Thursday, September 11, 2008

bTB and camelids

The popularity of camelids in GB can be seen from the estimated numbers of llamas and alpacas which are now conservatively put at 20,000 and 5,000 respectively. But recent spillover cases of "bovine" TB into this population has raised several problems. Correspondence in the Veterinary Record details a case of bTB in a commercial llama herd in Devon which resulted in the death of over half the animals.

The herd was established in Devon eight years ago with animals reared outside the county. At the time of disclosure of infection, it comprised 84 adult llamas and their crias. They graze outdoors all year round with occasional supplementary hay fed on the ground, and are only handled for routine vaccinations and worming. Water is provided in troughs, but the llamas also drink from a stream.

The authors point out "the only contiguous cattle herd has had repeated TB breakdowns since 2000 but that direct nose-to-nose contact is not possible between the llama and cattle herds along the common boundary." There have been 19 confirmed cases within a 5 km radius since 2001. Three active badger setts are located on the farm and one in immediately adjacent woodland, but no deer have been seen.

In February 2006, an adult female on the holding was euthanased on welfare grounds following chronic weight loss. Postmortem examination revealed widespread lesions in the lungs, pericardium, and bronchial and mediastinal lymph nodes and M. bovis spoligotype SB0274 (VLA type 11) was recovered. This is the spoligotype most commonly isolated from tuberculous cattle and road traffic accident survey badgers in the same part of Devon.

In May 2006, herd restrictions were applied and the outbreak reported to local consultants in communicable disease control in light of the zoonotic risk. There are no statutory requirements to register and identify South American camelids, or powers to test them for TB, but the owner agreed to have the remainder of the herd tested. But despite two clear herd skin test results, similar clinical signs to the initial case were seen in another adult female in August, which eventually required euthanasia. Lesions were found at postmortem examination and M bovis was subsequently isolated.
In light of this second clinical case and the previous negative herd test result in June, it was decided to blood sample other llamas in the herd to screen for antibodies to M bovis using a novel, non-validated in vitro lateral-flow assay, the VetTB STAT-PAK or `Rapid' test (Waters and others 2006). On the basis of either a positive sero logy result or being considered as dangerous contacts to the previous confirmed cases, 19 more adult llamas and two crias were culled and examined postmortem between August and November. TB associated with M bovis infection was confirmed in four of the adults. Two other adults and a cria also died over this period and on gross postmortem examination showed lesions typical of TB. Specific mycobacterial cultures are still in progress from these three animals.

Testing with both skin tests and bloods were continued for this herd and reactors to both tests were found.
Three tuberculin reactors and at least four seropositive llamas, one of which was a tuberculin reactor, have been identified. The results of postmortem and bacteriological examinations on all these llamas were not available at the time of writing, although one of the seropositive llamas, which had to be euthanased in extremis shortly after testing, presented with gross lesions of advanced TB.
The paper points out both the " susceptibility of llamas to M bovis infection and highlights the difficulty of making an accurate antemortem diagnosis using the tests currently available for this species." They repeat previous advice;
TB should be considered in the differential diagnosis of illthrift in llamas, with or without obvious respiratory involvement, particularly where the animals have been raised in areas of endemic TB in cattle and indigenous wildlife.

In a follow up letter to this report, the authors re-iterate the insensitivety of the intradermal skin test when used on camelids and point out other anomalies ;
Many of us working with camelids believe the test to be so poor as to be fairly meaningless. Nevertheless, this test remains the statutory DEFRA-approved method of checking for TB in camelids, both for importation, exportation, and here in the UK. Moreover, if an `infected' herd achieves two successive clear herd tests 90 days apart there is no requirement to test the herd ever again. Neither is there any requirement to keep movement records or carry out any further postmortem examinations. The `Rapid' blood test shows promise but it is not allowed to be used without the express permission of the State Veterinary Service. That permission is not always forthcoming even when clients have offered to pay privately for the test. Surely DEFRA should be furthering research by promoting blood testing, not hindering it.

They conclude that better methods of identification, surveillance and control of TB in camelids is needed, given the population of these animals within GB, and point out;
They should not be ignored in the overall campaign to eradicate bovine TB. The Devon incident may be only the tip of the iceberg.

As we posted here a similar breakdown affected a herd in Wales. We understand Welsh Assembly are currently 'consulting' on what to do about the situation of spillover bTB into camelids. And as we can find no such documents on the English side of Offa's Dyke, would that be like the 'consultation' on whether to sort out the maintenance reservoir in wildlife - a name they dare not speak - or keeping piling up dead cattle then? We won't be holding our breath.

1 comment:

Dianne Summers said...

Since Sept 2008 I have lost 4 alpacas to TB. Last Friday I put down 2 of my boys who were coughing and despite having negative skin tests 6 weks earlier they were both confimred Tb. I did get the research lab to conduct the stat - pak rapid test on the 2 I put down and they result was a strong positive.
The skin test is uselss. I am in touch with 7 other Tb affected alpaca owners and gathering data - timelines symptoms etc - many had it brought into their farms through matings etc. This is a serious issue and we need to be open and communicate with each other. I am also trying to set up a support network for all those affected. Please get in touch and any information will be confidential. Dianne Summers 01209 822422