PRESS RELEASE
The Veterinary
Services (VS) program of USDA’s Animal and Plant Health Inspection Service and
the Florida Department of Agriculture and Consumer Services (FDACS) are asking
veterinary practitioners, farmers, ranchers and animal owners in Florida to
be on the lookout for screwworm. Screwworm is the common name of a pest native
to the tropical areas of North, South and Central America that causes extensive
damage to domestic livestock and other warm blooded animals. The larvae of these
pests feed on the raw flesh of the host animal.
On February 27,
2000, 17 horses from Argentina entered the United States. Two of the horses
were eventually shipped to Georgia, five to California, one to Pennsylvania,
one to Texas, and eight to Florida. On March 2, 2000, a private practitioner
found one of the horses in Florida to have screwworm larvae; confirmed by the
National Veterinary Services Laboratory (NVSL) on March 4, 2000. The horse
and premises were treated March 3, 2000; the horse received a second treatment
March 6, 2000. Veterinary Services has conducted foreign animal disease investigations
of all the other horses in this shipment and have not found any of these horses
to be infested.
Based on the current
situation, APHIS is not planning to release sterile flies. Larvae were
collected from one horse. This horse was in a one-eighth acre paddock that
was isolated on three sides. The horse and the paddock were treated on March
3, 2000. The horse also received a second treatment on March 6, 2000. Two
or three horses in an adjacent paddock were examined; no wounds were observed
on these horses.
NVSL reported that
the screwworm larvae were at least 24 hours from maturity when they were collected
on March 2, 2000; thus, it is unlikely that any larvae dropped from the wound
on or before March 2, 2000. Thorough treatment of the premises on March 3,
2000 was provided to ensure that any larvae that may have exited the wound were
killed.
When larvae drop
from a wound, they burrow into the soil where they enter the pupal stage, which
lasts 5 to 7 days. Adult flies emerge from the pupal cases and are ready to
mate within 3 to 5 days. Thus, any new cases would not be seen until March
15, 2000.
In this situation,
sentinel animals are the best way to conduct surveillance for screwworm flies.
VS and FDACS will place sentinel animals around the Florida premises of the
horse that was infested. VS and FDACS are monitoring the situation. The decision
regarding release of sterile flies will be reevaluated as the situation evolves.
FDACS
has placed the state agriculture inspectors on increased alert to detect any
occurrence of screwworms in animals entering the marketing system at livestock
markets and special livestock sales.
Practitioners in
the area also are being notified to increase their surveillance for possible
screwworm infestations. Veterinarians should note that initial cases of screwworm
are often detected in pet animals. Animals are infested when the screwworm eggs
hatch in the wound of an animal and the larvae feed on the animal’s flesh.
Practitioners should be on the lookout for for:
ź
Wounds that may become
infested with maggots.
Wounds commonly
infested include those caused by feeding ticks, castration, dehorning, branding,
shearing, wire cuts, sore mouth in sheep, and shedding of the velvet in deer.
Navels of newborn mammals are a common site for screwworm infestation. It is
very difficult to see early stages of screwworm larvae feeding in a wound; only
slight movement may be observed. As the larvae feed, the wound is gradually
enlarged, becoming wider and deeper. In some cases, the openings in the skin
may be small with extensive pockets of screwworm larvae beneath.
ź
Bloody discharge from the
infested wounds
ź
Malodor
ź
Discomfort
ź
Decreased feed intake
ź
Decreased milk production
ź
Seclusion from rest of herd or flock. Animals may seek shady
or secluded areas to lie down.
Animals with screwworm
infestations may die in 7 to 14 days if wounds are not treated to kill the larvae,
especially in cases of multiple infestations. As many as 3,000 larvae may be
found in a single wound. Death results from toxicity and/or secondary infection.
A
factsheet about screwworm is available at www.aphis.usda.gov/oa/pubs/fsscworm.html
Suspect
cases should be reported to the Area Veterinarian in Charge, Veterinary Services,
APHIS at 1-800-342-0395 or to the State Veterinarian at (850)410-0910.
