The Disease

Caseous lymphadenitis is a bacterial disease, which was recorded for the first time in the United Kingdom in 1990 and is now spreading steadily (Baird, 1997a; Gilmour, 1990; Rizvi et al., 1997; Smith et al., 1997; Winter, 1997). It was believed to have been absent from the United Kingdom until the late 1980s, when it was introduced into this country in a herd of goats imported from Germany. The first positive diagnosis came in 1991.

The disease is caused by the bacterium Corynebacterium pseudotuberculosis (Renshaw et al., 1979). The bacteria produce an exotoxin called phospholypase D, a glycoprotein which dissociates the sphingomyelin of cell membranes. The disease has a long incubation period of up to 4 months. The bacteria can survive for prolonged periods in soil (8 months), straw and hay (2 months) and dip (24 hours) (Baird, 1997b; Brown and Olander, 1987).

There are two forms of the disease, superficial and visceral. In the superficial form there is enlargement of the animal's lymph nodes due to abscessation, which are visible as swellings. In recent outbreaks the lumps have been around the head and neck but they may also appear on the shoulder, groin or legs where the superficial lymph nodes are located. The visceral form of the disease is endemic, insidious and sometimes subclinical. It is commonly, however, manifested by wasting and in some cases, death (Gilmour, 1991; Lloyd, 1994).

Once established within the flock the disease will spread over a number of years and cause significant financial losses that arise from condemnation of affected carcasses and skins. At present there is no reliable blood test for the disease and it can only be detected by visual or physical examination. Diagnosis is confirmed by the culture of the causative organism from swabs or pus taken from abscesses (Baird, 1997b).