OVERVIEW

What is Angiostrongyliasis Cantonensis?

Angiostrongyliasis Cantonensis is a parasitic disease. It is primarily caused by consuming raw or undercooked freshwater snails (mainly Pomacea canaliculata, also known as golden apple snails) or mollusks containing larvae of Angiostrongylus cantonensis.

The larvae of Angiostrongylus cantonensis mainly parasitize the human brain and spinal cord, causing eosinophilic meningoencephalitis or acute meningoencephalitis.

Patients often experience sudden onset of symptoms, with early-stage fever followed by headaches, abnormal sensations in different parts of the body, facial or limb paralysis, or symptoms such as drowsiness, convulsions, epilepsy, agitation, and mental disorders.

Most cases of cerebral angiostrongyliasis can resolve on their own. There is some debate over whether antiparasitic drugs are necessary for treatment. Some studies in China suggest that albendazole and mebendazole are effective treatments for Angiostrongyliasis Cantonensis, and combining them with corticosteroids yields better results.

The key to prevention is avoiding raw or undercooked snails, crabs, slugs, frogs, freshwater shrimp, or vegetables contaminated by snails.

Is Angiostrongyliasis Cantonensis common? Where is it prevalent (endemic areas)?

Angiostrongyliasis Cantonensis is a relatively rare disease, with over 3,000 reported cases worldwide.

The disease is primarily found in Southeast Asia (especially Thailand, Malaysia, and southern Vietnam) and throughout the Pacific Basin, including Indonesia, the Philippines, Taiwan (China), mainland China, Japan, Papua New Guinea, Hawaii, and several smaller Pacific islands.

Additionally, due to the spread of infected rats via ships, the parasite has also been detected in Africa, South America, Australia, Cuba, Puerto Rico, and Jamaica, and has spread from New Orleans to other parts of Louisiana. Sporadic cases have been reported in Europe and the U.S., some of which are travel-related.

Pomacea canaliculata is an important intermediate host for Angiostrongylus cantonensis. The spread of these snails has accelerated the transmission of the disease.

From May to August 2006, an outbreak of Angiostrongyliasis Cantonensis occurred in Beijing, known as the "Beijing Pomacea canaliculata incident." During this period, over 100 people were infected after consuming improperly prepared Pomacea canaliculata dishes at a restaurant called "Shu Guo Yan Yi" and its branches.

SYMPTOMS

How long is the incubation period for Angiostrongyliasis?

It ranges from 1 day to over 6 weeks, with an average of 1–3 weeks.

What symptoms does Angiostrongyliasis cause?

• Symptoms during incubation: Symptoms are usually mild or absent. A few patients may experience abdominal pain or diarrhea, but these symptoms are minor and resolve quickly.

• Fever: After the incubation period, most cases develop abruptly, often with fever (38–39°C), which typically subsides within days but may persist for weeks in rare cases. Later, the larvae migrate to nervous or ocular tissues, causing corresponding symptoms.

• Neurological symptoms: These appear 2–35 days after infection.

  • The most common symptom is headache, affecting over 90% of patients. It is severe, acute, and often localized to the forehead, temples, or occiput, sometimes involving multiple areas. Typically intermittent, lasting minutes to hours, it may temporarily ease after a lumbar puncture. Most cases resolve within days, though some persist for weeks.
  • Headache is often accompanied by nausea, vomiting, and neck stiffness or rigidity, with resistance to movement.
  • 75% of patients experience abnormal sensations (e.g., pain, numbness, burning, tingling) in the head, torso, or limbs. Pain may be migratory and triggered by touch or wind, indicating hyperalgesia.
  • Rarely, temporary facial or limb paralysis, seizures, epilepsy, agitation, drowsiness, or psychiatric disturbances may occur.
  • Coma is very rare but signals a critical condition.

• Ocular symptoms: Rare cases involve intraocular infection, leading to unilateral vision impairment or blindness. Some patients report photophobia, double vision, or blurred vision.

• Pulmonary symptoms: Lung infections may cause cough, with imaging (e.g., X-ray, CT) showing shadows.

• Digestive symptoms: Abdominal pain, diarrhea, or constipation may occur, with occasional hepatomegaly or abnormal liver function.

What severe complications can Angiostrongyliasis cause?

Most symptoms (headache, neck stiffness, nausea, vomiting, sensory abnormalities, blurred vision) usually resolve within weeks. A small minority may experience chronic sequelae like persistent sensory issues, weakness, or cognitive decline, but these often improve over time.

How high is the mortality risk from Angiostrongyliasis?

Fatalities are rare (<5%). Worsening sensory deficits, severe limb weakness, or impaired consciousness (e.g., coma) indicate a critical condition with higher mortality risk.

CAUSES

What is the pathogen causing angiostrongyliasis cantonensis?

The pathogen of angiostrongyliasis cantonensis is Angiostrongylus cantonensis (previously known as Canton lungworm, Canton bloodworm, or rat lungworm), which belongs to the Nematoda phylum and the genus Angiostrongylus.

