OVERVIEW

What is paralytic shellfish poisoning?

Paralytic shellfish poisoning is a foodborne illness caused by shellfish toxins^[1], characterized by neurological paralysis.

Considered one of the most serious health hazards among shellfish poisonings, it frequently occurs in coastal areas and has been reported in China's coastal provinces like Zhejiang and Fujian.

SYMPTOMS

What symptoms may occur after paralytic shellfish poisoning?

Patients with paralytic shellfish poisoning often exhibit symptoms such as limb numbness, headache, nausea, motor incoordination, shortness of breath, and vomiting.

Early symptoms include numbness in the lips, tongue, and fingers, followed by numbness in the fingertips and toes. The numbness then spreads to the arms, legs, and neck, leading to muscle paralysis in the limbs, difficulty standing, and impaired voluntary movement. Concurrent symptoms may include difficulty speaking, drooling, headache, thirst, and vomiting, eventually progressing to respiratory distress. Severe cases may result in death due to respiratory paralysis ^[1,2].

How soon do symptoms appear after paralytic shellfish poisoning?

The incubation period for paralytic shellfish poisoning is short. After ingesting contaminated shellfish, the toxins are rapidly released, and clinical symptoms can appear within minutes to 20 minutes.

Reports indicate that the shortest incubation period for paralytic shellfish poisoning is 10 minutes, while the longest is 24 hours, with an average of 3 hours ^[3].

The severity and timing of symptoms depend primarily on the toxicity level of the consumed shellfish, individual sensitivity, and cooking or consumption methods. Generally, children are more sensitive than adults, coastal residents have higher tolerance than inland residents, and those who consume shellfish on an empty stomach or with the broth have higher incidence and mortality rates.

CAUSES

What is the cause of paralytic shellfish poisoning?

Paralytic shellfish poisoning occurs when humans consume shellfish contaminated with paralytic shellfish toxins.

The paralytic shellfish toxins in shellfish are primarily produced by marine dinoflagellates ^[4]. These algae produce extremely low levels of toxins themselves, which do not directly cause poisoning in humans. However, when shellfish ingest toxic algae, the toxins accumulate in their tissues in a bound state. When humans consume contaminated shellfish, the toxins are rapidly released from the shellfish meat, exerting toxic effects on the body and leading to poisoning.

What are the characteristics of paralytic shellfish toxins?

Paralytic shellfish toxins are highly toxic, diverse in type, and chemically stable.

High toxicity: Paralytic shellfish toxins are neuromuscular blocking agents that disrupt nervous system transmission in humans. They are currently the most hazardous and frequently occurring marine biotoxins. The toxicity of paralytic shellfish toxins is 80 times that of cobra venom and comparable to the nerve agent sarin, with a lethal oral dose for humans ranging from 0.5 to 1.0 mg ^[1].

Diverse types: Paralytic shellfish toxins consist of saxitoxin and its derivatives, all of which primarily cause neuroparalysis. They are classified into four major categories: carbamate toxins, decarbamoyl toxins, deoxydecarbamoyl toxins, and N-sulfocarbamoyl toxins. Among these, carbamate toxins are the most toxic, followed by decarbamoyl toxins ^[5].

Chemical stability: Paralytic shellfish toxins are resistant to acids and heat, making them difficult to destroy through conventional food processing methods. Studies show that even after heating at 116°C, 50% of the toxins remain active ^[6].

During which season is paralytic shellfish poisoning most common?

Paralytic shellfish poisoning is most prevalent in coastal areas during summer and autumn, with the peak season occurring from May to October.

During this period, harmful algal blooms (red tides, which discolor water due to excessive algae growth) are more likely to occur ^[1]. These red tides contain large quantities of dinoflagellates, which are ingested by shellfish, leading to toxin accumulation. Additionally, shellfish are more easily harvested during this time.

Which foods can cause paralytic shellfish toxin poisoning?

Paralytic shellfish toxin poisoning is commonly caused by bivalve mollusks such as mussels, clams, oysters, and scallops, which filter-feed and accumulate toxins in their tissues. Additionally, the nassarius snail (also known as the lychee snail) can also cause paralytic shellfish poisoning.

DIAGNOSIS

How should paralytic shellfish poisoning be diagnosed?

It is generally diagnosed through the following methods ^[3]:

1. History of consuming foods such as mussels, clams, oysters, scallops, or whelks.
2. Presence of symptoms such as numbness in the lips, tongue, or limbs, accompanied by clinical manifestations or signs like dizziness and weakness.
3. Testing the remaining food samples for paralytic shellfish toxins according to GB 5009.213-2016 "National Food Safety Standard—Determination of Paralytic Shellfish Toxins in Shellfish." Detection of these toxins confirms the diagnosis.

TREATMENT

What department should I go to for paralytic shellfish poisoning?

Paralytic shellfish poisoning progresses rapidly and usually requires emergency department treatment.

How is paralytic shellfish poisoning treated?

There is currently no effective antidote for shellfish poisoning. The most effective rescue measures are early induction of vomiting, gastric lavage, and catharsis to promptly remove toxins, along with symptomatic treatment ^[1,7].

Symptomatic emergency treatment mainly includes the following measures:

1. Closely monitor the patient's vital signs, especially respiratory function.
2. Be prepared to perform tracheal intubation or tracheotomy and provide ventilator-assisted breathing if necessary.
3. Administer neurotrophic agents, glucocorticoids, and respiratory stimulants as needed.

DIET & LIFESTYLE

What is the safe way to consume shellfish?

Freshly purchased shellfish should not be eaten immediately. Before consumption, they need to be cleaned and purged to remove internal organs. Shellfish can be kept in clean water for 1–3 weeks to expel toxins. Toxins in shellfish usually accumulate in specific parts of their internal organs. Before cooking, they should be thoroughly cleaned, and all dark-colored muscle tissues should be removed, leaving only the white muscle, which can effectively reduce toxins in the shellfish meat to safe levels ^[6].

When eating, boiling the shellfish and discarding the broth can minimize toxin intake. Although blanching shellfish preserves their fresh flavor, the short cooking time makes it difficult to remove toxins.

PREVENTION

How to Prevent Paralytic Shellfish Poisoning?

Paralytic shellfish poisoning can be prevented in the following ways:

1. Establish a monitoring network for timely warnings: Coastal areas should regularly conduct sampling tests on shellfish, with intensified inspections during red tide seasons. Upon detecting hazardous signals, immediate inspections and patrols should be carried out. Shellfish products from red tide-affected waters should be removed from shelves and destroyed, and the sale of contaminated shellfish is strictly prohibited.
2. As consumers, try to purchase seafood from reputable sources and enhance self-protection awareness.
3. Seek medical attention promptly if symptoms occur: If symptoms such as numbness in the mouth and limbs, nausea, vomiting, diarrhea, or dizziness appear after consuming shellfish, seek medical help immediately.