Slugs and snails can carry parasites called lungworms that can cause disease in humans and other animals. Lungworm infections are rare in humans, but cases have been documented when people accidentally ingest slugs or snails. This article will examine the relationship between slugs, lungworms, and human infection to answer the question: Can humans get lungworm from slugs?
What are lungworms?
Lungworms are parasitic roundworms that live in the lungs of various animal species. There are several different genera of lungworms, with some of the most common being:
- Angiostrongylus – commonly known as rat lungworm
- Aelurostrongylus – cat lungworm
- Crenosoma – dog lungworm
- Muellerius – deer lungworm
- Protostrongylus – sheep lungworm
Lungworms have complex life cycles that require intermediate hosts to develop into their infective stage. Snails and slugs are intermediate hosts for some species of lungworms. The worms lay eggs that are passed out of the definitive host through feces. These eggs hatch into larvae which are then eaten by a snail or slug. Inside the mollusk intermediate host, the larvae undergo further development into their infective stage.
The infective lungworm larvae encyst in the slug or snail and can then be transmitted to new definitive hosts if the mollusk is eaten raw. The larvae burrow into the intestinal wall before migrating to the lungs where they mature into adult worms. Here they reproduce and lay eggs, completing the life cycle.
Lungworm geographic distribution
Lungworms are found worldwide, though specific species have defined endemic regions. Some examples include:
- Angiostrongylus cantonensis (rat lungworm) – prevalent in Southeast Asia, Australia, Caribbean islands, and Pacific Islands
- Aelurostrongylus abstrusus (cat lungworm) – found in many parts of the world including North America, Europe, Africa, and Australia
- Crenosoma vulpis (fox lungworm) – primarily Europe and North America
- Muellerius capillaris (deer lungworm) – common in deer populations globally
The distribution of lungworms is linked to the range of their snail and slug hosts. Areas with mollusk species that can act as intermediate hosts have higher rates of lungworm transmission. Climate also plays a role, as lungworm larvae need moist environments to survive outside their hosts.
Lungworms in slugs and snails
Many different slug and snail species have been documented carrying lungworm larvae. Some common examples include:
- Garden slugs (Arion spp.)
- Glass snails (Oxychilus spp.)
- Field slugs (Deroceras spp.)
- Grove snails (Cepaea spp.)
- Vineyard snails (Cernuella spp.)
- Woodland snails (Arianta spp.)
- Brown snails (Helix aspersa)
In one study examining rat lungworm prevalence in slugs and snails in Hawai’i, researchers found:
| Species | Number Tested | % Infected |
|---|---|---|
| Garden slugs | 990 | 16% |
| O’ahu tree snails | 124 | 10% |
| Greenhouse snails | 63 | 5% |
This demonstrates that substantial percentages of mollusk populations may harbor lungworm larvae. Rates likely vary between regions and species. Overall, many different slugs and snails may potentially transmit lungworms.
Lungworm infections in humans
Most lungworms that infect snails and slugs do not use humans as a primary host. However, accidental ingestion of infected gastropods can lead to transmission of larvae and infection in people. The main lungworms known to infect humans include:
- Angiostrongylus cantonensis (rat lungworm) – the primary cause of human lungworm infection worldwide. Endemic in Southeast Asia and the Pacific Islands.
- Aelurostrongylus abstrusus (cat lungworm) – sporadic cases reported globally but more common in areas with higher rates of infected slugs/snails.
- Crenosoma vulpis (dog lungworm) – very rare human infections documented.
- Muellerius capillaris (deer lungworm) – single case reports of human infection.
The most common way humans ingest lungworm larvae is by eating raw or undercooked slugs/snails. For example, this could occur by:
- Eating uncooked snails, often incorrectly prepared as escargot
- Eating fresh produce such as lettuce or berries with small slugs/snails accidentally present
- Children purposely eating slugs/snails found in the garden
- Drinking untreated water contaminated with larvated slugs or snails
Lungworm larvae cannot penetrate intact human skin. Infection only occurs through ingestion.
After ingestion, the larvae penetrate the intestinal wall and travel through the bloodstream to the lungs after a period of 1-2 weeks. In the lungs the worms develop into adults and lay eggs, causing host reactions.
Symptoms of lungworm infection in humans
Lungworm symptoms may appear 2-35 days after ingestion of mollusks. However, mild cases may be asymptomatic. Common manifestations include:
- Fever
- Cough
- Chest pain
- Difficulty breathing
- Nausea and vomiting
- Headache
- Muscle pain
- Seizures and neurologic abnormalities (in serious cases)
In severe cases, angiostrongyliasis and other lungworm infections can lead to eosinophilic meningitis, paralysis, coma and even death. However, most human lungworm cases are mild and self-limiting.
Diagnosis involves microscopic identification of larvae or eggs in sputum or stool samples. Blood tests may reveal elevated IgE levels. Radiologic imaging can detect worm masses in the lungs.
Treatment
Most human lungworm infections do not require antihelmintic treatment as the worms do not develop into adults in the human host. Symptoms can be managed with rest, hydration, antipyretics, and anticonvulsants in severe cases.
If treatment is pursued, anthelmintics such as albendazole or ivermectin may shorten duration of larval infection by killing worms. Corticosteroids can reduce inflammatory responses. Serious cases with neurologic or respiratory involvement may require hospitalization.
Prevention
Preventing lungworm infection centers on avoiding ingestion of infected slugs and snails. Recommended precautions include:
- Wash all fruits and vegetables thoroughly, especially leafy greens
- Inspect and wash hands after gardening or playing outdoors
- Supervise children outside to prevent snail/slug eating
- Avoid purposefully eating raw or undercooked snails/slugs
- Protect drinking water sources from snail/slug contamination
In areas with high lungworm rates, public education helps raise awareness and prevent cases. Snail/slug control in gardens may also reduce local transmission.
Conclusion
To summarize, it is possible but rare for humans to get lungworm infections from ingesting infected slugs or snails. The main lungworms transmitted this way include rat lungworm, cat lungworm, dog lungworm, and deer lungworm. Eating undercooked snails or accidentally consuming slugs/snails on produce are the primary modes of transmission.
Symptoms vary but can include fever, cough, chest pain, nausea, and headaches. In a small percentage of cases, severe neurologic or respiratory complications develop. Preventive measures focus on avoiding consumption of raw slugs/snails through proper cooking and washing of produce. With appropriate precautions, lungworm infection from slugs and snails is avoidable.