Epidemiological Survey Of Porcine Circovirus Disease In East China And Prophylactic Measures Evaluation Isolation And

Porcine circovirus (PCV) is a small, non-enveloped virus with a circular, single-stranded DNA genome. Two genotypes of PCV, PCV1and PCV2, have been recognized. PCV type1(PCV1) was first detected as a contaminant of the porcine kidney PK15cell line (CCL-33) distributed by the American Type Culture Collection. Serologic surveys indicated that PCV1is widespread in swine, but no known animal disease has been associated with PCV1. The PCV2is found world widely in domestic pigs and has been demonstrated to be pathogenic. PCV2has been recently associated with a number of disease syndromes which have been collectively named porcine circovirus diseases (PCVDs). PCVDs include postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PNDS) and reproductive disorders. PCV2has been also involved in the porcine respiratory disease complex (PRDC). However, a clear causal association between PCV2and the development of disease has only been demonstrated for PMWS while its association with other diseases is still a matter of controversy.PMWS is now recognized as a multifactorial disease for which the presence of the virus is a necessary but not sufficient cause. Actually, most herds and pigs are PCV2seropositive but only a few suffer PMWS outbreaks or have individual PMWS cases. The disease most commonly affects pigs from2to4months of age, the late-nursery and early-fattening phases of production. Clinical signs include a marked increase in the mortality rate, wasting, generalized enlargement of lymph nodes, respiratory signs, and occasionally pallor, jaundice and diarrhea. For the production of PMWS activation of the immune system has been shown to be the pivotal event. PMWS-affected pigs exhibit a wide spectrum of concomitant infections. Porcine parvovirus, porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae all may enhance PCV2-associated lesions and increase the incidence of PMWS under experimental and field conditions. Although initial studies did not find any link between PCV2sequences and the occurrence of PMWS, later work suggested an association between novel epizootics and a new variant of PCV2. Epidemiological studies indicate that genotype PCV2b may be more virulent than PCV2a.Maternally-derived immunity against PCV2can protect pigs against the development of PMWS, and this protection is considered to be antibody titre-dependent. From a practical perspective, piglet vaccination should occur some weeks prior to the spread of PCV2, when maternally-derived immunity has waned, in order to avoid any interference with vaccine uptake. Four commercial vaccines against PCV2(one registered for use in breeding stock and three for use in piglets) are now available. The vaccination of sows and gilts increases PCV2antibody titres in serum and colostrum and protects piglets against the development of PMWS. Piglets are vaccinated after3weeks of age, as maternal antibodies wane. This elicits a neutralising antibody response and reduces or delays PCV2infection during weaning or fattening. Commercially available PCV2vaccines are all based on PCV2a but protect against both genotypes. However, given the antigenic differences between genotypes, it would be interesting to assess whether a vaccine based on PCV2b would have a higher protective efficacy.The aim of this work was to investigate the epidemelogical character of PCV2infection in east China during2008to2009and to evalutate the prophylactic measures. The details contents are as follows.1. To characterization of the serum epidemolgy of porcine circovirus type2on large scale swine farms in East China.180serum samples from health pigs and60serum samples from PMWS-affected pigs were collected during2008from breeding farms with sows over500in East China. Serum samples were analyzed for antibodies to PCV2by an immunoperoxidase monolayer assay (IPMA). The result indicated that PCV2was widely prevalence in the investigated pig farms. The total positive rate of serum samples from health pigs and PMWS-affected pigs were74%and100%respectively. In the health pig herds, the PCV2antibody positive rate of sows and breast-feeding piglets were100%and the8weeks growing pigs declined to the lowest. PCV2antibody positive rate increased most significant during the8weeks to12weeks old, suggesting that the peak period of pigs infected with PCV2. In order to further analyze the critical period of PCV2infection, pig serum samples selected from different ages of pigs and PCV2-specific IgM were detected. PCV2-specific IgMs seem to be short-lived and decreased below the detection limit2-3weeks after seroconversion. The results also show that the late nurseries and early fattening period is the key window times for pig infection PCV2. In order to further study the characteristics of PCV2antibodies of PMWS-affected pigs,16positive serum samples from healthy pigs and PMWS-affected pigs were randomly selected for total PCV2antibody (TA) and neutralizing antibody (NA) quantitative ananlysis. Within the PCV2-infected animals a positive correlation was detected between NA and TA titres