Sero-prevalence of anti-Leptospira antibodies and associated risk factors in rural Rwanda: A cross-sectional study

Abstract

Background: Leptospirosis is a zoonotic disease transmitted through the urine of wild and domestic animals, and is responsible for over 50,000 deaths each year. In East Africa, prevalence varies greatly, from as low as 7% in Kenya to 37% in Somalia. Transmission epidemiology also varies around the world, with research in Nicaragua showing that rodents are the most clinically important, while studies in Egypt and Chile suggest that dogs may play a more important role. There are no published studies of leptospirosis in Rwanda.

Methods & findings: We performed a cross-sectional survey of asymptomatic adults recruited from five occupational categories. Serum samples were tested using ELISA and Microscopic Agglutination Test (MAT). We found that 40.1% (151/377) of asymptomatic adults had been exposed to Leptospira spp. Almost 36.3% of positive subjects reported contact with rats (137/377) which represent 90.7% among positive leptospira serology compared with 48.2% of negative subjects (182/377) which represent 80.5% among negative leptospira serology (OR 2.37, CI 1.25-4.49) and 1.7 fold on prevalence ratio and 2.37 of odd ratio. Furthermore, being a crop farmer was significantly associated with leptospirosis (OR 2.06, CI 1.29-3.28). We identified 6 asymptomatic subjects (1.6%) who met criteria for acute infection.

Conclusions: This study demonstrates a high prevalence of leptospiral antibodies infection among asymptomatic adults in rural Rwanda, particularly relative to neighboring countries. Although positive subjects were more likely to report rat contact, we found no independent association between rats and leptospirosis infection. Nonetheless, exposure was high among crop farmers, which is supportive of the hypothesis that rats together with domestic livestock might contribute to the transmission. Further studies are needed to understand infecting Leptospira servers and elucidate the transmission epidemiology in Rwanda and identify means of host transmitters.

Fig 1. Venn diagram of the distribution of leptospirosis positive serum samples based on the three laboratory testing modalities that were used: MAT, ELISA IgG, and ELISA IgM.

There were 151 total positive samples by any method.

Fig 2. Bar chart of the distribution of leptospirosis MAT titers in serum samples collected from 377 asymptomatic adults in rural Rwanda.

Results ranged from 0 to 3200 with the majority (64.5%) being undetectable. MAT: Microscopic Agglutination Test.

Fig 3. Prevalence of leptospirosis by age group among asymptomatic adults in rural Rwanda.

The majority of unexposed subjects (52%) were age 21–31. Percentages are out of total positive or total negative.