engleski

Reproductive failures caused by PRRS

The PRRS virus (PRRSV) causes vascular collapse and asphyxia of fetuses. In the same litter can be present normal, vital, deadborn or mummificated piglets. Severity of gross and microscopic lesions in fetuses depends on the virus properties and the age of the fetus. Detection of PRRSV in fetal tissue is usually done by RT-PCR but also by immunohistochemistry, viral isolation and fetal serology. It is known that virus infects fetus in the last trimester because in this stage of embryogenesis communication between fetal and maternal circulation is possible. Virus primary causes damage on placenta and by electron microscopy micro separation can be seen. The results of experimental infection show that viral isolation from thoracic liquid is highly sensitive method for virus detection but extremely limited with autolysis. The good sensitivity was achieved with PCR, but surprisingly there was a low influence of autolysis. The same PCR results were from pooled internal organs or from thoracic liquid. Fetal serology and IHC for PRRSV infection of fetuses can be also used and depends by the time of infection and is in negative correlation. Also there is controversial data about specific organ for IHC detection of PRRSV. We sampled 83 fetuses from 8 large pig production units with significant reproductive losses, aborted in late gestation. After a complete post-mortem and microscopic examination we tested a sample of organs for presence of PRRSV by PCR and IHC and for some other agents like PCV2 and TTV. PRRSV was detected by PCR in only 7.23% of fetuses. The IHC detected PRRSV only in thymus of 23.89% fetuses. 3.61% fetuses were PRRSV positive with both methods of detection. There was a clear discrepancy between the results obtained with the two PRRSV detection methods. Thymus that appeares to be the only organ where PRRSV antigen was found by IHC was not submit for PCR. We found highly frequent patomorfological lesions, previously described as PRRS induced lesions, such as anasarca, multiple umbilical edema and bleedings, petehyal haemorrhages in lungs, lymphocytic hepatitis, microgliosis, hydrothorax, epicardial bleedings, petehyal haemorrhages. But it seems that only anasarca, multiple umbilical edema and bleedings, petehyal haemorrhages in lungs and lymphocytic hepatitis are more frequent lesions in PRRS positive animals and therefore specific for PRRSV infection. All other lesions previously described as PRRSV induced lesion were highly frequent found but equally or more frequent in PRRSV negative fetuses. All fetuses were positive for PCV2 presence by PCR. IHC and ISH to detect PCV2 were negative and there was no specific myocardial lesion for reproductive failures connected with PCV2 infection, so PCV2 is excluded as causative agent of reproductive disorders. The farms have permanent monitoring and vaccination program for PPV and ADV so this agents were also exclude. PEV and EMV are not excluding but is not known presence of this viruses in Croatia. It is interesting that a high frequency of TTV g2 infection in fetuses was detected. Until now TTV is not considered as abortificial agent

PRRS; reproductive failures

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