| Porcine respiratory disease complex (PRDC) is a multi-factorial respiratory syndrome and is the result of a combination of viruses, bacteria, mycoplasmas, parasites, bad breeding administration conditions, susceptible pig population and so on. To understand infectious status of PRDC in pig population in Guangxi,1686 tissue samples collected from 395 large scale pig farms scattered in 14 districts were tested for 12 PRDC-associated pathogens in this study using PCR, RT-PCR, and bacteria isolation assay from May 2007 to May 2009. Results showed that 292 farms and 1212 samples were all positive for PRDC. The PRDC positive rate of farm and sample were 73.92%(292/395) and 71.89%(1212/1686), respectively. Particularly, single or mixed infection positive rate of porcine reproduce and respiratory syndrome virus (PRRSV), porcine circovirus type 2 (PCV2), classical swine fever virus (CSFV), streptococcus suis (SS), pseudorabies virus (PRV), bordetella bronchiseptica (BB), swine influenza virus (SIV), eperythrozoon suis (ES), toxigenic pasteurella multocida (T+PM), haemophilus parasuis (HP), porcine parvovirus (PPV) and actinobacillus pleuropneumoniae (APP) were 51.36%(866/1686),36.54%(616/1686), 10.91%(184/1686),9.19%(155/1686),6.76%(114/1686),6.64%(112/1686),5.81% (98/1686),5.63%(95/1686),4.45%(75/1686),3.91%(66/1686),0.59%(10/1686) and 0 (0/1686), respectively.Aetiological Analysis In 1212 PRDC positive samples, only 351 samples were found to be single infection with a proportion of 28.96%, while the other 861 samples (accounting for 71.04%) were mixed infection. Furthermore, among these 861 mixed infection samples, the sample number of dual infection type, triple infection type, and quadruple infection type were 597 (69.34%),210 (24.39%) and 54 (6.27%), respectively. Microorganism co-infection analysis showed that 460 out of 861 samples were "virus and virus" mixed infection with a proportion of 53.43%, and the other 401 samples were "virus and bacterium" mixed infection holding the remaining 46.57%. Analysis on dominating pathogen of PRDC showed that 1054 samples were infected with PRRSV and/or PCV2 accounting for 86.96%of 1212 PRDC positive samples, and the number of "PRRSV+ PCV2 (+other pathogens)" co-infection sample was 428, which shares 49.71%in 861 mixed infection samples. The results suggest that large scale pig farms in Guangxi generally suffered from the PRDC characterized with major pathogen of PRRSV and PCV2, type of infection was complicated and various, and mixed infection was quite common, of which the "PRRSV+PCV2 (+other pathogens)" co-infection was the most common one.Histopatbological Observation Basing on the aetiological investigation, tissue or organ specimens of heart, liver, lung, kidney, spleen, and lymph node collected from 560 PRDC cases were fixed, paraffin embedded, H.E stained, and then histopathological features were observed via optical microscope. Histopathological features of 500 out of 560 PRDC cases were typic and similar. Among the 500 PRDC cases, the cases of single infection with PRRSV and PRV were 166 and 22, respectively; while the cases of co-infection with PRRSV+PCV2, PCV2+PRV, PRRSV+E-suis and PRRSV+CSFV+PCV2 +HP were 247,38,21 and 6, respectively. Specific histopathological features of 500 cases were listed as follows:As to single infection with PRRSV case, lung tissues generally developed into interstitial pneumonia lesions; kidney tissues developed glomerulonephritis lesions; lymph node expressed proliferative lesions of acute lymphadenitis; liver tissues suffered from deterioration hepatitis lesions; cardiac muscle generally showed metamorphic myocarditis lesions; and spleen showed lesions of splenic corpuscle volume reduction or necrosis, red pulp region hemorrhage and lymphopenia. As for cases of PRRSV and/or PCV2 co-infection with other viruses or secondary infection with bacteria, histological lesions became more typical, and many tissues and cells developed degeneration, even necrosis. Above results of systematic histopathological observation and description furthermore provided important supportive reference materials for establishment of histopathological technology standard for diagnosis on PRDC.Control and Prevention Measures Beginning in May 2009, a series of disease control and prevention measures in order to strengthen bio-safety and breeding management were established and implemented in 15 experimental pig farms. These measures mainly included:strict disinfection and access control on personnel, vehicles and items; termly disinfection of