Serological markers combined with spatial analysis offer a comparatively more sensitive means by which to measure and detect foci of malaria transmission in highland areas than traditional malariometric indicators. that seroprevalence can be used as an additional tool to identify hotspots of malaria transmission that might be difficult to detect using traditional cross-sectional parasite surveys or through vector studies. Our study findings identify ways in which malaria prevention and control can be more effectively targeted in highland or low transmission areas via serological measures. These tools will become increasingly important for COG3 PRT062607 HCL countries with an elimination agenda and/or where PRT062607 HCL malaria transmission is becoming patchy and focal but receptivity to malaria PRT062607 HCL transmission remains high. Introduction In the east African highland areas malaria transmission intensity generally decreases with altitude often becoming heterogeneous as altitude increases to a point where malaria is usually no longer transmitted.1-6 The main drivers behind these changes are thought to be a decrease in temperature and humidity that results in decreased mosquito vector density as altitude PRT062607 HCL increases. However clusters or hotspots of relatively high malaria transmission have been detected in highland areas often associated with proximity to vector breeding sites such as forests natural swamps highland floodplains or farmlands and pastures.7-14 Over a highland landscape the heterogeneity in distribution of malaria can thus reflect microclimates suitable for vector breeding coupled with differences in household structures or genetic factors.15-18 There is no standard definition of a malaria hotspot. The World Health Organization has previously defined foci of malaria as localities with continuous or intermittent epidemiological factors necessary for transmission.19 Bousema and others defined a hotspot as a geographical a part of a focus where malaria transmission exceeds the average level in surrounding areas.15 Hotspots are likely to persist in highland areas unless interventions are targeted toward them.8 20 21 This of particular importance because these sinks could act as temporal “seeds” that propagate malaria PRT062607 HCL outbreaks and epidemics should suitable conditions arise. Thus identifying the precise location of hotspots toward which interventions can be targeted could potentially prevent epidemic outbreaks in addition to targeting individuals or areas that contribute disproportionally to malaria transmission.22 However identifying hotspots of malaria in highlands is challenging. Standard measures such as entomological inoculation rates (EIRs) or parasite prevalence are more difficult to collect in low transmission areas due to very low numbers of either mosquitoes or infected individuals.23 In addition both measures are affected by seasonality so hotspots of transmission could be missed. Finally the impact of increased malaria control interventions as well as the effects of interannual climate variability make understanding trends in malaria transmission in highland areas particularly difficult. Conversely antibody responses to PRT062607 HCL some malaria parasite antigens have the potential to provide information about malaria transmission intensity over short or long periods of time. Drakeley and others estimated that merozoite surface protein-119 (MSP-119) antibodies persist for 49.8 years reflecting cumulative exposure to malaria infection.24 By examining seroprevalence in different age groups and for the population as a whole transmission intensity can be estimated for more recent as well as longer-term periods. Serological markers of transmission show greater sensitivity in low transmission areas and as a measure are less affected by seasonality due to the longer duration of specific antibody responses.24 Our study used serological measures to assess malaria transmission at different altitudes in southwest Uganda. In addition spatial analysis was used to determine whether hotspots of parasite-positive individuals are geographically similar to clusters of high antibody responses to MSP-119. Materials and Methods Study area and population. The ten villages included in the study were situated in the catchment areas of Kebisoni and Bufundi health facilities that are located in the.