Distribution of pathogenic Vibrio cholerae strains in aquatic environments in coastal areas of East Africa: Implication to cholera outbreaks and control

At present, the predominant portion of the World’s cholera cases occur in Africa, particularly in socio-economically frail areas. The bacterium causing cholera, Vibrio cholera, is a marine organism and coastal waters are important reservoirs of the organism. The objective of this project was to elucidate the ecology of the pathogenic V. cholerae strains, O1 and O139, and the relationship between the cholera outbreaks with environmental indices in the coastal regions of East Africa. Since an understanding of the social implications of, and coping strategies for cholera outbreaks at district and community levels are imperative for improved cholera prevention and control, these were also analyzed.

The study, applying interdisciplinary approach, was conducted in three coastal regions of Tanzania and one in Kenya, i.e., Pwani, Dar es Salaam and Tanga (Tanzania) and Kwale County (Coast Province in Kenya). Identification and characterization of both isolated and uncultured V. cholerae were performed using standard microbiological and molecular, PCR based, techniques. Data on the number of cholera cases and mortality as well as meteorological parameters were obtained from national data bases. Environmental factors were determined using standard oceanographic methods, in addition to remote sensed data. Assessments of social and economic factors were conducted using a combination of participatory and a questionnaire surveys techniques.

The first reported cholera epidemic in East Africa occurred in 1836 and was confined to the Indian Ocean coast (Olago et al., 2007). There were no reported cases of cholera in Africa for 100 years, between 1870 and 1970 (Waiyaki, 1996). Since the seventh and present pandemic, which began in South Asia in 1961 and reached sub-Saharan Africa in the 1970’s, all East African countries have been affected by outbreaks Olago et al., 2007; Gaffga et al, 2007; Emch et al., 2008). Following the seventh pandemic, the major epidemics in East Africa occurred in 1974 and 1977. Since then, sporadic epidemics have been re-occurring, especially during the rainy seasons and in areas with poor sanitation (Mhalu et al., 1979; Urassa et al., 2000; Acosta et al., 2001). A recent study from South-eastern Africa show significant exponential increase of cholera rates in humans (Paz, 2009).
Studies on the association between cholera outbreaks and environmental factors in East Africa are limited to the Lake Victoria Basin (Olago et al., 2007; Shapiro et al., 1999). Interestingly, as early as 1876, Christie associated cholera epidemics along the East African coasts with the onset of the monsoons winds (Christie, 1876). However, there has been no study investigating the distribution of V. cholerae in coastal waters of East Africa in association with environmental parameters. Based on the increasing awareness of the aquatic environment for the V. cholera life cycle, the present study aimed at analyzing the link between environmental factors (biotic and abiotic) as well as socio-economic factors and cholera epidemicity in coastal regions for improved control of the disease. Some of the major ecological research questions we also asked were; could V. cholerare be detected in the environment of the coast of Tanzania? Where in the environment, in zooplankton, phytoplankton, free living in the water or associated with sediment? If so, were the strains detected in the environment pathogenic? Were the strains detected in the environment the same as those identified in cholera patients? Furthermore, this study assessed the social economic factors, such as awareness of cholera symptoms, awareness of cholera prevention, accessibility to clean water, latrines coverage, and population density and perceptions of how cholera is spread and knowledge about cholera control.

1. To identify and characterize both isolated and uncultured V. cholerae O1 and O139 from selected aquatic environments along the coastal region of Tanzania and Kenya
2. To compare V. cholerae isolated from aquatic environments with clinical isolates
3. To determine environmental factors and fecal bacterial contamination indicators associated with V. cholerae prevalence in aquatic environments
4. To assess the social and economic factors which contribute to cholera outbreaks near coastal aquatic environments in Kenya and Tanzania coastal regions

Shakuru Yunusu, Assessment of risk factors related to cholera and coping strategies in Tanzania: rural urban comparisons – the case of Korogwe District and Temeke Municipality. MSc. Thesis, University of Dar es Salaam, 2011.