Nov 24, 2015 - Goose parvovirus (GPV) is a well-known causative agent of gosling plague (GP), an acute, contagious, and fatal disease referred to as Derzsy's ...
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Goose Parvovirus (Gosling Plague) Yakun Luo and Shangjin Cui
CONTENTS 77.1 Introduction...................................................................................................................................................................... 693 77.1.1 Classification, Morphology, and Genome Organization...................................................................................... 693 77.1.2 Replication............................................................................................................................................................ 693 77.1.3 Clinical Features................................................................................................................................................... 694 77.1.4 Diagnosis.............................................................................................................................................................. 694 77.2 Methods............................................................................................................................................................................ 694 77.2.1 Sample Collection and Preparation...................................................................................................................... 694 77.2.2 Detection Procedures............................................................................................................................................ 694 77.2.2.1 Virus Isolation...................................................................................................................................... 694 77.2.2.2 Passive Immunity Test......................................................................................................................... 694 77.2.2.3 Neutralization Test............................................................................................................................... 694 77.2.2.4 Cattle Sperm Agglutination Inhibition Test......................................................................................... 694 77.2.2.5 Agar Gel Precipitin Test....................................................................................................................... 695 77.2.2.6 Enzyme-Linked Immunosorbent Assay .............................................................................................. 695 77.2.2.7 Western Blotting.................................................................................................................................. 695 77.2.2.8 PCR...................................................................................................................................................... 695 77.2.2.9 Multiplex PCR..................................................................................................................................... 695 77.2.2.10 Fluorescent Quantitative Real-Time PCR .......................................................................................... 695 77.3 Conclusion........................................................................................................................................................................ 696 References.................................................................................................................................................................................. 696
77.1 INTRODUCTION 77.1.1 Classification, Morphology, and Genome Organization Goose parvovirus (GPV) is a well-known causative agent of gosling plague (GP), an acute, contagious, and fatal disease referred to as Derzsy’s disease [1]. Being a member of the genus Dependoparvovirus under the family Parvoviridae [2–5], GPV was first described as a clinical entity by Fang in 1962 [6]. GPV has attracted much attention owing to its ability to induce high rates of morbidity and mortality in geese, contributing to enormous economic losses in commercial goose production worldwide [1]. The GPV genome is a single-stranded DNA of 5106 nucleotides long and contains two open reading frames (ORFs) that encode regulatory and structural proteins. The left ORF encodes regulatory proteins, while the right ORF encodes three capsid proteins: VP1, VP2, and VP3, which are derived from the same gene by differential splicing. Additionally, VP2 is contained within the carboxyl terminal portion of VP1, and VP3 is contained within that of VP2 [10,11]. The capsids of GPV are nonenveloped, 20–22 nm in diameter, and assembled from 32 capsomers [12–15]. The classical detection of GPV by virus isolation in
gosling, cell cultures, and serological assays like enzymelinked immunosorbent assay (ELISA) is dependent on the availability of SPF gosling embryos and standard positive AQ1 control sera [16].
77.1.2 Replication Similar to other parvoviruses, GPV binds to a sialic acid– bearing cell surface receptor before entry into the host cell through clathrin-mediated endocytosis. Making use of the phospholipase A2 activity conferred by the amino-terminal peptide of the capsid VP1 protein, GPV penetrates into the cytoplasm and then permeabilizes the host endosomal membrane to facilitate its microtubular transportation toward the nucleus. Inside the nucleus, GPV begins uncoating, and its ssDNA is converted by cellular proteins into dsDNA, which functions as template for synthesis of mRNAs encoding the nonstructural (NS) proteins, NS1 and NS2, when host cell reaches to S phase. Moving out of the nucleus into the cytoplasm, the viral mRNAs are translated into viral proteins by the host ribosomes. After covalent binding to the 5′ genomic end, the NS1 endonuclease transactivates an internal transcriptional promoter that directs synthesis of the structural VP polypeptides. This initiates viral DNA replication via
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a unidirectional strand displacement mechanism, with the hairpin structure at the 3′ end acting as a self-primer to synthesize a plus-sense DNA, leading to the formation of double-stranded DNA. The growing strand can replicate back on itself to produce a tetrameric form that is then cleaved to generate two plus-sense and two minus-sense strands of DNA. Individual ssDNA genomes excised from replication concatemers can be further converted to dsDNA and serve as a template for transcription/replication, or encapsidated and packaged in a 3′ to 5′ direction to form new virions that are released by cell lysis.
77.1.3 Clinical Features GP was noted among goslings showing anorexia, wheezing, and locomotor dysfunction [1,17]. The specific lesions observed in the affected geese include myopathy of skeletal muscle, hepatitis, myocarditis, sciatic neuritis, and polioencephalomyelitis [3]. The disease affects mainly young goslings between 2 and 4 weeks old. However, infections in older birds also occur and are often asymptomatic except ascites or loss in featheriness. Under natural conditions, the adult geese can be infected without showing clinical symptoms, but can be spread by excreta and eggs of the disease. The disease has been reported in major goose-producing countries in the world.
77.1.4 Diagnosis
AQ2
For diagnosis of GPV infection, many methods are available, including direct electron microscopy, virus isolation and identification, agar diffusion test, immunoelectron microscopy, latex agglutination test, polymerase chain reaction (PCR), real-time PCR, hemagglutinin (HA), hemagglutination inhibition (HI), ELISA, and nucleic acid sequence analysis. Agar diffusion test and HA/HI are complex and time consuming, while ELISA, which is used to detect GPV antigen, is prone to false-positive and false-negative results [18]. The advent of molecular diagnostic techniques such as PCR has vastly improved the sensitivity, specificity, and speed of laboratory diagnosis of GPV.
Molecular Detection of Animal Viral Pathogens
prepared earlier. Observe daily for a total of 8 days. Embryo’s death may start on day 3, and most of the deaths usually occur in 5–7 days. Dead embryos often display thickening in chorioallantoic membrane, congestion in body skin, bleeding (in wing tips, toes, chest pores, neck, and beak), congestion in liver, hemorrhage in the heart and brain, and subcutaneous edema in head skin and ribs. At day 7, the embryo stops developing and appears very small. The virus may be detected in urine. 77.2.2.2 Passive Immunity Test The LD50 of the virus is first determined in susceptible goslings. Take 10 susceptible goslings, inject subcutaneously five goslings with 0.5 mL GPV hyperimmune serum, and the other five with 0.5 mL of saline as a control group. After 6–12 h, both groups of goslings are injected subcutaneously or intramuscularly with 100 LD50 dose of virus and observed for 10 days. If serum group has no gosling death, while the control group dies, GPV is present [20]. 77.2.2.3 Neutralization Test The virus to be tested is divided into two equal portions: one is added four times the amount of GPV hyperimmune serum (serum or rehabilitation) as the serum group and the other is added four times the amount of saline as a control group. After mixing, both preparations are kept at 37°C for 60 min. Virus preparation (0.2 mL) is then inoculated into the chorioallantoic membrane cavity of 5 susceptible goose embryos (of 12–14 in age), and the embryos are incubated at 37°C–38°C to hatch. Observation is made once daily until the seventh day. If serum group is healthy and alive, while the control group dies, displaying most or all of the typical embryo lesions, GPV is present. Gosling may also be used in place of the susceptible embryos for neutralization test, and the results are determined similarly [21]. In addition, virus neutralization test may be utilized to assess antibody levels in goose serum as well as antigen in dead geese [22]. A neutralizing index of
