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.

Herd immunity to Newcastle disease virus in poultry by vaccination.

Newcastle disease is an economically important disease of poultry for which vaccination is applied as a preventive measure in many countries. Nevertheless, outbreaks have been reported in vaccinated populations. This suggests that either the vaccination coverage level is too low or that vaccination does not provide perfect immunity, allowing the virus to spread in partially vaccinated populations.