Abstract
Pigs are often colonized by more than one bacterial and/or viral species during respiratory tract infections. This phenomenon is known as the porcine respiratory disease complex (PRDC). Actinobacillus pleuropneumoniae (App) and porcine reproductive and respiratory syndrome virus (PRRSV) are pathogens that are frequently involved in PRDC. The main objective of this project was to study the in vitro interactions between these two pathogens and the host cells in the context of mixed infections. To fulfill this objective, PRRSV permissive cell lines such as MARC-145, SJPL, and porcine alveolar macrophages (PAM) were used. A pre-infection with PRRSV was performed at 0.5 multiplicity of infection (MOI) followed by an infection with App at 10 MOI. Bacterial adherence and cell death were compared. Results showed that PRRSV pre-infection did not affect bacterial adherence to the cells. PRRSV and App co-infection produced an additive cytotoxicity effect. Interestingly, a pre-infection of SJPL and PAM cells with App blocked completely PRRSV infection. Incubation of SJPL and PAM cells with an App cell-free culture supernatant is also sufficient to significantly block PRRSV infection. This antiviral activity is not due to LPS but rather by small molecular weight, heat-resistant App metabolites (<1 kDa). The antiviral activity was also observed in SJPL cells infected with swine influenza virus but to a much lower extent compared to PRRSV. More importantly, the PRRSV antiviral activity of App was also seen with PAM, the cells targeted by the virus in vivo during infection in pigs. The antiviral activity might be due, at least in part, to the production of interferon γ. The use of in vitro experimental models to study viral and bacterial co-infections will lead to a better understanding of the interactions between pathogens and their host cells, and could allow the development of novel prophylactic and therapeutic tools.
Highlights
Respiratory disease in pigs is common in modern pork production worldwide and is often referred to as porcine respiratory disease complex (PRDC) [1]
This assay was done to confirm that inactivation of the toxins ApxI and ApxII in the mutant AppDapxIDapxIIC reduces cell death seen with Appwt strain
lactate dehydrogenase (LDH) cytotoxicity assays to detect cell death were performed on cells infected with porcine reproductive and respiratory syndrome virus (PRRSV) for 72 hours and co-infected with Appwt strain or AppDapxIDapxIIC
Summary
Respiratory disease in pigs is common in modern pork production worldwide and is often referred to as porcine respiratory disease complex (PRDC) [1]. There are a variety of viral and bacterial pathogens commonly associated with PRDC including porcine reproductive and respiratory syndrome virus (PRRSV) and Actinobacillus pleuropneumoniae (App) [1]. Both are considered pathogens of major importance or relevance for the pig industry [1]. Co-infections with Mycoplasma hyopneumoniae and swine influenza virus (SIV) exhibited more severe clinical disease [2], PRRSV and Streptococcus suis co-infection experiments confirmed that PRRSV predisposes pigs to S. suis infection and bacteremia [3] and increases the virulence of PRRSV in pigs [4], M. hyopneumoniae infection increases effectiveness of PRRSV infection and lesions [5], and PRRSV infection was able to accelerate Haemophilus parasuis infection and loads [6] Those studies on coinfections principally looked at the macroscopic lesions and at the clinical signs. It is crucial to develop new in vitro models to investigate in more details the mechanistic and the interactions involved in polymicrobial infections
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
