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ciguatera fish poisoning is the commonest seafood - borne illness that results from eating fish contaminated with ciguatoxin .
it has a unique clinical syndrome due to ciguatoxin , a colorless , odorless , lipid - soluble , heat - resistant , not affected by freezing , acid - stable , cyclic polyether compound with a molecular formula of c60h86o19 that is attracted to and is stable in the cell membrane lipid bilayer .
it has both cholinergic and adrenergic effects on muscle , nerve and cardiac cells . among the toxic manifestations , cardiovascular symptoms are uncommon .
a 16-year - old previously healthy man was brought to the emergency room for vomiting and watery non - bloody diarrhea associated with tenesmus and dizziness , beginning one hour after eating mackerel fish .
there was no relevant past medical or surgical history . on examination , he was conscious , oriented and diaphoretic .
echocardiography revealed a mild global hypokinesia of left ventricle without any evidence of chamber dilatation and the left ventricular ejection fraction was 45% .
. however , the bradycardia persisted . a continuous infusion of atropine with a total dose of 45 mg over 48 hours was given .
he was discharged on the third day without any complications and follow - up was uneventful .
electrocardiogram ( ekg ) of the patient 1 an 18-year - old healthy female , presented with complaints of dizziness , nausea , watery diarrhea , diffuse pruritis , circumoral tingling , and chest discomfort following consumption of mackerel fish .
her supine blood pressure was 80/40 mmhg with a heart rate of 42 beats per minute .
she required a total dose of 30 mgs of atropine over 48 hours for the correction of bradycardia .
she was discharged on day four , and follow - up did not reveal any abnormality .
however , both the patients did not show any abnormality in qrs complex or qt interval .
a 16-year - old previously healthy man was brought to the emergency room for vomiting and watery non - bloody diarrhea associated with tenesmus and dizziness , beginning one hour after eating mackerel fish .
there was no relevant past medical or surgical history . on examination , he was conscious , oriented and diaphoretic .
echocardiography revealed a mild global hypokinesia of left ventricle without any evidence of chamber dilatation and the left ventricular ejection fraction was 45% .
. however , the bradycardia persisted . a continuous infusion of atropine with a total dose of 45 mg over 48 hours was given .
he was discharged on the third day without any complications and follow - up was uneventful .
an 18-year - old healthy female , presented with complaints of dizziness , nausea , watery diarrhea , diffuse pruritis , circumoral tingling , and chest discomfort following consumption of mackerel fish .
her supine blood pressure was 80/40 mmhg with a heart rate of 42 beats per minute .
she required a total dose of 30 mgs of atropine over 48 hours for the correction of bradycardia .
she was discharged on day four , and follow - up did not reveal any abnormality .
however , both the patients did not show any abnormality in qrs complex or qt interval .
the clinical manifestations of ciguatera fish poisoning depend on the amount and parts of the fish eaten , fish species , fish size and the individual 's susceptibility .
the ideal method of diagnosing and quantifying ciguatoxin , as well as finding out susceptible population , has yet to be developed .
hence , diagnosing such cases is a challenging task to clinicians and emergency physicians . although it is difficult to compare and contrast cases , there are classical gastrointestinal , neurological and cardiac symptoms that occur in ciguatera cases .
gastrointestinal symptoms occur within 12 hours of ingestion ( acute phase up to 24 hours ) and persist for 1 or 2 days .
neurological symptoms may occur early or late , persist up to weeks or months or years after ingestion .
the cardiovascular symptoms are uncommon , and are observed in 1015% of those exposed to ciguatoxin during the acute phase , which slowly decline within a week .
site 5 on voltage - gated sodium channels , affecting them in an unusual manner by competitively inhibiting calcium 's membrane - polarizing influence on passive sodium channels , causing intracellular levels of sodium and calcium to increase .
the persistent opening of sodium channels in cell membranes increase sodium channel permeability . in animal model ,
ciguatoxin blocks voltage - gated potassium channels , which contributes to neuronal excitability in parasympathetic neurons and impairs sympathetic reflexes .