The adult worm is thread-like, with females slightly larger than males. The anterior end is tapered, while the posterior curves ventrally with a pointed tail. Adult worms parasitize the right heart and pulmonary arteries of definitive host rodents.

Female worms lay eggs, which enter the pulmonary capillaries via blood flow. After a few days, the eggs hatch into first-stage larvae, which exit the alveoli, ascend the trachea to the pharynx, are swallowed, and then pass through the stomach and intestines before being excreted in feces. These larvae can survive in the environment for up to two weeks.

If ingested by intermediate hosts (certain terrestrial or aquatic snails, slugs, or other mollusks), the larvae molt twice to become third-stage larvae, which can persist in the snails for extended periods and remain infectious to both rodents and humans. In China, the primary intermediate hosts for Angiostrongylus cantonensis include Pomacea canaliculata (golden apple snail) and Achatina fulica (giant African land snail).

Additionally, if fish, shrimp, crabs, frogs, or snakes consume snails containing third-stage larvae, the larvae can migrate and persist in these paratenic hosts, which also remain infectious.

When rodents ingest infected intermediate or paratenic hosts, the third-stage larvae (infective larvae) migrate to the rat's brain, develop into adults, and then enter the venous system, eventually reaching the heart and pulmonary arteries, completing the life cycle.

How does Angiostrongylus cantonensis cause illness in humans?

After consuming food contaminated with third-stage larvae of Angiostrongylus cantonensis, the larvae penetrate the intestinal wall into blood or lymphatic vessels and disseminate throughout the body, reaching organs such as the lungs, brain, liver, spleen, and kidneys.

The larvae primarily invade the central nervous system, affecting not only the cerebrum but also the cerebellum, brainstem, spinal cord, cranial nerves, and spinal nerve roots.

Mechanical irritation from larval migration and the host's immune response cause localized congestion, hemorrhage, tissue damage, and granulomatous inflammation, which is most pronounced around dead or degenerating larvae.

Eosinophils, Charcot-Leyden crystals, and macrophages may infiltrate around the larvae in the meninges, subarachnoid space, and brain tissue, sometimes forming eosinophilic granulomas. Affected meninges may thicken and adhere, leading to mild-to-moderate ventricular dilation and corresponding clinical symptoms.

How is angiostrongyliasis cantonensis transmitted? Can it spread between humans?

• Humans become infected by consuming raw or undercooked meat of intermediate hosts (e.g., snails) containing third-stage larvae.
• In endemic areas, infection can also occur by eating raw or undercooked paratenic hosts (freshwater fish, shrimp, crabs, frogs, snakes, etc.).
• Intermediate hosts crawling on vegetables or plants may deposit third-stage larvae, which can infect humans if the produce is eaten unwashed. Drinking contaminated water or contact with parasite-laden soil in endemic areas may also lead to infection.

In humans, adult worms migrate to the brain (or, rarely, the lungs or eyes) but do not produce eggs, so human-to-human transmission does not occur.

Who is at higher risk of angiostrongyliasis cantonensis?

All populations are susceptible. Individuals at higher risk include those who consume contaminated food or water, children playing in contaminated soil in endemic areas, and travelers who eat or drink contaminated items in affected regions.

DIAGNOSIS

Under what circumstances should Angiostrongyliasis cantonensis be suspected?

Recent consumption of raw or undercooked snail meat; ingestion of raw or undercooked meat from paratenic hosts (such as freshwater fish, shrimp, crabs, frogs, snakes, etc.); consumption of unwashed vegetables contaminated with third-stage larvae or drinking contaminated water; or a history of residence in endemic areas.

Presence of symptoms such as fever, headache, nausea, vomiting, abnormal skin sensations (e.g., pain, numbness, tingling, burning), facial or limb paralysis, convulsions, epilepsy, agitation, drowsiness, mental disorders, coma, photophobia, diplopia, blurred vision, unilateral vision impairment, or even blindness.

In such cases, Angiostrongyliasis cantonensis should be suspected.

What tests are needed when Angiostrongyliasis cantonensis is suspected?

• Physical examination: Including neurological examination (e.g., meningeal irritation signs) and vision-related assessments.

• Ancillary tests: For example:

• Complete blood count (CBC): May show increased total white blood cells and mild to moderate eosinophilia.

• Cerebrospinal fluid (CSF) examination: Obtained via lumbar puncture, may reveal elevated CSF pressure, eosinophilia, mildly increased protein, normal glucose and chloride levels, and rarely, detection of the parasite.

• Immunological tests: Detection of IgG, IgM antibodies, and circulating antigens (Cag) in the patient's serum or CSF.

• Pathogenic examination: Larvae or adult worms may be identified in CSF, eyes, or other parasitic sites. Pathogenic tests have low positivity rates, but a positive result confirms the diagnosis. Polymerase chain reaction (PCR) can sensitively detect parasite DNA.

