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Ciguatera Fish Poisoning
To quickly access the following sections click on the headings below. Ciguatera - General Description and IncidenceSymptoms and Duration of CiguateraTable of Ciguatera SymptomsCiguatera and Chronic Fatigue SyndromeThe Nature and Origin of Ciguatera ToxinsDiagnosis of Ciguatera PoisoningTreatment of Ciguatera PoisoningCiguatera PreventionLinks and References
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Ciguatera - General Description and Incidence |
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| Ciguatera is a type of sea food
poisoning caused by the consumption of fish, especially certain tropical
reef fish, which contain one or more naturally occurring neurotoxins from
the family of ciguatoxins and maititoxins. It has also been suggested that
ciguatera may be caused by occupational exposure to ciguatoxic fish organs
during repetitive handling or processing of fish ( Codella: pers. comm. ).
In confirmation of this are reports that cleaning of ciguatoxic fish may
cause tingling of the hands ( 18a ), clear evidence that ciguatoxins may
be absorbed through the skin ( 18
).
Ciguatera is reported to be the most common form of sea food poisoning in the world ( 1, 2, 4 ) with the estimated number of cases ranging from 50,000 ( 1, 2 ) to 1,000,000 ( 3, 9 ) annually. In view of the fact that only 2% - 10% of ciguatera cases are actually reported ( 2 ), and many doctors have never heard of ciguatera, it is clear that the true prevalence of this disorder could be much greater than these figures suggest. Although ciguatera is often considered to be a mild non fatal disease, it has a world wide mortality rate ranging between 0.1% - 12% ( 2 ) with isolated outbreaks as high as 20% ( 1, 8, 18 ). Symptoms and Duration of CiguateraSince ciguatera may be caused by a cocktail of different fat and water soluble toxins, this disorder may cause numerous different symptoms. The variation in symptoms in different cases, which may also follow a geographical pattern ( 2, 6, 12, 18, 30 ), is thought to be caused by the different biological effects of the various toxins which may be involved ( 1, 2, 11, 12, 18 ). Ciguatera typically presents as an acute gastrointestinal ( and perhaps neurological ) illness, which may, in some cases, only last for a few days ( 1, 5, 6, 12, 18 ), following the consumption of contaminated fish ( 1, 2, 12 ). This initial illness is then frequently followed by a chronic, mainly neurological illness, which may last for months, or even as long as ten years ( 5, 7 ), with claims that the toxin could even remain in the body for 25 years ( 18b ). Since ciguatera is particularly damaging to the nervous system, recovery may not occur until the damaged nerves regenerate and it seems that this may not always occur. Ciguatera, it should be emphasised, can also present as a psychiatric disorder or a dermatologic disorder. Ciguatera may also have a slow insidious onset if there is a gradual accumulation of toxins due to the continuing consumption of fish which have a low level of toxicity ( 10, 30 ). Such cases of course, would be most unlikely to obtain a correct diagnosis. Once a person has contracted ciguatera poisoning they may develop an extreme sensitivity to any further exposure to ciguatoxins ( 2, 18, 30 ). A second attack of ciguatera therefore, may be much more severe than the first one ( 2, 18, 32 ). Additionally, the person who has been exposed to ciguatera may, for a considerable period of time afterwards, suffer relapses following the consumption of seemingly innocuous foods ( 2, 12, 18, 32 ). For instance, consumption of nuts, nut oils, caffeine, alcohol, or animal protein foods, has been known to cause relapses months or years after the initial attack ( 2, 12, 18, 32 ). Consumption of any type of fish can also cause relapses ( 2, 18 ). Even the consumption of poultry which has been fed fish meal has been known to have this effect ( 18, 32 ). The symptoms of ciguatera poisoning, which predominantly effect the nervous system and the gastrointestinal system, and less commonly, the cardiovascular system, are listed below ( 1, 2, 5, 6, 7, 18, 30, 36 ). Symptoms of Ciguatera |
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Neurological symptoms Paraesthesias in extremities and around mouth including numbness, tingling, burning, and pain. Temperature reversal where hot feels cold and vice versa. Temperature sensitivity Vertigo Dental pain Blurred vision Tremor Psychiatric Pain on urination |
Gastrointestinal symptoms Nausea Vomiting Diarrhea Abdominal pain Dyspepsia Abdominal cramping Cardiovascular symptoms |
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| Other
symptoms Dermatitis, itch, rash, aches and pains, arthralgia, myalgia, general weakness, salivation, breathing problems, dyspnea, neck stiffness, headache, ataxia, exhaustion, fatigue, sweating, depression, and metallic taste in the mouth. Ciguatera, it should be noted, may also be sexually transmitted ( 2, 18 ) and may cause premature labour or spontaneous abortion ( 2, ). Ciguatoxins may also be transmitted via breast milk ( 2, 5, 18 ).
