Etiology and pathogenesis of necrotic enteritis

Sporulated oocysts ofEimeria acervulina were administered orally to cage-housed broilers at a dose of 3.5×10⁵ resulted in mild subclinical coccidiosis.Clostridium perfringens incorporated in feed at a level of 2.5×10⁸ organisms/g. produced lesions characteristic of necrotic enteritis. Mortality of 8% (7/80) occurred in birds fed a ration inoculated withCl. perfringens alone. Mortality of 35% (28/80) was observed in birds which received an oral dose ofE. acervulina and which were fed simultaneously with a ration containingCl. perfringens. Birds which were fed an inoculated ration two days after an oral dose ofE. acervulina showed 41% (33/80) mortality. Birds which received an inoculated ration for two days before administration of an oral dose ofE. acervulina demonstrated 18% mortality (15/80). Birds which were fed an inoculated ration four days after an oral dose ofE. acervulina showed 10% mortality. Infection withE. acervulina reduced the pH of intestinal contents with a simultaneous depression in serum protein. A 39% increase in intestinal passage time from 178 to 248 minutes occurred on the fifth day after infection withE. acervulina. These experiments suggest that necrotic enteritis, attributed to proliferation of a toxigenic strain ofCl. perfringens, followed intestinal stasis and minimal lesions induced by mild intestinal coccidiosis.     

The occurrence and significance of Campylobacter jejuni in man and animals

Campylobacter jejuni, which is now recognized as a discrete species, is a gram negative, microaerophilic, thermophilic, nalidixic acid sensitive, hippurate positive pathogen requiring special selective media for propogation. The organism is widely distributed in avian species, experimental and companion animals and in humans. Mammalian campylobacteriosis is characterized by an enterocolitis of variable severity. The prevalence of the condition is relatively high in young individuals, in underdeveloped countries and in subjects with diarrhea. Food animals, especially poultry, are reservoirs of the organism and infection occurs following consumption of untreated surface water, unpasteurized milk, incompletely cooked meat or other contaminated food products. Close contact with infected immature companion animals is a significant cause of campylobacteriosis in children and direct intrafamilial transmission and occupational infection have been documented. Campylobacteriosis attributable to C. jejuni is a condition of emerging significance which arises principally from deficiencies in hygiene inherent in the environment and in the food chain which extends from domestic animals to the consumer.     

Prevalence of Campylobacter jejuni in selected domestic and wild birds in Louisiana

Prevalence of Campylobacter jejuni was determined in a selected population of domestic and free-living birds submitted for necropsy to the Louisiana State Veterinary Medical Diagnostic Laboratory. The 445 cases examined included 13 orders of birds and yielded C. jejuni in 45 cases, representing an isolation rate of 10.1%. Prevalence was highest in Galliformes (25.2%), followed by Anseriformes (12.9%) and Columbiformes (8.3%). Only one isolation was made out of 179 Psittaciformes examined. Penner serotypes 1, 2, 4, and 16 were most commonly identified among the C. jejuni isolates. This study emphasizes the importance of Galliformes as reservoirs of C. jejuni. The commonality of these serotypes with isolates derived from humans suggests the zoonotic potential of Galliformes in relation to human campylobacteriosis. The isolation rate of 12.9% in Anseriformes implicates free-living and migratory waterfowl as carriers of C. jejuni. Results confirm that Psittaciformes represent a low risk of C. jejuni infection in humans.     

Evaluation of biosecurity in broiler breeders

The economic impact of management practices designed to limit the introduction of disease into a parent broiler breeder flock (biosecurity) was evaluated using benefit-cost analysis. Equations were developed to quantify the losses resulting from infection with one of four alternative categories of disease representing incremental levels of pathogenicity. Realistic costs and assumed values relating to the probability of infection were used to evaluate the ameliorative effect of three alternative levels of biosecurity. A microcomputer spreadsheet program was used to confirm that expenditure on protective measures can be justified by both the risk of introducing a disease and the magnitude of losses that may occur following infection.     

Campylobacter jejuni contamination of eggs

Contamination of commercial table eggs with a fecal suspension containing 4.4 X 10(6) CFU/g Campylobacter jejuni resulted in shell penetration in 3/70 eggs and recovery of the organism from homogenized egg contents in 1/70 eggs. Viability of C. jejuni on the shell surface was retained for only 16 hours, attributed to desiccation of the fecal suspension. A field survey of three commercial laying farms and their associated egg-packing plants showed that hens demonstrated to be fecal shedders of C. jejuni (12% to 62% incidence) did not produce infected eggs. The organism could not be detected in the environment of the packing plant, including grading machinery and effluent.     

Sequential mitogen stimulation of peripheral blood lymphocytes from chickens inoculated with infectious bursal disease virus

Chickens were inoculated wih the pathogenic Edgar strain of infectious bursal disease virus at 1 week, 2 weeks, or 1 day of age. In the 3 experiments, phytohemagglutinin stimulation of peripheral blood lymphocytes was significantly decreased on day 3 or 4 after inoculation. Subsequently, on days 7 through 21, stimulations were similar between lymphocytes from inoculated birds and those from control birds. Pokeweed mitogen stimulation was affected minimally in virus-inoculated chickens. In each experiment, on day 7, the spontaneous [3H]thymidine uptake was greater in nonstimulated lymphocyte cultures from inoculated chickens than in such cultures from control chickens. In an additional experiment, chickens 1 week of age were exposed to a pathogenic vaccinal virus given in their water. The vaccinal virus exposure resulted in significant decrease of phytohemagglutinin stimulation of lymphocytes on days 3 and 7 of the experiment. A significant decrease in pokeweed mitogen stimulation was observed on day 10 after inoculation.     

世界肉鸡业前景展望

本文介绍了全球鸡肉消费市场及肉鸡生产现状,详细分析了肉鸡生产经济学、人和家禽的健康及家禽福利等影响肉鸡发展的动力因素,指出肉鸡生产商需通过对未来鸡肉市场需求的预测采取理性的扩张计划,并依赖健康有效的生物新技术来提高生产效益。     

Genetic characterization of three unique operational taxonomic units of Eimeria from chickens in Australia based on nuclear spacer ribosomal DNA

Coccidiosis of chickens is one of the commonest and economically most important parasitic diseases of poultry worldwide. Given the limitations of traditional approaches, molecular tools have been developed for the specific diagnosis of coccidiosis. Recently, a polymerase chain reaction (PCR)-based capillary electrophoresis (CE) method, employing genetic markers in the second internal transcribed spacer (ITS-2) of nuclear ribosomal DNA, was established for both analytical and diagnostic purposes. The application of this method to investigate the epidemiology of coccidiosis and genetic structures of Eimeria populations on commercial chicken establishments has discovered genetic variants of Eimeria (i.e., new operational taxonomic units OTU-X, OTU-Y and OTU-Z) which were (based on CE analysis) distinct from those of species of Eimeria identified previously in chickens in Australia. The present characterization of these OTUs, based on their ITS-2 sequences and phylogenetic analyses of selected sequence data, provides first evidence to support that OTU-X represents a population variant of Eimeria maxima, and that OTU-Y and OTU-Z represent cryptic species of Eimeria. Further biological and genetic studies are needed to rigorously test these proposals and establish the specific status of these OTUs and their importance as pathogens in chickens. An understanding of the epidemiology of these population variants or cryptic species in Australia is central to designing and implementing effective vaccination and control strategies.