What can you expect to see and what can you do if Schmallenberg virus hits?
There have been two cases of Schmallenberg virus confirmed in Ireland with an increase now also occurring in the number of suspect cases being reported at farm level. The suspect cases are stemming from calves and lambs born with the characteristic symptoms of the disease (congenital deformities) and also from abortions in late pregnancy raising alarm bells.
These deformities or malformations in progeny can be exhibited in many ways, including animals born with fixed joints (will not bend as normal) or bent limbs, stiff necks, marked damage to the spinal cord (including curved spines) and animals born with a shorter lower jaw.
These offspring are generally stillbirth or die shortly after death, with early births or abortions also prevalent. The virus differs to other abortion-causing illnesses that can result in the birth of mummified or decomposing foetuses. Reports from 2012 also show that it is common for twin-bearing ewes to give birth to one healthy and one infected lamb. Animals can also be born and appear relatively free of physical malformations but can suffer from brain deformities or complications with the workings of their nervous system.
The prevalence within flocks ranged from 15% to 20% on average as the disease spread across the EU continent from 2011 to 2013 but some flocks/herds experienced higher losses. Experience from other countries shows that lambs are often at a greater risk.
What can be done?
There is no treatment for the virus and infected animals develop a natural immunity, although it is not yet known if this persists over their lifetime. The only real advice in dealing with a higher Schmallenberg risk is to implement higher supervision at lambing to ensure the risk of harm to the dam is lowered. This is as deformed foetuses can regularly give rise to difficult births with the natural birthing process affected in particular by fused, rigid or bent limbs restricting movement through the birth canal. For this reason it is important to proceed with caution and seek veterinary assistance in adequate time if you foresee a problem.
Vaccines were developed and released following the outbreak of the disease in 2013, including Bovilis SBV which is manufactured by MSD Animal Health and Zulvac SBV manufactured by Zoetis. These are unavailable in Ireland due primarily to low usage but even if they were available they would serve no use as they need to be administered approximately three weeks before the breeding season. This is required to provide cover during the main risk period.
Spread of the disease
The virus is spread from animal to animal by biting midges. Cattle, sheep and goats are all susceptible to the disease. The high-risk period for spreading the disease is during the vector season (midges active) which is normally April to November in Ireland. The most susceptible time for infected animals to pass the virus through to a foetus is during month three and four (also possibly month five) in cattle and during month two and into month three of gestation in sheep. This means that early lambing flocks and early spring calving herds are likely to be most at risk as was the case in 2012/2013 when the virus was largely most prevalent in pockets in counties in the southeast. The risk will also be influenced by midge activity in the area which is also largely influenced by climatic conditions.
The virus is not believed to cause sheep or goats to exhibit any clinical signs of the disease but adult cattle can exhibit clinical signs whereby it can cause reduced milk yield, fever, loss of body condition, loss of appetite and diarrhoea in bovines. Once bitten and infected, animals develop an immunity to the virus (cannot be infected in later life) after a relatively short period of time. It is reported that infected animals also carry the disease for around four days. During this period the infection can be picked up by healthy biting midges that come in contact and bite an infected animal.