Sporogonic development of Hepatozoon americanum (Apicomplexa) in its definitive host, Amblyomma maculatum (Acarina)

Light microscopic observations of the sporogonic development of Hepatozoon americanum are described in its acarine host, Amblyomma maculatum. Laborato ry-reared nymphal licks were fed on 2 dogs infected with H. americanium. Ny mphal ticks were sampled daily, starting 3 days after being placed on a par asitemic dog, until 18 days after infestation (PI), and then every 3 or 4 d ays until replete nymphs molted. Ticks were examined as unstained wet mount s and hematoxylin-eosin-stained paraffin sections. Gametes were found withi n the gut cells of nymphs 4 and 6 days PI. Although differentiation of gamo nts into gametes was not detected, syngamy and sporogony were observed. Spo rogony appears to occur wholly within tick gut cells, followed by release o f mature oocysts into the hemocoel. The earliest evidence of sporoblast for mation was observed 23 days PI and of sporozoite formation, 10 days later. Mature oocysts were first found 42 days PI in newly molted adult ticks. Mos t adult ticks (>98%) that were dissected contained mature oocysts. Oocysts were multisporocystic, and sporocysts contained a variable number of sporoz oites. Oocysts in various stages of development were often seen within the same tick, and the number of mature oocysts ranged from 4 to 573.