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Depopulation - an extreme action

 Added by  Sally
 3 Sep 2011, 2:21 PM

We now that in many countries TB free status has only been achieved by using depopulation. This is where the skin test is used as a herd test (what is was initially designed for) and not as a test for individual animals. If any reactors are found the whole herd is destroyed.
In the UK we do not use depopulation of complete herds unless a significant number of animals are revealed as reactors.
In France they have just identified one animal in a herd of 338 as bTB positive, ie a reactor. The herd concerned is in Cantal of Allanche (in the Auvergne). It is highly likely the whole herd will now be destroyed. An article (www.lamontagne.fr) tells us that the last case in France was in 2005 (France has apparently been TB free for 5 years).
Although testing at abattoirs does continue, routine testing does not take place on farms any more. It will therefore be a difficult task to trace the source of the infection. The farms in the area are now under restrictions and all animals near the affected farm will be screened.
In France any disease considered a zoonosis - as bTB is considered there - the owner of animals killed as a result is reimbursed enough to restock animals considered to be of the same financial value. France considers the risk of bTB to people is 'faible' (slight, weak, low level ...).
Information from Warmwel

It is up to Animal Health and depends on the levels of reactors and inconclusive reactors found in a herd. Defra's latest April 2014 'The Strategy for achieving Officially Bovine Tuberculosis Free status for England' (Page 44) states that depopulation of a cattle herd can be applied in cases where repeated testing does not, or is suspected not, to clear a herd of infection, although it is rarely applied in practice on a whole herd basis; partial depopulation is more commonly used.
A research paper published in 2002 (http://randd.defra.gov.uk/Default.aspx?Menu=Menu&Module=More&Location=None&ProjectID=10228) investigated 'Using herd depopulation for effectively controlling bovine tuberculosis.' Between 1996 and 2000 39 herds had been depopulated, 15 totally and 24 partially). These depopulations accounted for 1.0% of confirmed incidents, 4.5% of reactors and 0.8% of inconclusive reactors and 33% of precautionary culls. The depopulations required the removeal of 973 animals that passed the test. On slaughter the ration of infected animals was 4:1.
"In the UK we do not use depopulation of complete herds unless a significant number of animals are revealed as reactors"
Does anyone know what is considered significant i.e. what percentage of the herd would have to be positive to justify depopulation in the UK?
MICHIGAN The Michigan Department of Agriculture and Rural Development has completed its Saginaw County bovine tuberculosis investigation after testing 25,800 cattle on 373 farms.
The agency DEPOPULATED three TB-positive farms, quarantined another, and no other positive cattle have been revealed. As a result, the special surveillance areas have been released and the area is considered TB free.
MICHIGAN two cows suspected to be TB-positive were discovered during routine annual testing of an Alcona County cattle herd in February. After dissecting both cows, one was found to have a lesion in a lymph node in its throat. DNA tests confirmed it was bovine TB.
The infected herd, the 57th discovered since 1998, has since been depopulated, Smith said. The United States Department of Agriculture reached this decision after consulting with the farmer, who was compensated for the cows. The farm is in what's known as a modified accredited zone, so no additional testing of nearby farms is required.
