A batch of lambs with Maedi-Visna and Morel’s disease (abscess disease)
We received an inquiry regarding a batch of 230, 2-3 months old, lambs in which 100 of them presented lesions in one or more of the following organs: lymph nodes, lungs, kidneys, liver, peritoneal serosa... Cutaneous abscesses in the head region were also reported.
We received representative samples of the affected organs. The lymph nodes presented abscesses of up to 7-8 cm in diameter, with a highly fluidified, yellowish-greenish content. The cutaneous abscesses presented a very similar appearance. The histopathological study of these lesions revealed suppurative to pyogranulomatous lymphadenitis and panniculitis, in which cocci were observed arranged in tetrads and clusters. The microbiological study of all these lesions yielded pure cultures of abundant colonies of Staphylococcus coagulase +. These findings are compatible with Morel’s disease. This disease presents with abscesses ranging from 4 to 10 cm, generally close or within lymph nodes, affecting generally the head and neck region.
The lung revealed a multifocal generalized nodular pattern, with nodular and irregular areas of 0,3 cm showing greyish coloration, homogeneously distributed within the submitted lung fragment. Microscopically these nodules corresponded with foci of chronic interstitial pneumonia linked to lymphoid and pneumocyte type 2 hyperplasia. The kidneys revealed irregular multifocal to coalescing pale areas, mainly within the renal cortex. Histologically it corresponded to a chronic interstitial nephritis and diffuse membranoproliferative glomerulonephritis. These two findings are potentially compatible with an infection by the virus of Maedi-Visna, therefore we submitted these samples for a PCR against such virus to NEIKER laboratory, which resulted positive in both tissues. Although Maedi-Visna is complex and variable, it is characterized by interstitial pneumonia (generally diffuse but occasionally a multifocal-generalized pattern like the one in the present case), the already commented renal lesions and non-suppurative encephalitis, which wasn’t confirmed in our case.
Aside from that, the lesions reported in the liver and peritoneal serosa corresponded to cysticercosis and chronic colangiohepatitis of parasitic origin (trematodes). The presence of all these processes could be explained by a poor sanitary management of the farm, although the infection by the virus of Maedi-Visna, as it’s a chronic and consumptive process, could facilitate or aggravate the development of other pathologies (as in Morel’s disease). (AC)