Haemagglutination tests in the study of Ascaris epidemiology

Haemagglutination tests using adult Ascaris suum antigen were performed on sera from 810 people from three areas in Papua New Guinea and East Timor. In the area with the highest childhood Ascaris infection rates and egg-counts (Kaul), titres were highest and remained high throughout life. There was a significant negative correlation between titre and eosinophil count, and it is suggested that high titres in adult life result from continuous usually unsuccessful reinfection, and that the declining egg-counts and infection rates with increasing age may be the result of an immune mechanism, and not decreased exposure. In the two other populations the less intense Ascaris infection was reflected in the lower titres, with no correlation between titres, infection or eosinophilia. Although the haemagglutination test as used here is unsuitable as a diagnostic aid, it is valuable in studying the epidemiology of Ascaris infections.