Update - New tests for TB in Alpacas

In case anyone is under any illusion about just what 'tuberculosis' does to a lung when it takes hold, this is a photo of pulmonary cavitation in an alpaca called Willow. He had passed a skin test in late January 2009, and another in early May.

His companion developed a cough and was subsequently euthanased. This was just six weeks after a clear skin test and his very responsible owner agreed to have Willow put down as a dangerous contact at the same time. The postmortem showed pulmonary cavitation and lesions in his throat. But at no time did Willow show any of the physical symptoms normally associated with TB: no weight loss, unthriftyness or cough.

As an update on the testing saga of Dianne Summers' Cornish alpaca herd which we covered here, the news is mixed. Having volunteered and gained permission to use the Chembio Rapid Stat-Pak blood test on her herd, the results were 4positives. Miss. Summers then agreed to pay for X rays to confirm any lung damage ahead of proposed slaughter. The whole herd was Xrayed and when the films were read at the Cambridge Veterinary School, two animals gave 'cause for concern'.

These were not two of the four animals which were positive on bloods. These two animals were isolated, and will be Xrayed again this week. The four alpaca which were positive on bloods are also isolated separately and the herd will be Xrayed at regular intervals to confirm blood results.

Miss Summers points out that if she had relied on the skin test results, her herd would be clear, despite having animals with the tuberculous lungs pictured above.
If she had relied on the blood test, another four alpaca would be for the chop, but having Xrayed the herd she comments that:

" ... if I relied on the results of the blood test alone - 2 of my herd who have shown on X ray as a 'concern', [but] who didn't show positive on Blood test would have fallen below the radar and wouldn't have been isolated and therefore possibly infect my other animals. My 4 positive blood test alpacas have been isolated because the blood test may detect very early signs of TB before it shows up on X Ray.."

Miss Summers's alpacas are not out the woods yet, and the herd will continue to be monitored and Xrayed regularly. Any sign of lesions, will mean the animals are culled. The unreliable results on camelids of the intradermal skin test, described in a 2007 paper as 'so poor as to be meaningless' leave owners who want to protect their herds from tuberculosis little choice but to pioneer different diagnostic tests which in tandem, may give a degree of antemortem confirmation of disease.

Dianne finishes her story thus:

"I will continue to Xray my entire herd every 3 months and will cull any that show TB lesions. I am taking advice from industry experts and have done everything they have recommended.
This is important research but it is going to take a long time before we know how accurate any of this is but its a start. At least I am trying and this may just help currently infected herds and newly infected herds."

We wish her well.

Update.
On further Xrays, the two alpacas which gave cause for concern on Xrays, appear clear. Cambridge recommend a repeat screening in a few months. (Xrays will pick lesions less than 1/2 centimetre across, thus at a very early stage). Their results on these two state "So, in summary, the new films do NOT show areas of concern anymore."
And how that leaves the four alpacas, positive to the unvalidated Rapid Stat-pak blood test, (all of which were clear on skin), is anybody's guess.