Rat lungworm disease is caused by the parasitic nematode, Angiostrongylus cantonensis, often called the “rat lungworm” due to rats being its primary host. While rats are the definitive hosts, humans can become accidentally infected. This infection can lead to neurological symptoms.
The Parasite and Its Life Cycle
Angiostrongylus cantonensis primarily resides in the pulmonary arteries of rats, its definitive hosts. Female worms lay eggs that hatch into first-stage larvae within the rat’s lungs. These larvae then migrate to the rat’s throat, are swallowed, and passed in the feces.
First-stage larvae must be ingested by an intermediate host, typically snails or slugs, to continue their development. Inside these mollusks, the larvae develop into third-stage larvae, which are the infective stage for mammalian hosts. If an infected mollusk is consumed by a rat, the third-stage larvae migrate to the rat’s brain, develop into young adults, and then return to the venous system and pulmonary arteries to mature and complete the life cycle.
How Humans Get Infected
Humans acquire Angiostrongylus cantonensis infection by accidentally consuming raw or undercooked intermediate hosts, such as slugs or snails, that harbor the infective third-stage larvae. This can also happen by eating raw produce, like leafy greens, that contains small slugs, snails, or their parts. Contaminated water or certain paratenic (transport) hosts like freshwater shrimp, crabs, or frogs that have eaten infected mollusks can also transmit the larvae to humans if consumed, though this is less common.
Once ingested by a human, the larvae do not complete their full life cycle. Instead, these juvenile worms migrate from the gastrointestinal tract to the central nervous system, including the brain and spinal cord, or to the lungs. Symptoms arise from the inflammatory response triggered by these migrating and dying worms within the body.
Symptoms and Health Impacts
The most recognized manifestation of Angiostrongylus cantonensis infection in humans is eosinophilic meningitis. This condition is characterized by neurological symptoms, including severe headaches, a stiff neck, nausea, vomiting, and abnormal sensations like tingling or numbness.
The presence of larvae in the brain elicits a strong immune response, leading to inflammation. Other symptoms include low-grade fever, body aches, fatigue, cranial nerve abnormalities, double vision, or visual impairment. Diagnosis is suggested by a patient’s travel history or exposure to potential sources, along with laboratory findings such as an elevated number of eosinophils in the cerebrospinal fluid. Treatment for A. cantonensis meningitis primarily involves supportive care, including pain management with analgesics, corticosteroids to reduce inflammation, and the removal of cerebrospinal fluid. Most infections resolve on their own.
Preventing Infection
Preventing Angiostrongylus cantonensis infection involves avoiding the accidental ingestion of infective larvae. Thoroughly washing all fresh produce, especially leafy greens, before consumption is a primary preventative measure. This helps remove any small slugs, snails, or their mucus trails that might contain larvae.
If consuming snails or other potential intermediate hosts, cook them thoroughly to kill any parasites. Managing snail and slug populations in gardens and around homes can also reduce the risk of exposure. Educating children about the dangers of handling or consuming slugs and snails is another practical step to prevent accidental infection.