Pathogenicity of latent infectious laryngotracheitis virus in chickens

Groups of specific pathogen-free chickens were inoculated with the same dose of a field strain of infectious laryngotracheitis virus that had either been isolated from tracheal swabs taken from infected birds during acute phase shedding, or that had been isolated during an episode of virus shedding after a latent period of 12 to 17 weeks. Birds in both groups developed characteristic clinical signs of ILT including difficulty in breathing, rales and sneezing. Thus, ILT virus shed after a latent period is capable of causing disease in susceptible birds similar to that seen in the field.     

Detection of infectious bronchitis virus in experimentally infected chickens by an antigen-competitive ELISA

An antigen-competitive enzyme-linked immunosorbent assay (Ag-C-ELISA) was developed for the detection of infectious bronchitis virus (IBV) antigens, M41 strain, in tissues from experimentally infected chickens, or in allantoic fluid harvested from inoculated embryonated eggs. The detection limit of IBV in the Ag-C-ELISA was 10^4.1 median embryo infective doses (EID50)/well. Tracheal and lung samples from chickens vaccinated with 10^2.5 EID50 of live attenuated infectious bronchitis (H120) vaccine were negative in the direct detection Ag-C-ELISA. The results indicate that the Ag-C-ELISA has the potential to detect IBV, either directly in tissue samples or when combined with the passage of material in embryonated eggs, thereby constituting an alternative method for the diagnosis of IBV.     

Protection of chickens from infectious laryngotracheitis with a recombinant fowlpox virus expressing glycoprotein B of infectious laryngotracheitis virus

Infectious laryngotracheitis (ILT) is an economically important disease of chickens caused by a type I gallid herpesvirus, infectious laryngotracheitis virus (ILTV). The vaccines currently available are modified live viruses, which are effective in preventing disease outbreaks. However, they have often been associated with a variety of adverse effects including spread of vaccine virus to non-vaccinates, inadequate attenuation, production of latently infected carriers, and increased virulence as a result of in vivo passage. In this study, a recombinant fowlpox virus expressing glycoprotein B (gB) of ILTV (rFPV-ILTVgB) was constructed. Protection of specific pathogen free (SPF) and commercial chickens from ILT with the rFPV-ILTVgB and commercial ILTV vaccine (Nobilis ILT) were compared after challenge with a lethal dose of virulent ILTV.Both the rFPV-ILTVgB- and the Nobilis ILT-vaccinated SPF chickens were completely protected from death, while 90% of the unvaccinated chickens died after challenge. The immunized commercial chickens were also 100% protected with rFPV-ILTVgB, compared with 85% protected with Nobilis ILT. The protective efficacy was also measured by the antibody response to ILTV gB, isolation of challenge virus and polymerase chain reaction amplification of the ILTV thymidine kinase gene after challenge. The results showed that rFPV-ILTVgB could be a potential safe vaccine to replace current modified live vaccines for preventing ILT.     

T-Cell suppression by cyclosporin-A enhances infectious bursal disease virus infection in experimentally infected chickens

In this study, the role of T lymphocytes was investigated in chickens experimentally infected with infectious bursal disease virus (IBDV). Chickens were treated with cyclosporin-A (CS-A), a selective T-cell suppressant drug, by the intramuscular route, starting 3 days before virus infection and every third day thereafter,and infectious bursal disease pathogenesis was compared in such T-cell suppressed and intact chickens using a vaccine strain; namely, Georgia and a field isolate of IBDV. Treatment of chickens with CS-A caused a significant suppression of phytohaemagglutinin-A specific proliferative responses of peripheral blood mononuclear cells. The virus neutralizing antibody titres in such CS-A treated chickens were not suppressed. T-Cell suppression resulted in an increase in the severity of gross lesions caused by IBDV and extensive muscular haemorrhages were observed in such chickens between 15 and 21 days post-inoculation. Similarly, there was a marked increase in the severity of infectious bursal disease-specific microscopic lesions in the bursa of T-cell suppressed chickens. Consistently higher titres of virus were observed in bursa of CS-A treated chickens. Virus titres were 1 to 2 log10 higher in the T-cell suppressed chickens as compared with the intact ones. These studies suggest that T cells play a role in limiting the IBDV infection.     

