Statutory and Exotic Bacterial Diseases

The Statutory and Exotic Bacterial Diseases Programme provides surveillance and research of notifiable animal bacterial diseases.

The Statutory and Exotic Bacterial Diseases Programme supports Defra in protecting human health by providing surveillance and research activities focused on notifiable animal diseases caused by bacteria. Reference Laboratory responsibilities continue to form an important part of the strategic development of the Programme. The main areas of activity are bovine tuberculosis, brucellosis and mycoplasmosis; other areas include anthrax, contagious equine metritis, glanders and paratuberculosis.

Bovine Tuberculosis (TB)

Cases of bovine TB continue at a historically high rate and our substantial activities in this area have again reflected the importance Defra places on tackling this economically damaging zoonotic disease. Much of our work over the last ten years has been to support the Independent Scientific Group, whose final report was published in 2007. The VLA’s contribution, both surveillance and research, was fully recognised in this report and the Defra-commissioned Science Audit.
Several of our laboratories were again involved in mycobacterial culture and diagnosis. As in previous years, cattle samples predominated, but deer survey samples and submissions from other domestic and more exotic species continued to form an important part of the culture and molecular typing requirement.

Molecular typing data was used to construct ‘home range maps’ which reflect the geographical clustering of most Mycobacterium bovis genotypes in Great Britain. These maps can be used to identify quickly the spread of TB due to cattle movements. This is an important time for deciding on the future directions for both culture requirements during herd breakdowns and culture methodologies. This is the focus of one of several Defra reviews which will be reported on during 2008 and to which the VLA are contributing.

We are always looking to improve diagnostic approaches and this year saw the publication of important collaborative work on the use of PCR to detect M.bovis in cattle lesions and in the environment. These tests are now undergoing further validation as recommended by the OIE.
We also reported the development of blood tests for diagnosing TB in both cats and camelids.

The gamma interferon gamma (IFN-γ) test in cattle is now a well established assay at the VLA and our work has highlighted how the test can support the existing tuberculin skin test in clearing infections in both high and low risk areas of Great Britain.
We expect to continue developing this test especially as TB vaccine research progresses and the requirement for tests to differentiate infected from vaccinated animals (DIVA tests) becomes an important factor in deciding whether a vaccine could be deployed or not.

The difficult decisions that Defra has to face regarding culling badgers as a practical, humane and sustainable means of controlling cattle TB has thrown into high relief the potential importance of vaccine development and its application in wildlife and cattle. This whole area of work is set to be of particular importance for VLA over the next few years and we are currently working on several long term studies on cattle and badgers, with well established collaborations worldwide.

This year saw VLA publish the development of a gamma interferon test for badgers which is being used to underpin studies required to licence BCG for use in badgers. Significant progress was also made on cattle vaccines where potential markers of protective immunity were identified along with promising vaccine candidates that improve on the protection conferred by BCG.

In collaboration with the Sanger Institute and the Institut Pasteur we also identified the full range of point mutations present in the different strains of BCG. This information will help underpin the development of DIVA tests and improved BCG-based vaccines.

We have strengthened our links with several institutes in Africa through Wellcome Trust funding and this is providing a superb opportunity for studying the effects of different farm management practices on TB risk, sample generation (particularly for isolates and molecular epidemiology studies) and technology transfer.

Brucellosis

We are fortunate to be free of brucellosis in Great Britain, unlike many other countries where it remains an economic and human health burden. Monitoring this disease free status is by monthly milk sample testing, using VLA milk ELISA reagents and serological surveillance.

Defra reduced brucellosis testing considerably in 2007, with more reliance now placed on abortion investigations from all animal species. These are carried out at our Regional Laboratories and suspect isolates are sent to Weybridge for confirmation.
We work with modern molecular approaches to help understand the diversity and evolution of the brucellae and to identify useful markers, allowing us to develop novel diagnostic and epidemiological tools. A particular focus has been extensive sequence analysis of the group. This has provided a framework for identifying a number of novel brucella groups and identified pivotal sequence changes that have been used to design rapid diagnostic assays.

As an OIE Reference Laboratory, FAO and WHO Collaborating Centre, we are often approached by other organisations to help with their national control and eradication plans. This usually involves disease and test consultancy, laboratory workshops and design, provision of reagents, technical advice, methodology and control strategies. We train international visitors and intend to continue hosting workshops in the future. We have provided PCR reagents and technical support particularly to Armenia, Kyrgyzstan and Tanzania in exchange for material to use in our test development and validation exercises. As part of an OIE initiative we are proposing a twinning status with a national laboratory in Korea.

Collaboration with the Health Protection Agency remains important to us and this year we confirmed 18 isolates from humans in the UK who had become infected while travelling abroad. We also verified three cases of naturally acquired infection with marine mammal strains of brucellosis, possibly due to consumption of raw fish rather than association with marine mammals.

Mycoplasmosis

The reputation of our Mycoplasma Group continued to grow during the year with excellent reports received from the Science Audit and Defra’s Review of its Statutory and Exotic Disease Programme which are evaluated by international experts.

Mycoplasma mycoides subsp. mycoides SC, the cause of the OIE listed disease contagious bovine pleuropneumonia (CBPP), is remarkably homogeneous with few molecular typing tests capable of differentiating strains. We analysed the recently sequenced genome of the PG1 type strain and identified three variable number tandem-repeats (VNTR) which enabled us to classify 38 geographically diverse strains into 12 groups. VNTR analysis represents a new rapid tool for subtyping M.mycoides SC isolates which will be valuable for epidemiological tracing of outbreaks.

We have developed simple pen-side tests for the serological detection of CBPP and contagious caprine pleuropneumonia (CCPP). The tests BoviLAT and CapriLAT, based on latex beads coated with specific carbohydrate antigen, are available through VLA and can be performed rapidly in the field (with whole blood) or in the laboratory (with sera).

We confirmed an outbreak of severe CCPP in gazelles in a wildlife park in the Middle East, which saw high levels of mortality. The disease was previously thought to be restricted to goats and other small ruminants.

Mycoplasma bovis, a frequent isolate from pneumonic lungs, was detected in milk samples from several mastitic herds and a case of otitis. Increasing detections of Mycoplasma (formerly Eperythrozoon) wenyonii were made in blood samples from diseased cattle.

During the next year we hope to:

• complete experimental trials for our vaccine against Mycoplasma bovis using our calf pneumonia model.
• see the publication of the group-authored text entitled ‘Mycoplasma Diseases of Ruminants’.
• further our research on the role of biofilm in the pathogenicity and survival of important mycoplasmas.