Limits...
Potential effects of warmer worms and vectors on onchocerciasis transmission in West Africa.

Cheke RA, Basáñez MG, Perry M, White MT, Garms R, Obuobie E, Lamberton PH, Young S, Osei-Atweneboana MY, Intsiful J, Shen M, Boakye DA, Wilson MD - Philos. Trans. R. Soc. Lond., B, Biol. Sci. (2015)

Bottom Line: Small temperature increases (less than 2°C) might lead to changes in geographical distributions of different vector taxa.By contrast, analyses of field data on forest flies in Liberia and savannah flies in Ghana, in relation to regional climate change predictions, suggested, on the basis of simple regressions, that 13-41% decreases in fly numbers would be expected between the present and before 2040.Further research is needed to reconcile these conflicting conclusions.

View Article: PubMed Central - PubMed

Affiliation: Agriculture, Health and Environment Department, Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK r.a.cheke@greenwich.ac.uk.

ABSTRACT
Development times of eggs, larvae and pupae of vectors of onchocerciasis (Simulium spp.) and of Onchocerca volvulus larvae within the adult females of the vectors decrease with increasing temperature. At and above 25°C, the parasite could reach its infective stage in less than 7 days when vectors could transmit after only two gonotrophic cycles. After incorporating exponential functions for vector development into a novel blackfly population model, it was predicted that fly numbers in Liberia and Ghana would peak at air temperatures of 29°C and 34°C, about 3°C and 7°C above current monthly averages, respectively; parous rates of forest flies (Liberia) would peak at 29°C and of savannah flies (Ghana) at 30°C. Small temperature increases (less than 2°C) might lead to changes in geographical distributions of different vector taxa. When the new model was linked to an existing framework for the population dynamics of onchocerciasis in humans and vectors, transmission rates and worm loads were projected to increase with temperature to at least 33°C. By contrast, analyses of field data on forest flies in Liberia and savannah flies in Ghana, in relation to regional climate change predictions, suggested, on the basis of simple regressions, that 13-41% decreases in fly numbers would be expected between the present and before 2040. Further research is needed to reconcile these conflicting conclusions.

Show MeSH

Related in: MedlinePlus

Development times of immature stages of S. damnosum s.l. at different temperatures. (a) Eggs, (b) larvae, (c) pupae (Adapted from [26,27]) and (d) the temperature-dependent development function for O. volvulus (data extracted from articles where experiments were conducted in a variety of onchocerciasis vectors Simulium spp., see the electronic supplementary material, S1). Fitted lines are exponential functions, for which the formulae for a–c are given in table 3 (R2 values = 0.473, 0.496 and 0.391 for a, b and c, respectively). The fitted line for D is Duration to L3 = 49.884e−0.08T (where T = mean air temperature (°C); R2 = 0.695).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4342963&req=5

RSTB20130559F2: Development times of immature stages of S. damnosum s.l. at different temperatures. (a) Eggs, (b) larvae, (c) pupae (Adapted from [26,27]) and (d) the temperature-dependent development function for O. volvulus (data extracted from articles where experiments were conducted in a variety of onchocerciasis vectors Simulium spp., see the electronic supplementary material, S1). Fitted lines are exponential functions, for which the formulae for a–c are given in table 3 (R2 values = 0.473, 0.496 and 0.391 for a, b and c, respectively). The fitted line for D is Duration to L3 = 49.884e−0.08T (where T = mean air temperature (°C); R2 = 0.695).

Mentions: Cheke [26] collated data for the development of the different immature stages of the S. damnosum s.l. complex, a dataset which was extended by information from Crisp [27] and re-analysed. The temperature data for egg development ranged from 20°C to 33°C, those for larval development from 20°C to 31.5°C, and data for pupal development ranged from 24°C to 31.5°C; however, only five pupal data points were available. When temperature ranges were quoted in publications, weighted means were used in our analyses. All immature stages (eggs, larvae and pupae) showed a decrease in development time with increasing temperature, although data for low temperatures were unavailable. Functions of the form ΔS(Tw) = a exp(−bTw) were fitted to the data, where ΔS(Tw) is the development time of stage s (in days) as a function of water temperature Tw (°C), and s refers to eggs (E), larvae (L) or pupae (P). Parameter values for each stage are given in figure 2a–c.Figure 2.


