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bTB - Where are we now ?


Bovine Tuberculosis in Camelids – Where We Are Now?


Background

Bovine tuberculosis is a bacterial disease which can affect a wide range of mammal species, including man, which makes it a zoonosis, and it is therefore notifiable. Notifiable diseases must, by law, be reported to the government (in this case to the Animal Health and Veterinary Laboratories Agency, AHVLA) if they are suspected or confirmed.

The group of bacteria which cause bovine TB, human TB, avian TB, vole TB (and leprosy) are Mycobacteria. Diseases caused by this group of bacteria are characterized by a long course of infection where the patient can survive with infection (and be infectious) for months or even years. The human versions of these diseases are notoriously difficult to treat, and until relatively recently they were regarded as almost incurable. The disease we usually see in llamas and alpacas is caused by Mycobacterium bovis, also known as M. bovis.

What does bTB look like?

It would be really helpful if there was a set of signs which were always associated with TB infection. Unfortunately, they seem to be able to show a wide variety of signs, some very subtle, or none at all. When llamas and alpacas get bTB they may well become obviously ill with respiratory disease, fail to respond to treatment for pneumonia, and then die. However, they can also die quite suddenly without ever appearing ill, even while in good body condition. Many cases have been diagnosed after sudden death. This means that camelids showing no outward signs at all can be heavily infected. The vast majority of camelids culled for bTB have failed the Rapid Stat Pak test, but passed the skin test. Herds where bTB has been confirmed, and which elected to use the Rapid Stat Pak test, have found that perfectly healthy looking camelids with no outward signs of disease, were found to have bTB lesions. If these animals had remained undetected, then they may well have survived for some considerable time, and been a source of infection to the rest of the herd, and let us not forget, this is a zoonosis, so in contact humans are also at risk of infection.

History

Until about 10 years ago, the incidence of bTB in camelids seemed to be relatively low, but quite suddenly infection seemed to snowball:



This chart is on the AHVLA website:
publication date : 23/08/2012 next publication date : 31/10/2012
Table 3: Annual numbers of new incidents of culture-confirmed M.bovis identified on South American camelid premises in GB













































Year of disclosure Infected herds (with > 1 dead or culled animal) Type of herd infected (herd with > 1 culled animal) Location of affected herds
1999-2003 5 2x alpaca 3x llama Gwent (2 llama holdings), Gloucestershire (alpaca), Herefordshire (llama), Somerset (alpaca)
2004 1* alpaca Devon
2005 1 llama Avon
2006 2 (1) 1x alpaca 1x llama (1) Sussex (alpaca), Devon (llama)
2007 3 (3) 2x alpaca (2) 1x llama Carmarthenshire (llama), Powys (alpaca), Dorset (alpaca)
2008 11 (6) 9x alpaca (4) 2x llama Carmarthenshire (llama), Devon (1 llama, 1 alpaca), Avon (2), Cornwall, Gloucestershire (3), Herefordshire, Worcestershire
2009 12 (6) all alpacas Devon (3), Derbyshire, Gloucestershire (2), Shropshire, Somerset (2), Staffordshire, Worcestershire (2)
2010 15 (6) all alpacas Devon (4)***, Cornwall (3), Gloucestershire, Hampshire, Monmouthshire, Staffordshire (2), Warwickshire, Worcestershire
2011 6 (4) ** all alpacas Cornwall, Dorset, Gloucestershire (2), South Gloucestershire (near Bristol)****, Warwickshire
2012 (2nd quarter) 5 (1) ** 3x alpacas 2x llama (1) Carmarthenshire, Somerset, West Midlands, West Sussex, Worcestershire
(*) No culture possible, but typical histopathology and PCR positive for MTB complex. (**) The figure in parentheses may increase as some of those incidents have not been closed and ongoing live testing may identify further cases. (***) Three of those were epidemiologically linked via movements/purchases of infected animals and could therefore be considered one TB incident. (****) Location was incorrectly referred to as Avon in previous updates. Updated by Defra TB Programme 23rd August 2012

The number of herds under restriction for bTB at any one time fluctuates, but since herds come out of restriction almost automatically* after 6 months this is a poor guide to the number of herds which harbour infection. 61 herds have had bTB confirmed, but other herds may be placed under restriction from tracing, or for being contiguous with an infected herd, or in contact with an infected herd.

