The interest in Vibrio species worldwide stems from the history and epidemiology of cholera, a severe diarrhoeal disease thought to have originated from the Far East (Asia) thousands of years ago. The spread of cholera was sea-borne at first, affecting particularly coastal towns and fishing villages. As it gained foothold within the regions, the tribal behaviours of the populations, including funeral ceremonies, movement of people within and between countries, and the use of rivers for transportation, trade, and travel as well as source of domestic water became important factors in the dissemination of the disease on a scale reminiscent of the 19th century pandemics (1,2).
The long-distance spread of the disease to Europe and the Americas through the Middle East region is thought to have begun in 1817. The Ogawa serotype is reported to have arrived at the Atlantic coast of West Africa in 1868 when the first cholera outbreak was reported in the region (3,4). From September 1970, the disease invaded West African countries one after another-Guinea and Sierra Leone (28 September 1970), Liberia (October 1970), Ivory Coast (20 October 1970), Mali and Togo (both on 24 November 1970), Dahomey (16 December 1970), Upper Volta (Burkina Faso) (17 December 1970), Nigeria and Niger (27 December 1970) (1,5). The first recorded outbreak of the disease in Nigeria in 1970 was in Lagos, with three bacteriologically-confirmed cases. Since then cholera cases have been reported in various parts of the country (6,7).
Vibrio cholerae, the causative organism of cholera, is just one of over 33 species described in the genus Vibrio, among which 12 species, including V. cholerae, have been reported to be pathogenic to humans. Nine of these have actually been isolated in clinical conditions attributed to them (8); 8 among them have been associated with food-borne infections of the gastrointestinal tract (9). Infections due to food-borne Vibrio are common in Asia, including Hong Kong, and in sub-Saharan Africa, including Nigeria (6,7,10). Sea-foods and water are the major sources of infection, and Vibrio species have largely been isolated from these sources in the southeastern region of Nigeria (7,11,12). It is against this background that shellfish and water samples from five fishing islands in this region, which are the major sources of shellfish sold in inland markets of Nigeria, were screened for Vibrio species and pathotypes.
MATERIALS AND METHODS
Description of the project area
The study was carried out around five fishing islands--Asia-Obufa, Obio-Iwang, Ikot-Itie-Idung, Utam-Iyata, Utam-Antai located on the Bight of Biafra (Bonny) and belonging to Ibaka LGA of AkwaIbom State, Nigeria. Each island has 1,000-1,500 inhabitants. All inhabitants have homes in villages in the mainland and stay in make-shift shelters with their families to engage in daily out-sea fishing activities and shellfish processing for dispatch to the inland markets. The inhabitants have no toilet facilities and defaecate at the banks or inside the sea.
Collection of shellfish and water samples
Freshly-harvested crayfish and lobsters were purchased from fishermen as they came ashore after the night-fishing activities. These were immediately put in sterile polythene bags to avoid further contamination and conveyed to the laboratory sandwiched between ice-blocks in insulated ice-boxes.
Three sea-water samples (250 mL each) were also collected from each of the five islands as follows: using a sterilized conical flask, the sea-water samples were collected at 3 points in each island-one just at the ocean bank, the second at about 100 m from the shore, and the third at about 500 m from the shore into the sea. The conical flask was held with its mouth down and, in that position, it was submerged into depth of about 100 cm before the mouth was turned upwards under water to fill. All water samples were transported to the laboratory under the prevailing atmospheric conditions. …