A dose of 10(10) Mycobacterium avium subspecies paratuberculosis was administered orally on seven occasions to produce experimental paratuberculosis infection in 10 5-8-week-old goat kids. Bacteriological, immunological, and histopathological changes, their relationships, and the efficacy of the commonly used diagnostic methods were studied during the progressive disease up to 270 days postinfection (DPI). Significant lymphocyte proliferative responses in the peripheral blood of five goats were detected as early as 60 DPI. A lymphoproliferative test was also performed on lymphocytes purified from different compartments of the guts of five infected and five control goats. Significant proliferative responses were observed in lymphocytes of jejunal compartments of all five goats, of which four had also significant lymphocyte proliferation in the blood. The ileal lymphocytes from two goats, one each at 120 and 270 DPI, had significant proliferation. The histological lesions were mainly observed in the gut-associated lymphoid tissues of the ileocecal valve, the ileum, and the terminal jejunum. Acid-fast bacilli were demonstrated in the lesions of two goats at 60 and 210 DPI. Bacterial culture showed poor sensitivity, detecting positive results for only one goat in the fecal and tissue samples at 210 DPI, whereas polymerase chain reaction (PCR) detected one goat in fecal sample at 210 DPI and two goats in tissue samples at 60 and 210 DPIs, respectively. Enzyme-linked immunosorbent assay and agar gel immunodiffusion test were found to be 100% sensitive from 180 and 210 DPI onwards, respectively.
The diagnosis of subclinical paratuberculosis is still considered a major problem worldwide. As part of investigating diagnostic strategies for the paratuberculosis infection, sequential results of various diagnostic methods in a progressive experimental infection in goats were evaluated. Twenty-three goat kids were divided into three groups: the infected, contact and control, comprising 10, five and eight goats respectively. Animals of the infected group were orally inoculated on seven occasions with 5 ml of inoculum containing 2 x 10(9)Mycobacterium avium ssp. paratuberculosis per ml. Lymphoycte proliferation test using johnin PPD detected paratuberculosis infection from 60 days post-infection (DPI) onwards. The johnin PPD was found to be a better antigen for the proliferative assays as compared with the sonicated antigen. The faecal smear examination with acid-fast staining detected more goats as positive than bacterial culture and polymerase chain reaction (PCR). Lipoarabinomannan enzyme-linked immunosorbent assay (ELISA) started detecting infected goats from 150 DPI onwards followed by indirect ELISA and agar gel immunodiffusion from 180 DPI onwards. Histological examination was confirmatory and detected five infected goats as positive.
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