24 DISCOVERMAGAZINE.COM
FROM TOP: MAGNE FLÅTEN VIA WIKIMEDIA; LICHTINGER ET AL./THE AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE, FEB. 4, 2011gut parasites such as hookworm
and roundworm; an intestinal
invader known as Strongyloides; and
Schistosoma, a leaf-shaped parasitic
flatworm acquired by contact with
water fouled by human waste.
But what about worms
transmitted by an insect bite? Dr. K
hadn’t mentioned those exotic foes. I
suggested she ship Landry’s serum to
a special lab at the National Institutes
of Health. Several weeks later, my
suspicion was confirmed. Crawling
inside Landry was a worm exclusive to
West and Central Africa: Loa loa.
BITE OF A FLY
In 1979, I was a rookie doc at the
Hospital for Tropical Diseases in
London, a crumbling structure
straight out of a Dickens novel.
Every week I met patients from
different parts of the world. One of
them was an African woman with
unusual complaints.
She had originally told her general
practitioner that her limbs sometimes
swelled, that something was crawling
in her skin, and that once or twice a
transparent worm had slinked across
her eye. Her doctor thought she was
suffering from delusions and sent her
to a psychiatrist.
Months later, I saw her at the
London hospital. She had high
levels of eosinophils, and her blood
contained microscopic larvae of
L. loa, a threadlike worm that initially
enters humans via the bite of a
parasite-laden fly. But not just any
fly. The worm is transmitted only by
certain species of deerflies.
These cagey insects know how
to find a meal. After breeding in
mud along shaded streams, they
fly high above the ground in search
of warmblooded animals. Specific
activities attract them — for example,
animal motion, breath exhalations
and even rising puffs of woodsmoke.
Target found, they dive-bomb and
bite their quarry in order to siphon
a small amount of blood. Some
bites can transmit an early stage
of loa.
Months later, the larvae introduced
by bites become mature worms that
freely roam beneath their hosts’ skin,
sometimes traveling up to 1 centimeter
per minute and causing brief periods
of swelling. Adult worms have also
been known to cross the eyeball
during their travels through the body.
After mating, females give birth tonew waves of offspring that live in
the blood.
Today the parasite remains a
health problem, inhabiting roughly
12 million people, mostly living in
Africa’s backcountry.ROAD TO RECOVERY
Once Dr. K learned that Landry’s
blood tested positive for loa, she
called the Centers for Disease
Control and Prevention to obtain
diethylcarbamazine, or DEC. The
medicine is used to treat specific
parasitic infections and can kill loa
in its adult and larval stages.
Landry was admitted to a
hospital to begin treatment using
DEC, low-dose steroids and
allergy medications. After two days
of treatment, I visited him and his
indefatigable aunt on the ward. The
medicines appeared to be working.
According to the morning’s lab work,
Landry’s eosinophil count had already
gone down.
“Yes, thank you, I am feeling fine,”
he said in a musical lilt as Delphine
beamed. She smoothed her rumpled
clothes after spending the night on a
bed in the room.
“And how is school and life in LA?”
I continued. “I’m sure you also miss
home.”
“He’s doing very well in English,”
Delphine interjected as the teen
nodded. He then described
several happy summers spent in
his grandparents’ Cameroonian
village by a river thick with flies.
For the rest of the day, I
periodically thought of Landry. I
imagined all he had left behind in
his former country, and all that now
lay ahead for him in America. DClaire Panosian Dunavan is an infectious
diseases and tropical medicine specialist at
the University of California, Los Angeles.
The cases described in Vital Signs are
real, but names and certain details have
been changed.Could one of these
multicellular
creatures and its
offspring reside
within Landry?
And if so, what type?
Once inside a
human, the worm
sometimes crosses
the eyeball.L. loa
is transmitted
by certain species
of deerflies.Vital
Signs