Circulating eosinophilia and immunoglobulin a antibodies to parasite antigens in parasitological and clinically defined onchocerciasis patients

Abstract

Background: The role of eosinophils in helminthic infections is either directed against the parasite in killing and or causing pathological  sequela in the host. Eosinophils are involved in determining the clinical outcome of helminthic infection including lymphatic filariasis and onchocerciasis. Eosinophilia is a marker for exposure to one or more helminths’ infections particularly for travelers visiting tropical sub- Saharan Africa.

Aim: This study was to examine the cause and effect of peripheral eosinophil levels and serum IgA antibodies on the  presence or absence of filarial (adult worm and microfilaria), skin dermatitis and ocular disease.

Methodology: The correlation between  eosinophilia in onchocerciasis patients (n=95) aged 15 years and above with defined skin microfilarial load, palpable nodules, and in those  manifesting papular onchodermatitis, chronic skin and optic nerve disease were assessed using differential white blood cell (WBC)  and total leucocyte count of peripheral blood. Serum IgA antibody reactivity with Onchocerca volvulus sodium dodecyl sulphate adult  worm extracted antigens were evaluated using direct sandwich enzyme linked immunosorbent assay.

Results: The skin microfilaria  negative (0 mf/snip) individuals (n=15) had lower percentage and absolute blood eosinophil counts than the skin snip positive ones  (n=52). Among the latter group, those with low skin microfilaria load, ≤4.5mf/snip (n=18), had higher eosinophilia than the group having  ≥5mf/snip (n-44). The mean and standard deviation (±SD) of eosinophil count was more in the group of patients with evidence of optic  nerve disease (n=12) than those with chronic skin disease such as leopard skin, hernia, oedema and lichenoid onchodermatitis (n=20).  The observed insignificant rate of in situ de-granulation and vacuolation of eosinophils on stained slides did not attract further detail  analysis. There was no correlation between serum IgA and percentage and absolute eosinophil counts with regression coefficient, R² =  0.0000 and R² = 0.009. Both serum IgA and blood eosinophil counts had strong association with decreased skin microfilaria load. Secondly, the higher IgA and eosinophil were associated with the development of chronic skin disease and optic nerve disease,  respectively.

Discussion: The association of eosinophilia with skin clinical disease outcome is less likely as there was significant difference  between those without overt signs (n=33) having higher percentage eosinophil count than those with papular  onchodermatitis. However, the observed increase blood eosinophilia has a causal relationship with the development of optic nerve  disease manifestation among the sample population.

Conclusion: This study has amply demonstrated the possible influence of  antibodies on the pathology of skin clinical manifestations compared to the likely role of eosinphils in optic nerve disease. These  observations are in consonant with reports of autoantibody involvement in experimental onchocercal dermatitis and cytopathology of  ocular clinical lesions.