Foot-and-mouth disease is a highly contagious viral disease that affects more than 70 species of domestic and wild animals, including cattle, pigs, sheep, and goats. The virus cannot be transmitted to humans, but it causes considerable economic losses when infectious outbreaks occur on farms. Although the mortality rate associated with the disease remains relatively low, infected animals are weakened and spread the virus. The disease is mainly found in Africa, Asia, the Middle East, and certain South American countries. Western Europe is free of FMD. Characterising the strains circulating in the countries concerned is essential for combating the disease: “Vaccines against foot-and-mouth disease do not offer protection against several strains at the same time” explains Sandra Blaise-Boisseau, a scientist in the Joint Research Unit (UMR) for Virology at ANSES’s Laboratory for Animal Health. “As there are around 60 strains, we need to know which one is responsible whenever a new outbreak occurs”.
Strict transport conditions due to the contagiousness of the virus
To identify strains, samples must be sent from the areas where they are taken to the reference laboratories, which can safely carry out the necessary analyses. Most of these laboratories are located in Europe and North America, which means that samples may have to be transported over long distances. ANSES is the reference laboratory for FMD for France, the European Union, the World Organisation for Animal Health (WOAH), and the Food and Agriculture Organization of the United Nations (FAO). As such, it regularly receives samples for analysis. The transport protocol is strict: “Samples have to be packed with dry ice, respecting the cold chain and using triple packaging to prevent contamination” affirms Aurore Romey, from the same Virology UMR at ANSES. “Some countries don't have the resources to apply this protocol and therefore don’t send in their samples. We've also had situations where it took several weeks to find dry ice. When we received the samples, they were too damaged and we weren’t able to isolate the virus”.
An antigen test converted into a transport medium
As part of these reference mandates for WOAH and the FAO, ANSES has developed an alternative transport protocol that is quick and easy to implement and costs less than the standard protocol. The Agency's scientists based their work on materials already used for collecting samples when FMD is suspected: “Antigen tests, similar to self-tests for COVID, are used in the field” explains Sandra Blaise-Boisseau. “They can tell within a few dozen minutes whether animals have foot-and-mouth disease, but they don't indicate the strain involved. We therefore wondered whether this test medium could be used to transport samples to diagnostic laboratories”.
First of all, the possibility of recovering the virus and identifying the strain from the deposit on the test was confirmed. However, as the virus is infectious, it must first be inactivated before it can be transported. To achieve this, the Agency's scientists tested several disinfectants known to be effective against the FMD virus. They chose citric acid diluted to 0.2%. The chosen concentration inactivates the virus, rendering it incapable of infecting cells, while preserving enough of its genetic material to identify the strain to which it belongs at a later date.
Successful field trials
This method was tested in real-life conditions in Nigeria and Turkey. Pakistan also took part in the trials, using samples from its collections. “Each country sent us 20 samples. Our laboratory confirmed the presence of the FMD virus in all cases. The serotype involved, which constitutes the first level of strain characterisation, was identified for 86% of the samples. When we went further in terms of characterisation, the strain was identified for 60% of the samples” exclaim the scientists. For certain samples, the entire genome was preserved. “That's a real bonus! To identify strains, fragments of the genome are sufficient. But with the complete RNA, we were able to carry out what we call ‘virus rescue’”. In practical terms, this involves producing a live, infectious virus in vitro from its RNA, after introducing this RNA into animal cells. Having a live, infectious virus provides a way to test, in particular, whether a vaccine is effective against a new strain.
This work was funded by the FAO's European Commission for the Control of Foot-and-Mouth Disease (EuFMD), which recognised the usefulness of the method when the standard transport protocol cannot be used. It asked ANSES to test the method with brands of antigen tests other than the one used in the initial study. This work is ongoing.