A trypsin‐sensitive avian reovirus: Isolation and experimental infection of poults and chicks

Synergistic pathogenicity in sequential coinfection with fowl adenovirus type 4 and avian orthoreovirus

Hydropericardium hepatitis syndrome (HHS) is a fatal disease caused by fowl adenovirus serotype 4 (FAdV-4). Avian viral arthritis is an infectious disease characterized by movement disorders caused by avian orthoreovirus (ARV). In the early 2019, our epidemiologic survey on poultry diseases in eight commercial broiler farms in China showed that FAdV-4 and ARV have a high coinfection rate, accounting for 63 % of all ARV-positive samples. We designed chicken embryo and animal models to investigate the synergistic pathogenicity of FAdV-4 and ARV. Weakness and inappetence were observed in all specific-pathogen-free (SPF) chickens of the experimental group. FAdV-4 and ARV coinfection caused severe embryonic body and hepatic hemorrhage in SPF chicken embryos. Compared with the singular ARV-infected group, joint swelling was more severe in all coinfected groups. Compared with single virus infection, the coinfection of the two viruses increased the mortality of SPF chicken embryos and chickens. FAdV-4 and ARV coinfection resulted in significantly severe macroscopic and microscopic lesions of the liver, spleen, and kidney of SPF chickens. The detection results of viral load in allantoic fluid, liver, and cloacal swabs indicated that ARV enhanced FAdV-4 replication in SPF chicken embryos and chickens. Cytokine detection showed a significant change in interleukin-1 (IL-1), IL-6, and interferon-α (IFN-α) levels in coinfected groups compared with those in the single-infected groups. Additionally, FAdV-4 and ARV coinfection caused severe damage to the SPF chicken's immune system. In summary, these findings provide insights into the pathology, prevention, and treatment of FAdV-4 and ARV coinfection.

Serological detection of avian reovirus in different poultry flocks of Gazipur and Mymensingh districts of Bangladesh

Background and Aim:

Avian reovirus (ARV) is a constraint to poultry industry in Bangladesh as a cause of several diseases in chickens, especially in broiler. However, the actual status of the viral infection is not known because the large-scale study is not conducted in this country. Therefore, this study aimed to check the presence and distribution of ARV-specific antibody in respect to area, types of chickens (broiler breeder, broiler, and layer), vaccination status, and age of chickens in Gazipur and Mymensingh districts of Bangladesh.

Materials and Methods:

A total of 276 chickens’ blood samples were collected from two well-organized broiler breeder stock, seven broiler farms, and five layer farms located at two districts, namely Gazipur and Mymensingh of Bangladesh. Blood samples were collected from wing vein of the apparently healthy chickens using 3 ml of syringe and serum was harvested by keeping the syringe at room temperature in slanting position. The sera were transferred to the laboratory by maintaining the cool chain and further processing was performed by indirect enzyme-linked immunosorbent assay using ARV antibody test kit.

Results:

The results of serological test revealed that an average of 39.5% seropositive against ARV was recorded in chickens of Gazipur and Mymensingh districts. Among these, chickens of Gazipur district had the highest seropositivity of 50.5% than Mymensingh (30.7%). With respect to vaccination status, the seropositivity of vaccinated chickens in both areas was 100% and non-vaccinated chickens was 50.5% in Gazipur and 30.7% in Mymensingh district, respectively. However, regarding age groups, the seropositivity was higher in the age of 4-6 weeks (64.5%).

Conclusion:

The present serological findings showed a higher prevalence of ARV-specific antibodies in broiler birds. It indicates that the poultry industries of Bangladesh are contaminated with ARV which may naturally be transmitted to chickens either vertically or horizontally.

Efficacy of Five Commonly Used Disinfectants Against Turkey Arthritis Reovirus

Since late 2009, an unusual problem of reovirus-related lameness has been seen in market-age tom turkeys in the upper Midwest area of the United States. In this study, we determined the efficacy of five commonly used disinfectants (Virocid, Keno X5, Synergize, One Stroke, and Tek Trol) against turkey arthritis reoviruses (TARVs). For comparison, turkey enteric reovirus (TERV) and chicken arthritis reovirus (CARV) were also included. At their recommended concentrations, all five disinfectants were found to be effective virucidals, inactivating 99.99% of all viruses within 10 min. However, oxidizing agents and quaternary ammonium compounds + aldehyde types of disinfectants were more effective, killing the viruses in a shorter time (2-5 min) than the other types of disinfectants. These results indicate that these disinfectants can be an effective tool in the control of these viruses.

Experimental inoculation of mice with trypsin-resistant and trypsin-sensitive avian reoviruses

Groups of sucking Swiss albino mice were inoculated by the intracerebral (i.c.), intraperitoneal (i.p.) or oral route with a trypsin-sensitive avian reovirus (TR1) or a trypsin-resistant (R2) reovirus. The viruses caused a number of effects, the most severe occurring after i.c. inoculation and the least after oral inoculation. They included incoordination and tremors, oiliness of the hair, and retarded growth. Patterns of viral persistence in tissues were similar for the two viruses, with high titres in the brain on days 3 and 6 after i.c. or i.p. injection. Both viruses were still present in the brain 21 days after i.c. injection. No virus was found in any tissue when TR1 was given orally. All groups "seroconverted" except the one infected orally with TR1, but neutralization titres were low. The effects resembled those described for mammalian reoviruses in mice. The results indicate that, for short periods, wild mice may be capable of transmitting avian reoviruses between poultry flocks. Furthermore, in the production of monoclonal antibodies to avian reoviruses in mice, it is possible that pathological changes will occur.

Early pathogenesis in chicks of infection with a trypsin-sensitive avian reovirus

Experiments are described which show how the sensitivity to trypsin of avian reovirus strain TR1 restricts its replication in the intestine of the chicken in comparison with a trypsin-resistant strain R2. Following oral infection with a high dose (5.3 log10 TCID50), the trypsin-sensitive virus generally showed lower titres than the resistant one in all tissues examined. Infection of chicks with strain TR1 via the respiratory route enabled the virus to spread throughout the body and localize in the hock joint, an important target site for reoviruses. Trypsin-sensitive reoviruses might be transmitted via the respiratory route, even though TR1 caused little damage to the respiratory epithelium. Dose-response studies showed that TR1 injected via the footpad can localize in the hock joint after very low doses, but high oral doses (4-5 log10) are necessary for such localization. Intranasal infection was intermediate in effect.

Effect of cyclophosphamide immunosuppression on the immunity of turkeys to viral rhinotracheitis

Turkey poults, free of antibodies to turkey rhinotracheitis (TRT) virus were treated with cyclophosphamide on days 1, 2 and 3 after hatching and vaccinated by eyedrop when 10 days old with a Vero cell-attenuated preparation of TRT virus. No ELISA antibodies to TRT virus developed in the sera of these poults but they were as resistant to virulent virus challenge 21 days later as vaccinated groups which were not cyclophosphamide-treated but produced humoral antibodies. Following challenge with virulent virus at 31 days old cyclophosphamide-treated unvaccinated poults developed a more severe clinical response than untreated birds and had higher virus titres in tracheal swabs. The findings show that the respiratory tract of turkeys may be resistant to TRT despite the absence of ELISA antibodies in the serum.