华南地区猪圆环病毒和猪繁殖与呼吸综合征病毒检测分析

为了解华南地区猪圆环病毒及猪繁殖与呼吸综合征病毒的最新流行情况,采集了华南地区11个规模猪场各饲养阶段猪血清807份,用套式PCR(nPCR)检测猪圆环病毒1型(PCV-1)和猪圆环病毒2型(PCV-2);采集了若干猪场2010年1月至2011年8月期间有咳嗽、喘气、消瘦及疑似PDNS等临床症状的猪血清312份,以及无临床症状猪血清104份,以nPCR检测PCV-2,以一步法反转录PCR(RT-PCR)检测猪繁殖与呼吸综合征病毒。结果发现,所调查的11个规模猪场中只有5个检出PCV-1,所有猪场均检出PCV-2。PCV-2阳性率为30.61%,而PCV-1阳性率仅为4.21%;经产母猪和7周龄以上保育猪PCV阳性率最高;有临床症状的猪血清PCV-2阳性率为58.65%,PRRSV阳性率为37.82%,PCV-2阳性猪群中有39.89%的猪同时感染PRRSV;有症状猪群7月～9月的PCV-2感染率最高,而1月～3月最低;无临床症状猪血清PCV-2阳性率为27.9%,PRRSV阳性率为0.96%,PCV-2与PRRSV无混合感染。证明PCV尤其是PCV-2在华南地区仍广泛传播并流行,而且PCV-2与PRRSV混合感染致病情况较多。PCV-2的感染率与季节有一定的相关性,种猪带毒情况严重。     

Evaluation of a nested polymerase chain reaction assay to differentiate between two genotypes of Porcine circovirus-2.

Porcine circovirus-2 (PCV-2) is associated with several diseases in pigs, including postweaning multisystemic wasting syndrome (PMWS). A new genotype of PCV-2 was isolated from swine farms with and without clinical PMWS in North America. The new genotype was differentiated in a separate cluster by phylogenetic analyses and is now named PCV-2b compared with PCV-2a for the previously known genotype. The purpose of this study was to develop and evaluate a nested polymerase chain reaction (nPCR) assay to detect and differentiate between PCV-2a and PCV-2b. Genotype-specific primer sets were designed by using sequence data published for different PCV-2 strains. Specificity and sensitivity of the nPCR were examined by using PCV-2 isolates with known genotype. Nested PCR was found to be highly specific and sensitive for detecting and differentiating between the PCV-2 genotypes compared with the conventional 1-step PCR assay. Nested PCR was applied to detect PCV-2 and to identify the genotype in serum samples from swine farms with and without a clinical history of PMWS. Of 60 serum samples collected from 4 farms during clinical PMWS outbreaks, PCV-2a and PCV-2b were detected in 6 and 49 samples, respectively. Six of the 10 samples from one of the 4 farms had both PCV-2a and PCV-2b. Of 20 serum samples from 2 farms without PMWS, 11 were positive for PCV-2a only. These results suggest that the differential nPCR can be used to detect PCV-2 and to differentiate the 2 genotypes from field samples.     

Viral distribution and lesions in Kunming mice experimentally infected with porcine circovirus type 2b

The viral distribution and lesions in Kunming mice experimentally infected with porcine circovirus type 2b (PCV-2b) were investigated. Seventy special pathogen free mice were divided into 2 groups with 35 mice in each group. The test group (TG) was infected with PCV-2b, the control group (CG) was inoculated with sterile cell cultures. Five mice in each group were sacrificed at 3, 7, 14, 21, 28, 35 and 42 dpi (day post infection), respectively. Necropsies were performed on all mice and tissues were collected for testing by histopathology, immunohistochemistry, transmission electron microscope (TEM) and polymerase chain reaction (PCR). Apoptosis and necrosis in lymphoid organs were observed in virus-infected mice, and became severe from 14 to 28 dpi. The proportion of PCV-2b antigen-positive cells was moderate in lung, heart, thymus, liver or kidney, and low in brain from TG. In spleen and cervical lymph node, the proportions of PCV-2b antigen-positive cells were low to high from 7 to 28 dpi, and moderate from 35 to 42 dpi. PCV-2b DNA was detected in all tissues examined in TG from 7 to 42 dpi. Viral inclusion bodies presented in the cytoplasm of lymphocytes, macrophages, hepatocytes, podocytes, neurocytes, spermatids and uterine epithelial cells in TG. In CG, no viruses and viral lesions were detected. PCV-2b could replicate in mice, and PCV-2b associated lesions in mice were similar to those observed in pigs. The present results indicate that it is possible to use Kunming mouse as an animal model for PMWS research.     

