Murray Leinster 
Pariah Planet 

A terrible blue plague has struck on the planet of Dara, sending fear out across all of the nearby worlds in the region. Fear quickly leads to hate which threatens the peace of the universe and the lives of millions of innocent beings. A Medical ship commanded by Calhoun heads into the danger area… and soon finds himself in greater danger than he thought possible…and part of that trouble comes in the shape of beautiful, gun-toting space stowaway named Maril…