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Ciguatera and Chronic Fatigue SyndromeChronic ciguatera poisoning may so resemble CFS that it may be difficult to distinguish between the two illnesses ( 13, 31, 36 ). But are they separate illnesses? CFS it seems, has actually been caused by ciguatera ( 14, 15, 33, 36 ). It is indeed interesting to note that CFS may actually be caused by toxins which closely resemble ciguatoxin ( 37 ). This is not surprising to me since I have noted, after suffering from ciguatera for more than 12 months, the similarity between this illness and the other types of CFS I have had following various viral and bacterial infections. If, as current evidence suggests, CFS is a constitutional disease characterised by reduced adrenal capacity and subsequent stress intolerance, it would not be surprising if there are numerous possible triggering factors for this disorder. In fact, this would be expected. The common factor here is that all these infections or toxins may cause considerable and prolonged internal stress and therefore may have a considerable impact on the adrenal system. From my experience, the various triggering factors for CFS all result in a slight variation in the clinical picture. For instance, one virus may cause a disorder characterised by muscle pain while another may cause more gastrointestinal symptoms. In the case of ciguatera, at least in my case, it has been the neurological symptoms which really set it apart from other causes of CFS. The nature of ciguatoxins, both their persistence in the body and their extreme toxicity, ensures that ciguatera has a very real capacity to impact upon the adrenal system.
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The Nature and Origin of Ciguatera ToxinsCiguatera toxins or ciguatoxins, are said to be amongst the deadliest mammalian poisons known ( 2, 4, 36 ), reportedly being, volume for volume, 1000 times more potent than arsenic ( 10 ). These heat stable toxins originate from a type of microorganism which attaches to certain species of algae on dead or damaged coral in tropical areas around the world ( 1, 11, 18, 30 ). Increasing damage to coral reefs therefore correlates with an increasing frequency of ciguatera outbreaks ( 16, 18 ). Although there are various ciguatera toxins ( 1, 4, 11, 18, 30 ), the most important of which are the fat soluble neurotoxic ciguatoxins (11 ), it is believed that these toxins become altered as they become ingested by progressively larger fish and move up the food chain ( 2, 11, 16 ). The smaller reef browsing herbivorous fish first consume the toxic algae and then become consumed by the larger predatory carnivorous fish. Since the larger predatory fish can consume many of the smaller fish, the ciguatoxins become biotransformed and more concentrated as they move up the food chain. It is for this reason that large carnivorous tropical reef fish are considered to have the highest risk of toxicity (2, 3, 16 , 18 ). It has also been claimed that the toxins which accumulate in these fish are more toxic ( 2, 18 ). In view of the popularity of fish oil and fish liver oil supplements, it should be emphasised, that although fat soluble ciguatoxins may accumulate throughout the flesh of a fish, it is the organ areas such as the liver which accumulate the greatest concentration of these toxins (2, 11, 18 ). These parts of the fish are by far the most toxic ( 2, 11, 18 ). Since there is no simple routine test for the presence of ciguatoxins, stringent steps should be taken to ensure the source, and safety, of fish oil products.
