OBSERVATIONS ON TISSUE STAGES OF HEPATOZOON AMERICANUM IN 19 NATURALLY INFECTED-DOGS

Lesions and associated tissue stages of Hepatozoon americanum in 19 na turally infected dogs are described. Schizogony takes place in an unid entified host cell which, during the early stages of the asexual cycle , is contained within a broad, multilamellar mucopolysaccharide 'cyst' Material forming the cyst appears to be host-derived. An intense infl ammatory response follows rupture of the schizont and disintegration o f the cyst wall. There is unusually intense angiogenesis associated wi th the resulting granulomatous inflammation initiated by the freed mer ozoites. Phagocytized zoites enter the canine circulatory system throu gh the walls of these vessels. Evidence is presented that suggests a s ingle infecting episode can cause prolonged (19 months) infection, and further, that infection is perpetuated by repeated asexual cycles. Pa rasites in peripheral blood leukocytes include both those with and wit hout a visible nucleus. (C) 1998 Elsevier Science B.V. All rights rese rved.