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Plasmodium vivax
Image by Mae Melvin
New research indicates that most childhood malaria infections in Papua New Guinea (PNG) are the result of relapsed, not new, infections.
The data suggest that, among children ages 5 to 10 living in a malaria-hyperendemic region of PNG, relapses cause about 4 of every 5 Plasmodium vivax infections and 3 of every 5 Plasmodium ovale infections.
Investigators therefore concluded that relapses are important for sustaining malaria transmission in PNG.
The team reported their findings in PLOS Medicine.
“Our research has shown that one of the biggest problems in realizing malaria eradication is relapsing P vivax infections, which are critical for sustained transmission in the region,” said study author Leanne Robinson, PhD, of the Walter and Eliza Hall Institute of Medical Research in Parkville, Victoria, Australia.
“P vivax parasites are able to hide in the liver for long periods of time before ‘reawakening’ to cause disease and continue the transmission cycle. Mass drug administration that includes a drug that kills parasites in the liver is likely to be a highly effective strategy for eliminating malaria in PNG.”
To investigate this possibility, Dr Robinson and her colleagues analyzed 524 children, ages 5 to 10, living in a region of PNG where Plasmodium falciparum and P vivax are hyperendemic.
Roughly half the children (n=261) received an antimalarial treatment regimen that targets both blood-stage and liver-stage parasites (3 days of chloroquine, 3 days of artemether-lumefantrine, and 20 days of primaquine).
The other half (n=263) received antimalarial treatment targeting only blood-stage parasites (3 days of chloroquine, 3 days of artemether-lumefantrine, and 20 days of placebo).
The subjects were followed for 8 months. Compared to children in the placebo arm, those in the primaquine arm had a reduced risk of having at least 1 P vivax or P ovale infection during the follow-up period. The hazard ratio was 0.18 for P vivax (P<0.001) and 0.31 for P ovale (P=0.011).
“Children treated with drugs that targeted the liver and blood stages of infection had 80% fewer malaria infections than those treated with drugs that only targeted the blood stage of infection,” Dr Robinson said.
Children in the primaquine arm also had a reduced risk of having at least 1 clinical P vivax episode. The hazard ratio was 0.25 (P=0.002).
In addition, primaquine reduced the molecular force of P vivax blood-stage infection in the first 3 months of follow-up. The incidence rate ratio was 0.21 (P<0.001).
And children who received primaquine were less likely to carry P vivax gametocytes than children who received placebo, with an incidence rate ratio of 0.27 (P<0.001).
To build upon these findings, the investigators fed the trial data into a mathematical transmission model.
The model predicted that a mass drug administration program using blood-stage treatment alone would have only a transient effect on P vivax transmission levels. But a mass drug administration program that includes blood- and liver-stage treatment would be an effective strategy for P vivax elimination.
“We need a better way of identifying children who are chronically infected with malaria so that they can be treated,” said study author Ivo Mueller, PhD, of the Walter and Eliza Hall Institute.
“It is the only way to stop the malaria transmission cycle in PNG and is likely to be the case for eliminating malaria in other parts of the Asia-Pacific and Americas.”
Dr Mueller and an international team of collaborators are currently developing a test that identifies people with dormant malaria parasites in their liver. 
Plasmodium vivax
Image by Mae Melvin
New research indicates that most childhood malaria infections in Papua New Guinea (PNG) are the result of relapsed, not new, infections.
The data suggest that, among children ages 5 to 10 living in a malaria-hyperendemic region of PNG, relapses cause about 4 of every 5 Plasmodium vivax infections and 3 of every 5 Plasmodium ovale infections.
Investigators therefore concluded that relapses are important for sustaining malaria transmission in PNG.
The team reported their findings in PLOS Medicine.
“Our research has shown that one of the biggest problems in realizing malaria eradication is relapsing P vivax infections, which are critical for sustained transmission in the region,” said study author Leanne Robinson, PhD, of the Walter and Eliza Hall Institute of Medical Research in Parkville, Victoria, Australia.
“P vivax parasites are able to hide in the liver for long periods of time before ‘reawakening’ to cause disease and continue the transmission cycle. Mass drug administration that includes a drug that kills parasites in the liver is likely to be a highly effective strategy for eliminating malaria in PNG.”
To investigate this possibility, Dr Robinson and her colleagues analyzed 524 children, ages 5 to 10, living in a region of PNG where Plasmodium falciparum and P vivax are hyperendemic.
Roughly half the children (n=261) received an antimalarial treatment regimen that targets both blood-stage and liver-stage parasites (3 days of chloroquine, 3 days of artemether-lumefantrine, and 20 days of primaquine).
The other half (n=263) received antimalarial treatment targeting only blood-stage parasites (3 days of chloroquine, 3 days of artemether-lumefantrine, and 20 days of placebo).
