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

Cholera epidemics along the East African coasts have been associated with the onset of the monsoons winds (Christie, 1876). However, there has been no study investigating the distribution of Vibrio cholerae in coastal waters of East Afcrica in association with environmental parameters. The present study aimed at analyzing the link between environmental factors as well as socio-economic factors and cholera epidemicity in the WIO region for improved disease control. The study had the following specific objectives: (i) To identify and characterize both isolated and uncultured V. cholerae O1 and O139 from selected coastal aquatic environments, (ii) To compare V. cholerae isolated from aquatic environments with clinical isolates, (iii) To determine environmental factors and fecal bacterial contamination indicators associated with V. cholerae prevalence in aquatic environments and (iv) To assess the social and economic factors which contribute to cholera outbreaks near coastal aquatic environments. The project was conducted in two countries of the WIO region, namely Tanzania and Kenya with local and scientific community as well as decision and policy makers being primary targeted beneficiaries.

The study, applied interdisciplinary approach that comprised identification and characterization of both isolated and uncultured V. cholerae 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 databases. 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. Sampling was done in three coastal regions chosen because they experience frequent cholera outbreaks and were easily accessible i.e., Pwani, Dar es Salaam and Tanga in Tanzania and one (Kwale County -Coast Province) in Kenya. In each area one estuarine system was selected as a study site i.e., Mzinga Creek in Dar es Salaam, Ruvu Estuary in Pwani, Pangani Estuary in Tanga and Shimoni-Vanga in Kwale.

Results from this project provide an in situ evidence of the presence of the pathogenic V. cholerae strains, O1 and O139, in the coastal environment of East Africa, the identification of O139 being one of the first identifications of this epidemic strain in coastal samples of East Africa. Furthermore, a number of V. cholerae non O1/O139 that carry the cholera toxic gene were identified. Moreover, the results showed that coastal regions of Tanzania are more prone to cholera outbreaks than inland regions – the coastal regions of Tanzania accounted for 50% of the cholera cases and about 40% of all the cholera deaths – possibly due to their proximity to the ocean, which has been suggested to be the natural reservoir of V. cholerae. There was also a strong correlation between the number of cholera cases and air temperature, sea surface temperature and rainfall. Cholera was found to affect coastal communities both economically and socially Furthermore, it was established that although most respondents were aware of signs and symptoms of cholera such knowledge was found inadequate in terms of understanding linkages between how social, economic and environmental causes individually, or combined, contribute to frequent cholera outbreaks in the area. In addition, respondents had divergent views on the main cause of cholera.

Given the complex life cycle of V. cholerae this project provides information, and protocols with methodological details on complementary V. cholerae detecting techniques suitable to be implemented within the Tanzanian and Kenyan national health monitoring programs of cholera.  Furthermore, knowledge on the presence of V. cholerae in the coastal environments in Tanzania can contribute to cholera control guidelines since exposure to the pathogen could be broader than typically considered. Awareness of the ecological link of the pathogen among health workers and within the local coastal communities often hit by endemic cholera, may ease the stigma around cholera, facilitating the discussion and work on cholera prevention and control. Results from this project add useful knowledge for prediction and early warning systems for cholera management.

Further studies can focus on the survival of the pathogen in the coastal environment that can result in cholera transmission and magnitude of this kind of transmission. Furthermore, more comprehensive studies to elucidate cholera dynamics in order to properly manage the disease and develop early warning systems for the outbreaks are required. In addition, further social studies focused on investigating why available knowledge about cholera control is not as effective in the control of epidemics and how the socio economic problems arising in connection to cholera outbreaks can be best managed. Furthermore, studies should be undertaken to investigate how efficiently the Tanzanian and Kenyan health related policies reflect the needs of people and how efficient the exchange of information on the extent of outbreaks and management strategies is between neighbouring countries in the WIO region, and how it could be improved.