Detection of Low Pathogenic Avian Influenza Virus Subtype H10N7 in Poultry and Environmental Water Samples During a Clinical Outbreak in Commercial Free-Range Layers, Netherlands 2017.

Wild birds are the natural reservoir of the avian influenza virus (AIV) and may transmit AIV to poultry via direct contact or indirectly through the environment. In the Netherlands, a clinically suspected free-range layer flock was reported to the veterinary authorities by the farmer. Increased mortality, a decreased feed intake, and a drop in egg production were observed. Subsequently, an infection with low pathogenic avian influenza virus was detected. This study describes the diagnostic procedures used for detection and subtyping of the virus. In addition to routine diagnostics, the potential of two different environmental diagnostic methods was investigated for detecting AIV in surface water. AIV was first detected using rRT-PCR and isolated from tracheal and cloacal swabs collected from the hens. The virus was subtyped as H10N7. Antibodies against the virus were detected in 28 of the 31 sera tested. An intravenous pathogenicity index (IVPI) experiment was performed, but no clinical signs (IVPI = 0) were observed. Post-mortem examination and histology confirmed the AIV infection. Multiple water samples were collected longitudinally from the free-range area and waterway near the farm. Both environmental diagnostic methods allowed the detection of the H10N7 virus, demonstrating the potential of these methods in detection of AIV. The described methods could be a useful additional procedure for AIV surveillance in water-rich areas with large concentrations of wild birds or in areas around poultry farms. In addition, these methods could be used as a tool to test if the environment or free-range area is virus-free again, at the end of an AIV epidemic.

NetB-producing and beta2-producing Clostridium perfringens associated with subclinical necrotic enteritis in laying hens in the Netherlands.

Since 2006 increasing numbers of laying hen flocks with decreased production have been reported in the Netherlands. At necropsy, birds from affected flocks showed multifocal areas of necrosis in the duodenum. Histologically the duodenum had moderate to marked villus atrophy and fusion with crypt hyperplasia and a mixed inflammatory infiltrate within the lamina propria underlying focal areas of degenerative epithelium. Multifocally, free within the intestinal lumen and associated with epithelial necrosis, were marked numbers of large rod-shaped bacteria. Anaerobic culturing and subsequent toxin typing revealed, in 19 out of 73 affected birds, the presence of Clostridium perfringens strains, either type A or type C harbouring the atypical allele of cpb2 and netB. Eighteen out of these 19 birds carried C. perfringens strains capable of producing beta2 toxin in vitro and all of these birds harboured C. perfringens strains capable of producing NetB toxin in vitro. In contrast, specific pathogen free (SPF) birds lacked gross or histological lesions in their duodenum, and C. perfringens type C was isolated from four out of 15 SPF birds tested. One of these isolates harboured the consensus three allele of cpb2 that produced beta2 toxin in vitro. None of the C. perfringens isolates originating from SPF birds harboured netB. These findings might indicate that the NetB toxin produced by C. perfringens is associated with subclinical necrotic enteritis in layers, whereas the involvement of beta2 toxin in subclinical necrotic enteritis, if any, might be variant dependent.