The subjects were followed for 8 months. Compared to children in the placebo arm, those in the primaquine arm had a reduced risk of having at least 1 P vivax or P ovale infection during the follow-up period. The hazard ratio was 0.18 for P vivax (P<0.001) and 0.31 for P ovale (P=0.011).
“Children treated with drugs that targeted the liver and blood stages of infection had 80% fewer malaria infections than those treated with drugs that only targeted the blood stage of infection,” Dr Robinson said.
Children in the primaquine arm also had a reduced risk of having at least 1 clinical P vivax episode. The hazard ratio was 0.25 (P=0.002).
In addition, primaquine reduced the molecular force of P vivax blood-stage infection in the first 3 months of follow-up. The incidence rate ratio was 0.21 (P<0.001).
And children who received primaquine were less likely to carry P vivax gametocytes than children who received placebo, with an incidence rate ratio of 0.27 (P<0.001).
To build upon these findings, the investigators fed the trial data into a mathematical transmission model.
The model predicted that a mass drug administration program using blood-stage treatment alone would have only a transient effect on P vivax transmission levels. But a mass drug administration program that includes blood- and liver-stage treatment would be an effective strategy for P vivax elimination.
“We need a better way of identifying children who are chronically infected with malaria so that they can be treated,” said study author Ivo Mueller, PhD, of the Walter and Eliza Hall Institute.
“It is the only way to stop the malaria transmission cycle in PNG and is likely to be the case for eliminating malaria in other parts of the Asia-Pacific and Americas.”
Dr Mueller and an international team of collaborators are currently developing a test that identifies people with dormant malaria parasites in their liver.
Plasmodium vivax
Image by Mae Melvin
New research indicates that most childhood malaria infections in Papua New Guinea (PNG) are the result of relapsed, not new, infections.
The data suggest that, among children ages 5 to 10 living in a malaria-hyperendemic region of PNG, relapses cause about 4 of every 5 Plasmodium vivax infections and 3 of every 5 Plasmodium ovale infections.
Investigators therefore concluded that relapses are important for sustaining malaria transmission in PNG.
The team reported their findings in PLOS Medicine.
“Our research has shown that one of the biggest problems in realizing malaria eradication is relapsing P vivax infections, which are critical for sustained transmission in the region,” said study author Leanne Robinson, PhD, of the Walter and Eliza Hall Institute of Medical Research in Parkville, Victoria, Australia.
“P vivax parasites are able to hide in the liver for long periods of time before ‘reawakening’ to cause disease and continue the transmission cycle. Mass drug administration that includes a drug that kills parasites in the liver is likely to be a highly effective strategy for eliminating malaria in PNG.”
To investigate this possibility, Dr Robinson and her colleagues analyzed 524 children, ages 5 to 10, living in a region of PNG where Plasmodium falciparum and P vivax are hyperendemic.
Roughly half the children (n=261) received an antimalarial treatment regimen that targets both blood-stage and liver-stage parasites (3 days of chloroquine, 3 days of artemether-lumefantrine, and 20 days of primaquine).
The other half (n=263) received antimalarial treatment targeting only blood-stage parasites (3 days of chloroquine, 3 days of artemether-lumefantrine, and 20 days of placebo).
The subjects were followed for 8 months. Compared to children in the placebo arm, those in the primaquine arm had a reduced risk of having at least 1 P vivax or P ovale infection during the follow-up period. The hazard ratio was 0.18 for P vivax (P<0.001) and 0.31 for P ovale (P=0.011).
“Children treated with drugs that targeted the liver and blood stages of infection had 80% fewer malaria infections than those treated with drugs that only targeted the blood stage of infection,” Dr Robinson said.
Children in the primaquine arm also had a reduced risk of having at least 1 clinical P vivax episode. The hazard ratio was 0.25 (P=0.002).
In addition, primaquine reduced the molecular force of P vivax blood-stage infection in the first 3 months of follow-up. The incidence rate ratio was 0.21 (P<0.001).
And children who received primaquine were less likely to carry P vivax gametocytes than children who received placebo, with an incidence rate ratio of 0.27 (P<0.001).
To build upon these findings, the investigators fed the trial data into a mathematical transmission model.
The model predicted that a mass drug administration program using blood-stage treatment alone would have only a transient effect on P vivax transmission levels. But a mass drug administration program that includes blood- and liver-stage treatment would be an effective strategy for P vivax elimination.
“We need a better way of identifying children who are chronically infected with malaria so that they can be treated,” said study author Ivo Mueller, PhD, of the Walter and Eliza Hall Institute.
“It is the only way to stop the malaria transmission cycle in PNG and is likely to be the case for eliminating malaria in other parts of the Asia-Pacific and Americas.”
Dr Mueller and an international team of collaborators are currently developing a test that identifies people with dormant malaria parasites in their liver.