Sero-epidemiological surveillance of hypodermosis in yaks and cattle in north China by ELISA.

A large-scale serological surveillance was conducted for hypodermosis in the north of China. A total of 4175 sera samples of yaks and cattle were collected from five provinces in north China that included Xinjiang, Inner Mongolia, Heilongjiang, Jiling and Gansu provinces, between 2001 and 2002, and were examined for anti-hypoderma antibody by ELISA. The results indicate that the naturally infested positive rates of Hypoderma spp. in the above provinces were 51.77%, 27.02%, 13.00%, 6.03% and 44.41%, respectively. These results suggest a significant warble fly population in the north of China. Positive sera were collected from infested cattle in Pingliang county of the Gansu province monthly between August 2001 and July 2002. These sera were used to evaluate the seasonal kinetics of anti-hypoderma antibody. The kinetics demonstrated that anti-hypoderma antibody was elevated from October to December. Thus, serological surveillances associated with low infestation rates and chemical therapy would best be performed from October to December in the region.