Temporal variability of Loa loa microfilaremia

Abstract

Background The diurnal periodicity of Loa loa microfilaremia is well known but few studies have documented the short-term and long-term stability of microfilarial density. It seems stable over time at the community level, but significant variations have been observed at the individual level. Methods We assessed the temporal variability of L. loa microfilaremia at 5-days, 1-month and 16-months intervals and analyzed the influence of sex, age, level of microfilaremia, temperatures and time of sampling on this variability. Results At the community level, L. loa microfilaremia is very stable over time at 5-days, 1-month and 16-months intervals (Pearson correlation coefficients of 0.92, 0.91 and 0.78, respectively, all three with a P < 0.001). However, some individuals had significant variations of up to ± 50% of their initial microfilaremia at 5-days (33.0%), 1-month (36.5%) and 16-months (62.6%) interval, even in individuals with an initial microfilaremia density > 20,000 mf/mL (7.7, 23.1 and 41.4%, respectively for 5 days, 1 month and 16 months). We do not highlight any external factors that have a major impact on this variability. Conclusion Although at the community level, microfilaria density is very stable, we highlight some individuals with large variations both in the short- and long-term, which may have an important impact on onchocerciasis control campaigns and on longitudinal studies evaluating the impact of an intervention on L. loa microfilaremia.