Effect of Porcine Reproductive and Respiratory Syndrome Virus Infection on the Clearance of Haemophilus parasuis by Porcine Alveolar Macrophages


Article by:
G I Solano, E Bautista, T W Molitor, J Segales, and C Pijoan.

This study was performed in order to characterize the interaction between PRRSv and Haemophilus parasuis in Porcine Alveolar Macrophages.
Nineteen 4-5 week old piglets were selected (PRRSV negative and ADV negative). Four piglets were euthanized and their PAMs were used for the in-vitro studies: PAMS were inoculated with PRRSv and then exposed to Haemophilus parasuis in order to determine the phagocytosis capacity of these PAM.

Fifteen piglets were used for the ex-vivo studies; 9 were infected with PRRSv and 6 remained as controls. The animals were euthanized at different times (6h, 12h, 24h, 168h, and 216h post infection) and their PAMs collected for the rest of the study: PAMs were exposed to Haemophilus parasuis and phagocytosis and killing capacity was determined.

There was a reduction in bacterial uptake (phagocytosis) in PAMs collected after 168h (7d) of infection, which may suggest that phagocytic function may change with time following virus infection. The problem is that the time intervals were too short at the beginning and then from day1 until day there were no samplings.
When intracellular survival was evaluated, after 30 min there were higher numbers of H. parasuis in PAMs collected from piglets 168h and 216h post-infection as compared to PAMs from non-infected controls. Which indicated that PRRSV infected pigs had a marked decrease in the functional ability of their PAMs to kill H.parasuis and produce superoxide anion.

It can be suggested that in the later stages of infection (168 and 216h) the transitional decrease in superoxide production by AM may create a more permissive environment for bacterial colonization. This effect seems to be reverted after 4 weeks of infection as it is mentioned in the literature.