Jamaican vomiting sickness
Jamaican vomiting sickness is an acute illness caused by the toxin hypoglycin A, which is present in unripened fruit of the ackee tree. Hypoglycin A is present in the unripe arilli at levels of over 1000 ppm, which falls to less than 0.1 ppm in the fully ripened arilli. Hypoglycin B, found only in the inedible seed, is believed to be a derivative of hypoglycin A. Its concentration rises from 0.4 mg/g to 3.3 mg/g as the fruit ripens.
When ingested, hypoglycin A is metabolized to produce methylenecyclopropylacetic acid (MCPA). MCPA acts to inhibit the beta-oxidation of fatty acids in two ways. First, it interferes with the transport of long-chain fatty acids into the mitochondria. Also, it inhibits acyl-CoA dehydrogenases, so that only unsaturated fatty acids can be fully oxidized. Fatty acids accumulate in the liver in a microvesicular pattern that can be seen on biopsy. In the absence of fatty acid metabolism, the body becomes dependent on glucose and glycogen for energy. Octreotide can be used to reduce secretion of insulin by the pancreas, preventing severe hypoglycemia.
Inhibition of beta-oxidation of fatty acids, however, also depletes a necessary cofactor for gluconeogenesis. Once the liver glycogen stores are depleted, the body cannot synthesize glucose, and severe hypoglycemia results.
Abdominal discomfort begins two to six hours after eating unripe ackee fruit, followed by sudden onset vomiting. In severe cases, profound dehydration, seizures, coma, and death may ensue. Children and those who are malnourished are more susceptible to the disease.