The effect of vaccination against Porcine reproductive and respiratory syndrome virus (PRRSV) on the Porcine circovirus-2 (PCV-2) load in porcine circovirus associated disease (PCVAD) affected pigs

A diagnostic project was initiated across the United States in 2006 to improve the understanding of porcine circovirus associated diseases (PCVAD) as well as to identify co-factors in PCVAD-affected farms. A Porcine circovirus-2 (PCV-2) DNA real-time polymerase chain reaction quantitation (qPCR) was established according to a published method and sera from a total of 23pig farms across the United States were examined for viral loads for PCV-2 and analyzed for any possible effects of Porcine reproductive and respiratory syndrome virus (PRRSV) vaccination on this parameter. Vaccination against PRRS resulted in significantly lower viral loads for PCV-2 in animals 13 wk or older compared with nonvaccinated animals, but vaccination of pigs against PRRS had no effect on qPCR results for PCV-2 in 4- to 12-week-old pigs. Interestingly, PRRS vaccinates had significantly lower viral loads when peak wasting disease was observed in the herds. The qPCR method for PCV-2 proved to be an important tool for help in the antemortem diagnosis of PCVAD as well as in the monitoring of infection dynamics.     

Genetic typing of porcine circovirus type 2 (PCV-2) isolates from Slovakia

Of 120 clinical specimens obtained from pigs bred on 28 PMWS-affected farms in Slovakia, porcine circovirus type 2 (PCV-2) was detected by single PCR in 77 samples. A short 224 bp fragment of ORF2 was used for preliminary grouping of isolates by phylogenetic analysis. Nucleotide sequences of the entire ORF2 region provided more precise genetic typing and segregation of preselected isolates (n = 10) into two known genotypes, PCV-2a (n = 1) and PCV-2b (n = 9). Complete genome sequencing of three selected isolates allowed their definitive grouping into genotype PCV-2b, cluster 1A or genotype PCV-2a, cluster 2D. No correlation between the mutations and the geographic origin of isolates was observed. Results confirmed that many PCV-2 isolates are genetically very stable since similar viruses circulate in Central and Western Europe.     

Epidemiological characteristics of pulmonary pneumocystosis and concurrent infections in pigs in Jeju Island, Korea

Epidemiological characteristics of swine pulmonary Pneumocystis (P.) carinii and concurrent infections were surveyed on Jeju Island, Korea, within a designated period in 172 pigs submitted from 54 farms to the Department of Veterinary Medicine, Jeju National University. The submitted cases were evaluated by histopathology, immunohistochemistry, PCR/RT-PCR, and bacteriology. P. carinii infection was confirmed in 39 (22.7%) of the 172 pigs. Histopathologically, the lungs had moderate to severe lymphohistioctyic interstitial pneumonia with variable numbers of fungal organisms within lesions. Furthermore, porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV-2) co-infection was a common phenomenon (12.8%, 20.5%, and 48.7% were positive for PRRS, PCV-2, or both, respectively, as determined by PCR/RT-PCR). Infection was much more concentrated during winter (December to March) and 53.8% of the infected pigs were 7- to 8-weeks old. In addition, three pigs showed co-infection with bacteria such as Pasteurella multocida and Streptococcus suis. The results of the present study suggest that the secondary P. carinii infection is common following primary viral infection in swine in Korea. They further suggest that co-infection of P. carinii might be enhanced by the virulence of primary pathogens or might have synergistic effects in the pigs with chronic wasting diseases.     

PCR detection and characterization of type-2 porcine circovirus.

