 | Cattle and, in Africa, buffalo, are the main reservoir of the virus, which is highly contagious, and which can spread rapidly to other wild and domestic species, including pigs and sheep
Photo: Michael Ring | Highly contagious, the foot and mouth disease affects all cloven-hoofed animals, with mortality reaching 50% in herds of young animals.
Foot and mouth disease is a highly infectious viral infection that affects all cloven-hoofed animals. The causative agent is an aphthovirus from the family Picornaviridae. Seven serotypes of the virus (O, A, C, Asia 1 and Southern African Territories (SAT) 1, 2 and 3) are recognised. Many subtypes can occur, and vaccination against an individual serotype does not confer immunity against others.
Mortality caused by infection with FMD can reach 50% in herds of young animals, but the main financial impact of the disease stems from its effects on the reproductive potential of affected stock and implications for trade in both live animals and food products. Cattle and, in Africa, buffalo, are the main reservoir of the virus, which is highly contagious, and which can spread rapidly to other wild and domestic species, including pigs and sheep. Viral material is present in all secretions of acutely infected animals, and airborne transmission is a danger as well as direct contact with affected animals or their excretions.
Clinical signs include the appearance of vesicles on the feet, in and around the oral cavity and on the mammary glands of female animals. The severity of infection varies according to the strain of virus, degree of exposure and the age and breed of animals, as well as host species and the degree of immunity in affected herds or flocks.
Clinical differentiation from other vesicular diseases is impossible, and laboratory diagnosis is required to confirm outbreaks.
FMD is endemic in the Middle East, much of Africa and Asia, and large parts of South America. It has been eradicated in much of Europe and a number of other developed countries, where slaughter programmes have replaced prophylactic vaccination as the control strategy of choice – largely because of trade considerations. Vaccine banks for use in emergencies are maintained in a number of regions, however, including the European Union, and approaches to future outbreaks have altered following the epidemic experienced in the United Kingdom during 2001.
As the UK outbreak began to take hold, the EU authorised the vaccination of up to 180,000 cattle in an effort to contain the epidemic, but the vaccination option was not taken up. By the time the disease had finally been stamped out, more than 2000 cases had been confirmed, and around seven million animals had been slaughtered on farms affected by control measures.
The UK epidemic was caused by a type O strain of the virus that had been associated with outbreaks in Japan, South Korea and Russia.
The exact source of the initial infection was not pinpointed, but imported meat from affected animals was deemed the most likely cause. The scale at which international trade is conducted in both live animals and meat products has certainly increased the risk of spreading FMD, while the UK's failure to bring the outbreak under control at an early stage also highlighted the risks posed by the volume of animal movements being undertaken both within and between countries on a day-to-day basis. Live animals exported from the UK to France, Ireland and the Netherlands resulted in the confirmation of outbreaks in all three of those countries during 2001, but control measures prevented the disease spreading out of control beyond the UK. Register for free FMD
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> Email us for details | EU regulations governing member state responses to future FMD outbreaks have been reformed in the aftermath of the UK outbreak. Prophylactic vaccination against the disease is still banned in the region, but emergency vaccination – previously regarded as a policy of 'last resort' – has been moved to the forefront of control measures. Changes to rules governing international trade and the development of laboratory tests capable of distinguishing between vaccinated animals and naturally infected stock both undoubtedly played a part in driving that change. The financial and social impact of the UK outbreak was also a major factor behind the shift in policy, however.
Attitudes towards vaccination have also changed in the US since the terrorist attacks carried out there in September 2001. Bio-terrorism is now perceived as a real threat, and plans to deal with the impact of potential attacks, including the deliberate introduction of diseases such as FMD into US herds, have been drawn up. These include agreements with manufacturers covering emergency vaccine supply.
Recent events also prompted calls by the UN Food and Agriculture Organisation for the establishment of a global plan to control FMD. Efforts to develop improved vaccines against the disease are expected to play a major role, and substantial funds are being invested by several governments as well as commercial organisations in vaccine research programmes.
Existing vaccines are traditional inactivated products, manufactured variously by government-owned laboratories, national producers and a handful of multinationals. Efforts to develop new vaccines with enhanced levels of efficacy and safety are focused largely on the application of gene-deleted marker technology and the pursuit of effective subunit or DNA vaccines.
The complex nature of the FMD virus and the existence of several serotypes and many subtypes have presented major challenges to researchers in the field. Progress has been made in a number of areas, however, and the eventual development of safe and effective vaccines utilising recombinant DNA technology is expected to revolutionise approaches to both the control and eventual eradication of FMD.
Most major research projects are co-ordinated by national laboratories in the public sector. Key players in the sector include the Dutch research centre at Lelystad, the US government's research centre on Plum Island, the UK Institute for Animal Health and the CSIRO in Australia. Public sector laboratories in many other countries and a range of commercial organisations are also involved. In 2003 researchers from the UK, Canada, the US and Australia called for the development of a global effort to counter the disease, including research into novel FMD vaccines.
Of the many development-stage vaccine projects, work by US researchers at Plum Island appears particularly promising. This has resulted in the development of genetically-engineered vaccines containing the viral capsid and 3C protease coding regions from a number of FMD virus types. Using an adenovirus vector delivery vehicle vaccines have been administered to pigs in a series of challenge studies that produced promising results. > Login for the full story
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