Ciguatera

Ciguatera is a food-borne toxin found in fish that inhabit reefs in tropical and sub-tropical waters.The toxin is found in microscopic organisms that are concentrated as they move through the food chain from smaller fish to larger fish. Although the toxin can also affect fish, many suffer or show no ill effects. It is particularly dangerous because it is colorless, odorless, and is not destroyed by cooking. It effects between 20,000-50,000 people per year but exact figures are difficult to come by as the condition is not easy to diagnose.
Like most food-borne illnesses, symptoms usually start with gastro-intestinal distress. The symptoms then spread to the heart and nervous system. Unlike other forms of food poisoning, which often resolve within days, the symptoms can last for weeks, months or even years. Typically, the course of the disease is cyclical with improvement and relapse being common. As such, care must be taken to distinguish the condition from other similar neurological conditions, such as multiple sclerosis.
Ciguatera is one of the very few forms of toxic poisoning that can be transferred from person to person. The toxin can be transmitted through breast milk and even sexual intercourse. 
Most patients fully recover from the condition. As such, treatment focuses on providing supportive care, managing symptoms and avoiding foods that can trigger a relapse. 
Ciguatera at Wikipedia