R. C. Jones

A reverse transcriptase-polymerase chain reaction survey of infectious bronchitis virus genotypes in Western Europe from 2002 to 2006

A survey of infectious bronchitis virus (IBV) genotypes in poultry flocks in selected countries in Western Europe was carried out between March 2002 and December 2006. Identification of IBV was by reverse transcriptase-polymerase chain reaction of RNA extracted from oropharyngeal swabs taken from poultry flocks exhibiting signs of clinical disease thought to be attributable to IBV. Part of the hypervariable S1 gene of IBV was sequenced to differentiate between the various genotypes. During the survey, 4103 samples were processed, of which 2419 (59%) were positive for IBV. The predominant IBV genotypes detected were 793B and Massachusetts. The third and fourth most common genotypes were two new economically important field types: Italy02, and a virus similar to genotypes originally detected in China called QX. Analysis of the partial S1 sequences of the genotypes detected suggested that approximately 50% of all 793B, Massachusetts types and D274 IBVs were identical to the homologous commercially available live vaccines. Since 2004 the prevalence of Italy02 (present in all countries from which samples were received) has been declining in all countries except Spain, where it appeared to be the predominant genotype. Since 2004 an IBV genotype has been detected in Holland, Germany, Belgium and France similar to QX and the incidence has increased. QX was not detected in the United Kingdom or Spain. When detections thought to be attributable to vaccines were removed, the dominant genotype in France and Europe overall was 793B; in Germany, Holland and Belgium, it was QX-like IBV; and in the United Kingdom and Spain the dominant genotype was Italy02. The present study is the first to identify the prevalence of both Italy02 and QX field-type variants in poultry flocks in Western Europe. Several novel genotypes have also been detected.

Infectious bronchitis virus: Immunopathogenesis of infection in the chicken

SUMMARY The immunopathogenesis of infectious bronchitis virus (IBV) infection in the chicken is reviewed. While infectious bronchitis (IB) is considered primarily a disease of the respiratory system, different IBV strains may show variable tissue tropisms and also affect the oviduct and the kidneys, with serious consequences. Some strains replicate in the intestine but apparently without pathological changes. Pectoral myopathy has been associated with an important recent variant. Several factors can influence the course of infection with IBV, including the age, breed and nutrition of the chicken, the environment and intercurrent infection with other infectious agents. Immunogenic components of the virus include the S (spike) proteins and the N nucleoprotein. The humoral, local and cellular responses of the chicken to IBV are reviewed, together with genetic resistance of the chicken. In long-term persistence of IBV, the caecal tonsil or kidney have been proposed as the sites of persistence. Antigenic variation among IBV strains is related to relatively small differences in amino acid sequences in the S1 spike protein. However, antigenic studies alone do not adequately define immunological relationships between strains and cross-immunisation studies have been used to classify IBV isolates into ‘protectotypes’. It has been speculated that changes in the S1 protein may be related to differences in tissue tropisms shown by different strains. Perhaps in the future, new strains of IBV may arise which affect organs or systems not normally associated with IB.

The long view: 40 years of infectious bronchitis research

The remit of this review is to provide the non-specialist reader of Avian Pathology with an overview of research carried out on infectious bronchitis over the 40 years since the journal was first published. In order to do this, we felt it necessary to summarize the knowledge acquired previously, since the since the disease was first identified in the 1930s. Infectious bronchitis virus is a significant pathogen in the domestic chicken, affecting the respiratory and renal systems as well as the female reproductive tract. The virus exists in the form of many, ever changing, serotypic or genotypic variants, some of which have global distribution whilst others are found only in more local areas. This review mentions the major discoveries concerning both the virus itself and the types of disease it causes and considers recent changes in its pathogenesis. It also discusses the impact of developments in the field of molecular biology and highlights possible areas for future work.

Demonstration of sites of latency of infectious laryngotracheitis virus using the polymerase chain reaction.