Info from www.thealpenanews.com/page/content.detail/id/525481/State-holds-meeting-about-bovine-TB-herd.html?nav=5004
Interesting extract from Brian May's article about his visit to the EU to discuss cattle vaccine. Whilst talking to the Chef de Cabinet for Agriculture, Mr Georg Haeusler, and his colleagues there was a discussion about depopulation. The extract is below. Full article at http://brianmay.com/brian/brianssb/brianssboct12c.html#22
Mr Haeusler and his colleages went on to say that in their view the fact that Britain was the ONLY country in Europe to have a TV problem was not an accident. “You have had lean governments,” Haeusler said."They have not been willing to spend the money, or take a stand, on implementing all our recommendations." Over thirty years ago, with no option to vaccinate available, Europe decided to adopt a policy of search and destroy, when TB presented itself. The TB skin test was designed to identify reactors in a herd, indicating that the herd was infected. Policy was to destroy the whole herd. Haeusler says that this was hard and painful to do, but it eliminated the disease in a very short time. No action was taken against wildlife. But at some point, Britain decided to adopt a cheaper option. Instead of eliminating the whole herd when a reactor was found, the British opted for taking out the individual animal only. This is what still happens today. The unfortunate animal is then taken to slaughter, where, very often, heartbreakingly for the farmer, it is discovered too late that the animal was in fact perfectly healthy and NOT infected with TB. This is because the skin test is not reliable. Even multiple testing leaves a margin of error. What is worse is that the cow who WAS infected possibly did not show up in the test. So it remains in the herd. After this breakdown, the herd is effectively ‘closed down’ for a while, which compounds the frustration for farmers. When business returns to normal, it is very commmon for the situation to recur. The instinctive cry, encouraged by the NFU, is then … “It’s because of those bloody badgers. So kill them”. But in fact, it is no surprise – we have seen that in all probablity the herd was never cleansed of infection – because that is virtually impossible without vaccination. The TB micobacteria can also live on in water troughs and in the soil.
Defra did a report in 2002 (CSG 15 ' Using herd depopulation for effectively controlling bovine tuberculosis') which considered depopulation as an option for the UK. It is currently done only in a few cases because of the enormous cost implications. It appears little has been done on this subject since then.
See also http://archive.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/tb/isg/report/isg3.pdf

Farming Today interviewed Professor James Wood this am and he says there's greater potential for TB to spread within larger herds. This follows a study by academics at Cambridge University that has found that up to a fifth of cattle herds with previous TB problems may be harbouring hidden infection - despite testing clear of the disease. This is why other countries use the test as it was designed - as a herd test and then depopulate. A draconian measure but if the UK/EU insists on a policy of eradication it is inevitable.
We have struggled to find the policies of other countries but the information we can find is below, much of this is from the publication; 'Mycobacterium bovis Infection in Animals and Humans'.
OVERSEAS Little information can be found.
Data from WHO revealed more than 95% o the estimated 8 million new TB cases are in developing world and only 10% are caused by M.bovis (Economics of Bovine Tuberculosis, J Zinstagg, E Schelling, F Roth and R Zuzwala). Considered imperative back in 2006 that cheaper control methods are developed! Whilst the disease is allowed to persist in some countries, in a globalised world, with falling trade barriers, there will always be the risk of spread to disease-free zones.
After AIDs TB (human form) is responsible for more deaths each year than any other single disease. 50% of new TB cases now attributed to AIDs. However, it is unknown what % bTB plays in the rising TB epidemic in Africa. Studies in Malawi show high rates of bTB are not necessarily matched by a concomitant prevalence of TB (human form). Livestock industry for most of sub-sahara Africa is significantly underproductive compared to S Africa, Asia and Europe because of all kinds of disease, including bTB. Minimal control measures in place for 35/50 African countries reporting to the OIE. Not been able to eliminate or effectively control disease; lack of co-ordinating /surveillance data. Not reporting for political, social and economic motives. Thought to be widely distributed and at high prevalence in some animal populations (spillover hosts include baboon, lion, cheetah, uda, leopard, warthog, honey badger, genet.. Also affects small ruminants, camels and many other wildlife species. Nigeria has test and slaughter policy but limited implementation. Endemic in most of eastern and southern Africa.
In contrast, S Africa's livestock productivity is comparable with developed countries. However, buffalo act as wildlife reservoir. General opinion in medical circles is that M.bovis infection as a cause of TB is of negligible significance as a zoonotic disease (Bovine tuberculosis programme in S Africa: the impact of M. bovis infected wild species by N Kriek).
Cattle are houses closer to humans and so greater risk (zoonosis). Eating habits exacerbate any transmission of bTB (eg raw/undercooked meat consumed and milk not heat treated).
Eradicated only by complete depopulation of herds infected. Restocking only with clean animals after a waiting period. Incidents involving wild boar.
