An Overview of the Management of Mansonellosis

Abstract

Mansonellosis is caused by three filarial parasite species from the genus Mansonella that commonly produce chronic human microfilaraemias: M. ozzardi, M. perstans and M. streptocerca. The disease is widespread in Africa, the Caribbean and South and Central America, and although it is typically asymptomatic it has been associated with mild pathologies including leg-chills, joint-pains, headaches, fevers, and corneal lesions. No robust mansonellosis disease burden estimates have yet been made and the impact the disease has on blood bank stocks and the monitoring of other filarial diseases is not thought to be of sufficient public health importance to justify dedicated disease management interventions. Mansonellosis´s Ceratopogonidae and Simuliidae vectors are not targeted by other control programmes and because of their small size and out-door biting habits are unlikely to be affected by interventions targeting other disease vectors like mosquitoes. The ivermectin and mebendazole-based mass drug administration (iMDA and mMDA) treatment regimens deployed by the WHO´s Elimination of Neglected Tropical Diseases (ESPEN) programme and its forerunners have, however, likely impacted significantly on the mansonellosis disease burden, principally by reducing the transmission of M. streptocerca in Africa. The increasingly popular plan of using iMDA to control malaria could also affect M. ozzardi parasite prevalence and transmission in Latin America in the future. However, a potentially far greater mansonellosis disease burden impact is likely to come from short-course curative anti-Wolbachia therapeutics, which are presently being developed for onchocerciasis and lymphatic filariasis treatment. Even if the WHO´s ESPEN programme does not choose to deploy these drugs in MDA interventions, they have the potential to dramatically increase the financial and logistical feasibility of effective mansonellosis management. There is, thus, now a fresh and urgent need to better characterise the disease burden and eco-epidemiology of mansonellosis so that effective management programmes can be designed, advocated for and implemented.

Keywords: Mansonella ozzardi; Mansonella perstans; Mansonella streptocerca; Mansonellosis; Wolbachia; doxycycline.

Figure 1

Integrated life cycle of the three Mansonella spp. An infected female blood-sucking arthropod genus Culicoides (A) for all the three Mansonella species, or Simulium (B) only for M. ozzardi] introduces third stage filarial larvae (L3) into the human host. The larvae develop into adult filariae, which commonly reside in the pleural cavity (1); the peritoneal cavity (2) or the subcutaneous dermal layer (3). The female worms produce microfilariae, which are found in peripheral blood (M. perstans and M. ozzardi) or found in the skin (M. ozzardi and M. streptocerca). An arthropod ingests the microfilariae during a blood meal. After ingestion, the microfilariae undergo two molts to become infective L3. The life cycle in which Culicoides vectors are involved can occur both in Latin American and African settings. Simuliid species are known to transmit M. ozzardi in Latin America.