Acta Veterinaria Hungarica 45 (3) (1997)
of the World Veterinary Poultry Association
The structure and function of the avian immune system.
J. M. Sharma
Viral diseases of the immune system and strategies to control infectious bursal disease by vaccination.
Avian tumor viruses: persistent and evolving pathogens.
R. L. Witter
Epidemiology of avian diseases.
E. F. Kaleta
Towards the routine application of nucleic acid technology for avian disease diagnosis.
D. Cavanagh, K. Mawditt, K. Shaw, P. Britton and C. Naylor
Changing expectations in the control of Mycoplasma gallisepticum.
S. H. Kleven
Safe poultry meat production in the next century.
R. W. A. W. Mulder
Novel approaches to control of bacterial infections in animals.
P. A. Barrow
Eimeria spp. from the chicken: Occurrence, identification and genetics.
M. W. Shirley
Nutritional metabolic diseases of poultry and disorders of the biological antioxidant defence system.
M. Mézes, P. Surai, G. Sályi, B. K. Speake, T. Gaál and A. Maldjian
Biosecurity in poultry production: Where are we and where do we go?
G. Ph. te Winkel
DNA amplification methods for diagnosis and epidemiological investigations of avian mycoplasmosis.
Acta Veterinaria Hungarica 45 (3), pp. 229-238 (1997)
THE STRUCTURE AND FUNCTION OF THE AVIAN IMMUNE SYSTEM
J. M. Sharma
Veterinary PathoBiology, College of Veterinary Medicine, University of Minnesota,
St. Paul, Minnesota, U. S. A.
(Received June 6, 1997)
Among the avian species, the immune system of the chicken has been studied most extensively. There are many similarities between the general immune mechanisms of mammals and chickens. There are also important differences. Birds respond to antigenic stimulation by generating antibodies as well as cellular immunity. There are three principal classes of antibodies in birds i.e., IgM, IgG (also called IgY) and IgA. Antibody diversity is achieved by gene conversion. T cells are the main effector cells of cellular immunity. The avian T cells differentiate into two distinct pathways i.e., a /b and g /d . Avian T cell diversity is likely generated through combinatorial and junctional mechanisms similar to the mechanisms that operate in mammalian T cell receptors. As in mammals, avian T cells engage in helper and cytotoxic functions that are MHC restricted. The innate effector mechanisms include those mediated by natural killer (NK) cells and antibody dependent cellular cytotoxicity (ADCC). Recently, genes of several avian cytokines have been cloned and expressed. A number of naturally occurring viruses cause immunosuppression in chickens. There is much current interest in understanding the mechanisms of immunosuppression and developing strategies to enhance immune responsiveness in commercial poultry.
Key words: Avian immunity, T cells, B cells, NK cells, antibody, cellular immunity, vaccination, immunosuppression, immunomodulation, bursa of Fabricius, thymus
Acta Veterinaria Hungarica 45 (3), pp. 239-249 (1997)
VIRAL DISEASES OF THE IMMUNE SYSTEM
AND STRATEGIES TO CONTROL INFECTIOUS BURSAL DISEASE BY VACCINATION
Intervet International B. V., P.O. Box 31, 5830 AA Boxmeer, The Netherlands
(Received June 6, 1997)
Viral infections which are immunosuppressive can affect the economics of poultry production, often as a result of the chickens increased susceptibility to secondary infections and sub-optimal response to vaccinations. The mechanism of this immunosuppression has been studied in detail for certain chicken viruses. The replicating virus can have both direct and indirect effects on the cells of the immune system. The special role of the bursa of Fabricius, as a lympho-epithelial organ, will be mentioned. The effects of oncogenic viruses (MDV, REV and ALV) on the immune system will be discussed as will the present status of our knowledge on the immunosuppressive effects of certain respiratory viruses such as ILT, NDV and reovirus. Two major immunosuppressive agents are CAV and IBDV. The effects of IBDV will be described in more detail because of its economic importance. Advances made in the molecular biology of both the virus and the immune system give new opportunities to control the disease by vaccination. Successful vaccination strategies applied in the past and options for the future will be discussed.
