How the Institute for Animal Health rapidly diagnoses bluetongue

The test for antibody works for all of the 24 serotypes of bluetongue virus. It gives a result similar to that obtained in our tests for antibody against foot-and-mouth disease virus. After the test has been done using the kit of one manufacturer, if necessary we will test the samples again with a different kit to confirm the result.

Similarly, our first test for the virus’ genetic material is able to detect all of the 24 serotypes of bluetongue virus; the target is gene 1 of the virus.

This test is a real time PCR (polymerase chain reaction) test, in which a positive result can be seen on a computer screen even as the test is ongoing.

Demonstrating that the UK virus was the same as elsewhere in northern Europe

Later on the same day that the real-time PCR was used to confirm the presence of bluetongue virus in Suffolk (September 22^nd), additional PCR tests were done to identify exactly which serotype of the virus was present. The figure below shows the results obtained when bluetongue virus genetic material (RNA) from the Baylham farm was tested with reagents specific to each of the 24 serotypes of bluetongue virus. Only serotype 8 reagents gave a band of the correct size (indicated by an arrow), showing that the virus in Suffolk was of the same serotype as was in Belgium and neighbouring countries.

Sequencing the bluetongue virus’ genetic material then confirmed that the UK virus had come from Belgium or a neighbouring country.

Proof that bluetongue virus was being spread within England

The results of the antibody and genetic material tests, when considered together, are very valuable in being able to estimate when an animal actually got infected by a biting midge that contained bluetongue virus.

The blood samples from the first known cases of bluetongue in the UK (Baylham) gave results in category 2 above. Later tests on samples from elsewhere in the region gave results in category 1. They indicated that these later animals had been infected so recently that the animal’s immune system had not had time to make detectable antibodies against the virus. Most importantly, this was evidence that the virus was being spread from animal to animal, by midges, within East Anglia. By definition, England was experiencing an outbreak of bluetongue, its first.

Determining the extent of spread of the disease

In addition to testing blood samples from animals that have symptoms suggestive of bluetongue, Pirbright Laboratory also tests blood samples taken from animals in the control zone (in which infected animals have been confirmed) and in the surrounding protection zone. This helps to identify whether the disease is spreading further, and the limits to which it has spread

For more information about the outbreaks of bluetongue virus serotype 8 in northern Europe see especially http://www.iah.bbsrc.ac.uk/bluetongue/.
To speak with our bluetongue experts, contact:
Dr Dave Cavanagh at the Institute for Animal Health’s press office:
mobile 07789 941568 (message can be recorded);
office 01635 577241 (message can be recorded);
email dave.cavanagh@bbsrc.ac.uk.

* Pirbright Laboratory contains nine Reference Laboratories on behalf of various international agencies:

• World Reference Laboratory of the UN’s Food and Agriculture Organisation (FAO)
• Regional Reference Laboratory of the OIE (World Organisation for Animal Health
• Community Reference Laboratory of the EU

Each Reference Laboratory specialises in one type of virus. A reference laboratory maintains a collection of viruses and related reagents, and provides a diagnostic service.

• Bluetongue: OIE, EU
• African swine fever: OIE
• African horse sickness: OIE, EU
• Foot-and-mouth disease: FAO, OIE, EU
• Swine vesicular disease: OIE, EU
• Lumpy skin disease: OIE
• Sheep and goat pox: IE
• Peste de petits ruminants: FAO, OIE
• Rinderpest: FAO, EU