Listeria

Apparently we are expecting a hot summer although it has taken some time to arrive. Assuming that the settled weather will stay with us for a while this newsletter will deal with warm weather problems. I have already seen a ewe with listeria. This is a bacterium that lives in the soil and is particularly active when it is hot and in the winter when it has been able to contaminate baled silage. When ingested the infection will cause a mild increase in temperature as it gets established in the blood stream. This might be all that will happen and the natural defence mechanisms of the body will eliminate the bacteria and nothing further will occur. If the sheep or calf has ingested a significant amount of the infection more serious symptoms can occur. This is one of the few organisms that can penetrate through into the brain and cause meningitis. The brain is not able to cope well with infection. It is a soft structure with a copious blood supply that is enclosed within a rigid box. Any inflammation of the brain is serious as it will readily become compressed and will not be able to function properly.

Clinical Signs

Sheep and cattle with meningitis are usually found alone in a corner of a field. They will turn away from light with their head down close to the ground. Sometimes they are unable to see and will walk until they reach the corner of a field and then go no further. This is because the part of the brain that controls the eyes is at the front and it gets pushed forwards against the skull when pressure builds up in the head. Because listeria like Erysepelothrix rhusiopathiae and Fusobaceriun necrophorum that is the cause of foul in the foot, is a soil organism it if readily susceptible to antibiotics and there will not be any worries about these infections becoming resistant to the treatments. The problem with treating meningitis is that the brain has its own protective mechanisms that prevent drugs with a larger molecular structure passing the blood brain barrier. Fortunately this is broken to some extent when the membranes around the brain are inflamed so large doses of drugs given into the vein are able to get through. We tend to use oxytetracycline to treat meningitis because it is safe at high doses and can usually be relied on to clear the infection. Sometimes it is not easy to move animals with Listeria from a field if they are completely blind. They will do better if you can move them into a shed out of the sunlight, we often find that they are more settled if you can house them with a companion until they adapt to there reduced vision. Most animals with listeria will need high doses of antibiotics for five to seven days.  Some individuals may end up with permanent damage to their brain although most will adapt and be able to live with their disability. It is important to treat this disease at the first suspicion of infection if you want to get a successful outcome.

New Forest Disease

Eye infections used to be a seasonal problem that mirrored the fly season, a few calves would get involved in June with more and more cases and some in older cattle as the summer progressed. The sort of eye infections that flies carry are serious because Moraxella bovis will grow on the surface of the eye and dissolve the keratin of the cornea to cause an ulcer. This is followed by a severe inflammatory reaction the eye is red and produces a watery discharge that attracts more flies that will pass the infection on to others in the group. Usually only one eye is affected so the calf will retain some vision. Again this is a bacterial infection that will respond well to antibiotics in the initial stages. It is better to use a product that binds onto the surface of the eye for at least twenty four hours as all of the newer ointments do as they are not flushed out by the tears. Eye ulcers are always slow to heal and it might take two or three months for the scarring to fade away. Occasionally if no treatment is given infection will penetrate through into the anterior chamber of the eye and this is difficult to treat. Cattle seem to get some immunity from New Forest Disease as they only seem to get a severe bout of the infection once and are less likely to need treatment for this condition when they are adults.

Cattle with Sunburn

Photosensitization is a strange condition that is only apparent in the summer months. It is seen mainly in dairy cattle on permanent pastures. Some plants, notably St Johns Wort, contain toxins that can temporarily trigger changes in the liver that leaves the white areas of the skin sensitive to sunlight. The reaction will be quite mild if the sky is cloudy, but can be dramatic if there is a prolonged period of sunny weather. The first signs seem like severe sunburn on all of the white areas of skin that does not fade overnight. Mild case may respond to housing during the day and keeping affected animals away from pastures that are rich in herbs at night. In severe cases anti inflammatory drugs and antibiotics may be required to keep the cow comfortable. Cows that have been affected by this condition may show signs in following sunny summers.  

Pigs with Temperatures

Erysipelas is again a soil organism that can cause clinical disease at any time of the year. We get a peak of cases now as it is particularly active in the summer. Pigs of all ages can be affected by this infection. They will develop an infection in their blood stream to get very high temperatures. Some pigs with white skin will show signs of purple coloured diamonds developing in the skin as the disease progresses. Pregnant sows will abort their piglets as a reaction to the high temperature. Of more concern is that as the infection circulates in the blood stream it will cause progressing lesions on the heart valves. There is usually a good initial response to antibiotics, but the heart problem is more difficult to cope with and many animals will loose condition as a result of the damage that has been done to their circulation. There is a vaccine to prevent this infection, after the initial course booster injections should be repeated every six months to maintain the antibody levels.

Bluetongue

As far as I can determine there were two suspected new outbreaks of Bluetongue reported from Israel on the 29^th May but as yet no new cases are under investigation anywhere in Europe.

Drug Supply Problems

Pfizer have take over the marketing of Tetra Delta and Ubro Yellow, but already they have run into trouble with sourcing one of the components of these mastitis tubes so they will not be available for the time being. We have been fortunate in securing extra stock of Ubro Yellow but the supplies of Tetra Delta have already run out and we do not have many more in stock. Mulitject IMM is a close copy of Tetra Delta so it will be the best alternative but take care as it has a longer milk withhold time of 108 hours.

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