Slugs are terrestrial mollusks commonly found in moist environments, such as gardens and natural areas. Ingestion of these organisms, whether intentional or accidental, poses a significant health hazard because they act as intermediate hosts for various pathogens. Slugs often crawl across surfaces contaminated with animal waste, soil, and environmental toxins, making their tissues and external mucus carriers of harmful agents. The primary concern is parasitic infection, which can lead to severe neurological illness in humans.
The Primary Threat: Rat Lungworm Parasite
The most serious danger from eating a slug comes from the parasitic roundworm known as the Rat Lungworm, or Angiostrongylus cantonensis. This nematode uses slugs and snails as intermediate hosts. The parasite’s definitive host is the rat, which sheds the first-stage larvae (L1) in its feces.
Slugs and snails ingest these larvae from the environment, where they develop into the infective third-stage larvae (L3) within the mollusk’s tissues. This L3 stage is infectious to humans. When a person consumes a raw or undercooked slug, or produce contaminated by the slug’s slime, the larvae are released into the human digestive system.
In the human body, the larvae cannot complete their life cycle. Instead, they migrate from the intestines to the central nervous system, including the brain and spinal cord. This migration and subsequent death of the larvae causes an intense inflammatory response. The severity of the resulting illness is often directly related to the number of larvae ingested.
Understanding Eosinophilic Meningitis
The presence of the Rat Lungworm larvae in the central nervous system leads to a condition called Eosinophilic Meningitis, also known as neuroangiostrongyliasis. This is a form of meningitis characterized by a significant increase in eosinophils, a type of white blood cell, in the cerebrospinal fluid. Symptoms typically manifest one to three weeks after ingestion and can range from mild to extremely severe.
The onset of the illness often begins with an acute, severe headache, which is a hallmark symptom of the infection. Other common signs include a stiff neck, nausea, vomiting, and paresthesias, which are abnormal skin sensations like tingling or pain. In more serious cases, neurological issues can develop, such as cranial nerve palsies, which may affect eye movement or facial function.
Diagnosis is based on a patient’s clinical history, particularly a recent exposure to raw mollusks, and analysis of the cerebrospinal fluid (CSF) obtained through a lumbar puncture. Finding an elevated count of eosinophils in the CSF strongly suggests this parasitic infection. While many infections are self-limiting and resolve with supportive care, a heavy parasite load can cause permanent neurological damage, coma, or even death.
Treatment focuses on managing the symptoms and inflammation, as there is no specific anti-parasitic cure once the larvae are in the central nervous system. Corticosteroids are often administered to reduce the inflammation and pressure within the skull, which can help alleviate the severe headaches and other neurological symptoms. The use of antihelminthic drugs to kill the worms is controversial, as the rapid death of larvae in the brain can sometimes worsen the inflammatory response and exacerbate symptoms.
Secondary Health Risks
Beyond the primary parasitic threat, slugs carry other risks that stem from their natural habitat and feeding habits. Slugs continuously ingest bacteria from the soil and environment, making them potential mechanical vectors for common foodborne pathogens. This contamination is possible because slugs often crawl over animal feces and other waste material.
Pathogenic bacteria such as Salmonella species and specific strains of Escherichia coli, like E. coli O157, have been isolated from field slugs. Ingesting a slug could therefore transmit a bacterial infection, leading to gastrointestinal illness that causes diarrhea, abdominal pain, and fever. Studies have shown that slugs can carry viable E. coli on their external surface and shed it in their feces for up to three weeks.
Slugs also accumulate environmental pollutants, a process known as bioaccumulation, making them a potential source of chemical toxicity. As they consume vegetation and soil, they can absorb heavy metals such as lead (Pb), zinc (Zn), and iron (Fe) from contaminated areas. Furthermore, slugs are often exposed to pesticides like metaldehyde, a common ingredient in slug pellets. The ingestion of a slug that has recently consumed such a chemical could introduce these concentrated toxins into the human body.
Immediate Medical Steps After Ingestion
Anyone who has ingested a slug should seek immediate medical consultation, even if symptoms are not yet present. It is important to inform healthcare providers about the ingestion, including when and where the slug was eaten, to help assess the risk of parasitic exposure. Early intervention is a primary factor in mitigating the severity of the infection.
The medical team may initiate a prophylactic course of anti-parasitic medication, such as albendazole, particularly if the ingestion occurred within the last one to two weeks. This preventive treatment aims to kill the parasite larvae before they migrate to the central nervous system. The diagnostic process will likely involve blood tests and observation for neurological symptoms.
If symptoms of meningitis, like severe headache or stiff neck, appear, a lumbar puncture will be performed to check for the presence of eosinophils in the cerebrospinal fluid. Close monitoring and supportive care are crucial to manage any inflammation that develops.