Egg transmission of avian reoviruses in chickens: Comparison of a trypsin‐sensitive and a trypsin‐resistant strain

Co-circulation of multiple genotypes of ARV in poultry in Anhui, China

ABSTRACTPoultry production in China has been experiencing a high incidence of broiler arthritis /tenosynovitis caused by avian orthoreovirus (ARV) since 2013. In the spring of 2020 severe arthritis cases from broiler flocks were identified in a large-scale commercial poultry company in Anhui Province, China. Diseased organs from dead birds were sent for diagnosis to our laboratory. ARVs, including seven broiler-isolates and two breeder-isolates, were successfully harvested and sequenced. Interestingly, the genotypes of ARVs isolated from infected chickens were inconsistent between different flocks, or even between different houses on the same flocks. Pathogenicity testing in chicks confirmed that the seven broiler-isolates were pathogenic strains, which could cause arthritis in infected chickens. Subsequently, a total of 89.66% serum samples collected from apparently healthy adult broiler flocks not vaccinated against ARV tested positive for ARV antibodies, suggesting that low and high virulence reovirus strains may be co-circulating in the farm. To this end, we collected dead embryos of unhatched chicken eggs for pathogen tracing, and the two ARV breeder-isolates isolated indicated that vertical transmission from breeders to progeny should not be underestimated for the prevalence of ARV within broiler flocks. The findings have implications for the evidenced-based formulation of prevention and control strategies.

Avian Reoviruses in Poultry Farms from Brazil

Avian reovirus (ARV) is highly disseminated in commercial Brazilian poultry farms, causing arthritis/tenosynovitis, runting-stunting syndrome, and malabsorption syndrome in different meat- and egg-type birds (breeders, broilers, grillers, and layers). In Brazil, ARV infection was first described in broilers in the 1970s but was not considered an important poultry health problem for decades. A more concerning outcome of field infections has been observed in recent years, including condemnations at slaughterhouses because of the unsightly appearance of chicken body parts, mainly the legs. Analyses of the performance of poultry flocks have further evidenced economic losses to farms. Genetic and antigenic characterization of ARV field strains from Brazil demonstrated a high diversity of lineages circulating in the entire country, including four of the five main phylogenetic groups previously described (I, II, III, and V). It is still unclear if all of them are associated with different diseases affecting flocks' performance in Brazilian poultry. ARV infections have been controlled in Brazilian poultry farms by immunization of breeders and young chicks with classical commercial live vaccine strains (S1133, 1733, 2408, and 2177) used elsewhere in the Western Hemisphere. However, genetic and antigenic variations of the field isolates have prevented adequate protection against associated diseases, so killed autogenous vaccines are being produced from isolates obtained on specific farms. In conclusion, ARV field variants are continuously challenging poultry farming in Brazil. Epidemiological surveillance combined with molecular biological analyses from the field samples, as well as the development of vaccine strains directed toward the ARV circulating variants, are necessary to control this economically important poultry pathogen.

Infection and transmission dynamics of Turkey arthritis reovirus in different age Turkeys

Turkey arthritis reovirus (TARV) has been established as a cause of lameness in meat type turkeys in the past decade. However, no information is available on the age susceptibility of TARV or its transmission dynamics. We conducted this study to determine the age at which turkey poults are susceptible to TARV infection and whether infected birds can horizontally transmit the virus to their non-infected pen mates (sentinels). Five groups of turkeys were orally inoculated with TARV (∼10⁶ TCID₅₀/ml) at 2, 7, 14, 21 and 28 days of age (DOA). Two days after each challenge, four uninfected sentinel turkeys of equal age were added to the virus-inoculated groups. At one- and two-weeks post infection, turkeys from each group, including two sentinels, were euthanized followed by necropsy. Inoculated birds in all age groups had TARV replication in the intestine and gastrocnemius tendon with no statistically significant variation at p < 0.5. Furthermore, the inoculated birds at different age groups showed consistently high gastrocnemius tendon histologic lesion scores while birds in the 28-days-old age group had numerically lower lesion scores at 14 days post inoculation (dpi). The sentinels, in turn, also showed virus replication in their intestines and tendons and histologic lesions in gastrocnemius tendons. The findings indicate that turkeys at the age of 28 days or less are susceptible to infection with TARV following oral challenge. It was also found that TARV-infected birds could transmit the infection to naïve sentinel turkeys of the same age.

