What is the source of scombroid poisoning?

Scombroid poisoning is primarily caused by the presence of histamines in the muscle tissue of certain fish, particularly those that are poorly handled or stored. When fish such as tuna, mackerel, or sardines are not kept at the correct temperatures after being caught, bacteria can convert amino acids in the fish into histidine, which is then transformed into histamine. This histamine accumulation is what leads to the symptoms of scombroid poisoning, such as flushing, rash, and gastrointestinal distress.

The other options discuss different types of foodborne illnesses. Contaminated water supply suggests issues related to waterborne pathogens or chemical contaminants, which are not involved in scombroid poisoning. Improperly canned goods are associated with botulism, a distinct foodborne illness caused by the bacterium Clostridium botulinum. Lastly, parasites in shellfish can lead to different illnesses like shellfish poisoning but do not contribute to scombroid. Thus, the presence of histamines in fish is the definitive source of scombroid poisoning.