Ciguatera fish poisoning (CFP) is a food-borne disease affecting costal populations in tropical and subtropical regions throughout the world . It is caused by the ingestion of coral reef fish that have accumulated the toxins from naturally occurring marine toxin produced by dinoflagellates of the genus Gambierdiscus spp . Grazing of these dinoflagellates by fish begins the process of bioaccumulation and bio-modifications through food web with humans being at the end of the chain. The symptoms produced by CFP begin with gastrointestinal symptoms (diarrhoea, vomiting etc.) followed by the neurological (numbness of joins) to cardiovascular symptoms ( lower hear rate, hypertension). CFP has been occurring problem for centuries and the estimated, reported cases of this disease are as many as 50.000 per year, however the misdiagnosis and underreporting cases brought this number to as many as 500.000 cases per year! With such a high and long prevalence of this problem and with today’s knowledge and available technology, it would be reasonable to assume that there are measures put in place in order to prevent from occurring of this disease. However in practise this have proven to be not so simple task. First of all, ciguatera toxins are not affected by either freezing or cooking. There is also no way to distinguish affected fish by either visual or organoleptic means. Medical symptomologies in humans are elicited effective at very low (i.e. sub-ppb) ciguatoxin concentrations in fish. Although there exist few detection methods such polyclonal antibodies assay for detecting haptens via a luminescent probe was used for many years but it has also been under considerable analytical controversy. The process of developing effective and practical test have been generally very slow and is some cases proved misleading. The best way of prevention of CFP would be to have available simple test for fisherman so they could test the infected fish prior to sell.
Currently, the only ciguatera field test kit, called Cigua-Check ® has been used frequently however it had mixed reviews from fisherman and researchers. For this reason Bienfang et al. (2011) conducted study to quantitatively evaluate the practical usefulness of the kit. They assessed the consistency with which multiply users of the kit would come to a similar conclusion regarding the ciguatoxic status of fish being examined.
This study tested two parameters of reliability of the Cigua-Check®. These included the degree to which multiple readers of the same test strip agreed in their conclusions from their individual testing of identical Cigua-Check® and the degree to which those conclusions were consistent with the actual ciguateric status of those samples, as determined by a more robust laboratory assay of Na+-channel disruption measured by the N2a neuroblastoma bioassay. Study was conducted by sampling Main Hawaiian Islands . A104 samples of the carnivorous fish Cephalopholis argus, and 84 samples of herbivore, Acanthurus striatus, were examined using both the commercially available Cigua-Check® test kit and the Na+-channel specific N2a neuroblastoma mouse bioassay to generate dose response curve. The sodium channel specific N2a bioassay potentates depolarization of cellular membranes, and is used to detect sodium channel disruption caused by ciguatoxin. The limit of detection of 0.05 ug CTX/kg fish unlike Cigua-Check® with 0.10 ug CTX/kg fish limit.
The results showed that Cigua-Check® test strips present substantial insufficiencies in terms of its simplicity and reliability for testing ciguotoxis . Although some of the false negative results obtained by comparing test strips with bioassay could be to do with different sensitivities of these methods the low degree of agreement amongst test users of these same test strips shows serious uncertainty of the test strip results. In addition, the positive controls provided with those kits were variable in strength between different kits. Also the colouration (blue colour is developed if test is positive) was shown to be very unspecific. Therefore this test kit was proven to be unsuccessful and the development of quick field test is still a challenge for prevention of CFP.
This study was very interesting and very useful in terms of the evaluation of these test kits. According to many forums and news many people actually have bought this test kits going travelling and how disappointed they must have been! Most of the suppliers have quickly discontinued to sell these test kits but some of them, despite quite robust results still continues to sell them. It is quite surprising that despite all these years that disease have been present and with today’s knowledge and high tech it is still a quite big problem.
A review of Bienfang et al., 2011. Quantitative Evaluation of Commercially Available Test Kit for Ciguatera in Fish. Food and Nutrition Sciences. 2: 594-598
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