Ovine Diseases Flashcards
Name the 2 anaerobic bacteria responsible for footrot and scald.
Dischelobacter nodosus
Fusobacterium necrophorum
Why is dischelobacter nodosus only assocaited with ruminant hoof horn?
Its enzymes and proteases enable it to underrun hoof horn
What is the pathogenesis of footrot and scald?
Interdigital skin colonised by F.necrophorum causes inflamed, painful interdigital skin with no underrunning of horn in scald and with time it will then underrun hoof horn and cause footrot
Footrot = interdigital dermatitis = scald, all from infection with D.nodosus.
What are the risk factors associated with footrot?
Rainfall
Temperature >10˚C
Stocking rate
Breed of sheep
Virulence of D.nodosus. strain
Gathering sheep
How is footrot transmitted?
- Infectious disease transmitted via contaminated grazing/bedding
- Cannot survive off the hoof for long therefore can be controlled
How is footrot treated?
- Systemic treatment with long acting antibiotics
- Use antibiotic spray on feet to reduce ground contamination
Mark the animal
How is early footrot/scald treated?
- Foot bathing with Zinc sulphate
- Spray individuals with tetracycline spray (if pragmatic)
How is footrot and scald controlled?
- Rim if over grown but do not over trim
- Separate flock into affected and “clean”
- Pasture is “clean” when left for approximately 14 days
- Foot bath all with 10% zinc sulphate (need to stand for 5-10 minutes; longer the better
- Vaccination
- Metaphylactic use of antibiotics to control footrot
What is caused by over trimming?
Granulomas due to over-trimming, can be removed using local anaesthetics and cauterise with disbudding iron.
What is contagious ovine digital dermatitis?
- Severe lameness
- Initial ulcer-like lesion on the coronary band
- Often progress to loss of whole hoof-case
How is contagious ovine digital dermatitis treated?
Oxytetracycline LA, Amoxycillin LA, Micotil (vet administration), “Linco-spectam” footbaths
What is white line disease?
- Commonest form of non-infectious lameness
- Half-moon lesions
- Provide an environment for footrot
- Trim to tidy up lesions
What are interdigital growths?
- Fibromas removed surgically
- Do not breed from affected Suffolk rams
What is contagious lymphadenitis?
Bacterial infection caused by corynebacterium pseudotuberculosis, very resistant in environment
What are the clinical signs of contagious lymphadenitis?
- Chronic superficial abscesses mainly lymph nodes
- Parotid, submandibular and prescapular lymph nodes
- Lesions are thick walled and caseous
- Internal lesions cause severe weight loss
- Thoracic and mesenteric lymph nodes/lungs
- Mediastinal nodes/liver
How is contagious lymphadenitis controlled?
- Disinfect shearers and equipment using chlorine bleach
- Isolate animals with abscesses, surgically open and drain abscesses
- Disinfect pens with hypochlorite or 1% chlorhexidine
- Cull out whole flocks/herds
What is orf?
Zoonoses. Parapox virus can survive in the environment for up to 20 years. Need a cut or abrasion for the virus to enter
How is orf spread between sheep?
Spread by close contact, feeding troughs
Describe mild ocular signs of orf.
Tear staining associated with conjunctivitis. The cornea becomes cloudy and blood vessels are seen prominently at the periphery of the eye. The ocular discharge becomes thicker and pus-like as the disease progresses
What happens when both eyes are severely affected due to orf?
Sheep become temporarily blind, resulting in handling difficulties and losses due to misadventure. Extreme cases: the anterior chamber of the eye may ulcerate, rupture and become secondarily infected, resulting in permanent blindness.
What is bluetongue virus?
An arthropod-borne viral disease of ruminants
Associated with primary vascular damage
How is bluetongue virus controlled?
- Prevent entry
- Reduce exposure
- Vaccination – 1 annual dose in sheep, 2 doses in cattle and subsequent annual booster
What are the challenges of bluetongue virus on a molecular level?
Continual change in genetic sequence in replication vector and host, re-assortment and genetic drift, 24 serotypes/24 diseases
What are the challenges of bluetongue virus on a cellular level?
Avoid host defences, within the cell, extracellularly
What are the challenges of bluetongue virus on a host level?
Wide variation in virulence of the virus, variation in pathogenicity between species and breeds
What are the challenges of bluetongue virus on a vector level?
Virus factory which can widely disseminate the disease, potential for recruitment of new vector species
What is clostridial disease in sheep?
- Organisms are ubiquitous in soil and faeces
- All sheep farmed in UK should be vaccinated
- Very common cause of sudden death in sheep
How is clostridial disease in sheep controlled?
- Control fluke
- Lambs will be covered if fed colostrum from vaccinated ewes
- Don’t forget the rams
- Vaccinate effectively
What is the most common cause of abortion in sheep in the UK?
Chlamydophila abortus
Which of the following causes of ovine abortion have licensed vaccines in the UK?
Chlamydophila abortus and toxoplasma gondii
Which pathogen is associated with watery mouth in lambs?
Non-haemolytic strains of E.coli
How long does passive immunity against clostridial species last in lambs from ewes inoculated prior to lambing?
3 months
How long does active immunisation of lambs against clostridial disease last?
12 months
How long does passive immunity against Pasteurella persist in lambs from boosted ewes?
3 weeks
What is the vector for the bluetongue virus in ruminants?
Midge
A grazing ewe is found dead with her lambs calling and trying to feed from her. Which is the most likely cause of death?
Hypomagnesaemia/grass tetany
