Defining the enigma of physiological responses of chronic ciguatera

Shoemaker, R. C., House, D., & Ryan, J. C. (2010). Defining the neurotoxin derived illness chronic ciguatera using markers of chronic systemic inflammatory disturbances: a case/control study. Neurotoxicology and teratology, 32(6), 633-9. Elsevier Inc. doi:10.1016/j.ntt.2010.05.007

Ciguatoxins are potent neurotoxins; they originate in tropical marine dinoflagellates Gambierdiscus spp.. These toxins enter the food web and are consumed by fish and consequently humans. During trophic transfer ciguatoxins are biotransformed and biomagnified in multiple fish spp. Estimates indicate there are more than 100 000 cases a year, however the authors also report that this is underestimated.

There are multiple strands of ciguatera toxins produced by different Gamierdiscus spp., they are geographically specific i.e. different strains are found in the Pacific, Indian oceans and Caribbean oceans. These variations in toxins (both structure and potency) cause variability in the symptoms produced. The potency in different strains is also varied. Pacific ciguatoxin can cause human illness at 0.1 parts per billion, it is estimated to be 10 times more potent than Caribbean strands. The variation in the toxins from different oceanographic regions makes the diagnosis of ciguatera poisoning difficult, even in advanced labs. Most cases of poisoning last around 2 to 3 months, 5% of these victims develop chronic ciguatera (CC), which has multiple symptoms, and they are manifested in multiple physiological systems. CC can last for up to 10 years. Shoemaker et al. classify the symptoms as refractory symptoms e.g. fatigue, cognitive deficits, pain. These symptoms are indicative of many other ailments, thus confounding its diagnosis. The current diagnosis of CC poisoning is based on the immediate onset of the symptoms following the consumption of tropical reef fish.

The authors note that ciguatera is a central economic issue for export of tropical fish. The treatments available at the moment are limited, complimentative alternative medicines are often used. CC is thought to have similar symptoms as other syndromes such as chronic inflammatory response syndrome. This research measured a variety of biomarkers in an attempt to establish an understanding of CC syndromes pathophysiology, in order that therapies could target the causal mechanisms more effectively. Considered indicative parameters were tested in 59 control patients and 59 diagnosed patients, these were: visual contrast sensitivity and blood tests, which consisted of multiple physiological biomarkers, e.g. alphamelanocyle stimulating hormone (MSH), vasoactive intestinal peptide (VIP) and comprehensive metabolic panel (CMP).

Tests of difference were carried out between controls and diagnosed CC patients. Not all patients’ blood was analysed as 30 patients samples were considered as representative by the researchers. This may be debated as it is a relatively small sample size thus increasing the chances of a type 1 error. Their results indicate that immune system abnormalities are present in CC cases. They suggest the documentation of symptoms may improve the diagnosis of CC, which is a vast contribution to medical practices, provided their research is accurate. They state that abnormalities found in various biochemical pathways are indicative of the mechanisms that are part of the pathophysiological construct of CC poisoning. However although the empiricist intrinsic blood biomarkers are different, little understanding is gained about the development of the syndrome. This paper discusses how each blood parameter measured may contribute to the syndrome's immune homeostasis deregulation.

To conclude Shoemaker et al.’s findings establish physiological alterations of the dynamics of genetic expression, innate adaptive community and neuropeptide regulatory mechanisms in CC patients. Their findings support the hypothesis that CC is characterised by immune deregulation based on genetic control of the host’s responses. This evidence provides a basis for potential therapies. It would be interesting and mechanistically informative to carry out studies of patients over a temporal scale during the onset and development of CC, in order to further elucidate it's characteristics; In particular in relation to the developmental basis of the spectrum of ailments : fatigue, cognitive, neuralgic, rehematolgic, respiratory and other symptoms.