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Diagnosis of Ciguatera PoisoningSince there is no conclusive blood test for the presence of ciguatoxins, diagnosis usually depends upon the history and clinical features ( 5, 6, 18 ). Consumption of fish followed by an acute gastrointestinal and neurological illness is the usual diagnostic setting. Without this precise clinical picture, correct diagnosis is much more difficult and unlikely. A recent report however, indicates that there may be new hope for victims of ciguatera. According to Hyde ( 9 ), ciguatera may now be diagnosed by a simple eye test, termed a Visual Contrast Sensitivity test. It is claimed that neurotoxins, such as ciguatoxins, effect the eye in such a way that it loses the ability to accurately discern shades of white, grey, and black ( 3, 9, 17 ). It is indeed to be hoped that this test clarifies the diagnostic uncertainties regarding ciguatera.
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Treatment of CiguateraTreatment of ciguatera poisoning is also far from satisfactory. The use of mannitol has been recommended by various authorities ( 1, 2, 18 ), however this treatment is only effective if it is used in the first 48 - 72 hours of the illness ( 2, 18 ). Treatment of chronic ciguatera is usually symptomatic ( 1, 2, 18 ), although a recent report claims that the cholesterol lowering drug cholestyramine has been effective, even for disease which has been present for 10 years ( 9 ). From my experience, the two most effective treatments were the complete elimination of all sea food from the diet, and the use of megadoses of vitamin B12. After contracting ciguatera I found that I was experiencing a number of symptoms which were very similar to vitamin B12 deficiency. These symptoms were largely neurological and occurred predominantly below the waist, although I also experienced some similar symptoms around the scalp, face, eyes and mouth. It was the symptoms in the lower back and legs which were most severe however. These symptoms included burning sensations, numbness, and pain and weakness which would be greatly exacerbated by standing for only a few minutes. These symptoms were progressive until I began weekly supplements of 4000mcg tablets of vitamin B12 ( smaller doses were ineffective) My response to the B12 was dramatic with a very rapid improvement in vitality and well being and a more gradual improvement in the neurological symptoms. I found however, that if I did not take the B12 weekly I would relapse. This continued for several months when I then found I could discontinue the B12 with no repercussions. Vitamin B12 blood tests which were not done until after I began B12 supplements, revealed that my B12 levels were in the low end of the normal range, even less than 24 hours after taking the vitamin. This led to the suggestion that I was malabsorbing B12, however a subsequent vitamin B12 absorption test was normal. The reasons for these observations have never been determined. However, since toxins produce their toxic effects by disrupting normal metabolic pathways, it would not surprise if there was some kind of interaction between ciguatoxins and vitamin B12. In view of the ability of ciguatera to destroy nerve tissue, it is indeed interesting to note that high doses of methylcobalamin, the active form of vitamin B12, has recently been shown to stimulate regeneration of damaged nerve tissue ( 28, 29, 35 ). Futhermore, various neurological disorders have been linked to a deficiency of methylcobalamin ( 28, 29, 35 ).
