Sheep Scab, Lice and Keds Flashcards
What species of lice causes sheep scab?
Psoroptes ovis
What is the clinical name for sheep scab?
Ovine psoroptic mange
Where has sheep scab been eradicated?
New Zealand and Australia
Describe the life cycle of psoroptes ovis?
Egg develops to larvae with 6 legs (3 days)
Moults to protonymph (4 days
Moults to tritonymph (2 days)
Moults to adult (5 days)
What is the minimum amount of time the psoroptes life cycle takes place?
10 days
Is psoroptes burrowing or non-burrowing and what does it feed on?
Non-burrowing
Feeds at surface of skin, lipids, superficial fluids, cells, lymph
Why is a fleece an ideal location for lice?
Sensitive to desiccation
Describe the pathogenesis of sheep scab
Type 1 hypersensitivity response- serous exudate, pruritus Chronic exudative superficial dermatitis Centre of lesion forms a crust, mites move to edge, more hypersensitivity, lesion grows Lice density highest around moist edge Chronic skin changes- hyperkeratosis Lesions across neck, back, shoulders Weight loss Secondary bacterial infections
How is sheep scab diagnosed?
Clinical signs and mite ID
Part wool to examine for lesions
Skin scrapes using scalpel- edge of several sever animals
Macerate scabby material in 1-5% KOH for 5-10 mins to release mites
View under microscope, look for live mites, cuticles and eggs- chewing and forage mites may be present
Describe psoroptes ovis morphology
Thumb print pattern
Pointed mouthparts
Jointed tarsi with long pedicel (trumpet shaped)
Legs extend beyond body margins
How can forage and chewing lice be differentially diagnosed?
Forage mites/free-living mites easily identified by lack of thumb print striations
How can lice be transmitted?
Direct contact- neighbours sheep
Indirect- fomites- mites survive off host for upto 16 days
How are new infestations often caused?
Mixing with other farms- common grazing Bought in sheep not treated Contaminated rented land Poor fencing Contaminated lorries Contact in markets
When does sheep scab mainly occur and why?
Late autumn/winter
Longer fleece
What us the current legislation of sheep scab?
In Scotland legal requirement to treat entire flock
and is a notifiable disease
Sheep scab order 1977
Sheep scab order 2010 (Scotland)
How can an infestation be prevented
Avoid introduction- quarantine bought in sheep, considering options for returning from shows, disinfect shearing equipment
Treat prophylactically- Organophosphate dipe (60 days), Moxidectin injection- 28 days
Long acting moxidectin (60 days)
How should infestations and outbreaks be treated?
Dipping with organophosphate- 60 seconds head under 2x
Moxidectin injection 1%- 2 10 days apart
LA moxidectin
Doramectin injection
Ivermectin- 2 x 7 days
Is chorioptes bovis more or less common than sheep scab?
More common- less severe
What is pediculosis?
Infestation of lice
What is the common chewing louse of sheep and what does it cause and how is it diagnosed
Bovicula ovis
Wool loss, restlessness, itching, reduced appetite, rubbing, lesions
Diagnosis- adult lice next to skin
What two sucking lice can affect sheep?
Linognathus pedalis (foot louse), L.ovillus (face louse)
How is bovicula Ovis controlled?
Synthetic pyrethroids or organophosphate dip
What is the common name of Melophagus ovinus?
Keds
How are keds transmitted, when are they a problem and what do they cause and transmit?
Direct transmission
Winter problem
Suck blood, causes pruritus, loss of condition
Transmit non-pathogenic trypanosome melophagium- rare
