Rat Lungworm Parasite Confirmed in San Diego County Wildlife, Raising New Public-Health Monitoring Questions

A newly documented parasite in local animals

A parasitic roundworm known as rat lungworm (Angiostrongylus cantonensis) has been confirmed in San Diego County wildlife, marking the first documented evidence of locally acquired infections in animals in the continental United States west of Texas. The findings were published in February 2026 in a peer-reviewed federal infectious-disease journal and are based on testing conducted in 2025 in collaboration with veterinary and laboratory teams working with local wildlife and animal-care staff.

The report describes laboratory-confirmed infections in both accidental hosts (animals that become infected but do not typically complete the parasite’s life cycle) and definitive hosts (animals in which the parasite can mature and reproduce). Among the definitive-host evidence, a roof rat was confirmed infected through tissue testing. The same investigation also tested free-ranging slugs—recognized intermediate hosts in the parasite’s life cycle—and reported positive findings in invasive slug species collected locally.

How rat lungworm spreads

Rat lungworm’s life cycle typically involves rats as definitive hosts and snails or slugs as intermediate hosts. Humans and other animals can be exposed when they inadvertently ingest infected snails or slugs, or when produce is contaminated by small gastropods or their parts. In people, the parasite can migrate to the central nervous system and cause a form of meningitis; illness severity varies, and while many infections resolve, severe neurological complications have been documented in medical literature.

• Definitive host: rats, where adult worms live and reproduce
• Intermediate host: snails and slugs, where larvae develop into an infectious stage
• Accidental host: humans and some wildlife species, where the parasite can reach the brain

What the San Diego detection means

Public-health significance does not hinge solely on the presence of the parasite, but on whether ongoing transmission is established locally. The federal report states that identifying cases in San Diego County wildlife supports the possibility that the parasite could now be considered endemic in this part of Southern California, with potential to expand its geographic range.

Key point for residents: exposure risk is primarily tied to contact with slugs and snails and to food-safety practices around garden and backyard produce.

Practical steps and what to watch for

Health authorities generally emphasize prevention through basic food and garden hygiene: carefully washing produce, avoiding consumption of raw or undercooked snails or slugs, and preventing gastropods from accessing gardens where leafy greens are grown. People who develop severe headaches, neck stiffness, fever, or neurological symptoms after potential exposure should seek medical care promptly and disclose any contact with slugs/snails or unwashed produce.

The emergence of confirmed local animal infections adds urgency to surveillance questions: how widespread the parasite is across the county, which slug and snail species are carrying it, and whether human cases may occur or be under-recognized. Continued testing in wildlife and gastropods will be central to clarifying the scale of risk.