# Rapid serogroup classification of the footrot pathogen Dichelobacter nodosus using multiplex qPCR of lesion samples from sheep in the Netherlands

## TL;DR

This study introduces a faster and more accurate method for classifying the footrot pathogen in sheep using multiplex qPCR, which helps in understanding disease spread and vaccine development.

## Contribution

The study introduces a novel multiplex qPCR method for rapid and accurate serogroup classification of D. nodosus from sheep samples.

## Key findings

- Multiplex qPCR detected more serogroups and multiple serogroups in a single sample compared to conventional methods.
- 31% of samples contained two to five different serogroups, highlighting the complexity of D. nodosus infections.
- The method offers faster, more sensitive, and accurate classification for epidemiological studies and vaccine strategies.

## Abstract

Dichelobacter nodosus (D. nodosus) is the pathogen responsible for causing footrot in sheep and goats, which poses significant challenges to animal health and welfare. D. nodosus is classified into 10 different serogroups (A–I and M) based on the genetic variation of this fimbrial (fimA) gene. These fimbriae are immunogenic and play an important role in virulence, making serotyping of these fimbriae valuable for identification and vaccine development. In this study, three multiplex quantitative polymerase chain reaction (qPCR) assays, targeting the most commonly prevalent nine serogroups (ABC, DEF, and GHI), were studied for the detection of serogroups in foot swab samples collected from Dutch sheep farms. A total of 147 samples tested positive for D. nodosus using pnpA qPCR, and 144 (98%) samples exhibited a serogroup using qPCR. The multiplex qPCRs detected significantly more serogroups than conventional serogroup PCRs and detected more than one serogroup in a swab. In 46 samples (31%, 46/147), two to five different serogroups were identified from a single swab sample. In three samples, no serogroup was identified, likely due to sequence variation in the fimA gene in these samples. These direct multiplex qPCR tests provide faster, more sensitive, and accurate testing for the direct classification and quantification of D. nodosus serogroups for studying the epidemiology of footrot and for the formulation of serogroup-specific targeted vaccination strategies for prevention, control, and treatment of footrot.