Sheep ectoparasites

Question 1

How do ectoparasites in sheep affect welfare and production?

Answer 1

• mainly through losses in wool, meat and milk production
• negative effects on fertility and lamb growth rates

Question 2

Main ectoparasites in sheep are

Answer 2

• mites
• lice
• ticks
• flies
• keds

Question 3

Mites

Answer 3

○ Cause of different types of mange
○ Sheep scab - Psoroptes ovis, which can be severe and contagious
○ Chorioptic mange - Chorioptes ovis
○ Demodectic mange - Demodex ovis
○ Sarcoptic mange - Sarcoptes scabei var. ovis

Question 4

Lice

Answer 4

○ Sucking/blood feeders - Lignonathus ovillus and pedalis
○ Chewing/biting - Bovicola ovis
○ Lice infestations are typically less severe than mites, in particular sheep scab, but are associated with debility and weight loss

Question 5

Ticks

Answer 5

○ Ixodes ricinus, Dermacentor marginatus, Rhipicephalus spp., Haemophysalis punctata
○ Can cause anaemia in lambs, but are more important as a vector of diseases such as Louping ill, viral disease of the CNS, S.aureus and tick-borne fever (TBF, a rickettsial disease characterised by high fever and severe leucopaenia)

Question 6

Flies

Answer 6

○ Bottle fly (Calliphora spp. & Lucilla sericata) causes blowfly strike (Myiasis) and is a major welfare concern
○ Nasal blot fly (Oestrus ovis) causes parasitic rhinitis and although uncommon is very unpleasant
○ Head fly (Hydrotea irritans) is important for horned sheep as they cause lesions around the horns in young sheep and rams

Question 7

Keds

Answer 7

○ Melanophagus ovinus
○ Uncommon and typically not a big issue but can cause annoyance, pruritus and wool loss, and in cases of severe infestation, anaemia, as they are blood-sucking wingless flies

Question 8

Blowfly strike

Answer 8

• Ovine cutaneous myiasis
• Caused by the infestation of living tissues with the blowfly larvae of the genus Lucilia., Calliphora spp., and Phormia spp
• In the UK, blowfly strike is usually initiated by the greenbottle fly (Lucilia sericata)
• The gravid females are attracted by the odour of decomposing matter such as wounds or fleece soiling
• Each female lays up to 250 eggs that hatch after ~12h
• After 3d the mature larvae drop off the sheep and pupate in the soil
• Blowfly strikes usually occur in waves
• The 1st fly lays her eggs and the odour from this strike attract other flies Phormia terraenovae (blackbottle flies) and Calliphora erythrocephala (bluebottle flies)
• The flies are attracted by decaying animal tissues, infected or necrotic injuries and soiled wool
• They lay eggs in these areas, which hatch within 12h, and maggots feed on the tissue for 3-10d, before dropping off to become mature flies
• The entire lifecycle from egg to adult can occur in less than 10d in optimal conditions
• It’s a seasonal disease, aligning with blowfly populations which are typically greatest during the summer months, with a high-risk period between May and September
• Although due to changes in climate the risk period can be from as long as March to December in some lowland areas

Question 9

Blowfly strike - CS

Answer 9

• In mild cases, maggots don’t cause clinical disease and lesions heal quickly and completely
• However, any fly strike is of high risk of becoming a major welfare concern when high numbers of maggots feed on the host
• As the maggots develop, they actively feed using abrasive mouthparts, causing skin and muscle damage exacerbated by their secretion of proteolytic enzymes
• Toxins released by damaged tissues and ammonia secreted by the maggots are absorbed through the lesions into the sheep’s bloodstream, causing toxaemia, illness, and death
• Secondary bacterial infections are common and may also cause death if untreated
• The 1st signs in affected sheep are a patch of discoloured wool and agitation
• Further investigation of clinical signs will likely include separation from the flock, pruritus, restlessness, discolouration of the wool and unpleasant smell.

