The worms that invade your brain.
(CNN)Once
you consume them, they can move throughout your body -- your eyes, your
tissues and most commonly your brain. They leave doctors puzzled in
their wake as they migrate and settle to feed on the body they're
invading; a classic parasite, but this one can get into your head.
"It
had moved from one side of the brain to the other ... very few things
move in the brain," says Dr. Effrossyni Gkrania-Klotsas about a British
man found to have a tapeworm moving inside his brain in 2013. This form
of tapeworm had never been seen before in the United Kingdom.
The
patient, who was of Chinese descent, had recently visited China, which
along with South Korea, Japan and Thailand, has more regular occurrences
of the parasite known as Spirometra erinaceieuropaei. Four years
earlier the man had first experienced symptoms, such as headaches, which
the team of doctors at Addenbrookes Hospital, in Cambridge, had
treated as tuberculosis. But then he returned.
"When
he reappeared, he had new symptoms," says Gkrania-Klotsas. The worm was
now pushing on a new part of his brain, causing seizures and weakness
in his legs. The condition associated with his infection was in fact
Sparganosis. There is no known drug to effectively treat the infection
meaning that upon diagnosis doctors had to be quick to remove the worm
surgically.
Just
300 infections of the Spirometra tapeworm were recorded between 1953
and 2013, but they're thought to be more common in parts of Asia. The
rural nature of more affected populations means numbers are widely
unknown and very little is known about the worms.
"These
worms are pretty mysterious," says geneticist Hayley Bennett from the
Wellcome Trust Sanger Institute, in Cambridge, whose team recently sequenced the genome of the rare worm. "We know it has a very complicated life cycle."
The
adult form of the Spirometra tapeworm only occurs in the intestines of
cats and dogs but as these animals shed the worms' eggs in their feces
the eggs can enter, and contaminate, water. The resulting juvenile form
of tapeworm -- known as larvae -- can then stay in the water within
certain small crustaceans or end up in frogs and snakes. As larvae they
can invade humans through ingestion or direct contact with infected
animals. The patient in Cambridge was thought to have accidentally drunk
water whilst swimming in an infected lake, according to
Gkrania-Klotsas. The worm then took hold.
"The
larvae can encyst in the brain or somewhere else," says Bennett. The
consequences of these cysts can be tissue damage, blindness, paralysis
or even death. By sequencing the worm's genes, Bennett hoped to
understand the inner workings of the worms to aid future diagnosis and
treatment.
"Because it's such a rare
infection it's not economically viable to create a drug just for this
worm," she explains. "But by comparing it to other tapeworms we can see
which other drugs might apply."
The
team were given small samples of the worm, extracted from the infected
patient, and their sequencing identified an exceptionally large genome
and, importantly, genes which could help recognize resistance to drugs
as well as act as future drug targets. "You could also develop a
diagnostic test," adds Bennett.
Pork tapeworms
There
are many forms of tapeworm, three of which can readily infect the
brain. From a public health perspective, there's one in particular to
watch out for. "It's mainly the pork tapeworm that's the main brain
one," says Helena Helmby from the London School of Hygiene and Tropical
Medicine.
The pork species, known as
Taenia Solium, can infect humans in two forms. The first is by eating
undercooked pork from infected pigs, resulting in taeniasis -- an adult
worm residing in the intestine. The second, in the larval form, through
contact with the feces of an infected pig or human, which can go on to
infect many tissues. If the larval worm enters the nervous system,
including the brain, it can result in a condition known as
neurocysticercosis. Infection of this kind can often cause epilepsy once
inside the brain. Almost a third of epilepsy cases in countries where
the disease is native are people who have previously had
neurocysticercosis, according to the World Health Organization.
Neurocysticercosis
infection arises from poor sanitation and hygiene. "You can actually
infect yourself," says Helmby, as poor hygiene, such as failing to wash
your hands, could result in you eating the eggs of an adult worm living
in your intestine. "Self-infection is common."
The
global distribution of pork tapeworms is widespread with high numbers
across Latin America, Africa and Asia, according to the World Health
Organization. As a result of its higher prevalence and due to increased
international travel, Gkrania-Klotsas has three patients in her care in
Cambridge who have previously experienced neurocysticercosis.
Cause for concern?
Infections
with pork tapeworms are common but treatable with antihelminthic drugs
targeting the worm. Until now, treatment for Spirometra has been
surgical, but the recent genetic insight from Bennett's team in
Cambridge found that some drugs, such as praziqantil, which is used
against schistosomiasis (snail fever), could have an effect. Certain
drugs used against cancer were also identified as potential treatments.
Both
Helmby and Gkrania-Klotsas are concerned about risks from increased
international travel and the global food trade. "Food import and export
is increasing and increasing risks of consuming infected goods," says
Helmby, who feels there is a need for more vigilance with food
inspection. She predicts more cases will occur in places like the United
Kingdom where such infections have been virtually eliminated.
"I'm
confident there will be more of this in the future," agrees
Gkrania-Klotsas, who has seen patients infected without having traveled
abroad. "People are getting infections without going anywhere."
Those
who do travel, however, also need greater awareness when visiting
regions where infections are commonplace. But if health teams are ready
for the consequences, this rise can be controlled.
"We
need to be able to treat these infections," says Helmby. "That's the
challenge at the moment." A challenge where genetics researchers could
prove invaluable, as their sequencing continues to reveal the secrets of
these parasites.
