Following the recent launch of the new Schmallenberg vaccine (Bovilis SBV by MSD) here is some further information regarding the disease and the reasons and logistics in vaccination:
- SBV is much more widely and rapidly spread than BTV (partly due to fact midges carry 10x the viral load of SBV than BTV).
- SBV is in the Simbu serogroup of viruses, these replicate in the nerve cells of the foetus and cause massive damage, classically arthrogryposis hydrancephaly syndrome (rigid joints and swollen, fluid filled head).
- Malformed calves have occurred in every month of the year so far, which means that there is no real vector free period, although the summer months are considered to be the main time of transmission.
- It has been found in bull and ram semen, but as yet it is unknown whether this can cause infection in the dam or foetus.
- Adult cattle are viraemic for 7 to 10 days, they get pyrexia (temperatures of up to 106F), scour, decreased milk yield (can be severe and never fully recovers in that lactation) and an increase in late embryonic death.
- Up to 20% of cows can be affected over days/weeks in any 1 herd, conception rates drop by around 50% in the acute period, but do seem to recover.
- The neonate/foetus gets the AHS syndrome because the damaged nerves do not flex/contact the muscles in utero as normal, so they don't develop and the limbs become rigid and distorted.
- The danger period for this is from 80 to 180 days gestation for cows and from 28 to 60 days in sheep. If infection occurs before this, then you tend to get early embryonic death and repeat breeders.
- "Dummy calves" can be born alive, these often can't walk properly and have obvious neural deficits. They will not do well and euthanasia is recommended.
- MSD have done some research into sero-prevalence on herds that had been shown to be SBV positive. The % of individuals affected on these farms ranged from 0 to 75% with an overall average of 35%. Thus leaving 65% of the herd still susceptible to the disease.
- While immunity resulting from exposure to this group of viruses is thought to be strong and long-lived in those in the herd/flock that have actually been exposed. The level of immunity attained after vaccination is higher than that of natural exposure.
- The vaccine is a dead vaccine and its current licence is for prevention of viraemia in cattle and reduction of viraemia in sheep.
- Cows get 2 doses (Intramuscular). Sheep get dose 1 (Subcutaneously), this is because the single dose vaccination is body weight dependent and cows are too big for it to work.
- The vaccine is not currently licensed for pregnant animals, though this may change as further research and licencing proceeds. The vaccine can be given form 2 months of age in cattle and 4 months in sheep.
Uptake of the vaccine has been high in parts of the country where the impact of the disease was significant last year. While obvious clinical and economic effects were seen in our practice, these were at a relatively low level compared to what we were concerned might happen.
What the research shows however, is that the potential for these problems is very much still there in terms of susceptible animals and presence of the disease. On this basis our advice has to be that if you have valuable stock and want to avoid the risks that SBV poses, then only vaccination can provide this. The obvious animals to target are cattle young stock from 2 months old up to pre-bulling stage and all breeding sheep and rams (>4 months old) before tupping.
To protect adult cattle, detailed vaccination protocols need to be worked out with your vet on a farm by farm basis to take into account the fact that the vaccine cannot currently be used in pregnant animals.
Please do call us if you have any questions about this disease or vaccine. For further information and vaccine protocols click here.