Hazard identification and characterisation: Initial symptoms include tingling or burning sensation in the mouth, rash on the upper body and drop in blood pressure. Frequently, headaches and itching are encountered. The symptoms may progress to nausea, vomiting and diarrhoea that require hospitalisation, particularly in the case of elderly or impaired patients (FDA 2003).
The onset of intoxication is rapid, ranging from immediate to 30 minutes. The duration of the illness is usually three hours, but may last several days (FDA 2003).
Due to uncertainty about its aetiology it is difficult to determine the susceptible population for scombrotoxicosis. A wide range of histamine concentrations in implicated foods, particularly the increasing number of incidents associated with low histamine concentrations, suggests that some individuals are more susceptible to the toxin than others. Differences may be due to the activity of histamine-degrading enzymes in the stomach. Symptoms can be severe for the elderly (FDA 2003) and for those taking medications such as isoniazid, a potent histaminase inhibitor (Morinaga et al. 1997).
The toxic dose for histamine is not precisely known and scombroid poisoning has occurred at histamine concentrations as low as 50 mg/kg. However most incidents involve fish with histamine concentrations of 200 mg/kg and over (Fletcher et al. 1998).
Clifford and Walker (1992) suggest that neither histamine nor biogenic amines are responsible for scombrotoxicosis. Volunteers fed mackerel with 6000 mg/kg histamine reported only mild tingling around the mouth. Lehane and Olley (1999) speculate that urocanic acid may be the missing factor (‘scombroid toxin’) in histamine fish poisoning.