Question 10

Blowfly strike diagnosis

Answer 10

• Visual inspection
• Legal requirement to inspect all sheep daily during the highest risk periods for signs of blowfly strike; disease is easily detected by observing sheep whilst grazing

Question 11

Blowfly strike tx

Answer 11

• Treatment includes the application of insecticides (usually synthetic pyrethroids, although organophosphate dips are also licensed for treatment) coupled with shearing and cleaning of the affected areas
• Topical antibiotics may be used, along with systemic antibiotics in severe cases
• NSAIDs
• The rest of the flock should be closely monitored for any signs of strike

Question 12

Blowfly strike prevention

Answer 12

• Involves reducing sheep susceptibility and reducing fly abundance at high risk times
• Fly numbers can be reduced by trapping, but most control measures focus on reducing sheep susceptibility. This can include:
• Mechanical control measures, such as dagging, shearing or tail docking
• Chemical control measures, such as organophosphate dips, synthetic pyrethroids or insect growth regulators
• Reducing faecal soiling (e.g. ensuring nematode control) and close monitoring of any open wounds
• Selecting breeds with an open fleece and avoiding excessive skin folds around the breech or vulva may also help in some systems

Question 13

Lice infestation (Pediculosis)

Answer 13

• Mallophaga (biting lice): Damalinia (Bovicola) spp
• Anoplura (sucking lice): Haematopinus spp, Linognathus spp
• Live on skin surface and can be seen easily by naked eye
• Dark grey/brown in colour and ~ size of a flattened pin-head
• Life cycle: direct and simple
• eggs -[2w]-> nymphs -[2w]-> adults (live 4 weeks)
• slowly progressive disease, so tend to see a gradual increase in itching

Question 14

Pediculosis signs

Answer 14

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

Question 15

Pediculosis diagnosis

Answer 15

• Visual inspection.
• Direct microscopy of hair samples

Question 16

Sheep lice tx

Answer 16

1. Pour-on synthetic pyrethroid preparation such as deltamethrin or cypermethrin. Kills biting lice
2. Organo-phosphate dips (not sprays or jet systems) kills everything including humans 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 ML wormers are not effective against biting sheep lice

Pour-ons are less effective in fully fleeced animals

Shearing can get rid of ~50% of the infestation alone

Question 17

Diseases spread by ticks

Answer 17

• looping ill
• tick borne fever
• tick pyaemia

Question 18

Louping ill

Answer 18

• 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)
• If colostrum management is good, young lambs should be protected against louping ill

Question 19

Tickborne fever

Answer 19

• 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 naive rams may become infertile
• Lambs born in endemic areas are infected within the 1st 2wk of life and have mild symptoms
• Naive animals introduced to endemic areas show more severe signs

Question 20

Tick pyaemia

Answer 20

• Staphylococcal infection of lambs, often following immunosuppression due to tickborne fever. (i.e. not directly caused by the tick, but a staph infection which can enter the body/skin through a tick bite)
• Lambs are mainly affected at 2-12 weeks old with abscesses developing throughout the body, often in joints, tendons, muscle and brain.
• Can look like joint ill
• 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 21

Tick Control - host control

Answer 21

• 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.

Question 22

Tick control - environmental control

Answer 22

• 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 23

Mange

Answer 23

Surface feeders*
- Chorioptes spp
- Psoroptes spp

Burrowing mites
- Sarcoptes spp
- Demodex spp

Question 24

Sheep scab

Answer 24

• Psoroptes ovis
• Notifiable in Scotland
• Legal requirement to treat or slaughter in all parts of the UK
• Estimated to cost the UK sheep industry £78 to £202 million per year
• Mite – highly contagious
  – viable off the host
  – PP: 14 days
• acute/chronic allergic reaction

Question 25

Sheep Scab epidemiology

Answer 25

• winter
• lots of contact

Question 26

Sheep scab diagnosis

Answer 26

• Skin scrape (just about visible to eye) from the edge of lesions (as this is where the mites tend to be)
  – Oval-shaped mites identified by their three-segmented pedicels and funnel-shaped suckers.
• Blood coproantigen ELISA (early dz)

Question 27

Sheep scab tx options

Answer 27

1. Organo-Phosphate plunge dipping
   – Diazinon
   – Difficult to perform
2. ML injections
   – One injection of moxidectin gives at least 28 days residual protection (1% lasts ~28d, 2% lasts ~60d)
   -> BUT moxidectin resistance
   -> 1% moxidectin is contraindicated if the sheep have ever had footvax
   -> Use 1% if not contraindicated and if have clean space to put them, otherwise use 2%
   – 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.
   – Ivermectin gives no residual protection.
   -> Two ivermectin injections 7 days apart required to tx scab

Question 28

Sheep Scab – Control challenges

Answer 28

• safety: of chemical control measures (humans, animals, environment)
• resistance: of mites to MLs, and concern over increasing exposure of endoparasites to MLs
• Sub-clinical: scab infestations
• biosecurity: risk increases with scab-infested neighbours and common grazing
• farmer motivation - social stigma leading to under reporting/fatalistic view of scab control

Question 29

Sheep Scab – Control solutions

Answer 29

• 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)