About the diseases
Maedi Visna/Caprine Arthritis Encephalitis
Maedi Visna (MV) is a viral infection with a long incubation period that spreads slowly within a flock. This means that, by the time a problem is suspected, a large number of sheep in the flock will give positive results when blood tested for antibodies to MV. The name derives from two Icelandic words which describe the main clinical signs of pneumonia and wasting.
Caprine Arthritis Encephalitis (CAE) lentivirus is closely related to the MV and treated as the same disease for the purposes of the scheme.The disease primarily affects the joints and the brain, although the udder and lungs can also become infected. In a survey in Britain, nearly 5 goats in every 1000 sampled tested positive for CAE. These conditions are highly infectious, difficult to diagnose on clinical signs alone, and there is no cure.
Disease is spread by close contact between sheep/goats, and via colostrum and milk. It can be transferred between animals on hands or on equipment such as dosing guns. It survives for less than a week in the environment.
Ill thrift and/or an increased incidence of pneumonia or mastitis in adult animals can be the first signs of a problem. Low yields of colostrum and milk can result in increased young lamb/kid losses and poor growth rates. The flock/herd may experience issues with arthritis, premature birth rates, reduced conception rates and a higher proportion of culling. The virus can affect the nervous system and affected ewes may drag one hind leg and become increasingly uncoordinated.
Breeding replacements should ideally be sourced from MV/CAE accredited flocks. Otherwise screening added animals for antibodies to MV/CAE is recommended. It can take up to 6 months for antibodies to be produced following infection. In order to establish whether or not MV/CAE is present in a flock testing can be targeted to thin animals. Offspring born to MV/CAE positive animals should not be kept as breeding replacements.
Mycobacterium avium paratuberculosis is the bacteria responsible for Johne’s disease in both cattle, sheep and goats. Johne’s bacteria can be spread by wildlife e.g. deer and rabbits. The bacteria can survive for many months on pasture.
Multiplication of this bacteria within the wall of the intestine causes damage that leads to protein loss and ill thrift. Affected sheep/goats remain bright with a good appetite but will progressively lose condition until they die or are culled. Diarrhoea can occur but is much less common in sheep and goats than cattle. Bottle jaw (swelling under the jaw) may be seen in the later stages.
The disease has a long incubation period extending from months to years. Young lambs and kids are most at risk of infection but symptoms may only develop several years later. Infected, but apparently healthy, animals will periodically shed the Johne’s disease bacteria in their faeces. This contaminates the environment where the bacteria can survive for up to 12 months if the conditions are right. Depending on the strain type, sheep can infect cattle and vice versa.
Screening healthy sheep to confirm infection with Johne’s disease can be challenging. There is no perfect test for this disease, however it is still worthwhile screening animals. The long incubation period means that repeated annual screening of a flock is required to prove freedom from Johne’s disease. Investigation of ill thriven animals is also important.
A vaccine is available which will reduce the effects of, but not eliminate, Johne’s disease from a flock. Vaccinated sheep will however test positive in the blood test. Where lambs born to Johne’s positive ewes can be identified they should not be kept as breeding replacements. In order to establish whether or not Johne’s disease is present in a flock testing can be targeted to thin ewes.
A solution for farmers with EAE in their flock is to use a vaccination programme and buy in only EAE Accredited replacements.Buying EAE accredited stock and vaccinating them makes financial sense as it has been estimated that each abortion will cost from around £95 per ewe.
Enzootic Abortion Of Ewes (EAE)
Enzootic Abortion of Ewes (EAE) ranks as one of the most common causes of abortion in sheep in the UK. It is primarily a disease of low ground flocks and disease can spread rapidly in intensively managed systems. Once established, the infection is persistent and difficult to erradicate. EAE is also a human health hazard which can pose a serious threat to pregnant women.
EAE can cause abortion storms and lamb loss leading to huge economic loss. The Financial loss to the industry is estimated to be £15 million per year. A 5% abortion rate can reduce potential gross margin by 10%. Each ewe that aborts can represent a reduction in gross margin of £95.
Unfortunately it is a difficult disease to control for the following reasons:
- Infected ewes show no signs of ill health so you could be buying in disease without realising. Animals that have been infected in one lambing season can abort on your farm in the following spring. It won’t be until lambing time when it’s too late that your ewes will either abort 2 or 3 weeks before lambing is due to start or give birth to weak non-viable lambs.
- Once EAE infection is established within a flock it is persistent and difficult to eradicate. Following an abortion, ewes will lamb normally in subsequent years. However, these ewes are disease carriers and may infect their own lambs and any other sheep that they are in contact with.