A polymerase chain reaction (PCR) assay was developed for detecting porcine circovirus (PCV). The assay readily detected type-2 PCV (PCV-2) and type-1 PCV (PCV-1). The PCR primers were designed based on DNA sequences conserved in all reported PCV genomes. Type 1 PCV and type 2 PCV both produced 438 bp amplification products, which were easily identified and differentiated from one another by restriction fragment length polymorphism (RFLP) analysis. Porcine circovirus was detected in 55% (931/1693) of randomly tested pigs with various clinical signs and lesions, most of which were difficult to differentiate from those associated with porcine reproductive and respiratory syndrome (PRRS). The PCR products from all positive clinical samples were identified by RFLP to be only PCV-2; DNA tested by PCR was extracted directly from one or more of lung, mesenteric or mediastinal lymph nodes, and tonsil. Type 2 PCV was also detected in 6% (2/34) of DNA extracted directly from semen of randomly chosen healthy boars. Positive PCR reactions from 554 diseased pigs were characterized by RFLP and categorized into 5 different profiles (A-E), of which 82.8% were PCV-2A (456/554), 3.0% were PCV-2B (17/554), 9.9% were PCV-2C (55/554), 1.1% were PCV-2D (6/554), and 3.2% were PCV-2E (18/554). The complete genomic nucleotide sequences of PCV-2A, B, C, D, and E were determined and found to have at least 95% homology compared with one another and with all other PCV-2 found in the GenBank database. All PCV-2 had less than 76% homology with PCV-1. This PCR assay will hopefully be useful to veterinary diagnostic laboratories for routine testing and surveillance of infection with PCV-2. The RFLP profiling system might be useful for preliminary characterization and identification of PCV isolates and might also benefit studies on the molecular epidemiology of PCV.     

Quantitative polymerase chain reaction for Porcine circovirus-2 in swine feces in a Porcine circovirus disease-affected commercial herd and a nonaffected commercial herd

This study examined if pigs in a Porcine circovirus disease (PCVD)-affected herd (n = 100) had shed more Porcine circovirus-2 (PCV-2) in their feces than pigs in a PCVD-nonaffected herd (n = 101), and if differences in shedding among production stages within and between the herds existed. The PCV-2 shedding was quantified by real-time polymerase chain reaction. The highest median PCV-2 shedding was found in the nursery of the PCVD-affected herd and in the grower of the PCVD-nonaffected herd. The PCV-2 shedding was significantly higher in earlier stages (newly weaned, nursery, and pregrower) in the PCVD-affected herd (Wilcoxon rank sum; P < 0.001) compared with the PCVD-nonaffected herd. Porcine circovirus-2 DNA was not detected in a significant proportion of lactating sows (parity ≥ 3) in the PCVD-nonaffected herd (Fisher’s exact test; P = 0.001). The results of this study suggest there may be an association between the presence of PCV-2 in the feces of lactating sows and increased PCV-2 shedding in younger pigs.     

Seroprevalence of economically important viral pathogens in swine populations of Trinidad and Tobago,West Indies

The objective of this study was to evaluate the seroprevalence and identify the strains of swine influenza virus (SwIV), as well as the seroprevalence of porcine parvovirus (PPV), transmissible gastroenteritis virus (TGEV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine respiratory coronavirus (PRCV), porcine circovirus type 2 (PCV-2), and classical swine fever virus (CSFV) in pigs in Trinidad and Tobago (T&T). Blood samples (309) were randomly collected from pigs at farms throughout T&T. Serum samples were tested for the presence of antibodies to the aforementioned viruses using commercial ELISA kits, and the circulating strains of SwIV were identified by the hemagglutination inhibition test (HIT). Antibodies against SwIV were detected in 114 out of the 309 samples (37%). Out of a total of 26 farms, 14 tested positive for SwIV antibodies. HI testing revealed high titers against the A/sw/Minnesota/593/99 H3N2 strain and the pH1N1 2009 pandemic strain. Antibodies against PPV were detected in 87 out of the 309 samples (28%), with 11 out of 26 farms testing positive for PPV antibodies. Antibodies against PCV-2 were detected in 205 out of the 309 samples tested (66%), with 25 out of the 26 farms testing positive for PCV-2 antibodies. No antibodies were detected in any of the tested pigs to PRRSV, TGEV, PRCV, or CSFV.     

