Pulse - January 2025 - 18

INDUSTRY INSIGHTS
In 2025, We Could Be
Screwwormed!
Christopher A. Lee, DVM, MPH, DACVPM
M
aggots are gross! Everyone knows
when a maggot case arrives in a hospital
- there is a large rush of people in
either direction: some to see it and some
to avoid it at all costs. In a veterinary
professional's life, we have all witnessed
myiasis, the infestation of a living pet with
fly maggots. Myiasis, or fly strike, is common
in debilitated animals with infected or
necrotic tissue.
Despite their revolting sight (and sound if you are close
enough), these baby dipterans are often helping the pet. As
one of the people moving towards the case, I typically transect
the maggot and examine each end under the microscope to
identify the species of fly.
The most common offender is Lucila sericata, the common
green bottle fly. Parasitologists, forensic entomologists,
and some doctors find fascination in these insects. L. sericata
often recognizes the death of an individual before anyone else.
Within minutes of a person or animal's death, these flies will
lay eggs upon the new and still-warm corpse.
This nearly exact egg-laying timing allow the maggots to be
used to help determine the time of death in forensic investigations.
The maggots' larval instar, or stage, can help scientists
know when the fly eggs were laid.
While far less commonly used today, L. sericata has been
intentionally used as a surgical maggot since the early 1800s.
This myiasis leads to improved tissue regeneration and lower
bacterial levels within patients. Maggot-infested wounds of
injured Civil War soldiers left in the field were noted to be
unusually bright and clean, and the effect was given the term
" Angel's Glow. "
Now, Civil War Angel's Glow did not arise from maggots,
per se. The greenish-blue bioluminescence arose from a nematode-associated
bacteria which infected the wound. However,
field wound survival was a team effort. The maggot's removal
of necrotic tissue combined with the bacteria's antimicrobial
properties combined to help save lives. Since the bacteria's
part was not recognized till 2001, it was the flies that took
the credit.
Secondary myiasis is not painful because these fly larvae
stop eating at the edges of healthy tissue. Calliphorids are also
known as blowflies, which most sheep producers detest due to
their propensity in laying eggs in wool. Any skin disease, such
as infection, can quickly lead to unwanted myiasis.
18
Speaking of unwanted myiasis, L. sericata only provides
secondary myiasis, meaning that tissue must be damaged
or necrotic to be infested. Primary myiasis caused by the
New World screwworm (NWS), Cochliomyia hominivorax
was eradicated in the US in 1966. It is currently endemic in
Cuba, Haiti, the Dominican Republic, and countries in South
America.
NWS has recently spread north to Costa Rica, Nicaragua,
Honduras, Guatemala, and now Mexico. USDA is expecting
the US reinvasion of NWS imminently. Everyone agrees that
this is terrifying. While also a family member of Calliphoridae,
NWS generates primary myiasis-its larvae eat healthy
tissue of any warm-blooded animal they can. This includes
cattle, sheep, pigs, dogs, cats, and, yes, humans.
Since primary myiasis eats living tissue, there is no painfree
Angel's Glow here. These maggots are painful, destructive,
and potentially fatal to their victims. When this foreign animal
disease (FAD) arrives here, we will witness an onslaught
of myiasis cases like we haven't seen before. Take a nap in the
backyard with your dog, and you may both awaken with C.
hominivorax eggs laid upon you.
The US has canceled all Mexican cattle importation, with
NWS being identified in Chiapas, Mexico. Despite this measure,
there is elevated concern that the northern movement
JANUARY 2025
PULSE
Pulse - January 2025

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