Figure 1.
Experimental design for the stage-specific studies.
Donor mice were used to infect one batch of 25 or 40 experimental mice with either P. vinckei vinckei or P. vinckei petteri, respectively. Mice then were randomly separated into groups of 5 consisting of untreated, artesunate treated (AS) rings, trophozoites (trophs), and schizonts. Amodiaquine treated parasites were included as a positive drug control. Parasitemia were monitored for 30 days.
Figure 2.
P. v. vinckei morphology in mice before treatment and 24 hr following treatment with artesunate.
A. Two representative images are shown for each stage of development in vivo. Ring-stage (R), young trophozoite (Y-troph), mid-term trophozoite (M-troph), old trophozoite (O-troph), and schizont. (SCH). B. Treated ring-stage parasites (top row) have a condensed nucleus and pyknotic appearance. Older parasite stages treated with artesunate (bottom row) appear to have an absence of hemozoin and loss of membrane integrity.
Figure 3.
The stage-specific effects of a single dose of AS.
A. Plasmodium vinckei petteri-infected mice (n = 8 mice per group) were treated with one dose of AS (64 mg/kg). Comparison of peak parasitemias revealed that all treated groups had significantly lower peak parasitemias when compared to the untreated control (Dunnett's multiple comparison test, p<0.001). * = statistically significant difference. B. Assessment of average daily parasitemias showed that the ring stage had the highest average parasitemia when compared to treated trophozoites and schizonts. Both the ring and trophozoite groups had a secondary peak on days 27 and 14 PI, respectively. Overall, the treated trophozoites took the longest to clear and had the lowest average parasitemia. Data are means ± SD. C. Mice infected with the lethal strain P. v. vinckei (n = 5 mice per group) were treated with one dose of AS (64 mg/kg). The median day of survival for untreated mice, and mice treated when mostly rings, trophozoites, or schizonts were present was 7.0 and 9.0, respectively. No significant difference in survival was observed among the treated groups.
Figure 4.
Experimental design for the repeated dosing studies.
Donor mice were used to infect one batch of 50 experimental mice with P. vinckei vinckei. Mice then were randomly separated into groups of 10 containing 5 mice each and dosed on different days.
Figure 5.
The effects of repeated dosing with AS on P. v. vinckei-infected mice.
Mice were treated with a total dose of 256 mg/kg of AS and monitored for recrudescence (n = 5 mice per group). A. Mice treated for three or four consecutive days had the highest percent survival (70%) when compared to the untreated (Dunnett's multiple comparison test, p<0.01). B. In the variable group, mice treated on days 3 and 7 post-infection (PI) had the highest percent survival (80%) when compared to the untreated (Dunnett's multiple comparison test, p<0.05).
Table 1.
Artesunate dosing schedule for mice infected with P. v. vinckei.
Table 2.
Experimental survival rates using P. v. vinckei (Pvv), a lethal strain, compared to peak parasitemias from a previous study using P. v. petteri (Pvp), a non-lethal strain.
Table 3.
Artesunate dosing schedule for mice infected with P. v. petteri.
Table 4.
Survival and time to recrudescence following inoculation of artesunate-treated P. v. vinckei parasites.
Figure 6.
Rate of dormant parasite recrudescence in intact and asplenic mice.
Rate of recrudescence was defined as the time to reach >5.0% parasitemia following injection of normal untreated or dormant parasites (n = 5 mice per group). Data are shown as mean total parasitemia +SD versus time. A. In the intact group, rate of recrudescence from dormancy occurred in a dose-dependent manner, with the highest dilution recovering faster. B. In the asplenic group, rate of recrudescence occurred in a dose-dependent manner from 4×104 to 4×106, after which the separation is not as well-defined. DORM = dormant parasites.
Figure 7.
Intact and asplenic mouse survival following exposure to dormant P. v. vinckei parasites.
Mice were exposed to varying numbers of untreated and dormant (dorm) parasites (n = 5 mice per group). A. Only 20.0% of intact mice exposed to 40 normal untreated parasites, and 4×102 and 4×105 dormant parasites survived until day 30 post-infection (PI). All mice exposed to 40 dormant parasites survived unto day 30 PI. B. Asplenic mice exposed to 4×102 and 40 dormant parasites had a 20.0% and 40.0% survival rate, respectively.
Figure 8.
Primary stages present during dormant parasite recrudescence in intact mice.
The average parasitemia versus time in relation to the number of dormant parasites are shown in the figure (n = 5 mice per group). Rate of recrudescence from dormancy was defined as the average time to >5.0% parasitemia. In all treatment groups, with the exception of the untreated 4×106, rings are the predominant stage present as parasites begin to recover. A (untreated 4×106), B (untreated 4×101), C (dorm 4×106), D (dorm 4×105), E (dorm 4×104), F (dorm 4×103), G (dorm 4×102) andH (dorm 4×101). Ring (R), young trophozoite (YT), mid-term trophozoite (MT), old trophozoite (OT), and schizont (SCH).