The history, current situation and control measures for infectious bronchitis virus (IBV) variants are reviewed. A large number of IBV variants exist worldwide; some being unique to a particular area, others having a more general distribution. The possible reasons why some strains spread readily over major parts of the world, whereas other strains stay more localized are discussed. The advantages and disadvantages of strain classification by protectotyping, serotyping and genotyping are discussed in relation to in vivo protection. The different vaccination strategies are also considered.

Since the end of 2003, strains of the D388 serotype (QX genotype) of infectious bronchitis virus (IBV) have caused considerable damage to the Dutch poultry industry. In order to better understand the pathogenesis of infection caused by this infectious bronchitis variant and to be able to support the poultry industry with substantiated advice to prevent or decrease the damage caused by the D388 strain, several vaccination and challenge experiments were performed in young specific pathogen free layers, young layers with maternally derived antibodies against the D388 strain and young commercial broiler breeders. The experiments confirmed the field observations that the D388 strain of the QX genotype is a very pathogenic strain that is able to cause cystic oviducts in a high percentage of birds, mortality due to nephritis and respiratory distress with complete tracheal ciliostasis and airsacculitis. Vaccination programmes using different combinations of heterologous live vaccines at day 0 or at days 0 and 14 induced a reasonable to high level of protection in the trachea, kidney, oviduct and air sacs against challenge with the D388 strain at 28 days of age. However, for very early protection, maternally-derived D388-neutralizing antibodies were shown to be very important. Titres of 9 to 10 log₂ maternally-derived D388 virus-neutralizing antibodies, which provided partial protection against tracheal damage and a high protection against replication of D388 in the kidney after challenge at 6 or 10 days of age, could be achieved using a broad heterologous live priming and subsequent boosting using inactivated IBV vaccines containing two or three heterologous IBV antigens.

Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are of clinical and economic importance for the global poultry industry. Many countries and integrations are involved in monitoring programs to control both mycoplasma species. This review provides an extensive historic overview of the last seven decades on the development of the knowledge regarding the factors that influence the clinical expression of the disease, the epidemiology and monitoring of both MG and MS. This includes the detection of new virulent strains, studies unravelling the transmission routes, survival characteristics and the role of other avian hosts. Also the role of molecular typing tests in unravelling epidemiology, and factors that complicate the interpretation of test results such as heterologous mycoplasma infections, use of heterologous oil-emulsion vaccines, use of antibiotic treatments, occurrence of MG and MS strains with low virulence, and last but not least the use of live and/or inactivated MG and MS vaccines are discussed.

The factors influencing the outcome of infectious bronchitis vaccination and challenge experiments regarding the respiratory and renal systems are reviewed. Advantages and disadvantages of the available techniques for measuring protection against an infectious bronchitis virus challenge are discussed, including the definition of protection itself. Suggestions are made regarding some ways in which progress towards standardization of a recognized protocol for performing experimental challenge studies can be made and areas where more work is needed are indicated.

In the present paper, we report the unexpected discovery of a new virus in samples from chicken and turkey flocks with clinical disorders such as tenosynovitis, enteric problems, or runting and/or stunting-like conditions. Since 1987, several virus isolation attempts on samples from these flocks resulted in the same macroscopic characteristic lesions in embryonated specific pathogen free eggs, being mortality with bright-red discolouration of legs and wing-tips, a swollen dark-red liver and oedema. Initial work suggested the presence of an agent with characteristics of a non-enveloped RNA virus. Further work, which is described in this paper, showed that the isolated strains formed a new group of avian nephritis viruses, which is genetically and antigenically distinct from known avian astroviruses. Inoculation of a representative strain (isolate 19) of this new group of avian nephritis viruses, provisionally named avian nephritis virus-3, in specific pathogen free layer chicks resulted in diarrhoea, runting and stunting, and even mortality.

Infectious bronchitis virus (IBV) is, in spite of vaccination, still a major cause of respiratory problems in broilers and of poor egg production in breeders and layers in many parts of the world. A possible cause of the insufficient protection induced by vaccination is an inadequate application of the vaccine. This paper reports the results of two field studies. In the first, the results of the alpha-IBV IgM enzyme-linked immunosorbent assay (ELISA) on post-vaccination sera were compared with the efficacy of the IBV vaccination against homologous challenge of the same broilers. The results showed that groups with at least 50% positive sera in the IgM ELISA at 10 days post vaccination had a high level of protection against challenge. Most groups of broilers with a low level of IgM ELISA positives had a low or moderate level of protection against challenge. In a second field study, the IgM response to IBV vaccination was compared with detailed information of the vaccination process of 360 spray-vaccinated flocks of about 2-week-old broilers, layer pullets, broiler breeders and broiler grandparents. The information included parameters such as flock size, type of chicken, housing, age of the chicken, application route, vaccine, dose, water quantity and temperature, ventilation and light management, combination with other vaccines and temperature of the house. The aim was to identify factors that might be associated positively or negatively with the IgM response and thereby with the expected level of protection against homologous challenge under field conditions. Significant associations were detected between the level of IgM response and factors regarding type of bird, flock size, housing type, ventilation management, light management, age/interval of vaccination, interval between vaccination and blood sampling, and temperature of the water that was used to reconstitute the vaccine. This knowledge can be useful to improve the average efficacy of IBV vaccination in the field.