How is the presence of liver fluke affecting the testing for bTB? Research has shown that it does encourage false results when testing for bTB. The wet summers of the past few years have encourages liver fluke and it is now believed to be in a high percentage of herds.
18 Oct 2012, 6:06 PM
Badger Trust Press Release 'Liver fluke soars to disrupt test results'
As MPs prepare to debate badger killing next Thursday (October 25th) two developments show how bovine tuberculosis (bTB) is rooted in cattle.
· At least a fifth of cattle herds and possibly a half may be harbouring bovine tuberculosis (bTB) even after they are thought clear of infection, according to a Cambridge University research article . Worse, there is greater potential for TB to spread within the larger herds which are now becoming more prevalent. These conclusions further justify urgent introduction of cattle as well as badger vaccination
These conclusions emphasise that the effect of cattle-to-cattle contact is even greater than previously thought and so wildlife culling is even less significant.
· A second problem has been the massive increase in liver fluke which affects the accuracy of the standard test for bTB. This parasite is carried by snails and both thrive in warm, wet summers. Up to a third of cattle with bovine tuberculosis (bTB) could be missed by the standard test for the disease if they are also carrying the parasite, hampering the eradication programme according to research by Prof Diana Williams of Liverpool University . This carried forward work published in May last year by the Veterinary Sciences Division of the Agri-Food and Biosciences Institute of Northern Ireland .
The Badger Trust says both these revelations oblige the Coalition to abandon the killing of badgers until the comparatively enormous reservoir of disease in herds is cleared and to introduce compulsory annual testing of all cattle with the more sophisticated techniques now available such as the interferon-γ(IFN) . The killing of a protected wildlife species is even less relevant.
The Cambridge team estimates that there is a high rate of re-introduction particularly in high incidence areas. The authors add that the high rate of external infection, both through cattle movements and environmental sources, must be addressed if recurrence is to be reduced.
The team’s results are in line with the main conclusion of the £50 million Randomised Badger Culling Trial of 1998-2007: while badgers are implicated in bTb, killing them could make no meaningful contribution to its control, and that weaknesses in cattle testing regimes mean that cattle themselves contribute significantly to the persistence and spread of disease in all areas where TB occurs. It added that in some parts of Britain cattle were likely to be the main source of infection and called for the rigid application of cattle-based control measures .
'It has been known for some time that the skin test for BTB loses sensitivity when cattle are infected with liver fluke. In a paper published last week (Fasciola hepatica is associated with the failure to detect bovine tuberculosis in dairy cattle) www.nature.com/ncomms/journal/v3/n5/full/ncomms1840.html it is claimed that the loss of sensitivity may be so high that one third of infected cattle are not being detected in areas with high liver fluke occurrence. The authors go on to suggest that this may be causing entire areas, not just individual cattle or herds, to be falsely deemed of low incidence, with resultant spread of infection.
Rethink suggest that a further factor in the spread of BTB has been unmasked – the unwillingness of Defra to consider evidence if it upsets established views. Instead of hurrying to study the paper and consider the implications, Defra have (according to the BBC www.bbc.co.uk/news/science-environment-18118124 ) dismissed the research adding:
"The absence of positive cases of bovine TB in some areas co-inciding with large amounts of liver fluke cannot be used to claim liver fluke is hiding cases, as cattle carcasses are inspected in abattoirs and we would see evidence of TB in the slaughtered animals if this was the case."
If they had read the paper they would realise that is only part of the argument, and anyway other work quoted by the authors has suggested lesions may also be suppressed.'
24 May 2012, 8:24 PM
Dont agree that the treatment of liver fluke is complicated.I have treated cows at drying off with a product called Fasinex for a couple of years.If there is a product with a 3 day witholding period for milk,I dont see that as much of a problem for treating an individual cow showing signs of fluke.Most vet meds have some milk witholding time,often longer than 3 days. Ironically,I was told by a ministry vet 2 years ago that liver fluke could cause a false positive result for TB,which is one of the reasons Ive really tried to get on top of it.Fluke should be treated anyway,as it reduces milk yield and quality.Plus off course anything that attacks the liver is no good for the overall health of the cow.
24 May 2012, 1:31 PM
Email from RH dated 22/5/12 saying 'just one thought, obviously fluke like wet warm area's the west of england and wales are wet and warm where is the worst TB cases ??? = well wouldn't you know it ... plus I think probably TB does well in those conditions too.'
... and summary in Nature www.nature.com/news/bovine-tb-disguised-by-liver-fluke-1.10685, with interesting extracts below:
'Bovine tuberculosis (bTB) could be spreading across Britain because the most widely used test for the disease is ineffective when cattle are infected with a common liver parasite.'
