It can be impossible to identify full virus particles from empty ones based on size or shape alone. The particle's buoyant density can help you to distinguish between otherwise identical populations. An analytical ultracentrifuge (AUC) in your lab can make quick work of particle partitioning. For more details, visit beckman.com/home.
Infected animals given chloroquine while pregnant had fetuses with a far lighter viral load in their brains than untreated mice did.