Update on Schmallenberg virus
Department of Agriculture releases survey findings
The Department of Agriculture, Food & the Marine recently completed a preliminary survey of cattle herds and sheep flocks (under taken since the Schmallenberg virus was first discovered here) to establish just how wide spread exposure to the virus has been during 2012.This was with a view to trying to predict the likely impact of the infection during the 2013 spring calving and lambing season.
To date the infection has been confirmed in foetuses obtained from a further 20 cattle herds and 12 sheep flocks(33herds/flocks in total). All of these confirmed cases have been confined to Co.Cork(16cases) and South Eastern counties(8 in Wexford, 7 in Kilkenny, 1 in Wicklow and 1 in Waterford).
The preliminary data suggests that the greatest risk of exposure of flocks/herds to this virus during 2012 was in the South and East of the country and towards the end of the vector season.
What does this mean for herd and flock owners?
Firstly it is important to emphasise that to date we have only confirmed 33 clinical cases despite the evidence of widespread exposure to the virus. However, there are now numerous reports from flock owners of malformed lambs being born to early lambing flocks in the South East and a small number of these affected lambs have been submitted to Kilkenny and Cork Regional Veterinary Labs since Christmas.
Problems with malformed calves and lambs are most likely to arise when pregnant cows and sheep are exposed to the virus during a critical time window in early to mid pregnancy (estimated to be 40-120 days gestation in cattle and 20-80 days gestation in sheep). As the time of exposure is uncertain it is too early to estimate what percentage of exposed herds/flocks are likely to have affected calves/lambs.
Based on the pattern in the UK and elsewhere, between 4-6% of holdings are likely to be affected – likely to be mild in most cases at 2-5% of affected pregnancies, but moderate at worst. The highest level of problems would be expected in herds that have synchronised breeding programmes and where large numbers of animals were infected during the critical period of pregnancy in 2012.
Impact of infection in Spring 2013
- It will be relatively small in most infected herds and flocks
- It is entirely dependent on the stage of pregnancy at which cows and ewes are infected
- It will be greatest in southern and eastern counties because of greater risk of exposure to the virus
- It is likely to be greatest in herds with compact calving and flocks with synchronised breeding programmes
- DAFM does NOT impose any restrictions on infected holdings.
- Herd/Flock owners will need to be extra vigilant as foetal malformations can give rise to significant lambing and calving difficulties with associated welfare problems.
Farmers are advised that as malformed lambs and calves may be alive at birth they should seek appropriate advice from their veterinary surgeon.
Farmers who suspect they have problems caused by SBV should discuss with their veterinary surgeon what action they should take including the submission of samples, if appropriate, to the local Regional Veterinary Laboratory. Deformed lambs or calves can be tested for the presence of virus. Alternatively, blood or milk samples can be tested for antibodies to confirm that the cow (or ewe) has been exposed to SBV.
Further spread to unaffected herds/flocks in northern and western counties is very likely to occur during the 2013 vector season but should have relatively little impact in non-pregnant livestock. It is generally impractical to attempt midge control measures except for valuable breeding stock and it would be hoped that a strategy of exposure of non-pregnant animals may in fact be beneficial pending the development of an effective vaccine.
Exposed animals develop a strong immunity and are unlikely to suffer any ill-effects if exposed to the virus on a subsequent occasion. If this viral infection becomes endemic the ill-effects are likely to be confined to younger animals and cows and ewes that have not been previously exposed. Although vaccine development is in progress there is likely to be some delay before any candidate vaccine is licenced and becomes commercially available, but the Department will monitor developments closely.
This update is extracted from a report by Bernard Bradshaw, Veterinary Laboratory Service and Sally Gaynor, National Disease Control Centre, issued by the Department of Agriculture, Food and the Marine (DAFM) on 17th January 2013.