<abstract><p>A recent discovery highlighted that mosquitoes infected with <italic>Microsporidia MB</italic> are unable to transmit the <italic>Plasmodium</italic> to humans. <italic>Microsporidia MB</italic> is a symbiont transmitted vertically and horizontally in the mosquito population, and these transmission routes are known to favor the persistence of the parasite in the mosquito population. Despite the dual transmission, data from field experiments reveal a low prevalence of <italic>MB</italic>-infected mosquitoes in nature. This study proposes a compartmental model to understand the prevalence of <italic>MB</italic>-infected mosquitoes. The dynamic of the model is obtained through the computation of the basic reproduction number and the analysis of the stability of the MB-free and coexistence equilibria. The model shows that, in spite of the high vertical transmission efficiency of <italic>Microsporidia MB</italic>, there can still be a low prevalence of <italic>MB</italic>-infected mosquitoes. Numerical analysis of the model shows that male-to-female horizontal transmission contributes more than female-to-male horizontal transmission to the spread of MB-infected mosquitoes. Moreover, the female-to-male horizontal transmission contributes to the spread of the symbiont only if there are multiple mating occurrences for male mosquitoes. Furthermore, when fixing the efficiencies of vertical transmission, the parameters having the greater influence on the ratio of MB-positive to wild mosquitoes are identified. In addition, by assuming a similar impact of the temperature on wild and <italic>MB</italic>-infected mosquitoes, our model shows the seasonal fluctuation of <italic>MB</italic>-infected mosquitoes. This study serves as a reference for further studies, on the release strategies of MB-infected mosquitoes, to avoid overestimating the MB-infection spread.</p></abstract>