in health herds, some PMWS-affected pigs had high titres at IPMA but low or absent NA. It was shown that PMWS-affected pigs developed low NA titres to PCV2, while the majority of subclinical infected animals had significantly higher titres. These results reinforce the notion that NA are essential to cope with viral dissemination through blood. Thus, the inability of some pigs to develop a strong neutralizing antibody response could be interpreted either as a cause or consequence of the development of the PMWS.2. Since late2006, the swine industry in the Southeast China has experienced a significant increase in death rate related to postweaning multisystemic wasting syndrome (PMWS). The objective of the present investigation was to ascertain the etiological character of postweaning multisystemic wasting syndrome (PMWS) in large scalce swine farms in Southeast China. During2008and2009,182tissure and serum samples from PMWS cases were collected and PCV-2was the only virus that could be found consistently by PCR in all samples. The PCR detection results obtained for other viruses revealed the following:51%were positive for porcine reproductive and respiratory syndrome virus (PRRSV),8%for porcine parvovirus (PPV),12%for pseudorabiaes virus (PrV),32%for swine torque teno virus type1(swTTV1) and46%for swine torque teno virus type2(swTTV2). The2viruses that were found in higher proportion by PCR in PCV-2positives cases were PRRSV and swTTV with43%and37%positive samples, respectively. It is well known that PRRSV is a major pathogen that can lead to PMWS when present in PCV-2infected swine. It indicated that PCV2and PRRSV coinfection were the main pathogeny of PMWS in large scalce swine farms in Southeast China during2008and2009. The results suggest that swine TTV may be widespread in post-weaning pigs and could play aetiological roles in pig diseases in China even though the potential role and effect of swTTV during coinfection with PCV-2is even more obscure.300serum samples of healthy pigs at different ages from six large-scale pig farms in the East China were also analysis in the present study. As the result PCV2antibody positive rate of breeding piglets, nursery piglets, finishing pigs, sows, younger sows and boars were3%,35%,76%,12%,27%and18%respectively. Which indicating that PCV2infection in pigs occurs mainly during the late of nursery and early fattening period. These above findings provide a theoretical basis for prevention and treatment of PMWS in large scale swine farms.3. The aim of the present study was to clarify the molecular epidemiologic character of PCV2prevalent in intensive pig farms in East China.200serum samples from suspected PMWS pigs and healthy pigs from10large-scale pig farms were collected for PCV2analysis in2009. As the result, PCV2positive for samples from suspected PMWS pigs was96%, and49%for samples from health pigs.20PCV2positvie samples were randomly selected for futher PCR-RFLP genotyping. The result revealed that both PCV2a and PCV2b are prevalent in East China and genotype2b PCV2has become dominant on these farms. Majority of the pig farms contain one certain genotype of PCV2, but it was also found that in a pig farm suspected PMWS pigs infected PCV2b and healthy pigs infected PCV2a. The PCV2genome copy number of samples of suspected PMWS was significantly higher than samples of healthy pigs. The incidence of PMWS of PCV2b infected pigs were significantly high than pig herds infected PCV2a. The data of PMWS status and pig slaughter rates from different pig farms revealed that PCV2b may have greater pathogenicity.4. It was the purpose of this field study to evaluate the efficacy of a newly marketing recombinant ORF2subunit vaccine for active immunization of pigs against PCV2. Two bathes of triales were carried out in a farm with about1800sows which suffering from post-weaning multi-systemic wasting syndrome (PMWS). In the trial, piglets were allocated randomly into two treatment groups at approximately21days of age. Groups received either recombinant PCV2Cap protein vaccine by single intramuscular injection or left uninoculated. Primary parameters such as Average daily weight gain, mortality and FCR were evaluated. Study animals were followed from the time of vaccination until the end of finishing. Onset of PCV2viraemia and clinical signs of PMWS (wasting, cough, dyspnoea, pallor and lethargy) were observed when animals were approximately11weeks old. Vaccinated pigs had a significantly higher mean PCV2antibody titre4weeks after vaccination and a considerably higher mean PCV2antibody titre at the time of seroconversion (11weeks of age) compared to un-treated animals. Compared to untreated pigs, vaccinated pigs had a significantly reduced PCV2viral load and duration of viraemia. During the period of study (from3to25weeks of age) vaccinated animals exhibited a reduced mortality rate (3.03%vs.13.53%, difference-10.5%; p<0.001), an improved average daily weight gain (713.59g/day vs.685.92g/day; difference+27.67g/day; p<0.001). These data demonstrate that vaccination against PCV2alone can significantly improve the overall growth performance of pigs in a multi-factorial disease.