General

Axel Heiser on foot-and-mouth disease

29 July 2022
Axel Heiser on foot-and-mouth disease

The spectre of Foot-and-Mouth Disease (FMD), and the devastating impacts an outbreak would have for New Zealand, looms large as other countries in the region grapple with outbreaks.

While the actual risk of this animal disease spreading to New Zealand from the current outbreak zone in Indonesia is not considered high, and it is reassuring to see it being treated with utmost seriousness by our authorities; it is unnerving nonetheless for people to see news reports such as those out of Australia recently about viral fragments being detected in imported food products (though these are not infectious and FMD has not spread into Australia at the time of writing this piece).

The impact of FMD becoming established in New Zealand cannot be underestimated, with a significant economic shock and losses estimated in the area of $16 billion over four to five years as food exports are heavily affected. There will be a massive impact from mass culling of farmed animals on the wellbeing of farmers, those in rural communities and the general public.

On the positive side, New Zealand does have the benefit of access to a body of international research on FMD, as well as significant expertise in livestock infectious disease and crisis management to draw on. The recent experience with Mycoplasma bovis, while at a different scale to what FMD may present, also helps in the preparation for any outbreak in NZ.

So, what do we know about FMD?

FMD is one of the most devastating diseases affecting the meat and dairy industry globally. It is caused by the FMD virus (FMDV) that infects cattle, sheep, goats, pigs, deer and other cloven-hoofed animals. Symptoms of lesions in the mouth and on the hooves, excessive drooling, fever, decreased appetite, and weight loss are most significant in young animals where mortality is 20% or higher.

The FMDV spreads easily through contact and airborne transmission and quickly infects entire herds. The virus can also be transmitted via farming equipment, shoes, clothing, vehicle tyres and more.

Why is it so potentially damaging?

Once it enters New Zealand, FMD likely spreads rapidly, before it is even detected. Its presence will have a significant impact in terms of New Zealand’s trading partners halting imports of our animal products.
Even a small and local outbreak would affect the whole of New Zealand.

Control of the disease would likely be attempted by culling all animals on infected premises, potentially neighbouring properties, and by strict animal movement controls. The response would continue until FMD is eradicated, which will be confirmed by nationwide testing.

Reaching freedom from disease will take months after a small outbreak, and much longer after a large outbreak.

Testing for FMD

Confirmation of the infection needs to be performed in specialised laboratories that meet strict requirements for containment of the virus. The commonly used tests are PCR and serotyping. The genetic code of the FMDV is RNA which can be directly detected using so-called real-time reverse-transcription (RT)-PCR.

Usually, two separate highly sensitive RT-PCR assays are used to detect two different regions of the RNA genome.

Another direct detection is concurrent virus isolation in cell culture systems and subsequent whole genome sequencing. In contrast to the direct detection by PCR, serotyping detects the immune response against the virus, specifically the antibodies made by infected animals.

These antibodies are detected by measuring the binding of the antibodies to parts (proteins) of the FMDV by enzyme-linked immune-absorbance assays (ELISA). This kind of test is also used to certify animals for import/export and provide evidence for absence of infection.

Can the disease be treated or vaccinated against?

No treatments for infected animals are currently available.

Around the world inactivated, wild-type FMDV vaccines are used to control FMD outbreaks. They are produced using large amounts of infectious FMD viruses, which bears the risk of virus escape from manufacturing facilities or incomplete inactivation during the manufacturing process. Many attempts to develop better vaccines for FMD that are not inactivated virus have failed to induce sterile immunity.

Testing and vaccines

FMDV vaccines and natural infections with FMDV both induce antibodies that bind to the virus, specifically proteins and other large molecules (as building blocks of the virus). The serological tests cannot usually separate these responses, making infected animals indistinguishable from vaccinated ones. Also, the RNA in inactivated FMDV vaccines can result in positive PCR results. This is the reason that there are market restrictions for FMDV vaccinated animals.

The issue can be avoided by developing combinations of vaccine and diagnostic test using different antigens. They are called ‘differentiation of infected and vaccinated animals’ (DIVA), but so far none are available for FMD.

The research response

Due to biosafety concerns, there has been no research on live FMDV in New Zealand. However, AgResearch’s Animal Health Solution Team are among those experts prepared to assist the lead biosecurity agency, the Ministry for Primary Industries, with FMD eradication efforts, including the development and validation of tests.

Our team at AgResearch, working closely with partners, is involved in the control of bovine tuberculosis by providing routine blood testing, PCR and culture of tissue in our PC3 specialist laboratory and whole genome sequencing. It is developing new diagnostic tests for the detection of Mycoplasma bovis and other pathogens.

It has also been developing veterinary vaccines in the past that are now commercially available and used throughout New Zealand. More recently the team has conducted research around vaccines against bovine TB, bovine mastitis, ovine pneumonia, and mastitis. It is also developing a novel platform utilising micro-RNA for veterinary diagnostics.

The more research that can be done in the infectious disease space, the better we will be prepared for any highly damaging disease outbreaks.

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