Comparative infection efficiency of Porcine reproductive and respiratory syndrome virus field isolates on MA104 cells and porcine alveolar macrophages

Isolation of Porcine reproductive and respiratory syndrome virus (PRRSV) on MA104 or MARC-145 cells is frequently used in PRRS diagnosis. However, the ability of recent field isolates to grow on these established simian cell lines has not been determined. The aim of this study was to characterize the growth of PRRSV field isolates on primary porcine alveolar macrophages (PAMs) and MAl 04 cells in comparison with the growth of the laboratory-adapted strain VR-2332. A cytopathic effect was observed in 70% of serum samples after 1 passage on PAMs and was verified by immunofluorescent staining or reverse transcriptase- polymerase chain reaction. Field isolate growth was observed on MA104 cells for only 1 of 50 serum samples after 14 d. Strain VR-2332 grew readily in MA104 cells [maximum titer, 10⁷ TCID₅₀ (median tissue culture infective dose) per milliliter at 30 h] but not in PAMs (102 TCID ₅₀/mL at 72 h). These results show that PAMs are superior to simian cells for diagnostic isolation of current field PRRSV strains.