Abstract
The continuous emergence of foot-and-mouth disease virus (FMDV) serotype A variants in South East Asia is of concern for international FMDV antigen banks, especially when in vitro tests predict a low antigenic match. A vaccination-challenge study was performed by using two emergency FMDV vaccines with A22 Iraq 64 (A22 IRQ) and A Malaysia 97 (A MAY 97) strains, against challenge with a variant strain of FMDV A/Asia/G-IX/SEA-97 lineage at 7- and 21-day post-vaccination (dpv). At 7 dpv, three of five female calves vaccinated with A MAY 97 and four of five vaccinated with A22 IRQ did not show lesions on the feet and were considered protected, while at 21 dpv all five calves were protected with each vaccine, indicating equal efficacy of both vaccine strains. Calves were protected despite relatively low heterologous neutralizing antibody titers to the challenge virus at the time of challenge. All the calves developed antibodies to the non-structural proteins, most likely due to the direct intradermolingual (IDL) inoculation. Only one calf from the A MAY 97-7 group had infectious virus in the serum 1–3-day post-challenge (dpc), while no virus could be isolated from the serum of cattle challenged on 21 dpv. The virus could be isolated from the oral swabs of all calves, 1–7 dpc with viral RNA detected 1–10 dpc. Nasal swabs were positive for virus 1–6 dpc in a small number of calves. The time between vaccination and infection did not have an impact on the number of animals with persistent infection, with almost all the animals showing viral RNA in their oro-pharyngeal fluid (probang) samples up to 35 dpc. Despite the poor in vitro matching data and field reports of vaccine failures, this study suggests that these vaccine strains should be effective against this new A/Asia/G/SEA-97 variant, provided they are formulated with a high antigen dose.
Highlights
Foot-and-mouth disease (FMD) is an infectious disease of domestic and wild even-toed animals.The disease can be a major constraint to animal production, especially in dairy cattle, where a reduction in milk yield is often significant, but it has economic consequences on meat and draught cattle.Due to its infectious nature and potential impact on trade, it is important to prevent the accidentalVaccines 2020, 8, 80; doi:10.3390/vaccines8010080 www.mdpi.com/journal/vaccinesVaccines 2020, 8, 80 introduction of the virus into a previously “FMD free” country
The study described here measured the efficacy of the abovementioned vaccine strains against challenge with an FMD virus (FMDV) variant virus of A/Asia/G-IX/Southeast Asia (SEA)-97 lineage at 7 dpv to determine early protection and at 21 dpv when the immune response is fully developed
The time interval between the vaccinations and infection is unpredictable in an outbreak, and this study confirms previous reports that the number of days between vaccination and infection significantly influences the outcome whilst emergency vaccines with a higher antigen content can be effective despite a poor antigenic match [17,22,31,32,33,34]
Summary
Foot-and-mouth disease (FMD) is an infectious disease of domestic and wild even-toed animals.The disease can be a major constraint to animal production, especially in dairy cattle, where a reduction in milk yield is often significant, but it has economic consequences on meat and draught cattle.Due to its infectious nature and potential impact on trade, it is important to prevent the accidentalVaccines 2020, 8, 80; doi:10.3390/vaccines8010080 www.mdpi.com/journal/vaccinesVaccines 2020, 8, 80 introduction of the virus into a previously “FMD free” country. Foot-and-mouth disease (FMD) is an infectious disease of domestic and wild even-toed animals. The disease can be a major constraint to animal production, especially in dairy cattle, where a reduction in milk yield is often significant, but it has economic consequences on meat and draught cattle. Vaccines can play a vital role in effective control of the disease, both to limit the spread of the virus during epidemics and the economic impact [1]. FMD virus (FMDV) exists as seven distinct serotypes (O, A, C, Asia-1, SAT-1, SAT-2 and SAT-3), with numerous topotypes, genotypes or lineages within each serotype [2]. Serotype A viruses have been classified under three major geographically restricted genotypes namely, Euro-SA, Asia and Africa [3] and several genetically distinguishable subgroups [4,5].
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