floor, wall, ceiling, air and tools involved in swine feeding; appropriate vaccination programme and monitoring of primary pathogens of PRRSV. CSFV, PRV, SIV and PCV2; prevention of environmental pests, mice, mosquitoes, flies and other biological disasters; control on ventilation, temperature and humidity; better breeding administration measures such as empty pit, cleaning, disinfection, all-in/all-out, reasonable stocking density, balanced nutrition, no mixing of batches, no mixing in-between compartments, stress minimization, prompt isolation of sick pigs from healthy population and treatment to prevent secondary infection, and strict free-pollution disposal and disinfection of dead pigs and all the polluted items.The most important measures were disinfection, surveillance and free-pollution disposal. The detailed measures were listed as follows:strict disinfection of personnel, vehicles and items that went into the pig farms; routine disinfection of floor, wall, ceiling and tools of farrowing house, nursing house and fattening house 2 times/week,1 times/week and 2 times/month, respectively, and 2 times disinfection for all houses after all pigs out and before new pig population in; fumigated disinfection of air of farrowing house and nursing house 1 times after all pigs out and before new pig population in; disinfection of outside environment of the pig farm 2 times/month; isolation and elimination of sick pigs, and strict free-pollution disposal and disinfection of dead pigs and all the polluted items in time.Control and Prevention Effects Pass rates of immune antibodies against CSFV in these experimental farms increased significantly, accompanied with positive rates of major pathogens drastically decreased. From May 2009 to June 2010, Detection results of 16974 sera and 1589 tissue samples from 15 pig farms showed that the average pass rate of immune antibody against CSFV jumped from 91.18% of pre-experiment to 95.90% of post-experiment, while average CSFV positive rate decreased from 8.55% to 6.04%; in addition, average pass rate of PRRSV antibody climbed from 86.46% to 88.11%, with the decline from 15.80% to 13.15% in average PRRSV positive rate; average positive rate of PCV2 fell from 26.61% to 22.28% as well; furthermore, average positive rate of PRV gE specific antibody in sera and PRV in tissue samples dropped from 5.53% and 6.43%, respectively, to 4.51% and 5.16%; similarly, average positive rate of SIV infectious antibody in serum samples and virus in tissue samples sank from 5.51% and 6.37%, respectively, to 5.30% and 4.97%.Pig mortality declined generally. Average mortality of 15 farms decreased from 8.28% one-two months after experiment to 7.24% eleven-twelve months after experiment.Reproduce performance of breeding pig and survival rate of piglet promoted significantly. For example, average number of survival piglet per year of each Landrace sow increased by 0.84 from 20.73 to 21.57; average mortality of Landrace piglet decreased from 8.54% to 6.86%. Similarly, average number of survival piglet per year of each Duroc sow rise by 0.28 from 18.95 to 19.23; average mortality of Duroc piglet decreased from 7.44% to 6.55%. In large Yorkshire groups, average number of survival piglet per year of each sow climbed 0.57 from 19.97 to 20.54; average mortality of piglet decreased from 7.42%to 6.39%.Growth performance of piglet upgraded greatly. For example, the age to 30kg (AGE30) and the age to 100kg (AGE100) of Landrace piglet shortened 2.1 days and 3.3 days, respectively, the average daily gain from 30kg to 100kg (ADG) increased 30. 1g, the feed conversion ratios (FCRs) of nursery pig and fattening pig decreased 0.063 and 0.098, respectively. The AGE30 and AGE100 of Duroc piglet reduced 2.1 days and 3.9 days, ADG increased 24.6g, FCRs of nursery pig and fattening pig fell 0.029 and 0.089, respectively. Similarly, the AGE30 and AGE100 of Yorkshire piglet decreased 1.9 days and 3.6 days, ADG added 21.5g, FCRs of nursery pig and fattening pig dropped 0.023 and 0.056, respectively.In sum, from May 2009 to June 2010, after the implementation of above integrated measures, epidemic of major disease in 15 experimental pig farms were effectively controlled, accompanied with remarkable decrease of morbidity and morality, and significantly promotion on immunoprotective level of pig groups, reproduction performance of breeding pigs, growth performance of piglets, and other production parameters, which led to good economic and social profits. |
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