Statistics from Altmetric.com
SIR, — We would like to report a severe outbreak of tuberculosis (tb) caused by Mycobacterium bovis in golden Guernsey goats. Reports of caprine tb have been very rare in the uk since the introduction of a mandatory tb testing and slaughter scheme for cattle herds in the 1950s. However, the extent of the current outbreak illustrates that goats are susceptible to M bovis infection and tb should be considered as a differential diagnosis in goats with respiratory signs and weight loss, particularly if kept in regions of high bovine tb incidence.
As part of defra's scanning surveillance programme, an adult female golden Guernsey goat from a holding in the west of Wales was submitted to the Veterinary Laboratories Agency (vla) regional laboratory in Carmarthen early in June 2008. It had shown anorexia, a fall in milk production, weight loss and a chronic cough. Postmortem examination revealed two large lesions and multiple smaller lesions in the lungs. A Ziehl-Neelsen-stained smear showed acid-fast bacilli and tb was suspected. Bacteriological culture from the lesions identified M bovis spoligo type sb0140 (vla type 9). Before the culture results were available, the remaining goats in the herd were pre-emptively tested using the intradermal comparative tuberculin test. Thirteen of 20 animals tested were disclosed as reactors using the standard bovine interpretation. Postmortem examination of these goats at the vla showed gross lesions similar to the first case in all but one of the reactors. Four other non-reactor goats, slaughtered as dangerous contacts, did not show any gross tuberculous lesions at postmortem examination. Three goats with negative test reactions, all belonging to a separate management group, remain on the holding.
Goats in the disclosing herd showed anorexia, particularly refusing concentrate food, a sometimes precipitous fall in milk production, a chronic intermittent cough and sometimes loss of weight. Pulmonary lesions were the most obvious pathological sign on postmortem examination, with abscesses 2 to 10 cm in size (Fig 1) containing liquid pale yellow pus. Lesions in the bronchial, mediastinal, and mesenteric lymph nodes were more caseous, sometimes with ‘gritty’ calcification (Fig 2). Lesions have also been seen in the retropharyngeal lymph nodes, liver, spleen and udder.
The most likely source of infection for the herd appears to be the movement in May 2007 of three golden Guernsey goats from another herd in west Wales that was dispersed last April. Tracings from these two herds are being investigated by Animal Health and include goats moved to other holdings in England and Wales. At the time of writing, tracings involve 20 destination herds in 13 different counties of England and Wales. To date this has revealed a further eight herds with skin test reactor golden Guernsey goats presenting with tuberculous lesions at slaughter. Mycobacterial cultures on tissues from these goats are in progress.
This outbreak has shown that goats can be very susceptible to M bovis infection and that the within-herd prevalence of infection can be high. It also highlights the importance of considering the risk of the introduction of M bovis infection when moving animals between herds and the potential consequences of failing to do so.
The positive predictive value of tuberculin skin tests performed so far on the at-risk goats has been very high. People handling infected goats or drinking their milk unpasteurised are at risk of zoonotic M bovis infection, although the indications so far are that all but one of the herds investigated were not selling milk for human consumption. The relevant local public health authorities have been notified of this herd and of the other seven goat herds containing test reactors with evidence of tb at slaughter. Any remaining goats on these holdings, like those in the disclosing herd, remain under movement restrictions and will be subject to repeat skin testing at 60-day intervals.
Practitioners should consider tb when investigating goats with chronic respiratory disease and weight loss, and goats that die or are euthanased should undergo postmortem examination. Any suspicion of tb must be reported to the Divisional Veterinary Manager (dvm). Where caprine tb cannot be ruled out at postmortem examination, laboratory tests will be carried out free of charge at the vla in order to identify the causative mycobacteria. Any veterinary surgeon undertaking skin testing of goats must seek prior permission from the dvm and notify Animal Health of the results.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.