The Effect of Increasing Water Temperatures on Schistosoma mansoni Transmission and Biomphalaria pfeifferi Population Dynamics: An Agent-Based Modelling Study

Abstract

IntroductionThere is increasing interest in the control and elimination of schistosomiasis. Little is known, however, about the likely effects of increasing water-body temperatures on transmission.MethodsWe have developed an agent-based model of the temperature-sensitive stages of the Schistosoma and intermediate host snail life-cycles, parameterised using data from S. mansoni and Biomphalaria pfeifferi laboratory and field-based observations. Infection risk is calculated as the number of cercariae in the model, adjusted for their probability of causing infection.ResultsThe number of snails in the model is approximately constant between 15–31°C. Outside this range, snail numbers drop sharply, and the snail population cannot survive outside the range 14–32°C. Mean snail generation time decreases with increasing temperature from 176 days at 14°C to 46 days at 26°C. Human infection risk is highest between 16–18°C and 1 pm and 6–10 pm in calm water, and 20–25°C and 12–4 pm in flowing water. Infection risk increases sharply when temperatures increase above the minimum necessary for sustained transmission.ConclusionsThe model suggests that, in areas where S. mansoni is already endemic, warming of the water at transmission sites will have differential effects on both snails and parasites depending on abiotic properties of the water-body. Snail generation times will decrease in most areas, meaning that snail populations will recover faster from natural population reductions and from snail-control efforts. We suggest a link between the ecological properties of transmission sites and infection risk which could significantly affect the outcomes of interventions designed to alter water contact behaviour – proposing that such interventions are more likely to reduce infection levels at river locations than lakes, where infection risk remains high for longer. In cooler areas where snails are currently found, increasing temperatures may significantly increase infection risk, potentially leading to new, high-intensity foci of infection.

Experimental and modelling investigations of Opisthorchis viverrini miracidia transmission over time and across temperatures: implications for control

“…This influence of temperature on transmission outcomes via host-parasite encounter modulation has been similarly reported in several other host-parasite systems (Tubbs et al, 2005; van Dijk and Morgan, 2008; Tinsley et al, 2011), including other parasites of medical and veterinary significance such as Fasciola hepatica (Mas-Coma et al, 2009) and Schistosoma spp. (McCreesh and Booth, 2013, 2014a, b). …”

The spatial distribution of Schistosoma mansoni infection in four regions of western Côte d’Ivoire

“…*Significant correlation based on 95% confidance interval or 95% Bayesian credible interval. (Foster, 1964;Appleton, 1978;Kloos et al, 2001;Malone, 2005;McCreesh and Booth, 2014). A possible explanation for the observed higher prevalences of S. mansoni infection in the lower parts of the mountainous Tonkpi region may be the favourable temperature and velocity of rivers for B. pfeifferi (Shiff and Husting, 1966).…”

“…Altitude is also an important factor associated with the occurrence of schistosomiasis (Kabatereine et al, 2004;Raso et al, 2005). Biomphalaria pfeifferi, the intermediate host snail of S. mansoni, requires temperature values ranging between 15 and 31°C and pH values ranging from 6.8 to 8.6, to thrive successfully (Utzinger et al, 1997;McCreesh and Booth, 2014;Walz et al, 2015). Bulinus globosus, one of the intermediate host snails of S. haematobium, shows preferences for freshwater bodies with temperatures ranging from 14 to 32°C and pH values from 6.0 to 7.8 (Woolhouse and Chandiwana, 1990;Yapi et al, 2014c;Walz et al, 2015).…”

Universal Stress Proteins as New Targets for Environmental and Therapeutic Interventions of Schistosomiasis

“…The range in water temperature has important bearing on the hatching of eggs and shedding of cercariae. Warming of water may decrease or increase the number of snails, especially in endemic areas, which in turn has an effect on snails being infected with cercariae [37]. Eggs hatch between 10 °C and 30 °C even though temperatures vary between 30 °C and 38 °C in a period of 17 days based on the time miracidia first penetrate snail tissue and snails release cercariae [38].…”