Abstract
Caseous lymphadenitis (CLA), caused by Corynebacterium pseudotuberculosis, is a chronic contagious disease that affects small ruminants and still remains an important problem for many lamb-producing countries. Animals are considered clinically infected when occurs abscesses in superficial lymph nodes. Visceral or internal form can coexist which no apparent clinical signs of infection are seen. The best procedure to avoid spread of the disease is elimination of infected animals. However, as the chronic and subclinical nature of the infection of CLA alternative methods are required for detection and screening. In this study, we described the performance of indirect Enzyme-Linked Immunosorbent Assay (ELISA) for diagnosis of CLA in asymptomatics sheep. Also, test culture and biochemical identification were achieved to confirm CLA infection. The serological diagnostic was performed in sheep symptomatics (n=50) and asymptomatics (n=374) from nine flocks. Analysis reported high positivity of 71% for ELISA in 85% of asymptomatic animal for CLA with a sensitivity of 88% and specificity of 31%. Results from ELISA test in asymptomatic animals against culture for caseous lymphadenitis were more specific (97%) and permitted to exclude healthy animals without symptoms. This study concluded that C. pseudotuberculosis infection could be widely disseminated in sheep flocks in Northwestern region of the state of Sao Paulo, Brazil and only one screening test is not enough. The association with indirect ELISA test and culture could better indicate the real problem of CLA in sheep flocks.
Highlights
Caseous lymphadenitis (CLA), caused by Corynebacterium pseudotuberculosis, is a chronic contagious disease that affects the majority of sheep-rearing areas worldwide [1,2,3,4]
This study evaluated the diagnostic performance of indirect Enzyme-linked Immunosorbent Assay (ELISA) method to detect CLA infection by secreted antigens in sheep sera from nine flocks, which were realized in association with clinical inspection
A 2×2 table was used to evaluate the association between clinical inspection and indirect ELISA test results (Table 2), from a total of 424 sheep clinically examined, where 50 were symptomatic and 374 asymptomatic (Table 1)
Summary
Caseous lymphadenitis (CLA), caused by Corynebacterium pseudotuberculosis, is a chronic contagious disease that affects the majority of sheep-rearing areas worldwide [1,2,3,4]. The identification of infected animals, with or without clinical symptoms, is the best procedure to avoid spread and to control this disease. The classical or gold standard diagnosis of CLA is represented by the culture test and the identification of C. pseudotuberculosis from abscesses. This classical diagnosis may not always be advantageous or possible since chronic external lesions with little pus containing few viable organisms or visceral lesions cannot be sampled [1]. In such case, various diagnostic techniques have been developed. Enzyme-linked Immunosorbent Assay (ELISA) has already proven to be a versatile method to aid in CLA-control from herds and to identify sheep with visceral form without appealing to bacteriology resources [7,8,9,10,11]
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