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Schmallenberg Virus

Acute SBV disease in cattle was reported in mainland Europe in 2016, with clinical signs of milk drop fever, sometimes with diarrhoea. Cases of SBV have been reported in cattle and sheep in GB:

SBV in Great Britain Winter 2016/17 (as at 5th July 2017)

Cattle:

  • 10 cases of SBV have been confirmed in calves in Scotland. Most cases were identified in the south/border region, with 1 case in Clackmannanshire (central belt).
  • In England 65 cases of SBV were confirmed in calves, these included 6 cases in neighbouring counties to Scotland; Cumbria (11) cases and Northumberland (12)
  • In Wales 1 case of SBV was confirmed in May 2017 (North Wales)

Sheep:

  • 2 cases of SBV in lambs have been identified in Scotland; Dumfries (1) and Roxburgh (1).
  • In England 97 cases of SBV have been identified, these include 23 cases in neighbouring counties to Scotland; Cumbria (14) and Northumberland (3).
  • In Wales 42 cases of SBV were confirmed across the country, between January and March 2017.

History

Schmallenberg Virus (SBV) is a new disease which was first identified in Germany in 2011. The disease was seen in England in 2012.  The first case in of SBV in Scotland was identified 2013 through active surveillance.

The virus is carried principally by midges (Culicoides) and causes disease in cattle and sheep, particularly birth abnormalities in calves and lambs. Birth abnormalities are a result of infection early in cattle (60-172 days) and sheep (28-56 days) pregnancy causing damage to the developing central nervous system of the foetus. This results in brain and limb deformities in newborn lambs and calves. SBV is not a notifiable disease and no restrictions are placed on infected premises.

Farmers are advised to contact their veterinary practitioner or SACC Veterinary services if they encounter the following symptoms, and SBV infection is suspected:

  • Foetal abnormalities, stillborn animals or newborn lambs or calves showing signs of nervous disease
  • Clinical signs such as a transient drop in milk yield, fever and diarrhoea in adult dairy cattle.

What is EPIC doing?

Looking at the potential spread of SBV in Scotland

EPIC scientists have highlighted the importance of two risk factors for the spread of SBV in Scotland: environmental temperature and timing of introduction of the disease.

Role of Temperature

Modelling of SBV suggests that risk of spread in Scottish sheep and cattle, under 'the right conditions' is high, but is highly sensitive to temperature; too early in the season and it will be too cool with insufficient vectors to establish the disease. An introduction of SBV into Scotland later in the summer limits spread on account of the end of the vector season and declining temperatures.

Role of seasonal timing of disease introduction

The most vulnerable time for pregnant ewes carrying spring lambs is December and January. Low levels of midge activity during this time contribute to the small numbers of cases seen in Scotland. Early lambing flocks, where pregnant ewes are present whilst vectors are still active, are most at risk. The lack of SBV being identified in either early lambing flocks or all-year-round calving dairy herds in 2016 suggests the SBV infected midge population likely entered Scotland in late autumn 2016 presumably following a northward progression.  The greatest at risk animals are cattle mated in summer 2016 located in the border counties. The risks of birth abnormalities in cattle following infection are considerably greater due to the greater proportion of the year that cattle are serviced and the greater at-risk window during pregnancy in cattle.

If there is a re-emergence of SBV in Europe, Scottish farmers should consider possible control options, specifically altering the timing of mating or vaccinating if mating is to be during an at-risk period. Vaccinating animals can both protect those vaccinated and other animals by reducing transmission. The option of vaccination is subject to vaccine availability. In conjunction with their vet, farmers should monitor the situation in Europe and their own animals for clinical signs.

Modelling potential for SBV spread in the marginal disease environment of Scotland

SBV spread in Scotland is potentially governed by a number of factors which EPIC’s disease spread models take into account.

  • Number of flies infected from a single infected animal per day. Expected number of vector bites per day
  • Location suitability for competent Culicoides species.
  • Number of Culicoides over time Temperature
  • Temperature dependant vector mortality rate.
  • Virus incubation period within vector
  • Time interval between bites
  • Probability of transmission between host and vector.
  • Number of susceptible livestock.
  • Probability of transmission from vector to host
  • Period between infection and viraemia within the animal
  • Period of infectiousness of an animal
  • Vaccination 
  • Cullicoides host feeding preference between cattle and sheep. 

Details see Bessell et al., 2013 & Bessell et al., 2014

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