A Review of the Emerging White Chick Hatchery Disease

White chick hatchery disease is an emerging disease of broiler chicks with which the virus, chicken astrovirus, has been associated. Adult birds typically show no obvious clinical signs of infection, although some broiler breeder flocks have experienced slight egg drops. Substantial decreases in hatching are experienced over a two-week period, with an increase in mid-to-late embryo deaths, chicks too weak to hatch and pale, runted chicks with high mortality. Chicken astrovirus is an enteric virus, and strains are typically transmitted horizontally within flocks via the faecal-oral route; however, dead-in-shell embryos and weak, pale hatchlings indicate vertical transmission of the strains associated with white chick hatchery disease. Hatch levels are typically restored after two weeks when seroconversion of the hens to chicken astrovirus has occurred. Currently, there are no commercial vaccines available for the virus; therefore, the only means of protection is by good levels of biosecurity. This review aims to outline the current understanding regarding white chick hatchery disease in broiler chick flocks suffering from severe early mortality and increased embryo death in countries worldwide.

A Review of the Emerging White Chick Hatchery Disease

White chick hatchery disease is an emerging disease of broiler chicks with which the virus, chicken astrovirus, has been associated. Adult birds typically show no obvious clinical signs of infection, although some broiler breeder flocks have experienced slight egg drops. Substantial decreases in hatching are experienced over a two-week period, with an increase in mid-to-late embryo deaths, chicks too weak to hatch and pale, runted chicks with high mortality. Chicken astrovirus is an enteric virus, and strains are typically transmitted horizontally within flocks via the faecal–oral route; however, dead-in-shell embryos and weak, pale hatchlings indicate vertical transmission of the strains associated with white chick hatchery disease. Hatch levels are typically restored after two weeks when seroconversion of the hens to chicken astrovirus has occurred. Currently, there are no commercial vaccines available for the virus; therefore, the only means of protection is by good levels of biosecurity. This review aims to outline the current understanding regarding white chick hatchery disease in broiler chick flocks suffering from severe early mortality and increased embryo death in countries worldwide.

Retrospective Analysis of Turkey Arthritis Reovirus Diagnostic Submissions in Minnesota

Turkey arthritis reovirus (TARV) causes tenosynovitis in turkeys, resulting in decreased profits for producers due to the increase in morbidity, mortality, and feed conversion ratio. There is limited information on TARV epidemiology, including the dynamics of diagnostic submissions to veterinary diagnostic laboratories. In this study, we retrospectively analyzed 719 cases of lameness in turkeys submitted to the Minnesota Veterinary Diagnostic Laboratory from March 2010 to May 2018. Almost all submissions were tendon pools, which were tested by virus isolation and/or real-time reverse transcription-polymerase chain reaction. Most of the submissions were from Minnesota. We found 52% of the submitted cases to be positive for TARV. The TARV-positive submissions increased considerably in the last few years. There was no statistical evidence that TARV diagnostic submissions were seasonal, although positive submissions were higher in January, April, July, and December. TARV-positive submissions also increased as flocks aged. In summary, we found that TARV submissions have increased in the last few years, have varied over time, and are correlated with age of the bird. This information is important guidance for conducting more studies to understand TARV infection dynamics.

Specific-pathogen-free Turkey model for reoviral arthritis

Turkey arthritis reovirus (TARV) infections have been recognized since 2011 to cause disease and significant economic losses to the U.S. turkey industry. Reoviral arthritis has been reproduced in commercial-origin turkeys. However, determination of pathogenesis or vaccine efficacy in these turkeys can be complicated by enteric reovirus strains and other pathogens that ubiquitously exist at subclinical levels among commercial turkey flocks. In this study, turkeys from a specific-pathogen-free (SPF) flock were evaluated for use as a turkey reoviral arthritis model. One-day-old or 1-week-old poults were orally inoculated with TARV (O'Neil strain) and monitored for disease onset and progression. A gut isolate of turkey reovirus (MN1 strain) was also tested for comparison. Disease was observed only in TARV-infected birds. Features of reoviral arthritis in SPF turkeys included swelling of hock joints, tenosynovitis, distal tibiotarsal cartilage erosion, and gait defects (lameness). Moreover, TARV infection resulted in a significant depression of body weights during the early times post-infection. Age-dependent susceptibility to TARV infection was unclear. TARV was transmitted to all sentinel birds, which manifested high levels of tenosynovitis and tibiotarsal cartilage erosion. Simulation of stressful conditions by dexamethasone treatment did not affect the viral load or exacerbate the disease. Collectively, the clinical and pathological features of reoviral arthritis in the SPF turkey model generally resembled those induced in commercial turkeys under field and/or experimental conditions. The SPF turkey reoviral arthritis model will be instrumental in evaluation of TARV pathogenesis and reoviral vaccine efficacy.

