International recognition
for new NZ-developed molecular test to determine infectious bovine rhinotracheitis (IBR) status of bovine semen for international trade
By Jianning Wang; Joseph O'Keefe; Susan Cork; Della Orr, Animal Health Laboratory, IDC
Scientists at the Animal Health Laboratory of the Investigation and Diagnostic Centre, Wallaceville, have developed a new molecular test for detection of infectious bovine rhinotracheitis (IBR) virus in bovine semen. This test has been accepted by the World Organisation for Animal Health (OIE) as a prescribed test for international trade, and has opened the way for a resumption of New Zealand exports of bovine semen to Europe.
IBR is caused by a bovine herpesvirus and is an economically important disease of cattle. Several different strains of herpesvirus infect cattle. Bovine herpesvirus type 1 (BoHV-1) causes IBR and infectious pustular vulvovaginitis/balanoposthitis (IPV/IBP). This virus can be transmitted via respiratory and genital routes, and by artificial insemination with virus-contaminated semen.
BoHV-1-infected bulls may potentially shed virus intermittently in their semen, long after the primary infection. Therefore, cattle infected with BoHV-1 are regarded as lifelong carriers and potential shedders of the virus. BoHV-1 is endemic in New Zealand.
Test required for trade
For international trade, it is frequently required that no IBR virus is present in bull semen. Virus isolation using a cell culture system is used routinely and is an OIE-prescribed test. This procedure can take weeks to complete, however. It is laborious and can lack sensitivity. Moreover, technical difficulties may be encountered with virus isolation in examination and interpretation of test results, due to the toxic effects caused by the semen in cell culture.
Previously, the European Union (EU) accepted a negative virus isolation test as being sufficient for the importation of bovine semen. This changed in December 2004, because of concerns raised by some researchers about the low sensitivity of the virus isolation test. From 1 January 2005, only semen from IBR sero-negative bulls may be exported to the EU. There was a need, therefore, for a more sensitive method to be developed that could be acceptable to the EU.
Real-time PCR test proposed
At that time, there was no internationally accepted polymerase chain reaction (PCR) test available for this purpose. (The PCR test is of superior sensitivity and specificity when compared with virus isolation.) This lack of an acceptable test potentially put the New Zealand bovine semen export trade in jeopardy. To address this, we proposed an alternative diagnostic method, a real-time PCR test, which is at least twice as sensitive as virus isolation from semen.
International acceptance of this PCR procedure required approval by the OIE. The development of the test was funded by MAF and Livestock Improvement Corporation (LIC). Before the test could be used, it had to be validated to meet specific criteria for assay validation by the OIE. Validation also included an inter-laboratory ring test using an agreed protocol and well-designed test samples. This required extensive collaboration with other laboratories, including OIE reference laboratories in the EU.
International collaboration to validate test
Scientists at the Animal Health Laboratory (AHL) have been collaborating on this project with scientists from eight countries in Europe and North America since 2005. Six laboratories from five countries, including the OIE Reference Laboratory for IBR at Weybridge (United Kingdom) and the OIE Collaborating Centre for PCR at Uppsala (Sweden) were involved in the validation of the new test. Representatives from participating laboratories met twice in the United Kingdom and New Zealand to exchange technical information and review results. They compiled a complete test validation dossier, which was submitted to the OIE for accreditation.
The new PCR test was first approved by the OIE Biological Standard Commission in September 2006, and ratified by the OIE as a prescribed test for international trade at its 75th General Session of OIE in May 2007. This is the first real-time PCR assay that has been approved as a prescribed test for international trade, and also the first New Zealand-developed diagnostic test accepted by the OIE.
The success of this project has raised IDC's technical profile internationally. It is also an international endorsement of the quality of the diagnostic methods used by New Zealand to facilitate trade.
New Zealand effort recognised internationally
New Zealand's efforts and achievement in this field have been well recognised and appreciated internationally. Dr Malcolm Banks, the head of the OIE Reference Laboratory at Weybridge, described the work as "a long road" and offered congratulations for having "the initiative to begin and the determination to complete this difficult job". Dr P Thoren, of the OIE Collaborating Centre for Molecular Diagnostics in Sweden, described the study as "a very good example of successful and meaningful cooperation".
Dr Jianning Wang presented the results of this project at the seventh International Congress of Veterinary Virology in Portugal in September 2006, where he also met with the President of the OIE Biological Standard Commission and the President of the European Society for Veterinary Virology. They both highly appreciated New Zealand's efforts and the outcome of this project. The project results have been published in the international journals of virology and microbiology.
Recently, the European Commission notified MAF that the suspension of intra-community trade in semen imported from New Zealand between 2004 and 2007 had been withdrawn, as it was considered there was no significant IBR risk. The suspension was lifted following the negative IBR results of samples of semen, using the newly developed test.
For further information on exports of germplasm:
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Page last updated: 30 April 2008