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- Title
Tuberculosis in goats on a farm in Ireland: epidemiological investigation and control.
- Authors
Shanahan, A.; Good, M.; Duignan, A.; Curtin, T.; More, S. J.
- Abstract
Context This paper describes the field investigation into an outbreak of tuberculosis (TB) in a dairy goat herd (farm C) in Ireland, with epidemiological linkages to two other farms with dairy goats (farms A and B). It illustrates the course of infection, as judged by diagnostic tests, through to apparent resolution. It also highlights some of the practical difficulties that arose during the management of the infected goat herds. The paper provides an overview of the TB control plan for non-bovine TB-susceptible dairy animals, as required under EU Regulation 853/2004/EC. Main conclusion There is a need for increased public awareness of TB susceptibility in goats. This is particularly important among hobbyist goat keepers, many of whom consume raw milk and/or milk products and are not legally obliged to have a TB control plan. Approach Epidemiological investigations were conducted, focusing on farm C but with additional work on farms A and B, to determine the source of infection and potential for withinherd transmission, evaluating both the goat herd (housing, feeding, husbandry, preventive health programme, goat movements, herd mortality and morbidity) and the farm (the integrity of the farm boundary, other susceptible species, opportunities for cross-species contact). On farm C, a qualitative assessment was undertaken to determine the risk of introduction of Mycobacterium bovis infection and/or onward within-herd transmission, based on evaluation of inward movements to, and biosecurity practices on, the farm; TB prevalence in the locality; and the likelihood of within-herd transmission. Further assessments and control measures to minimise transmission potential were implemented on farm C based on diagnostic test results as they became available. The single intradermal comparative tuberculin test (SICTT) was performed on adult goats using standard cattle methods. SICTT-positive animals were slaughtered and examined postmortem. Bulk milk samples and milk samples from one individual goat with mammary problems were submitted for M bovis culture. Ancillary testing using the interferon-γ (IFN-γ) assay and the Enferplex ELISA was also performed, and a comparison of results from different diagnostic tests was assessed using k statistics. Results In January 2008, clinical cases of caprine M bovis infection and caseous lymphadenitis (CLA), confirmed by bacterial culture of M bovis and Corynebacterium pseudotuberculosis, were detected in adult goats on farm A (southern Ireland). There were strong epidemiological links with farms B (Irish midlands) and C (north-east Ireland). A detailed log is described of health and other relevant events on farm C, including a detailed risk assessment (in July 2008) and subsequent TB diagnosis (with an apparent herd prevalence of 66.3 per cent) in October 2008. At this time, rigorous control measures were implemented to minimise the risk of further within-herd transmission, including early isolation of reactors, attention to effective biosecurity, and the formation and management of specific 'risk' groups. Testing was conducted using SICTT, IFN-g and the Enferplex ELISA, with no further positive reactors detected from April 2009. During the investigation, there was good correlation between the three diagnostic tests: SICTT and IFN-γ assay (κ=0.800), SICTT and Enferplex TB (κ=0.867), and Enferplex TB and IFN-γ assay (k=0.938). In each assessed case on farm C, the VNTR profile was 11, 7, 4, 3, 2. The same strain had been identified in M bovis isolates from farm A goats, and from badgers from the midlands in the locality of farm B. Interpretation In the farm C outbreak, it is most likely that infected goats (from farm B) were the source of infection. Within-herd transmission was facilitated by direct contact between infected animals, rather than by indirect contact via shared personnel. Respiratory excretions were most likely infectious given the extensive within-herd spread and the detection of a reactor by all three tests after only six weeks in contact. Cattle on farm C all subsequently tested negative. Mixed clinical infection with caprine M bovis infection and CLA was confirmed on farm A; thus, gross visible lesions on this farm were not necessarily tuberculous. Key control objectives during the farm C outbreak included rapid detection and removal of any potentially infected animals, minimisation of any zoonotic risks and limiting further spread. The results of the initial risk assessment proved somewhat misleading, suggesting that the potential for infection in this herd was low. During this outbreak, the SICTT proved a very effective means to identify potentially infected animals. There was substantial agreement between the three tests used, and the use of the IFN-g assay and the Enferplex ELISA in kids, and in adults between the scheduled SICTTs, helped increase the speed at which potentially infected animals were identified and removed. Given subsequent events, the strategy adopted in using SICTT results to separate the goats on the basis of risk categorisation appears useful in limiting further within-herd transmission. It also facilitated the introduction of rational biosecurity measures including disinfectant footbaths and controlled personnel movement. Significance of findings Goats are susceptible to TB, with the potential for rapid within-herd transmission and between-herd spread. Control was achieved on farm C through rigorous control measures. There is a need for increased public awareness of this issue, particularly among hobbyist goat keepers. The implementation of a control plan to screen for TB in dairy goat/sheep herds is important, as outlined under EC Regulation 853/2004, to provide food safety and public health assurance.
- Subjects
IRELAND; GOAT diseases; MYCOBACTERIUM bovis; TUBERCULOSIS in animals; FARMS
- Publication
Veterinary Record: Journal of the British Veterinary Association, 2011, Vol 168, Issue 18, p484
- ISSN
0042-4900
- Publication type
Article
- DOI
10.1136/vr.c6880