Estimation of the specificity of an antibody ELISA for paratuberculosis generated from a sector of the UK cattle population using results from a paratuberculosis control programme.

In the United Kingdom (UK) a voluntary programme to control paratuberculosis in cattle based on herd management and serological screening has been operating since 1998. The programme assigns a risk level to each participating herd according to the within herd seroprevalence and the confirmation of the presence of infection with Mycobacterium avium subspecies paratuberculosis (MAP) by faecal culture or polymerase chain reaction (PCR). From the outset a general concern over the specificity of the paratuberculosis antibody enzyme-linked immunosorbent assay (ELISA) resulted in the use of a faecal screen for the causal organism to negate or confirm infection in individual seropositive animals. Progress in improving the diagnostic tests has been gradual throughout the life of the programme and the under-pinning approach to using tests to determine the risk of paratuberculosis for a herd required to be re-examined. This study used a large data set of more than 143,000 test results over five years from the lowest paratuberculosis risk level category of herds to estimate the specificity of a commercially available paratuberculosis antibody ELISA for cattle. In each year of the study the estimated specificity reached or exceeded 0.998. We also examined the apparent impact that annual or more frequent application of the single intradermal comparative cervical tuberculin (SICCT) test for tuberculosis (TB), using purified protein derivatives of Mycobacterium bovis and Mycobacterium avium subspecies avium, had on specificity of the antibody ELISA for paratuberculosis. We found a statistically significant difference in three of the five years with herds that were officially tuberculosis free and not subject to frequent SICCT testing. This difference was small and considered to be of little practical importance for the paratuberculosis assurance programme. We concluded that, in the UK the mandatory TB surveillance programme of cattle herds is not a limiting factor in the use of serological testing to support herd-level assurance schemes for paratuberculosis. Furthermore, in paratuberculosis, where shedding of MAP is intermittent and the sensitivity of the commercially available PCR tests for detection MAP is highly variable, faecal screening of seropositive animals is an unreliable method for negating infection in seropositive cattle.

Counterintuitive increase in observed Mycobacterium avium subspecies paratuberculosis prevalence in sympatric rabbits following the introduction of paratuberculosis control measures in cattle.

Paratuberculosis (Johne's disease) is caused by the bacterium Mycobacterium avium subspecies paratuberculosis (Map). Achieving herd-level control of mycobacterial infection is notoriously difficult, despite widespread adoption of test-and-cull-based control strategies. The presence of infection in wildlife populations could be contributing to this difficulty. Rabbits are naturally infected with the same Map strain as cattle, and can excrete high levels in their faeces. The aim of this study is to determine if implementation of paratuberculosis control in cattle leads to a decline in Map infection levels in rabbits. An island-wide, test-and-cull-based paratuberculosis control programme was initiated on a Scottish island in 2008. In this study annual tests were obtained from 15 cattle farms, from 2008 to 2011, totalling 2609 tests. Rabbits (1564) were sampled from the 15 participating farms, from 2008 to 2011, and Map was detected by faecal culture. Map seroprevalence in cattle decreased from 16 to 7.2 per cent, while Map prevalence in rabbits increased from 10.3 to 20.3 per cent. Results indicate that efforts to control paratuberculosis in cattle do not reduce Map levels in sympatric rabbits. This adds to mounting evidence that if Map becomes established in wild rabbit populations, rabbits represent a persistent and widespread source of infection, potentially impeding livestock control strategies.

Factors associated with bovine neonatal pancytopenia (BNP) in calves: a case-control study.

Bovine neonatal pancytopenia (BNP; previously known as idiopathic haemorrhagic diathesis and commonly known as bleeding calf syndrome) is a novel haemorrhagic disease of young calves which has emerged in a number of European countries during recent years. Data were retrospectively collected during June to November 2010 for 56 case calves diagnosed with BNP between 17 March and 7 June of the same year. These were compared with 58 control calves randomly recruited from herds with no history of BNP. Multivariable logistic regression analysis showed that increased odds of a calf being a BNP case were associated with its dam having received PregSure® BVD (Pfizer Animal Health) vaccination prior to the birth of the calf (odds ratio (OR) 40.78, p<0.001) and its herd of origin being located in Scotland (OR 9.71, p = 0.006). Decreased odds of a calf being a BNP case were associated with the calf having been kept outside (OR 0.11, p = 0.006). The longer that a cattle herd had been established on the farm was also associated with decreased odds of a calf in that herd being a BNP case (OR 0.97, p = 0.011).