Assessment of helminth egg carriage by house flies following experimental exposure to Ascaris suum and Taenia saginata eggs

House flies are suspected mechanical transmitters of faecal-borne helminth diseases. To better understand their role in disease transmission, controlled experimental studies are required. This study investigates the short-term carriage of helminth eggs on the exoskeleton and inside the digestive tract of house flies ( Musca domestica L.) following experimental exposure to faeces containing eggs of Ascaris suum and Taenia saginata . Forty-eight house flies, allocated to eight cages, were exposed to non-human primate faeces spiked with 10,000 A. suum and 5000 T . saginata eggs per gram of faeces under controlled environmental conditions (30 °C, 60% relative humidity). After three hours, eggs were recovered from the flies' exoskeleton and digestive tract and microscopically counted using previously validated protocols. Additionally, eggs were recovered from the interior cage surfaces and fly contact duration with the faeces was recorded at cage level. Of the 48 flies examined, 75.0% (36/48) carried at least one helminth egg, with 227 eggs recovered in total. Egg presence and median egg counts were significantly higher in the digestive tract (33/48, 222 eggs) than on the exoskeleton (4/48, 5 eggs). Overall, T. saginata eggs were detected more frequently and in higher numbers (33/48, 181 eggs) than A. suum eggs (20/48, 46 eggs). Females showed significantly increased A. suum egg presence and median egg counts in the digestive tract (13/21, 35 eggs) compared to males (5/27, 9 eggs), whereas T. saginata egg presence and median egg counts were comparable between sexes (females: 14/21, 103 eggs; males: 17/27, 75 eggs). At the cage level, fly contact durations ranged from 29 to 207 min. Across all cages, a total of 65 eggs were recovered from the cage surfaces, including 17 A. suum and 48 T . saginata eggs. This study confirms the potential for house flies to acquire helminth eggs under favourable conditions, primarily through ingestion. Clarifying their actual contribution to disease transmission will require future research on the duration of egg carriage and the subsequent deposition of ingested eggs onto relevant surfaces, as well as field studies assessing the real-world significance of mechanical transmission.