Key words: Viral diseases, chicken, immunosuppression, oncogenic viruses, infectious bursal disease virus, control strategies, vaccination
Acta Veterinaria Hungarica 45 (3), pp. 251-266 (1997)
AVIAN TUMOR VIRUSES:
PERSISTENT AND EVOLVING PATHOGENS
R. L. Witter
Avian Disease and Oncology Laboratory, USDA Agricultural Research Service,
East Lansing, Michigan, USA
(Received May 29, 1997)
Most neoplasias of lymphoid and other hematopoietic cells in commercial poultry are caused by viruses which belong to one of four distinct groups. Mareks disease virus (MDV) is an oncogenic herpesvirus. Avian leukosis virus (ALV), reticuloendotheliosis virus (REV) and lymphoproliferative disease virus (LPDV) are oncogenic retroviruses. Each group is distinguished by nucleic acid type, molecular structure, antigenicity, epidemiology, host range and other characteristics. However, most of these viruses have in common a unique ability to persist, both in the host and in the ecosystem. In addition, both the viruses and the virushost relationships for several members of the group have demonstrated a propensity to evolve with time, creating new dilemmas for diagnosis and control. A focus on the persistence and evolution of avian tumor viruses will be used to address a number of current issues with individual viruses of economic importance. Issues of primary concern include (1) the evolution of MDV towards greater virulence with concomitant reduction of vaccine efficacy and expansion of host range, (2) the emergence of subgroup J ALV as a major pathogen in meat-type breeder stocks, and (3) the increasing prevalence of REV and its evolving role as a pathogen in chickens and turkeys.
Key words: Neoplasm, tumor, chicken, turkey, avian, virus, retrovirus, herpesvirus, Mareks disease, lymphoid leukosis, myelocytomatosis
Acta Veterinaria Hungarica 45 (3), pp. 267-280 (1997)
EPIDEMIOLOGY OF AVIAN DISEASES
E. F. Kaleta
Institute for Avian and Reptile Medicine, Justus Liebig University Giessen,
Frankfurter Straße 87, D-35392 Giessen, Germany
(Received May 20, 1997)
A large number of diseases occur in domestic, farm-raised poultry. Only two of the many different diseases are notifiable and subject to governmental control: highly pathogenic avian influenza and Newcastle disease. Diagnosis and treatment or prevention of all other conditions are left to the skills of farmers and their veterinarians. Poultry production is aimed at providing more and tastier food for the ever growing human community. Infectious diseases and technical errors during production and processing need to be minimised. The concept of hazard analysis critical control point (HACCP) has already been introduced into food processing and quality assessment. The regulations laid down in ISO 9000 will soon become a powerful and practical tool for monitoring and improving the productivity of live poultry. Approved epidemiological concepts and tools will enable the poultry industry to achieve constant and safe production. Certification on the basis of ISO 9000 of all areas of poultry production is a new approach for maintaining the health of poultry, for tracing and subsequently eliminating breaks in productivity, and securing production without health hazards for the consumer.
Key words: Epidemiology, diseases, poultry, production, HACCP, certification
Acta Veterinaria Hungarica 45 (3), pp. 281-298 (1997)
TOWARDS THE ROUTINE APPLICATION OF NUCLEIC ACID TECHNOLOGY
FOR AVIAN DISEASE DIAGNOSIS
D. Cavanagh, K. Mawditt, K. Shaw, P. Britton and C. Naylor
Institute for Animal Health, Compton Laboratory, Compton, Newbury RG20 7NN, UK
(Received May 5, 1997)
The use of nucleic acid technology (polymerase chain reaction, probing, restriction fragment analysis and nucleotide sequencing) in the study of avian diseases has largely been confined to fundamental analysis and retrospective studies. More recently these approaches have been applied to diagnosis and what one might call real-time epidemiological studies on chickens and turkeys. At the heart of these approaches is the identification and characterisation of pathogens based on their genetic material, RNA or DNA. Among the objectives has been the detection of pathogens quickly combined with the simultaneous identification of serotype, subtype or genotype. Nucleic acid sequencing also gives a degree of characterisation unmatched by other approaches. In this paper we describe the use of nucleic acid technology for the diagnosis and epidemiology of infectious bronchitis virus, turkey rhinotracheitis virus (avian pneumovirus) and Newcastle disease virus.
