A brain‑invading parasite better known as rat lungworm has quietly surfaced in San Diego County, turning up in wild animals and even a zoo‑housed wallaby in what scientists say is the first confirmed local detection in California. The cases, uncovered during routine necropsies and wildlife rehab exams, have triggered stepped-up surveillance and a fresh alert to doctors and vets to keep the parasite in mind when patients show up with mysterious neurological symptoms. Human infections are still rare, but the worm can cause serious disease in both people and pets.
The detections are laid out in a new paper in the CDC journal Emerging Infectious Diseases, written by veterinarians with the San Diego Zoo Wildlife Alliance and staff from Project Wildlife. The report documents locally acquired Angiostrongylus cantonensis infections in a zoo parma wallaby, free‑ranging Virginia opossums, and roof rats in San Diego County and notes that most of the confirmed cases appeared in 2025.
From zoo exhibit to neighborhood rats
According to the Los Angeles Times, trouble at the San Diego Zoo started in mid‑December 2024, when a 7‑year‑old parma wallaby developed worsening neurologic problems. After 11 difficult days, the animal was euthanized; a necropsy later found six A. cantonensis worms in its brain.
That discovery prompted a broader look around the grounds. Zoo staff trapped and examined 64 free‑ranging roof rats on the property and found lungworms in two of them. At the same time, Project Wildlife submitted 10 dead opossums for postmortem testing; seven showed evidence of infection. Researchers say the cluster of infected rats and opossums points to local transmission in at least parts of southern California, rather than a one‑off import.
What rat lungworm can do to people
The Centers for Disease Control and Prevention says the overall risk to the public remains low, but A. cantonensis is nothing to shrug off. The parasite can cause eosinophilic meningitis, along with severe neurologic symptoms that may include intense headaches, stiff neck, sensory changes, fever, and nausea. Treatment, the CDC notes, works best when started early and can involve high‑dose corticosteroids to tamp down inflammation, lumbar puncture to relieve pressure and pain, and, in some cases, antiparasitic drugs such as albendazole (CDC).
Snails, slugs and smart precautions
State wildlife officials point out that certain nonnative snails and slugs known to carry rat lungworm are already established in parts of California, including San Diego County, which means these slimy intermediate hosts could help sustain local transmission (California Department of Fish and Wildlife). Local responders are urging residents not to handle sick or dead wildlife, to keep pets from scavenging slugs, snails, or rodents, and to wash produce thoroughly before eating. The San Diego Humane Society’s Project Wildlife program, which operates the county’s wildlife rehab center, has managed several sick opossums tied to the investigation (Project Wildlife).
The authors of the new report encourage clinicians in the region to include angiostrongyliasis in the differential diagnosis when they see unexplained central nervous system disease, a recommendation detailed in Emerging Infectious Diseases. At the same time, state public‑health officials told the Los Angeles Times they are not yet ready to declare the parasite established across California and say no human cases have been identified so far.
