The avian immunosuppressive and neoplastic diseases are great threats to the poultry industry, causing huge economic losses worldwide. Most recently, the emerging hypervirulent variants of Marek’s disease virus (HV-MDV), partially co-infected with avian leukosis virus (ALV) and/or reticuloendotheliosis virus (REV), have been identified as the key driver of tumour outbreaks in vaccinated chicken flocks, but the role of chicken infectious anemia virus (CIAV) remains unclear. Herein, we have investigated the prevalence and co-infection of CIAV in 71 clinical tumour-bearing flocks collected from central China during 2021–2023, which has shown a CIAV positivity rate of 59.2% (42/71). Notably, the incidence of CIAV mono-infection increased significantly from 0% (0/29) in 2021 to 23.7% (9/38) in 2023, whereas CIAV + MDV co-infection decreased from 65.5% (19/29) to 31.6% (12/38). A total of 20 viral genomes of epidemic CIAV isolates from diverse sources were obtained, and the phylogenetic analysis, including 91 reference isolates were clustered into four major lineages (A–D), with clade C further subdivided into subclades C1 and C2. Clade C1 consisted predominantly of Asian isolates, with 88.5% (46/52) of the isolates originating from mainland China. Among the 20 new isolates, 17 were clustered in subclade C1, two in C2, and one in B. The VP1 gene phylogeny showed a topology largely consistent with that of the whole-genome analysis. Moreover, all newly characterized isolates contained glutamine (Q) at VP1 residue 394, a molecular marker associated with high pathogenicity. Collectively, our data suggest that prevalent HV-MDV variants together with CIAV co-infections are the primary drivers of the ongoing tumour outbreaks in Chinese poultry flocks. Notably, the significantly increased CIAV mono-infections, possibly resulting from an independently evolving lineage among circulating Chinese strains, are likely to pose a new challenge for future control of disease.

Marek’s disease (MD), caused by pathogenic Marek’s disease virus serotype 1 (MDV-1), is one of the most important avian immunosuppressive and neoplastic diseases and has led to huge economic losses to the poultry industry worldwide. Rapid and accurate clinical diagnosis is of great significance for efficient control of the disease. Herein, we have established a multiplex PCR (mPCR) method to simply differentiate all of the three types of MDV, using five specific primers targeting to MDV-1 oncogene meq or MDV-2 and MDV-3/HVT gB genes. Simultaneously, it can detect any type of virulent or vaccine MDV strains in one PCR reaction, with amplicons of the short (S) and long (L)-meq of MDV-1 strains, and the gB of MDV-2 and HVT vaccine strains. Non-specific amplifications of avian leukosis virus (ALV), reticuloendotheliosis virus (REV), or fowl adenovirus virus 4 (FAdV-4) were not observed, indicating a good specificity of this method. A total of 522 clinical samples of tumor-bearing or suspected diseased birds collected from 30 poultry farms were detected. The results demonstrated that the newly developed mPCR method accurately detected and differentiated epidemic MDV-1 infections and vaccine strains, and provided nearly 100% consistency for detecting clinical wild-type infections compared with conventional PCR amplification of the meq gene. Collectively, our data has provided a highly efficient method for early differential diagnosis of MD clinical cases, virus identification and future evaluation of vaccination efficacy in healthy chicken flocks, which would be meaningful for efficient control of the disease.

Background/Objectives: Mycoplasma hyopneumoniae (Mhp), porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) are major contributors to porcine respiratory disease complex (PRDC), causing substantial economic losses. Methods: This study evaluated a commercial PCV2-Mhp bivalent vaccine, Cirbloc^® M Hyo (Vaccine A), containing recombinant PCV2 Cap protein and inactivated Mhp antigen, vs. two reference bivalent vaccines (B and C) in an Mhp challenge model. Eighty-two healthy 3-week-old specific-pathogen-free piglets were randomly allocated to five groups (three vaccinated, unvaccinated challenged control, unvaccinated unchallenged control). Pigs received a single intramuscular vaccination at 3 weeks of age and were challenged intratracheally with virulent Mhp lung homogenate five weeks later. Clinical signs, serology, lung lesions, histopathology, and Mhp DNA detection in lungs were assessed. Results: No vaccine-related adverse reactions occurred. Vaccine A induced earlier and higher Mhp-IgG seroconversion before challenge than reference vaccines. Following challenge, Vaccine A significantly reduced mean lung lesion scores compared with the unvaccinated challenged control (2.28 ± 2.37 vs. 6.56 ± 4.03; p < 0.05), with markedly reduced peribronchiolar inflammation and lymphoid hyperplasia and the lowest Mhp DNA detection rate among challenged groups. Conclusions: Cirbloc^® M Hyo provided enhanced protection against experimental Mhp challenge, as shown by reduced lung lesions and milder histopathological changes, supporting its use for comprehensive PRDC management.

The avian immunosuppressive and neoplastic diseases are great threats to the poultry industry causing huge economic losses worldwide. Most recently, the emerging hypervirulent variants of Marek’s disease virus (HV-MDV), partially co-infected with avian leukosis virus (ALV) and/or reticuloendotheliosis virus (REV), have been identified as the key driver of tumour outbreaks in vaccinated chicken flocks, but the role of chicken infectious anaemia virus (CIAV) remains unclear. Herein, we have investigated the prevalence and co-infection of CIAV in 72 clinical tumour-bearing flocks collected from central China during 2020-2023, which has shown a CIAV positivity rate of 59.7% (43/72). Notably, the incidence of CIAV mono-infection increased significantly from 0% (0/30) in 2020-2021 to 26.2% (11/42) in 2022-2023, whereas CIAV+MDV co-infection decreased from 66.7% (20/30) to 28.6% (12/42). A total of 20 viral genomes of epidemic CIAV isolates from diverse sources were obtained, and the phylogenetic analysis including 91 reference isolates were clustered into four major lineages (A–D), with a clade C further subdivided into subclades C1 and C2. Clade C1 consisted predominantly of Asian isolates, with 88.5% (46/52) of the isolates originated from mainland China. Among the 20 new isolates, 17 were clustered in subclade C1, two in C2, and one in B. The VP1 gene phylogeny showed a topology largely consistent with that of the whole-genome analysis. Moreover, all newly characterized isolates contained glutamine (Q) at VP1 residue 394, a molecular marker associated with high pathogenicity. Collectively, our data suggest that prevalent HV-MDV variants together with CIAV co-infections are the primary drivers of the ongoing tumour outbreaks in Chinese poultry flocks. Furthermore, the increased pathogenicity observed in CIAV mono-infections, likely resulting from an independently evolving lineage among circulating Chinese strains, will pose a significant challenge for future control of disease.