Rat Lungworm: A Neurological Threat Emerges in California

A parasitic disease known as rat lungworm, or Angiostrongylus cantonensis, has been detected in San Diego County, California, marking its first established presence in the state and a notable expansion of the parasite’s range in North America. The discovery, initially reported in December 2024, has prompted health officials to urge vigilance among physicians and the public.

What is Rat Lungworm?

Rat lungworm is an invasive, zoonotic metastrongyle nematode that causes neurological disease in humans and other vertebrate hosts. The Centers for Disease Control and Prevention (CDC) identifies it as an emerging public health concern. The parasite typically infects rats, but can also be found in snails, slugs, and other animals. Humans become infected through consuming raw or undercooked infected animals, or produce contaminated by their mucus.

Recent Findings in California

Researchers from the San Diego Zoo Wildlife Alliance, in collaboration with partners, identified the parasite in a 7-year-old male Parma wallaby at the San Diego Zoo in December 2024. The wallaby exhibited neurological symptoms including head shaking, blindness, and limb rigidity, and ultimately died eleven days after diagnosis.

Subsequent testing of wildlife in the area revealed the parasite in other animals. Of 64 deceased rats tested, three were positive for the lungworm. Seven out of ten sick Virginia opossums tested positive. These findings suggest a lasting foothold for the parasite in San Diego County, with the potential for further spread.

Symptoms and Risks

Rat lungworm infection can cause a range of neurological symptoms in humans, including severe headaches, stiff neck, tingling or painful skin sensations, low-grade fever, nausea, and vomiting. In severe cases, it can lead to coma and even death. The CDC notes that while the risk to the general public is low, the infection can be fatal.

The primary risk factors include consuming raw or undercooked freshwater crabs, prawns, frogs, snails, and unwashed produce. Infection can occur by eating produce contaminated by snail or slug mucus. Though, the parasite cannot survive on dry surfaces.

What to Do If You Suspect Infection

Health officials recommend that physicians in the region consider rat lungworm infection when evaluating patients with unexplained neurological disorders. Early treatment with corticosteroids and antiparasitic medications, such as albendazole, can be effective. Treatment is most successful when initiated promptly, even before laboratory confirmation.

Prevention and Precautions

To minimize the risk of infection, the California Department of Public Health recommends the following:

• Do not consume raw or undercooked wild snails or slugs.
• Thoroughly wash all produce before consumption.

Current Status and Ongoing Monitoring

The California Department of Public Health is conducting additional monitoring and testing to determine whether the discovery in San Diego County represents an isolated incident or ongoing local transmission. As of March 6, 2026, no human cases have been reported outside of San Diego County, and officials are not yet classifying the disease as endemic to the state.