Evaluation of the McLintock syringe as a cause of non-specific reactions in the intradermal tuberculin test used for the diagnosis of bovine tuberculosis

The objective of this study was to elucidate whether the use of the McLintock syringe, used to inject tuberculin in cattle in several countries and based on an intradermal inoculation by needle, may, in itself, cause skin reactions that can be interpreted as positive reactions regardless of the real tuberculosis (TB) infection status of the animals. Forty-four cattle from an officially TB-free (OTF) herd were selected for the experiment. Each animal received four inoculations [one with sterile phosphate buffer saline (PBS) with 10% of glycerol and three with bovine purified protein derivative (PPD), as performed during the single intradermal tuberculin (SIT) test], two on each side of the neck (n = 176 inoculations). Three different McLintock syringes (n = 132 inoculations, PBS and bovine PPD) and one Dermojet syringe (n = 44 inoculations, PBS) were used to carry out the inoculations. No positive reactions (increase in skin-fold thickness > 3 mm) in response to the bovine PPD or PBS inoculations were observed regardless of the syringe used. No significant differences (p > 0.05) in the skin fold thickness increase (in mm) were observed between inoculation sites. Significant differences (p < 0.05) in the skin fold thickness were observed when PPD was injected in comparison to the PBS but no differences between McLintock and Dermojet were detected when PBS was injected. The McLintock syringe did not cause reactions per se that could be misunderstood as positive in TB-free cattle demonstrating that it is not a significant factor associated with the previously reported imperfect specificity of the SIT test.