Porcine Circovirus Type 2 and Porcine Circovirus-Associated Disease

Porcine circovirus type 2 (PCV2) belongs to the viral family Circoviridae and to the genus Circovirus . Circoviruses are small, single-stranded nonenveloped DNA viruses that have an unsegmented circular genome. PCV2 is the primary causative agent of several syndromes collectively known as porcine circovirus-associated disease (PCVAD). Many of the syndromes associated with PCVAD are a result of coinfection with PCV2 virus and other agents such as Mycoplasma and porcine reproductive and respiratory syndrome virus. PCV2 infection is present in every major swine-producing country in the world, and the number of identified cases of PCVAD is rapidly increasing. In the United States, the disease has cost producers an average of 3–4 dollars per pig with peak losses ranging up to 20 dollars per pig. The importance of this disease has stimulated investigations aimed at identifying risk factors associated with infection and minimizing these risks through modified management practices and development of vaccination strategies. This paper provides an overview of current knowledge relating to PCV2 and PCVAD with an emphasis on information relevant to the swine veterinarian.     

猪圆环病毒病

现已确认猪圆环病毒病(PCVD)发生于全世界,对养猪业带来了严重的经济损失。尽管最近全世界许多实验室对此病进行的研究使我们获得了大量的有关知识,但我们对其病程的了解仍有重要缺陷,因而仍然无法对其进行有效防制。     

猪圆环病毒病的防控

猪圆环病毒(PCV)属于圆环病毒科圆环病毒属,为环状、单股DNA病毒,含1767-1768个核苷酸,是动物病毒中最小的一员.圆环病毒分1型和2型,其中2型(PCV2)致病性明显大于1型,临床表现的相关性疫病主要由2型引起.     

Porcine atrophic rhinitis

SUMMARY: In snouts of pigs from 5 of 8 piggeries in New South Wales examined, there was evidence of severe atrophic rhinitis. In 220 pigs examined from one piggery there was no correlation between the severity of atrophic rhinitis and growth rate or back-fat thickness. There was also no correlation between the extent of lung pathology and back-fat thickness. Pleurisy or pericarditis did cause a significant reduction in growth rate.     

Porcine Neonatal Coccidiosis

Coccidia were identified in intestinal sections from 82 piglets comprising 37 consignments from 34 farms, and represented a yearly increasing incidence in the three years 1978 to 1980. Piglets were primarily from medium to large farms with intensive, continuous-farrowing, confinement-rearing programs. Piglets, usually five days to 15 days old, had yellow, fluid diarrhea, became unthrifty and sometimes died. In six piglets from two farms, a green, adherent, fibrinonecrotic membrane was seen throughout most of the jejunum and ileum. Significant gross lesions were not observed in the other 76 piglets. Moderate to severe villous atrophy of jejunum and ileum was seen histologically. Various asexual and sexual stages of coccidia were seen within parasitophorous vacuoles of villar epithelial cells. Multifocal erosions with necrosis of villar tips and occasionally more diffuse mucosal necrosis with fibrinocellular exudate were seen. Isospora suis oocysts were identified in feces from several weaners from one farm. Amprolium and decoquinate mixed in the sow ration at 1 kg/tonne for three weeks prior to and postfarrowing was moderately successful in stopping outbreaks of neonatal diarrhea associated with coccidiosis.     

Porcine circovirus diseases

Porcine circovirus type 2 (PCV2) is a member of the family Circoviridae, a recently established virus family composed of small, non-enveloped viruses, with a circular, single-stranded DNA genome. PCV2, which is found all over the world in the domestic pig and probably the wild boar, has been recently associated with a number of disease syndromes, which have been collectively named porcine circovirus diseases (PCVD). Postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS) and reproductive disorders are the most relevant ones. Among them, only PMWS is considered to have a severe impact on domestic swine production. PMWS mainly affects nursery and/or fattening pigs; wasting is considered the most representative clinical sign in this disease. Diagnosis of this disease is confirmed by histopathological examination of lymphoid tissues and detection of a moderate to high amount of PCV2 in damaged tissues. Since PMWS is considered a multifactorial disease in which other factors in addition to PCV2 are needed in most cases to trigger the clinical disease, effective control measures have focused on the understanding of the co-factors involved in individual farms and the control or elimination of these triggers. PDNS, an immuno-complex disease characterized by fibrino-necrotizing glomerulonephritis and systemic necrotizing vasculitis, has been linked to PCV2, but a definitive proof of this association is still lacking. PCV2-associated reproductive disease seems to occur very sporadically under field conditions, but it has been characterized by late-term abortions and stillbirths, extensive fibrosing and/or necrotizing myocarditis in fetuses and the presence of moderate to high amounts of PCV2 in these lesions. Taking into account that scientific information on PCV2 and its associated diseases has been markedly expanded in the last 8 years, the objective of this review is to summarize the current state of knowledge of the most relevant aspects of PCV2 biology and PCVD.     

牛肠道病毒的分离鉴定

本研究从内蒙古某奶牛场的犊牛粪便样品中分离的一株牛肠道病毒(BEV),命名为BHM26,通过电镜观察显示和分子生物学鉴定,发现病毒粒子在细胞浆中呈结晶状排列,单一病毒粒子呈典型小RNA病毒粒子形态,直径为25nm～30nm,无囊膜;病毒的部分3D蛋白编码区和全长3'UTR区段的1 026bpDNA片段的RT-PCR扩增和序列分析表明,其核苷酸序列与GenBank登录的参考病毒株核苷酸序列同源性为71.9%～87%,其中与BEV Wye-3A株同源性最高,为87%.分析表明中国BEV分离株与国外参考毒株具有较大差异.