The three cases newly confirmed by the US Centers for Disease Control and Prevention are unrelated, and affected three adult travelers from mainland United States.
All five of this year's cases were contracted on Hawaii Island, also known as the Big Island. That island is one of several in the state of Hawaii.
However, rat lungworm can also cause severe effects on a person's brain and spinal cord, according to the CDC. Symptoms vary, and the most common are severe headaches and neck stiffness. The most serious cases experience neurological problems, severe pain and long-term disability, the CDC says.
The exact moment of infection is unknown for each of the three newly confirmed Hawaii cases, though one individual remembers "eating many homemade salads while on vacation," while another ate unwashed raw fruits, vegetables and other plants straight from the land, according to the Department of Health.
One of last year's 10 total confirmed cases became sick after purposely eating a slug on a dare, according to the Department of Health. Most people, though, become ill by accidentally ingesting a snail or slug infected with the parasite, it said.
The illness usually lasts between two weeks and two months, and on average, the incubation period is one to three weeks. However, an infection can incubate in only a single day or in six weeks, according to the CDC.
Endemic in Hawaii
The parasite can fully mature in rats. Garden-variety slugs and snails, which eat rat feces, can serve as intermediate hosts, allowing the parasite to grow to a stage where it's capable of causing infection, though never to full adulthood (and so never capable of reproduction).
When the parasite gets into a human, it can get lost, and in some cases "go to the brain," Walden explained.
In such cases, meningitis, a swelling of the thin membrane covering the spinal cord and brain, may be the result. The ingested parasite "can also move to the eye, and you can get ocular angiostrongylus," Walden said. Surgical removal may be necessary in these cases. In the best of cases, patients develop mild illness and simply get better on their own.
People sick with rat lungworm disease do not become contagious.
Preventing an infection
"It's important that we ensure our visitors know the precautions to take to prevent rat lungworm disease," Hawaii Health Director Bruce Anderson said in a statement.
The state's Health Department recommends you wash all fruits and vegetables -- especially leafy greens -- under clean, running water to remove any tiny slugs or snails. Snail, slug and rat populations need to be controlled around homes, gardens and farms by clearing debris where they might live, and also using traps and baits.
Also inspect, wash and store produce in sealed containers, regardless of whether it came from a local retailer, farmer's market or backyard garden.
Anyone worried that they might be infected should consult a health care provider.