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Abstract. To differentiate the skin-dwelling filariae Mansonella streptocerca and Onchocerca volvulus, a nested polymerase chain reaction (PCR) assay was developed from small amounts of parasite material present in skin biopsies. One nonspecific and one specific pair of primers were used to amplify the 5S rDNA spacer region of M. streptocerca. Biopsies with different microfilaria densities obtained from 104 Ugandans living in an area endemic for M. streptocerca were tested using both the nested PCR assay and standard parasitologic assessment of microfilariae. All 82 samples from microfilaria carriers were positive when tested using the nested PCR assay. In addition, M. streptocerca DNA could be detected in 16 samples thought to be microfilaria negative. Furthermore, six days following ivermectin treatment, M. streptocerca DNA was found in 12 of 14 microfilaria-negative biopsies. Control skin samples from patients infected with O. volvulus were all negative in the nested PCR assay. This assay improves the diagnosis of M. streptocerca and will facilitate further epidemiologic studies.When evaluating skin disease cases in large regions of Africa, the two skin-dwelling filarial species, Mansonella streptocerca and Onchocerca volvulus, must be considered as possible causative agents. Mansonella streptocerca infection is characterized by acute and more often chronic papular dermatitis mainly on the upper part of the body, which make it difficult to differentiate streptocerciasis and onchocerciasis clinically. 1, 2 In addition, after treatment with diethylcabarmazine or ivermectin, persons infected with M. streptocerca also show a typical Mazzotti reaction. 1, 3 Cross-reactions between O. volvulus and Mansonella species impede the differentiation of these parasites by serologic diagnosis using worm extracts. 4 Although isolated microfilariae (mf) of both species can be differentiated morphologically, species differentiation in histologic sections is difficult. Since the mf densities of M. streptocerca are often relatively low, methods other than the standard skin snip technique are required for accurate detection of this species. Collagenase digestion of the skin snips is an appropriate procedure, 2 but if a patient is also heavily infected with O. volvulus it may be difficult to detect one M. streptocerca mf among hundreds of O. volvulus mf. In these cases, a specific but more sensitive assay to detect M. streptocerca is clearly required.The polymerase chain reaction (PCR) is a sensitive technique to detect parasite DNA. Sensitive and specific PCR assays have been developed for the diagnosis of the human filarial parasites Wuchereria bancrofti, Brugia malayi, Loa loa, and O. volvulus. 5-10 All of these assays are based on different repetitive target sequences found only within a distinct filarial genus. In the present study, we have developed a PCR assay based on a target sequence present in all filarial and all other nematode species. 11 The 5S rDNA spacer region was amplified from DNA prepared from human skin biopsi...

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SummaryWe studied the short-term effects of a single dose of 150 g/kg body weight ivermectin on Mansonella streptocerca in an area endemic for streptocerciasis, but not for onchocerciasis, in western Uganda. Six and 12 days after treatment no microfilariae (mf) were found in the skin of 53 out of 96 mf carriers living in 3 villages, and the geometric means of the mf densities of remaining mf carriers were only 33-40% of pretreatment levels. This reduction of mf density was highly significant (P<0.0001). Immunohistological examination of skin biopsies showed degenerated and disintegrating mf surrounded by activated eosinophils (positive for activated cationic protein), macrophages, and neutrophils (positive for myeloperoxidase and defensin) on day 6 after treatment. Remarkable was the invasion of young, L1 protein-positive macrophages and the release of neutrophil defensin as signs of acute inflammation. We conclude that ivermectin has a strong microfilaricidal activity against M. streptocerca. Common adverse effects were increased pruritus and acute papular dermatitis in 45% of 86 mf carriers on day 6 after treatment. No serious adverse side-effects were noticed in about 700 treated persons.