Results
Reduction of microfilaria densities
Preliminary observations in Kasiri village had shown
a marked reduction of mf loads in the skin of 29
M. streptocerca mf carriers 6 days after ivermectin.
Subsequently, 3 other villages were selected for
re-examination: Bubomboli with a crude prevalence
of 89% in adult persons on day 6 and Ntandi (51%)
and Bundibulangya (63%) on day 12 after a single
dose of 150 ìg/kg ivermectin. In all villages the mf
density of mf carriers before treatment was relatively
low, only 4% presented more than 10 mf/mg skin
(Figure 1). In Bubomboli the geometric mean mf
density was 3.2 mf/mg on the shoulder of 28 mf carriers.
Six days after treatment no mf were detected in
the skin snips of 14 persons (Table 1), and in the
other 14 people the geometric mean decreased from
3.3 to 1.1 mf/mg. Arithmetic means of the 28 counts
were significantly reduced after treatment (Table 1).
The geometric means of mf density of 40 mf
carriers in Ntandi and of 28 mf carriers in
Bundibulangya were both 0.7 mf/mg before therapy.
Twelve days after treatment 39 of these 68 mf
carriers no longer had mf in their skin biopsies, and
in the other people the geometric means decreased
from 1.0 and 0.9 mf/mg to 0.4 and 0.3 mf/mg,
respectively. The arithmetic means decreased
significantly in both villages (Table 1). The shift in
frequency of mf densities found before and 12 days
after treatment demonstrates clearly the micro-
filaricidal effect of ivermectin (Figure 1).
Histology of microfilariae in the skin
Live microfilariae.
We saw only intact, viable mf in skin biopsies from
untreated persons (Figure 2A). These mf were not
surrounded by inflammatory host cells. Infiltrates
were mainly around the blood vessels (Figure 2A).
On day 2 after ivermectin administration, 0–5 intact,
viable mf were found in each of 7 biopsies selected
for their pretreatment mf loads of 1.9–4.7 mf/mg.
Intact, viable mf without adjacent inflammatory
cells were also visible in 14 of the 32 skin biopsies
collected on day 6 after treatment (Figure 2B).
Figure 1 Frequency of the microfilaria (mf) densities
observed in 68 mf carriers in Ntandi and Bundibulangya ,
before and ., 12 days after treatment with a single dose of
150 ìg/kg ivermectin. Relatively low pretreatment levels
were common in areas also w