The influence of cattle breed on susceptibility to bovine tuberculosis in Ethiopia

Abstract

Bovine tuberculosis in domestic livestock such as cattle is an economically important disease with zoonotic potential, particularly in countries with emerging economies. We discuss the findings of recent epidemiological and immunological studies conducted in Ethiopia on host susceptibility differences between native zebu and the exotic Holstein-Friesian cattle that are increasingly part of the Ethiopian National herd, due to the drive to increase milk yields. These findings support the hypothesis that native Zebu cattle are more resistant to bovine tuberculosis. We also summarise the results of experimental infections that support the epidemiological data, and of laboratory experiments that suggest a role for the innate immune response, and in particular interleukin-6, in the outcome of bovine tuberculosis infection.

Fig. 1

Typical smallholder herd in the study area (Selalle, North-Western Shoa region, Ethiopia). Shown are examples of Arsi zebus and Holstein-zebu crossbreeds. For example, the animal on the right is such a cross-bred animal. (Photo source: M. Vordermeier.)

Fig. 2

Breed differences in tuberculin skin test prevalence. Comparative tuberculin skin tests were applied to Arsi zebu, Holstein, and crossbreed animals, n = 1921, 925, 2578, respectively. Two interpretation criteria for the skin test were applied: reaction sizes of bovine tuberculin PPD minus avian PPD > 2 mm or > 4 mm. Data are expressed as Odds ratios. Data from Refs. .

Fig. 3

Pathology and IFN-gamma responses; a slaughterhouse study. (A) Mean pathology scores in skin test-positive cattle. Holstein, n = 50; Zebu, n = 73. Post-mortem analysis and scoring were performed as described in . Figure from . (B) IFN-γ responses to mycobacterial antigens in Holstein and zebu cattle after stimulation with avian and bovine PPD (used at 10 μg/ml), ESAT-6/CFP-10 proteins (each at 5 μg/ml) and PHA as positive control (5 μg/ml). IFN-γ as determined by BOVIGAM ELISA, data are expressed as mean ± standard error (from [27]).

Fig. 4

Results of experimental M. bovis infection. Groups of 6 Boran and 6 Holstein calves (around 6 months old) were infected intratracheally with a UK M. bovis isolate (AF2122/97 [43]). Post-mortem examinations were performed after 4 months and pathology was scored as described . Data are expressed as mean total pathology scores ± standard errors.

Fig. 5

Innate responses: Cytokine production in Holstein CD14 monocytes infected with virulent mycobacteria (M. bovis or M. tuberculosis, MOI =2) relative to responses of monocytes isolated from Sahiwal zebus (horizontal line = responses observed with zebu monocytes). Cytokine responses in culture supernatants were determined using a bovine cytokine/chemokine multiplex system . Data from .