Background: Ambient temperature is an important determinant of malaria transmission and suitability, affecting the life-cycle of the Plasmodium parasite and Anopheles vector. Early models predicted a thermal malaria transmission optimum of 31 degrees C, later revised to 25 degrees C using experimental data from mosquito and parasite biology. However, the link between ambient temperature and human malaria incidence remains poorly resolved.
Methods: To evaluate the relationship between ambient temperature and malaria risk, 5833 febrile children (< 18 years-old) with an acute, non-localizing febrile illness were enrolled from four heterogenous outpatient clinic sites in Kenya (Chulaimbo, Kisumu, Msambweni and Ukunda). Thick and thin blood smears were evaluated for the presence of malaria parasites. Daily temperature estimates were obtained from land logger data, and rainfall from National Oceanic and Atmospheric Administration (NOAA)'s Africa Rainfall Climatology (ARC) data. Thirty-day mean temperature and 30-day cumulative rainfall were estimated and each lagged by 30 days, relative to the febrile visit. A generalized linear mixed model was used to assess relationships between malaria smear positivity and predictors including temperature, rainfall, age, sex, mosquito exposure and socioeconomic status.
Results: Malaria smear positivity varied between 42-83% across four clinic sites in western and coastal Kenya, with highest smear positivity in the rural, western site. The temperature ranges were cooler in the western sites and warmer in the coastal sites. In multivariate analysis controlling for socioeconomic status, age, sex, rainfall and bednet use, malaria smear positivity peaked near 25 degrees C at all four sites, as predicted a priori from an ecological model.
Conclusions: This study provides direct field evidence of a unimodal relationship between ambient temperature and human malaria incidence with a peak in malaria transmission occurring at lower temperatures than previously recognized clinically. This nonlinear relationship with an intermediate optimal temperature implies that future climate warming could expand malaria incidence in cooler, highland regions while decreasing incidence in already warm regions with average temperatures above 25 degrees C. These findings support efforts to further understand the nonlinear association between ambient temperature and vector-borne diseases to better allocate resources and respond to disease threats in a future, warmer world.
1.Stanford Univ, Sch Med, Infect Dis & Geog Med, Stanford, CA 94305 USA 2.Stanford Univ, Sch Med, Dept Pediat, Div Infect Dis, Stanford, CA 94305 USA 3.Kenya Govt Med Res Ctr, Ctr Global Hlth Res, Kisumu, Kenya 4.Tech Univ Mombasa, Dept Environm & Hlth Sci, Mombasa, Kenya 5.Stanford Univ, Dept Biol, Stanford, CA 94305 USA 6.Msambweni Cty Referral Hosp, Dept Pediat, Msambweni, Kenya 7.Diani Hlth Ctr, Dept Pediat, Ukunda, Kenya 8.RTI Int, Washington, DC USA 9.Univ Nottingham, Epidemiol & Publ Hlth Div, Nottingham, England 10.USRA, Greenbelt, MD USA 11.NASA Goddard Space Flight, Biospher Sci Lab, Greenbelt, MD USA 12.Morgan State Univ, Greenbelt, MD USA 13.Hosp Univ Penn, Dept Med, Philadelphia, PA 19104 USA 14.Childrens Hosp Philadelphia, Dept Pediat, Philadelphia, PA 19104 USA
Recommended Citation:
Shah, Melisa M.,Krystosik, Amy R.,Ndenga, Bryson A.,et al. Malaria smear positivity among Kenyan children peaks at intermediate temperatures as predicted by ecological models[J]. PARASITES & VECTORS,2019-01-01,12