'The liver fluke Fasciola hepatica was already known to affect the standard skin test for bTB, but it was unclear whether the fluke stopped the disease developing or merely hid the symptoms. A study published today in Nature Communications suggests that the latter is more likely, and that the effect is significant. It estimates that around a third of bTB cases in England and Wales are undiagnosed because the test is less sensitive in cattle infected with the fluke'.
'Researchers tested milk from dairy herds across England and Wales for antibodies against F. hepatica, an indication of infection, and added the data to an existing model of bTB transmission. If they assumed that a fluke infection inhibited bTB detection, they achieved a closer match between the model and actual bTB detection rates. The authors suggest that the fluke may alter the production by T lymphocytes — key cells in the immune system — of the protein interferon-γ, which is crucial to a genuine result in both the skin test and the second most common test for bTB, the interferon-γ release assay (IGRA) blood test.'
'Eradicating liver fluke could increase the sensitivity of the skin test and allow better control of infected cattle, but this poses its own difficulties. Farmers can keep cattle away from damp fields that are home to the fluke’s snail host, but treating infected dairy cattle is complicated. In 2010 the European Union (EU) banned most flukocide drugs because they leave toxic residues in milk. The milk from cows that receive the remaining two allowed drugs is undrinkable for three days after treatment.'
'Although more experiments are needed to confirm the precise interaction between flukes and the skin test, Dirk Werling, an immunologist at the Royal Veterinary College in Hatfield says there could be implications beyond cattle. Human liver flukes are rife in tropical and sub-tropical regions, and bTB causes 10% of human tuberculosis deaths in Africa.'
'Liver fluke could also explain epidemiological mysteries, such as why bTB has never gained a foothold in north-west England. “Our knowledge has holes in it,” says William Wint, an ecologist at the University of Oxford, UK, who has become frustrated by the badger-centric debate. “If this can make people look more at epidemiology than politics, that would be marvellous.”'
24 May 2012, 1:26 PM
... and here is the report 'Fasciola hepatica is associated with the failure to detect bovine tuberculosis in dairy cattle' at www.nature.com/ncomms/journal/v3/n5/full/ncomms1840.html
Abstract Bovine tuberculosis (BTB) is a significant and intractable disease of cattle caused by Mycobacterium bovis. In the United Kingdom, despite an aggressive eradication programme, the prevalence of BTB is increasing with an unexplained, exponential rise in cases year on year. Here we show in a study involving 3,026 dairy herds in England and Wales that there is a significant negative association between exposure to the common, ubiquitous helminth parasite, Fasciola hepatica and diagnosis of BTB. The magnitude of the single intradermal comparative cervical tuberculin test used to diagnose BTB is reduced in cattle experimentally co-infected with M. bovis and F. hepatica. We estimate an under-ascertainment rate of about one-third (95% confidence interval 27–38%) among our study farms, in the hypothetical situation of no exposure to F. hepatica. This finding may in part explain the continuing spread of BTB and the failure of the current eradication programme in the United Kingdom.
24 May 2012, 1:23 PM
www.bbc.co.uk/news/science-environment-18118124,'Parasite may aid cattle TB spread', interesting extracts below.
'The spread of an animal parasite across the UK may be hampering moves to curb cattle tuberculosis, research suggests.'
'Scientists have known for a few years that cows carrying both TB and the fluke Fasciola hepatica are less likely to show positive on the normal TB test.'
'Now researchers have shown that this could lead to a reduction of one-third in the detection of infected cattle.'
'It has been known since at least 2006 that under experimental conditions, infection with F. hepatica lowers a cow's reaction to the skin test. The 3cm long parasite fends off the cow's natural defence mechanisms by "turning down" its immune system.
"We started this work thinking that infection with the liver fluke might make animals more susceptible to pathogens that are normally controlled by an inflammatory immune response, and TB is the obvious one to think about," said research leader Diana Williams from the University of Liverpool. We were surprised, because we suspected there would be a TB increase in cattle infected with fluke; but what we found from the data was a negative association - more fluke, less apparent TB."
'Their conclusion is that the sensitivity of the test in picking up TB infection is reduced in areas where lots of cows carry liver fluke.'
'If the chances of detecting TB through the skin test really do go down by a third, as the researchers conclude, that would mean infected cattle are not being detected during routine testing - which in turn means they can infect other cows in the same herd and be eligible for transport from farm to farm.'
