Factors associated with the periodicity of Loa loa microfilaremia in the Republic of the Congo

Abstract

Background: Loa loa microfilariae circulate in the peripheral blood of human hosts following a diurnal periodicity, with maximal microfilaremia levels generally observed between 10:00 am and 3:00 pm. Few studies have assessed factors potentially associated with this periodicity. Methods: Microfilaremia data were collected repeatedly between 9:00 am and 8:00 pm from 13 individuals in the Republic of Congo. Using local polynomial regression (LOESS), we determined the best models representing the dynamics of microfilaremia over this time period. In a second step, using cosinor models we evaluated the influence of sex, age and body temperature on the periodicity of L. loa microfilaraemia in blood.Results: All subjects had their maximum microfilaremia reached between 10:00 am and 4:00 pm. Individual microfilaremia showed different patterns between individuals and some clearly showed multiple peaks within a day. LOESS provided good fit to the observed data. Without adjustment, the maximum microfilarial density was reached around 11:00 am. Adjustment revealed three distinct modes of microfilaremia, occurring around 10:00 am, 1:00 pm and 4:00 pm.Cosinor models also provided good fit to our data. After adjustment on body temperature, the L. loa microfilaremia fluctuation amplitude decreased significantly from 1684.8 to 310.6 mf/mL and the predicted peak was estimated at 12:02 pm. Conclusion: We characterized the periodicity of Loa loa microfilaremia mathematically with 2 different approaches: cosinor models and LOESS regression. Both models suggest that body temperature plays a role in the variation of microfilaremia within a day. Further studies are needed to identify individual cofactors affecting microfilaremia.