Pulse - March 2021 - 19

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MEDICAL LEEWAY

The Secret to the Most Prolific
Serial Killer is Laziness
Christopher A. Lee, DVM, MPH, DACVPM

ale University confirms that serial killers murder
almost three-quarters of a million people annually
- more than war, terrorist attacks, and homicides
combined worldwide. One group of serial killers, that
is, the mosquito. Despite over 3500 species across 122
genera, only a relatively small number victimize humans.
One species prefers it.
How does this mosquito outcompete other species in killing
people? By being the largest? Nope, that title goes to the vegetarian species, the Australian elephant mosquito (Toxorhynchites
speciosus). Farthest flight? The Eastern Saltmarsh Mosquito (Aedes
sollicitans) travels up to one hundred miles for a savory meal. Fastest? Most mosquitoes average 1-1.5 miles per hour. Thus, being
slower than butterflies, speed isn't the key.
The secret to one of the deadliest mosquitoes for people and
pets, Aedes aegypti, amounts to laziness. Not being early risers, they
wait for a couple of hours after sunrise to feed. They return to bite
a few hours before sundown and will continue through the night,
but only if the home is well lit.
Their flight ranges rarely exceed five hundred meters, or just
under a third of a mile. Beyond not traveling far, they don't even
fly high and have earned the " ankle-biting " mosquito moniker.
How does this underachiever overachieve so well? They are
anthropophilic; that is, A. aegypti prefers to live near people. Choosing the world's dominant mammal helps one become the world's
most successful parasite. Averaging eighty-seven people per square
mile, and up to 283 people per square mile in metropolitan regions,
human US population density facilitates a short flight range.
Making life even cushier, the mosquito's ideal hosts live in
homes, apartments, and condominiums that provide comfortable
temperatures and shelter from wind, rain, and predators. Human
residences make excellent mosquito homes to live and raise progeny in. Entomologists label this indoor preference as " endophilic. "
Scientists further describe the mosquito's " skip oviposition, "
where they spread their eggs into multiple strategic areas that
might have water exposure, such as flowerpots, pet bowls, or vases.
Being lazy imparts patience. Their resilient eggs survive up to 8
months waiting for water exposure, stick to virtually any surface,
and visually pass as small, black dirt.
When outside the home, this species takes advantage of a throwaway society and successfully reproduces in anything that holds
water - tires, trash, and even water-bottle caps! With this love of
clutter, A. aegypti bears higher numbers in areas of lower socioeconomic status and in households with toddlers.
Several viruses noticed these efficient, lazy, evolutionary tactics. Today, A. aegypti represents a top distributor of dengue, yellow fever, chikungunya, and Zika viruses.Yellow fever alone infects
over 200,000 people a year and kills 30,000 of them. The common
name for this mosquito is the yellow fever mosquito.

PULSE

MARCH 2021

A recent US study demonstrated that A. aegypti enjoyed
living around humans but only
fed off them 31% of the time.
They siphoned warm meals from
dogs 50% of the time, cats 12%,
and other wild and domestic animals 7%. This multi-species feeding helps provide a vector-disease
highway for pathogens.
Long before this 2020 study,
Dirofilaria immitis, the roundworm
known as heartworm, recognized
this relationship. CAPC confirms
over 150,000 annual US canine
heartworm cases. We assume
similar robust numbers for larval
invasion for cats who may have experienced heartworm-associated
respiratory disease (HARD) symptoms.
A. aegypti doesn't just threaten pets but the world of epidemiology, specifically ecological mapping. As these mosquitoes boast
non-ambitious flight ranges, they generate microcosms of risk that
cannot be mapped. While able to drill down to county levels, risk
maps cannot focus on a 250-meter radius surrounding an infected
dog, an area also known as a " neighborhood. "
Although the lazy mosquito savors the pampered indoor life,
other mosquito species prefer the great outdoors. These flying, sylvatic pests can vector heartworm from wildlife reservoirs to dogs
enjoying a weekend hike or nature walk. Back home, the lazy mosquitoes then redistribute this parasite from recovering weekend
warriors to other indoor and outdoor pets in the neighborhood.
Thoughtful pet owners, looking outside at their frosty backyard,
may decide to skip the heartworm preventives on " mosquito off-seasons. " After posting an adorable Instagram picture of their dog and cat
cuddling on the rug, they dial up the thermostat to mosquito supporting levels and pour themselves another cup of warm tea.
Then on a cool, crisp morning, one lazy mosquito ambitiously
decides to make the most of her small flight range and ventures outdoors. Quickly seeking solace due to her endophilic nature, she enters
a neighboring house. She rests and feeds off a new host, sleeping
soundly on a soft couch. Silently sipping warm blood, she transfers
two to three L3 larvae through her proboscis. Little does she know;
she just added to our epidemiological data and helped her fellow
mosquitoes maintain rank as the world's greatest serial killer. P
References, supplemental reading, and
podcasts available at www.MyVetZone.com
or search " vetzone " on Spotify.

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Pulse - March 2021

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