This image of a pig snout demonstrates the effects of foot-and-mouth disease.

New tools for foot-and-mouth disease diagnosis

CSIRO scientists have produced recombinant antibodies against foot-and-mouth disease (FMD) and used them in a test able to differentiate vaccinated from infected animals.

• 20 June 2008 | Updated 14 October 2011

• The issue
• What CSIRO did
• Results
• Acknowledgments

CSIRO researchers have developed the first foot-and-mouth disease (FMD) test that can both:

• identify all seven strains of the virus in a single test
• distinguish between unexposed, vaccinated and infected animals.

The issue

Economically, foot-and-mouth disease (FMD) is the most important viral disease of livestock worldwide.

The FMD outbreak in the United Kingdom in 2001 was the largest in history, causing losses of more than eight billion pounds sterling (approximately A$19 billion) and devastating the country's livestock and tourism industries.

The mass culling of animals to control a FMD outbreak results in enormous livestock losses and is viewed by many as an unacceptable practice. 

Incorporating vaccination into the control strategy can reduce these losses, however it complicates the process of establishing freedom from disease following an outbreak, as standard tests can't distinguish between vaccinated and infected animals.

Quality diagnostic tests to differentiate infected from vaccinated animals (termed DIVA) are needed in order to demonstrate disease freedom and allow trade in livestock products to resume.

With such tests, vaccination can be used more effectively, allowing the option of vaccinating to live.

FMD vaccines consist of chemically inert, semi-purified virus depleted of most of the non-structural proteins.

The presence of antibodies to non-structural proteins will indicate exposure to live replicating virus and will only be present in animals naturally infected with FMD virus, not those that have been vaccinated.

Diagnostic tests that can identify and differentiate between antibodies to structural FMD virus proteins and non-structural FMD virus proteins are mainly enzyme-linked immunosorbent assays (ELISAs) incorporating antigens (viral proteins) and monoclonal or polyclonal antibodies in an indirect or blocking format.

All current FMD virus DIVA tests rely on antibody reagents (materials) conventionally produced through animal immunisation or hybridoma cell lines. It can be difficult to prepare and maintain these antibodies in a quality-assured manner and in the large quantities that would be required for post-outbreak surveillance.

Recombinant antibodies, on the other hand, can be produced in large quantities at low cost, genetically tailored according to need.

Further advantages of recombinant antibodies are:

• no need for infectious virus
• no need for the use of laboratory animals
• costly maintenance of hybridoma cell lines is no longer required.

What CSIRO did

CSIRO researchers at the Australian Animal Health Laboratory (AAHL) in Geelong, Victoria, generated chicken recombinant antibodies to the FMD virus non-structural protein 3ABC using gene technology.

The recombinant antibodies were evaluated in a competitive ELISA (C-ELISA) format with blood samples from pigs, sheep and cattle that were either:

• naïve (no exposure to virus or vaccine)
• FMD virus-infected or
• FMD virus-vaccinated.

Results

Chicken recombinant antibodies paired with a bacteria-derived recombinant 3ABC non-structural protein (antigen) were able to differentiate infected from vaccinated animals in a C-ELISA.

This represents the first serological test in which both the detecting antibody and the coating antigen are derived from a bacterial host and thus can be produced safely and economically.

The test can identify naïve, vaccinated and infected animals in different species for all seven serotypes (strains) of the virus.

Further evaluation with larger numbers of different blood samples is required to validate the C-ELISA for routine diagnostic application.

Acknowledgements

Blood samples used in this study were kindly provided by:

• Institute of Animal Health, Pirbright, United Kingdom
• Plum Island Animal Disease Center, New York, United States of America
• Regional Animal Health Centre, Ho Chi Minh City, Vietnam
• Central Institute for Animal Disease Control, Lelystad, the Netherlands (now the Central Veterinary Institute)
• AAHL, Geelong, Victoria, Australia.

This project was funded in part by the Australian Biosecurity Cooperative Research Centre (CRC) under the project titled: Application of new platform technologies for the development of protein-based rapid multi-analyte detection tests.

Learn more about  Dr Hans Heine: improving diagnosis of animal disease.