Sorry to miss your post. How is your son doing now? Is he still fighting constant infections?
Viruses can cause a decrease in platelets and decrease bone marrow cellularity. Usually the body can recover from this on its own, but if the immune attack gets out of control, aplastic anemia can evolve.
For some people with AA, platelets can also be the first blood line to drop.
Hopefully, your son is regaining his strength now!
52 yo female, dx 9/08, AA/hypo-MDS, subclinical PNH, ATG/CsA 12/08, partial response. Tried slow cyclosporine taper over 4+ years. Platelets fell, so back on cyclosporine. Trisomy 6 clone in 5% of cells.