Published: June 24, 2024 | Source: Centers for Disease Control and Prevention

The Unsettling Name, The Straightforward Facts

Rat lungworm disease sounds like something out of a tropical adventure novel, but it is a real, though uncommon, parasitic infection. Despite its alarming name, human cases are rare, and most people who contract it recover fully without specialized medication. Understanding how the parasite moves through the environment and how to avoid it is the simplest way to keep yourself and your family protected.

What Exactly Is Rat Lungworm?

Rat lungworm, scientifically known as Angiostrongylus, is a parasitic worm that naturally infects rodents. The adult worms live in the lungs of rats, where they produce microscopic larvae. These larvae are excreted in rat droppings and are then consumed by snails and slugs. Inside these mollusks, the larvae develop further but do not mature into adults. The life cycle completes only when a rat eats an infected snail or slug, allowing the parasite to finish its development.

Humans are accidental hosts. We do not complete the parasite's life cycle, but if we ingest the larvae, they can migrate through the body and cause illness before eventually dying off.

How Do People Get Infected?

The most common route of infection is consuming raw or undercooked snails or slugs that carry the parasite. In some cultures, snails are a traditional food, and infections have occurred when they are not cooked thoroughly. Children have also been infected after swallowing snails or slugs on a dare.

More frequently, infection happens accidentally. Tiny snails, slugs, or even small fragments can hide on unwashed raw produce, particularly leafy greens like lettuce. When these are eaten raw, the larvae can be ingested unknowingly.

Other animals, including freshwater shrimp, crabs, and frogs, have occasionally been found to carry the larvae. While eating them raw or undercooked could theoretically pose a risk, the evidence is far less clear than with snails and slugs. One important clarification: fish do not spread rat lungworm.

Symptoms: What to Watch For

Many people infected with rat lungworm never develop noticeable symptoms, or they experience only mild, short-lived discomfort that resolves on its own. In some cases, however, the parasite can trigger a rare condition called eosinophilic meningitis, which occurs when the immune system responds to the parasite in the central nervous system.

Symptoms may include:
- Persistent or severe headache
- Stiff neck
- Tingling, burning, or unusually painful sensations on the skin
- Low-grade fever
- Nausea and vomiting

A related species, Angiostrongylus costaricensis, is found primarily in Latin America and the Caribbean. Instead of affecting the nervous system, it can cause eosinophilic gastroenteritis, leading to abdominal pain, digestive discomfort, and intestinal inflammation.

Where Is It Found?

Historically, rat lungworm was most prevalent in Southeast Asia and the tropical Pacific islands. Over the past few decades, its recognized range has expanded. Infections have now been documented in parts of Africa, the Caribbean, Latin America, and the United States, particularly in warm, humid regions where rats, snails, and slugs thrive side by side.

Prevention: Simple Habits That Work

You do not need to avoid fresh produce or outdoor activities to stay safe. A few practical precautions dramatically reduce your risk:

Never eat raw or undercooked snails, slugs, frogs, or freshwater shrimp and prawns
Wash all fresh fruits and vegetables thoroughly, paying special attention to leafy greens and herbs
Wear gloves when handling snails or slugs in the garden, and always wash your hands afterward
When traveling to regions where the parasite is common, avoid raw salads and uncooked vegetables
Keep outdoor dining areas, gardens, and play spaces clear of damp debris where snails and slugs hide

Diagnosis and Treatment

If you develop symptoms after potential exposure, schedule an appointment with a healthcare provider. Diagnosis typically involves a physical examination, a detailed review of your travel history and food exposures, and possibly blood tests. If meningitis is suspected, a spinal fluid analysis may be recommended to check for elevated eosinophils, a type of white blood cell that rises in response to parasitic infections.

The most reassuring aspect of rat lungworm disease is that the parasite cannot survive long-term in the human body and eventually dies on its own. Because of this, most patients do not require antiparasitic drugs. Treatment focuses on managing symptoms while the immune system clears the infection. This may include:
- Pain relievers for headaches and nerve discomfort
- Anti-inflammatory medications to calm the body's immune response
- Supportive care for severe cases of meningitis, which may involve hospitalization

Recovery can take several weeks or a few months, depending on symptom severity, but the vast majority of patients heal completely without lasting complications.

The Bottom Line

Rat lungworm disease may sound intimidating, but it is highly preventable and usually self-limiting. By cooking high-risk foods thoroughly, washing produce carefully, and avoiding accidental ingestion of snails or slugs, you can virtually eliminate your risk. If you ever suspect exposure, early medical evaluation and straightforward symptom management are all you need to get back to full health.

Stay informed, practice simple food safety habits, and enjoy the outdoors with confidence.

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