One of 1st countries in world to commence programme to deal with disease (1897). Free testing (caudal fold skin test), later done via meat inspections. Found in bison, cervids. Depopulation with vacant periods before re-stocking plus extensive disinfection. Now any meat with TB lesions traced back to farm and herds depopulated (also all livestock from that farm killed and restrictions placed on neighboring farms. Still found in bison (1980's emerged). . The once enormous herds of plain bison now reduced to a handful in private ownership. Wood bison reduced to small areas of woods. Now endemic (47%) free roaming bison herds in and around Wood Buffalo Nature Park (important for tourism/hunting). In view of its location considered low risk to cattle, although expected risk will increase! Now buffer zones around wildlife parks. Also some evidence in wild elk and deer but rates fall in these animals when cattle controlled. Cattle mainly free of TB except in Manitoba but the wildlife reserves of disease threaten to reintroduce to cattle.
Many years of prevention and treat (this interesting but very little info) campaign. Still occurs spasmodically among cattle populations. Depopulation of infected herds.
Rare until 1916. Various possible (unconfirmed) reasons for this including; relatively high resistance of indigenous breed, low virulence of infective organisms or natural limitation of spread of disease, resulting from husbandry practices of cattle in India. In one study it was found that a large % of animals that test positive for TB do not develop a rapidly progressive form of the disease. Lesions in Indian cattle generally localized and restricted to a few lymph nodes. (Of course this may be the case in other countries too but all reactors slaughtered without investigation!)
TB test and segregation of reactors, with slaughter only for those showing clinical signs of disease. Eradication plan to build up clean herd (presumably using this method!?) from 20% to nil in 2.5 years. Does not seem to have been met! It states the reason for choosing a test and segregation policy may be that a high % of TB positive animals exist in several areas - wholesale destruction may reduce number of milk animals and working bullocks used as power for agricultural operations - thus unduly affecting economy of Indian agriculture! Another reason put forward is public opinion against destroying animals that look healthy! (The Status of M.Bovis in India by R Verma).
Free of TB. Control in 1959. Strict controls, slaughter of positives and also calves of infected dams. All areas disinfected. 10-15cm soil removed, sub soil disinfected.
Incidents involving wild boar
It took USA 50 years to eliminate disease from 'most' herds. Programme began 1917. It states (pg 90) 'although public and animal health were synergistic motivations for the US, the public health benefits were more from the result of pasteurisation than of reduction in the prevalence of TB in cattle. 1901-1937 M. bovis responsible for 158 (13%) of 1200 human cases of TB in US. Pasteurisation commenced 1908 and nearly eliminated human illness caused by M. bovis! 1954-68 responsible for just 6 (0.2%) of 2086 human cases of TB.Since 1917 estimated prevalence of infected cattle declined from 5% to about 0.001%. Programme focussed on individual animal testing from 1917 - 1959 (prevalence estimated as number of reactors detected by number of cattle tested in a given year). Since 1959 surveillance shifted to greater reliance on slaughterhouse inspection of carcasses. Trend is downwards.
Page 213 gives example of bull that died. It had extensive lesions when PM'd yet had tested negative in all skin tests. Its herd subsequently depopulated.
Incidents involving wild boar (N America).
24% of cattle population in the region is only partly or not controlled at all.
Other than the outbreaks in South of France this year can't find much!
Control enforced in 1954 - compulsory slaughter of bovines showing clinical signs. Initially voluntary but since 1977 compulsary for every breeding herd, except specialised an separated fattening units. 1995-2001 annual herd prevalence dropped frtom 1.3% to 0.63%. Annual single intradermal skin test (ie no avium comparison). Slaughter of reactors within 30 days, part compensated by govt. In 2003 herd prevalence 0.98% (but 5.94% in Sicilia!). 4775000 cattle submitted to periodic controls, 6573 found positive (half of these in Sicilia!). A few cases (considered insignificant) in buffalo (of 319,000, 109 positive).
