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Control

How FMD is best managed depends on (1) the epidemiological situation and (2) rural development policies (livestock development and wildlife conservation in particular) in the locality (region or country) concerned. Generic international standards and recommendations are available on the OIE website (www.oie.int – Animal Health Code for Terrestrial Animals; FMD chapter) but these cannot cover all situations throughout the world. For that reason, management of FMD ‒ which is usually the responsibility of the official veterinary service of the country ‒ needs to be carefully considered in the light of the above two factors. As an example, while many countries of the world aim at establishing and maintaining freedom of the country (or one or more zones within it) from infection with FMD viruses, that is exceptionally difficult for many parts of southern and eastern Africa because wildlife populations maintain SAT serotypes, rendering eradication impossible unless buffalo were to be removed. Thus, in parts of sub-Saharan Africa, eradication or even creation of effective FMD-free zones, is not presently feasible and alternative approaches to manage the disease impacts are necessary.

In sub-Saharan Africa FMD may be endemic as a result of two situations, i.e. where SAT serotype infection is maintained by wildlife populations (African buffalo being crucial in this respect) or where infection with SATs or other serotypes (A or O) is maintained by cattle populations. Of course, both may occur in the same locality.

There are presently only 3 interventions practiced in sub-Saharan Africa against FMD:

  • Vaccination of domestic animal populations (usually only cattle) in which infection with one or more (usually several) serotypes is endemic or where the cattle population is at risk of infection from sympatric or nearby wildlife populations;
  • Separation of infected or high-risk populations of wildlife and/or domestic livestock from uninfected populations; enabled through fencing systems;
  • Careful management of the movement of animals and animal products between localities of different FMD-status or FMD-risk; usually effected through permit systems operated by the official veterinary service of the country concerned.

The OIE recognizes two types of FMD-freedom for both countries and zones, viz. freedom where vaccination is practiced or is not practiced. However, so far, although some southern African countries (i.e. Botswana, Namibia, South Africa) have zones recognized as FMD-free where vaccination is not practiced, no country of the Region has attempted to gain recognition of freedom from FMD where vaccination is applied (see Animal Health Code for Terrestrial Animals, FMD Chapter - www.oie.int). In other parts of the world this has been done.

Because pigs excrete large quantities of FMD virus, especially in the case in large piggeries which may contain many thousands of pigs, prevention of pigs becoming infected is vital in the control of FMD. For that reason the feeding of swill or at least untreated swill is illegal in most countries.



Once an outbreak has been confirmed in a region previously free from FMD,
all cloven-hoofed animals in the focus area should be slaughtered in situ
(so-called "stamping out") and the carcasses disposed of by burial as quickly as possible

Vaccines and vaccination

Presently all vaccines used around the world (with the possible exception of China) are inactivated, i.e. they contain viruses grown in cell cultures, concentrated and chemically ‘killed’ using an aziradine compound. Increasingly, ‘purified’ vaccine is being manufactured, i.e. the NSPs are removed which enables application of DIVA systems (see above). The other important component of FMD vaccines is the adjuvant. Traditionally, the adjuvant of choice is a composite of aluminium hydroxide (alum) and saponin (an extract of tree-bark with surface-active properties). However, various oil emulsions are increasingly replacing the traditional adjuvant because they may stimulate longer-lasting antibody responses.

As is the case for many inactivated vaccines, establishment of effective primary immunity using alum/saponin-adjuvanted vaccine requires two inoculations of vaccine initially 2-8 weeks apart. Ideally, vaccine should only be administered to calves that have lost maternally-acquired antibodies to FMD virus. These antibodies may persist in calves for up to 6 months of age. Thereafter, booster doses need to be applied at least bi-annually and more frequently in high risk situations. However, once cattle are 4-5 years old, annual revaccination is normally adequate. Thus young animals may need to be vaccinated 4-5 times a year which is logistically taxing and expensive. Alum/saponin-adjuvanted vaccines are ineffective in pigs.

It is frequently overlooked that the aim of prophylactic vaccination is to generate a level of herd immunity (HI) that will reduce the reproductive number of an infection to less than 1. If this is achieved any infection introduced into the vaccinated population will not be able to sustain itself even though one or more animals may become infected. However, the level of HI required for FMD under southern African conditions is yet to be determined. It is, nevertheless, generally agreed that HI levels of 70-80% are likely to be adequate (Thomson & Bastos, 2004a). Generating such HI levels is extremely difficult for two reasons: (1) the immunological relationship (degree of matching) between field viruses and viruses incorporated into the vaccine may be poor and (2) very often the way vaccine is stored, handled and administered in the field is less than optimal. This means that expensive vaccination programmes frequently do not achieve the required HI level. For that reason monitoring of vaccination programmes is vital but, unfortunately, rarely conducted effectively. Without auditing of vaccination programmes and addressing the deficiencies identified, it is impossible to be sure that expensive and logistically complicated vaccination programmes are worthwhile.

Recent investigation has shown that the current common practice in southern Africa of immunizing high-risk cattle populations at 6-monthly intervals is inadequate to generate levels of HI with currently available vaccine. Trials to establish more cost/effective schedules are being planned. In the meantime, advice should be sought from vaccine manufacturers when it comes to devising immunization schedules.