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(The paper below is posted on the European Livestock Association and warmwell websites at the invitation of Dr Paul Sutmoller. August 2007 )


Control and eradication of Foot and Mouth Disease

 

Paul Sutmoller, Simon S. Barteling, Raul Casas Olascoaga and  Keith J. Sumption

Virus research 91 (2003) 101-144

 

Summary of conclusions

 

 

FMD Virus infection

 

 

Transmission of FMD virus

  •         Large-scale animal movements create a special hazard regarding the spread of FMD.
  •         Transport of FMD infected animals and hauling of infected carcasses must be done in sealed containers to prevent escape of virus.  Rendering of FMD-infected carcasses must be done under strict bio-safety conditions
  •  

  •         People can be efficient mechanical transmitters of FMD, in particular if they go from farm to farm and carry out clinical examinations.

  •         Protective clothes and heavy rubber gloves must be worn when handling contaminated materials, particularly infected animals and cadavers.

  •         Sanitary disposal of contaminated clothing and gloves is essential.

     

    Airborne diffusion of FMD virus

     

     

    FMD virus dissemination by wildlife and vermin

     

  •         Vermin might spread FMD from infected premises, particularly when cleaning and decontamination have eliminated normally available feed sources

     

    Persistent infection with FMD virus

     

  •         In epidemiological terms a "carrier" is a persistently infected animal able to disseminate that infection, yet remain clinically without symptoms of the disease. The FMD "carrier" does - with the exception of the African buffalo - not fit that definition because so far there is no real proof that it is contagious.

  •         The carrier state often occurs in FMD convalescent animals, particularly in cattle and the Cape buffalo. The duration of the carrier state depends on the individual animal, animal species, and virus strain. Among the domestic species the largest number of carriers occurs in cattle followed by sheep and goats. Pigs or camelids do not become carriers.

  •         Vaccination by itself does not cause the carrier state. A vaccinated animal must be exposed to FMD virus to become a carrier. Vaccination suppresses the amount of FMD virus in the environment and thus the (final) number of carriers in the population.

     

    FMD Vaccination

     

     

    Vaccine banks

     

     

    Differentiation between FMD-infected animals and  vaccinated non-infected animals

     

  •         EITB tests and ELISA measuring a-NSP antibodies are useful serological indicators of current and past infection.

  •         These tests are not 100% sensitive in individual animals, but perform very well if used for screening on a herd basis; combinations of tests can raise the sensitivity yet further.

  •         Viral isolation (probang) tests and PCR to detect viral RNA can be used to confirm the presence of persistent infection in individual animals. The significance of the detection of viral RNA by PCR remains to be determined.

  •         Vaccines prepared from presently available highly purified FMD antigens - like those in vaccine banks - will in combination with tests for antibodies against non-structural proteins perform like a "marker" vaccine. Vaccines prepared from purified antigens will not induce antibody to NSP that interfere with the interpretation of the serological surveys. 

  •         Tests to discriminate between carriers and vaccinated animals have been widely used and the results are, in general, internationally accepted.

  •         Serological surveillance - after vaccination - for anti-NSP antibodies does not require bio-security laboratories.

  •         If an FMD outbreak is controlled by vaccination, testing for antibodies against non-structural proteins amongst vaccinated livestock contributes to risk reduction.

  •         International experience and data from around the world show that, after emergency vaccination, efficient screening programs can be designed to determine the prevalence of a-NSP positive animals. The risk of (vaccinated) carriers not detected by such screening programs is very low.