There have been six cases of a rare parasitic infection called “rat lungworm” in Maui in the last three months, health officials reported this week. The number is small, but it’s a dramatic jump from the normal number of cases. In the decade before this period, the island had only seen two other cases.

The surprising uptick has health officials and residents alike worried about the rise of the worm, which can invade the human brain. In infected people, the infection may be symptomless and resolve on its own. But for others, rat lungworm moves into the brain and can cause inflammation, pain, and other neurological problems such as tremors. In those cases, it can be fatal. In all cases, rat lungworm is very difficult to diagnose, and there is no treatment.

So far, at least three of the six cases have been confirmed by the state. There’s also a seventh possible case.

In April, one of the patients with a confirmed infection, 47-year-old Tricia Mynar, told Honolulu Civil Beat: “The parasites are in the lining of my brain, moving around.” She described the feeling as if “every once in a while somebody opens the top of my head, sets a hot iron inside my brain, then pushes the steam button.”

As the name suggests, rat lungworm is a parasitic roundworm (Angiostrongylus cantonensis) that infects rats’ lungs as well as their blood and brains. Infected rats poop out worm larvae, which can be picked up by snails, slugs, lizards, land crabs, and freshwater shrimp. These are intermediate hosts that shed the worm. Humans can pick up the infection by handling or eating any infected critter or by eating produce that has been contaminated by roaming infected snails and slugs.

In Maui, the current uptick appears to be linked to a boom in the population of an invasive “semi-slug” that is a particularly good carrier of the worm. While native slugs and snails may be carriers around 25 percent of the time, the invasive semi-slug has a carriage rate of around 70 to 80 percent of the time, The Maui News reported.

Once alerted to the problem, residents reported seeing the semi-slugs in their yards and gardens. They’re taking steps to knock back the population, as well as rein in the rats.

But, as The Atlantic noted, the rise of the rat lungworm has been a long time coming. Researchers have noted that with climate change and increasing global travel, the parasite has been spreading to new places and causing more cases.

The first human case was recorded in 1944 in Taiwan, and it was thought to be spread around during World War II. Since then, rat lungworm has been prevalent in parts of Southeast Asia and Western Pacific Islands, including Australia. In the past few decades, the parasite made its way to the US, reaching Hawaii, California, Oklahoma, Alabama, Louisiana, Florida, and other parts of the Gulf Coast.

In Hawaii at least, rat lungworm seems to be there to stay. “The problem isn’t going to go away,” Maui Invasive Species Committee Manager Adam Radford told The Maui News. “Our focus is on educating the public and determining the extent through social media and potentially [a] survey.”