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Onchocercal dermatitis: ultrastructural studies of microfilariae and host tissues, before and after treatment with
Abstract:
Specimens of skin from four Cameroon patients with severe onchocercal dermatitis, before and after treatment with diethylcarbamazine (DEC), were studied by light and electron microscopy. Microfilariae of Onchocerca volvulus have ultrastructural features resembling those of microfilariae of other genera. Between the surface layer of the cuticle and the trilaminate membrane, there is an electrolucent zone which is much wider in degenerating microfilariae than in intact microfilariae. Widening of the zone may result from DEC-induced release of component(s) of the cuticle, possibly collagen or mucopolysaccharide. Between the cuticle and dermal collagen there are granular deposits which might be immune complexes involving the collagenous component of cuticle. Others have shown that DEC does not kill microfilariae in vitro. Treatment with DEC presumably "unmasks" microfilariae in the skin so that they are recognized as foreign bodies and are destroyed by the host's defenses. Histiocytes and eosinophils are seen in close proximity to degenerating microfilariae. Enzymes from histiocytes and eosinophils might readily penetrate the cuticle altered by DEC treatment, and digest various components within the microfilariae. Alternatively, the widening of the electrolucent zone might result directly from the action of leucocytic or histiocytic enzymes, after the microfilaria has been killed by other mechanisms.
Insights
Diethylcarbamazine (DEC) treatment appears to alter Onchocerca volvulus microfilariae in the skin, making them vulnerable to host immune defenses. This leads to their destruction by immune cells like histiocytes and eosinophils.
Area of Science:
- Onchocerca volvulus research
- Dermatology
- Parasitology
Background:
- Onchocercal dermatitis is a severe skin condition caused by Onchocerca volvulus.
- Diethylcarbamazine (DEC) is a treatment used for onchocerciasis.
- The mechanism by which DEC affects microfilariae in the skin is not fully understood.
Purpose of the Study:
- To investigate the ultrastructural changes in Onchocerca volvulus microfilariae after DEC treatment in patients with severe onchocercal dermatitis.
- To elucidate the potential mechanisms of microfilarial destruction by host defenses.
Main Methods:
- Skin specimens from four Cameroon patients were studied using light and electron microscopy.
- Microfilariae were examined before and after DEC treatment.
Main Results:
- Ultrastructural analysis revealed a widening of the electrolucent zone between the microfilarial cuticle and trilaminate membrane in degenerating microfilariae.
- This widening may be due to DEC-induced release of cuticle components (e.g., collagen, mucopolysaccharide).
- Granular deposits, possibly immune complexes, were observed between the cuticle and dermal collagen.
Conclusions:
- DEC treatment likely "unmasks" microfilariae in the skin, enabling recognition and destruction by host immune cells (histiocytes, eosinophils).
- Altered microfilarial cuticle may allow easier penetration by histiocytic and eosinophilic enzymes.
- Widening of the electrolucent zone could also result from direct enzymatic action on DEC-killed microfilariae.