• Imaging studies: Most patients show no significant abnormalities on brain MRI; chest X-rays or CT scans may reveal lung lesions, typically peripheral eosinophilic pulmonary infiltrates, or linear/nodular shadows.

How is Angiostrongyliasis cantonensis diagnosed?

Medical diagnostic criteria include: meeting items 1–4 for clinical diagnosis, item 7 for pathogenic diagnosis, and items 5–6 for auxiliary diagnosis.

1. Epidemiological history, such as recent consumption of raw or undercooked snail meat.
2. Presence of corresponding symptoms (e.g., fever, headache, etc., as detailed above).
3. Elevated eosinophil percentage and absolute count in CBC.
4. Increased CSF pressure and eosinophilia.
5. Positive IgM antibodies or Cag in immunological tests.
6. Imaging findings (chest X-ray/CT or brain MRI) consistent with the disease.
7. Pathogenic confirmation by detecting larvae or adult worms in CSF, eyes, or other sites.

Which diseases resemble Angiostrongyliasis cantonensis? How to differentiate them?

Angiostrongyliasis cantonensis must be distinguished from viral meningoencephalitis, tuberculous meningoencephalitis, Japanese encephalitis, epidemic meningoencephalitis, and other cerebral parasitic diseases (e.g., paragonimiasis, schistosomiasis, cysticercosis, sparganosis, and gnathostomiasis). Key differentiating factors include epidemiological history and pathogenic examination.

TREATMENT

Which department should I visit for Angiostrongyliasis cantonensis?

Infectious Diseases or Neurology.

Is isolation necessary if Angiostrongyliasis cantonensis is suspected?

No isolation is needed. Humans are abnormal hosts for Angiostrongylus cantonensis. While adult worms may migrate to the brain (or, rarely, to the lungs, eyes, etc.), they do not produce eggs in humans, so the disease is not transmissible between people, and isolation is unnecessary.

How is Angiostrongyliasis cantonensis treated?

Most cerebral angiostrongyliasis cases resolve spontaneously. The use of antiparasitic drugs is somewhat controversial, with some medical researchers advising against deworming treatment.

Some studies in China suggest that albendazole and mebendazole are effective treatments for Angiostrongyliasis cantonensis, especially when combined with glucocorticoids. The antiparasitic course typically lasts 7–10 days, with possible side effects including headache, liver damage, rash, and fever.

Beyond antiparasitic treatment, supportive care is the main approach—providing symptom relief as needed (medically termed symptomatic treatment). For example, intracranial pressure can be reduced if elevated, analgesics may be given for severe headaches, and worms in the eye should first be surgically removed by an ophthalmologist before antiparasitic therapy. Glucocorticoids may also be used depending on the condition.

Without reinfection, migrating larvae will gradually die, and the resulting inflammation and symptoms will subside.

How is Angiostrongyliasis cantonensis treated in infants? Can infants take antiparasitic drugs?

Infants can take antiparasitic drugs. A widely used treatment regimen in China is albendazole combined with glucocorticoids (dexamethasone or prednisone).

The recommended dosage of albendazole is 20 mg/kg body weight per day, divided into three doses, for 7–10 days.

Liver function should be monitored during treatment, and the albendazole dosage adjusted as needed.

How is Angiostrongyliasis cantonensis treated in pregnant women?

Pregnant women primarily receive symptomatic treatment (see above). Treatment may increase the risk of adverse pregnancy outcomes, such as miscarriage.

Can Angiostrongyliasis cantonensis be completely cured? Will there be sequelae?

Most patients fully recover without sequelae. In rare cases, chronic disability or even death may occur.

DIET & LIFESTYLE

What dietary precautions should be taken during the treatment of Angiostrongyliasis cantonensis?

There are no specific dietary requirements during the treatment of Angiostrongyliasis cantonensis. It is recommended to consume light and easily digestible foods.

What lifestyle precautions should be taken during the treatment of Angiostrongyliasis cantonensis?

• For headaches, patients are advised to rest in bed with their head elevated 30°–40° above heart level to reduce vascular congestion and prevent further increases in intracranial pressure.
• During fever, patients should drink plenty of fluids to prevent dehydration from excessive sweating, and change bedding promptly to keep sheets clean and dry.
• If antiparasitic drugs are used, monitor for allergic reactions, such as rashes, itching, or red spots on the neck and chest.

PREVENTION

How to prevent Angiostrongyliasis cantonensis?

• Avoid eating raw or undercooked snail meat.
• In endemic areas, also avoid consuming raw or undercooked paratenic hosts (freshwater fish, shrimp, crabs, frogs, snakes, etc.); thoroughly wash vegetables before eating; never drink untreated water.
• Those involved in snail meat processing should take extra care to avoid contamination.
• Food regulatory authorities should strengthen monitoring and management of snail-based foods.
• Enhance rodent control efforts.

Can people infected with Angiostrongyliasis cantonensis gain lifelong immunity? Can they be reinfected?

People infected with Angiostrongyliasis cantonensis do not acquire lifelong immunity. Without proper precautions, reinfection is possible.