RESUMEN
1101 children and young adults between 2 and 17 years age, residing in Bancroftian filariasis endemic area of the Jharia Coalfields in Bihar, were examined by Indirect Immunofluorescent Test (IIFT) against Dipetalonema Vitae. The results, along with those of two night blood surveys conducted in the same area, covering 2148 and 2246 persons respectively, are reported. In the prepubertal age groups there was no statistically significant variation in the percentage of children showing positive antibody titre in either sex, but a sudden fall of more than 50 per cent in the antibody level was observed in females at the onset of puberty. This did not occur in males. Analysis of the night blood results also indicated a remarkable fall in microfilaria rate and density in females at the onset of puberty and a low level was then maintained over the whole of the child bearing age. No such change was observable in males. Sex differences in the susceptibility of the host to helminthic infections is well-known and in animal experiments the effect of sex hormones in modifying such susceptibility has been established. In human filariasis the probable part played by the male and female sex hormones in bringing about abrupt changes in immunoresponse and infection rate at the onset of puberty is discussed.