Preparation and evaluation of goose reovirus inactivated vaccine

Background

Infection with Goose Reovirus (GRV) can cause serious economic losses in the goose breeding industry. In this study, the GRV allantoic fluid was concentrated and used as an antigen in a formalin-inactivated oil-emulsion vaccine.

Results

When 6 day-old geese were inoculated, antibodies against GRV became detectable at 6 days post-vaccination, their concentration peaked at 3 weeks. These antibodies were maintained for longer than 2 weeks. As the most susceptible age for GRV infection is birds under 2 weeks of age this vaccine should provide adequate cover for the most at risk birds. When geese were exposed to reovirus at different time intervals after immunization, the data revealed that the vaccine can provide a protection rate of 80%. The developed vaccine has good stability and could be stored at 4 °C for at least 12 months.

Conclusion

These results indicate that the developed GRV vaccine is safe, effectively absorbed, efficacious in inducing a rapid immune response, and effective in controlling GRV infection. Our results should be useful for the application of vaccines for controlling GRV in different goose flocks.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1134-0) contains supplementary material, which is available to authorized users.

Prevalence of histopathological intestinal lesions and enteric pathogens in Dutch commercial broilers with time

Intestinal disease has a major impact on the broiler industry due to economic and welfare reasons. Intestinal disease might occur due to a large number of reasons varying from well-defined pathogens to non-specific enteritis and complex syndromes. However, knowledge about the nature of intestinal disease and presence of enteric viruses in the Dutch broiler industry is largely absent. Therefore, a large-scale field study, in which 98 broiler flocks from 86 farms were sampled weekly, was started to assess the prevalence of histopathological lesions in the jejunum, a number of enterotropic viruses by real-time quantitative reverse transcriptase PCR (RT-qPCR) and coccidia by lesion scoring. Histopathological lesions indicative of intestinal disease were found in all flocks examined. The pathogens investigated were chicken astrovirus (99% of flocks positive), avian nephritis virus 3 (100%), rotavirus A (95%), rotavirus D (52%), reovirus (100%), Eimeria acervulina (94%), E. maxima (49%) and E. tenella (40%). The enteric viruses were more prevalent in the first weeks of the growing period, while coccidiosis was more frequently found at 4 and 5 weeks of age. The abundant presence of the enteric viruses and enteric disorders stresses the need to elucidate the role of these viruses in intestinal disease. Furthermore, the high prevalence of coccidiosis despite the use of anticoccidials shows that the current coccidial management programmes might be insufficient in controlling this disease.

Avian Immunosuppressive Diseases and Immunoevasion

Subclinical immunosuppression in chickens is an important but often underestimated factor in the subsequent development of clinical disease. Immunosuppression can be caused by pathogens such as chicken infectious anemia virus, infectious bursal disease virus, reovirus, and some retroviruses (e.g., reticuloendotheliosis virus). Mycotoxins and stress, often caused by poor management practices, can also cause immunosuppression. The effects on the innate and acquired immune responses and the mechanisms by which mycotoxins, stress and infectious agents cause immunosuppression are discussed. Immunoevasion is a common ploy by which viruses neutralize or evade immune responses. DNA viruses such as herpesvirus and poxvirus have multiple genes, some of them host-derived, which interfere with effective innate or acquired immune responses. RNA viruses may escape acquired humoral and cellular immune responses by mutations in protective antigenic epitopes (e.g., avian influenza viruses), while accessory non-structural proteins or multi-functional structural proteins interfere with the interferon system (e.g., Newcastle disease virus).

Identification of a new reovirus causing substantial losses in broiler production in France, despite routine vaccination of breeders

Numerous cases of tenosynovitis appeared in France causing high morbidity in free-range and standard broilers. The main clinical findings were lameness, stunting and non-uniform bodyweights. Although the natural mortality was low, the economic losses due to birds that had to be removed from the flock prematurely, downgrading of carcases and lower average weights at slaughter were substantial. Postmortem examinations, bacteriological, virological and serological examination confirmed the aetiology of avian orthoreovirus (ARV)-induced tenosynovitis. The isolated ARVs were analysed serologically and genetically. Sequencing of σC RT-PCR products and phylogenetic analysis revealed a new type of ARV. The virus was not neutralised in serum neutralisation test using monovalent sera from vaccinated chickens. Together with the flock data, epidemiology of these recent reovirus outbreaks in France was reconstructed. It is concluded that these reovirus isolates differ serologically and genetically from the well described reovirus isolates used in commercial vaccines which were not capable of preventing the disease. The outbreaks resulted in substantial losses in broilers from vaccinated breeders.