Associations between weather and Plasmodium vivax malaria in an elimination setting in Peru: a distributed lag analysis

BackgroundPlasmodium vivax (Pv) is the predominant malaria species in countries approaching elimination. Environmental factors can guide intervention targeting.Yet, research that considers the long-term relapse periodicity of Pv is limited, particularly in Latin America. MethodsWe merged Pv malaria incidence data from 2017-2024 from 136 communities in the Peruvian Amazon with hourly weather data from the ERA5 dataset. Predictors included weekly minimum and maximum temperature and total weekly precipitation. We fit non-linear distributed lag models using a lookback period of 2-16 weeks. We conducted sub-group analyses by community type (adjacent to river versus highway) and El Nino Southern Oscillation (ENSO) period. Temperature models were adjusted for total precipitation; precipitation models were adjusted for maximum temperature. FindingsMinimum temperature at the 90th percentile (23.7{degrees}C) was associated with 10% (95% CI 5%-14%) higher malaria incidence compared to the lowest minimum temperature (20.4{degrees}C) at a 7-week lag. Maximum temperature at the 90th percentile (33.7{degrees}C) was associated with 10% (95% CI 8%-13%) higher malaria incidence compared to the lowest maximum temperature (29.6{degrees}C) at a 9-week lag. Total weekly precipitation at the 90th percentile (1000mm) was associated with 29% (95% CI 24%-33%) higher malaria incidence compared to weeks with no precipitation at an 11-week lag. Incidence was higher and associations were stronger in communities adjacent to rivers versus highways. Malaria incidence was lower during El Nino periods, and there was evidence of interaction on the multiplicative scale for the association between incidence, all weather predictors, and ENSO period. InterpretationPv malaria incidence was positively associated with higher temperatures and precipitation in an elimination setting in Peru, particularly in riverine communities during non-El Nino years, with longer lag periods than previously reported for such associations. These findings can inform malaria elimination interventions to combat the long-lasting effects of weather on Pv transmission. Research in contextO_ST_ABSEvidence before this studyC_ST_ABSWe searched PubMed for ("weather" OR "climate" OR "temperature" OR "precipitation") AND ("malaria") AND ("Amazon"). The search yielded 76 results. The most relevant studies looked at the influence of weather variables on all malaria incidence in neighboring Brazil and Venezuela. The study in Brazil found positive associations with temperatures between 25-30{degrees}C and precipitation >4.46cm at 1-week lags, but negative associations with temperatures >25{degrees}C at 2-3-week lags. The study in Venezuela found positive associations with mean temperatures in the range 20-30{degrees}C and no association with precipitation. Both studies emphasized that malaria transmission was highly heterogeneous. Added value of this studyOur study used a distributed lag analysis to account for the long-term relapse periodicity common in Pv malaria, which is predominant in the Peruvian Amazon. Our study is, to our knowledge, the first to exclusively focus on climatic drivers of Pv malaria at long-term lags in an elimination setting dominated by the Ny. darlingi vector. This transmission system is especially understudied compared to Plasmodium falciparum malaria, yet Pv malaria is the predominant species in elimination settings worldwide. Implications of all the available evidenceOur study contributes to an important body of literature characterizing climatic drivers of Pv malaria in the Peruvian Amazon. Our findings indicate that over 1-4-month lags, higher temperatures and precipitation could contribute to higher malaria incidence, particularly during neutral El Nino Southern Oscillation (ENSO) years. We also found that communities near rivers were more sensitive to changes in temperature, while communities near highways were more sensitive to changes in precipitation.