Dy = Day of vaccination; Dx = Onset of immunity

Animals vaccinated with an inactivated vaccine can be traded at these times:
• 14 days after the onset of immunity if a virus test is negative at that time
• At the onset of immunity if the animal was grazing on pasture within a seasonally BTV-free zone and during a seasonally vector-free period for at least 60 days before vaccination

†Seasonally BTV-free zone during a seasonally vector-free period

Category 3: Animals not vaccinated but having natural immunity (from a BTV exposure)

An immune animal that tests serologically positive can be traded at these times:
• 60 days after the first positive serological, test if a second serological test is positive at least 7 days before movement
• 30 days after the first positive serological, test if a virus test is negative at least 7 days before movement

Summary and Conclusion

A dramatic increase in the number of BTV outbreaks in Europe, along with the presence of the virulent BTV 8 serotype, has caused the EU to tighten restrictions on trade in ruminants in BTV-affected areas.

For producers to engage in transport and sale of ruminants, it is essential that the animals be proved BTV-immune or BTV-negative. Protection from Culicoides midges, vaccination against BTV disease and regular serological screening for BTV are necessary for controlling the disease and limiting economic losses.

References:

1. European Commission, Directorate General for Health and Consumers. Bluetongue restriction zones as of 18 July 2008. Available at: http://ec.europa.eu/food/animal/diseases/controlmeasures/index_en.htm. Accessed 24 July 2008.
2. See the following European Commission documents for specific regulations: Commission Regulation (EC) No 1266/2007 of 26 October 2007, Commission Regulation (CE) No 384/2008 of 29 April 2008, and Commission Regulation (EC) No 394/2008 of 30 April 2008.

Pourquier* Bluetongue Blocking ELISA

The Pourquier Bluetongue Blocking ELISA accurately detects BTV antibodies in sheep, cattle, goats and other ruminants. The assay can be used to determine the immune status of animals before slaughter or before transport from BTV-affected zones.

The Pourquier BTV assay is based on the VP7 structural protein, which is specific to BTV. The VP7 protein is very well conserved and induces a strong immune response, making it easy to detect.

Results are expressed as a ratio of the optical density (OD) of the samples to the mean OD of the negative control:

Validation tests demonstrate 100% sensitivity and specificity in tested populations.

The assay detects all 24 known BTV strains (including BTV 8, which can kill both sheep and cattle).

Sensitivity and Detectability

A total of 116 samples were taken from animals known to be infected with BTV. Results from all sera were strongly positive, well below the 35% cutoff.

In 2006, EU ring trials showed the Pourquier assay to detect BTV in sheep at 8 days postinfection (dpi) and in cattle beginning at 9 days dpi.1

Specificity

A total of 151 samples were taken from animals in areas known to be free of BTV. Results for all 151 sera were strongly negative, well above the 45% cutoff.

Serological Testing Helps Ensure Safe Trade in BTV-Affected Areas

You can use the Pourquier Bluetongue Blocking ELISA with confidence to:
• Screen nonimmune animals to determine their BTV status and detect disease early.
• Save money on vaccine by screening for immunity. There is no need to vaccinate naturally immunized animals.
• Monitor the efficacy of vaccinations and confirm the onset of immunity.
• Determine the immune status of animals before slaughter or trade.
• Confirm the negative status of animals protected from BTV exposure.

Features of the Pourquier Bluetongue Blocking ELISA Kit

• Comes with 2, 5 or 10 plates.
• Detects all 24 known BTV serotypes.
  
   

  BTV 1	BTV 5	BTV 9	BTV 13	BTV 17	BTV 21
  BTV 2	BTV 6	BTV 10	BTV 14	BTV 18	BTV 22
  BTV 3	BTV 7	BTV 11	BTV 15	BTV 19	BTV 23
  BTV 4	BTV 8	BTV 12	BTV 16	BTV 20	BTV 24

   
• Works with either serum or plasma.
• Gives definitive results; no additional testing is needed.
• Supported by IDEXX technical service expertise at no extra charge.
• Can be used with IDEXX xChek* Information Management Software (as a user-defined assay) for data interpretation.

For more information about the Pourquier Bluetongue Blocking ELISA or to place an order, please contact your local Institut Pourquier or IDEXX Representative.

References:

1. Batten CA, Bachanek-Bankowska K, Bin-Tarif A et al. Bluetongue virus: European Community inter-laboratory comparison tests to evaluate ELISA and RT-PCR detection methods. Vet Microbiol. 2008;129:80–88.

Testing the Calibration of a Microplate Reader

It is good laboratory practice to periodically test the calibration of your microplate reader. IDEXX checks the calibration of its readers using calibration test plates. Calibration test plates can be purchased from most reader manufacturers or from laboratory equipment providers.

Important: The calibration plate must be calibrated for the wavelength you normally use for testing (e.g., 630, 650, 450 nm). The calibration can be performed by the manufacturer of the calibration plate.

It is easy to run a calibration test plate and to print the results.

Using xChek* software:
 
1. Start the xChek software and log on.
2. Turn on the plate reader, and place the calibration plate in the holder.
3. From the File menu, select Read.
4. Choose an assay you normally use, then select the “blank” template (you may need to scroll to the end of the template list to find the “blank” template).
5. Click OK twice.
6. After the data is displayed, display the data in Plate View.
7. From the File menu, select Print.
8. Select Plate View, then click OK.
9. Using the printout, compare the optical density (OD) values for specific wells to the OD values on the calibration plate test card for the wavelength used.

Without using xChek software:
 
1. Turn on the plate reader, and place the calibration plate in the holder.
2. Make sure the reader is connected to a printer.
3. Read the plate, using the most commonly used wavelength (one that matches the wavelength specified for the calibration plate).
4. Compare the OD values for specific wells to the OD values on the calibration plate test card for the specified wavelength.

If the values are out of the expected range, consult the reader manual or the reader manufacturer for steps to take.

Please contact your local IDEXX Representative if you have questions on calibration plates or where to purchase them.

Events Around the World

• Upssala, Sweden—September 16–19, 2008
  7th International ESVV Pestivirus Symposium
  www.pesti2008.org 
  
  
• Bad Staffelstein, Germany—September 17–19, 2008
  AVID
  www.dvg.net 
  
  
• St. Paul, MN, USA—September 20–23, 2008
  Allen D. Leman Swine Conference
  www.cvm.umn.edu/outreach/events/adl/home.html
   
• Lleida, Spain—September 23, 2008
  AVEDILA Symposium
  www.avedila.com/avedila/
   
• Charlotte, NC, USA—September 25–27, 2008
  41st Annual Conference of the American Association of Bovine Practitioners (AABP)
    www.aabp.org
   

See the following documents to learn more about updated BTV regulations and about BTV disease:

COMMISSION REGULATION (EC) No 384/2008 of 29 April 2008

COMMISSION REGULATION (EC) No 394/2008 of 30 April 2008

COMMISSION REGULATION (EC) No 1266/2007 of 26 October 2007

To learn more about bluetongue virus, see chapter 2.1.3, “Bluetongue”, in Manual of Diagnostic Tests and Vaccines for Terrestrial Animals 2008 by the World Organisation for Animal Health.

*Pourquier, HerdChek and xChek are trademarks or registered trademarks of IDEXX Laboratories Inc. or its affiliates in the United States and/or other countries.