Renata Novak

Abundance of IFN-α and IFN-γ mRNA in blood of resistant and susceptible chickens infected with Marek's disease virus (MDV) or vaccinated with turkey herpesvirus; and MDV inhibition of subsequent induction of IFN gene transcription

Summary.The effects of the very virulent RB-1B strain of Marek’s disease virus (MDV) and turkey herpesvirus (HVT), a vaccinal strain, on abundance of IFN mRNA in the blood were investigated. MDV and HVT infection did not change the circulating level of IFN-γ mRNA 1 and 7 days p.i., but they increased IFN-α mRNA levels slightly in genetically susceptible (to tumour development) B13/B13 chickens. The total number of circulating leukocytes was unchanged and increase in message was accompanied by an increase in circulating CD8α+ and MHC Class II+ cells. On the contrary, both viruses slightly increased IFN-γ transcripts and decreased IFN-α transcripts in genetically resistant B21/B21 chickens. Further, oncogenic MDV was able to block the response to inactivated Newcastle disease virus, a potent inducer of IFN, in both chicken lines. The inhibiting effect on transcription was present for both IFN at days 1 and 7 p.i. in susceptible B13/B13 chickens, but only at day 7 p.i. in resistant B21/B21 chickens. By contrast, non-oncogenic HVT did not interfere with induction of either message at one day p.i. and MDV had a more suppressive effect than HVT on IFN gene transcription 7 days p.i. in B21/B21 chickens. Thus, the strong ability of MDV to block induction of IFN gene transcription detected in the blood as soon as one day after infection in susceptible chickens, as opposed to resistant chickens, not only causes immunosuppression but also may be related to the virus’s oncogenicity.

Short Communication: Chicken Anemia Virus and Infectious Bursal Disease Virus Interfere with Transcription of Chicken IFN-α and IFN-γ mRNA

Chicken anemia virus (CAV) and infectious bursal disease virus (IBDV) are the two most important viruses that cause immunosuppression in commercial chickens. Because inapparent, subclinical infections by these viruses cause immunosuppression, there is need for assessment of the immune status of chickens. Interference with induction of transcription for chicken interferon-α (ChIFN-α) and ChIFN-γ was noted after subclinical infections with either CAV or IBDV. Because the immunosuppressive viruses of chickens may interfere with transcription for ChIFN-α and ChIFN-γ, we propose using this interference to assess the immune status of chickens.

Immune status assessment by abundance of IFN-alpha and IFN-gamma mRNA in chicken blood.

Avian diseases, including such viral infection as infectious bursal disease, infectious anemia, and Mareks disease, often cause immunosuppression, leading to more severe infection, problems with secondary infection, and inadequate responses to vaccination. Immunosuppression thus causes serious economic losses in commercial poultry production. To date, methods for assessing immune status have been too slow to be of practical help. Reasoning that immunosuppression should be reflected by reduced production of interferons (IFN) in response to a viral antigen, we have developed competitive nucleic acid hybridization microtiter plate assays for chicken IFN-alpha (ChIFN-alpha) and ChIFN-gamma mRNA. To evaluate the assay, chickens were challenged with inactivated Newcastle disease virus (iNDV). Whole blood samples were collected at various times subsequently and preserved with a cationic detergent. Later, total RNA was extracted, and mRNA for both ChIFN-alpha and ChIFN-gamma was measured. Both rose from undetectable levels to reach a peak by 4 h, remained high for about 3 days, and fell to undetectable levels by day 5. Results were similar in chickens aged between 1 and 28 days. In later experiments, blood was collected 4 h after viral challenge. When chickens were immunosuppressed by administering 4-5 mg cyclophosphamide (CY) daily for 3 days and challenged with iNDV, they transcribed less ChIFN-alpha and ChIFN-gamma mRNA, and their antibody response was impaired. Our results suggest that suspected immunosuppression in a commercial flock could be assessed within 2-3 days by challenging birds with iNDV and measuring the amounts of ChIFN-alpha and ChIFN-gamma mRNA in blood obtained 2-4 h later.

Immune suppression of commercial broilers in Croatia, Slovenia, and Bosnia and Herzegovina from 1981 to 1991.

A continuous decline in immune responses to Newcastle disease (ND) vaccine was observed in commercial broiler flocks in Croatia, Slovenia, and Bosnia and Herzegovina beginning in 1982. Floating mean haemagglutination inhibition (HI) titres declined from log(2) 4 in 1983 to a low of log(2) 2.4 in 1986, then were log(2) 2.9 in 1990. Several causes of the decline were discounted, leaving mycotoxins in feed and infection with chicken anaemia virus (CAV) as the two most likely causes. Mycotoxins in feed could not be evaluated retrospectively, but archival tissues were available from Croatia and Slovenia. Tissue sections were examined by in situ hybridization for CAV. Whereas only one chicken from early in the decade was infected, all but one of the chickens from late in the decade were. The increase in CAV detection correlated inversely with ND HI titres. Whereas this correlation does not establish cause and effect, CAV cannot be eliminated as a contributory cause of immune suppression.

In situ Hybridization on Blood Smears for Diagnosis of Chicken Anemia Virus in Broiler Breeder Flocks

Chicken anemia virus (CAV) infection was suspected in progeny from broiler breeder hens raised in a location that was geographically different from where most pullets were raised for one Georgia production company. These breeder pullets were raised in new or relatively new houses. Progeny from these pullets experienced a 10-fold increase in average daily mortality over progeny from flocks raised in established breeder houses. Lesions in the broilers included severe necrotizing dermatitis, pale bone marrow, and small thymus glands. Infection with CAV was confirmed in the breeders by enzyme-linked immunosorbent assay, indirect immunofluorescence, and in situ hybridization on peripheral blood smears. The in situ hybridization identified three broiler breeder flocks that were actively infected with CAV and were probably the source of infection in broiler flocks.