Age-dependent prevalence of Loa loa amicrofilaremia and microfilaremia status as defined by two markers: microfilaria and specific IgG4

Loiasis infection is characterised by long term stability in infection status. The bases of such stability are not well known. As preliminary step toward verification of possible genetic involvement in this stability, a survey in a homogeneous population (n = 106) of a village from an endemic zone of Gabon was undertaken. The distribution of Loa loa microfilaremia according to age revealed a significant relationship between age and the presence of microfilariae in the blood (p = 0.0059). The proportion of microfilaremic individuals increased with age until 45 years old, and did not exceed 34% as its maximum. The other marker (specific IgG4) increased also significantly with age (p = 0.0038), but in contrast to microfilaremia, the prevalence of specific IgG4 in the group from 45 years onward reached 100%. These observations show the importance of age for the definition of the amicrofilaremic or microfilaremie individual status in an endemic area and are in agreement with the hypothesis suggesting the existence of genetic factors controlling the outcome of the parasitological status in L. loa infection.