How can an infection of lower respiratory tract lead to a skin infection?
One might argue that since replication takes place in erythroblasts (Brown, Anderson, &amp; Young, 1993), that it's not actually a respiratory infection either.  Fluids are simply more hospitable to the virus and more transmissible.  

As for the rash, perhaps it is because the P antigen receptor that erythrovirus uses to infect erythroblasts is also expressed on endothelial cells, like those in skin (and alveolar) capillaries .