Enhanced mucosal immune response in cattle persistently infected with foot-and-mouth disease virus Maddur S. Mohan a , Mukund R. Gajendragad a,b, * , Subodh Kishore a , Ashok K. Chockalingam a , V.V.S. Suryanarayana a , S. Gopalakrishna a , Nem Singh c a Indian Veterinary Research Institute, Bangalore 560024, Karnataka, India b Project Directorate on Animal Disease Monitoring and Surveillance, Hebbal, Bangalore 560024, Karnataka, India c Joint Directorate of Research, Indian Veterinary Research Institute, Izatnagar 243122, UP, India Received 19 July 2007; received in revised form 26 January 2008; accepted 30 May 2008 Abstract The mucosal immune response to foot-and-mouth disease virus (FMDV) type Asia 1 was examined in experimentally infected cattle by assaying antibodies by the virus-neutralizing test (VNT) and IgA ELISA in two secretory fluids, oesophageal pharyngeal fluid (OPF) and oro-nasal fluid (ONF). Out of 17 animals infected by the intradermo-lingual route, 12 became persistently infected (carriers), as defined by positive antigen capture RT-PCR reactions for FMDV RNA in OPF samples collected at 28 days or later after exposure. This proportion of carriers (71%) with FMDV Asia 1 is comparable to other serotypes of the virus. When the two groups were examined, the carriers and non-carriers showed no difference in the serum antibody titre until the end of the experiment at 182 days post-infection (DPI). However, despite an initial similarity significantly higher neutralizing antibody titres and FMDV- specific IgA response were detected among the carriers than the non-carriers in both of the secretory fluids. The response was higher and more stable in ONF compared to OPF. Thus, mucosal antibody assays have the potential to be used as a means of differentiating carrier from non-carrier cattle. Furthermore, the findings are consistent with the higher mucosal antibody response in carriers being an effect of persistent infection rather than the cause. # 2008 Elsevier B.V. All rights reserved. Keywords: Cattle; FMDV carriers; IgA response; Mucosal immune response; Neutralizing antibody titre; Non-carriers; Persistent infection; Viral persistence 1. Introduction Foot-and-mouth disease virus (FMDV) is a Picor- navirus that causes an acute and highly contagious disease of cloven-hoofed animals with serious eco- nomic implications. The main route of infection is via droplets through the upper respiratory tract, the initial site of infection being in the pharyngeal region (Jubb et al., 1993; Alexandersen et al., 2003). The financial consequences of FMDV outbreaks include direct loss from deaths and reduced productivity, along with the indirect loss due to international trade embargoes. The www.elsevier.com/locate/vetimm Available online at www.sciencedirect.com Veterinary Immunology and Immunopathology 125 (2008) 337–343 Abbreviations: Ag RT-PCR, antigen capture reverse transcrip- tase-polymerase chain reaction; DPI, days post-infection; FMDV, foot-and-mouth disease virus; OPF, oesophageal–pharyngeal fluid; ONF, oro-nasal fluid; VNT, virus neutralizing test. * Corresponding author at: Project Directorate on Animal Disease Monitoring and Surveillance (PD_ADMAS), Bangalore 560024, Karnataka, India. Tel.: +91 80 23412531/23419576; fax: +91 80 23415329. E-mail address: gajendragad@gmail.com (M.R. Gajendragad). 0165-2427/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2008.05.031