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