A proposed model to explain persistent infection of host cells with Coxiella burnetii.

L929 mouse fibroblast cells and J774 macrophage-like cells are both susceptible to persistent infection with the Q fever agent Coxiella burnetti. Previously this laboratory has shown that persistently infected cell populations multiply with unaltered generation times or cell cycle progression. It has also been reported by others and us that highly infected cells typically exhibit one large parasite-containing vacuole. We now report that lightly and heavily infected cells are capable of division and in the process segregate the parasite-containing vacuole into one of the emerging daughter cells; the companion daughter cell emerges parasite-free. This asymmetric division of infected cells, revealed via photomicrography of stained cells, accounts for the appearance of uninfected cells within persistently infected host cell populations that were previously 100% infected. Some of the persistently infected L929 populations were maintained in culture for over two years without the addition of normal cells.