2.5 Co-Infection with Multiple
Viruses
Alongside single and dual infections, multiple (including triple or more
viruses) infections are also prevalent among pigs(Opriessnig,
Gimenez-Lirola, & Halbur, 2011). PRDC is caused by the combination of
infectious pathogens, differences in production systems and
environmental factors (Hansen et al., 2010). Previous study have
demonstrated that PRRSV and Mhp were well known to potentiate
PCV2-associated lesions, surprisingly, PRRSV vaccine was found to
enhance PCV2 replication and it can be related to the failure of PRRSV
vaccine in vaccinated co-infected pigs compared to non-vaccinated
co-infected pigs (C. Park, Oh, Seo, Han, & Chae, 2013). Pallares et al
have detected that the coinfection rate of PCV, PRRSV and Mhp was 16%
(77/484) in 484 cases diagnosed as PMWS (Pallares et al., 2002). A
survey also demonstrated that co-infection ratios with three and four
pathogens were 17.3% and 7.3% respectively in 110 pneumocystis spp.
positive lung samples of Austrian pigs with pneumonia
(Weissenbacher-Lang et al., 2016). Vaccination against Mhp significantly
protected pigs against multiple viral infections, suggesting that
vaccination against Mhp decreases the risk of PMWS and PRDC, and reduces
susceptibility of pigs to the other viral pathogens (Chae, 2011). These
data indicate that Mhp plays an important role in the co-infection of
dual or multiple pathogens in vivo .