# Molecular serotyping and virulence assessment of Avibacterium paragallinarum strains circulating in Chinese poultry flocks

## TL;DR

This study examines the spread and virulence of Avibacterium paragallinarum in Chinese poultry, revealing regional and seasonal patterns and the dominance of certain serotypes.

## Contribution

The study provides updated epidemiological data and molecular serotyping of A. paragallinarum strains in China.

## Key findings

- A. paragallinarum prevalence was highest in Anhui, Guangxi, and Guangdong provinces.
- Serotype A was the most common, followed by C and B, with phylogenetic clustering matching serotype classification.
- Both serotype A and C isolates caused infectious coryza in SPF chickens, with direct inoculation leading to more severe symptoms.

## Abstract

Infectious coryza, caused by Avibacterium paragallinarum (A. paragallinarum), is a highly contagious respiratory disease that poses a significant threat to poultry production in China. Updated information on the epidemiology, serotype distribution, and virulence of circulating strains is essential for formulating effective regional control and vaccination strategies.

A total of 200 clinical samples from nine provinces were analyzed to determine the prevalence, serotype distribution, and seasonal dynamics of A. paragallinarum. The bacterial isolation, characterization, species-specific PCR, and molecular serotyping based on the hmtp210 gene were performed. Phylogenetic relationships were inferred using the neighbor-joining method. The pathogenicity of representative isolates (serotype A and C) was assessed using SPF chickens.

A. paragallinarum prevalence varied geographically, with the highest isolation rates in Anhui, Guangxi, and Guangdong provinces, and no detection in Sichuan or Hubei. A distinct seasonal pattern was observed, with peaks in late autumn and winter. 22 isolates were recovered and serotyped: serotype A predominated (n = 15), followed by serotype C (n = 5), and serotype B (n = 2). Phylogenetic analysis of hmtp210 revealed clear clustering congruent with serotype classification. Both serotypes induced typical infectious coryza, with directly inoculated birds exhibiting more severe clinical signs than contacts.

This multi-provincial study provides contemporary insights into the epidemiology, serotype distribution, and virulence of A. paragallinarum in China. These findings underscore the necessity for region-specific surveillance and support the development of targeted vaccines based on locally prevalent, virulent strains.