Rat lungworm disease, or angiostrongyliasis, is an infection caused by the parasitic nematode Angiostrongylus cantonensis. This parasite can cause serious neurological illness in humans. Simple direct contact with a slug’s outer surface is not the primary way the disease is transmitted. The actual risk of infection lies almost entirely in accidentally ingesting the microscopic larvae that the mollusk carries.
Understanding the Rat Lungworm Parasite
The causative agent of this disease is the roundworm Angiostrongylus cantonensis. Its lifecycle involves two primary hosts: the definitive host and the intermediate host. Adult worms reside in the pulmonary arteries of the definitive host, typically a rat. The female worms lay eggs that hatch into larvae, which the rat then excretes in its feces.
Slugs and snails serve as the intermediate hosts, becoming infected by ingesting these larvae. Inside the mollusk, the larvae mature into the third-stage infective form, which is capable of causing human disease. The parasite is concentrated in tropical and subtropical regions worldwide, including Southeast Asia, the Pacific Basin, the Caribbean, and parts of the continental United States, such as Hawaii and the Gulf Coast. This geographic range is expanding due to the global movement of both hosts.
How Infection Occurs: Ingestion vs. Contact
Infection in humans occurs when the third-stage larvae are swallowed, making ingestion the necessary mechanism for transmission. Simple contact, such as touching a slug or snail with bare hands, does not transmit the parasite. The infectious larvae must enter the digestive system to begin their migration through the body. The primary danger comes from consuming raw or undercooked mollusks, which may contain the living larvae.
Accidental ingestion is a common route, often involving raw produce contaminated by tiny, unnoticed mollusks or pieces of them. The larvae can also be present in the slime trails left behind on unwashed fruits and vegetables, particularly leafy greens. Humans can also become infected by consuming paratenic hosts like freshwater shrimp, crabs, or frogs.
Symptoms and Health Outcomes of Angiostrongyliasis
Once ingested, the larvae migrate from the digestive tract and travel to the central nervous system, including the brain and spinal cord. The human body is an incidental host, meaning the parasite cannot complete its lifecycle or mature into adult worms; instead, the larvae die in the neural tissue. This process triggers a strong inflammatory reaction, which is the cause of the illness.
The most common outcome is Eosinophilic Meningitis, an inflammation of the membranes surrounding the brain and spinal cord. Symptoms typically appear one to three weeks after ingestion and often include a severe, persistent headache, neck stiffness, and nausea or vomiting. Some patients also report paresthesia, which are tingling or painful sensations on the skin.
While many cases resolve spontaneously over several weeks or months, the illness can occasionally lead to more severe neurological problems. Larval migration can cause nerve damage, visual impairment, or even result in coma and death. Diagnosis is typically confirmed by performing a spinal tap to analyze the cerebrospinal fluid, which usually shows a high concentration of eosinophils, a type of white blood cell.
Practical Steps for Prevention
Prevention focuses on eliminating the chance of ingesting infective larvae through contaminated food or water. Thoroughly washing all raw produce is advised, especially leafy greens that grow close to the ground. Washing should involve separating the leaves and rinsing them vigorously under running water to remove any tiny slugs, snails, or their residual slime.
Cook any mollusks, such as snails or slugs, completely before consumption, as heat effectively kills the larvae. Ensure other potential paratenic hosts, like freshwater shrimp or crabs, are also cooked thoroughly. Controlling the populations of slugs, snails, and rats around homes and gardens reduces the presence of the parasite. Proper hand hygiene is always advised after gardening or handling any potentially contaminated objects or surfaces outdoors.