Diphtheria is an acute infectious disease affecting the upper respiratory tract and occasionally the skin and is caused by the action of diphtheria toxin produced by Corynebacterium diphtheriae, Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. Corynebacterium infections are usually difficult to control due to their epidemic patterns, the emergence of new strains, novel reservoirs and their dissemination to susceptible human and animal populations.1 Although C. diphtheriae is largely controlled through mass immunization programmes, diphtheria escalated to epidemic proportions within the Russian Federation and the former Soviet Republics in the 1990s, highlighting the potential for this disease to cause morbidity and mortality when immunization programmes are disrupted.2 A recent review of global diphtheria epidemiology, which included an analysis of cases and information about age, showed age distribu­tion shifts and found that the majority of cases occur in adoles­cents and adults.3 Shifts in age distribution, from children to adolescents and adults, were observed from countries in the Western Pacific Region such as the Lao People’s Democratic Republic,4 the Philippines3 and Viet Nam.5

Toxoplasma gondii is an important zoonotic parasite causing significant health problems to humans and animals. In recent years, a number of investigations about the seroprevalence of T. gondii in China have been reported, but little is known on the prevalence of toxoplasmosis in sheep in northern China. In the present study, a total of 288 sheep serum samples were collected from Inner Mongolia, Heilongjiang, Jilin and Hebei provinces of northern China for T. gondii antibody survey using a latex agglutination test (LAT). Of these, 87 (30.2%) serum samples were positive for antibodies to T. gondii, and the antibody titres ranged from 1:64 to 1:1,024. Seroprevalence of T. gondii infection in sheep was 17.1% in Inner Mongolia, 33.8% in Heilongjiang, 24.6% in Jilin and 46.3% in Hebei. Age and rearing system significantly affected seropositivity. The present survey indicates antibodies to T. gondii are widely prevalent in sheep in northern China, which may cause public health problems in these provinces.