HILO, Hawaii Island — Rat lungworm in Hawaii has gotten a fair amount of publicity lately. The tiny worm can cause meningitis, paralysis, brain damage, blindness and an array of other illnesses in humans.
The state had at least 18 confirmed cases of the disease in humans last year, and has had at least three this year — with most occurring on the Big Island.
But Dr. Alfred Mina sees several rat lungworm cases a month.
Mina is a veterinarian in Hilo. His rat lungworm patients are mostly dogs, especially puppies.
“The dogs at that age — around six to nine weeks — are curious,” says Mina. “They put anything in their mouths.”
“Anything,” apparently, includes snails, slugs and semi-slugs. The worms normally live out their life cycle in rats and mollusks. If an animal eats a slug, it can get infected. In humans, the results can include spinal damage, brain damage and blindness.
According to Mina, dogs in the early stages of the disease often become sluggish. As the symptoms progress, they exhibit weakness in their back legs, then generalized pain and finally paralysis, especially in the hindquarters.
The good news is that in dogs, the disease is treatable — maybe even preventable. The bad news is that treatment is expensive.
“We put them on corticosteroids, then an antibiotic, then a de-wormer and pain medication,” says Mina. “The majority bounce back when caught early. There are few cases that take longer to recover, if they presented when it was already painful and they barely could walk.”
Treatment, he says, can take three to six weeks for advanced cases, but “only a week if they’re caught early.”
The de-wormer of choice, he says, is moxidectin, which is used primarily for heartworms. It also apparently can prevent a rat lungworm infestation. Mina uses it in a heartworm prevention medicine called Pro-Heart, but, “The only thing we have is a six-month preparation, that I’m familiar with.”
Dogs are far from the only animals affected. Picture any creature that might ingest a slug: grazers such as cows and sheep, birds ranging from chickens to cockatoos. In Australia, it’s been found in foxes, monitor lizards, wallabies, brush-tailed opossums and various birds, especially a little bird called a “tawny frogmouth.” In Florida, a gibbon and an orangutan caught the disease. And about a decade and a half ago, Hilo’s Panaewa Rainforest Zoo lost several squirrel monkeys.
“At that time, no one knew it was rat lungworm,” recalls zoo director Pam Mizuno. “It actually was diagnosed in the last one that we lost.”
Since then, the zoo has erected 14-inch-high copper barricades to keep slugs out of the enclosures of any animals that might eat them.
Mina doesn’t know of any cases in cats. But state Rep. Richard Creagan, who represents South Kona and Kau and is also a physician, suspects one.
“One of my session staff at the Legislature had a cat who got classic rat lungworm, which starts with hind limb weakness,” Creagan says. “The cat had been observed playing with and mouthing an African giant snail. Neither the owner nor the vet recognized rat lungworm at the time and the cat was euthanized.
Creagan says it appears rat lungworm is rare in cats because they vomit up rat lungworm larvae.
In Hawaii during the 1960s, Alicata successfully infected dogs and cats with rat lungworm under laboratory conditions.
Zoos are particularly vulnerable to the worms, according to Australian veterinarian Richard Malik, an expert on the disease who visited Hawaii last May to give a public lecture at the University of Hawaii Hilo’s Daniel K. Inouye College of Pharmacy. He also met with local veterinarians, legislators and zoo officials on the Big Island and Oahu.
According to Malik, Hawaii is “not just a hot spot, it’s the hot spot for severe cases of rat lungworm disease” worldwide. The reason, he believes, is the semi-slug, a mollusk with a tiny residual bit of shell on its back.
Semi-slugs are a recently introduced invasive species that’s spread rapidly across the islands. Each semi-slug can carry a huge load of lungworm larvae at once. In the worm’s complex life cycle, which normally involves moving from rats to rat feces to mollusks and back, the only stage of lungworm larvae that invades other creatures, including dogs and humans, is one that’s found in the mollusks.
Since 1988, Malik has tracked the disease’s spread along the entire eastern coast of Australia, which roughly corresponds to the area where black rats and Norway rats are prevalent (west of Australia’s Great Dividing Range, bush rats remain supreme, and the worms haven’t gotten established). In those two decades, he said, he’d not seen as many cases as Mina has — and Mina is only one of several local veterinarians who are diagnosing and treating the disease.
Like Mina, Malik said it was possible, but expensive, to prevent rat lungworm in dogs; he suggested treatment every three to four weeks using a “safe and readily available” anti-worm medication called Advantage Multi, which also contains moxidectin.
Several websites sell Advantage Multi for around $80, though one had it on sale for $54.
“There is a need for a cheap preventative product for dogs … even poor people can afford to buy,” said Malik.
Malik was hoping to get local veterinarians to coordinate their efforts and share their findings. Hawaii has no veterinary school; local vets tend to be oriented more toward practical treatment than publication, so no hard numbers exist about how many dogs or other animals have been diagnosed with the disease.
Malik noted that even getting an ironclad diagnosis of rat lungworm disease was expensive, adding, “a simpler, cheaper test needs to be devised.”
Meanwhile, some simple home measures could help reduce the risks to pets. Slugs love cat and dog food and they’re most active at night, so bringing pet food dishes into the house every evening, checking late at night for slugs inside the house, and watching for tell-tale trails of slug slime around pet dishes could be helpful.
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