Environmental exposure and leptospirosis, Peru

Abstract

Human infection by leptospires has highly variable clinical manifestations, which range from subclinical infection to fulminant disease. We conducted a population-based, cross-sectional seroepidemiologic study in Peru to determine potential relationships of environmental context to human exposure to Leptospira and disease associated with seroconversion. Three areas were studied: a flooded, urban slum in the Peruvian Amazon city of Iquitos; rural, peri-Iquitos villages; and a desert shantytown near Lima. Seroprevalence in Belen was 28% (182/650); in rural areas, 17% (52/316); and in a desert shantytown, 0.7% (1/150). Leptospira-infected peridomestic rats were found in all locales. In Belen, 20 (12.4%) of 161 patients seroconverted between dry and wet seasons (an incidence rate of 288/1,000). Seroconversion was associated with history of febrile illness; severe leptospirosis was not seen. Human exposure to Leptospira in the Iquitos region is high, likely related both to the ubiquity of leptospires in the environment and human behavior conducive to transmission from infected zoonotic sources.

Figure 1

Typical views of the residential areas of Belen, Iquitos, Peru. A. Houses near the river edge are built on stilts. B. Conditions abound for the proliferation of peridomestic rats in the same places where people live and play. This view is adjacent to the major market area of Belen, where Rattus spp. are commonly observed, even during the day in the middle of commercial activities.

Figure 2

A typical view of a rural village area near Iquitos. Near Villa Buen Pastor, located 21 km along the major (unfinished) road that leads from Iquitos to Nauta, substantial secondary growth of forest is evident after removal of primary forest for human agricultural and living activities. One must walk approximately 1–2 km from the road to get to the village and a further 1–2 km from Villa Buen Pastor to Moralillo, another village studied in this report.

Figure 3

Prevalence of antileptospiral immunoglobulin (Ig) M/IgG antibodies by age group. Number above each bar is the sample size for the specified age group and site. The trend of increasing prevalence by age is significant for Belen and the rural communities (p = 0.018 and p = 0.012, respectively).