bradycardia was attributed to inhibition of cholinesterase by ciguatoxin without any effect on qrs complex or qt interval .
overall , toxin inhibits repolarization and keeps the cell in depolarized state , hence prolongation of action potential with induction of leakage current occurs .
in particular , the excitability and instability of the cell membrane at the sinoatrial node weaken the action potential due to the difference in the current flow of sodium ion eventually , decrease the action potential and results in sinus node dysfunction .
additionally , the altered sodium and calcium levels increase the frequency and force of muscle contractions with greatest effect on cardiac muscle , since ciguatoxin has an increased affinity to binding site on cardiac muscle cells .
inotropic effects of ciguatoxin on cardiac tissues mainly depend on toxin concentration , sensitivity of autonomic nerve terminals and ciguatoxin induced increase of sodium influx all of them contribute to cardiac cell dysfunction .
further , ciguatoxin stimulates the unmyelinated afferent cardiac branches of the vagus nerve which leads to a tonic inhibition of central vasomotor centers with reduced sympathetic output and peripheral vascular resistance , causing bradycardia , continued hypotension , and peripheral vasodilatation .
ciguatoxin action on the human heart thus appears to be related primarily to indirect effects on intrinsic nerves , rather than a direct effect on myocardial cells .
lewis et al , demonstrated the effect of ciguatoxin on the contractility of human cardiac musculature via neural mechanism . at times ciguatoxin
primary prevention is to educate the general population periodically through audio - visual media on the effects of ciguatera fish ( mackerel fish ) poisoning .
once a person is exposed , the individual and his / her family/ friends have to be counseled on diet a ) high protein and carbohydrate diet for 3 to 6 months after acute phase , and b ) avoidance of foods such as nuts and seafood , as well as alcohol as these may prolong or exacerbate chronicity after initial exposure .
subsequent reactions to ciguatoxin may be more damaging due to the storage of toxin in the adipose tissue and/or host 's accelerated immune response from memory which may contribute for slow release of ciguatoxin into circulation . also , transmissibility of toxin from affected individual through sex , breast milk and placenta may be highlighted .
pregnant women may be told that ciguatoxin does not affect fetal development , but accelerates fetal movement .
primary prevention is to educate the general population periodically through audio - visual media on the effects of ciguatera fish ( mackerel fish ) poisoning .
once a person is exposed , the individual and his / her family/ friends have to be counseled on diet a ) high protein and carbohydrate diet for 3 to 6 months after acute phase , and b ) avoidance of foods such as nuts and seafood , as well as alcohol as these may prolong or exacerbate chronicity after initial exposure .
subsequent reactions to ciguatoxin may be more damaging due to the storage of toxin in the adipose tissue and/or host 's accelerated immune response from memory which may contribute for slow release of ciguatoxin into circulation .
also , transmissibility of toxin from affected individual through sex , breast milk and placenta may be highlighted .
pregnant women may be told that ciguatoxin does not affect fetal development , but accelerates fetal movement .
it presents with characteristic gastrointestinal , neurological , and cardiovascular symptoms . with widespread travel to tropics
, increasing consumption of fish as part of a healthy heart diet and increased availability of exotic frozen fish may increase the occurrence of ciguatera poisoning and no longer is it confined to the endemic area .
ciguatera fish poisoning shall be considered , when a previously healthy individual presents with an unexplained bradycardia , hypotension , arrhythmias , and atrioventricular block .
there is a need to create an awareness of this entity among health care professionals , emphasizing accurate reporting , testing of fish containing ciguatoxin prior to consumption , and develop simple laboratory methods to diagnose such cases .
ciguatera fish poisoning occurs with ingestion of fish containing ciguatoxin . 
 it causes a clinical syndrome that comprises classic gastrointestinal , neurological and cardiovascular symptoms . 
 ciguatoxin is a sodium channel agonist with cholinergic and adrenergic activity . 
 although cardiovascular symptoms are rare with ciguatoxin , we report two cases with bradycardia and hypotension . fatality and long - term sequelae are not uncommon with ciguatoxin poisoning and educating the general population is essential .