From page 39
disease . ❑ Usually , infection occurs when the animals are very young . ❑ Infection lies latent and may flare up to cause obvious disease later in life . ❑ In cattle and sheep the signs of disease usually develop when the animals are middle-aged and the disease progresses over a period of months or years . ❑ In goats the signs can
Sheep infected with Ovine Johne ’ s Disease
appear from about eight months of age and they can develop quickly , causing death within weeks . The cause of OJD is a bacterium , Mycobacterium paratuberculosis . The disease spreads when bacteria are shed in the faeces of infected animals , whether they have diarrhoea or not . The disease can spread from mother to young in the womb , and via her milk or as a result of faecal
contamination of her udder when the baby suckles . An important feature of the disease is that animals are most susceptible to infection when they are young . It is likely that most infections occur in the first few weeks or months of life . The sheep disease of the greatest concern in South Africa at present is ovine Johne ' s disease ( OJD ), which can come into a flock by purchasing just one " normal " sheep . According to the Ruminant Veterinary Association of South Africa ( RuVASA ) it is important to avoid the disease on your property if you keep sheep , for the following reasons : ❑ It can be introduced to a flock by buying just one apparently healthy sheep ; ❑ Once in a flock OJD is virtually impossible to eradicate ;
LIVESTOCK
❑ Being positive means eternal quarantine ; ❑ Control rests on neverending vaccination ; ❑ Vaccination is very effective in lowering the impact of OJD but does not eliminate it ; ❑ Left unmanaged , it can cause annual deaths of 10 % or more of the breeding ewes . Johne ' s disease should not be
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Emaciated cattle
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