal resistance, changing climate, epidemics from other infectious diseases, ecological instability and human activities

Summary

Introduction

African animal trypanosomosis is a major constraint to sustainable livestock development in sub-Saharan Africa [1]. Tsetse flies (genus: Glossina) are the biological vectors of AAT caused by extracellular protozoan parasites of the genus Trypanosoma. The major causal organisms in livestock and wildlife are T. congolense, T. vivax and T. brucei brucei. There are other trypanosome species which are of significant importance to the livestock herds such as T. evansi and T. simiae. There are complexities in the transmission dynamics of AAT. While Trypanosoma brucei rhodesiense, a common human pathogen has been incriminated to infect cattle in eastern Africa [2], the pathogen is absent in western Africa. Trypanosoma brucei gambiense which affect humans in West Africa is rarely observed in livestock [3]

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Conclusion