the underside of the abdomenal and pectoral regions. C. pseudotuberculosis can also cause infection of the distal limbs, a manifestation known as ulcerative lymphangitis. It is usually a unilateral lesion and the affected limb is painful, swollen, and contains draining ulcerative and nodular lesions. Diagnosis Diagnosis of C. pseudotuberculosis can be difficult due to vague clinical signs such as weight loss and general ill thrift. To confirm infection in animals with the external form, a bacteriological culture of the purulent material from an intact abscess should be taken. Biopsies may also be useful. If C. pseudotuberculosis is isolated, then this provides definitive diagnosis. Confirming diagnosis in animals infected with the internal form of the disease is more difficult, but ultrasonography or radiography may be useful. PCR has shown promising results for diagnosis, and a double-antibody sandwich ELISA can be used in sheep and goats. Pathogenicity and virulence C. pseudotuberculosis has two well documented virulence factors, phospholipase D (an endotoxin), and a mycolic acid surface lipid. Both virulence factors are proposed to be independent of plasmids, as no plasmid has been found in C. pseudotuberculosis. Phospholipase D Every isolate of C. pseudotuberculosis in research so far has had the phospholipase D virulence factor. Studies that examine the absence or mutation of the phospholipase D gene in C. pseudotuberculosis-infected mice have been shown to fail to develop chronic abscessation. This phospholipase encoding gene has been isolated to pathogenicity island 1. At least seven pathogenicity islands have been recorded in C. pseudotuberculosis. Phospholipase D is an ester bond-cleaving exotoxin that provides the bacterium with the ability to cleave sphingomyelin, which is a glycerophospholipid eukaryotic cell-wall component, so by destruction or cleavage of this component, the cell wall becomes damaged. This can cause death or loss of function of eukaryotic cells. This effect may help the invasion of C. pseudotuberculosis. Phospholipase D also increases vascular permeability, possibly due to sphingomyelinase effects. The increase in permeability may allow increased lymphatic drainage, leading to one of the mechanisms of migration to the lymph nodes, where C. pseudotuberculosis causes chronic abscessation. Mycolic acid Another mechanism of lymphatic transport is facilitated by the presence of a mycolic acid surface lipid. This coats the C. pseudotuberculosis organisms. Mycolic acid provides a protective barrier, allowing the bacterial cell to resist lysosomal degradation by eukaryotic, phagocytic, white blood cells. This allows the bacteria to act as facultative intracellular parasites once they