Mature laying chickens were inoculated intratracheally with a field strain of infectious laryngotracheitis (ILT) virus. Tracheal swabs were collected regularly from all birds for virus culture. At various times post-inoculation, pairs of birds were killed and tissues removed for detection of virus products using conventional tissue homogenization and culture, organ culture, indirect immunofluorescence (IF) and also the polymerase chain reaction (PCR). The latter was used to detect a DNA sequence from the ILT virus thymidine kinase gene. Following inoculation the birds developed mild respiratory disease with clinical signs characteristic of ILT from 3 to 10 days post-inoculation. Trachea and turbinate tissues were virus-positive as determined by virus isolation, organ culture, IF and PCR on day 4 post-inoculation. After recovery from the acute phase, virus shedding initially ceased, then intermittent, low level shedding was recorded for five of the six remaining birds. In an attempt to locate sites of latency, pairs of birds were sampled at 31, 46 and 61 days post-inoculation. Virus was not detected in upper respiratory tract or ocular tissues by conventional techniques, or in the trigeminal, proximal and distal ganglia. All tissues were also negative by PCR, except for the trigeminal ganglia of five of the six birds. All PCR-positive birds had previously shed ILT virus intermittently between days 19 and 59 post-inoculation. As we did not detect viral DNA in any of the other tissues sampled from clinically recovered birds, we conclude that the trigeminal ganglion is the main site of latency of ILT virus.

Latency and reactivation of infectious laryngotracheitis vaccine virus.

SummaryLatency and reactivation of a commercial infectious laryngotracheitis virus vaccine were demonstrated in live chickens. Virus was re-isolated at intervals between seven and fourteen weeks post-vaccination and this may be of epizootiological significance.

Experimental infection of laying turkeys with Rhinotracheitis virus: Distribution of virus in the tissues and serological response

Twenty-four laying turkey hens shown to be free of antibodies to turkey rhinotracheitis virus were inoculated intranasally with an isolate of the virus. A mild respiratory disease developed between 5 and 9 days post infection (pi). Two birds were selected at random at intervals between days 1 and 20 pi, killed and tissues examined for the presence of virus. At autopsy between days 2 and 12 abnormalities were found in the oviducts including the deposition of inspissated albumen. Yolk material was occasionally found in the abdominal cavity and there was one instance of egg peritonitis. Eggs with abnormal shells were found in the uterus on days 3 and 9. By direct immunofluorescence (IF) staining, virus was detected in the trachea between days 1 and 7 pi and in the turbinates between days 2 and 5 pi. Virus could also be isolated from these sites using turkey embryo tracheal organ cultures but this method was slightly less sensitive than IF for these tissues. No virus was demonstrated in the lungs or air sacs. Viral antigens were detected by IF in the epithelium of the uterus on day 7 pi and in this and all other regions of the oviduct on day 9 pi. Virus was isolated only from middle magnum and vagina on day 9 pi. On other occasions up to 20 days pi the above tissues and spleen, ovary, liver, kidney and hypothalamus were all negative for virus. Antibodies detected by ELISA and serum neutralisation both reached, high titre by 12 days pi and were maintained at a high level (Iog2 12-15) throughout the period of observation (89 days).

Exacerbation of Mycoplasma gallisepticum infection in turkeys by rhinotracheitis virus.

Groups of 1-day-old turkey poults from a parent flock free of antibodies to turkey rhinotracheitis virus (TRTV) and the pathogenic mycoplasmas, were infected by eyedrop with virulent TRTV, with Mycoplasma gallisepticum (Mg) or with both agents together. Dual infection resulted in increased morbidity compared with those groups given single infections. The presence of the Mg in the dual infection had no apparent effect on the pathogenesis of the virus, but the virus caused the Mycoplasma to be more invasive. Mg infection caused a transient depression in TRTV ELISA antibody titres at 29 days post-inoculation. At 14 days post-infection Mg haemagglutination inhibition (HI) and rapid serum agglutination (RSA) titres were higher (P <0.01) in the mixed infection group compared with those infected with Mg alone, but there was no significant difference between ELISA antibody titres of these two groups.

