Interactions Between Water, Sanitation, and Hygiene (WASH) and Mosquito Dynamics in Western Kenya: Implications for Diarrheal and Mosquito-Borne Diseases

Abstract

Background: Diarrheal illness and Plasmodium falciparum infection (malaria) remain leading causes of death for all age groups in Kenya, despite extensive efforts to improve sanitation and vector control. Outdoor latrines, semi-sheltered structures with high humidity and no vector control, may provide ideal environments for vector-human contact. This study aimed to evaluate how latrine use influenced diarrheal illness, P. falciparum infection, and other potential mosquito-borne diseases in a malaria-endemic area of western Kenya. Methods: A cross-sectional, population-based survey was conducted from July to September 2023, targeting individuals aged four years or older. Monthly mosquito sampling was carried out from July 2023 to April 2024 in 50 houses and their corresponding outdoor latrines using Prokopack aspirators. Results: Of 528 individuals analyzed, 263 (50%) were children and 265 (50%) were adults. Overall, latrine use was more frequent among adults than children, for defecation than urination, and during the daytime and early morning than at night. Individuals who felt safe walking to latrine at night were 9.47 times more likely to use latrines for urination (adjusted prevalence ratio [aPR]=9.47, 95%Credible Interval [CrI]: 3.17-28.28) and 2.71 times more likely for defecation (aPR=2.71, 95%CrI: 1.24-5.91) compared to those who perceived it as neither safe nor unsafe. No significant associations were found between latrine use and either diarrheal illness (children, adjusted relative risk [aRR]=1.12, 95%CrI: 0.55-2.28; adults, aRR=0.56, 95%CrI: 0.19-1.64) or P. falciparum infection (children, aPR=2.22, 95%CrI: 0.93-5.27; adults, aPR=0.66, 95%CrI: 0.22-1.91). Among anophelines, the An. funestus group was the most common, followed by An. gambiae s.l. in houses and latrines. Many Culex and some Mansonia species were also found in both locations. Of the mosquitoes analyzed for blood meal sources, the human blood index in anopheline species was 50% (15/30) in houses and 33% (4/12) in latrines, while the bovine blood index was 60% (18/30) in houses and 67% (8/12) in latrines. Conclusions: Safety influenced latrine use at night. We did not find effects of latrine use on diarrheal disease or P. falciparum infection. However, the presence of human blood-fed Anopheles, Mansonia, and Culex species in latrines may pose a potential risk for P. falciparum infection and other mosquito-borne diseases. Implementation: Ensuring safe access to latrines is crucial for improving latrine use and preventing diarrheal illness. Given the presence of human blood-fed Anopheles, Mansonia, and Culex species in latrines, public health professionals should encourage individuals to take preventive measures, such as wearing long-sleeved shirts and pants, to reduce mosquito exposure in these settings.