Effects of reticuloendotheliosis virus on the response of chickens to infectious laryngotracheitis virus

Effects of reticuloendotheliosis virus (REV) on the response to infectious laryngotracheitis virus (ILTV) were investigated in young chickens with and without maternally derived antibody (MAb) to REV. In the first experiment a group of 1-day-old chickens without REV MAb were inoculated at 1 day of age with REV whilst another group of similar chickens were left uninoculated. All chickens were vaccinated with ILTV at 7 days of age. There was a significantly higher proportion of infectious laryngotracheitis (ILT) post-vaccinal ophthalmia (p.v.o.) in the group inoculated with REV. In the second experiment chickens with and without MAb to REV were inoculated at 1 day old with REV. These chickens, together with others not inoculated with REV, were vaccinated with ILTV isolate SA-2 8 days later. A virulent ILTV isolate, G, was used to challenge all the chickens 20 days after vaccination. Again the chickens without MAb to REV inoculated with REV showed a higher proportion of ILT p.v.o. and a significantly higher mortality rate due to ILT following vaccination. In the chickens inoculated with REV at 1 day of age and not vaccinated but challenged with ILTV there was a significantly higher mortality and rate of clinical signs due to ILT in those birds without than in those with REV MAb. In both experiments chickens from REV negative parents were found to be free of REV neutralising MAb. However, only 30% of chickens originating from a flock known to be infected with REV had a titre of 1/40 or higher. In spite of this, this group was significantly more resistant than the group without REV MAb to the immunosuppressive effect of inoculation at 1 day old with REV. This was demonstrated by their lower susceptibility (i.e. less p.v.o. and mortality) to the vaccination and challenge with ILTV. Chickens without REV MAb developed neutralising antibodies within 2 weeks of inoculation with REV. Irrespective of the REV MAb status 1-day-old chickens inoculated with REV were viraemic within a week.     

Infectious laryngotracheitis virus in chickens

Infectious laryngotracheitis (ILT) is an important respiratory disease of chickens and annually causes significant economic losses in the poultry industry world-wide. ILT virus (ILTV) belongs to alphaherpesvirinae and the Gallid herpesvirus 1 species. The transmission of ILTV is via respiratory and ocular routes. Clinical and post-mortem signs of ILT can be separated into two forms according to its virulence. The characteristic of the severe form is bloody mucus in the trachea with high mortality. The mild form causes nasal discharge, conjunctivitis, and reduced weight gain and egg production. Conventional polymerase chain reaction (PCR), nested PCR, real-time PCR, and loop-mediated isothermal amplification were developed to detect ILTV samples from natural or experimentally infected birds. The PCR combined with restriction fragment length polymorphism (RFLP) can separate ILTVs into several genetic groups. These groups can separate vaccine from wild type field viruses. Vaccination is a common method to prevent ILT. However, field isolates and vaccine viruses can establish latent infected carriers. According to PCR-RFLP results, virulent field ILTVs can be derived from modified-live vaccines. Therefore, modified-live vaccine reversion provides a source for ILT outbreaks on chicken farms. Two recently licensed commercial recombinant ILT vaccines are also in use. Other recombinant and gene-deficient vaccine candidates are in the developmental stages. They offer additional hope for the control of this disease. However, in ILT endemic regions, improved biosecurity and management practices are critical for improved ILT control.     