Limited susceptibility of three different mouse (Mus musculus) lines to Porcine circovirus-2 infection and associated lesions

Porcine circovirus associated disease (PCVAD), a major global problem for pork producers, is characterized microscopically by depletion and histiocytic replacement of follicles in the lymphoid tissues. The objectives of this study were to determine 1) if Porcine circovirus-2 (PCV-2) inoculated mice (Mus musculus) can develop PCV-2 associated lymphoid lesions and serve as a model for PCVAD, and 2) if differences in PCV-2 host susceptibility exist among mice lines. Three groups (n = 48/group) of 4-wk-old male mice were used: BALB/c, C57BL/6, and C3H/HeJ. A 2 × 2 factorial analysis was designed for each group using PCV-2 inoculation and keyhole limpet hemocyanin in incomplete Freund’s adjuvant injections on day 0 and 7 as factors. Necropsies were performed on days 12, 17, 22, 27, 32, and 37. Serum samples collected at each necropsy tested negative for anti-IgG PCV-2 antibodies in all mice at all time points by 2 different PCV-2 enzyme-linked immunosorbent assays (ELISA). The PCV-2 DNA was detected by polymerase chain reaction (PCR) in 93% (100/108) of tissues and 42.6% (46/108) of serum samples from PCV-2-inoculated mice from days 12 to 37. Microscopic lesions consistent with PCV-2 infection were not observed in any mice and PCV-2 DNA and PCV-2 antigen were not detected in tissues by in-situ-hybridization or immunohistochemistry assays, respectively. Based on incidence of PCV-2 DNA in serum samples, the C57BL/6 mouse line was more resistant to PCV-2 infection than the other lines. The results indicate the mouse model likely has limited utility to advance understanding of the pathogenesis of PCV-2 associated lesions, but mice could potentially be important in the epidemiology of PCV-2.     

Detection of porcine circovirus 2 (PCV-2) DNA by nested PCR from formalin-fixed tissues of post-weaning multisystemic wasting syndrome (PMWS) pigs in Thailand

A retrospective study for the detection of porcine circovirus 2 (PCV-2) DNA was conducted by nested PCR method in 16 cases of swine post-weaning multisystemic wasting syndrome (PMWS) in Thailand. Histopathology showed characteristic lesions of PMWS and intracytoplasmic viral inclusion bodies in macrophages infiltrating in lymphoid tissues. PCV-2 DNA was detected from formalin-fixed and/or formalin-fixed paraffin-embedded tissues from all pigs with PMWS. The amplified products were digested with Hae III.     

广东省猪PCV-2感染的病原学调查

2004年-2006年从广东省4个不同地区458个规模化猪场采集2128份病料,进行了PCV-2的抗原检测,结果表明,被检地区的猪群中普遍存在PCV-2感染,检测的458个规模化猪场中有372个猪场有PCV-2阳性猪,平均阳性率达到81．22%;2128份被检病料样品中有863份为阳性,平均阳性率达40．55％（863／2128）;不同地区不同时段猪场阳性率为63．64％～92．86％,病料样品的阳性率为24．00%～48．00％。     

Clinical and pathological observations on pigs with postweaning multisystemic wasting syndrome

The aim of this work was to characterise the lesions and agents present in clinically normal and clinically affected pigs on a farm during an outbreak of postweaning multisystemic wasting syndrome (PMWS), and to evaluate the diagnostic techniques for detecting porcine circovirus type 2 (PCV-2) and other microorganisms. Four pigs in the early stage and 11 pigs in the late stage of the disease, and eight clinically normal pigs were necropsied. Samples of lymphoid tissue and serum were also obtained from 12 slaughter pigs from the same farm. The tissues were examined histopathologically, and in situ hybridisation, serology and PCR were used to detect porcine circovirus type 1 (PCV-1) and/or PCV-2 in tissues and/or sera. The presence of porcine reproductive and respiratory syndrome virus (PRRSV), Aujeszky's disease virus (ADV) and porcine parvovirus (PPV) were also investigated. Characteristic microscopical lesions of PMWS were observed in the lymphoid tissues of the pigs in all three necropsied groups; the lesions were most common and severe in the pigs in the early stage of the disease, less so in the pigs in the late stage of the disease, and least in the clinically normal pigs. PCV-2 infection was detected in all the necropsied pigs by in situ hybridisation and PCR. Only three pigs had the PCV-1 genome in serum or lymph node tissue. In contrast, the slaughter pigs had no microscopical lesions and no PCV-2 nucleic acid in their serum or tissues, and only one of them had the pCV-1 genome in its serum. Immunohistochemical, serological and PCR studies revealed that PRRSV and ADV were also present on the farm during the outbreak.     

