Ectoparasites - Sheep

Question 1

Myiasis

Answer 1

Infestation of organs or tissues of living animals by fly larvae.

Question 2

This obligate myiasis species of fly is also known as the sheep nasal bot fly.

Answer 2

Oestrus ovis

Question 3

Is calliphoridae an obligate myiasis species? Where is it found on the animal?

Answer 3

No, its facultative. It is found cutaneously

Question 4

Name the five relevant species of blow fly in sheep.

Answer 4

Lucilia sericata, Lucilia cuprina (greenbottles),Phormia terranovae (blackbottles), Calliphora vicina (bluebottles), C. vomitoria

Question 5

Describe the morphological features of the blowfly adult and larvae.

Answer 5

Adult - 1cm, dorsal bristles, metallic sheen

Larvae - Smooth, segmented, 10-14mm, anterior oral hooks

Question 6

Outline the lifecycle of Lucilia sericata.

Answer 6

Temperature-dependent. Adult flies lay eggs on the wool, close to the skin. First stage larvae (1mm) at 8 - 24hrs. Second and third stage feed. The third stage larvae (10mm) wandering phase & falls to the ground and pupate. Adult flies hatch, 7 -10 days later unless they diapause the 3rd stage larvae enter diapauses and over-winter

Question 7

How do the second and third stage larvae of L. sericata cause skin lesions on sheep?

Answer 7

They penetrate the skin with hooked mouth parts and secretion of proteolytic enzymes, creating a red, raw lesion.

Question 8

What is the egg to adult interval of L. sericata?

Answer 8

2 weeks with optimal conditions.

Up to four generations a year in April/May and Sept/Oct

Question 9

Which areas of the sheep are most commonly affected by blowfly strike?

Answer 9

Breech, Tail, Body, Poll, Penile sheath, foot

Question 10

Which species of blowfly are common UK primary and secondary blowflies?

Answer 10

Primary blowflies – nitiate strike - Lucilia sericata, Phormia sp.
Secondary blowflies – cannot initiate strike. Calliphora sp

Question 11

Outline the pathology of blowfly strike.

Answer 11

Larvae emerge and digest tissue. Odour, bacterial infection Loss of condition, anorexic, dull, isolated. Wool not lost, but at skin level larvae can be seen in wound. Death from toxaemia.

Question 12

How can infestations with blowfly be controlled?

x9

Answer 12

Separate sheep, Clip lesion, Insecticides, Docking tails, Dagging and crutching, Prevention of scours, Carcase disposal, Treatment of wounds, foot rot etc, Mules operation

Question 13

Name ectoparasiticides which can be used to treat blowfly strike.

Answer 13

Diazinon, cypermethrin (+alpha), deltamethrin.

Question 14

What is problematic about control of blowfly control?

Answer 14

Short time on host, Repeated infestations, Rapid tissue damage, Extensive breeding sites

Question 15

Describe the characteristic features of Oestrus ovis.

Answer 15

Short-lived obligate parasite of sheep worldwide, Common in some parts of Southern UK but sig. local variations. Adult flies are larviparous, L1 squirted into the nose. Active in July mainly, grey body, vestigial mouth

Question 16

Outline the lifecycle of Oestrus ovis.

Answer 16

L1 deposited by adults in sheeps nose, feeds in nasal passages and sinuses, moult to L2, moult to L3 in frontal sinus, L3 moves to nostrils, sneezed out and pupariates, fly emerges 3-8 weeks later.

Question 17

Which larval stages of Oestrus ovis overwinter and where?

Answer 17

L1/2 overwinter in the nasal passages of the sheep and move to the frontal sinus in Spring.

Question 18

Which ectoparasiticides can be used to control Oestrus ovis infection in sheep? Which lifecycle stages are they effective against?

Answer 18

IVM, MOX has efficacy against the 3 larval stages

Question 19

Which tick borne diseases are transmitted to sheep by Ixodes ricinus? (x3)

Answer 19

Anaplasma phagocytophilum (fever), louping ill virus (zoonotic, vaccine available, red grouse), tick pyaemia (joint infection by S.aureus, paralysis/lameness)

Question 20

Which ectoparasiticides are recommended for control of ticks in sheep?

Answer 20

Diazinon, cypermethrin, deltamethrin

Question 21

This species of fly has losts is wings and so is often known as a louse fly.

Answer 21

Melophagus ovinus

Sheep ked

Question 22

Describe the characteristic features of sheep keds and their disease process.

Answer 22

Flattened in the same way as lice, they have short legs with stout claws. Females develop larvae within (cf tsetse flies)
Larvae pupariate in the wool, and the flies emerge 2-5 weeks later.
Transmission is sheep to sheep. Winter problem.
Suck blood, causes pruritis, loss of condition.
Transmits non-pathogenic Trypanosoma melophagium.

Question 23

Sheep scab is caused by which species of mite?

