Distinct loiasis infection states and associated clinical and hematological manifestations in patients from Gabon

Abstract

Background: Loiasis-a filarial disease endemic in Central and West Africa-is increasingly recognized as significant individual and public health concern. While the understanding of the disease characteristics remains limited, significant morbidity and excess mortality have been demonstrated. Here, we characterize clinical and hematological findings in a large cohort from Gabon.

Methods: Loiasis-related clinical manifestations and microfilaremia, hemoglobin and differential blood counts were recorded prospectively during a cross-sectional survey. For analysis, participants were categorized into distinct infection states by the diagnostic criteria of eye worm history and microfilaremia.

Results: Analysis of data from 1,232 individuals showed that occurrence of clinical and hematological findings differed significantly between the infection states. Eye worm positivity was associated with a wide range of clinical manifestations while microfilaremia by itself was not. Loa loa infection was associated with presence of eosinophilia and absolute eosinophil counts were associated with extent of microfilaremia (p-adj. = 0.012, ß-estimate:0.17[0.04-0.31]).

Conclusions: Loiasis is a complex disease, causing different disease manifestations in patients from endemic regions. The consequences for the affected individuals or populations as well as the pathophysiological consequences of correlating eosinophilia are largely unknown. High-quality research on loiasis should be fostered to improve patient care and understanding of the disease.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Frequencies of signs and symptoms within the three loiasis infection states and in uninfected individuals as bar plots and adjusted p-values of inter group comparisons, if significant.

All intergroup comparisons are adjusted to sex, age and Mansonella PCR. * p-adj. <0.05; **p-adj. <0.01; *** p-adj. <0.001; * LN = No sign of loiasis infection; MF = detectable microfilaremia but no history of eye worm; EW = positive history of eye worm but no detectable microfilaria; EWMF = positive history of eye worm as well as detectable microfilaremia.

Fig 2

Distribution of hematological findings including median and interquartile range of hemoglobin (A), total white blood cell count (B), absolute (C) and relative eosinophil counts (D) within the four infection states. Adjusted p-values of intergroup comparisons are provided if <0.05. All intergroup comparisons are adjusted to sex, age and positivity of Mansonella PCR. * p-adj. <0.05; **p-adj. <0.01; *** p-adj. <0.001; LN = No sign of loiasis infection; MF = detectable microfilaremia but no history of eye worm; EW = positive history of eye worm but no detectable microfilaria; EWMF = positive history of eye worm as well as detectable microfilaremia.

Fig 3. Graphic presentation of the hematological and clinical findings within the study population.

3A is a diagram depicting the distribution and overlap of the diagnostic findings of history of eye worm, microfilaremia and eosinophilia in the study population (Eosinophilia data missing for 133 (10.8%) participants, see supporting information Table D). 3B depicts the distribution of the three mutually exclusive infection states in the same diagram based on diagnostic criteria. These include microfilaremic (MF), positive history of eye worm (EW), and individuals positive for both (EWMF). 3C displays the clinical outcome of eye worm positive loiasis and 3D the hematological outcome of microfilaremic loiasis in this schematic display. Note that these outcomes are not mutually exclusive, but overlap in individuals who are positive for both diagnostic criteria.