Potential effects of warmer worms and vectors on onchocerciasis transmission in West Africa.

Cheke RA, Basáñez MG, Perry M, White MT, Garms R, Obuobie E, Lamberton PH, Young S, Osei-Atweneboana MY, Intsiful J, Shen M, Boakye DA, Wilson MD - Philos. Trans. R. Soc. Lond., B, Biol. Sci. (2015)

Development times of immature stages of S. damnosum s.l. at different temperatures. (a) Eggs, (b) larvae, (c) pupae (Adapted from [26,27]) and (d) the temperature-dependent development function for O. volvulus (data extracted from articles where experiments were conducted in a variety of onchocerciasis vectors Simulium spp., see the electronic supplementary material, S1). Fitted lines are exponential functions, for which the formulae for a–c are given in table 3 (R2 values = 0.473, 0.496 and 0.391 for a, b and c, respectively). The fitted line for D is Duration to L3 = 49.884e−0.08T (where T = mean air temperature (°C); R2 = 0.695).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4342963&req=5

RSTB20130559F2: Development times of immature stages of S. damnosum s.l. at different temperatures. (a) Eggs, (b) larvae, (c) pupae (Adapted from [26,27]) and (d) the temperature-dependent development function for O. volvulus (data extracted from articles where experiments were conducted in a variety of onchocerciasis vectors Simulium spp., see the electronic supplementary material, S1). Fitted lines are exponential functions, for which the formulae for a–c are given in table 3 (R2 values = 0.473, 0.496 and 0.391 for a, b and c, respectively). The fitted line for D is Duration to L3 = 49.884e−0.08T (where T = mean air temperature (°C); R2 = 0.695).
Mentions: Cheke [26] collated data for the development of the different immature stages of the S. damnosum s.l. complex, a dataset which was extended by information from Crisp [27] and re-analysed. The temperature data for egg development ranged from 20°C to 33°C, those for larval development from 20°C to 31.5°C, and data for pupal development ranged from 24°C to 31.5°C; however, only five pupal data points were available. When temperature ranges were quoted in publications, weighted means were used in our analyses. All immature stages (eggs, larvae and pupae) showed a decrease in development time with increasing temperature, although data for low temperatures were unavailable. Functions of the form ΔS(Tw) = a exp(−bTw) were fitted to the data, where ΔS(Tw) is the development time of stage s (in days) as a function of water temperature Tw (°C), and s refers to eggs (E), larvae (L) or pupae (P). Parameter values for each stage are given in figure 2a–c.Figure 2.

Bottom Line: Small temperature increases (less than 2°C) might lead to changes in geographical distributions of different vector taxa.By contrast, analyses of field data on forest flies in Liberia and savannah flies in Ghana, in relation to regional climate change predictions, suggested, on the basis of simple regressions, that 13-41% decreases in fly numbers would be expected between the present and before 2040.Further research is needed to reconcile these conflicting conclusions.

View Article: PubMed Central - PubMed

Affiliation: Agriculture, Health and Environment Department, Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, UK r.a.cheke@greenwich.ac.uk.

ABSTRACT
Development times of eggs, larvae and pupae of vectors of onchocerciasis (Simulium spp.) and of Onchocerca volvulus larvae within the adult females of the vectors decrease with increasing temperature. At and above 25°C, the parasite could reach its infective stage in less than 7 days when vectors could transmit after only two gonotrophic cycles. After incorporating exponential functions for vector development into a novel blackfly population model, it was predicted that fly numbers in Liberia and Ghana would peak at air temperatures of 29°C and 34°C, about 3°C and 7°C above current monthly averages, respectively; parous rates of forest flies (Liberia) would peak at 29°C and of savannah flies (Ghana) at 30°C. Small temperature increases (less than 2°C) might lead to changes in geographical distributions of different vector taxa. When the new model was linked to an existing framework for the population dynamics of onchocerciasis in humans and vectors, transmission rates and worm loads were projected to increase with temperature to at least 33°C. By contrast, analyses of field data on forest flies in Liberia and savannah flies in Ghana, in relation to regional climate change predictions, suggested, on the basis of simple regressions, that 13-41% decreases in fly numbers would be expected between the present and before 2040. Further research is needed to reconcile these conflicting conclusions.

Show MeSH
Related in: MedlinePlus