Long-Term Use Summary (2019-2021) of a Reovirus 2, Live Non-Attenuated Virus as Controlled Exposure Vaccination in Heavy Breeder Chickens in Israel

Abstract

Reovirus is the most important causal agent of arthritis/tenosynovitis in chickens, especially in heavy breeds. Early infection with Reovirus causes inflammation and scarring of the gastrocnemius and flexor tendons, leading to lameness, tendon rupture, and abnormal leg spreading. Arthritis/tenosynovitis leads to economic losses and critical welfare issues in the poultry industry in many countries. In Israel, the economic impact of the disease is higher due to the significant condemnation rates related to Jewish Kosher laws. Sigma C sequencing of  isolated reoviruses in Israel demonstrated that the same group of reoviruses (Reovirus-Cluster
2 today defined as Reovirus GC-5) caused more than 95% of the cases reported in broilers and breeders since 2015. The use of commercial or autogenous Reovirus inactivated vaccines based on different strains of Reovirus, did not prevent the infection or the shedding of the virus to the progeny under field conditions. Extensive use of inactivated Reovirus vaccines only reduced the time of virus shedding to the progeny from 5-7 weeks before the introduction of the vaccines to 3-4 weeks of shedding. Controlled exposure of breeding flocks during the rearing period using a live non-attenuated Reovirus 2 live vaccine (GC-5) was tested in controlled laboratory and field trials during 2017-2018. Following successful controlled field trials,
commercial implementation of vaccination using the non-attenuated Reovirus 2 live vaccine commenced in Israel in 2019. Since 2019, nearly 100% of the heavy breeders in Israel have been vaccinated during their rearing period. Close monitoring of all vaccinated flocks and their progeny was carried out between 2019 and 2021. No clinical complications or adverse reactions in any breeding flock following the use of the live vaccine were reported during the rearing period and production. A significant reduction in the number of clinical cases and Reovirus isolations were observed in breeding and broiler flocks following the introduction of the nonattenuated Reovirus 2 live vaccine. This report summarizes the information accumulated from the large-scale use of the controlled exposure method using the Reovirus 2 live vaccine.

Keywords: Poultry; Avian; Reovirus: Arthritis/Tenosynovitis; Vaccination; Poultry Welfare; Controlled Exposure.

Introduction

New emerging reoviruses appeared in many countries during the last decade, causing viral tenosynovitis and severe economic and welfare issues. (1, 2, 3, 4, 9, 10, 11, 12, 14). Genetic diversity among ARV strains occurs through segment reassortment and mutations in the viral genome, mainly the S1 segment encoding the Sigma C (σC) protein (3). The σC protein of Reovirus is responsible for its attachment to the cell receptors and induction of specific neutralizing antibodies (4, 5).

Control of reovirus tenosynovitis is based on the vaccination of breeding flocks during the rearing period. The lack of efficacy of commercial vaccines against the newly emerging strains of Reovirus led the industry to develop and use autogenous Reovirus inactivated  vaccines based on homologous strains (1, 2, 3, 4, 6, 7, 8). The epidemiological data provided by the regional diagnostic laboratories in Israel (Egg and Poultry Board Laboratories-EPB) clearly showed that since 2015 despite the extensive use of commercial and autogenous inactivated Reovirus vaccines, most cases of tenosynovitis in broilers were related to egg transmission after infection of the breeding flocks. Epidemiological studies carried out in Israel at the Kimron Veterinary Institute demonstrated that most of the cases of arthritis/tenosynovitis in broilers in Israel were caused by reoviruses related to cluster 2 or as defined today, GC- 5 (16).

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