Mansonellosis: current perspectives

Abstract

Mansonellosis is a filarial disease caused by three species of filarial (nematode) parasites (Mansonella perstans, Mansonella streptocerca, and Mansonella ozzardi) that use humans as their main definitive hosts. These parasites are transmitted from person to person by bloodsucking females from two families of flies (Diptera). Biting midges (Ceratopogonidae) transmit all three species of Mansonella, but blackflies (Simuliidae) are also known to play a role in the transmission of M. ozzardi in parts of Latin America. M. perstans and M. streptocerca are endemic in western, eastern, and central Africa, and M. perstans is also present in the neotropical region from equatorial Brazil to the Caribbean coast. M. ozzardi has a patchy distribution in Latin America and the Caribbean. Mansonellosis infections are thought to have little pathogenicity and to be almost always asymptomatic, but occasionally causing itching, joint pains, enlarged lymph glands, and vague abdominal symptoms. In Brazil, M. ozzardi infections are also associated with corneal lesions. Diagnosis is usually performed by detecting microfilariae in peripheral blood or skin without any periodicity. There is no standard treatment at present for mansonellosis. The combination therapy of diethylcarbamazine plus mebendazole for M. perstans microfilaremia is presently one of the most widely used, but the use of ivermectin has also been proven to be very effective against microfilariae. Recently, doxycycline has shown excellent efficacy and safety when used as an antimicrobial against endosymbiotic Wolbachia bacteria harbored by some strains of M. perstans and M. ozzardi. Diethylcarbamazine and ivermectin have been used effectively to treat M. streptocerca infection. There are at present no estimates of the disease burden caused by mansonellosis, and thus its importance to many global health professionals and policy makers is presently limited to how it can interfere with diagnostic tools used in modern filarial disease control and elimination programs aimed at other species of filariae.

Keywords: M. ozzardi; M. perstans; M. streptocerca; filariasis; mansonellosis; neglected disease.

Figure 1

Neighbor-joining phylogenetic tree. Notes: Tree compares the ITS1 partial sequences of human Mansonella spp. present in the GenBank (accession numbers are indicated in parentheses or with an internal code when not submitted to the GenBank). A sequence of L. loa (EU272176) was used as the out-group. Significant bootstrap values are indicated.

Figure 2

Distribution of human Mansonella based on published reports before and after the year 2000. Notes: 1, Before; 2, after. Abbreviations: Mp, Mansonella perstans; Ms, Mansonella streptocerca; Mo, Mansonella ozzardi.

Figure 3

Comparison of the three agents causing mansonellosis illustrating the morphological characteristic of each microfilariae. Notes: (A) M. perstans microfilariae seen in Giemsa-stained thick blood smear with blunt rounded tail and nuclei extending to the tip of the tail: M. perstans parasite from São Gabriel da Cachoeira (Amazonas state, Brazil) (A1); African M. perstans (A2). (B) M. streptocerca microfilariae from a skin-snip fixed and Giemsa-stained showing the characteristic hooked tail. (C) M. ozzardi microfilariae from São Gabriel da Cachoeira (Amazonas state, Brazil) stained with Giemsa (C1, C2).