Statutory and Exotic Bacterial Diseases
Richard Clifton-Hadley Statutory and Exotic Bacterial Diseases Programme Manager
The Statutory and Exotic Bacterial Diseases Programme provides surveillance services and research to support Defra in protecting human health by early detection and control of principally notifiable animal bacterial diseases. Reference Laboratory responsibilities in the main diseases are also an important part of the programme.
Bovine Tuberculosis (TB)
A broad range of surveillance functions
for bovine tuberculosis, including post
mortem examination of various farm and
wild animal species, routine use of the
IFN-
test at Regional Laboratories (see
feature article on page 14), mycobacterial
culture and molecular typing of all
Mycobacterium bovis isolates were carried
out during the year. Although most
samples received were from cattle, there
was a growing awareness of the risks of
TB in deer, cats, badgers, pigs, llamas and
alpacas.
Laboratory at VLA Starcross
M.bovis isolates, collected by VLA over the last 10 years, have provided a basis for understanding the population biology of M.bovis in Great Britain. This data has indicated that the strict clonality of M.bovis has moulded the distribution and population structure of bovine TB in the British Isles. The practical implications of applying this knowledge is to understand the spread of infection and the development of improved vaccines and diagnostic tests.
VLA continues to run the international spoligotyping database through its membership of VenoMyc, an EU network focusing on TB and Johne’s disease. This typing data, cattle movement information and a joint project with the Environmental Research Group, Oxford using predictive models, have enabled us to demonstrate the impact of cattle movement taking disease into nonendemic areas and pre-movement testing on disease incidence.
Mycobacterium bovis
VLA’s status as the World Health Organisation Collaborating Centre on Brucellosis has been extended for a further four years.
The risk to human health from M.bovis was highlighted this year when we supported the Health Protection Agency (HPA) in investigating a cluster of six human cases in young, UK-born people. With the exception of the index case, there was an absence of zoonotic links or history of consuming unpasteurised dairy products, suggesting that person-toperson transmission had occurred.
Diagnostic kit for Brucellosis
Vaccine studies in cattle and badgers have been on-going in collaboration with many institutes throughout the world. We have now evaluated a number of TB vaccine candidates, currently in safety trials for human use, for their ability to protect cattle against bovine tuberculosis. In collaboration with the Institut Pasteur and the Sanger Institute we described the genome sequencing, genealogy and expression analysis of Bacille Calmette- Guérin (BCG), which will help underpin research aimed at improving the vaccine efficacy of BCG.
The first stage of the Badger BCG Vaccine Field Study has been successful, which is an important step towards the licensing of BCG for use in badgers.
Grey seal (Halichoerus grypus)
Brucellosis
Brucellosis remains a severe human health hazard and economic burden in many countries. VLA‘s role is to carry out disease surveillance to maintain UK’s disease free status, carry out confirmatory tests for human Brucella isolates on behalf of the HPA and, as part of our International Reference Laboratory function, provide expert advice. VLA’s status as the WHO Collaborating Centre for Reference and Research on Brucellosis has been extended for a further four years and formal collaborations have been agreed with the Pendik Institute, Istanbul and the Istituto Zooprofilattico Sperimentale in Sicily.
Marine mammal isolates, collected over a 12 year period, were used in an extensive study using molecular techniques and standard phenotypic methods. Results indicated that the group can be divided into three subtypes with preferred hosts and that all three naturally acquired human infections with marine mammal Brucella were caused by an identical genotype. This highlights the possible enhanced zoonotic potential of this genotype.
Many brucellosis vaccines for livestock, trigger immune responses that are indistinguishable from field infection making them incompatible with test and slaughter based control policies. Two candidate DNA vaccines, with significant protective effect against B.melitensis, have been identified at VLA. These novel vaccines evoke an equivalent protective effect as the live B.melitensis vaccine but have the advantage of being non-live, antigenically defined, therefore posing no risk of infection to an intended or accidental recipient and able to trigger immune responses that can be discriminated from those invoked by field infection.
A panel of recombinant proteins has been identified, which has the potential to improve the specificity of brucellosis immunodiagnostic assays. Research has been focused on combining these improved assays in order to reduce the impact of false positive results. These assays may also have the capacity to measure infection-specific profile results that are distinguishable from responses induced by vaccination.
Pen-side testing in Namibia
Mycoplasmosis
Contagious caprine pleuropneumonia (CCPP) is a serious disease of goats in Africa and the Middle East with outbreaks recently confirmed close to the European border.
Research studies involving comparative genomics and shotgun sequencing of this organism have revealed a number of potential virulence factors, adhesion related genes and over 50 surface expressed lipoproteins. Improvements to culture media and the development of ‘pen-side’ tests will enable us to rapidly identify outbreaks of disease.
Biofilm studies of the causative agent of contagious bovine pleuropneumonia, Mycoplasma mycoides subsp. mycoides SC, have demonstrated that adherence to a surface and formation of a biofilm enclosed in a polysaccharide layer may not only help the organism to persist both in the environment and the host, but may result in altered gene expression affecting the virulence of the organism. Fundamental studies of this type have never been undertaken in mycoplasmas before.
Significant improvements to our existing diagnostic techniques have been achieved with the development and improvement of the polymerase chain reaction/denaturing gradient gel electrophoresis (PCR/DGGE) test. This technique has enabled us to detect and
differentiate over 70 Mycoplasma species and to dramatically decrease the time taken to identify Mycoplasmas directly from tissue. New and unusual Mycoplasma infections have been identified including M.canadense, previously diagnosed only twice in the last twenty years and the non-culturable Mycoplasma wenyonii.
In 2006, VLA hosted the International Organisation for Mycoplasmology Congress at Cambridge, attracting 270 delegates from 31 countries. The Agency’s international reputation has been further enhanced by the OIE designating VLA as the Reference Laboratory for contagious agalactia and by entering into formal collaborative agreements with the Instituti Zooprofilattico Sperimentale in Teramo, Lazio and Sicily.
Anthrax/Contagious Equine Metritis Organism (CEMO)/ Glanders/Johne’s Disease
Surveillance for these diseases has continued and a confirmed case of CEMO and one confirmed and several suspected anthrax submissions have underlined this requirement. An outbreak of anthrax in the Scottish Borders and other related issues were discussed by the InterLab Forum to test our readiness to respond to this type of emergency.
In collaboration with the Scottish Agricultural Colleges and the Department of Agriculture and Rural Development, Northern Ireland, we have been undertaking a prevalence survey in dairy herds for Johne’s disease. Results are expected early next year.