Doctors rely on clues, such as what people ate, where they traveled or where they lived, to determine possible exposure to the parasite. But that requires being constantly aware of the prevalence and distribution of the worms, Dr. Martell said.
If all signs point to an infection, doctors can test a patient’s cerebrospinal fluid. This can help relieve the intense pressure on the brain and spinal nerves, as well as provide more clues for diagnosis. A high level of eosinophils — a type of white blood cell — can indicate that the patient’s immune system is trying to fight off a rat lungworm infection.
Unfortunately, a positive result does not always show up in the first test, said Sue Montgomery, a parasitologist at the Centers for Disease Control and Prevention. In those cases, doctors may need to conduct another painful lumbar puncture and sample additional spinal fluid. They can also request special molecular tests to confirm the presence of rat lungworm DNA.
Researchers at the University of Hawaii at Hilo are hoping to develop a cheaper, less invasive blood test to enable faster diagnosis. Results have been promising: Early data in rats indicate that the test can detect parasitic DNA circulating in the blood at various times after infection.
The team also has successfully detected rat lungworm DNA in greenhouse and coqui frogs, cane toads, centipedes, dogs, cats, mongooses and horses, according to Susan Jarvi, a disease specialist leading the research.
“Our rats on east Hawaii Island are highly infected,” Dr. Jarvi said. “So it’s not a surprise that you find the disease occurring in other mammals.”
Rat lungworm has been present in Hawaii for several decades, likely brought over on ships from Southeast Asia. But a newer Asian transplant, a semi-slug called Parmarion martensi, may have helped the spread the parasite more widely, Dr. Jarvi said.