24 May 2012, 1:14 PM
KL sent us the following links that shows many other links - what is clear from reading these is that liver fluke is very common indeed. www.afbini.gov.uk/search.lsim?qt=bovine+tuberculosis+test+2012+liver+fluke&sr=0&nh=10&cs=iso-8859-1&sb=0&hs=0&sc=& oq=bovine+tuberculosis+test+2012&ha=afbi-cms&mt=1
http://www.ucd.ie/vetmed/newsevents/title,116266,en.html Rojas and Golden's image 'Casual Parasitic Encounter' captures the common liver fluke, Fasciola hepatica, which is a well-established parasite of livestock in Ireland, it is estimated that 80% of cattle herds show evidence of infection. The fluke can survive for long periods in the mammalian host aided in part by a targeted manipulation of the immune response. Their research group studies this manipulation by the liver fluke and has discovered that in cattle, response to co-infection by Mycobacterium tuberculosis, the cause of bovine tuberculosis, can be masked. “Casual Parasitic Encounter” shows a cross section of the liver fluke stained with antibodies from animals given their experimental vaccine
21 May 2012, 1:21 PM
Look at Defra's 'Bovine TB - The Facts' document, (http://archive.defra.gov.uk/foodfarm/farmanimal/diseases/atoz/tb/documents/tb-facts.pdf) pages 12 and 13 which discusses liver fluke under 'Compromising Factors for TB Testing' and concludes that '... fluke, through compromising immunity might make animals more susceptible to infection and/or might make infected animals less likely to react to the skin test (infected animals may therefore be missed)'.
So yet again we have what could be a vital area, that has not been researched properly.
R Bennett et al, Economic Assessment of Livestock Diseases in Great Britain, 2003 estimated that liver fluke affects 377 cattle per 1,000 head.12 Since then it has worsened as weather changes. In some abbatoirs up to 50% of cattle are seen to have fluke damage.
21 May 2012, 12:30 PM
A report by This is Somerset (www.bovinetb.co.uk/forum_topic.php?thread_id=8&page=1) refers to new research which could pour cold water on Government claims linking badgers with the spread of bovine TB. The research, which comes from the Government’s own scientists, suggests that rather than the badgers spreading the disease, cows could be carrying TB for years without detection, spreading it to other members of their herds.
The warning comes in two reports from the Agri-Food and Biosciences Institute, Northern Ireland, a leading research centre. One, already published, warns the tests used for TB often produce negative results if cattle are co-infected with liver flukes. This is because the flukes secrete hormones that suppress the immune response on which the TB test depends.
21 May 2012, 12:23 PM
Interestingly a recent report in This is Somerset (http://www.thisissomerset.co.uk/Somerset-badger-cull-plans-cattle-spreading/story-16143800-detail/story.html) mentions two reports from the Agri-Food and Biosciences Institute, Northern Ireland, a leading research centre. One, already published, warns the tests used for TB often produce negative results if cattle are co-infected with liver flukes. This is because the flukes secrete hormones that suppress the immune response on which the TB test depends.
A report in the Veterinary Record July 17th 2010, under the Surveillance section (during May 2010) highlights the high incidence of liver fluke in cattle herds in England and Wales. The incidence of liver fluke (fasciolosis) seen in the first quarter of the year remained high following the increase seen between 2007 and 2009. This was reflected in the 20% condemnations of bovine livers reported by the Meat Hygiene Service in the first quarter of 2010.
5 Jul 2010, 6:22 PM
Interestingly the summer of 2008 was exceptionally wet and so greatly benefitted the life-cycle of the liver fluke and its intermediate snail host. In fact diagnostic figures produced by the Veterinary Laboratories Agency (VLA) for acute liver fluke in sheep provided good evidence that it increased substantially over this period. Between 2004 and 2007 the percentage of submissions (sheep) diagnosed with acute fasciolosis was less than 1% but in 2007 it was 3% and in 2008 over 4%. Acute infection in the autumn usually precedes chronic infection in cattle and sheep for the rest of the winter. Interestingly we see that in Wales there were more cattle slaughtered after failing the TB test in 2008. The numbers are now coming down.
2 Mar 2010, 6:38 PM
Interesting - we have had several different vets and Animal Health testers over the last 2 years testing our herd and some have suggested we treat for liver fluke.
2 Mar 2010, 6:37 PM
Interesting information sheet Bovine Tuberculosis and Fasciola hepatica infection (Veterinary Laboratories Agency) by JM Broughton and others (www.svepm.org.uk/posters/2009/Broughan;%20Bovine%20tuberculosis%20and%20Fasciola%20hepatica%20infection.pdf) which concludes that the risk of an animal having confirmed TB decreased in the presence of liver fluke anti-bodies but increased if flucicide had been given in the past year. It goes on to say that this suggests that dairy cattle that have been exposed to liver fluke but untreated are more likely to give false positive reactions in the SICTT, and are thus less likely to have infection with M.bovis confirmed despite being classified as reactors (by the skin test). Liver fluke antigens, it says, are potent stimulators of T-helper (Th2) responses. Possibly infection with liver fluke modulates this inflammatory response to the SICTT leading to a lower predictive value of the test. It suggests these findings need further investigation as the literature suggests that sensitivity is increased.
