Resumen de Epidemiology of bovine tuberculosis: evaluation of surveillance and sociological factors in spain
The present PhD thesis aimed to increase knowledge on bTB epidemiology and control and to investigate sociological factors that might hinder the success of the bTB eradication programme.
In the first study, we developed a stochastic dynamic model that allowed estimating the cattle-to-cattle bTB transmission parameters within Spanish herds, using field data from the eradication campaign. Then, we used those parameters to simulate the average number of secondary cases caused by a single infected animal introduced into a herd (Rh), considering different control frequencies. The median transmission coefficient (β) was 5.2 newly infected animals per infectious animal per year; however, results evidenced a great variability in the estimates among the 22 study-herds, with median estimates ranging between 1.8 and 8.3. The overall median duration of the latent period (α) was 3.2 months, with an interquartile range varying from 2.4 to 5.4 months. Considering a 6-month interval between tests, the mean Rh was 0.23, increasing to 0.82 for annual intervals, and to 2.01 and 3.47 with testing intervals of 2 and 4 years, respectively.
The second study was directed at evaluating the efficiency of the components of bTB surveillance system: routine skin testing, slaughterhouse surveillance and pre-movement testing; and, to assess their variability among Spanish provinces, by using a modified version of the model previously developed. Under the average Spanish conditions, the overall sensitivity (i.e. probability of detection per year) of the national bTB surveillance system was 79.7% and the mean time until detection 221.6 days. Routine testing was the most efficient component, while the efficiency of slaughterhouse surveillance and pre-movement testing was much lower; although these components also contributed to detection of some infected herds. Looking at the province level, the efficiency of the different components of the bTB surveillance varied significantly, but no obvious spatial pattern was identified. Our results evidence that in many Spanish provinces, the intensity of surveillance efforts was not correlated to the herd prevalence in the area.
In the third study, we used qualitative approaches to investigate opinions and attitudes of farmers and veterinarians toward the Spanish bTB eradication programme. Face-to-face exploratory interviews were used to identify main themes, followed by in-depth interviews. Main results suggested that the bTB programme is perceived as a law enforcement duty without an adequate motivation of some stakeholders. The complex bTB epidemiology combined with gaps in knowledge and weak communication among stakeholders contributed to generate disbelief towards control measures and, in turn, different kinds of guesses on the disease. Low reliability in the skin test was expressed and some pressures faced by private veterinarians during field activities also emerged. People perceived very few benefits of being bTB-free and comparative grievances to wildlife, other domestic reservoirs and bullfighting farms arose.
In the fourth study, the sociological factors previously identified were investigated through a structured questionnaire, telephonically interviewing a sample of 706 farmers and 180 veterinarians. Multiple Correspondence Analysis, followed by Hierarchical Clustering on Principal Components were used to identify opinion profiles; and, a logistic regression model was developed to quantify the main differences between groups. Different attitudes toward the bTB eradication programme were characterised by opinions on the bTB diagnostic tests, the perception on the impact of bTB and the importance of other domestic and wildlife species. There were people with positive and with negative attitudes toward the programme and a third group with a clear tendency to not respond. Opposite profiles were observed among farmers. Differently, veterinarians were more homogeneous and the vast majority of them expressed a positive attitude; however, some veterinarians showed a negative attitude toward the bTB eradication programme, which deserve a special attention.
