Abstract
Oocysts are the environmentally resistant stage of the protozoan parasite Toxoplasma gondii. They are responsible for foodborne infections in humans and animals worldwide. Infectious oocysts contain sporozoites that have to exit the sporocyst and oocyst walls to initiate replication of the parasite within the host tissues. Given their robustness and resistance to chemical degradation, it is still unclear how the oocyst and sporocyst walls release the sporozoites. This process called excystation is thought to occur in the small intestine as a result of the combined action of digestive agents, yet to be identified. By using an oocyst-macrophage co-culture platform, we previously demonstrated in vitro that the excystation of sporozoites and their differentiation into replicative tachyzoites could occur in absence of digestive factors, following phagocytosis by macrophages. Here, we further characterize the dynamics of the oocyst phagocytosis at the single-cell level by using optical tweezers and micropipette aspiration techniques. Our results show that the oocyst internalization kinetics can vary among a given population of macrophages, but similar processes and dynamics could be observed. Most of the cells manipulate oocysts for ~15 min before internalizing them in typically 30 min. This process mainly involves the actin cytoskeleton of the macrophages. Liberated sporozoites within macrophages then differentiate into tachyzoites within 4–6 h following oocyst-macrophage contact. Tachyzoites appear to develop better in macrophages challenged with free sporocysts or sporozoites than with whole oocysts, suggesting that opening of the oocyst wall is one of the most limiting steps for sporozoite excystation completion.
Highlights
The apicomplexan parasite Toxoplasma gondii can persist throughout the environment as a robust infectious stage called the oocyst (Shapiro et al, 2019)
We developed in vitro oocyst-macrophage co-cultures to investigate whether phagocytic cells could mediate sporozoite excystation following oocyst phagocytosis (Freppel et al, 2016)
Tachyzoites developed better in macrophage cultures challenged with free sporocysts or sporozoites than with whole oocysts (p < 0.001) (Figure 4)
Summary
The apicomplexan parasite Toxoplasma gondii can persist throughout the environment as a robust infectious stage called the oocyst (Shapiro et al, 2019). Oocysts are excreted in cat feces and become infectious following a 1–2 week sporulation process. Oocysts can infect many avian and mammal species worldwide, including humans, through the Toxoplasma Oocyst Phagocytosis by Macrophages consumption of water or raw vegetables and fruits contaminated with cat feces (Shapiro et al, 2019). Sporozoites excyst from the sporocyst and oocyst walls, invade host enterocytes, and lamina propria macrophages and dendritic cells prior to differentiation into tachyzoites (Delgado Betancourt et al, 2019). Infection results in the development and persistence of the parasite as tissue cysts, mainly in the brain and muscles. Irrespective of the ingested stage, most infections are asymptomatic except in congenitally infected children and immunocompromised people, who may suffer severe ocular, cerebral, or multivisceral complications (Robert-Gangneux and Dardé, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