The appearance of viral antigen and antibody in the trachea of naive and vaccinated chickens infected with infectious laryngotracheitis virus

In chickens vaccinated with SA-2 infectious laryngotracheitis (ILT) virus, viral antigen could no longer be detected in tracheal washings from day 7 post infection (pi). Total specific antibody was detected in tracheal washings from day 5 pi, IgA antibody appeared at day 6 pi, but neutralising antibody could not be detected until day 14. In the serum of vaccinated chickens, total antibody appeared on day 5 pi and neutralising antibody on day 7. However, no IgA antibody could be detected in serum. There was a substantial increase in the numbers of IgA- and IgG-synthesising cells in the trachea by day 3 pi, with a marked increase in the numbers of IgA-positive cells at day 7 pi. Following challenge with virulent CSW-1 ILT virus, no virus could be detected in the trachea of vaccinated chickens. There was also no evidence of an anamnestic antibody response in the trachea or in serum up to day 10 post challenge, and there was no significant change in the numbers of IgA- or IgG-synthesising cells in the tracheas of vaccinated chickens up to day 7 post challenge.     

Capripoxvirus tissue tropism and shedding: A quantitative study in experimentally infected sheep and goats

Sheeppox virus and goatpox virus cause systemic disease in sheep and goats that is often associated with high morbidity and high mortality. To increase understanding of the pathogenesis of these diseases, we undertook quantitative time-course studies in sheep and goats following intradermal inoculation of Nigerian sheeppox virus or Indian goatpox virus in their respective homologous hosts. Viremia, determined by virus isolation and real-time PCR, cleared within 2 to 3 weeks post inoculation. Peak shedding of viral DNA and infectious virus in nasal, conjunctival and oral secretions occurred between 10 and 14 days post inoculation, and persisted at low levels for up to an additional 3 to 6 weeks. Although gross lesions developed in multiple organ systems, highest viral titers were detected in skin and in discrete sites within oronasal tissues and gastrointestinal tract. The temporal distribution of infectious virus and viral DNA in tissues suggests an underlying pathogenesis that is similar to smallpox and monkeypox where greatest viral replication occurs in the skin. Our data demonstrate that capripoxvirus infections in sheep and goats provide additional and convenient models which are suitable not only for evaluation of poxvirus-specific vaccine concepts and therapeutics, but also study of poxvirus-host interactions.     

Sequential skin lesions in chickens experimentally infected with Marek's disease virus

Skin biopsies taken at weekly intervals from the same specific-pathogen free (SPF) chickens inoculated with Md/5 Marek's disease virus revealed two distinctive patterns of perifollicular cutaneous lesions, tumour-associated and non-tumour-associated. The tumour-associated pattern was subdivided into two types. The progressive type was manifested by a continuous increase of lymphoid cell aggregates (LCA) in the skin, resulting in the development of gross skin tumours with or without visceral tumours, and the regressive type showed initially increased and finally regressed LCA in the skin, associated with the development of visceral tumours. The non-tumour-associated pattern was characterized by initial transient small LCA in the skin without evidence of tumour formation. Birds with the tumour-associated pattern, regardless of type, had persistent nuclear inclusions (NI) and positive reactions against MDV1-specific phosphorylated polypeptides in the feather follicle epithelium (FFE) and initial R(1)-type (consisting mainly of small lymphocytes with a few lymphoblasts) to advanced T-type (consisting predominantly of lymphoblasts) feather pulp lesions (FPL). On the other hand, birds with the non-tumour-associated pattern formed transient NI and positive reactions against MDV1-specific phosphorylated polypeptides in the FFE and Ri-type to R(2)-type (consisting mainly of plasma cells with oedema) FPL. Antigen-positive lymphoid cells against MDV1-specific phosphorylated polypeptides were detected in both inflammatory and tumourous lesions, especially in the necrotic tumour lesions in the skin of birds showing the progressive type.     

