Studies on syndemic infection of porcine reproductive and respiratory syndrome virus with porcine circovirus 2 in backyard pigs of Mizoram, India.

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus 2 (PCV2) are among one of the most prevalent and important infectious agents, which cause a severe economic impact on pig farming worldwide. Circulation of these viruses together in the same pig population may lead to the syndemic infection with altered pathogenicity and thereby pathology and clinical manifestation of the diseases. The present study evaluated syndemic infection between PRRSV and PCV2 in the pig population reared in the backyard farms in Mizoram state of India. The syndemicity between PRRSV and PCV2 was confirmed by clinico-pathological studies followed by simultaneous detection of both the viruses in tissue samples by polymerase chain reaction (PCR) and reverse transcription-PCR (RT-PCR), immunohisto-chemistry and SYBR green-based real-time PCR / RT- PCR. The syndemicity resulted to a more severe respiratory disease in affected pigs. Pathological studies on affected pigs revealed a combined picture of hemorrhagic lesions with lymphadenopathy. The SYBR green-based absolute quantification assay estimated the PCV2 load in more quantities than that of PRRSV in all the tissues. The highest PRRSV load was detected in the lungs, while the highest PCV2 load was detected in mesenteric and inguinal lymph nodes. The co-circulation of different pathogenic viruses and their persistent infections in a population is always a matter of great concern to pig producers across the world. The present findings highlighted the similar situation with syndemic infection of PRRSV with PCV2 for the first time in Mizoram, India, that caused severe respiratory disease in affected pigs.