That German Virus

At the time of writing the Schmallenberg virus has been identified on seventy eight sheep farms and five cattle farms. The latest cases were in the Isle of Wight, Wiltshire, Berkshire and Gloucester. The chances are that with all of the publicity over the week end further cases will be reported this week. None of the affected farms have imported animals from France or Germany so the assumption is that the virus has travelled with the midges across the channel last October.

Those Midges Again

DEFRA scientists are used to tracking metrological data and wind movements as they use this data to track the spread of viral diseases such as Foot and Mouth Disease and more recently Bluetongue. At certain times of the year there is an increase in the midge population and they can be carried high into the sky on air currents. In 2006 researchers at Oxford University demonstrated Culicoides midges are not always passengers blown on the wind. Working with the Bluetongue virus they demonstrated that 38% of infections in northern Europe were up wind of the infected farms. This shows that the midge can move against prevailing winds for significant distances so we have to accept that they can be efficient vectors of viral diseases.

Future Developments

It is still not clear whether this new virus can be spread between animals once it arrives in a flock. At the moment there is no serological test to detect it. It would appear that the affects of the virus are so mild that it can pass through the flock undetected unless the ewes happen to be in the early stages of pregnancy when it occurs the developing foetus will show limb and central nervous system abnormalities. Most viruses are present in the blood stream of host animal for a few days before they are rejected by the immune system. This is a new virus so none of the ruminants in this country will have any resistance to it. If all goes well the chances are that the virus will spread rapidly when the weather warms up in the spring and early summer. It may well be that by the time the ewes are pregnant again, in most parts of the country the ewes would have been exposed to the virus and their unborn lambs will be safe.

Publicity

It is not clear why the Schmallenberg Virus should suddenly be in the headlines. We can only hope that the people who read the stories will get the true facts about the disease and continue to buy meat. It may be to our advantage if Shropshire stays on the edge of this outbreak that buyers will be confident to buy replacement stock from here rather than getting animals from farms that have been directly affected by the disease.

Unexpected Diagnosis

On Saturday a two week old lamb was brought to the surgery that had been found on his side in a field. This animal had a ring on his tail and testicles, both of these wounds seemed to be clean, there was no sign of infection. I did not need to look at this lamb too closely to realise that he was suffering from tetanus. All four limbs were rigid, it was impossible to bend them and his mouth was clamped shut, it was not possible to move his jaw in any direction. The lamb was stranded as if his feet had been stuck to the consulting room table. It was not long before I realised there was more to this case than the tetanus. It was soon apparent that there were twenty to thirty sheep scab mites crawling across the surface of the black table.

Un noticed Visitors

There is no practical treatment for tetanus in young lambs. It is impossible to get them to feed. They will respond sometimes to high doses of crystalline penicillin and tetanus anti toxin, but the treatment is prolonged and expensive and most animal will relapse as soon as the injections are stopped. It was decided that the most humane thing to do was to put this lamb to sleep. Careful inspection revealed that there was no sign of rubbing or itching. The lamb came from a farm where they do have problems with sheep scab, they have come to the end if their firsts batch of lambing and have not treated any cases recently. It is known that lambs pick up scab mites from their mothers and do not normally show signs of the disease until the following winter. I was fascinated to see that the mites had decided to abandon their new host as if they realised he could not survive they would make a determined effort to find a better home. Later that day the ewe was caught and closely examined, there was no sign of irritation or wool loss. If this animal had been seen on the farm we would still have no idea that there is scab there.

Vaccination Survey

In the autumn of 2010 the University of Cardiff undertook a telephone survey of farmers from six different locations in England. The researchers asked 31 different questions to determine your attitudes to the vaccination of badgers. Veterinary Surgeons are often asked to take part in telephone surveys, usually by drug companies, and I am always sceptical as to their true worth. They always take longer to complete than you are first told and so much depends on the way the questions are phrased. It is quite likely that these questions were phrased with a bias towards a positive response as it was DEFRA who had asked for the survey.

Not Convincing

The published result were that just 40% thought badger vaccination was an acceptable way of dealing with Tuberculosis and 48% did not think it would prevent the spread of the disease. There were concerns about the practicalities of vaccinating badgers, less than a quarter thought the Government would be able to manage a vaccination programme competently and nearly all of the farmers asked did not see why it should be there responsibility to pay for the injections. It is reported that there were no significant differences in the answers of farmers from the different locations and that farm size and bTB history did not alter the opinions given.

Badger Vaccine

The Bacillus Calmett-Guéin vaccine is the human vaccine that is made by growing a weakened strain of bovine tuberculosis on a special medium 230 times over a period of 13 years so that it does not cause any pathology when it is given as a vaccine to people. It was first used in 1921 and has been found to be up to 80% effective against preventing the disease in man after a single dose for a period of up to fifteen years. I understand a larger dose is given to badgers and it is recommended that the dose is repeated each year for five years.

The Big Experiment

There are so many unknowns here. The vaccine has been modified to use in badgers, but it is unclear how they will react to it. Some badgers may already have the disease before the injections are given. It is very unlikely that an individual will be trapped each year for five years to complete the course of injections. Only time will tell.

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