Spatial clustering in the spatio-temporal dynamics of endemic cholera

<p>Abstract</p> <p>Background</p> <p>The spatio-temporal patterns of infectious diseases that are environmentally driven reflect the combined effects of transmission dynamics and environmental heterogeneity. They contain important information on different routes of transmission, including the role of environmental reservoirs. Consideration of the spatial component in infectious disease dynamics has led to insights on the propagation of fronts at the level of counties in rabies in the US, and the metapopulation behavior at the level of cities in childhood diseases such as measles in the UK, both at relatively coarse scales. As epidemiological data on individual infections become available, spatio-temporal patterns can be examined at higher resolutions.</p> <p>Methods</p> <p>The extensive spatio-temporal data set for cholera in Matlab, Bangladesh, maps the individual location of cases from 1983 to 2003. This unique record allows us to examine the spatial structure of cholera outbreaks, to address the role of primary transmission, occurring from an aquatic reservoir to the human host, and that of secondary transmission, involving a feedback between current and past levels of infection. We use Ripley's K and L indices and bootstrapping methods to evaluate the occurrence of spatial clustering in the cases during outbreaks using different temporal windows. The spatial location of cases was also confronted against the spatial location of water sources.</p> <p>Results</p> <p>Spatial clustering of cholera cases was detected at different temporal and spatial scales. Cases relative to water sources also exhibit spatial clustering.</p> <p>Conclusions</p> <p>The clustering of cases supports an important role of secondary transmission in the dynamics of cholera epidemics in Matlab, Bangladesh. The spatial clustering of cases relative to water sources, and its timing, suggests an effective role of water reservoirs during the onset of cholera outbreaks. Once primary transmission has initiated an outbreak, secondary transmission takes over and plays a fundamental role in shaping the epidemics in this endemic area.</p

Diel behaviour and trophic ecology of Scolopsis bilineatus (Nemipteridae)

Nemipterids are ubiquitous mid-sized fishes on Indo-Pacific reefs. We investigated the trophic ecology of the nemipterid species Scolopsis bilineatus at two locations on the Great Barrier Reef: One Tree Island and Orpheus Island. Fish ate a variety of benthic invertebrate taxa represented by rank: polychaetes, ophuiroids, sipunculids, nemerteans and small crustaceans. Polychaetes dominated the diet of fish of all sizes. Feeding behaviour and habitat utilization varied with the size of fish. Juveniles fed diurnally and adults nocturnally. Most juveniles fed rapidly in sand and rubble habitat during the day. In contrast, adults occupied shelter sites during the day, but dispersed onto sand to feed at night. A manipulative experiment demonstrated that small adult S. bilineatus exhibit opportunistic behaviour by responding to disturbance of the substratum for the purposes of feeding. Diurnal opportunistic feeding probably has a minimal influence on overall dietary intake. Identification of nocturnal feeding for adult S. bilineatus is of significant ecological importance, as nocturnal fishes often play unique and important roles in energy and nutrient cycling on reefs