Virological, immunological and pathological findings of transplacentally transmitted bluetongue virus serotype 1 in IFNAR1-blocked mice during early and mid gestation

M Saminathan,B S Chandel,A A P Milton,S K Biswas,Sushila Maan,P P C Mertens,N S Maan,K P Singh,G B Manjunathareddy,H C Chauhan,M A Ramakrishnan,Madhulina Maity,D Hemadri,S Vineetha,V K Gupta

doi:10.1038/s41598-020-58268-0

Abstract

Transplacental transmission (TPT) of wild-type Indian BTV-1 had never been experimentally proved. This study was first time investigated TPT of Indian BTV-1 (isolated from aborted and stillborn goat fetal spleens). The sequential pathology, virological and immune cell kinetics (CD4+, CD8+ T-lymphocytes and NK cells in spleen and PBMCs), and apoptosis in IFNAR1-blocked pregnant mice during early (infected on 1 GD) and mid (infected on 8 GD) gestation have been studied. There was higher rate of TPT during mid stage (71.43%) than early (57.14%) stage. In early stage reduced implantation sites, early embryonic deaths, abortions, and necro-haemorrhagic lesions had observed. Mid stage, congenital defects and neurological lesions in foetuses like haemorrhages, diffuse cerebral edema, necrotizing encephalitis and decreased bone size (Alizarin red staining) were noticed. BTV-1 antigen was first time demonstrable in cells of mesometrium, decidua of embryos, placenta, uterus, ovary, and brain of foetuses by immunohistochemistry and quantified by real-time qRT-PCR. BTV-inoculated mice were seroconverted by 7 and 5 dpi, and reached peak levels by 15 and 9 dpi in early and mid gestation, respectively. CD4+ and CD8+ cells were significantly decreased (increased ratio) on 7 dpi but subsequently increased on 15 dpi in early gestation. In mid gestation, increased CD8+ cells (decreased ratio) were observed. Apoptotic cells in PBMCs and tissues increased during peak viral load. This first time TPT of wild-type Indian BTV-1 deserves to be reported for implementation of control strategies. This model will be very suitable for further research into mechanisms of TPT, overwintering, and vaccination strategies.

Highlights

Bluetongue (BT) is a non-contagious, insect-borne disease of domestic and wild ruminants, caused by bluetongue virus (BTV)
This study demonstrated the distribution of BTV-1 antigen in reproductive organs, immune cell kinetics and apoptosis in BTV-1 infected pregnant animals during early and mid stages of gestation
The clinical signs were recorded over a period of 20/21 gestation day (GD) in both infected and control groups

Summary

Introduction

Bluetongue (BT) is a non-contagious, insect-borne (mainly biting midges of Culicoides spp.) disease of domestic (primarily sheep) and wild ruminants, caused by bluetongue virus (BTV). Subclinical or mild signs are seen in cattle and goats, until the emergence of BTV-1 and BTV-8 in Northern Europe[2,3]. The infection thereafter spread to most parts of the northern Europe and caused disease in sheep and cattle[10,11]. The drawbacks of experimental studies in natural host species like ruminants includes expensive, ethical issues, inclusion of less number of animals, and difficult in getting BTV sero-negative animals[17,18]. To overcome these constrains, an alternative adult mice model is required. Calvo-Pinilla et al.[17] characterized an IFN alpha/beta receptors deficient [IFNAR(−/−)] adult mice model for in vivo study of various BTV serotypes

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