Researchers from the University of Hawaii at Hilo are getting closer to finding treatment options for rat lungworm disease.
Three recent articles from the Department of Pharmaceutical Sciences at the Daniel K. Inouye College of Pharmacy in Hilo analyzed data from around the world to study different medications.
“The treatment aspects for rat lungworm, especially using anti-parasitic drugs, has been controversial for decades,” said John Jacob, author of the three studies from UH-Hilo. “There were some concerns that if we kill the parasite, and that parasite is in the brain, it could cause a severe inflammatory response that could result in further clinical complications.”
One of the articles from 2021 analyzed results from 144 global studies using the anti-parasitic drug albendazole, used to treat hookworm, for the treatment of rat lungworm.
“In our review, we looked at patient outcomes,” Jacob said. “The great majority showed it was beneficial, without any adverse effects.”
While a few cases without an official diagnosis had mixed results, over 2,500 positive outcomes were reported using albendazole.
“From those with a confirmed diagnosis, 100% of the patients were treated and all reported beneficial results, without any adverse effects,” he said
The problem is the price. Two 200-mg tablets of albendazole can cost as much as $500 in the U.S.
“For the treatment of rat lungworm, you need two to three pills a day for two to three weeks,” Jacob said. “So, you’re easily looking at around $6,000 to $9,000 just for albendazole.”
The medication has not yet been approved by the Food and Drug Administration for the treatment of rat lungworm, meaning patients would likely pay out-of-pocket even with a prescription.
But in countries such as Tanzania, the pill is just 4 cents.
Part of the reason for the vast price difference is the drug’s overall demand.
“Albendazole is used exclusively for parasitic infection, and in the U.S., parasitic infections are not that common,” Jacob said.
Because the drug’s patent expired decades ago, other companies can sell the generic version, but for medications specific to tropical diseases like rat lungworm, pharmaceutical companies have been reluctant to manufacture them.
A 2022 article analyzed the effects of another medication, pyrantel pamoate, used to treat pinworm, to treat rat lungworm.
The in vitro study tested the drug directly on infected L3 larvae from slugs and snails and found that it paralyzed the parasite, which then died of starvation.
To see if the drug would have the same effect in animals, the group took part in a collaborative study with the USDA APHIS department in Hilo, where it tested the drug on rats.
“Our conclusion was, administering the pinworm medication pyrantel pamoate early on, as early as immediately, could significantly reduce the worm burden, or the number of parasites that are involved in the infection,” Jacob said.
The number of parasites directly correlates with the severity of symptoms.
“Since pyrantel pamoate can reduce the number of parasites, it could, in theory reduce the symptoms and also buy you more time,” he said.
Compared to albendazole, the pinworm medication is an over-the-counter drug that costs just $11 per bottle.
The study was the first of its kind to look into the efficacy of pyrantel pamoate to treat rat lungworm.
Hilo Medical Center took notice of the results and has started including the use of pyrantel pamoate as an early mitigation tool or post-exposure prophylactic for rat lungworm cases.
The trouble with pyrantel pamoate is the drug has minimal effect after the parasite leaves the stomach.
“Once it crosses into the blood, the pinworm medication doesn’t do anything,” Jacob said. “The rule is, if you think you ate a slug, vomit out as much as you can, go to a pharmacy, get the pinworm medication, go to your doctor, then get albendazole.”
An untreated case of rat lungworm can have severe long-term complications.
“I’ve met people that were infected 10 years ago, and ever since, every day of their life, they’ve been experiencing severe headaches, memory loss, trouble with hand-eye coordination, vision problems,” he said. “Some people have even ended up being paralyzed or have died, because that’s how severe the infection was.”
Jacob speculates the severity of the disease in Hawaii is tied to the 32 species identified as carriers, especially the presence of the semi-slug found on the Big Island.
“I personally had one baby semi-slug that carried about 9,000 parasites, whereas, if you look at other slugs and snails, that number is only in the hundreds,” he said.
Sue Jarvi, head of the Hawaii Island Rat Lungworm Working Group and co-author of the articles, also attributed an increase in infections to the semi-slug.
“The number of cases prior to 2002, 2003 were really low on the Big Island,” said Jarvi, who noted the semi-slug was introduced and documented in Pahoa around 2004.
“The semi-slug seems to be a lot more mobile and a highly efficient carrier, and they do like residential areas,” she said. “You see them pretty much everywhere. We don’t know how far exactly they’ve gone across the island, but they certainly have spread along the Honokaa coast.”
Additional studies are underway involving the governor’s rat lungworm task force to determine how a combination of medications including pyrantel pamoate and albendazole could help fight the disease.
“We all agree we shouldn’t wait until we get a confirmed diagnosis, especially in the Hilo area, if the symptoms are even close to rat lungworm,” Jacob said. “The more you wait, the more parasites are getting into your brain.”
Email Grant Phillips at gphillips@hawaiitribune-herald.com.