Emily
Editor, Senior Moderator
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0043422
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Probable Congenital Transmission of Reticuloendotheliosis Virus Caused by Vaccination with Contaminated Vaccines.
Contaminated vaccine is one unexpected and potential origin of virus infection. In order to investigate the most likely cause of disease in a broiler breeder company of Shandong Province, all 17 batches of live-virus vaccines used in the affected flocks and 478 tissue samples were tested by dot-blot hybridization, nested PCR, and IFA. The results suggested the outbreak of disease was most probably due to the vaccination of REV-contaminated MD-CVI988/Rispens vaccines and ND-LaSota+IB-H120 vaccines. Furthermore, the REV was probably transmitted to the commercial chickens through congenital transmission.
Citation: Wei K, Sun Z, Zhu S, Guo W, Sheng P, et al. (2012) Probable Congenital Transmission of Reticuloendotheliosis Virus Caused by Vaccination with Contaminated Vaccines. PLoS ONE 7(8): e43422. doi:10.1371/journal.pone.0043422
Editor: Roger Le Grand, Commissariat a l?Energie Atomique(cea), France
Received: April 30, 2012; Accepted: July 20, 2012; Published: August 17, 2012
Copyright: ? Wei et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by National Natural Science Foundation of China (30972183, 30740077), Special Fund Research of Public Welfare Industries of Ministry of Agriculture (200803019), and Science and Technology Development Plan of Shandong Province (2012GNC11020). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
# These authors contributed equally to this work.
Introduction Top
The avian reticuloendotheliosis virus (REV), classified as a gamma-retrovirus, causes runting, immunosuppression, and lymphoma in a variety of avian hosts including chicken, turkey, duck, goose, pheasant, and peafowl [1], [2]. In recent years, immunosuppressive viruses represented by REV have been prevailing in China. Cheng et al. [3] performed serosurvey on broiler breeders in China during the period from September 2008 to November 2009, and discovered the antibody positive rate of REV was 42.6%. Yue et al. [4] detected the positive rate of REV was 59.0% among chickens of Sichuan Province by real-time polymerase chain reaction (PCR) in 2010. Because the outbreak of reticuloendotheliosis usually occurs at about 80 days of age in chickens, and REV often infects together with Marek?s disease virus (MDV) and avian leukemia virus (ALV) [2], [3], the vaccine manufacturers and the chicken keepers tend to neglect the detection and precaution against REV, which provides opportunities for the spread of REV.
In September 2010, three flocks (Flocks 2, 3, and 5; 25?30 weeks old) of a broiler breeder company in Shandong Province of China suffered emaciation and sporadic death with the death rate of around 0.8% in a week. Seven percent of the dead chickens showed the symptoms of visceral lymphomas. The egg production and hatchability were both lower than those of other normal flocks, and the death rate of embryos bred by the three broiler breeder flocks reached 2% after 19 days of hatching. Further investigation revealed that commercial chickens bred by the three broiler breeder flocks suffered poor and irregular growth, and demonstrated a poor immunological response to vaccination with Newcastle disease vaccines and avian influenza vaccines. Further, the 30 days old commercial chickens had a livability of about 93%. All of these respects corresponded to the typical characteristics of REV-infection. Case investigation showed that the grandparent-generation chickens, parents of broiler breeders, were imported from America with no disease record, which helped to exclude the factor of congenital transmission. In addition, the breeding conditions of the affected flocks presented no loopholes and the effects of other stimuli were extremely slight. Finally, when the source of infection could not be determined, we suspected the possible target-vaccine.
Nowadays, the quality of vaccines is becoming increasingly worthy of attention in poultry husbandry. For one thing, live-virus vaccines produced by using unauthentic SPF chickens or virus-free cells probably carried cell-free REV. For another, REV could be integrated into genome of DNA viruses such as MDV and fowlpox virus (FPV) etc. [5], [6], possibly leading to the contamination of the commercial vaccines. In the 1970s, the use of Marek?s disease (MD) vaccines accidentally contaminated with REV had been reported to induce a runting disease characterized by immunodepression and abnormal feathering in the vaccinated flocks in Japan and Australia [7]?[9]. Fadly and Witter [10] proved by in vivo and in vitro test that REV was a contaminant in a live virus fowl pox (FP) vaccine of poultry in 1997; Awad et al. [11] reported that one of the 30 detected FP vaccine samples was contaminated by REV in 2010. However, up to the present, there are few reports on Newcastle disease (ND) vaccines or infectious bronchitis (IB) vaccines of poultry contaminated with REV.
Here, we described an infection of REV in three broiler breeder flocks that had been vaccinated with commercial MD vaccine and ND+IB vaccine contaminated with REV. The data also demonstrated that the REV might be congenitally transmitted to 1 day old commercial chickens. The current paper emphasized a lack of quality control at the level of SPF production and vaccine production...
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