Prevalence of infection with porcine circovirus-2 (PCV-2) and porcine reproductive and respiratory syndrome virus (PRRSV) in an integrated swine production system experiencing postweaning multisystemic wasting syndrome

The objective of this study was to evaluate the prevalence of infection with porcine circovirus-2 (PCV-2) and porcine reproductive and respiratory syndrome virus (PRRSV) through a longitudinal study in an integrated swine production system (7 farms) experiencing postweaning multisystemic wasting syndrome (PMWS). Risk factors for PCV-2 infection and for PCV-2 and PRRSV coinfection were also evaluated. Fifteen sows from each herd and 4 non-cross-fostered piglets from each sow were randomly selected at farrowing and ear-tagged at birth. Serum samples were analyzed for antibodies to PCV-2 and for detection of the PCV-2 and PRRSV genomes. Statistical analyses involved 2 approaches. The 1st approach characterized the dynamics of PCV-2 infection and their relationship with PRRSV infection. The 2nd approach analyzed the probability of being infected by PCV-2 or by both PCV-2 and PRRSV through a generalized linear mixed model incorporating sow and farm characteristics. At the 1st sampling time (1 wk of age), there was a significant relationship between sow PCV-2 infection and piglet PCV-2 infection (P < 0.0001). The risk of PCV-2 and PRRSV coinfection was 1.85 times greater in piglets from a sow with low titers of PCV-2 antibodies than in piglets from sows with medium to high titers (P = 0.03) and was 2.54, 2.40, and 2.02 times greater, respectively, in piglets from primiparous sows, PCV-2-infected sows, and farms in an area of high pig density than in piglets from sows of higher parity (P = 0.004), noninfected sows (P = 0.04), and farms in a low-density area (P = 0.09).     

Postweaning multisystemic wasting syndrome of pigs in Korea: prevalence, microscopic lesions and coexisting microorganisms

A retrospective study was performed on natural cases of postweaning multisystemic wasting syndrome (PMWS), recorded from January 1999 to December 2000, to determine the prevalence, microscopic lesions, and other coexisting pathogens associated with PMWS. PMWS is diagnosed based on three criteria: the presence of clinical signs (retardation of growth), characteristic microscopic lesions (granulomatous inflammation and inclusion body), and the presence of porcine circovirus (PCV)-2 within these lesions. One hundred and thirty three (8.1%) of the 1634 pigs submitted from 1243 pig farms were diagnosed for PMWS. The affected pigs were from 25 to 120 days old, the majority (78 cases, 58.6%) being 60 to 80 days old. PMWS occurred each month during the two-year study period, but the incidence peaked in May (38 cases, 28.6%), followed by April (18 cases, 13.5%) and June (13 cases, 9.8%). The most consistent and characteristic lesions were multifocal, granulomatous inflammation in lymph nodes, liver and spleen, characterized by infiltration of epithelioid macrophages and multinucleated giant cells. The majority of cases (113 cases, 85.0%) was dual infection with other pathogens. The combination of PCV-2 and Hemophilus parasuis (43 cases, 32.3%) was shown to be the most prevalent followed by PCV-2 and porcine reproductive and respiratory syndrome virus (39 cases, 29.3%). The consistent presence of PCV-2, but lower prevalence of other viral and bacterial pathogens in all pigs examined with PMWS, has led to the speculation that PCV-2 is the etiological agent causing PMWS.     

上海及周边地区猪圆环病毒2型基因型分析

采集上海及周边地区猪内脏样本,进行猪圆环病毒2型（Porcine circovirus type 2,PCV-2）病原学检测,并对阳性样本的ORF2序列进行分析和比对。结果显示,发病猪群PCV-2阳性率为39.06%（25/64）,健康猪群阳性率为13.51%（5/37）,PCV-2总阳性率为29.70%（30/101）。30份阳性样本中PCV-2a亚型为2株,检出率为1.98%（2/101）,其余28株均为PCV-2b亚型,检出率为27.72%（28/101）。PCV-2的ORF2序列与已登录的ORF2序列的同源性在90.7%~100%。2株PCV-2a株相互间的同源性为99.6%;28株PCV-2b株的同源性在94.4%~100%,PCV-2b株中只有4株与已登录株DQ141322、AY321984和AY484413株同源性关系最近,处于同一分支中,而另外24株与Q151643中国株同源性关系最近且处于同一分支中。研究结果表明上海及周边地区PCV-2感染比较普遍,发病猪场的感染率远高于健康猪场,且感染率比往年有升高,PCV-2在猪场疫病的爆发和传染中起着重要的协同作用;在PCV-2的感染病例中,PCV-2b亚型为感染的优势毒株;绝大多数PCV-2b ORF2片段的同源性与已登录的一株中国株同源性关系密切,在基因进化树上处于同一分支,但是否可以推断其为PCV-2的另一个亚型有待进一步考证。     

