The increasing interest in Rift Valley fever virus (RVFV) and its potential impact on naive animal populations deserve revisiting experimental reproduction of RVFV infection, particularly in those animal breeds for which no data about their susceptibility to RVFV infection have ever been recorded. In this study we show the susceptibility of 9-10 weeks old European sheep (Ripollesa breed) to RVFV infection, showing a mild, subacute form of disease. Four different viral isolates efficiently replicated in vivo after subcutaneous experimental inoculation, and consistent viral loads in blood and virus shedding (variable in length depending on the RVFV isolate used) were detected, showing horizontal transmission to a noninfected, sentinel lamb. RVFV infection caused transient pyrexia in adult lambs and no other clinical symptoms were observed, with the exception of corneal opacity ("blue eye") found in 3 out of 16 subcutaneously inoculated sheep. In conclusion, adult sheep from this European breed are readily infected with RVFV without apparent clinical manifestations.

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.

No abstract