Key words: Diagnosis, molecular, infectious bronchitis virus, turkey rhinotracheitis virus, Newcastle disease virus
Acta Veterinaria Hungarica 45 (3), pp. 299-305 (1997)
CHANGING EXPECTATIONS IN THE CONTROL
OF MYCOPLASMA GALLISEPTICUM
S. H. Kleven
University of Georgia, Department of Avian Medicine, Athens, Georgia 306024875, USA
(Received May 16, 1997)
Mycoplasma gallisepticum (MG) is traditionally controlled by maintaining MG-free flocks on single-age production sites and maintaining them MG-free utilizing good biosecurity and a consistent serological monitoring program. In recent years, several changes have taken place which have changed our ways about thinking about MG control. There have been significant improvements in detection methods. For example, polymerase chain reaction now represents a rapid and sensitive method for detecting the organism. ELISA kits are now much improved. DNA technology now allows rapid identification of specific strains (DNA fingerprinting) for epidemiological studies. On the other hand, the industry world-wide is growing rapidly, and there are huge populations of poultry in small geographic areas, making control utilizing biosecurity more and more difficult. Also, multi-age production sites are becoming more common, especially in commercial egg production. This has led to increased usage of live MG vaccines, which are effective in controlling economic losses and may be used as tools in eradication programs.
Key words: Mycoplasma gallisepticum, vaccination, ELISA, serology, polymerase chain reaction (PCR)
Acta Veterinaria Hungarica 45 (3), pp. 307-315 (1997)
SAFE POULTRY MEAT PRODUCTION
IN THE NEXT CENTURY
R. W. A. W. Mulder
ID-DLO Institute for Animal Science and Health, Agricultural Research Department, P.O. Box 65, 8200 AB Lelystad, The Netherlands
(Received May 22, 1997)
The revolutionary industrialisation of the poultry industry in the last 30 years has made the food poultry meat available for large groups of consumers. Due to its nutritional, sensory and economical characteristics, poultry meat is by far the most popular animal food product world-wide. Epidemiological reports, however, incriminate poultry meat as a source for outbreaks of human food poisoning. The organisms involved are Salmonella spp., Campylobacter spp. and, to a lesser extent, Listeria monocytogenes, Escherichia coli, Staphylococcus aureus, Yersinia enterocolitica, Clostridium perfringens and Aeromonas spp. Contamination of the end-product with pathogenic microorganisms is a reflection of the contamination of the live birds and, therefore, measures to be taken by industry to avoid contamination of the consumer-ready product should start at that level. In terms of the critical control point approach of the HACCP concept, the quantitative contribution of critical phases in the production chain towards end-product contamination should be estimated in order to take the necessary intervention or corrective steps. To guarantee the production of safe poultry meat, knowledge of the capability of microorganisms to colonise the gastrointestinal tract is needed and the use of vaccines, antimicrobials and competitive exclusion microfloras as well as the implementation of new processing technology should be encouraged.