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Ciguatera PreventionSince ciguatoxins are unaffected by cooking or processing of food ( 1, 2, 5, 16, 26, 32 ), and contaminated fish is not detectable by appearance, taste, or smell ( 1, 2, 5, 26, 32 ), prevention of this disorder can only be achieved by avoiding contaminated fish ( 2, ). There is however, a home test kit available for those consumers who wish to reduce the risk of ciguatera by testing the fish before it is consumed ( 27 ). The cost of this five test kit though, $AUD120.00, would seem to preclude its use for routine testing. Since it is has been demonstrated that ciguatoxins may be absorbed directly through the skin ( 18 ), the possibility of contracting ciguatera as a result of the repeated handling of the organs of ciguatoxic fish should also be borne in mind. According to Codella ( pers. comm. ), a marine biologist, strict hygiene should be exercised to prevent the possibility of this type of occurrence. Ciguatera may be caused by some 400 different species of tropical reef fish around the world ( 1, 16, ), and, in theory at least, the avoidance of these species will considerably lower the risk of falling victim to ciguatera. However, the idea that ciguatera is merely a tropical disease which is confined to an area between 35ºN and 35ºS of the equator ( 1, 11, 30 ) is no longer tenable. Tropical fish are marketed throughout the world ( 1, 6, 9, 11, 26, 18, 32 ) and some species, like skipjack tuna and dolphin fish ( 20, 32 ), may also migrate considerable distances. In Australia for instance, there have been numerous outbreaks of ciguatera poisoning in Sydney, 63 people being affected in one outbreak ( 18 ), and even as far south as Melbourne ( 34 ). The species of fish which may cause ciguatera include those listed below ( 7, ). For a more comprehensive list of species go to http://www.fishbase.org/search.cfm and search for ciguatera under topic search. |
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| Spanish mackerel Dog tooth tuna Skipjack tuna Pacific kingfish Barracuda Trigger fish Jacks Snapper(Lutjanidae) Various species of cod or groper Sea bass Barramundi |
Reef shark Moray eel Coral trout Dolphin fish Trevally Sea perch Parrotfish Surgeon fish Yellowtail Mullet Pigeye shark |
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Of these fish, large carnivorous reef inhabiting fish such as the barracuda are generally considered the most toxic species ( 2, 9, 11,18, 26 ) although pelagic fish like the Spanish mackerel seem to cause the most outbreaks of ciguatera ( 18 ) Some fish, such as red bass ( bohar snapper ) and paddletail, may be banned from sale in some localities ( 18, 32 ). Although it is often considered that so called pelagic fish ( ie. fish which prefer the open sea ) are free from the risk of ciguatera, this is not necessarily true (18 ). Certain commercially important species from the tuna and mackerel family for instance, are known conveyors of ciguatera, so much so in fact, that in Queensland, 65% of ciguatera cases are caused by pelagic fish such as mackerel ( 18 ). These include both skipjack tuna and dog tooth tuna as well as the various species of mackerel ( 7, 18, 30 ). Even pelagic fish like tuna may frequent coastal areas during certain seasons or when breeding ( 19, 21, 30 ). Skipjack tuna in particular, is a well known cause of ciguatera poisoning ( 20 ). This is extremely important since the dark fleshed skipjack is by far the most commercially important species of tuna in the world, comprising 50% of the total world tuna trade in 1999 ( 22, 23 ). This compares to 32% for yellow fin tuna and 6% for albacore tuna ( 22, 23 ). Although the white fleshed albacore, and also the yellow fin, neither of which are a known cause of ciguatera, are the preferred species for the canning industry ( 24 ), the use of skipjack for canning has been blamed for ciguatera poisoning resulting from the consumption of canned tuna. It should be noted however, that the species of choice for 'white' canned tuna is albacore tuna ( 25 ), while the darker fleshed forms of canned tuna may contain skipjack, yellowfin, or bluefin ( 25 ). The implications of all this for the fish consumer are clear. Since it is impossible to say where a given fish has been, or where its dietary victims have been, it is impossible to guarantee the absolute safety of a particular fish. As has been aptly noted, "any fish living in the sea may be a potential vector of ciguatoxin ( 18, 18c ). Having said this however, it is clear that the risk of ciguatera may be minimised by selecting a suitable species of fish. Although I would otherwise suggest that fish is by far the best form of animal protein for those who require it, after having had ciguatera for more than 12 months I am now compelled to conclude that the consumption of any fish is simply not worth the risk. This is especially true for those who have become sensitised to ciguatoxins. For an excellent detailed and lengthy review of ciguatera, see the
review by Lehane ( 18
). 1. http://www.emedicine.com/cgi-bin/foxweb.exe/showsection@/em/ga?
See: Arnold, T., eMedicine Journal, May 23 2001, Volume 2, Number 5.
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