In wild board reported 1930's =- sporadic cases where there are many wild boar or feral pig populations,
IRELAND no ref in book but see http://www.agriculture.gov.ie/media/migration/animalhealthwelfare/disease/tuberculosistbandbrucellosis/publicationsleaflets/Bovi...
Introduced pasteurisation in 1940 when rates of bTB declined sharply.
in 1930's around 30% of slaughtered cattle had lesions. (130 - 40 control intensified and in 1958 was one of 1st countries in the world declared OTF. Sporadic cases occurred since. The compulsory skin test was abolished in 1970, now based only on meat inspections. Only wildlife infection recorded is in 2 cases in 1940 - both in free living moose. Around 10 cases reported annually in humans but these mainly in elderly (latent infection) or immigrants. However, in 1991 diagnosed in farmed deer! 13 farms - voluntary control programme, based on TB testing, implemented July 1994, becoming compulsory in 2003. Deer farming in Sweden is popuylar, increasing in 1990's with government subsidies to promote alternative use of farmland. Deer farms with TB depopulated. As at 2005 there were 239 empty, depopulated herds and 85% had TB free status. Interestingly not spread to cattle so status not affected (so other animals can have disease and status still TB free!).
CENTRAL EUROPE (Bosnia, Herzegovina, Croatia, Czech Rep, Hungary, Poland, Slovakia, Slovenia)
1953 - 80 eliminated.
Czech - 2004 declared TB free. In these countries all reactors to single intradermal skin test are tested again 6 weeks later. Animals repeatedly positive are slaughtered.
bTB eradication programmes have had little success in countries in which transmission of of M. bovis from domestic to wild animals has led to the emergence of wildlife reservoirs of this disease. As a consequence, in many countries, persistence of bTB in cattle populations has been attributed to reservoirs of the disease in wildlife and feral animals. However, only a small proportion act as maintenance hosts (ie sustain the disease) eg bush tail possums (NZ), badger (UK, Ireland), bison (N America), deer (N America), buffalo (Africa). PROTECTION OF CATTLE AGAINST INFECTION VIA VACCINATION IS AN IMPORTANT CONTROL STRATEGY WHERE WILDLIFE RESERVOIRS PERSIST.
Depopulation is the action taken in many countries. Take a read of this extract from a recent blog at http://www.agweb.com/blog/Dairy_Talk_199/bovine_tb_study_reaffirms_need_for_national_id/
It discussed the newly published paper “Assessment of Pathways for the Introduction and Spread of Mycobacterium bovis (bovine tuberculosis) in the United States... which 'virtually goes herd by herd through the 60-some dairy and beef operations in California, Michigan, Minnesota and New Mexico that have come up TB-positive during the past decade. There are two things painfully clear after reading (OK, reading some, skimming most) this document.
A. You never, ever want your herd, your neighbor’s herd or even a herd a county over infected with TB.
B. The lack of a national animal identification program leaves the U.S. vulnerable to containing disease outbreaks, and puts the U.S. at risk of shutting down commerce if a disease more onerous than TB (think Foot and Mouth) ever is found within our borders.
First, Point A. If your herd comes up with a positive animal, you are faced with two options: Total depopulation or complete herd testing, removal of any positive animal, and a quarantine of your herd for at least four years. If your neighbor’s herd is positive, you’re at greater risk of infection due to potential fence-to-fence contact or wildlife bringing the disease with them as they move from farm to farm. If a herd a county away is infected, it’s likely your herd will face annual herd tests and may or may not be allowed to move animals without health certificates'.
Point B relates to the introduction of a tracing system - apparently 'Nineteen percent of TB-positive animals found at slaughter plants from 2001 through 2009 could not be source identified. That’s one out of five, folks'.
Email from RH 2/9/11
Read it the other day, actually I'm all for depopulation in continued breakdown herds...dare I say it.
Take our neighbour - hhe has been on restriction for 5 full years now. This year he has already lost 120 cattle out of 250.
What does he do - he keeps restocking, and keeps getting reactors - there should be restocking delays.
If you can't clear TB from your herd the whole lot goes and you're not allowed to restock for 2 years.


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