sheep scab, lice and keds

= psoroptes ovis

• mite

sheep scab/ vine psoroptic mange

intense itching, lesions, wool loss, weightloss or reduced weight gain in lambs, ear twitching, dirty marks around shoulders where there scartching with there back legs

similar clinical signs to louse infestations, scrapie

• skin scraping or ELISA to differentiate

worldwide - eradicated in New Zealand and Australia

primarily sheep and also cattle

psoroptes ovis life cycle and feeding

non-burrowing = feeds at surface of skin, lipids, superficial fluids, cells in serous exudate, bacteria, lymph

sensitive to desiccation so longer fleece ideal - provides micorclimate to them so see outbreaks or increased in severity of clinical signs in winter period

~ 16d life cycle - can be as fast as 10d when warmer

males look different to females

psoroptes ovis pathogenesis

type I hypersensitivity response( to things in faeces) -get serous exudate that might feeds on and then it heals over and mites move to edge of scab and same occurs, severe pruritis

chronic exudative superficial dermatitis

centre of lesion forms a crust, mites move to edge, more hypersensitivity, lesion grows

can cover ¾ of body within 6-8wks - can be fatal

mite density highest around moist edge of lesion

clinical signs =

• chronic skin changes, hyperkeratosis

• aural haematomas

• lesions across neck, back, shoulders, flanks

• intense pruritis - even after treatment due to dead mites still being stuck in the fleece so need time for mites to drop off

• 30% decrease weight gain

• weight loss

• decreased birth weight - about 10% if lamb born to a ewe who had an active infestation

• restlessness

• wool loss

• epileptiform seizures - touching sheep may induce seizures

• death if left untreated

• secondary bacterial infections

psoroptes ovis diagnosis

blood ELISA - detects IgG in sheep serum 2 weeks after infestation and before appearance of clinical signs

• useful for brought in sheep for detecting infestations before you introduce them into the flock and prevents unnecessary treatments

clinical signs and mite ID - skin scrapes

• part wool to examine for lesions

• superficial skin scrapes using scalpel - around edge of lesion - do several lesions and several animals - absence of mites doesn’t confirm absence of mites in flock so used to confirm diagnosis

• macerate scabby material in 1-5% KOH for 5-10mins to release mites

• view under microscope, look for live mites, cuticles from moulting mites, eggs

• co-infestation with chewing lice and forage mites may also be present

psoroptes ovis - morphology/ID

thumbprint pattern

pointed mouth parts

jointed tarsi with long pedicel

legs extend beyond margins of body

long setae = hairs on mite

males a little bit smaller than females

tarsi = pedicels

forage mites and chewing lice

forage mites/ free living mites easily identified by lack of thumbprint striations

• globular and darker

bovicola ovis = chewing louce may also be present

can get coinfection

transmission of psoroptes ovis

direct contact

• common grazing

• neighbours sheep - single fence

indirect - fomite

• mites survive off-host for ~16 days

how are new infestations introduced to farm

mixing with other farms on common grazing

bought in sheep not treated on arrival

rented land contaminated by previous occupants - if <16d between them

poor fencing - stray sheep, contact with neighbours sheep

contaminated lorries, shears, trailers etc - if <16d between uses

contact in markets or fomites in showing pens

epidemiology and risk factors of sheep scab

late-autumn/ winter disease

longer fleece in winter

shearing reduces population in summer as it reduces microclimate for mites

• resevoirs of infection - axilla, ears, skin folds - protects them from UV so stay here through summer

upland regions and areas with common grazing have higher probability of reporting sheep scab - highlands, wales, peaks, lakes, northumberland, SW England

most outbreaks are repeat outbreaks

• most common risk factor was common grazing

current legislation

sheep scab order 1997(England and Wales)

sheep scab(Scotland) order 2010

• legal requirement to treat affected sheep and entire flock - if they show any clinical signs or confirmed cases

• movement restrictions

• notifiable disease - Scotland only

preventing infestation

avoid introduction

• quarantine and test/ treat bought-in sheep - ELISA 14d after purchase, treat(if high risk or ELISA+) with OP dip or a macrocyclic lactone = moxidectin (injection)

• consider options for sheep returning from shows/markets

• disinfect shearing equipment/ transport

prevent contact

• double fencing with gap in between - expensive

treat prophylactically - esp if using common grazing or come into contact with other sheep regularly

• organophosphate dip(diazinon) - protects for 60d

• moxidectin injection 1% - protectd for 28d

• moxidectin injection LA(long-acting) - protects for 60d

treating infestations/ outbreaks

treat all individuals in flock

1. dipping with organophosphate(diazinon) - should be in swimming dip for 60secs and head must go under 2x

2. moxidectin injection 1% - 2× 10d apart

3. moxidectin injection LA(long-acting) - only need 1 injection

4. doramectin injection - some resistance to it

5. ivermectin injection - 2× 7d apart - to kill larvae and nymph that have emerged from the eggs since the first injection

beware of retreatment intervals and of selection for resistance

choriotpes bovis - chorioptic mange

• sheep adapted strain

affect hairless areas rather than wooly areas

more common than sheep scab but less severe

lice of sheep

bovicola ovis - chewing louse, common worldwide

suckling lice less important - linognathus pedialis( foot louse) and L. ovillus(face louse)

• less important as sheep treated regularly with MLs

Bovicola ovis and diagnosis

wool loss

restlessness

itching

reduced appetite

rubbing

lesions attract blowflies

diagnosis = adult lice next to skin, eggs on wool

Bovicola ovis epidemiology and control

11% prevelance

upland farms and common grazing are risk factors

quarantine brought-in stock for 3 weeks

remove potential fomites from housing can persist in wool

severity varies between individuals

shearing reduces populations in summer

need accurate diagnosis to inform correct control

• differential = p.ovis(sheep scab)

treatment = synthetic pyrethroids or organophosphate dip(diazinon)

treatment options for chewing lice

melophagus ovinus - sheep keds

diptera - flies without wings - entire life cycle is on sheep

direct transmission

mainly winter problem

suck blood, causes pruritis, loss of condition

transmits non-pathogenic trypanosoma melophagium

rare in UK as sheep are treated by macrocylic lactones - systemic injections - blood feeding