Avian Avulavirus 1 Outbreaks in Bulgaria During 2016 and 2017

Abstract

Newcastle disease is one of the most important and highly contagious disease for poultry. The causative agent Avian avulavirus 1 belongs to genus Avulavirus, Family Paramyxoviridae, order Mononegavirales. There are two evolutionary related groups AAvV-1 – class I and class II. The classification is based on complete genome analysis. Class I and class II being further divided in genotypes. However, the isolation and identification of novel avulaviruses of varying pathogenicity and genotypes from a wide range of hosts suggests a continuous virus evolution with subsequent implications for disease spread. Subsequent to evolution, the emergence of novel genotypes and sub-genotypes are now increasing over a period of time. Despite the introduction of a broad vaccination program in industrial poultry farms in Bulgaria, the birds in the backyard farms have not been vaccinated and the disease has become endemic. Almost every year there is at least one outbreak in poultry or wild birds. The earlier AAvV-1 isolates, from 1959 to 1998, belong to many different genetic lines: 2, 3b, 3c, 4 and 5b. The last AAvV-1 isolates (from 2004 to 2013) from chickens belong to genetic line 5d and wild bird isolates belongs to 1, 2, 4b and 6. The first appearance of genetic line 5a is in the beginning of 2013. All this necessitates in-depth studies of AAvV-1 in the population of both wild and synanthropic birds and vaccinated hens. This study was conducted to ascertain the genetics of the circulating AAvV-1 that causes disease outbreaks in 2016 and 2017.