BOVINE TUBERCULOSIS - UK (05): (ENGLAND) ALPACA

Date: Sat 25 Jul 2009
Source: The Veterinary record 165: Letters, pp 121-2 [abridged, edited]
<http://veterinaryrecord.bvapublications.com/cgi/reprint/165/4/121>
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Suspected transmission of _Mycobacterium bovis_ between alpacas


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Four adult female alpacas from a herd in Devon
(A) had visited a breeding herd in south-east
England (B) from October to December 2008. The
owner noticed clinical signs in 2 of these,
including lethargy, weight loss, and occasional
coughing, 4 and 8 weeks after returning to herd
A, respectively. The disease was progressive and,
despite treatment under veterinary supervision,
both alpacas eventually died in May 2009. At
postmortem examination, both animals were in poor
body condition, weighing 41 [90 lb] and 62 kg
[137 lb]. They both showed extensive caseous
necrosis of the lungs and thoracic lymph nodes.
Additionally, pulmonary cavitation and a few
calcified lesions of approximately 1 mm diameter
in both kidneys were identified in one alpaca.
Acid-fast bacilli were demonstrated on
Ziehl-Neelsen staining of fresh tissue smears,
and typical granulomatous lesions of TB with
acid-fast bacilli were demonstrated by
histopathology. _M. bovis_ with spoligotype
pattern SB0134 (VLA [Veterinary Laboratories
Agency, Weybridge, UK] type 35) was subsequently
isolated. This was unexpected as _M. bovis_
spoligotype SB0274 (VLA type 11) is more commonly
isolated from TB cases in this geographic area.
Strains with spoligotype pattern SB0134 represent
fewer than 0�1 percent of cattle isolates in
Devon, with none originating from the vicinity of herd A.



After searching the VLA TB database for South
American camelid submissions, only one other
isolate of _M. bovis_ spoligotype SB0134 was
recorded, also in an alpaca. This animal
originated from a herd (C) situated in an area of
Shropshire where strains of spoligotype SB0134
are frequently recovered from tuberculous cattle.
In February 2009, this alpaca developed weight
loss and respiratory disease over 3 weeks and
died despite treatment under veterinary
supervision. A postmortem examination was carried
out by the attending veterinary surgeon and
caseous necrosis suggestive of TB was seen in the
lungs. Further testing of affected lung tissue
confirmed the diagnosis by demonstrating
acid-fast bacilli in Ziehl-Neelsen-stained
smears, typical histopathology, and positive mycobacterial culture.



This confirmed case from herd C had not been
moved off the premises for at least 16 months.
However, another alpaca from herd C had visited
herd B in September 2008 and remained there until
December 2008 when it developed respiratory
disease and died. Although a postmortem
examination was not carried out to confirm TB,
the clinical signs were consistent with this
disease. It is therefore possible that this herd
C alpaca transmitted mycobacterial infection to
some of the herd A animals temporarily resident
in herd B. The pattern of animal movements and
isolation of _M. bovis_ spoligotype SB0134 from
herds in different counties strongly suggests
alpaca-to-alpaca transmission. Strains with this
spoligotype have not been isolated from the
vicinity of herd B, which is an area of low TB
incidence, and transmission from a local
reservoir in south-east England is therefore
unlikely. Furthermore, there had been no other
animal movements between herd A and other
premises to provide an alternative explanation
for transfer of strains with this spoligotype.



In accordance with existing Defra policy, herds A
and C are now under movement restrictions pending
the outcome of 2 successive intradermal
comparative postaxillary tuberculin tests on all
of the remaining animals, carried out at 90-day
intervals. The 1st of these has already been
completed for both herds with no reactors
identified. Restrictions will be lifted if no
reactors are detected at the 2nd herd tests,
provided that there is no indication of TB based
on clinical or pathological evidence.



Following a veterinary risk assessment, herd B
was also placed under precautionary movement
restriction, but this has now been lifted
following tuberculin skin testing of the herd with no reactors identified.



The predominant distribution of tuberculous
lesions in the lungs and associated thoracic
lymph nodes is similar to most TB cases diagnosed
in British South American camelids. Because of
this heavy concentration of thoracic
mycobacterial infection, the respiratory route is
the most likely means of transmission between
animals in close contact. This effect may well be
enhanced when some of the lesions show pulmonary
cavitation. The identification of histologically
confirmed mycobacterial granulomas in the kidneys
of one alpaca from herd A also raises the
possibility of transmission via infected urine.



Movement of South American camelids between
premises is reported to be common in Britain. The
biosecurity risk associated with alpaca movements
has already been highlighted, with documented
cases of bovine viral diarrhoea virus infection
and sarcoptic mange occurring as a direct result.
These new TB cases provide evidence of the risk
of spreading _M. bovis_ infection through
uncontrolled movements of South American camelids
between holdings, particularly those situated in
recognised endemic TB regions. Herd owners should
be encouraged to seek veterinary advice regarding
appropriate biosecurity measures when animal movements are necessary.



If private skin testing is being considered,
permission to do so must be sought from, and test
results reported to, Animal Health. As previously
advised, TB should be considered in South
American camelids showing clinical signs of
progressive weight loss and respiratory disease.
The detection of suspect tuberculous lesions
during postmortem examination of South American
camelids must be notified to Animal Health. The
protracted disease course, particularly in herd
A, illustrates the potential for further spread.
The zoonotic risk to human contacts is also a
serious consideration to those handling potentially infected animals.



[Byline: DF Twomey, TR Crawshaw, AP Foster, RJ
Higgins, NH Smith, L Wilson, K McDean, JL Adams, R de la Rua-Domenech]