Reinfection dynamics of owned dogs with Echinococcus granulosus sensu lato in endemic rural areas of central Iran: Implications for cystic echinococcosis control

BACKGROUND: Cystic echinococcosis (CE), caused by the tapeworm Echinococcus granulosus sensu lato (E. granulosus s. l.), is highly endemic worldwide including in Iran, where dogs serving as definitive hosts play a critical role in transmission dynamics of the disease. Regular deworming of dogs is an essential part of any successful CE control program. However, dogs can become easily reinfected after praziquantel (PZQ) administration, and the rate of reinfection of dogs in an endemic area is considered an indicator of the intensity of CE transmission. This study aimed to evaluate reinfection rate in the owned dogs after PZQ treatment in Semnan province, in North of Iran. METHODS: A cohort of 381 guard and sheepdogs was monitored for 15 months post-treatment with PZQ. Reinfection was assessed at 3, 6, 9, 12, and 15 months by fecal sampling. Samples were microscopically examined for taeniid eggs after formalin-ether sedimentation, and were confirmed by PCR using E. granulosus s. l.-specific primers. Kaplan-Meier survival analysis was used to calculate the cumulative survival rate over a 15-month period. A Cox proportional hazards regression model was employed to identify risk factors associated with the time to reinfection with E. granulosus s.l. RESULTS: Fecal samples from 151 sheepdogs and 230 guard dogs from 290 farms, were examined. At baseline, microscopic and copro-PCR analyses revealed that 12.6% positive for taeniid eggs, of which 31 samples (8.1%) were positive for E. granulosus s. l. The reinfection rate was estimated as 9.6%, 10.7%, 15.6%, 22.5%, and 33.2% at 3, 6, 9, 12, and 15 months after initial treatment with PZQ, respectively. Sheepdogs showed significantly higher reinfection risks (29.8%) compared to the guard dogs (16.7%). Dogs whose owners practiced home slaughter were 2.02 times more likely to become reinfected. Only 17.3% (66/381) of the dogs were reported to be regularly dewormed by the owners. CONCLUSION: This study demonstrates that re-infection of dogs with E. granulosus s.l. is common in CE-endemic regions of Iran. The high rate of re-infection has significant implications for CE control, particularly in determining the most effective frequency for administering PZQ to prevent sustained transmission.