Laboratory culture and life cycle of Thelazia callipaeda in intermediate and definitive hosts

Abstract Background: Human thelaziasis caused by Thelazia callipaeda (Spirurida, Thelaziidae) is being increasingly reported worldwide. Notably, it shows an epidemic trend in Guizhou Province, Southwest China. Whether Phortica okadai distributed in Southwest China can act as a vector of T. callipaeda and human-derived T. callipaeda animal infections have not been widely reported, there is also limited literature on animal models with T. callipaeda infection.Methods: T. callipaeda was isolated from cases of human infection and identified by morphological and molecular analyses. P. okadai was cultured in a laboratory and experimentally infected with first-stage larvae (L1) collected from adult worms. Dead P. okadai were subjected to PCR assay and dissected every two days to detect T. callipaeda. Live flies were then used to infect a rabbit using a special device. The infection procedures were performed once a day (20 min) for two weeks. The infected rabbit was examined every two days for worms in the eyes. Results: The nematode causing parasitic infection in the patient's eyes was identified as T. callipaeda. L1 collected from adult T. callipaeda successfully parasitized P. okadai captured in Zunyi, a city in Southwest China, and developed into L3. Experimentally infected P. okadai, as a vector of T. callipaeda, could then be used to transmit L3 to rabbits. A rabbit was successfully infected with T. callipaeda using P. okadai as the intermediate host. Conclusions: The present study demonstrates a human-derived T. callipaeda infection in rabbits, through P. okadai, under laboratory conditions for the first time. These results indicate that there is a transmission cycle of T. callipaeda and suggest a likely epidemic risk due to an increasing trend of this zoonotic nematode in southwest China.