Summary about Disease
Neurotoxic Shellfish Poisoning (NSP) is an illness caused by consuming shellfish contaminated with brevetoxins. Brevetoxins are potent neurotoxins produced by the dinoflagellate Karenia brevis, which causes harmful algal blooms (HABs) also known as red tides. NSP primarily affects the gastrointestinal and neurological systems. It's not typically life-threatening, but the symptoms can be quite unpleasant.
Symptoms
Symptoms of NSP typically appear within minutes to hours after consuming contaminated shellfish. Common symptoms include:
Nausea
Vomiting
Diarrhea
Abdominal pain
Tingling or numbness of the lips, tongue, and extremities (paresthesia)
Muscle aches
Dizziness
Headache
Reversal of hot/cold sensation
Pupil dilation In severe cases, neurological symptoms can include incoordination and convulsions. Respiratory symptoms, such as shortness of breath and wheezing, can occur due to airborne brevetoxins during red tide events.
Causes
The primary cause of NSP is the consumption of shellfish (such as oysters, clams, and mussels) that have accumulated brevetoxins from Karenia brevis blooms. These shellfish filter-feed, concentrating the toxins in their tissues. Exposure can also occur through inhalation of airborne brevetoxins near affected coastal areas, especially during strong winds or wave action.
Medicine Used
There is no specific antidote for brevetoxin poisoning. Treatment for NSP is primarily supportive and focuses on alleviating symptoms.
Gastrointestinal symptoms: Anti-nausea medications (antiemetics), antidiarrheals, and intravenous fluids for hydration may be administered.
Neurological symptoms: Management focuses on controlling seizures with anticonvulsants if they occur.
Respiratory symptoms: Bronchodilators may be used to open airways, and oxygen therapy may be necessary.
Is Communicable
Neurotoxic Shellfish Poisoning is not communicable. It cannot be spread from person to person. It is solely caused by consuming contaminated shellfish or inhaling airborne brevetoxins.
Precautions
Heed warnings: Pay attention to official warnings and advisories issued by public health agencies regarding shellfish harvesting closures during red tide events.
Avoid harvesting: Do not harvest or consume shellfish from areas known to be affected by red tides or where blooms are present.
Cooking does not help: Cooking does not destroy brevetoxins, so contaminated shellfish will remain unsafe to eat even after cooking.
Stay informed: Stay informed about local red tide conditions and shellfish advisories.
Limit exposure: During red tide events, minimize exposure to airborne brevetoxins by avoiding beaches and coastal areas, especially when winds are onshore.
How long does an outbreak last?
An NSP "outbreak" duration depends on the duration of the Karenia brevis bloom that causes it. The bloom may last from weeks to several months. Shellfish can remain contaminated for varying lengths of time after a bloom subsides, so advisories may remain in effect. Individual illness durations are shorter, typically resolving within a few days.
How is it diagnosed?
NSP is usually diagnosed based on a combination of factors:
Patient history: Recent consumption of shellfish, especially from a known affected area.
Symptoms: Presence of characteristic gastrointestinal and neurological symptoms.
Red tide presence: Knowledge of a current or recent red tide event in the area.
Laboratory testing: While not always readily available, brevetoxins can be detected in shellfish tissue or, in some cases, in patient samples (e.g., blood or vomit), although this is more for research or confirmation purposes.
Timeline of Symptoms
Within minutes to hours: Onset of gastrointestinal symptoms (nausea, vomiting, diarrhea, abdominal pain).
Within hours: Tingling or numbness of the lips, tongue, and extremities; muscle aches, dizziness, headache.
Hours to days (severe cases): Neurological symptoms (incoordination, convulsions); respiratory symptoms (shortness of breath, wheezing).
Resolution: Symptoms typically resolve within 1-3 days with supportive care.
Important Considerations
Vulnerable Populations: Young children, the elderly, and individuals with pre-existing health conditions may be more susceptible to severe symptoms.
Look-alikes: Symptoms of NSP can mimic other conditions, such as allergic reactions or other types of shellfish poisoning (e.g., paralytic shellfish poisoning, amnesic shellfish poisoning).
Reporting: Report suspected cases of NSP to local health authorities to aid in monitoring and managing red tide events.
Global Warming considerations: Harmful algal blooms and their toxins have been predicted to worsen as sea temperatures continue to rise.