Vaccinated cattle constitute an obstacle against utilization of ELISA for diagnosis of mycobacterium bovis in infected cattle in Egypt

الملخص EN

In this study 420 cattle from different localities at Minufiya and Gharbia governorates Egypt .Were tested by application of tuberculin test , 9 cattle (2.14 %) were positive tuberculin reactors while the remaining were negative.

From these negative reactor cattle 6 were vaccinated with Bacillus Calmette Guerin (BCG), and retesting of these vaccinated animals with tuberculin test has been done after 8 weeks and gave negative tuberculin reaction .Positive tuberculin tested animals were slaughtered and examined to determine the post mortem lesions which were 8 (88.9%) out of 9 cattle gave Visible lesions and 1(11.1 %) gave Non visible lesions.

The lymph nodes and tissue samples were collected from the positive tuberculin (9) cattle.

On the bacteriological examination of the tuberculin positive cattle tissues which were (8 with VL and 1 with NVL), 8 (88.9%) acid fast bacilli were isolated.

The total 8 tissues expressed visible lesions grew on Lowenstein-Jensen medium with sodium pyruvate and all the 8 isolates (100 %) gave positive with Ziehl neelsen (ZN) stain.

After application of PCR using IS6110 indicated that higher prevalence of Mycobacterium tuberculosis complex in all (9) cattle cases and that confirmed by the genotyping using MIRU technique that detected M.

bovis typical types.

ELISA was applied using 4 types of antigens (PPD, ESAT-6, CFP10, and MBP70) to discriminate between negative, infected and vaccinated animals .This test reflected that all positive tuberculin reactor animals gave positive results in infected and vaccinated cattle while the negative tuberculin reactor cattle gave negative results except with MBP70 only one cattle gave positive result1 / 6 (16.7 %).

The data collected in this study indicated that the ELISA test cannot discriminate between vaccinated and infected cattle.

And using of these antigens in ELISA test each one alone proved that it cannot discriminate between Mycobacterium tuberculosis complexes (MTUC) infected cattle.

So further investigations using other types of antigens are required.