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ZOONOSES
Fleeing from fleas:
The most efficient killers in human history
By Barbara R. Schmitz, LCSW
A young stray dog recently found his
way into our home and hearts. He ad-
justed well, but we didn’t. Everywhere we
walked, fleas would jump on our legs and bite
us. None of the other animals had fleas before
this fella arrived. We thought, “What’s going on?
Do fleas attack humans?” Yes, they do! With warm
weather comes an explosion in the flea population, which thrives
in moist, warm environments.
Dr. Edward Wozniak, Texas State Veterinarian, said there are
many types of fleas in our area, the most common of which is the
cat flea, which both dogs and cats carry. Cat fleas love to attack hu-
mans, and their bite hurts.
“Flea bite dermatitis and murine typhus (Rickettsia muris and
R. felis) are the primary risks associated with it,” Wozniak said.
“Both species cause a rash and fever much like Rocky Mountain
Spotted Fever with a slightly different distribution on the rash.”
The flea, a wingless insect that attacks mammals and birds unmer-
cifully, is a blood-sucking parasite. The word flea comes from the
Old English fleah or fleon, “to flee.” The Latin is Pulex, meaning
dust. Fleas are insects which seem to fly with their legs.
Fleas look like a prawn with a hard, pointed or rounded head. They
have an excellent sense of smell and taste, and poor sight. Some do
not have eyes. They have powerful leg muscles and tendons and re-
silin in the thorax. Resilin is a rubber-like protein that delivers power taining an anticoagulant before blood sucking begins. (Can this saliva
faster than a contracting muscle when it is compressed. Resilin is
what powers the wing beat in flying insects and is efficiently used by
nonflying insects. They have muscles attached to the outside of their
skeleton that they use to jump as much as 130 times their own body
length, subjecting themselves to a G force of 200. Their ability to
pull up to 50 times their own weight was what prompted humans to
have flea circuses through the 1950s.
18 San Antonio Medicine • July 2015
LITTLE PERFORMERS
These charming little performers are the
most efficient killers in human history.
The flea is a member of the insect order
Siphonaptera. There are more than 1,370
species, of which 238 are found in North America.
Fleas have no family life and are not a social insect.
They lay large white eggs that are about l/50-inch-long. Eggs are
laid in feathers, fur, carpets, upholstery, bedding, cracks in hardwood
floors, dirt and decaying material found in nests, and living quarters
of various animals. The flea goes through a metamorphosis. The lar-
vae are small, legless maggots with a pair of antennae and biting jaws.
A cocoon forms where larvae mature into adults who must have a
steady diet of blood to survive. Larvae can drown or dry out and die.
The adults live on live animals. Some even burrow into the host’s
skin. Most must have a blood meal before they can develop and lay
eggs. Then the cycle starts all over. Most can live several months.
Their bite causes irritation and passes organisms into the blood of
the host often causing infections. The flea’s mouth has a thin tube
formed from three serrated needle stylets that are used for piercing
animals and sucking up blood. Clawed feet are used for grasping
feathers, fur or hair and getting down to the skin and biting. The
three-segmented thorax has a pair of legs attached to each section.
Hard plates encase the abdomen where you find its reproductive or-
gans, digestive, respiratory, and circulatory systems. The snap you
hear when you attempt to kill a flea is this plated abdomen cracking.
To protect itself, the flea can curl into a ball. They inject saliva con-
be used as a blood thinner?)
Most fleas live on rodents, insectivores and bats. Humans, pigs,
cats, dogs, primates, opossums, hedgehogs and some birds are known
to have infestations. Aquatic mammals and most hoofed mammals