QUESTIONS AND ANSWERS ABOUT LYMPH NODE APLASIE (LNA)

NB – LNA is not a disease

In 2016 SRUC looked at three lambs with severe orf and lymph nodes were absent in all cases. An hereditary condition was suggested but the offer of further investigation was declined. No further cases were seen until 2021, when three flocks submitted lambs. This year there have been more flocks diagnosed with LNA.

Following an open meeting with Heather Stevenson, SRUC and Neil Laing the following are a list questions that arose.

·       If we have an outbreak of Orf does that mean that the lambs have no Lymph nodes?

Not necessarily, as Orf is a naturally occurring common virus within sheep and can flare up in young lambs very easily. Normal Orf will clear up within 4/6 weeks, with or without treatment.

·       Does this severe Orf spread between lambs?.

No as it is caused by no lymph nodes, it is not infectious. Affected lambs are born without lymph nodes which are an important part of the immune system.  The other parts of their immune system appear to function normally.

·       Why have the lambs got no lymph nodes?

It is likely that it is a heredity condition that is caused by a rogue gene that is present in both the sire and dam of affected lambs.

·       What time of year would we see Lymph node aplasia?

LNA is most often diagnosed in lambs between July and September and the lambs will not recover from the severe Orf and if not put down they will die. They are unlikely to live longer than 4/6 months of age.

·       Do lambs die of other conditions if they don’t have lymph nodes?

Listeriosis and cryptosporidiosis have also been diagnosed as causes of death in lambs with no lymph nodes. 

·       Does the use of Scabivax cause the problem?

No, it is the fact they have no lymph nodes and when they are exposed to the live vaccine the severe Orf will manifest.

·       Is this an issue within a lot of flocks?

There have been 14 flocks so far confirmed with LNA. Each farm provided information on dam and sire lines from at least 2 affected lambs.  Data for 18 lambs in total.

·       Is there a test for tups?

At the moment there is no screening test for tups. SRUC need further sets of affected lamb/dam/sire bloods to increase the likelihood of identifying the mutation(s).  Only then will it be possible to investigate the feasibility of developing a screening test for tups. Roslin have not been able to find the gene/genes responsoble so far in the samples they have looked at. 

·       How do we prevent getting LNA within our flock or what to do if we have had it?

Use as diverse genetics as possible, do not use rams that are closely related to your ewes. Do not inbreed and do not breed from affected animals.

·       Should a bought tup be scratched for Orf and see if the severe Orf occurs.

No, one should never treat sheep with the Orf vaccine if you don’t have Orf on the farm.

·       Is it better not to use lambs?

Using shearlings will give you more confidence, although they could still be carriers. 

·       Do other breeds have LNA?

It has not yet been found in any other breeds, but other breeds have had issues caused by genetic defects.

·       What do I do if I think I have a problem?

If you think you have a case, speak to your vet and get your lamb/lambs sent to an SRUC laboratory, where they will postmortem them free of charge and if they have LNA you will then need to give blood samples from the sire and dam.

·       Has this been caused by AI?

No, AI has not caused LNA, but by using AI breeders may have completely involuntary spread the rogue gene being unaware that it even existed.

·       What is the next step?

Genotyping of both affected flocks and control flocks will have to be undertaken. The cost of the test is circa £650 per test and then the results will have to be analysed. SRUC, Roslin Institute and the Blackface Sheep Breeders Association will put together a proposal for going forward and prepare budget to try and secure some funding for this work. 

If you have any further questions please contact Heather Stevenson, SRUC heather.stevenson@sruc.ac.uk T: 07425160900.

Or Aileen McFadzean, Blackface Sheep Breeders Association T: 07768820405