Key words: Poultry meat, food safety, critical points, intervention strategy
Acta Veterinaria Hungarica 45 (3), pp. 317-329 (1997)
NOVEL APPROACHES TO CONTROL
OF BACTERIAL INFECTIONS IN ANIMALS
P. A. Barrow
Institute for Animal Health, Compton, Newbury, Berkshire RG20 7NN, United Kingdom
(Received May 6, 1997)
Bacterial infections of poultry remain of great importance world-wide in terms of economic effects and public health. They include infections caused by Salmonella, Escherichia coli, Campylobacter and Pasteurella. Through the introduction of rigid hygienic measures it is possible to breed and rear poultry free of these pathogens. However, the cost to the industry would be prohibitive and economically disastrous. Biological measures have been introduced albeit in a relatively empirical way. Antibiotic therapy and prophylaxis is used extensively with the associated problems of development of resistance. Killed vaccines are used but are not usually very effective. Live vaccines are increasingly becoming acceptable and studies are under way to increase our understanding of the pathogenesis of these infections so that vaccine development may become less empirical. Work with live vaccines to be used against Salmonella has shown that they may be administered orally to newly-hatched chicks. The vaccine strain colonises the gut extensively and prevents re-infection by other Salmonella strains by a genus-specific mechanism which is similar to that which occurs during down-regulation of bacterial growth in stationary-phase nutrient broth cultures. The mechanism of this phenomenon is currently being studied. This approach may also be applied to control Campylobacter infections. Bacteria of the Pasteurella group and E. coli may produce septicaemic infections in poultry. Recent work with K1+ E. coli infections in mice has shown that virulent bacteriophages may be used to treat or prevent septicaemias and meningitides. This work has been extrapolated to chickens with a similar degree of success and it suggests that some infections of this sort in animals and man may be amenable to this approach. In-bred lines of chickens have been found to vary greatly in their susceptibility to systemic Salmonella infections. This is probably mediated by one gene and the effect is dominant and not linked to sex or MHC. The mouse natural resistance gene (Nramp1) does not appear to contribute greatly to this effect. Differences in the extent of gut colonisation by Salmonella in in-bred and out-bred lines can also be detected. These results are very exciting and open up opportunities for disease control for the future.
Key words: Bacterial infections, Salmonella, live vaccines, competitive exclusion, bacteriophages, innate resistance
Acta Veterinaria Hungarica 45 (3), pp. 331-347 (1997)
EIMERIA SPP. FROM THE CHICKEN:
OCCURRENCE, IDENTIFICATION AND GENETICS
M. W. Shirley
Institute for Animal Health, Compton Laboratory, Compton, Nr Newbury,
Berks, RG20 7NN, England
(Received May 28, 1997)
Many fundamental aspects of the biology of Eimeria spp. from the chicken remain poorly understood and some have not been investigated in detail for many years. New molecular tools are now available that could be used to underpin some of the more practical aspects of disease control. For example, a far better understanding of the epizootiology of the parasites, with precise knowledge of the characteristics of individual species and strains that are prevalent in the field might, in the future, be incorporated into strategies that see a more rational use of the available drugs and vaccines. The recent use of electrophoretic variation of enzymes to investigate parasite epizootiology is described and the general case for the development of specific, more sensitive DNA-based technologies is discussed. A wealth of DNA probes is potentially available from the large genome of Eimeria spp. and the genetic complexity of these parasites has recently been illustrated in more detail. In addition to a large nuclear genome comprising at least 14 linear chromosomes, studies on E. tenella have shown that, like Plasmodium and Toxoplasma, it also possesses a mitochondrial genome and a newly discovered "plant-like" genome that probably resides within an uncharacterised organelle and was acquired when an ancestor engulfed and kept and algal cell containing a chloroplast. A double-stranded RNA genome has also been identified in some species.
Key words: Eimeria, epizootiology, genetics, DNA
Acta Veterinaria Hungarica 45 (3), pp. 349-360 (1997)
NUTRITIONAL METABOLIC DISEASES OF POULTRY
AND DISORDERS OF THE BIOLOGICAL ANTIOXIDANT DEFENCE SYSTEM
M. Mézes1, P. Surai2, G. Sályi3, B. K. Speake2, T. Gaál4 and A. Maldjian2
1Department of Nutrition, Gödöllő University of Agricultural Sciences, H2013 Gödöllő, Páter K. u. 1, Hungary; 2Biochemical Sciences Department, Scottish Agricultural College, Auchincruive, KA6 5HW, Scotland; 3Central Veterinary Institute, H1581
Budapest, P.O. Box 2, Hungary; 4Department of Internal Medicine, University of Veterinary Science, H1400 Budapest, P.O. Box 2, Hungary
