Final answer:
Ciguatera intoxication occurs when humans consume fish that contain toxins produced by certain algae, and cooking does not deactivate these toxins.
Step-by-step explanation:
Humans become sick from ciguatera intoxication by ingesting fish contaminated with toxins produced by algae. Ciguatera is a form of food poisoning that occurs when fish that feed on this algae or on other fish that have consumed the algae accumulate toxins in their tissues. These fish are then caught and consumed by humans. Unlike some foodborne illnesses, the toxins that cause ciguatera do not become inactive with cooking, so even properly cooked fish can still be toxic.