Scombroid poisoning: causes, symptoms, and treatment

Scrombroid poisoning also known as histamine poisoning, is the most common form of seafood toxicities. As per the CDC statistics, histamine poisoning accounts for 37% of all seafood related poisoning and 5% of all food related toxicities. [Daniel Noltkamper] Scrombroid poisoning occurs due to the metabolic conversion of histidine, a natural amino acid found in the fish flesh into the toxic histamine by the activity of bacteria. This occurs most rapidly when the fish are exposed to ambient temperatures of 21.1°C-32.2°C for a few hours, or even at temperatures greater than 7.2°C. Since majority of the seafood consumed in the United States is imported from abroad, the FDA had implemented quality control standards in 1995 known as the Hazard Analysis Critical Control Point (HACCP) to check the quality of all imported seafoods. However, as the 2003 statistics showed, barely 5 to 7% of all imported seafoods from more than 8500 importers were checked for the HACCP standards. [CDC] the fact that not all foreign and local fishing boats are covered under the HACCP implies that the risk of outbreak of scromboid poisoning is quite real and a concerning problem. Let us have a brief overview of scrombroid poisoning, its cause, symptoms, treatment and the preventive measures to avoid this fish poisoning.

Current Understanding

Scrombroid poisoning was thought to be caused by the consumption of putrefied fish belonging to the families of Scombroidae and Scomberesocidae such as mackerel, tuna, swordfish, albacore, etc. However, today we understand that dark skinned nonscromboid fishes such as amberjack and mahimahi also cause histamine poisoning. [Gerry predy] Today we know that Histidine decarboxylase (HDC) present in Escherichia coli, Proteus, Klebsiella and other species of bacteria is the main causative agent for histamine poisoning as it converts the histidine amino acid into toxic histamine when exposed to room temperature for a few hours. These bacteria live on the fish tissues and under favorable conditions (high temperature) multiply and metabolize histidine to histamine. It is estimated that histidine to histamine ratio which is usually 0.1 mg/100 g in a healthy living fish can quickly shift to 100 mg/100 g. [Daniel Noltkamper] We now know that anything that exceeds 20mg/100g for histidine histamine ratio is a toxic dose. However, there is still much to be uncovered about the mechanism of toxicity, as laboratory attempts to recreate symptoms by oral intake of toxic levels of histamine, have failed. This in spite of the fact that patients administered with anti-histamines tend to respond well and recover from the symptoms indicates a possible role of other agents. It is postulated that symptoms manifest when histamine combines with other biological amines. [Marta Ferran] People affected by scromboid poisoning may present with symptoms ranging from heachache, vomiting, skin rashes, palpitations, to urticaria and acute bronchospasm in severe cases. Though mortality is very rare immediate and efficient management of symptoms is of utmost importance in order to avoid any serious complications from developing.

Research on Histamine poisoning

Since we only know that histamine is involved but are still unaware of the mechanism of toxicity currently research is focused on unraveling these hidden details. Some studies and clinical analysis have indicated the potential role of other byproducts of histidine metabolism such as Urocanic acid, cadaverine or putrescine. Putrescine, in particular, has been found to increase circulatory histamine levels by increasing the release of histamine from mucosa. Other studies have focused on the histamine intolerance and the role of secondary factors such as enzymes Diamine oxidase and histamine N-methyltransferase that metabolize histamine inside the body. Histamine is a biogenic amine, synthesized and used as a mediator for several biological process including neurotransmission, immunomodulation, hematopoiesis, healing of wounds, etc. While the enzyme Diamine oxidase (DAO) is involved in the extra cellular metabolism of histamine, HNMT is believed to be involved in intracellular catabolism of histamine. Thus it is found that patients who are under drugs that suppress DAO activity (DAO-blocking drugs) are more at risk for histamine intolerance. [Laura Maintz] Therefore patients presenting with symptoms of histamine poisoning must be checked for the use of DAO inhibitors. One recent research that studied the scrombroid outbreak in California in 2003 found very high levels of histamine (2000 to 3800 ppm) and a very rare agent for scrombroid poisoning, the escalor fish. This research also indicated that people who were under medication exhibited more varied and prolonged symptoms compared to those who were not under any kind of medication. [K.A. Feldman et.al, 2005]