Abstract
Porcine circovirus 2 (PCV2) is the etiological agent that causes porcine circovirus diseases and porcine circovirus-associated diseases (PCVD/PCVAD), which are present in every major swine-producing country in the world. PCV2 infections may downregulate the host immune system and enhance the infection and replication of other pathogens. However, the exact mechanisms of PCVD/PCVAD are currently unknown. To date, many studies have reported that several cofactors, such as other swine viruses or bacteria, vaccination failure, and stress or crowding, in combination with PCV2, lead to PCVD/PCVAD. Among these cofactors, co-infection of PCV2 with other viruses, such as porcine reproductive and respiratory syndrome virus, porcine parvovirus, swine influenza virus and classical swine fever virus have been widely studied for decades. In this review, we focus on the current state of knowledge regarding swine co-infection with different PCV2 genotypes or strains, as well as with PCV2 and other swine viruses.
Highlights
The porcine circovirus (PCV) belongs to the family Circoviridae and contains a single-stranded circular DNA genome [1,2,3]
One hundred and eighteen porcine circovirus type 2 (PCV2)-positive DNA samples isolated from diseased pigs were analyzed using a modified differential polymerase chain reaction (PCR) assay, and the results indicated that the coexistence rates of PCV2 genotypes were 32.2% (38/118) in sick pigs [13]
Replication in later stages of the infection [107]. These results indicated that co-infection with PCV2 and Porcine Epidemic Diarrhea Virus (PEDV) resulted in more severe clinical symptoms compared to animals infected with PEDV alone, and PCV2 may enhance PEDV-induced disease and lesions
Summary
The porcine circovirus (PCV) belongs to the family Circoviridae and contains a single-stranded circular DNA genome [1,2,3]. Co-infections of different PCV2 strains, which cause recombination and genomic shifts in recent years, are reviewed. The sequencing results of 38 co-infected samples showed that the coexisting genotypes were PCV2a-PCV2b (12/38), PCV2a-PCV2d (15/38). Further studies have demonstrated that pigs with dually heterologous inoculation or naturally infected with multiple PCV2 genotypes or strains displayed more severe lesions [36,37]. These results suggest that the coexistence of different strains of PCV2 might contribute to the development of more severe clinical symptoms in pigs and more recombination events between strains in the field [13,35,36,37]. More studies need to focus on analyzing the recombination trends of PCV2 strains, which may provide a better strategy for vaccine development and vaccination strategy
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