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

Abstract

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 microfilaremic 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.

Analysis of diagnostic test outcomes in a large loiasis cohort from an endemic region: Serological tests are often false negative in hyper-microfilaremic infections

“…Overall, 76.9% in the under 15-year-old age group were positive and serological negativity was rare. Both findings are in line with previous reports [20][21][22]. Interestingly, comparison of different loiasis sub-groups showed lower median AU in the microfilaremic population than in patients with occult loiasis.…”

“…microfilaremic or occult loiasis, has repeatedly been described [ 19 , 20 ]. Further, it was found that Loa-specific IgG4 positivity can reach up to 100% in individuals living in high transmission areas [ 21 ]. Here, only total IgG was analyzed rather than specific subclasses, but still differences between loiasis subgroups were found.…”

“…Furthermore, the level of AU was found to inversely correlate with the density of microfilaremia. Comparison with and interpretation of available serological results in literature is difficult, due to the use of different antigens, assay protocols and definitions of loiasis [18][19][20][21]. However, an association between IgG subclass levels and loiasis infection types, i.e.…”

“…Importantly, the use of serological assays is limited in endemic regions, as they do not allow differentiation between active and past infections and are limited by a high level of cross-reactivity with other helminth infections. Furthermore, there are no biomarkers identified to date for the reliable detection of amicrofilaremic loiasis [18][19][20][21][22]. Recently, a rapid diagnostic test for antibodies against the recombinant L. loa SXP-1 antigen (Ll-SXP-1-RDT) has been developed and has been proposed as an epidemiological screening tool for loiasis [23].…”

The Human Filaria Loa loa: Update on Diagnostics and Immune Response

“…2014;13(4):593-597. 97 Third, serum from amicrofilaremic individuals can kill microfilariae via a mechanism involving antibodies and eosinophils cells. 56 Fourth, several molecules seem to be the preferential target of amicrofilaremic antibodies but not antibodies from microfilaremic individuals.…”