In the piece posted on our website on 11th October we show the timeline for our rapid laboratory diagnosis of FMD during phase 1 and 2. Here we outline and illustrate the technologies that we use.

 

Rapid diagnosis at the Institute for Animal Health (IAH) is an important contribution to Defra’s management of the outbreak: time is of the essence. Since the 2001 outbreak of FMD in the UK, the IAH’s scientists have introduced new technologies that have speeded up the diagnostic process and enabled quick genetic fingerprinting of the virus on each affected farm.

 

IAH has not only developed a suite of tests for rapid diagnosis of FMD (within an hour, with confirmatory results within four hours), but we are also able to get a genetic fingerprint of the virus within 24 hours. This enables the identification of the particular type (strain) of FMD virus involved, to a very precise degree. This can help to identify the origin and route of spread of the virus during an outbreak.

 

IAH laboratory diagnosis when animals on a farm are showing signs of disease e.g. blisters on the tongue

 
Test 1 -

The first test that we apply uses technology (a lateral flow device) similar to that of a home pregnancy test. Our test detects FMD virus particles; if FMD virus is present then a red band forms. We get a result within about an hour of samples from a farm getting into the laboratory.

 
lateral flow device

Results from the 2007 FMD outbreak.
The lower red line in the samples above show that they contain FMD virus.
The upper red line in both samples is a positive control.
 

We do not rely just on one test. Whilst the lateral flow device test is underway, we embark on four additional tests.

 
Test 2 - This is another test to detect FMD virus particles. In this test the yellow colour indicates that virus is present.

Test 3 - A test for the virus’s genetic material (which is RNA). 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.
Real time genetic detection (PCR test) of FMD virus
 

Tests 2 and 3 usually give results within four hours of receipt of samples in the laboratory, as was the case in the recent UK outbreaks. If test 3 is positive, we sequence the genetic material of the virus to give a genetic fingerprint. This tells us precisely what type (strain) of FMD virus it is, which enables us to build a picture of how the virus spread.

 
genetic fingerprint sequence data
The precise type (strain) of FMD virus is determined by genetic fingerprinting.
This figure shows some actual sequence from a sample from the first infected premises of the 2007 outbreak.
 
Test 4 - We test blood samples for the presence of antibodies to FMD virus, getting the results within 24 hours.
Test 5 - We inoculate cells cultured in the laboratory with sample tissue e.g. from blisters on the tongue of an animal, to see if any FMD virus grows in them. This procedure is not as quick as the others but it is very sensitive. It is especially useful if the earlier tests are negative. If the cell culture test also gives a negative result then the animals are accepted as not being infected with FMD virus.
 

IAH laboratory diagnosis when animals on a farm are NOT showing signs of disease

 

We not only test animals that have obvious signs of FMD e.g. blisters on the tongue; we also investigate animals that might be in an early stage of infection (pre-clinical stage). For this we use the test for the virus’s genetic material (which is RNA; Test 3 above), starting with blood samples. This test is so sensitive that it can detect the small amounts of FMD virus that are present in the bloodstream at an early stage of infection. (Tests 1 and 2 are not sensitive enough to detect virus particles before disease is obvious).

 

This pre-clinical genetic material test is used in a number of situations. Some farms have a number of holdings that are not contiguous. If animals on one holding have been confirmed as having FMD, animals on the other holdings are tested. Other high risk farms such as those neighbouring an infected area are also tested with this technique.

 

The value of genetic fingerprinting

 

The genetic material (RNA) test gives a product that can be sequenced to obtain the genetic fingerprint of FMD virus from each farm. This sophisticated data can provide a highly accurate and probabilistic picture of the likely spread and transmission of the disease in the field. Of particular interest currently are theories as to whether the virus has continued to circulate in Surrey or was a new introduction of FMD virus. The genome sequence data permit the best value judgement of the possibilities, as the number and type of mutations within the genetic code can offer important clues to epidemiologists who need to determine the routes and timings of infection in an outbreak.