Consuming crab that is improperly handled, stored, or naturally contaminated can result in serious illness, ranging from severe gastrointestinal distress to life-threatening neurological conditions. “Bad crab” refers to crustacean meat tainted either by harmful bacteria introduced through poor sanitation and storage, or by naturally occurring marine toxins accumulated in the crab’s tissues. The health consequences depend entirely on the type of contaminant ingested, requiring different responses.
The Biological Agents That Cause Illness
The risk of illness from crab falls into two main categories: bacterial contamination and exposure to potent marine biotoxins. Bacterial contamination frequently arises from poor handling, inadequate storage temperatures, or cross-contamination after cooking. Pathogens like Vibrio parahaemolyticus are naturally present in marine environments and multiply rapidly in seafood not kept sufficiently cold. This bacterium is a leading cause of seafood-related foodborne illness globally.
Another common bacterial culprit is Salmonella, which contaminates crab if sanitation is inadequate during harvesting or processing. In rare cases involving improperly preserved products, the neurotoxin produced by Clostridium botulinum is a concern. Proper cooking generally kills vegetative bacterial cells, but toxins produced by some bacteria are heat-stable and may remain.
Marine biotoxins represent a distinct and often more dangerous threat because cooking or freezing does not destroy them. These toxins are produced by microscopic algae during harmful algal blooms, or “red tides,” and crabs accumulate them by feeding on contaminated organisms. Paralytic Shellfish Poisoning (PSP) is caused by saxitoxins, potent neurotoxins accumulated in the crab’s tissues, particularly in the tomalley, or “crab butter.” Other toxins include brevetoxins, causing Neurotoxic Shellfish Poisoning (NSP), and domoic acid, causing Amnesic Shellfish Poisoning (ASP). These toxins are undetectable by sight or smell and are unrelated to the crab’s freshness.
Common Symptoms of Crab Poisoning
Symptoms vary significantly depending on whether the illness is due to bacterial infection or toxin exposure. Bacterial food poisoning typically manifests as severe gastrointestinal distress, including nausea, vomiting, abdominal cramps, and profuse diarrhea, sometimes accompanied by a fever.
The onset of bacterial symptoms usually occurs between four and forty-eight hours after consumption, depending on the pathogen and amount ingested. For example, Vibrio infection often causes vomiting and watery diarrhea. A high fever and blood in the stool may suggest a more serious bacterial infection like Salmonella. Most bacterial illnesses are self-limiting, resolving within a few days.
In contrast, marine biotoxin poisoning, such as PSP, presents with rapid and severe neurological symptoms, often beginning within minutes to an hour. The first sign is usually a tingling sensation or numbness starting around the lips and tongue, spreading to the face, neck, and extremities. This can progress to a lack of coordination, dizziness, and a feeling of floating.
More severe toxin exposure leads to muscle weakness, difficulty swallowing, incoherent speech, and respiratory difficulty. In the most serious cases of PSP, toxins can cause paralysis of the breathing muscles, potentially leading to death from respiratory failure within hours. Amnesic Shellfish Poisoning is uniquely characterized by short-term memory loss in severe cases.
Immediate Steps and Medical Treatment
Immediate action is necessary upon suspecting crab poisoning. For mild gastrointestinal cases, the first priority is preventing dehydration by drinking plenty of clear fluids, such as water or electrolyte solutions. Rest and avoiding solid foods until symptoms subside are recommended for mild nausea and cramps.
Emergency medical care is required immediately if neurological symptoms occur, as these indicate marine toxin poisoning. Immediate medical attention is also necessary for severe bacterial illness symptoms.
When to Seek Emergency Care
- High fever above 101°F.
- Blood in the stool.
- Inability to keep liquids down due to persistent vomiting.
- Tingling and numbness of the mouth.
- Loss of coordination or paralysis.
- Difficulty breathing.
Medical treatment is primarily supportive, focusing on managing symptoms and stabilizing the patient. For severe dehydration, intravenous (IV) fluids are administered to restore electrolytes. Physicians generally advise against using most over-the-counter anti-diarrheal medications, as they can slow the expulsion of the infectious agent. In cases of severe neurotoxin exposure, the patient may require urgent interventions like mechanical ventilation if respiratory paralysis occurs.
Ensuring Safety When Handling Crab
Preventing illness starts with careful selection and handling. When purchasing live crab, ensure the animals are active and discard any with broken shells. Live crabs should be stored in a cool environment, ideally around 50°F, in a breathable container, not submerged in melting ice or water.
Proper refrigeration at 40°F or below is necessary for all crabmeat, fresh or cooked, to inhibit bacterial growth. Cooked crabmeat should be consumed within a few days. It is crucial to avoid cross-contamination by keeping raw crab separate from cooked food and ready-to-eat items.
Thorough cooking to an internal temperature of 140°F to 145°F eliminates bacterial pathogens. However, cooking does not neutralize marine biotoxins. Consumers should avoid consuming the tomalley or “crab butter” entirely, as these organs concentrate toxins. If there are known red tide warnings, all crab harvested in that area should be avoided.