CASE HISTORY
A dairy farm located in northern Ethiopia and with a herd size of 100 cattle (86 crossbreeds of Holstein-Frisian and Zebu breeds and 14 Zebu breeds) was screened for bTB by the SICCT test. As it was learned from its history, the farm was newly established just a year earlier through the purchase of cows and heifers from dairy farms and markets in Mekelle City and nearby towns, including Adigrat and Humera. The SICCT testing was conducted on the herd in 2016 by Mekonnen et al. 6 and a prevalence of 12% (95% CI: 7 to 19.8%) was recorded. One of the reactors was a three weeks old calf (ID 8A0597) and its skin induration was 8 mm according to the calculation of the SICCT test result. All positive reactors (including the calf) were removed from the herd following disclosure of the test results. It was observed from the husbandry of the farm that all calves in the farm were sharing the same housing with the adults. Moreover, the calves were fed on pooled milk obtained from milking cows in the herd including one SICCT reactor cow, and looked after by the same individuals who were looking after the adult cattle.
The dam of the calf (ID 8A0417) was a 10 years old cross of Holstein-Frisian and Zebu breeds. The body condition of this cow was rated as ‘Good’ and it was negative for bTB by the SICCT test according to the interpretation recommended by OIE.7 In addition, nasal discharge was collected from the dam using a cotton swab designed for such purpose, and the PBS wash of the swab was centrifuged at 4000 rpm for 15 min. Genomic DNA was extracted from the pellet using a Qiagen DNA extraction kit as per the manufacturer’s instruction,8 and the eluent tested by an RD4-based PCR assay for specific identification of M. bovis . The primers defined by Brosch et al. 9 were used in the PCR assay procedure described by Berg et al .10