Foot-and-mouth disease virus (FMDV) type A is one of the most important pathogens causing FMD in pigs.

Characteristics and antigenicity

Characteristics

Viral structure: FMDV belongs to the family of small RNA viruses (Picornaviridae), and the viral particles are non-enveloped icosahedra, with a diameter of about 25-30 nm.

Genome: The genome of FMDV is a single-stranded positive-stranded RNA, approximately 8,500 nucleotides long, encoding a polyprotein, which is cleaved by a virus-encoded protease to produce multiple structural and non-structural proteins.

Viral variation: The genome of type A FMDV is highly variable, resulting in a wide range of antigenic properties, giving this type of virus different subtypes and antigenic variants.

Antigenicity

Antigenic structure: The major antigenic determinants of FMDV are located on the capsid proteins VP1, VP2, and VP3, with the G-H loop of VP1 being the most important antigenic site, which is prone to mutation.

Antigenic variation: The antigenic variation of type A FMDV is frequent, and strains prevalent in different regions and at different times may have significant antigenic differences, which increases the difficulty of vaccine development.

Cross-protection: Due to antigenic variation, vaccines against type A FMDV usually protect only against specific strains or subtypes of the virus, with poor cross-protection.

Clinical symptoms and disease severity

Clinical signs

Oral and hoof lesions

Blisters and ulcers: blisters appear in the mouth, tongue, gums, nasal passages, hoof crowns and hoof forks, and ulcers form when the blisters rupture.

Salivation: infected pigs salivate profusely due to pain in the mouth.

Lameness: due to blisters and ulcers on the hooves, the infected pig becomes lame and has difficulty standing.

Systemic symptoms

Fever: elevated body temperature, usually above 40°C.

Anorexia and lethargy: loss of appetite and depression.

Reduced lactation: significant reduction in lactation in lactating sows.

Piglet symptoms

Acute death: especially in lactating piglets, sudden death may occur due to myocarditis and severe dehydration.

Disease severity

High pathogenicity: Type A FMDV infection is symptomatic and may lead to high mortality, especially in piglets and pigs with weakened immunity.

Long-term effects: Infected pigs, even if they recover, may suffer from hoof damage and reduced productivity that affects growth and reproduction.

Vaccine development and control measures

Vaccine development

Inactivated vaccines: Inactivated vaccines are currently used primarily to prevent FMDV infection. Inactivated vaccines are made by culturing the virus and then inactivating it, but they need to be prepared in a targeted manner according to the prevalent strains.

Recombinant vaccines: Recombinant vaccines developed using genetic engineering techniques, such as those based on the VP1 protein, offer better safety and stability.

Vaccine selection: Due to the antigenic variability of type A FMDV, vaccine selection needs to be based on locally prevalent strains to ensure that the vaccine matches the antigenicity of the prevalent strains.

Vaccine efficacy: The protective efficacy of the vaccine needs to be verified by laboratory and field tests, including antibody level tests and protection tests.

Preventive measures

Vaccination

Regular vaccination: vaccinate pig herds regularly, especially in high-risk areas and during the season of epidemics.

Booster vaccination: in the event of an outbreak, boost vaccination of high-risk herds to ensure effective immunisation coverage.

Biosecurity measures

Isolation and quarantine: Strictly isolate newly introduced pigs and implement quarantine measures to prevent virus introduction.

Disinfection measures: Thoroughly disinfect pig houses, equipment and personnel to prevent virus transmission.

Environmental management: Keep pig houses clean and dry, and regularly clean up faeces and dirt to reduce the virus load in the environment.

Monitoring and emergency response

Regular monitoring: Regularly monitor the health of pig herds and quickly detect and report suspected cases.

Emergency response: once an outbreak is detected, quickly take emergency measures such as isolation, blockade and culling to prevent the virus from spreading.

Education and training

Training of breeders and veterinarians: to improve knowledge of foot-and-mouth disease and skills of prevention and control.

Publicise knowledge of disease prevention: Improve the awareness of disease prevention and self-protection ability of pig farms through publicity and education.