Optimization and evaluation of a non-invasive tool for peste des petits ruminants surveillance and control

Abstract

Peste des petits ruminants (PPR) is a highly contagious and devastating viral disease affecting mainly sheep and goats, but also a large number of wild species within the order Artiodactyla. A better understanding of PPR transmission dynamics in multi-host systems is necessary to efficiently control the disease, in particular where wildlife and livestock co-occur. Notably, the role of wildlife in PPR epidemiology is still not clearly understood. Non-invasive strategies to detect PPR infection without the need for animal handling could greatly facilitate research on PPR epidemiology and management of the disease in atypical hosts and in complex field situations. Here, we describe optimized methods for the direct detection of PPR virus genetic material and antigen in fecal samples. We use these methods to determine the detection window of PPR in fecal samples, and compare the sensitivity of these methods to standard invasive sampling and PPR diagnostic methods using field samples collected at a wildlife-livestock interface in Africa. Our results show that quantitative reverse transcription PCR (RT-QPCR) amplification of PPRV from fecal swabs has good sensitivity in comparison to ocular swabs. Animals infected by PPRV could be identified relatively early on and during the whole course of infection based on fecal samples using RT-QPCR. Partial gene sequences could also be retrieved in some cases, from both fecal and ocular samples, providing important information about virus origin and relatedness to other PPRV strains. Non-invasive strategies for PPRV surveillance could provide important data to fill major gaps in our knowledge of the multi-host PPR epidemiology.

Figure 1

Kinetics of viral shedding in fecal material of PPRV infected goats. Viral shedding was monitored by (a) RT-QPCR (expressed in Ct, limit of detection = 40 Ct) and (b) antigen capture ELISA (expressed in Sample/Positive Control % following the manufacturers’ instructions, limit of detection = 20%). Samples were collected from four Saanen goats infected by an intranasal route with the highly virulent Peste des Petits Ruminants strain Morocco 2008. Fecal material was tested for presence of PPRV genetic material from day 4 post infection (dpi) until the end of the experiment. ID numbers used in Figure label indicates animal ID numbers.

Figure 2

PPRV N gene phylogenetic analysis. Neighbour-joining tree showing the relationship between the partial N gene sequence obtained in this study (indicated by black dot) and sequences publically available in GenBank (indicated by the country and sample name, the year and the GenBank Accession Number). The numbers at the nodes are bootstrap values obtained from 1000 replicates. Only bootstrap values > 50 are shown.