ABSTRACT
<p><b>BACKGROUND</b>Human cystic echinococcosis (CE) is a parasitic zoonosis of major public health importance throughout the world. CE is endemic throughout central Asia including northwestern China. In China, CE has been reported in 21 provinces, autonomous regions and municipalities, covering approximately 87% of China's territories. It is most common in the pastoral and semi-pastoral western provinces and regions. This study aimed to reveal the natural history, curative effect and possible re-infection risk factors of human CE through long termed follow-up of treated and untreated CE cases in Hobukesar, Xingjiang, China.</p><p><b>METHODS</b>Follow-up studies on CE were performed twice in Hobukesar from August 2005 to October 2008, after an initial mass screening performed in 1995 and 1996. Ultrasound scan was the primary diagnostic method.</p><p><b>RESULTS</b>Among 24 patients with confirmed CE, 22 were treated (surgery in 19 and chemotherapy in three). Two recurrent cases and one re-infection case were subsequently found during follow-up. The CE type of one of the recurrent cases reverted from CE4 to CE3, as classified using World Health Organization (WHO) guidelines.</p><p><b>CONCLUSIONS</b>Ultrasound was required to differentiate primary, recurrent and re-infection cases during epidemiological investigation and follow-up of CE. Most patients did not change their habits, which may be one possible cause of reinfection. One recurrent case suggested that, despite initial suggestion from the WHO Informal Working Group on Echinococcosis, CE4-type cysts are not inactive.</p>