Dynamics and risk of transmission of bovine tuberculosis in the emerging dairy regions of Ethiopia

The Ethiopian government has several initiatives to expand and intensify the dairy industry; however, the risk of bovine tuberculosis (bTB) spread is a challenge. To assess the rate of expansion and risk factors for transmission of bTB within-herds, we carried out a repeated cross-sectional survey at two time points, 2016/17 and 2018, in three regional cities, namely, Gondar, Hawassa and Mekelle, representing the emerging dairy belts of Ethiopia. The total number of herds involved was 128, comprising an average of 2303 cattle in each round. The Single Intradermal Comparative Cervical Tuberculin (SICCT) test was used to identify reactor status and data on herd-level risk factors were collected using a structured questionnaire. In the first survey, the apparent prevalence of bTB, as measured by the SICCT test, was 4.5% (95% CI 3.7–5.4%) at the individual animal-level and 24% (95% CI 17.5–32%) at the herd-level. There was no statistically significant change in the overall apparent prevalence or regional distribution at the second survey, consistent with the infection being endemic. The incidence rate was estimated at 3.6 (95% CI 2.8–4.5) and 6.6 (95% CI 3.0–12.6) cases/100 cattle (or herd)-years at the animal- and herd-levels, respectively. Risk factors significantly associated with the within-herd transmission of bTB were age group and within-herd apparent prevalence at the start of the observation period. We noted that farmers voluntarily took steps to remove reactor cattle from their herds as a consequence of the information shared after the first survey. Removal of reactors between surveys was associated with a reduced risk of transmission within these herds. However, with no regulatory barriers to the sale of reactor animals, such actions could potentially lead to further spread between herds. We therefore advocate the importance of setting up regulations and then establishing a systematic bTB surveillance programme to monitor the impact prior to implementing any control measures in Ethiopia.

A retrospective sero-epidemiological survey of bovine brucellosis on commercial and communal farming systems in Namibia from 2004 to 2018

Cattle production is the major livestock production activity and the mainstay of Namibia's economy. Sustained beef exports are contingent on a sound sanitary environment where diseases such as brucellosis are under control. In this retrospective study, 49,718 bovine brucellosis testing results from 2004 to 2018 were analyzed to determine the proportion of sero-positive cattle and herds, and the spatial distribution of positive reactors from commercial and communal areas. In total, 244 positive reactors were identified based on the Rose Bengal Test (RBT) and the Complement Fixation Test (CFT) in series, giving an overall proportion of infected animals of 0.49% (244/49,718; 95% CI, 0.43-0.56%) and an overall proportion of infected herds of 9.26% (78/842; 95% CI, 7.49-11.41%). There was a higher proportion of sero-positive communal herds (33.09%) and cattle (10.27%) than commercial herds (4.67%) and cattle (0.24%; p < 0.05). Annually, the proportion of positive reactors was 0-1.37% in the commercial area and 0-52.38% in the communal areas, with a clear decline in positive reactors in the communal areas. Within the commercial sector, the proportion of positive reactor dairy, beef, and export cattle was 0.19% (51/27,067; 95% CI, 0.14-0.25%), 0.30% (48/16,098; 95% CI, 0.22-0.40%), and 0.33% (16/4811; 95% CI, 0.20-0.54%), respectively. Abortions were found to be the major reason for Brucella testing in the communal areas. About 12.65% (96/759) of abortion-linked sera tested positive in the communal areas, but none were positive in beef or dairy cattle. Widespread vaccination of cattle and robust planned surveillance is recommended to reduce the incidence of the disease, its associated production losses and public health risk.

Bayesian estimation of seroprevalence of small ruminant lentiviruses in sheep from Poland

In Poland, no systematic survey of ruminant lentiviruses (SRLVs) infection was performed, neither at the national nor at the regional level and only limited knowledge exists on the prevalence of SRLVs among sheep. The aim of the present study was to establish the true prevalence of SRLVs infection in sheep from Poland at the animal and herd-levels. The blood samples used for this study were the fraction of samples collected by Veterinary Inspection during an official sampling for the national monitoring program for brucellosis. Under this program the animals and herds were randomly selected using the data available from ARMA (Agency for Restructuring and Modernisation of Agriculture). The sampling unit was the herd and the target population included at least 5% of sheep, over 6 months old, from each of 16 voievodships (provinces) of Poland. Two-stage cluster sampling design was performed in this study offering the possibility to determine the prevalence of SRLVs infection, when only a fraction of herds and a fraction of animals in the herds are tested. In total, 8233 sheep serum samples coming from 832 herds were tested by indirect ELISA. 1474 (17.9%) samples were positive and 261 (31.4%) herds with at least one seropositive animals were identified. The overall true prevalence estimated by the Bayesian framework was 9.3% (95% CI 6.8, 11.3) and 33.3% (95% CI 26.5, 38.2) on the animal and herd level, respectively. Large variation in the animal and herd prevalence between the voivodships was observed. True prevalence on the herd level varied from 0.0% (95% CI 0.0, 0.0) to 71.6% (95% CI 67.6, 75.9) whereas true prevalence on the animal level ranged from 0.0% (95% CI 0.0, 0.0) to 55.3% (95% CI 50.0, 61.2). The true prevalence of SRLVs infection at animal and herd level increased according to herd size as was proved by posterior probabilities (POPR).