There is no evidence to suggest that liver fluke is the reason why more cattle are showing up as IRs or reactors! However, there may be a small likelihood of false positive skin tests in fluke infected cattle that are not regularly treated. This is because fluke infection stimulates or turns up the Th2 response, the helper T cell response, in the bovine immune effort to control fluke. This is the same response as is detected in a TB skin test, the T helper cells invading the skin where the TB antigen is deposited, causing an indurated lump.
Interesting to see that only 5 of your cattle revealed any signs of lesions. Despite a compulsory testing regime for some fifty years we are no further forward with controlling the disease. Its status in any area is based solely on the results of a test that has not really changed since it was originally developed and that many now believe may not be as reliable as is claimed. For example, just how accurate and up to date is the scientific data behind the claims of its sensitivity and positive productive value? A high percentage of cattle slaughtered (such as your situation and we have the same situation here too with our herd) have no evidence of disease and whilst reasons are given for this, they seem weak and open to challenge.
I would be interesting to hear more about your reference to the continuous exposure to m.bovis excreted from free ranging wildlife and the proof you have for this. I believe strongly that the wildlife reservoir issue is not as significant as claimed. Over the last decade or so the cattle/badger link seems to have occupied a disproportionate amount of time and resources. The bacteria that causes bTB is endemic in the environment so it is likely to remain in our pastures and gardens. Badgers are not the only mammal susceptible - what about cats - more numerous and likely to be in closer proximity? Will they be the next target? A ministry tester we talked to during one of our tests was convinced they posed a greater risk than badgers.
After 50 years of compulsory testing and a continued failure to even control the disease in some areas (despite the slaughter of supposedly infected cattle and badger culls in some areas) isn't it about time for farmers and their unions to be campaigning strongly for a vaccination for cattle and and the necessary change in EU legislation to facilitate. Vaccination has been successfully used over the last fifty years to control human form of TB and its efficacy would appear to be similar to the claims made for the existing system.
It is difficult to verify how stringent the testing system is in other countries. Certainly in the EU countries are keen to maintain TB free status to protect exports. It is not really about human health or animals welfare. Disturbingly, no account is taken of the intolerable burden for many farming families, particularly those that experience herd breakdowns, the constant testing (a very time consuming process for which the farmer is not reimbursed) the severe stress, the emotional loss of cattle and welfare issues involved, the businesses that suffer, the financial consequences of being on stop for long periods of time, the increased health and safety implications from increased cattle handling, the inflexible bureaucracy and the need for expensive equipment - but you would, of course, be aware of all this. I doubt it would be tolerated in any other sector but most farmers are held to ransom because of fear of losing income from subsidies.
27 Dec 2009, 4:46 PM
So if we dose cattle with flukicide there'll be fewer (or no) TB reactors or IRs. Is that what you're saying?
Been there done that. Ditto, with BVD, a previous condition thought to influence test results. Hate to burst your bubble but it doesn't work - and it's a pretty wide ranging assumption for those of us who do look after our cattle. We had a closed herd, vaccinated for BVD annually and fluked for the last 3 years. We've also had eight years under almost continuous restriction now, around 70 cattle shot of which just 5 have had very early, closed V Lesions. The rest had had continuous exposure to m.bovis excreted from free ranging ' wildlife'.
Very little influences the results of the skin test. If it did, no other country would have been able to clear its cattle herds using it, and keep them clear. It shows exposure to the bacteria which causes tb - m. bovis. And that in enough quantity to provoke a cellular immune response. (Just 70 units is enough and a badger with kidney lesions excretes up to 300,000 units in just 1ml of urine, and void 30ml at each squirt)
The skin test does not show disease or any indication that full blown TB will develop. Around 50 percent of cattle slaughtered as reactors, IRs or DCs will have no visible lesions, and be incapable of culture. That doesn't mean the test is flawed. It is doing what it says on the tin. Showing exposure to something which has no business plastered across our pastures and gardens.
Slaughtering sentinel tested cattle is a most friutlessly stupid and wastefully expensive exercise, if the cause of their exposure is left to continue infecting all mammals which happen to cross its path. And it is the owners of those spillover victims, who assume quite wrongly that 'bovine' TB only affects cattle, and 'cattle are killed anyway' (we know that because the Badger Trust told us) who will jerk this crazy situation up the political agenda.
Matt @ www.bovinetb.blogspot.com
26 Dec 2009, 8:39 PM
If so why is there so many TB breakdowns in Shropshire an area of low fluke and low rain fall ,as apposed to Gwynedd with high rain fall and high levels of fluke and as yet few TB breakdowns. Although the traditional Welsh Black would have some resistance to fluke the various continentals which dominate in that region don't,and if your theory is correct there should be a lot of reactors in and around the Snowdonia national park ,which has the wettest terrain in the Principality.:-(