Evidence of subclinical foot-and-mouth disease virus infection in young calves born from clinically recovered cow under natural condition

Tropical Animal Health and Production - Foot-and-mouth disease (FMD) is a highly contagious and economically important, transboundary viral disease of cloven-hoofed animals. It is known that an...     

Emergence of antigenic variants with in serotype A foot and mouth disease virus in India and evaluation of a new vaccine candidate panel

Emergence of genetically and antigenically divergent lineages/genotypes and poor intergenotypic antigenic coverage is a major concern in serotype A foot-and-mouth-disease virus (FMDV) in India. In 2009, to cover antigenic diversity emerged in serotype A virus field isolates, IND40/2000 was selected as the new vaccine strain for incorporation in the trivalent FMD vaccine formulation used in India. Although current vaccine strain (IND40/2000) covers most isolates antigenically, a few VP3(59)-deletion group isolates showed low r-value in routine vaccine matching exercise. The VP3(59)-deletion group within genotype 18 emerged first in late part of 2002 and in 2007 causing outbreaks along with non-deletion isolates of the same genotype. In case of emergence or re-emergence of more antigenically divergent isolates in future, a need for a new vaccine candidate to cover maximum isolates of both deletion and non-deletion group may arise. Four alternate candidate vaccine strains (IND281/2003, IND195/2007, IND360/2007 and IND123/2008) were selected based on set criteria and antigenic relationships with field isolates sampled between 2002 and 2009 were analyzed using a micro-neutralization test. Phylogenetic analysis based on capsid region of serotype A isolates revealed existence of two broad distinct clusters (VP3(59)-deletion and non-deletion group) within genotype 18. The VP3(59)-deletion group has diversified genetically with time giving rise to three different sub-lineages (clade18a, 18b and 18c). The present study indicates that the virus candidates IND281/2003 (VP3(59)-deletion group) and IND195/2007 (non-deletion group) can be used as an adjunct or alternative strain to currently used vaccine strain IND40/2000 in case of emergence of more antigenically divergent isolates in future.     

Assessment of suitability of two serotype A candidate vaccine strains for inclusion in FMD vaccine in India

The recent type A foot and mouth disease virus field isolates recovered in India are shown to be antigenically quite divergent from the in-use vaccine strain (IND 17/82), warranting the selection of a suitable vaccine strain which can cover this diversity in antigenic spectrum. In earlier studies employing neutralization test with anti-146S rabbit sera raised against eight candidate vaccine strains, IND 81/00 and IND 40/00 belonging to genotype VII were found to offer the best antigenic coverage. In order to assess the credibility of IND 81/00 and IND 40/00 as vaccine strains, 17 recent isolates received during 2005-2006 and representative isolates from older genotypes were subjected to two-dimensional micro-neutralization assay using bovine convalescent serum (against IND 81/00 and IND 40/00) and bovine vaccinate serum (against IND 40/00). From the results it is evident that both the isolates IND 81/00 (antigenic relationship 'r-value' >0.40 with 86% of isolates) and IND 40/00 ('r-value' >0.40 with 78% of isolates) show nearly equal antigenic relatedness with the recent field viruses and hence both of these are effective vaccine candidates in present context. Though very limited in its extent, these useful data obtained with antisera raised in homologous host system are logical extension of the on going quest for the appropriate vaccine strain and circumvents species disparities in the immune recognition of epitopes.     

Serosurveillance of foot-and-mouth disease in sheep and goat population of India

Serological investigation to detect foot-and-mouth disease (FMD) virus circulation in the domestic small ruminant population of India was conducted. A total of 4407 and 4035 serum samples from sheep and goats, respectively were collected at random covering majority of the states across the country during 2010–2012. These samples were analyzed for antibodies against the non-structural proteins (NSP) of FMD virus in an indirect 3AB NSP ELISA and against the structural proteins (SP) in a liquid phase blocking (LPB) ELISA. A total of 20.35% sheep and 13.60% goats were found to be positive for 3AB NSP antibodies providing a serological evidence of extensive viral activity. In LPB ELISA, only 4.54% sheep and 6.27% goats were found to have protective antibody (log₁₀ titre of ≥1.8) against all three serotype strains in the vaccine, which correlates with “no or sparse vaccination” scenario in these species in the country. Hence, to check silent amplification and dissemination of virus in a mixed farming set up, small ruminants may be brought under the ambit of routine vaccination and surveillance programmes.