*It is at present legally permissible for restrictions to be lifted following two consecutive clear skin tests, and since the skin test for bTB in camelids has been shown to be less than 5% effective, it means that even a herd with active bTB infection can have its restrictions lifted quite legally, because infection will be missed by the skin test.

Transmission of infection

Infected alpacas and llamas tend to have very extensive tuberculous abscesses throughout their internal organs, and will shed infection in sputum, (and therefore spit) and faeces. There is also the possibility of infection via milk, since abscesses have been found in the udder. No secretion from an infected animal should be regarded as safe.

For these reasons, if an animal is suspected of having infection, it must be treated as a serious potential threat both to the other members of the herd and to people – there are two documented cases of infection transferring to humans from infected camelids. (Interestingly, despite the much greater number of cattle, bTB transmission from them to humans is rare.) Suspect animals must be isolated with a companion animal (which may end up being sacrificed if infection is confirmed) at least 3 metres from nose to nose contact with any other stock, and sharing no troughs, water or walkways.

Sources of Infection

Other infected camelids in direct contact, or their secretions on ground, feed, feeding utensils.

Wildlife, especially badgers which secrete huge numbers of bTB bacteria when infected.

Infected farm animals, in practice, most likely to be cattle, via direct contact or body secretions on ground or feed or water. (This includes colostrum from infected cows.)

Tests for bTB infection

At present the only legally accepted test is the comparative intradermal skin test, as used in cattle. Research into other tests which use blood samples has demonstrated that the skin test is less than 5% sensitive, which means that for every one infected animal detected by the skin test at least 20 will be missed. However, blood tests which detect the immune response to bTB have undergone trials in camelids and demonstrated a better accuracy; AHVLA have very recently decided on the best way to deploy these in the fight against bTB, and what is absolutely clear, is that we can not control bTB using the skin test alone. Please see links to the Open Letter from DEFRA TB Policy to all Keepers of South American Camelids in the UK.

Early research has been, and is being done on the molecular biology technique known as PCR. This stands for Polymerase Chain Reaction, and can detect tiny quantities of target DNA (in this case bTB). Preliminary results are encouraging, and as it can be done on sputum and faeces, which can be taken from live animals, it opens the possibility of detecting infection in a herd
before the first animal actually dies of the disease. It is a much quicker process than culture, so the 8-12 week wait for culture results which is currently required before infection can be confirmed in a herd would be hastened. Infected animals would then not remain in a herd to spread more infection for as long as they do at present.

Control of bTB Nationally

At present control measures are entirely voluntary. There is no routine surveillance for bTB in camelids. The infection is discovered only when a camelid dies, and the owner is responsible enough to have it examined post mortem. This is obviously a concern, since very many owners neglect to have all of the camelids they lose go to post mortem examination.

What you can do – THINK!

PM all of your losses: This is the only way to be sure that you are not losing animals to bTB.

Practise good biosecurity – don’t allow your animals to mix with those from other premises. If new animals come onto your property do a risk assessment on the source farm, or else keep them isolated from your herd. bTB has definitely been transmitted via agisted matings, where females travel to a different farm and stay there until pregnant and are kept with other females from different farms. bTB infection has also been bought in with new stock many times. When camelids move around they take any infection, bTB included, with them. You may find that you are placed under restriction because you are agisting, or have bought animals from farms which go down to bTB, and your farm becomes a “tracing”.

Use foot dips when you have visitors to your herd, and don’t allow other farms’ vehicles onto your land without thorough wheel disinfection.

Keep wildlife, especially badgers, away from your stock. Feed and water sources are especially important.
Never feed from the ground, use hay racks, and troughs which are cleaned and up ended when not in use. Raise water troughs so that badgers can not reach them; fitting a roller bar around a trough so a climbing badger can not get a grip is a good trick.

For further information, visit www.alpacatb.org

Gina Bromage