Page 12 - Livestock Matters - Summer 2014

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Given the highly contagious nature
of this disease and that just one
egg-laying female mite is required to
initiate flock infestation, effective
treatment and prevention strategies rely
on co-ordinated whole flock treatment.
Co-ordinating treatment with
neighbouring farms is likely to reduce
the risk of infestation/re-infestation.
Treatment is based upon injection with
systemic endectocides (ivermectin,
doromectin or moxidectin) or plunge
dipping organophosphate (OP) or
synthetic pyrethroid (SP) dip.
When plunge dipping, sheep should be
submerged for at least one minute with
their heads submerged twice during
this period. Care must also be taken
to maintain correct dip concentration.
Dipping once in diazinon (an OP dip)
is usually sufficient, while certain SP
formulations require a second dip
14 days later.
Systemic endecticide injection may
take several days to kill all scab mites,
while effective plunge dipping provides
a more immediate kill.
Biosecurity is essential in order to
prevent infestation. Isolation and
observation of all bought-in stock for
three weeks prior to introduction into
the main flock is advised.
EXTERNAL PARAS I TES
11
LIVESTOCK MATTERS
WORKING
TOGETHER
FOR A HEALTHIER FUTURE...
Sheep Scab
Sheep scab
Sheep scab is a highly contagious skin
condition caused by the mite Psoroptes ovis,
which, since the withdrawal of compulsory
dipping in 1989, has become fairly
widespread. In the UK, clinical disease is
most commonly encountered during the
months of October till March and is a
source of considerable economic loss
in affected flocks.
Clinical signs result from the affected sheep’s
hypersensitivity reaction to the presence of
these host-specific mites, which are capable
of survival in the environment for up to 17
days in cold, damp conditions.
Sheep often display only itchiness initially,
gradually leading to wool loss and fleece
discoloration. The secretion of serum from
the skin follows, giving the fleece a moist
yellow appearance. Live mites are found at
the periphery of such lesions, as progression
to wool loss and skin thickening takes place
at the centre.
Around eight weeks or so following
infestation, large areas of bare, thickened,
serum-encrusted skin are visible, by
which stage the individual will have lost
considerable body condition. Diagnosis is
based on clinical signs and confirmation
of the presence of live P. ovis mites by a
veterinary surgeon. This is usually carried
out by examination under a microscope of
scrapings taken from the skin at the edge
of suspicious lesions.
Sheep scab treatment and prevention
Sheep Scab can lead to wool loss and fleece discoloration