The isolation and Characterisation of six avian infectious bronchitis viruses isolated in morocco

The first isolation and characterisation of infectious bronchitis (IB) viruses from poultry flocks in Morocco are reported. Five isolates designated D, E, F, H and M were related serologically to the Massachusetts serotype, while the sixth, isolate G, was found to be different from any previously reported serotype of IB virus. Neutralising antibodies to isolate G have been detected in sera collected from commercial flocks in Britain, although the virus has not been isolated. While all six isolates caused respiratory disease typical of IB in experimentally infected 3-week-old specified pathogen-free (SPF) chickens, isolate G was unusual in that it could be isolated from several parts of the alimentary tract for up to 21 days post inoculation, and from the duodenum up to 28 days. H120 vaccines protected chicks challenged with isolates E and F but not isolate G.

Reovirus‐induced tenosynovitis in chickens: The effect of breed

The effect of breed of chicken on infection with an arthrotropic avian reovirus strain R2 was studied by oral or footpad inoculation of 1-day-old chicks of the following breeds: (1) specific pathogen-free (SPF) light-hybrid, (2) commercial White Leghorn egg-layer, and (3) commercial Ross I broiler, and observed to 12 weeks of age. Although most inoculated birds of all three breeds developed swelling of one or both legs below the hock joint at 3 to 4 weeks of age, gross lesions of tenosynovitis became progressively more severe and extended above the joints only in broilers, whereas in most orally-infected SPF and commercial light chickens gross lesions were intermittently severe and regressed with time. Cloacal virus shedding continued up to 2 weeks in the lighter breeds and 3 weeks after infection in broilers. From a small proportion of infected chickens, reovirus was also reisolated from heart, pancreas and caecal tonsils. In all breeds, the tissue in which virus persisted longest was the hock joint/tendon. There was a poor correlation between isolation of virus and the presence of gross lesions in chickens of 12 weeks of age, especially in broilers. Virus-neutralisation tests demonstrated that seroconversion in the lighter breeds occurred predominantly at 3 weeks and in broilers at 4 weeks after infection. In all three breeds the footpad infection gave significantly lower growth rates than were found in the control and oral-infection groups. Oral infection had no apparent effect on growth rates. The greater susceptibility of broilers to reovirus infection is discussed.

Viral respiratory diseases (ILT, aMPV infections, IB): are they ever under control?

Abstract1. The use of vaccines is the main approach to control of the economically important poultry viral respiratory diseases infectious laryngotracheitis (ILT), avian metapneumovirus (aMPV) infections and infectious bronchitis (IB). This paper appraises the current methods of vaccine control in the light of the nature of each virus and epidemiological factors associated with each disease. 2. Infectious laryngotracheitis virus (ILTV) exists as a single type with a wide range of disease severity. It is a serious disease in certain regions of the world. Recent work has distinguished molecular differences between vaccine and field strains and vaccine virus can be a cause of disease. Vaccines have remained unaltered for many years but new ones are being developed to counter vaccine side effects and reversion and reactivation of latent virus. 3. Avian metapneumoviruses, the cause of turkey rhinotracheitis and respiratory disease in chickens exists as 4 subtypes, A, B, C and D. A and B are widespread and vaccines work well provided that accurate doses are given. Newer vaccine developments are designed to eliminate reversion and possibly counter the appearance of newer field strains which may break through established vaccine coverage. 4. IB presents the biggest problem of the three. Being an unstable RNA virus, part of the viral genome that codes for the S1 spike gene can undergo mutation and recombination so that important antigenic variants can appear irregularly which may evade existing vaccine protection. While conventional vaccines work well against homologous types, new strategies are needed to counter this instability. Molecular approaches involving tailoring viruses to suit field challenges are in progress. However, the simple use of two genetically different vaccines to protect against a wide range of heterologous types is now a widespread practice that is very effective. 5. None of the three diseases described can claim to be satisfactorily controlled and it remains to be seen whether the newer generations of vaccines will be more efficacious and cost effective. The importance of constant surveillance is emphasised and the testing of novel vaccines cannot be achieved without the use of vaccine-challenge experiments in poultry.