An extract (see below) from a recent Freedom of Information request reveals there is obviously concern regarding co-infection and cross-reactions relating to Johne's disease. I wonder what percentage of cattle are killed because of this disease - particularly as I understand over 50% of the herds here are infected with this disease? See http://www.fwi.co.uk/Articles/06/01/2010/119362/Strategy-to-eradicate-Johne39s-disease-needed-now.htm Results from a DEFRA study released at the conference estimated up to 42.5% of UK dairy herds were infected with MAP when sampled in 2006. "It is likely the figures have carried on rising since then," commented Mr Cutler.
Defra is co-funding a new research project SE3270 “Development of novel diagnostic strategies for the ante-mortem immunodiagnosis of bovine tuberculosis and Johne's Disease” which is a cross-Europe project looking at developing improved diagnostics for both diseases and also examining the problems caused by co-infection and cross-reactions. Details of this project will appear on the http://randd.defra.gov.uk/ website when they are finalised
23 Apr 2013, 9:37 AM
Rethink BovineTB askes - 'Is Johnes the real enemy for Dairy Industry?'
Source: tweet dated 22/04/13
23 Apr 2013, 9:35 AM
... and in an article in the Farmers Weekly 15 October 2012 (http://www.fwi.co.uk/articles/15/10/2012/135745/johne39s-disease-affecting-herds39-lifetime-yields.htm) it is clear that Johnnes disease is now in 60-70% of UK dairy herds according to Ben Bartlett, NMR business development manager. Speaking at Sixways Stadium in Worcester in October 2012, he explained how results from a 2011 NMR study of 710 herds, which showed 73% of herds had one or more cows test positive for the disease. He said studies into the origin of infected animals found about 25% had been brought in.
"The risk of spreading disease is far greater than it has been in the past," he added.
"The suspicion is that Johne's will affect the immunity system with the cow, so she is going to be more susceptible to infections," he added.
So, Johnnes' disease, as well as compromised the sensitivity of the tuberculin skin-test to detect bovine tuberculosis, also lower the immune system so cattle are more susceptible to disease - including, presumably, bovine TB.
Abstract The single intradermal comparative cervical tuberculin skin-test (SICCT) remains the primary surveillance tool to diagnose bovine tuberculosis (BTB) in the UK. Therefore, understanding the potential confounding influences on this test is important. This study investigated the effects of vaccination against Johne's disease (JD) on the immunodiagnosis of BTB using a Mycobacterium bovis BCG vaccination model as a surrogate of M bovis infection. Calves were vaccinated with either BCG (an attenuated live vaccine) or the JD vaccine, Gudair (a heat-inactivated suspension of Mycobacterium avium subspecies paratuberculosis), or a combination of both, and SICCT responses were measured approximately six and 12 weeks postvaccination. Animals vaccinated with Gudair only were negative to the SICCT test, thus supporting the specificity of the SICCT test following Gudair vaccination. However, while animals vaccinated with BCG-only demonstrated a bovine tuberculin-biased response as expected, covaccination with Gudair resulted in a bias towards avian tuberculin in the SICCT test. Therefore, our model demonstrates the potential of the Gudair vaccine to reduce the sensitivity of the SICCT. In addition, while we also demonstrate that Gudair vaccination can compromise the specificity of serological tests to detect JD, the specificity of defined M bovis antigens in serological or interferon gamma-based blood assays was not compromised by the vaccine.
Rethink Bovine TB @Rethinkbtb 7h #askDefra @DefraGovUK @AHVLA Does Johnes Disease Vacc comprise performance of Tb Skin Test and how?
Defra UK @DefraGovUK 7h hi @Rethinkbtb @AHVLA Johnes vacc does compromise skin test by increasing avian response #askdefra
Rethink Bovine TB @Rethinkbtb 7h @DefraGovUK @AHVLA How could this effect the performance of skin test? More false negatives?
No answer to this from Hewinson but if Johns Vacc increases avian response then it effectively reduces sensitivity of skin Test which means less likely to pick up positives. 1:42 PM - 18 Apr 13 ·
27 Apr 2012, 1:48 PM
Interesting snippet in Issue 50, Spring 2012 Highland Cattle Club of wales Newsletter - part of a report from the British Cattle Breeders Conference Telford, January 2012. It seemed to be in connection with export requirements
"It was confirmed that TB an Johnes, although different diseases, are from a similar family, and as a consequence a Johnes blood sample must be taken before a TB test is initiated or there is a small chance of obtaining a Johnes 'false positive' result."
Johne's disease is also caused by Mycobacteria. In reality know one knows how Johne's disease influences the bTB skin test and it may well be more than admitted. This could be important, particularly as Johne's disease is in more than 50% of UK herds, and the skin test is the sole indication of bTB levels.
10 Apr 2012, 10:28 AM
Extract from page 14 of the BOVINE TB ADVISORY GROUP - Department of Environment, Food and Rural Affairs - April 2009 BOVINE TB – THE FACTS
Q11. Is TB testing compromised by the presence of Johne‟s disease?
A11. Yes. Exposure to Johne‟s disease can cause cross reactivity when using the skin and gamma interferon tests for bovine TB.
Background: Johne‟s disease, caused by infection with the bacterium Mycobacterium avium subspecies paratuberculosis (abbreviated „MAP‟) is a chronic and insidious disease of cattle and other ruminants which is believed to be endemic in the UK and many other countries worldwide. It is well known that exposure of cattle and other animals (including man) to MAP and environmental mycobacteria can cause cross reactivity to components of the bovine PPD tuberculin used in the skin and gamma interferon tests for bovine TB. In particular, this reduces the specificity of the single tuberculin skin test (in the neck or the caudal fold) in TB-free herds infected with (or vaccinated against) MAP.
In the UK and Ireland, however, responses to the test reagent avian-PPD are used alongside the bovine PPD tuberculin in the routine screening test for bovine TB to provide a comparative measure of cattle exposed to non-pathogenic environmental mycobacteria. Hence the higher specificity of the comparative skin test over the single test. The same principle applies to the Bovigam test, where optical density levels of gamma interferon released by white blood cells stimulated with avian tuberculin are subtracted from those measured in blood stimulated with bovine tuberculin.
We have no direct data on the effect of (MAP) infection on the sensitivity of the comparative skin and gamma interferon tests for bovine TB in GB. Experimental studies in calves pre-sensitised with M. avium subspecies avium (a bacterium closely related to MAP) have shown that raised responses to avian tuberculin in the comparative skin and gamma interferon tests may mask the detection of M. bovis infection, even when the specific antigens (ESAT-6 and CFP-10) are employed (Howard et al. 2002, Hope et al. 2005). In Spain, Aranaz et al. (2006) studied a herd with both MAP and bovine TB infection that was followed up for 3.5 years. The comparative tuberculin skin test, gamma interferon assay and a serological test for MAP were used in parallel. Overall, the skin test detected 65.2% of all animals in the herd that were culture-positive for bovine TB and the gamma interferon test detected 69.6% of them. These percentages are in the lower part of the accepted normal range. Both the skin test and the gamma interferon test were able to detect bovine TB-infected animals in the first part of the trial, but the blood test was the only test able to detect such animals in the last three tests.