An epidemiological and ecological study of human alveolar echinococcosis transmission in south Gansu, China

Human alveolar echinococcosis (AE) is usually a rare, highly pathogenic zoo notic disease, transmitted across the northern hemisphere between fox and r odent hosts. In China the first cases were described in 1965: however very few epidemiological studies have been undertaken since. Following identific ation in 1991 of a serious focus of human AE in south Gansu province, detai led village-based community and ecological studies were carried out between 1994 and 1997. Hepatic ultrasound mass screening with serological testing (five tests) identified 84/2482 new AE cases (3%). An overall prevalence of 4.1% (135/3331) was recorded for the area when previous cases were also in cluded. Based on a seropositive result only, without an ultrasound scan ind ication, no additional AE cases were identified. Of the evolutive AE cases, 96% were seropositive in at least one test, while up 15-20% of individuals who exhibited hepatic calcified lesions and 12-15% exhibiting hepatic nodu lar lesions were seropositive for specific Em2 or Em18 antibodies. Village (n = 31) human AE prevalence rates varied from 0 to 15.8%. Questionnaire an alysis indicated that total number of dogs owned over a period was a risk f actor (P < 0.006), but not a history of red fox hunting (P > 0.6). Rodent e cology studies revealed an association between density indices of voles (Mi crotus limnophilus) and village AE prevalence rates, on the one hand, and v illage landscape characterised by a ratio of scrub/grassland to total area above 50% (P < 0.005). Long-term transmission of Echinococcus multiloculari s and risk of zoonotic infection of south Gansu farmers may be related ulti mately to a process of deforestation driven by agriculture. This in turn pr obably results in creation of optimal peri-domestic habitats for rodents th at serve as intermediate host species (such as M. limnophilus) and subseque nt development of a peri-domestic cycle involving dogs. (C) 2000 Elsevier S cience B.V. All rights reserved.