Transmission - alpacas

We are grateful for sight of this week's Veterinary Record, where a report investigates an outbreak of disease which appears to be the result of convoluted movements, undertaken by some of this country's alpacas.

We have touched on the thorny problem of tuberculosis and camelids before with an on-going breakdown in a herd of Cornish alpacas covered by Farmers Guardian.

The report was submitted by VLA staff at Starcross, Exeter and follows the fortunes of some Devon alpacas, sent to a herd in south-east England for mating, where they were mixed and stirred with alpacas from different parts of GB, there for the same purpose. All are subsequently dead, with we understand, some onwards transmission from this outbreak evidenced on the Devon farm. The spoligotype isolated from the Devon females was neither Devon nor West Sussex, but proved to be Shropshire. A female from Shropshire visited the stud over a similar time period, and she had subsequently died.

The report points out that there is little or no documentation on the transmission of tuberculosis between alpacas - but as we have said, if a scientist hasn't seen something, that does not mean it does not happen. The saga of this deadly triangle is described thus:

"Four adult females alpacas from a herd in Devon (A) visited a breeding herd in south-east England (B) from October to December 2008. The owner noticed clinical signs in two of these, including lethargy, weight loss and occasional coughing, four and eight weeks respectively after returning to herd A. The disease was progressive and despite treatment under veterinary supervision, both alpacas eventually died in May 2009."

The report describes clinical postmortem results, including extensive lung lesions, pulmonary cavitation and lesions on the kidney in one alpaca. M.bovis was cultured and identified as VLA type 35 or SBO134. (The part of Devon from which the alpaca came is usually home to badgers and spillover sentinel cattle hosting VLA type 11)
Searches of VLA's extensive database revealed that SBO 134 had been reported in a Shropshire alpaca (Herd C) which had presented with weight loss and respiratory disease over a period of three weeks, and which had died in February 2009. This animal had not been off the farm for 16 months, but another female from the herd had visited the stud farm in the south east (Herd B) in September 2008, and remained there until December, when it developed 'respiratory disease' and died. It was not postmortemed, although clinical signs were consistent with TB.

The Veterinary Record report is submitted by D.F Twomey and T.R. Crawshaw of Exeter VLA, who describe the predominant distribution of tuberculous lesions in alpacas which they had postmortemed as "within the lungs and associated thoracic lymph nodes", which they say, is "similar to most TB cases diagnosed in British South American camelids."

The illustration shows an camelid lung, with extensive necrosis and cavitation. The authors of the VR report consider that a "heavy concentration of thoracic mycobacterial infection" indicates that the respiratory route is the most likely means of transmission between these animals in close contact. This effect they say "may well be enhanced when some of the lesions show pulmonary cavitation".

In other words, camelids are very susceptible to TB, the disease advances extremely quickly, most lesions are found in the lungs and, unlike cattle lesions, these are pretty loaded with a 'heavy concentration' of bacteria, especially when 'pulmonary cavitation' occurs.

Control over this potential swamp of tuberculosis is non-forthcoming from Defra, who believe it to be 'a minor problem'. Camelids are outside the TB regulations in England, thus movement records, AHO entry to trace-back premises and herd restrictions may be considered 'voluntary'. Or kicked into the 'too difficult' box? And then there is the thorny question of a test. At the moment the intradermal skin test is the only test recognised to indicate TB free herds - of any animal, including camelids. No matter that it is 'meaningless' on camelids (Vet Record 2007.) Nevertheless, herds are exporting alpacas, being released from TB restriction (always assuming they have actually reported ill-health or deaths of their animals, and not buried the evidence) and tested or untested, offering mating services such as undertaken with such devastating results by the Devon herd described above, and exhibiting these delightful creatures within children's play areas in tourist attractions and agricultural shows.

The VR report concludes:

"These new TB cases provide evidence of spreading M.Bovis infection through uncontrolled movements of South American camelids between holdings, particularly those situated in recognised endemic TB regions." and they warn "The zoonotic risk to human contacts is also a serious consideration to those handling potentially infected animals".

That risk is ever thus, as we posted here.