Rare brain parasite cases spread in Hawaii
Adapted from Susan Scutti,
cnn.com, April 11, 2017.
The Hawaii State Department of Health has confirmed six cases of rat lungworm
disease on the island of Maui and three cases on the Big Island over the past
three months, an official said Monday. No deaths have been reported. Typically,
the state gets reports of one to nine cases of rat lungworm each year, with two
related deaths since 2007.
Rat lungworm disease, a parasite officially known as Angiostrongylus cantonensis, that can affects the brain and the spinal cord.
Rat lungworm can affect the brain and the spinal cord in humans.
Heather Stockdale Walden, an assistant professor in the department of infectious
diseases and pathology at the University of Florida, said rat lungworm disease
has "been endemic in Hawaii for at least 50 years, so it's been there for a
while."
Most cases result from consuming raw or undercooked snails and slugs that are
infected with the parasite.Transmission can also occur when people eat infected
crabs, shrimp and frogs, though this is believed to be less common, Walden said.
There may also be very rare cases of contamination through water.
"Angiostrongylus cantonensis can
present differently in adults and children. So usually, in adults, one of the
main things that you hear complaint of is a headache," Walden said. She added
that adults commonly report neck stiffness, nausea and vomiting.
"In children, it's more the nausea and vomiting, not so much the headache," she
said. Children will also run fevers and feel abdominal pain more than adults.
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.
People do not become contagious, so they cannot transmit the infection to
someone else.
Disease Cycle
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 is capable of causing infection, though never to full adulthood
(and so never capable of reproduction).
"What happens is that the parasite gets into humans -- humans are not the host
that it can complete its life cycle in, as opposed to being in a rat -- so when
it gets in a human, it can get lost, and it will go to the brain, and it'll stay
there," Walden said.
"When it gets to the brain, you can have eosinophilic meningitis," she said.
This form of meningitis, a swelling of the thin membrane covering the spinal
cord and brain, specifically caused by the parasite. Doctors tend to treat it
with a combination of therapies, including anthelmintics -- antiparasitic drugs
-- cortical steroids and supportive care.
Since the parasites cannot mature or reproduce in humans, they will die
eventually, but in the meantime, they may cause physical problems.
The ingested parasite "can also move to the eye, and you can get ocular
Angiostrongylus," Walden said. "If
the parasite goes to the eye, sometimes you can surgically remove it."
"The detection rate is pretty low,". Over 2,800 cases have been reported in
about 30 countries, most of them in parts of Asia and the Pacific Islands, with
fewer cases appearing in the Caribbean and Africa. In the Hawaiian islands,
about 80% of land snails are carriers of the parasite, according to a 2014
research paper.
Preventing infection
Prevention begins with cleanliness and proper cooking. "So making sure that the
foods you eat are cooked properly, your vegetables are washed -- that would help
you prevent infection," Walden said.
The Hawaii State Department of Health recommends that people do not handle
snails and slugs with their bare hands. Boil snails, freshwater prawns, crabs
and frogs for at least three to five minutes before eating.