Streptocercosis is caused by Mansonella streptocerca (formerly Dipetalonema streptocerca). This nematode is confined to Central and West Africa. The parasite is transmitted by Culicoides midges. It may be a zoonosis as morphologically identical parasites are found in chimpanzees. Adult worms live in the skin. Live worms’ cause no lesions but a local inflammatory reaction occurs when they die, with papules and possibly subsequent fibrosis. There are no eye lesions. Differentiation from onchocerciasis is necessary.
Many infected people are asymptomatic. The most frequent symptom is chronic pruritus. The skin is thickened and there are papules. Hypopigmented patches can occur which must be distinguished from leprosy, endemic treponematosis and onchocerciasis. Lymph nodes can be enlarged.
The microfilariae are found in the skin. Detection is as for onchocerciasis (skin snip, scarification with collection of dermal fluid). In the event of doubt or suspicion of leprosy, a biopsy is useful. DEC causes a Mazzotti reaction as in onchocerciasis.
DEC is micro- and macrofilaricidal for Mansonella streptocerca. Ivermectin is highly active against this parasite.
Table: Overview of characteristics of microfilariae
|
Species |
Location |
Sheath |
Period |
Length |
Tail nucleus |
|
Loa loa |
blood |
+ |
Day |
275 µm |
+ terminal |
|
W. bancrofti |
blood |
+ |
Night (periodic strain) |
260 µm |
– |
|
Brugia malayi |
blood |
+ |
Night (periodic strain) |
220 µm |
+ isolated |
|
Brugia timori |
blood |
+ |
Night |
290 µm |
+ isolated |
|
M. ozzardi |
blood |
– |
– |
200 µm |
– |
|
M. perstans |
blood |
– |
– |
<200 µm |
+ double row |
|
M. streptocerca |
skin |
– |
– |
210 µm |
+ and hook |
|
O. volvulus |
skin |
– |
– |
250 µm |
– |