Outbreak of avian botulism and its effect on waterbirds in the Wilderness Lakes, South Africa

Avian botulism is a non-infectious bird disease resulting from the ingestion of toxins produced by the gram-positive bacterium Clostridium botulinum (Rocke & Friend 1999). Seven different types of botulism neurotoxins occur, labelled A to G (Collins & East 1998), as well as mosaics that have characteristics of two toxins (Rocke & Friend 1999). Avian botulism outbreaks are typically caused by type C (Wobeser 1997), mosaic C/D (Anza et al. 2014) or type E (Getchell & Bowser 2006; Rocke & Friend 1999). Fish die-offs are typically caused by type E (Cromie et al. 2012). Clostridium botulinum is reportedly widespread in wetland sediments where outbreaks are common, and typically requires a source of protein, warm temperatures and low oxygen conditions to activate and produce toxin (Espelund & Klaveness 2014). The salinity and pH of sediments and water may also affect the probability of botulism outbreaks in aquatic ecosystems (Rocke & Friend 1999). The disease in birds is characterised by a flaccid paralysis of the muscles and is invariably fatal (Rocke & Friend 1999). Death typically results from respiratory failure or drowning.