Ectoparasites in sheep

Question 1

What ectoparasites are sheep most prone to?

Answer 1

Psoroptes ovis (sheep scab mite) – Severe and contagious

Myiasis (blowfly strike) – massive welfare concern

Lice – Less severe than sheep scab but associated with debility and weight loss

Ticks – vector for Louping ill, S.aureus, TBF

Question 2

When id pediculosis most likely to occur?

Answer 2

disease of housing when it is cold and fleece is long

Question 3

What are the clinical signs associated with pediculosis? How is it diagnosed? How is it treated?

Answer 3

Signs
* Asymptomatic
* Pruritus
* Excoriation
* Fleece damage and loss.
* Severe infestations can result in anaemia.
* Can look similar to scab

Diagnosis
* Visual inspection.
* Direct microscopy of hair samples

• Shearing can reduce the population of lice by 30-50%.
• As in cattle, pediculosis may be an indicator of underlying health problems.

Treatment
1. Pour-on synthetic pyrethroid preparation such as deltamethrin or cypermethrin. Kills biting lice. Far better used on sheep that have been sheared
2. Organo-phosphate dips (not sprays or jet systems) kills everything but can cause harm to people too so be very careful that correct PPE and protocols are used

All sheep in direct contact must be treated. Treat at start of winter housing period

NB: unlike cattle injectable Macrocyclic Lactones wormers are not effective against biting sheep lice

Question 4

What is the most common sheep tick? What is its life cycle?

Answer 4

Ixodes Ricinus

Question 5

What 3 diseases are ticks vectors for in sheep?

Answer 5

Louping ill
* Viral infection (RNA Flavivirus) causing encephalomyelitis resulting in death, seizures, paralysis and death.
* Most common in weaned lambs and yearlings (lambs get passive protection in colostrum).
* Mainly affects sheep and grouse, but can cause disease in other animals and is zoonotic
* Control is mainly through tick control, although vaccination can play a role (but not currently available)

Tickborne fever
* Immunosuppressive disease caused by bacteria Anaplasma phagocytophilum. Bacteria infects and destroys WBC causing leucopaenia.
* Affected animals are pyrexic, anorexic and depressed. Pregnant ewes may abort and naïve rams may become infertile.
* Lambs born in endemic areas are infected within the first 2 weeks of life and have mild symptoms. Naïve animals introduced to endemic areas show more severe signs.

Tick pyaemia
* Staphylococcal infection of lambs, often following immunosuppression due to tickborne fever.
* Lambs are mainly affected at 2-12 weeks old with abscesses developing throughout the body, often in joints, tendons, muscle and brain.
* Lambs may display severe lameness, paralysis of the backend and death in severe cases. Up to 30% of lambs in a group may be affected.

Question 6

How can you control spread of ticks in your sheep flock?

Answer 6

Host Control
* Avoid buying in naïve animals
* Synthetic pyrethroids (deltamethrin and cypermethrin)
◦ Better operator safety than OP dips and longer protection, but no immediate kill.
* Organophosphate dips
◦ Requires care with application, but also protects against blowfly strike, scab, lice and keds. Also provides immediate kill.

Environment Control
* Active and start to feed in early spring – expose lambs while they have some passive protection.
* Avoid tick prone pastures if possible?
◦ Attempts to decrease tick population = pasture improvement
‣ drainage and scrub clearance

Question 7

What is the most common mite affecting sheep? How do sheep present? How is it diagnosed? How is it treated?

Answer 7

Sheep scab - Psoroptes ovis
* Notifiable in Scotland
* Legal requirement to treat or slaughter in all parts of the UK
Highly contagious
◦ viable off the host for 17 days
◦ PP: 14 days
* Sheep with early disease may show no signs, or simply be restless/rub against posts/have stained areas of fleece or toss their heads.
* Lesions become more severe and form bleeding wounds.

Diagnosis
* Skin scrape (just about visible to eye)
* Oval-shaped mites identified by their three-segmented pedicels and funnel-shaped suckers.
* Blood antibody ELISA (early dz)

Treatment
* Organo-Phosphate plunge dipping
◦ Diazinon
◦ Difficult to perform
* ML injections
◦ One injection of moxidectin gives at least 28 days residual protection (1% vs 2% formulations)
‣ BUT moxidectin resistance
‣ Contraindicated with footvax
‣ Moxidectin 1% protects for 28days, 2 injections 10 days apart required to treat sheep scab.
‣ Moxidectin 2% protects for 60 days – only thing we can use if there’s nowhere ‘clean’ for sheep to go.
‣
◦ Doramectin gives 14 days residual protection
‣ BUT persistence of mites in environment (17days) and time taken to kill P.ovis mites post-treatment (up to 10 days) means having to move the treated sheep onto scab-free pasture immediately after treatment and don’t mix with other groups for 14 days.
◦ Ivermectin gives no residual protection.
‣ Two ivermectin injections 7 days apart required to tx scab

Question 8

How can you control sheep scab?

Answer 8

• Quarantine treatment key to avoid bringing in scab
• ML resistance means OP dipping is the only consistently reliable way to protect against scab.
• Qualification now required to purchase OP dip and there are contract dippers who cover the country
• Serology – blood test with high sensitivity and specificity provides ability to detect scab within 2 weeks of infestation (Bayesian modelling being used to improve interpretation of ELISA results - incorporates ‘prior knowledge’ to help improve interpretation)
  ◦ can be used to quarantine and test a cohort of a group before mixing.