Lessons for the future: Qualifying and quantifying South Asia's first widespread ciguatera poisoning outbreak

South Asia has long had a fish eating tradition as well as a growing domestic and export fishing industry. However, recently there have been sporadic reports of ciguatera fish poisoning (CFP) from this region. This is a circumtropical disease transmitted by eating carnivorous fishes that contain toxins accumulated from their food and is characterised by gastrointestinal and neurological symptoms which may result in disablement and/or death. Despite the known presence of the dinoflagellate Gambierdiscus spp., one of the most common causative agents of CFP, in the region (Indian Ocean and Arabian Sea) there has been no previously recorded large-scale CFP incident in this area until now. On 1st October 2016 South Asia's first widespread CFP outbreak occurred in the city of Mangalore, Karnataka, on the coast of SW India, resulting in several hundred hospital attendances and admissions. This is believed to be as a result of the consumption of locally caught carnivorous fish, such as the red snapper, Lutjanus bohar, contaminated with ciguatera toxins. These fish were originally intended for a fish processing plant in the city but were also sold at the Mangalore fish market. This recent outbreak presents a unique opportunity to qualify and quantify the presence of the causative algal species, whilst at the same time conduct state-of-the-art toxin analysis of contaminated seafood samples in a region of the world currently underrepresented both in terms of sampling coverage and technological analysis of an algal-born toxin outbreak event. Increased seawater temperatures and lowered salinity are known to favour the regional dinoflagellate community in general, and specifically Gambierdiscus spp. The previous 12 months have seen sea surface temperatures in the Indian Ocean consistently 0.5-1.0 degrees C above average coinciding with the ongoing El Niño Southern Oscillation and this season's monsoon has been particularly sustained, lowering coastal salinity. Data gathered during the proposed study will allow us to make predictions for the occurrence of further outbreaks of CFP along the South Asian coastline and elsewhere, including in the face of global climate change. Our aim to implement a rapid response screening and management programme in response to future CFP events will help to ensure the health and wellbeing of those who depend on fishing as a protein and/or economic resource.

Fish is an important component of the diet of people in South Asia. Furthermore, South Asia has a growing domestic and export fishing industry which is a significant protein and/or economic resource for a high proportion of the population. As this industry expands, increasing numbers of people are also employed indirectly such as in fish processing plants providing stable employment opportunities for South Asia's growing population. These establishments buy fish from different local fishing locations often processing the more valuable fillets of large fish for export with the remaining head and viscera being sold in local markets where they remain a popular local delicacy. The October 2016 CFP outbreak in Mangalore is believed to be a result of the consumption of locally caught carnivorous fish, such as the red snapper, Lutjanus bohar, contaminated with ciguatera toxins, the head and viscera of which came via a fish processing plant in the city to be sold at the Mangalore fish market. Although it is likely that abiotic factors are ultimately driving this particular outbreak of CFP, e.g. the temperature and salinity changes and eutrophication in Indian Ocean and Arabian Sea coastal waters mediated by the effects of this year's El Niño, it is also possible that if there was no large scale fish processing/selling of fish in the city then this event would have been limited in terms of numbers of persons affected. This event demonstrates how fast a large-scale outbreak of CFP can be perpetrated and immediately highlights food safety issues surrounding microalgal born marine toxins. There is currently no central or local government policy or protocol for screening locally produced seafood for marine toxins such as is available in many other countries.

Previous small-scale events of seafood poisoning in Mangalore (and elsewhere in South Asia and worldwide) have demonstrated that even though usually only specific species are involved, consumer confidence in marine products drops and fish consumption significantly decreases. This not only leads to loss of livelihoods for those who are involved in fishing, but also deprives the community of a nutritious component of their normal diet. In South Asia in particular this can quickly have significant social-economic knock-on effects.

To help consumers make informed decisions, it is vital to provide information on specific fish species to be avoided at specific periods. Fishermen need to be informed about areas and seasons when certain fish species can carry toxins, so that they can avoid those during risk periods. The data generated in this project will be used in the development of a ciguatera risk profile for fish from Mangalore and the greater coastal Karnataka area. Such a risk profile will inform the development of advisories for all stakeholders including fishers, fish vendors, fish processors and fish consumers. Such advisories would help ensure fish safety and maintain fish consumption.

Furthermore, ciguatoxins themselves are colourless, odourless and are not destroyed by cooking. Data from newly characterised toxins e.g. from previously un-sampled species and populations such as those addressed in the current study will also assist with the development of rapid, cheap, portable testing kits available for ciguatoxin detection by the lay person. This will further safeguard public health, especially within South Asia where fish consumption is important both culturally and economically. In addition, there is no human biomarker for ciguatoxin which often means further delays in diagnosis even if those affected attend hospital. Symptoms can last from weeks to years, in some cases up to 20 years after exposure which can cause long term health problems. These can have far reaching social-economic implications especially in countries in South Asia where there is very limited social security and access to a high standard of healthcare is not guaranteed.