Sheep Scab, Lice and Keds

Question 1

What species of lice causes sheep scab?

Answer 1

Psoroptes ovis

Question 2

What is the clinical name for sheep scab?

Answer 2

Ovine psoroptic mange

Question 3

Where has sheep scab been eradicated?

Answer 3

New Zealand and Australia

Question 4

Describe the life cycle of psoroptes ovis?

Answer 4

Egg develops to larvae with 6 legs (3 days)
Moults to protonymph (4 days
Moults to tritonymph (2 days)
Moults to adult (5 days)

Question 5

What is the minimum amount of time the psoroptes life cycle takes place?

Answer 5

10 days

Question 6

Is psoroptes burrowing or non-burrowing and what does it feed on?

Answer 6

Non-burrowing

Feeds at surface of skin, lipids, superficial fluids, cells, lymph

Question 7

Why is a fleece an ideal location for lice?

Answer 7

Sensitive to desiccation

Question 8

Describe the pathogenesis of sheep scab

Answer 8

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

Question 9

How is sheep scab diagnosed?

Answer 9

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

Question 10

Describe psoroptes ovis morphology

Answer 10

Thumb print pattern
Pointed mouthparts
Jointed tarsi with long pedicel (trumpet shaped)
Legs extend beyond body margins

Question 11

How can forage and chewing lice be differentially diagnosed?

Answer 11

Forage mites/free-living mites easily identified by lack of thumb print striations

Question 12

How can lice be transmitted?

Answer 12

Direct contact- neighbours sheep

Indirect- fomites- mites survive off host for upto 16 days

Question 13

How are new infestations often caused?

Answer 13

Mixing with other farms- common grazing
Bought in sheep not treated
Contaminated rented land
Poor fencing 
Contaminated lorries
Contact in markets

Question 14

When does sheep scab mainly occur and why?

Answer 14

Late autumn/winter

Longer fleece

Question 15

What us the current legislation of sheep scab?

Answer 15

In Scotland legal requirement to treat entire flock
and is a notifiable disease
Sheep scab order 1977
Sheep scab order 2010 (Scotland)

Question 16

How can an infestation be prevented

Answer 16

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)

Question 17

How should infestations and outbreaks be treated?

Answer 17

Dipping with organophosphate- 60 seconds head under 2x
Moxidectin injection 1%- 2 10 days apart
LA moxidectin
Doramectin injection
Ivermectin- 2 x 7 days

Question 18

Is chorioptes bovis more or less common than sheep scab?

Answer 18

More common- less severe

Question 19

What is pediculosis?

Answer 19

Infestation of lice

Question 20

What is the common chewing louse of sheep and what does it cause and how is it diagnosed

Answer 20

Bovicula ovis
Wool loss, restlessness, itching, reduced appetite, rubbing, lesions
Diagnosis- adult lice next to skin

Question 21

What two sucking lice can affect sheep?

Answer 21

Linognathus pedalis (foot louse), L.ovillus (face louse)

Question 22

How is bovicula Ovis controlled?

Answer 22

Synthetic pyrethroids or organophosphate dip

Question 23

What is the common name of Melophagus ovinus?

Answer 23

Keds

Question 24

How are keds transmitted, when are they a problem and what do they cause and transmit?

Answer 24

Direct transmission
Winter problem
Suck blood, causes pruritus, loss of condition
Transmit non-pathogenic trypanosome melophagium- rare