Daphnia parasites are known to affect different life-history traits of their host and by that to have an important influence on the host population. We investigated a fungal brood parasite and its implications on the Daphnia host. It infects egg and embryonic stages in the brood pouch of Daphnia females. In Lake Greifensee, Switzerland, it displays a biannual cycle with two infection peaks, one in spring and one in late autumn. Since it was not possible to establish the infection in the laboratory, we sampled uninfected and infected Daphnia from the lake and used them in our experiments. Our main question was, whether brood parasite infected females can get rid of the infected brood and produce a healthy following one. Further we wanted to know if there are some physical constraints to the mother after the infection. Indeed, females had released the infected brood during molting and after that they produced healthy eggs which did not differ from a control, neither in number nor developmental success. Moreover, female increase in body size was not affected by the parasite. Infected Daphnia, however, had an increased mortality rate. Additionally to the loss of one whole clutch, the most striking feature of this parasite is that it increases the susceptibility of infected Daphnia in respect to an unidentified bacterium parasite. This evidence of increased susceptibility was investigated with further experiments.