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http://www.iob.org/editorial_display.asp?edname=791.htm&cont_id=24

In My View

 

(April 2001) 

Paul V Barnett CBiol, MIBiol, PhD
Intemational FMD Vaccine Bank
Institute for Animal Health, Pirbright


Foot-and-mouth disease - the vaccine

As the United Kingdom comes to terms with its current foot-and-mouth disease (FMD) outbreak, many questions are raised, not least the current control measure of mass slaughter of animals. While slaughter is the only assured method of eradicating the virus, and therefore the resumption of export trade, is it defensible? Media comment has revealed some misconceptions about this and the alternative policy of vaccination. This is an opportunity for clarification.

FMD is an acute, highly contagious disease that affects cloven-hoofed wild and domesticated animals. It is characterised by the formation of vesicles in and around the mouth and on the feet, It reduces feeding and often causes lameness. Abortion, sterility, permanent decline in milk yield, decrease in meat production, and reduction in breeding ability are common sequelae. Mortality can result and although low for adult animals, can be higher than 50% in the young. The virus needs to be eliminated to re-establish disease-free status; failure would have serious economic consequences.

FMD can spread rapidly by several mechanisms and so it is a very difficult disease to control. The cull of all infected and in-contact livestock, the so-called 'stamping-out' policy (along with associated zoo-sanitary measures and movement restrictions) is aimed at eliminating the virus as quickly as possible. The reality of mass slaughter has raised public concern, notably as to why such actions are required when vaccines are available.

Vaccination, in whatever form, is always an option, and one that could be implemented in three major ways. Routine immunisation of animals (pan-vaccination) and/ or temporary mass vaccination utilising 'conventional' vaccine. The third method is ring vaccination around a discrete focus of infection, not adequately controlled by slaughter, using high potency 'emergency' vaccine. To understand the reluctance of the UK to initiate any vaccination measures we must reflect on the arguments that led to such a policy in this and other countries which are normally free of FMD.

Arguments for a vaccination policy

  • Assuming the most appropriate vaccine strain was used, the amount of virus in the environment and associated with livestock should be reduced.
  • Mass vaccination, particularly under circumstances of wide geographical dissemination, could be used if 'stamping-out' and associated zoo-sanitary measures failed. Where a single epicentral outbreak occurred, 'emergency' ring-vaccination could be implemented.
  • Vaccination would eliminate the need for 'stamping-out'.

Arguments for a non-vaccination policy

  • Control of disease without resorting to vaccination should lead to a quicker return to disease free status and the removal of export embargoes.
  • L'Office International des Epizootics (World organisation for Animal Health) requires countries that suffer an outbreak of FMD and which do NOT vaccinate to wait for a period of at least 3 months after the last case before they can regain their FMD free status, provided stamping out and serological surveillance have been applied. By contrast, if stamping out is not carried out and if vaccination is employed, the period until FMD free status can be regained is 24 months.1
  • If it were decided to vaccinate there would be a delay until immunity develops. Vaccination should then protect against clinical signs but not against local virus replication in the oropharynx of ruminants. If vaccinated animals are challenged by virus they can become carriers' irrespective of their immune state and can therefore be a potential source for further transmission.
  • Surveillance for the disease is easier under a non-vaccination regime, particularly where clinical signs are often obscure e.g., sheep.
  • Routine vaccination is costly, logistically difficult and labour intensive. Wild life would still be susceptible and they could harbour the virus.
  • For effective pan-vaccination, antigenic matching of the vaccine and field strains is essential.
  • Continued vaccination campaigns are considered by many countries to be an indication of uncertainty about the presence of the virus.
  • A non-vaccination policy was considered to be more economical.2
  • Non-vaccination would allow free movement of livestock and animal products.2
  • With pan-vaccination, the export trade in bloodstock to many parts of the world would be lost.

Although arguments for non-vaccination outweigh those for vaccination, the UK situation must be monitored constantly before further action is considered. The decision to vaccinate would he taken at Ministerial level with advice from the Chief Veterinary Officer and others. It remains an option if other control measures are not working. But because vaccination would isolate us from other EU members, and countries like the United States that do not vaccinate, there is an understandable reluctance to use vaccine.

References
  1. Office International des Epizooties (OIE), International Animal Health Code for Mammals, Birds and Bees, Edition 1999.
  2. Commission of the European Communities (1989) Report from the Commission to the Council on a study carried out by the Commission on policies currently applied by Member States in the control of foot-and-mouth disease. SEC (89) 1731 final, 61 pages.
Paul V Barnett CBiol, MIBiol, PhD
Intemational FMD Vaccine Bank
Institute for Animal Health
Pirbright