Coinfection with Haemophilus parasuis serovar 4 increases the virulence of porcine circovirus type 2 in piglets

Background: Postweaning multisystemic wasting syndrome (PMWS) is an emerging disease in swine. Pigs with
PMWS are often infected with a variety of other pathogens, including bacteria, viruses and mycoplasm, in addition
to porcine circovirus type 2 (PCV2). PCV2 and Haemophilus parasuis serovar 4 (HPS4) coinfection remain epidemic
in China.
Methods: Here we report construction of a three-week-old naturally farrowed, colostrum-deprived (NFCD) piglet’s
infection model and demonstrate that PCV2-infected piglets with the HPS4 coinfection increased the virulence of
PCV2 and these pathogens interact acquired PMWS.
Results: All the single infected piglets were transiently bacteremic or viremic. All the PCV2/HPS4 coinfected piglets
developed PMWS, characterized by dyspnea, anorexia, prostration and lose weight severely. Co-infection with PCV2
and HPS4 resulted in an increased amount of virus in serum and tissues, presented a slower generation and lower
levels of antibodies against PCV2. Co-infection with PCV2 and HPS4 resulted in further reductions in total and differential
peripheral blood leukocyte counts. Meantime, PCV2/ HPS4 coinfection potentiated the severity of lung and lymphoid
lesions by PCV2-associated, increased the virulence of PCV2-antigen and enhanced the incidence of PMWS in piglets.
Conclusion: Co-infection with PCV2 and HPS4 induce the exacerbation of system injuries and enhance the pathogenicity
of PCV2 in piglets.