Bigeye Tuna

Scombroid poisoning from fish is a common type of food poisoning.  We are all aware of food poisonings due to E. coli, salmonella, and natural toxins from mushrooms and pufferfish, but scombroid poisoning is a bit different.  The source of scombroid poisoning is from the chemical histamine, which comes naturally from decaying fish.  Its name, scombroid, is derived from the fish family Scombroidea, which is comprised of mackeral and tuna, fish most highly linked to scombroid poisoning due.  These fish, and others, have high amounts of the amino acid histidine.  When the captured and dead fish are exposed to temperatures above 60 ºF (16 ºC) histidine is enzymatically decarboxylated to histamine.  This is why fish need to be kept below 40 ºF (4 ºC), to prevent formation of histamine.  Histamine, once formed, is not removed or destroyed during cooking, and the signature “honey comb” like flesh and metallic taste can be masked by sauces.

So how common is scombroid poisoning?  Well, according to the CDC scombroid poisoning accounts for approximately 0.5% of reported food borne illnesses.  This number is likely low, as many poisonings go unreported because symptoms may be short lived, not severe, or difficult to differentiate between other illnesses.  The reporting of such poisonings is also not required under many state and federal laws.

The symptoms of scombroid poisoning are typically flushing of the face, headache, diarrhea, shortness of breath, and tachycardia.  Onset can be as short as 15 minutes or as  long as 3 hours, with symptoms lasting as long as 8 hours.  There is no “antidote”, but it can be treated with antihistamines and  in extreme situations supportive care in emergency departments.  Scombroid poisoning is rarely fatal, but recently a “perfect storm” took the lives of an Australian mother and daughter vacationing in Bali.

Histamine

Noelene Bischoff and her young daughter, according to autopsy reports, died of scombroid poisoning.  Their exposure to high levels of histamine and medical history of asthma led to their deaths.  So how are the two related?  In the body, one role of histamine is as a chemical signal in immune responses.  In response to an allergan, such as a bee sting, pollen, or molds, histamine is released and the immune response starts.  This is why bee stings become inflammed and pollen makes our noses itch and drip.  It is also why we take anti-histamines, to block this immune repsonse and alleviate these symptoms.  In the lungs, histamine causes bronchoconstriction and bronchial muscle contraction – in short, difficulty breathing and a tightness of the chest.

The Bischoff’s also had asthma, which is chronic inflammation of the lungs resulting in increased bronchial muscle contriction.  During an immune response the airways produce mucus to cleanse itself of the allergen, and with asthma the airways overreact and create too much mucus, closing off the lungs airways even more.  The combination of inflammation of the lungs and general constriction, combined with an increase of histamine from poisoned fish that sent their immune response into hyperdrive, led to their deaths.

There are FDA established limits for safe and unsafe levels of histamine in fish.  Fresh fish may contain less than 10 mg/kg of fish, with levels of 200 mg/kg producing symptoms, while 500 mg/kg is established as hazardous.  Most reported and investigated outbreaks of scombroid poisoning far exceeds the 500 mg/kg threshold.  The take home message is that fish, particularly the mackerels and tunas, should be properly refrigerated at all times – from the time they are caught to the time they are prepared for eating.  Natures poisons are everywhere, and can have disastrous effects.