Sheep Resp Disease - Adults Flashcards
What type of organisms causes Maedi Visna?
Lentivirus - non-oncogenic slow RNA retrovirus
How does Maedi Visna initially present? What does it go on to do to the immune system?
- Initial Oro-nasal infection –> slow replicating lymphoid hyperplasia. Mainly affecting monocytes, macrophages & dendritic cells are main target cells.
- MV latent in genome of the monocytes (Trojan horses) so evade host immune system.
What are the 3 possible manifestiations of maedia visna?
Up to 3 manifestations of the same condition:
- 1st: Maedi – dyspnoea & heavy lungs 4-5y post infection
- 2nd: Visna – progressive nervous signs 2-3y post infection – dragging back legs (top right pic)
- 3rd: Indurative lymphocytic mastitis
How is maedi visna spread?
- SPREAD- Close contact - respiratory spread in aerosol
- Also spread in milk or colostrum of infected ewe, so their lambs are effected
- Some transfer possible via placenta & semen – small importance compared to respiratory and milk spread
How can you control maedi visna?
- Easier to prevent infection than to eradicate it, difficult to eradicate as have to test large numbers of sheep and some sheep incubate it that don’t show up on the test
- Buy in MV accredited replacements or isolate & test
- Prevent contact with neighbouring flocks
- Eradication easier if at low level (test & cull)
If you have a high level of infection, how can you control maedi visna?
Cull flock & restock with accredited sheep – possibly most cost effective. But accredited sheep are largely pedigrees, so if you want commercial ewes – wont find these accredited mule producers.
- Try and reduce losses through management:
- keep flock young
- split into older & younger sheep for management as far as possible, so younger sheep are at less risk
- cull thin/suspect cases, or offspring of suspect sheep – reduces spread
- Run a less intensive system to reduce spread
Is there a diagnostic test for maedi visna?
What is the problem with it?
- Aim to increase awareness of the disease, using screening tests
- Blood sample 12 thinner/suspect cases/older sheep – probably 12 culls anyway.
- Package price £35 & VAT – expensive and long term commitment to try and get rid of MV in the flock
- NB Make sure you know what you will do if you find it!
Is there a vaccine available for Maedi Visna?
Prospect of vaccination is unlikely, this virus evades immune system of flock.
What kind of organism causes Ovine Pulmonary Adenocarcinoma?
Jaagsiekte sheep retrovirus (JSRV) - a beta retrovirus
How does the disease with Ovine Pulmonary Adenocarcinoma initially present and how does it progress?
•Oronasal infection
–> neoplastic proliferation of Clara cells & type II pneumocytes (within lungs)
–> adenocarcinoma with ++white foaming fluid.
What is the incubation for Ovine Pulmonary Adenocarcinoma?
What ages is it seen in most?
Long incubation – seen mainly above 2 years old [possible 2 m - 11 y!]
What breed have a predominance of Ovine Pulmonary Adenocarcinoma?
Predominance in Scottish black face, mules and greyface. Low numbers in some breeds such as Suffolk’s – is there genetic effect? Likely there is s genetic predisposition. But also worse in some parts of the country
Can you test for Ovine Pulmonary Adenocarcinoma?
- No immune response so no serology possible
- PCR test possible in respiratory system & peripheral blood lymphocytes – But this test has a low sensitivity as virus levels fluctuate & for this reason this test is not commercially available
- Effectively no test in the live animal!! So cannot say what is prevalence of OPA in a flock. One of the best ways is to open them up
What is the problem with testing for Ovine Pulmonary Adenocarcinoma?
- Effectively no test in the live animal!! So cannot say what is prevalence of OPA in a flock. One of the best ways is to open them up
- Monitoring very 4 months for 2 years showed presence of virus in individuals very variable – often +ve & then –ve 4 months later. No animals consistently positive and none consistently negative.
- None were consistently +ve & some consistently –ve.
- Only 1 in 20 infected animals actually developed disease.
What is the control for Ovine Pulmonary Adenocarcinoma?
- Identify & cull infected & offspring – very difficult without a test.
- Manage in single age groups – keep young separate from adults
- Reduce close contact – try not to house, reduce stocking density, try not to trough feeding as secretions are full with virus. Need good hygiene!
- Snatch lambing & rear artificially – successful in German case study (Voigt)
What is Caseous Lymphadenitis caused by?
Cause by Corynebacterium pseudotuberculosis
(bacterium with lipid coat)
How long does caseous lymphadenitis survive for?
What is its incubation period?
- Survives for a long time: 8mths in soil, 24h in dip. Difficult to get rid of once in!
- Incubation = 42 days-4mths
How does caseous lymphadenitis spread and progress? I.e. what causes the disease?
- Infected wound → Bacteria spreads to draining lymph node → inflammation → micro abscesses → coalescence of abscesses → green pus (bacteria, cellular debris, eosinophils) → caseation of puss → walling off → further multiplication → release of exotoxin → typically caseous abscess with ‘onion ring’ appearance of the abscess
- Exotoxin, Phospholipase D, damages cell membranes & is essential in pathogenesis
Can caseous lymphadenitis be sorted with antibiotics?
No
How is caseous lymphadenitis spread?
Respiratory spread
Spread at close contact – at Gathering, Clipping, Dipping, Showering – any where they are close togethers
What increases the risk of a sheep getting caseous lymphadenitis?
- Longer time spent gathered post-clip/dip/shower
- Showering sheep instead of other treatments
- Gathering into dusty yards under cover
- Older ewes have a higher prevalence than younger ewes
- Ram have higher prevalence than ewes (?management)
- Risk is very low pre-weaning transfer is low, so not so important to snatch lambs at birth
- Submandibular and parotid LNs is where you often see it, large areas of swelling
- The longer time they spend gathered, increased risk of getting it
Where is caseous lymphadenitis common in rams?
- CLA common in inguinal & scrotal lymph nodes of rams at breeding soundness exam as they are checked for fertility, but predominantly seen in the LNs around the head and neck
- BUT semen quality was normal & no organism excreted in semen
- 18% of UK terminal sire flocks estimated to be infected 12 yrs ago
What is the diagnosis of caseous lymphadenitis?
- Culture of organism – though don’t lance abscesses & encourage spread – reveals organism and cause contamination locally! If already have burst abscess, then swab that and send for culture, but don’t lance an abscess!
- ELISA – detects antibodies to the surface antigen Phospholipidase D (PLD) (Sensitivity 87% & Specificity 98%). From blood sample. Pretty poor sensitivity, so means 13% will be a false negative. But high specificity, if you get a positive, means its likely to definitely be positive!
What is vacciantion like for caseous lymphadenitis?
Glanvac (6-in-1; Zoetis) – Australian vaccine - we dont really like it here!! A last resort to use this vaccine accordingto lady on the podcast!
- Can only use in UK under Special Import License (VMD)
- Made up of formalin-killed bacteria & toxoid – not the greatest vaccine, fairly crude
- Flock protection varies from 25%-90% - very variable!
- Needs 2 doses of vaccine a month apart & annual booster
- Maternal Derived Immunity affects lamb immune response up to ~10 weeks old
- Affects any eradication program using serology as not DIVA
