Prevalence and Characterisation of Non-Cholerae Vibrio spp. in Final Effl uents of Wastewater Treatment Facilities in Two Districts of the Eastern Cape Province of South Africa: Implications for Public Health
Municipal wastewater, even if treated, may still contain a wide range of pathogens that are excreted by diseased humans (Arceivala 1997; Wen et al. 2009), contributing to increased densities of pathogens in the receiving water bodies. Surface water bodies are major sources of potable water whose unabated contamination has led to many water-related disease outbreaks in the past (Mishra et al. 2004; Nair et al. 2004; Obi et al. 2004). Although wastewater treatment technologies can, with optimised performance, reduce bacterial and viral pathogens by approximately 90% (Asano and Levine 1998; Jiménez et al. 2004), it is not possible for the microbial
quality of the effluents to match the microbial quality of the water in the receiving water bodies. Discharge of effluents will, therefore, despite the level of treatment, potentially alter the microbial content of the receiving water bodies (Drury et al. 2013). Previous studies show that some Vibrio species survive the activated sludge-based wastewater treatment process as free cell and as plankton-associated entities (Igbinosa et al. 2009, 2011), suggesting that the provision of wastewater treatment facilities does not, in itself, ensure satisfactory effluent water quality. The most common clinical presentation of Vibrio infection is self-limited gastroenteritis, but wound infections and primary septicaemia may also occur (Levine and Griffin 1993). Healthy carriers of Vibrio cholerae excrete Vibrios intermittently, with chronic convalescent carriers shedding Vibrios intermittently for periods of 4 to 15 months (Nevondo and Cloete 2001). Survival of Vibrios in the aquatic environment relates sharply to various chemical, biological and physical characteristics of the aquatic milieu, with V. cholerae known to remain viable in surface waters for periods ranging from 1 h to 13 days, while faecal contamination from victims of epidemics and healthy carriers may continue to reinforce their concentrations in water (Nevondo and Cloete 2001). As a result, cholera and cholera-like infections continue to be a substantial health burden in developing countries, especially in Africa and Asia, compromising the primary health of vulnerable members of society (Bourne and Coetzee 1996; Pegram et al. 1998; Mackintosh and Colvin 2003). Vibrio species have been incriminated in cases of diarrhoea, accounting for a substantial degree of morbidity and mortality in different age groups worldwide (Obi et al. 2004). The most notable of Vibrio pathogens are V. cholerae, Vibrio parahaemolyticus, Vibrio vulnificus and Vibrio fluvialis (CDC Centers for Disease Control and Prevention 1999; Finkelstein et al. 2002; Kothary et al. 2003; Chakraborty et al. 2006) which are mainly transmitted via water and food. They all cause diarrhoea, but in entirely different ways; V. vulnificus and V. parahaemolyticus are invasive organisms, affecting primarily the colon, while V. cholerae is non-invasive, affecting the small intestine through secretion of an enterotoxin (Todar 2005), and is the etiologic agent of cholera. The clinical symptoms of V. fluvialis gastroenteritis are similar to cholera with the additional manifestation of bloody stools which is suggestive of an invasive pathogen (Oliver and Kaper 2001). Other Vibrios like Vibrio
Prevalence and Characterisation of Non-Cholerae Vibrio spp. 29
alginolyticus, Vibrio cincinnatiensis, Vibrio furnisii, Vibrio harveyi, Vibrio metschnikovii and Vibrio mimicus have occasionally been reported as causes of human infections (Farmer and Hickman-Brenner 1992; Abbott and Janda 1994; Carnahan et al. 1994). However, of all the Vibrio species which have been associated with illness in humans, the most important are V. cholerae subgroups O1 and O139, the causative agents of epidemic cholera (Heymann 2008). Heidelberg et al. (2002) have reported large numbers of Vibrios, about 4.3 × 106/mm2, attached to the external surface of plankton (zooplankton and phytoplankton), pointing to a close association between Vibrios and planktons. This association has also been observed in municipal wastewaters (Ahmadi et al. 2005; Chindah et al. 2007; Mukhopadhyay et al. 2007). V. fluvialis, in particular, has been identified as an important cause of cholera-like bloody diarrhoea and primary septicaemia in immunocompromised individuals, especially in underdeveloped countries with poor sanitation (Igbinosa and Okoh 2010). This organism has been isolated from treated wastewater effluents in South Africa (Igbinosa et al. 2009), and there are reports linking it to food poisoning (Kobayashi and Ohnaka 1989), especially due to consumption of raw shellfish (Levine and Griffin 1993). While adequate and timely rehydration therapy remains the gold-standard treatment for cholera and cholera-like bloody diarrhoea (Heymann 2008), antimicrobials are also prescribed for the management of severe cases in order to shorten the duration of illness and reduce the volume of rehydration solution required. However, some Vibrio strains are resistant to a number of antimicrobials including tetracycline, co-trimoxazole, trimethoprim and sulfamethoxazole. This resistance to antimicrobials, in addition to other properties such as virulence factors and ability to cause epidemics, makes Vibrios pathogens of public health concern. Knowledge of the prevalence and antimicrobial resistance profile of local strains is, therefore, important for the management of complicated cases in the case of an epidemic. At times, a cholera outbreak is reported without any clear linkage of the index case to neighbouring countries or travel to affected areas. This usually leaves health authorities asking themselves where the cholera causing bacteria could have come from. We hypothesise that such outbreaks could be related to either persistence of organisms in free-living, altered or adapted forms capable of reverting to a pathogenic variety or to continuous year-round transmission by sub-clinical cases or
a combination of both. Routine analysis of the microbial quality of treated wastewater effluents is therefore warranted in order to maintain the microbial load of receiving water bodies within acceptable limits for both human use and lotic ecosystems survival. There is, however, paucity of information on the molecular epidemiology of Vibrios in the aquatic milieu of the Eastern Cape Province (ECP) of South Africa. Compounding the challenge is the production of poor-quality effluents by wastewater treatment plants in the ECP which is acknowledged as mostly non-urban, poor and without adequate infrastructure (Mohale 2003; BLACKSASH 2010). Also, the documentation of final effluent compliance of the wastewater treatment plants to set guidelines with respect to bacteriological quality remains poor in the province. This study was, therefore, aimed at assessing the prevalence of non-cholerae Vibrios in the final effluents of 14 wastewater treatment facilities in the ECP of South Africa, characterising them into species and determining their antibiogram properties and evaluating the public health implications of the findings. While there are at least 12 pathogenic Vibrio species recognised to cause human illness (Janda et al. 1988), this work was based on the prevalence and characterisation of V. vulnificus, V. fluvialis and V. parahaemolyticus.