Answer 23

Psoroptes ovis

Question 24

Describe the morphology of psoroptes ovis.

Answer 24

pointed mouthparts, legs extend beyond margin of body, jointed pedicels, trumpet shaped suckers (c.f. Chorioptes), thumb print pattern on dorsum

Question 25

What are the feeding habits of Psoroptes ovis?

Answer 25

Non-burrowing and feed at surface of skin, feeding on lipids, superficial fluids, cells, bacteria, lymph

Question 26

Outline the lifecycle of Psoroptes ovis.

Answer 26

Adults lay eggs which go through three larval stages before moulting to an adult which lives 40-60 days. The lifecycle lasts a min of 10d (mostly 11-19d)

Question 27

What are the pathogenic features of sheep scab?

Answer 27

Chronic exudative superficial dermatitis, type I hypersensitivity due to ES antigens particularly in mite faeces, hyperkeratosis, Aural haematomas, Intense irritation, decreased weight gain, epileptiform seizures, death

Question 28

Where would you find psoroptes mites on sheep scab lesions?

Answer 28

On the moist edge of the lesions.

Question 29

How can Psoroptes ovis mites be isolated from lesions?

Answer 29

Scrape edge of lesions, macerate scab in 1-5%KOH for 5-10 mins (releases mites), view under microscope (lifecycle stages, eggs, cuticles)

Question 30

Name three clinical signs of sheep scab on a flock level.

Answer 30

Signs of severe pruritis and irritation: sheep scratch against posts, walls, wire etc, standing or found lying alone
depressed, clean areas of fleece where biting, dirty areas of fleece where rubbing, tags of wool in mouths or on flanks

Question 31

Name five clinical signs of sheep scab on an individual sheep level.

Answer 31

Part wool and examine, ’nibble’ reflex, possible seizure on contact, restlessness, pruritis
wool loss, lesions on neck, back, shoulders, flanks, weight loss, secondary bacterial infections

Question 32

How is sheep scab transmitted?

How long can mites survive off the host?

Answer 32

Direct contact, contaminated environment, fomites

Mites can survive off the host ~14-16 days

Question 33

Sheep scab is often known as a winter disease, why?

Answer 33

Fleece length, Climate, Mixing and stocking density increase, Off host survival increases

Question 34

Which areas of the sheep can be reservoirs of Psoroptes ovis?

Answer 34

Axilla, ears and folds of skin

Question 35

Outline the history of legislation pertaining to sheep scab.

Answer 35

1953; eradicated from UK, 1973; reintroduced into Lancs, 1983; compulsory double dipping, 1989; single dipping, 1992; deregulated as a notifiable disease.

Question 36

In which area of the UK is sheep scab still a notifiable disease?

Answer 36

Scotland

Question 37

Notifiable disease

Answer 37

any disease that is required by law to be reported to government authorities. The collation of information allows the authorities to monitor the disease, and provides early warning of possible outbreaks. In the case of livestock diseases, there may also be the legal requirement to destroy the infected livestock upon notification

Question 38

Outline the control measures used against sheep scab.

Answer 38

Dipping (an organophosphate, Diazinon), Injectable (Ivermectin, Doramectin, Moxidectin),Biosecurity measures; Common land grazing, Fencing, Markets, Shearing equipment, vehicles, Regular Flock inspection, Quarantine

Question 39

This species of Psoroptes primarily affects rabbits. Which part of the rabbits anatomy does this regularly affected?

Answer 39

Psoroptes cuniculi, localises to the ears and causes amange in the auditory canal.

Question 40

How does Chorioptes bovis cause disease in sheep? Is this mite more or less severe than psoroptes?

Answer 40

Chorioptic mange results from chewing (rather than skin piercing) activity; considerably less severe than psoroptic mange but is far more common.

Question 41

Which areas of the body are affected by chorioptes?

Answer 41

All haired areas; especially lower hind limb and abdomen with hair loss and thickened skin.

Question 42

This mite species feeds on scabs/ fungus of sheep.

Answer 42

Forage mites

Question 43

Name one biting/ chewing louse and two species of sucking lice of sheep.
Which species is more pathogenic and why?

Answer 43

B/C: Damalinia ovis. S: Linognathus pedalis, L. ovillus

Damalinia since it is more active.

Question 44

How can lice be controlled in sheep?

Answer 44

Consider quarantine for incoming stock for at least 3 weeks and Remove all debris (wool etc) from contaminated housing

Question 45

What are the epidemiological features of lice infection in sheep?

Answer 45

Breed, fleece length, overall health of the host, temperature. Lice populations thrive during winter. Shearing reduces populations by 30-50%.

Question 46

What injectable and dip ectoparasiticides can be used in the control of lice in sheep?

Answer 46

Injectable; moxidectin, doramectin, ivermectin (ML). Dip; organophosphate