Neurological lesions in chickens experimentally infected with virulent Newcastle disease virus isolates

Distribution, character, and severity of lesions were evaluated in tissues from the central nervous system of chickens inoculated with 10 different Newcastle disease virus (NDV) isolates: CA 1083, Korea 97-147, Australia (all velogenic viscerotropic), Texas GB and Turkey North Dakota (both velogenic neurotropic), Nevada cormorant, Anhinga and Roakin (all mesogenic), and B1 and QV4 (lentogenic). Tissues for the present study included archived formalin-fixed, paraffin-embedded brain (all strains) plus spinal cord (two strains). Encephalitis was observed in all velogenic viscerotropic and velogenic neurotropic strains, and in some mesogenic strains. In general, the encephalitic lesions began at 5 days post infection, with more severe lesions occurring around 10 days post infection. At this time point, especially in the grey matter of the brain, cerebellum and spinal cord, there were neuronal necrosis, neuronal phagocytosis, and clusters of cells with microglial morphology. Axonal degeneration and demyelination was also observed. Immunohistochemistry (IHC) for viral nucleoprotein confirmed the presence of virus. In the areas of encephalomyelitis, IHC for CD3 revealed that many of the inflammatory cells were T lymphocytes. IHC using an antibody for glial fibrillar acid protein showed reactive astrogliosis, which was most pronounced at the later time points.     

Immune responses to infectious laryngotracheitis virus

Infectious laryngotracheitis (ILT) is an upper respiratory tract disease in chickens caused by infectious laryngotracheitis virus (ILTV), an alphaherpesvirus. Despite the extensive use of attenuated, and more recently recombinant, vaccines for the control of this disease, ILT continues to affect the intensive poultry industries worldwide. Innate and cell-mediated, rather than humoral immune responses, have been identified as responsible for protection against disease. This review examines the current understandings in innate and adaptive immune responses towards ILTV, as well as the role of ILTV glycoprotein G in modulating the host immune response towards infection. Protective immunity induced by ILT vaccines is also examined. The increasing availability of tools and reagents for the characterisation of avian innate and cell-mediated immune responses are expected to further our understanding of immunity against ILTV and drive the development of new generation vaccines towards enhanced control of this disease.     

Hemagglutination with avian infectious laryngotracheitis virus

Summary Avian infectious laryngotracheitis virus grown in primary chicken kidney cell cultures was tested for hemagglutination (HA) with erythrocytes of a variety of species at 4°C, 22°C, and 37°C. HA was observed at all temperatures with mouse erythrocytes but not with cattle, sheep, goat, swine, rabbit, guinea pig, chicken, and goose erythrocytes. A strain variation between mice in the agglutinability of their erythrocytes necessitated selection of mice to obtain erythrocytes. The HA reaction was inhibited by specific antiserum. Some factors involved in the HA and HA-inhibition (HI) were investigated and standard HA and HI tests were established. HI antibody titers of individual chicken sera had a significant positive correlation with their neutralizing antibody titers.     

Relationship between SMON virus and avian infectious laryngotracheitis virus

Archives of Virology - A new virus, SMON virus, isolated from human cases of subacute myelooptico-neuropathy (S.M.O.N.) was neutralized by anti-avian infectious laryngotracheitis (ILT) virus immune...     

Latency and reactivation of infectious laryngotracheitis vaccine virus

Summary Latency 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.     

Leukocyte subpopulations in kidney and trachea of chickens infected with infectious bronchitis virus

Using immunohistochemical methods, we studied the nephropathogenicity of the infectious bronchitis virus (IBV)-strain V1648- and the leukocyte phenorypes in the pathological lesions in the kidneys and the trachea formed after inoculation with this virus strain. One-day-old WLA chickens were intravenously inoculated, and after 5, 7 and 11 days their kidneys, trachea and lungs were removed. Monoclonal antibodies were used to detect viral antigen, and lymphoid and non-lymphoid cell populations. In serial sections, the detection of the viral antigen was correlated to the phenotypes of the cells. At days 5 and 7 after inoculation, viral antigen was detected in the epithelium and the interstitium of the kidney tubuli and in the epithelium of the trachea. The infiltrated cells in these tissues were mainly of the T cell phenotype. The cellular immune reaction was correlated with the detection of viral antigen.