Highly pathogenic avian influenza subtype H5Nx clade 2.3.4.4 outbreaks in Dutch poultry farms, 2014-2018: Clinical signs and mortality.

Janneke Schreuder,Thijs T M Manders,Armin R W Elbers,Francisca C Velkers,Arco N Spek,J Arjan Stegeman,Ruth J Bouwstra

doi:10.1111/tbed.13597

Abstract

In recent years, different subtypes of highly pathogenic avian influenza (HPAI) viruses caused outbreaks in several poultry types worldwide. Early detection of HPAI virus infection is crucial to reduce virus spread. Previously, the use of a mortality ratio threshold to expedite notification of suspicion in layer farms was proposed. The purpose of this study was to describe the clinical signs reported in the early stages of HPAI H5N8 and H5N6 outbreaks on chicken and Pekin duck farms between 2014 and 2018 in the Netherlands and compare them with the onset of an increased mortality ratio (MR). Data on daily mortality and clinical signs from nine egg‐producing chicken farms and seven Pekin duck farms infected with HPAI H5N8 (2014 and 2016) and H5N6 (2017–2018) in the Netherlands were analysed. In 12 out of 15 outbreaks for which a MR was available, MR increase preceded or coincided with the first observation of clinical signs by the farmer. In one chicken and two Pekin duck outbreaks, clinical signs were observed prior to MR increase. On all farms, veterinarians observed clinical signs of general disease. Nervous or locomotor signs were reported in all Pekin duck outbreaks, but only in two chicken outbreaks. Other clinical signs were observed less frequently in both chickens and Pekin ducks. Compared to veterinarians, farmers observed and reported clinical signs, especially respiratory and gastrointestinal signs, less frequently. This case series suggests that a MR with a set threshold could be an objective parameter to detect HPAI infection on chicken and Pekin duck farms at an early stage. Observation of clinical signs may provide additional indication for farmers and veterinarians for notifying a clinical suspicion of HPAI infection. Further assessment and validation of a MR threshold in Pekin ducks are important as it could serve as an important tool in HPAI surveillance programs.

Highlights

In recent years, different subtypes of highly pathogenic avian influenza A (HPAI) viruses have caused outbreaks in different poultry types worldwide (Lee, Bertran, Kwon, & Swayne, 2017; Napp, Majó, Sánchez-Gónzalez, & Vergara-Alert, 2018).Clearly, early detection of HPAI virus infection on poultry farms is essential to reduce risks for virus spread and minimize the socio-economic impact of the disease (Backer, van Roermund, Fischer, van Asseldonk, & Bergevoet, 2015; Elbers, Fabri, et al, 2004), which is increasingly reflected in legislation and contingency plans worldwide
To improve sensitivity of detection of low pathogenic avian influenza (LPAI) and HPAI virus infections and at the same time maintain a high level of specificity, Gonzales and Elbers (2018) developed new reporting thresholds based on increased mortality and drops in egg production for layer farms, and evaluated the performance of those indicators with HPAI H7N7 outbreak data from 110 infected layer flocks in the Netherlands in 2003
A case series study was performed on a total of 16 poultry farms that were diagnosed with HPAI infection caused by viruses of subtypes H5N8 or H5N6 in the Netherlands between 2014 and 2018, which included six farms with laying hens, three farms with broiler breeders and seven farms with Pekin ducks (Table 1)

Summary

| INTRODUCTION

Different subtypes of highly pathogenic avian influenza A (HPAI) viruses have caused outbreaks in different poultry types worldwide (Lee, Bertran, Kwon, & Swayne, 2017; Napp, Majó, Sánchez-Gónzalez, & Vergara-Alert, 2018). European Union legislation on the control of HPAI (EU, 2005a, 2005b) stipulates that early detection systems, aimed at a rapid reporting of any sign of avian influenza in poultry and other captive birds by owners or keepers to the competent veterinary authority, need to be in place For both LPAI and HPAI outbreaks, sudden changes in mortality have shown to be an indicator of infection (Elbers, Holtslag, Bouma, & Koch, 2007; Gonzales & Elbers, 2018; Malladi, Weaver, Clouse, Bjork, & Trampel, 2011), as well as clinical signs (Elbers, Kamps, & Koch, 2004; Elbers, Koch, & Bouma, 2005; Velkers et al, 2006). We calculated the MR and daily mortality for each outbreak and provide an extensive inventory of the species-specific clinical signs and how these developed over time in the days before official notification, as observed by poultry farmers and veterinarians

| METHODS

Findings

| DISCUSSION