WBabesia divergens
WCoccidia
WCovering sickness
WCryptocaryon
WEimeria
WEquine protozoal myeloencephalitis
WGiardia duodenalis
WHaemoproteus
WHistomoniasis
WIchthyophthirius multifiliis
WKlossiella
WLeucocytozoon
WPlasmodium gallinaceum
WSurra
WVelvet (fish disease)