We recently published a paper showing that haemosporidian parasites have an evolutionary history dominated by host-switching events, but there is a degree of co-divergence with their non-passerine hosts at the Family taxonomic level.
PDF: Santiago-Alarcon, D., Rodríguez-Ferraro, A., Parker, P.G., and Ricklefs. R.E. 2014. Different meal, same flavor: cospeciation and host switching of haemosporidian parasites in some non-passerine birds. Parasites & Vectors 7: 286