Evaluation of actions of the official veterinary service to mitigate outbreaks of infectious laryngotracheitis and improve biosecurity on laying hen farms

Abstract

Infectious laryngotracheitis (ILT), caused by an Alphaherpesvirus (Gallid herpesvirus-1; GaHV-1), has been noticed in the region of the Terras Altas da Mantiqueira, Minas Gerais. From 2010 to 2018, the “Serviço Veterinário Oficial” (SVO) of the “Instituto Mineiro Agropecuário” (IMA), implemented measures to prevent spread of the virus to other regions and control the disease in the area. Due to the close proximity and consequent epidemiological link among farms, the region was considered a unique epidemiological unit. To check the efficiency of the ILT control measures, we carried out: (1) a seroepidemiological survey, (2) questionnaires for evaluating biosecurity measures; and (3) an evaluation of the influence of farm population density on the occurrence of ILT. In 2016, 2017, and 2018, ILT was investigated using epidemiological and clinicopathological methods, along with GaHV-1 molecular detection. Serological survey was carried out on 24 farms in the quarantined region and on 13 farms from other regions of the state. In 2010 and 2018, questionnaires were applied to collect data and determine indicators of biosecurity practices in all farms of the quarantined area. The differences were then assessed (Wilcoxon’s p<0.05). The results indicated positive serology throughout the region, although only on four farms (16.6%) the chickens have clinical signs, macroscopic and histological lesions of ILT. The prevalence of viral infection increased from 2016 (27%) to 2017 (50%) and was higher in farms with a high stock density (p=0.033). No disease, virus or antibodies were detected in the farms outside of the quarantined area. Although the biosecurity indicators had improved on all farms in the quarantined area (p<0.05), the virus was active and circulating in the region. The contingency measures have contained the outbreak, but biosecurity practices are paramount in the control of new outbreaks. Official control will be maintained in the region, including surveillance of new cases and biosecurity procedures to mitigate the risk of the virus reaching other regions.

A five-year surveillance study of vaccination schedules using viral-vectored vaccines against infectious laryngotracheitis in a high-density layer region

“…The biosecurity measures implemented at the start of the outbreak (Hergot et al 2021) varied among the farms, as did the immunization protocols using either HVT or FPV based ILTV recombinant vaccines. Chickens were initially vaccinated in 2011 and sampled for diagnostic purposes thereafter (Fig.…”

Challenges to and advancements of the official veterinary service of the Federal District, Brazil

“…When health/veterinary services fail, the occurrence of endemic disease and the risk of disease entry from a border are likely to increase (Lubroth et al, 2017). Hergot et al (2021) studied the actions of the official veterinary service (OVS) to mitigate outbreaks of infectious laryngotracheitis (ITL -GaHV-1) and improve biosecurity on laying hen farms in the Minas Gerais State (Brazil) and observed that the actions of the OVS were fundamental to preventing the spread of the virus to other regions. The main actions were: vaccination of chickens quarantined on the farms; manure treatment and controlled transportation of manure, chickens and other waste from farms; sanitary education programmes; farms outside the quarantined area were kept infection free for eight years (2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018); restrictive measures to improve biosecurity and monitoring of ILT cases.…”