Simulated Microgravity Causes Faster Replication During Acute Infection of <scp>ME49</scp> ‐ <i>Toxoplasma Gondii</i> and Alterations in Host Cells

ABSTRACT Spaceflight is important to explore the universe. However, astronauts face many health challenges in space including the increased risk of infection. During spaceflight, the microgravity weakens immunity, which causes opportunistic infections with pathogens such as herpesvirus. However, we have no information about the effects of microgravity on infections caused by other pathogens with a latent stage in their life cycle. In addition, there are no reports on host cell responses or the mechanisms that modulate changes under microgravity conditions. Due to the high cost and effort required for space study in actual microgravity, simulated microgravity plays an important role in mimicking conditions that allow researchers to study risks during spaceflights. Toxoplasma gondii is one of the top five important economic pathogens; it causes toxoplasmosis, may reactivate from the latent phase in immunocompromised individuals, and there is no active drug or vaccine. In this study, we observed the effect of simulated microgravity on T. gondii and on host cells. Simulated microgravity using a 3D clinostat induced host cell proliferation and caused aggregated cells to form three dimensional multicellular spheroids in Vero cells and HFF. Rapid egress and growth of tachyzoites during the acute phase of type II ME49 infection were observed under simulated microgravity.