Skin diseases in sheep

Question 1

How do sheep get scrapie

Answer 1

Mainly via placental transmission
Some horizontal transmission

Question 2

Symptoms of scrapie in sheep

Answer 2

Hind limb, high stepping gait, wild/excitable, pruritis (with wool loss), emaciation

Question 3

How do we confirm scrapie diagnosis

Answer 3

Brainstem testing; THEN MUST REPORT AS NOTIFIABLE

Question 4

What is the cause and symptoms of chorioptic mange

Answer 4

From mite Chorioptes bovis
> Often asymptomatic: lesions on base of tail, perineum,, udder, scrotum, lower limbs, hooves, ears

Question 5

What is the cause of sheep scab

Answer 5

= Ovine psoroptic mange
> From Psoroptes ovis
- Used to be notifiable
Spread mainly sheep to sheep but can survive in environment for 3 weeks

Question 6

Symptoms of sheep scab

Answer 6

Wool loss and formation of progressive scab lesions
Lesions expand from subclinical to clinical as mite numbers increase; find mites at edges of lesions

Question 7

Detecting sheep scab

Answer 7

Look for reaction to massaging the lesion
- Ranges from slight reflex to epileptiform fit

Question 8

What two mites can cause problems in the ear

Answer 8

1) Psoroptes ovis; in sheep scab cases
2) Psoroptes cuniculi

Question 9

Differences between scab and lice in sheep

Answer 9

Scab is more acute, more intense irritation, wool loss, mortality higher, crusty scabs with definitie point of origin

Whereas live: more chornic, irritation less intense, rare to get mortality, no definitive point of origin

Question 10

Treating sheep scab/lice

Answer 10

Organophosphate dips = gold standard

Synthetic pyrethroid spot ons are good for chewing lice but not good for sheep sca

Can use macrocyclic lactones: e.g moxidectin; BUT don’t do every year because of resistance risk

Question 11

Which chewing lice species affects sheep and which sucking

Answer 11

Chewing = Bovicola ovis
Sucking = Linognathus ovillis, pedalis

Question 12

What is an example of a permanent fly i.e whole life cycle on host

Answer 12

Keds = Hippoboscid flies
e.g melophagus ovinus

Question 13

What diseases can biting midges transmit

Answer 13

Schamellenberg virus; bluetongue virus
+ can cause bite allergies in hosts

Question 14

What type of fly is the head fly; hydrotaea irritans

Answer 14

Secretophagous

Question 15

What does myiasis mean

Answer 15

The infestation of living tissue by larvae of true flies

Question 16

Example of an obligate and facultative agent of myiasis

Answer 16

Obligate = oestrus ovis (nasal bot fly)
Facultative = lucilla seratus; sheep blow fly strike

Question 17

How does sheep blow fly strike work

Answer 17

Lucilla sericata flies are attracted to odours from sheep; lay eggs mainly on tail head
- Larvae need >70% moisture; hatch and migrate down to breech skin and use hooked mouthparts and salivary secretions to eat into in
> Exudate from wound wets the wool and creates an odour that attracts MORE FLIES

Question 18

What is the cause of death from sheep blow fly strike

Answer 18

Waste products of the larvae
= lipid soluble ammonia which is absorbed by skin into blood; bypasses normal detoxification
-> Get organ damage

Question 19

How can we treat sheep blow fly strike

Answer 19

Clip wool
Clean wound to remove larvae and waste products
Give synthetic pyrethroids and avermectin to make animal TOXIC
+ antibiotics and NSAIDs

Question 20

How do triazine derived IGRs work

Answer 20

e.g Cyromazine
> Via interference with moulting and pupation

Question 21

How do pyrimidine derived IGRs work

Answer 21

e.g Dicyclanil
> Via interference with chitin metabolism

Question 22

Life cycle of sheep keds (melophagous ovinus)

Answer 22

Obligate permanent parasite
> wingless blood sucking flies; eggs and larvae develop WITHIN THE FEMALE; so L3 pupate directly after deposition and attach to wool; then emerge in 2 weeks

Question 23

Control of ticks two products

Answer 23

OPs (organophosphates)
SPs (synthetic pyrethroids)

Question 24

Cause of contagious pustular dermatitis (orf)

Answer 24

a parapox virus

Question 25

Pathogenesis of orf

Answer 25

Lesions on lips of lambs and udders of ewes
= papular crusting lesions; progressing to vesicles and pustures

Can give live vaccines to ambs from 1 day old (BUT DON’T GIVE UNLESS FARM HAS ORF ALREADY AS IT IS A LIVE VACCINE AND WILL GET IT FOREVER)

Question 26

What bacteria causes fleece rot

Answer 26

Pseudomonas

Question 27

What is big head

Answer 27

Clostridial cellulitis

Question 28

Primary and secondary causes of photosensitisation in sheep

Answer 28

Primary = via photodynamic agents e.g St John’s wort
Secondary = via liver damage e.g from pog asphodel or liver disase

Question 29

What metal deficiency can cause skin disease

Answer 29

Zinc

Question 30

What is wool slip

Answer 30

Where high cortisol release in response to stress causes partial or complete wool loss a few weeks later due to breakage