Comarison of direct microscopic examination, Enzyme Linked Immunosorbent Assay (ELISA), culture and Nested-PCR for diagnosis of herds bulk tank milk infection with Mycobacterium avium subspecies paratuberculosis

Abstract

Causative agent of Johne’s diseases is Mycobacterium avium subspecies paratuberculosis (MAP) and each year, it hurts dairy cattle industry worldwide by depression of production and reproductive indexes and culling of affected animals. This bacteria is known as a zoonotic pathogen and recent researches explain its probable role in Crohn’s disease in humans. This study compared four laboratory diagnostic tests; including Enzyme Linked ImmunoSorbent Assay (ELISA), direct microscopic examination, milk culture and Nested-PCR for diagnosis of herds bulk tank milk infection with MAP bacteria. 100 bulk tank milk samples were obtained from 100 industrial dairy herds of Tehran province. Samples were screened by four tests and 82 samples (82%) detected as positive in culture media, 94 milk samples (94%) were positive by Nested-PCR test and 98 samples were positive in ELISA test results (98%). But direct microscopic examination identified just 33 milk samples as positive. Four positive samples of ELISA test were detected as negative samples by Nested-PCR. These 4 samples in addition to 12 other samples which diagnosed as positive by ELISA, had no growth in culture media (16 samples). These results indicated superiority of Nested-PCR among these four tests for diagnosis of bulk tank milk infection with MAP bacteria. Furthermore, the results represent high prevalence of MAP bacteria in bulk tank milk of dairy herds in Tehran province and it needs more serious eradication efforts.

Keywords

• Johne’s diseases
• Mycobacterium avium
• Subspecies paratuberculosis
• Cattle
• Nested-PCR
• ELISA
• Milk calture
• Direct microscopic examination