BackgroundIn 2010, 18 States of Nigeria reported cholera outbreaks with a total of 41,787 cases including 1,716 deaths (case-fatality rate [CFR]: 4.1%). This exceeded the mean overall CFR of 2.4% reported in Africa from 2000–2005 and the WHO acceptable rate of 1%. We conducted a descriptive analysis of the 2010 cholera outbreak to determine its epidemiological and spatio-temporal characteristics.MethodsWe conducted retrospective analysis of line lists obtained from 10 of the 18 states that submitted line lists to the Federal Ministry of Health (FMOH). We described the outbreak by time, place and person and calculated the attack rates by state as well as the age- and sex-specific CFR from cholera cases for whom information on age, sex, place of residence, onset of symptoms and outcome were available.ResultsA total of 21,111 cases were reported with an overall attack rate and CFR of 47.8 cases /100,000 population and 5.1%, respectively. The CFR ranged in the states between 3.8% and 8.9%. The age-specific CFR was highest among individuals 65 years and above (14.6%). The epidemiological curve showed three peaks with increasing number of weekly reported cases. A geographical clustering of LGAs reporting cholera cases could be seen in all ten states. During the third peak which coincided with flooding in five states the majority of newly affected LGAs were situated next to LGAs with previously reported cholera cases, only few isolated outbreaks were seen.ConclusionOur study showed a cholera outbreak that grew in magnitude and spread to involve the whole northern part of the country. It also highlights challenges of suboptimal surveillance and response in developing countries as well as potential endemicity of cholera in the northern part of Nigeria. There is the need for a harmonized, coordinated approach to cholera outbreaks through effective surveillance and response with emphasis on training and motivating front line health workers towards timely detection, reporting and response. Findings from the report should be interpreted with caution due to the high number of cases with incomplete information, and lack of data from eight states.
Abstract. The population dynamics and reproductive strategies of two rare wet heathland species, Gentiana pneumonanthe and Rhynchospora, were studied in experimental permanent plots in a wet heathland near Bremen, NW Germany, to assess how effective sod cutting and mowing are in promoting these species. In one experiment, small plots (0.25 m2 ‐ 4 m2) were sod‐cut or mown; in the second, one large plot 30 mx 50m) was sod‐cut. The development of the vegetation and the number of shoots of the two target species were recorded annually. Sod cutting lead to the highest shoot numbers of Gentiana in the long run, whilst mowing was more effective at the beginning of the experiment. Seedlings and adult shoots slowly became more and more abundant after sod cutting. In contrast, Rhynchospora soon formed closed stands after sod‐cutting, first through seed germination and then through fast clonal growth of the established individuals. Moist soil or short inundations promoted the germination and seedling establishment of Gentiana, whereas drought negatively affected seedling recruitment. Long periods of inundation severely reduced the population at first, but high numbers of seedlings were found in the following growing season. For the disturbance‐dependent Gentiana and Rhynchospora, the availability of gaps within the vegetation is of crucial importance. To promote existing populations, we suggest small‐scale sod cuttings which create gaps without disturbing existing flowering individuals too much. For degenerated stands of wet heathland we recommend large‐scale sod cutting to activate the seed bank. Additionally, seed introduction may be helpful to encourage the development of a wet heathland with characteristic floristic composition.
Abstract. Question: The significance of disturbances caused by periodical inundation was investigated with respect to its effects on vegetation dynamics, species richness and fluctuations, and to the relevance of certain plant properties. Location and Method: At a sod‐cut stand within nutrient‐poor inland sand dunes, permanent plots along a transect were surveyed over a period of up to nine years after sod cutting. Results: In contrast to never inundated plots, periodically inundated plots were characterized by low vegetation cover and by high numbers of species belonging to many different communities, each of them with a low cover. Periodical inundations favoured the presence of pioneers, species tolerant of disturbances, species adapted to wet conditions and stoloni‐ferous species. Furthermore, annual fluctuations of species within each plot were higher and most species occurred only sporadically. Discussion: A comprehensive model is presented describing the relevant processes identified in the littoral zone. Changing water tables result in the creation of gaps. The re‐colonization of these gaps follows mainly from vegetative regeneration and less to the dispersion of diaspores. Highest species numbers in the zone of moderate disturbances result from a high rate of re‐colonization in spite of local extinctions following each disturbance event. It is suggested that colonization abilities are among the most important features for species occurrence at a site rich in disturbances (more important than competitive abilities and more important than a slow rate of displacement). For nature conservation such sites are very important, because they allow (rare) pioneer species to survive for longer periods of time.
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