Necrotic enteritis (NE) is one of the most important enteric diseases in poultry and is a high cost to the industry worldwide. It is caused by avian-specific, Necrotic Enteritis Beta toxin (NetB)-producing, strains of Clostridium perfringens that also possess in common other virulence-associated genes. In Europe the disease incidence has increased since the ban on in-feed “growth promoting” antibiotics. Because of this, many recent studies of NE have focused on finding different ways to control the disease, and on understanding its pathogenesis. Frustratingly, reproduction of the disease has proven impossible for some researchers. This review describes and discusses factors known to be important in reproducing the disease experimentally, as well as other considerations in reproducing the disease. The critical bacterial factor is the use of virulent, netB-positive, strains; virulence can be enhanced by using tpeL- positive strains and by the use of young rather than old broth cultures to increase toxin expression. Intestinal damaging factors, notably the use of concurrent or preceding coccidial infection, or administration of coccidial vaccines, combined with netB-positive C. perfringens administration, can also be used to induce NE. Nutritional factors, particularly feeding high percentage of cereals containing non-starch polysaccharides (NSP) (wheat, rye, and barley) enhance disease by increasing digesta viscosity, mucus production and bacterial growth. Animal proteins, especially fish meal, enhance C. perfringens proliferation and toxin production. Other factors are discussed that may affect outcome but for which evidence of their importance is lacking. The review compares the different challenge approaches; depending on the aim of particular studies, the different critical factors can be adjusted to affect the severity of the lesions induced. A standardized scoring system is proposed for international adoption based on gross rather than histopathological lesions; if universally adopted this will allow better comparison between studies done by different researchers. Also a scoring system is provided to assist decisions on humane euthanasia of sick birds.

This review discusses key factors important in successful experimental reproduction of necrotic enteritis (NE) in chickens, and how these factors can be adjusted to affect the severity of the lesions induced. The critical bacterial factor is the need to use virulent, netB-positive, strains of Clostridium perfringens; disease severity can be enhanced by using netB-positive C. perfringens strains that are also tpeL-positive, by the use of young rather than old broth cultures, and by the number of days of inoculation and the number of bacteria used. Use of cereals rich in non-starch polysaccharides can enhance disease, as does use of animal proteins. Administration of coccidia, including coccidial vaccines, combined with netBpositive C. perfringens, increases the severity of experimentally-induced NE. Dietary manipulation may be less important in coccidia-based models since the latter are so effective. Disease scoring systems and welfare considerations are discussed.

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Assessment of the clinical severity, pathogenesis, and prognosis of canine chronic liver disease poses significant challenges to clinicians and pathologists, relating in part to a lack of standardized terminology and assessment methods and also to a lack of understanding of the pathogenesis of chronic liver disease in the dog. This study graded the severity of necroinflammatory activity in chronic liver disease in dogs using a modification of Ishak's grading scheme for human chronic liver disease and examined the association of grade score with hepatocellular apoptosis, regeneration, nitric oxide synthase isoform expression, copper and iron accumulation, and indicators of oxidative stress. Formalin-fixed, paraffin-embedded hematoxylin and eosin (HE)-stained liver biopsies from 45 dogs with chronic liver disease and 55 healthy control dogs were graded for various morphologic components of liver injury and response. The cumulative score for grade of necroinflammatory activity was strongly and significantly correlated with immunoreactive labels for hepatocellular proliferation (Ki-67); apoptosis (cleaved caspase-3); inducible nitric oxide synthase (iNOS) in lobular, portal, and septal stromal cells; endothelial nitric oxide synthase (eNOS) in hepatocytes and lobular, portal, and septal stromal cells; and total stainable hepatic iron. A weaker significant correlation was found between grade and accumulation of hepatocellular copper. No significant correlation was found between grade and immunoreactivity for malondialdehyde-protein adducts. These results document a method for grading of the severity of necroinflammatory disease in canine liver biopsies and show an association with increased iNOS and eNOS expression.

We evaluated the extent of hepatic fibrosis in chronic liver disease of dogs using a modification of Ishak's staging criteria for human chronic liver disease, and examined the association of stage of fibrosis with immunophenotypic markers of transdifferentiation of hepatic sinusoidal endothelial cells and hepatic stellate cells. Formalin-fixed, paraffin-embedded, hematoxylin and eosin-stained liver biopsy specimens from 45 case dogs with chronic liver disease and 55 healthy control dogs were scored for the presence and extent of fibrosis. This stage score for fibrosis strongly correlated with upregulated von Willebrand factor (vWF) expression in lobular sinusoidal endothelial cells (Spearman correlation coefficient [SCC] = 0.57, p < 0.05). Immunoreactivity for vWF factor was identified in 68.9% of case biopsies, varying in distribution from periportal to diffuse, whereas vWF immunoreactivity was identified in only 14.5% of control specimens, and was restricted to the immediate periportal sinusoids. The majority of both case and control biopsies exhibited similar prominent lobular perisinusoidal expression of alpha-smooth muscle actin (α-SMA). A minority of specimens (17.8% of case biopsies, 1.8% of control biopsies) exhibited low perisinoidal α-SMA expression, and there was a weak negative correlation between α-SMA expression and stage of fibrosis (SCC = -0.29, p = 0.0037). These results document a method for staging the severity of fibrosis in canine liver biopsies, and show a strong association between fibrosis and increased expression of vWF in hepatic sinusoidal endothelial cells.