Seasonality and circadian variation of microfilaremia in dogs experimentally infected with Dirofilaria immitis.

•The changes in microfilaremia were observed for up to 3 years in 16 dogs experimentally infected with Dirofilaria immitis.•Seasonality was found in all dogs with microfilaremia-peaks in summer and 5–49-times lower counts in winter.•The circadian cycle of D. immitis microfilariae in the peripheral blood varied considerably between dogs and season.