Climate change and African trypanosomiasis vector populations in Zimbabwe's Zambezi Valley: A mathematical modelling study

Abstract

BackgroundQuantifying the effects of climate change on the entomological and epidemiological components of vector-borne diseases is an essential part of climate change research, but evidence for such effects remains scant, and predictions rely largely on extrapolation of statistical correlations. We aimed to develop a mechanistic model to test whether recent increases in temperature in the Mana Pools National Park of the Zambezi Valley of Zimbabwe could account for the simultaneous decline of tsetse flies, the vectors of human and animal trypanosomiasis.Methods and findingsThe model we developed incorporates the effects of temperature on mortality, larviposition, and emergence rates and is fitted to a 27-year time series of tsetse caught from cattle. These catches declined from an average of c. 50 flies per animal per afternoon in 1990 to c. 0.1 in 2017. Since 1975, mean daily temperatures have risen by c. 0.9°C and temperatures in the hottest month of November by c. 2°C. Although our model provided a good fit to the data, it cannot predict whether or when extinction will occur.ConclusionsThe model suggests that the increase in temperature may explain the observed collapse in tsetse abundance and provides a first step in linking temperature to trypanosomiasis risk. If the effect at Mana Pools extends across the whole of the Zambezi Valley, then transmission of trypanosomes is likely to have been greatly reduced in this warm low-lying region. Conversely, rising temperatures may have made some higher, cooler, parts of Zimbabwe more suitable for tsetse and led to the emergence of new disease foci.

Bibliometric analysis of peer-reviewed literature on climate change and human health with an emphasis on infectious diseases

“…For example, changes in temperature have serious adverse effects on the pattern and incidence of infectious diseases [22]. Global warming favors the survival and transmission of causative pathogens or vectors of the causative agent [23][24][25][26][27]. Climate change influences the dynamics of vector-borne, water-borne, foodborne, rodent-borne, and air-borne infectious diseases [28,29].…”

Models for the rates of pupal development, fat consumption and mortality in tsetse (Glossinaspp)

“…Temperature takes centre stage in relation to various aspects of the fly's life, affecting rates of mortality and of fat metabolism in adults and pupae, and rates of larviposition and pupal development. These rates provide important inputs for an increasing number of models of tsetse population dynamics (Vale & Torr, 2005;Torr & Vale, 2011;Hargrove et al, 2012;Moore et al, 2012;Ackley & Hargrove, 2017;Lord et al, 2018), using techniques varying from spreadsheet models to differential equations. Recently, there has also been a growing interest in using agent-based modelswhere the lives of individual tsetse are followed at short discrete time intervals (Alderton et al, 2013(Alderton et al, , 2016(Alderton et al, , 2018Lin et al, 2015;Grébaut et al, 2016).…”

The weakest link: uncertainty and sensitivity analysis of extinction probability estimates for tsetse (Glossina spp) populations

“…Accordingly, in order to investigate the sensitivity to this uncertainty we sample values from prior distributions of these parametes. We define prior probability distribution functions for each of the input parameters, based on the studies done on the life cycle of tsetse published in the literature [17, 18]. The probability distribution functions are given in Table 3, where β, N and U denote beta, normal and uniform distributions, respectively.…”