(Received May 30, 1997)
Deficiencies or disturbances of nutrition cause a variety of diseases and can arise in different ways. The amount of a particular nutrient in the diet may be insufficient to meet the requirements, the diet may contain substances that inactivate the nutrient or inhibit its absorption/utilisation, or metabolism may be upset by the interaction of dietary and environmental factors. Peroxidation of lipids or oxygen free radical generation in general is a physiological process important for cell metabolism, division and differentiation and also for the biosynthesis of hormones and prostaglandins. Free radicals generated through these processes are effectively scavenged by the antioxidant defence system. Uncontrolled lipid oxidation caused by disturbances of that system may play a crucial role in some important poultry diseases and toxicoses. The first route of lipid peroxide loading of the organism is via the feed, such as through oxidised lipids. Oxidised fatty acids are absorbed from the intestine mainly in the form of unsaturated keto compounds and initiate lipid peroxidation in the tissues. The second problem is the insufficient amount of antioxidants in the feed, e.g. vitamin E deficiency. Nutritional encephalomalacia is a problem in poultry production which depends both on the actual vitamin E supply and the dietary amount of polyunsaturated fatty acids. In young birds the primary target of vitamin E deficiency is the brain because it contains low amounts of vitamin E, and the vitamin E content of the liver acting as store decreases rapidly during the first week of life. Besides vitamin E, other components of the antioxidant system, e.g. the antioxidant enzymes (catalase and glutathione peroxidase) also have low activity in the brain as compared to other major tissues. The brain is highly susceptible to oxidative stress because of the accumulation of polyunsaturated fatty acids. The third source of free radical generation is the toxic level of different feed ingredients, e.g. toxicoses caused by vitamin A, selenium, and ionophore antibiotics. Other important aspects of antioxidants (e.g. vitamin E and selenium) in poultry are stimulation of the immune response (e.g. in the case of vaccination) and reduction of the risks of free radical formation as a result of macrophage function.
Key words: Antioxidants, free radicals, lipid peroxidation, nutritional metabolic diseases, poultry
Acta Veterinaria Hungarica 45 (3), pp. 361-372 (1997)
BIOSECURITY IN POULTRY PRODUCTION:
WHERE ARE WE AND WHERE DO WE GO?
G. Ph. te Winkel
Euribrid B. V., P.O. Box 30, 5830 AA Boxmeer, The Netherlands
(Received June 3, 1997)
An overview is given about the importance of biosecurity in the poultry industry, and a comparison is made with other systems of disease control such as vaccination and medication. Different measures considered to be important in biosecurity are reviewed and some expectations for the future are given. Furthermore, some attention is paid to the animal welfare aspects.
Key words: Biosecurity, disease control, vaccination, medication, animal welfare, poultry
Acta Veterinaria Hungarica 45 (3), pp. 373-386 (1997)
DNA AMPLIFICATION METHODS FOR DIAGNOSIS
AND EPIDEMIOLOGICAL INVESTIGATIONS
OF AVIAN MYCOPLASMOSIS
CNEVA Ploufragan, Unité Mycoplasmologie Bactériologie, Zoopôle Les Croix, BP 53, 22440 Ploufragan, France
(Received May 27, 1997)
Rapid, sensitive and specific tests that detect nucleic acid from pathogenic mycoplasmas are very attractive for the laboratory detection of infected flocks, and methods for direct detection of the four main pathogenic mycoplasmas have been developed. Moreover, most avian mycoplasma species can be differentiated, according to their unique restriction fragment length polymorphism (RFLP) patterns generated with different restriction enzymes. However, this method is limited to the identification of pure cultures of avian mycoplasmas as other bacteria may be amplified by the set of primers chosen. Another application of PCR-RFLP is the ability to distinguish between very closely related species such as M. gallisepticum and M. imitans. In order to characterise isolates below the species level, PCR-based subtyping methods have been introduced. One of them, arbitrarily primed-PCR, results in strain-specific arrays of DNA fragments that can distinguish even closely related strains of a given species. This method was successfully used to investigate the molecular epidemiology of vaccine strains or of Mycoplasma gallisepticum conjunctivitis in songbirds. Major issues in the development of DNA amplification tests concern the selection of the appropriate target for amplification, specimen collection, DNA preparation and detection of amplification reaction inhibitors. Detection of amplified products is most commonly performed after gel electrophoresis or probe-based methods. Careful consideration to the design and work flow of the facility are necessary to avoid false-positive results.
Key words: Avian mycoplasmosis, PCR, diagnosis, epidemiological study