上海市规模化猪场猪圆环病毒2型血清学调查

为了解和掌握上海市PCV-2的感染情况,2003年-2005年对上海市猪群PCV-2的感染情况进行了血清学调查。用间接酶联免疫吸附试验,对上海市9个规模化猪场的768份血样进行了PCV-2抗体检测。被检猪场均有PCV-2抗体阳性,而且在2005年有明显增加的趋势。     

Effects of the timing of the administration of Mycoplasma hyopneumoniae bacterin on the development of lesions associated with porcine circovirus type 2

To determine whether there is an effect of the timing of vaccination on porcine circovirus type 2 (PCV-2) replication and PCV-2-associated lesions, 78 pigs were randomly assigned to eight groups: group 1 (10 pigs) was vaccinated with a commercial Mycoplasma hyopneumoniae vaccine at two and four weeks of age, group 2 (nine pigs) was vaccinated at four and six weeks of age, group 3 (10 pigs) at six and eight weeks of age and group 4 (10 pigs) at eight and 10 weeks of age; group 5 (nine pigs) was vaccinated once with a double dose at four weeks of age, and group 6 (10 pigs) was vaccinated once with a double dose at eight weeks of age. Groups 7 and 8, both of 10 pigs, were not vaccinated. At eight weeks of age, the pigs in groups 1 to 7 were inoculated with PCV-2. Fourteen days after they had been inoculated, the pigs in groups 1, 4 and 5 had significantly (P<0.05) more copies of the PCV-2 genome in their serum than the unvaccinated pigs. Microscopically, 14 of the 68 inoculated pigs had normal lymphoid tissues, 40 had mild PCV-2-associated lymphoid lesions and 14 had moderate lesions. The mean overall lymphoid lesions (lymphoid depletion, granulomatous inflammation, and quantity of PCV-2 antigen in spleen, tonsil, and five lymph nodes) were significantly (P<0.05) more severe in groups 4 and 5 than in groups 2, 3, 7 and 8.     

Comparative analyses of humoral and cell-mediated immune responses upon vaccination with different commercially available single-dose porcine circovirus type 2 vaccines

The objective of this study was to compare the induction of humoral and cell-mediated immune responses by four commercially available single-dose porcine circovirus type 2 (PCV-2) vaccines. A total of 50 3-week-old piglets were assigned to five groups (10 pigs per group). Four commercial PCV-2 vaccines were administered according to the manufacturer's instructions and the piglets were observed for 154 days post vaccination (dpv). Inactivated chimeric PCV-1-2 vaccines induced higher levels of PCV-2-specific neutralizing antibodies (NA) and interferon-γ-secreting cells (IFN-γ-SC) in pigs than did the other three commercial PCV-2 vaccines. The proportions of CD4⁺ cells were significantly higher in animals vaccinated with inactivated chimeric PCV-1-2 and PCV-2 vaccines than in animals vaccinated with the two subunit vaccines. To our knowledge, this is the first comparison of humoral and cell-mediated immunity induced by four commercial single-dose PCV-2 vaccines under the same conditions. The results of this study demonstrated quantitative differences in the induction of humoral and cell-mediated immunity following vaccination.     

广东省猪PCV-2感染的调查

2005年-2006年,对广东省12个市（县／区）共40个猪场108头病例,应用病理学及病原检测方法对PCV-2感染情况进行调查。结果表明,PCV-2阳性44例,占总病例数的40．7％。从,10日龄到120日龄均有感染,以60日龄～70日龄多发。在PCV-2感染的病例中,混合感染占95．5％。以混合感染PRRSV（11例,25％）最多,混合感染APP次之（10例,22．7％）。另外,调查显示该病可全年发生,但5月份为发病高峰。