Skip to main content
NCBI home page
Parasite Epidemiology and Control logoLink to Parasite Epidemiology and Control
. 2026 Feb 18;33:e00484. doi: 10.1016/j.parepi.2026.e00484

Efficacy of primaquine-chloroquine combination on Plasmodium vivax transmission and parasite clearance in Ethiopia: a randomized controlled trial

Mesay Melaku a,b, Biniam Wondale a, Girum Tamiru a, Ribka Getu a, Tinsae Kumsa a,c, Yilikal Tesfaye d, Bernt Lindtjørn a, Fekadu Massebo a,⁎
PMCID: PMC12936756  PMID: 41768389

Abstract

Primaquine (PQ) targets the hypnozoite stage of Plasmodium vivax and prevents transmission by targeting mature gametocytes. However, limited information exists on how quickly adding PQ reduces parasite transmission and clears parasites. We aimed to assess whether adding PQ can reduce P. vivax transmission and improve parasite clearance compared to using CQ alone. We conducted an open-label, randomized controlled trial. Patients aged 15 or older diagnosed with P. vivax mono-infection by microscopy were recruited from a health facility. One group received PQ at a dosage of 0.25 mg/kg daily for 14 days, in addition to CQ, in accordance with national treatment guidelines. A membrane feeding assay was performed using the colony Anopheles arabiensis before and after treatment. Mosquito midgut dissections were conducted on day 8 to observe oocyst development and on day 12 to detect circumsporozoite protein (CSP). We followed the patients for 28 days. We used a zero-inflated Poisson regression model to analyze how predictor variables influenced oocyst count and binary logistic regression with generalized estimating equations to predict the proportion of sporozoite-positive mosquitoes. Fifty-six patients completed the three-day mosquito feeding experiments, and forty-nine completed the 28-day follow-up. Before treatment, 57% (16/28) of patients in the CQ group and 82% (23/28) in the CQ-PQ group were infectious to mosquitoes (P = 0.08). After one day of treatment, the percentage of reduction was significantly higher in the CQ-PQ group than in the CQ alone group (P < 0.0001). When considering the oocyst number, the decline was significantly more pronounced in the CQ-PQ group (P < 0.001). The rate of CSP reduction was higher in the CQ-PQ group (P = 0.002). One day after treatment, the number of patients with gametocytes was lower in the CQ-PQ group compared to the CQ-alone group (P = 0.02). There was no significant difference in the asexual parasite clearance rate between the two groups three days post-treatment (P = 0.42). The results indicate that adding PQ reduced parasite transmission to mosquitoes; however, some patients remained infectious up to 24 h post-treatment.

This trial was registered on the Pan African Clinical Trial Registry: PACTR202408837266041.

Keywords: Gametocyte clearance, Infectious patients, Plasmodium vivax, Mosquito infection, Ethiopia

Highlights

  • •

    After 1 day, the CQ-PQ group had fewer patients infectious to mosquitoes than the CQ-alone group.

  • •

    Oocyst count declined more sharply in the CQ-PQ group than in the CQ alone group.

  • •

    One day after treatment, the CQ-PQ group had fewer gametocyte-positive patients than the CQ-alone group.

  • •

    Asexual parasite clearance rate was comparable in both the CQ-PQ and CQ alone groups.

  • •

    Adding PQ reduced transmission; however, some patients remained infectious to mosquitoes for up to 24 h.

1. Introduction

Plasmodium vivax (P. vivax) is one of the most prevalent human malaria parasites, affecting approximately 2.5 billion people worldwide (Howes et al., 2016). It is most commonly found in the Horn of Africa, Southeast Asian, and Western Pacific regions (Battle et al., 2019).

Although P. vivax likely originated in Africa (Sharp et al., 2024), its significant burden remains largely confined to the Horn of Africa countries, namely Ethiopia, Djibouti, Eritrea, Somalia, South Sudan, and the island of Madagascar (Howes et al., 2015). The distribution of P. vivax may be linked to Duffy-positive individuals as it requires the Duffy receptor to invade reticulocytes and cause disease (von Seidlein and White, 2021). The expression of the Duffy antigen is infrequently observed among most individuals in Africa, leading to their presumed resistance against P. vivax infection. However, some findings indicated the emergence of P. vivax infection in Duffy-negative individuals in Africa (Gunalan et al., 2018). In Ethiopia, P. vivax is the second most common type of malaria parasite and is responsible for 30–40% of all malaria cases annually. The parasite's prevalence varies by region, and it causes occasional malaria epidemics in the highlands (Ketema et al., 2021).

Plasmodium vivax can develop in mosquitoes at lower temperatures. It also has a dormant liver stage, known as hypnozoites, which can be activated after weeks, months, or even years of the initial mosquito-transmitted infection (White, 2011). Additionally, the early production of gametocytes enhances its transmission to mosquitoes (Bantuchai et al., 2022). Mosquitoes become infected when they consume male and female gametocytes during blood feeding. The development of Plasmodium oocysts in the midgut wall of mosquitoes is a reliable indicator of successful transmission from humans to mosquitoes. The oocysts then enlarge and release sporozoites, which make the mosquitoes infectious (Bradley et al., 2018).

Chloroquine (CQ) has been the primary treatment for malaria caused by P. vivax (WHO, 2022), effectively eliminating the blood-stage parasites (Pukrittayakamee et al., 2014). However, P. vivax can form dormant liver stages known as hypnozoites, which can cause relapses without new mosquito bites (Chu and White, 2016). To address these dormant forms, the World Health Organization (WHO) recommends primaquine (PQ), which also helps reduce malaria transmission by killing mature gametocytes (Fernando et al., 2011; Kiszewski, 2011). The use of PQ, however, is limited by the risk of hemolysis in individuals with G6PD deficiency (de Pina-Costa et al., 2021). In Ethiopia, where G6PD deficiency is uncommon (Assefa et al., 2018), PQ has been administered without prior testing since 2018 (FMoH, 2018).

In Ethiopia, the combination of PQ and CQ has been evaluated in patients with P. vivax mono-infection to assess its clinical and parasitological effects (Mekonnen et al., 2023). However, the impact of antimalarials on the transmission of the parasite to mosquitoes remains understudied. This aspect is crucial, as it reflects a drug's true potential in breaking the transmission cycle. Few studies have explored the effects of PQ and CQ on early transmission to mosquitoes (Andrade et al., 2023; Klein et al., 1991). Drugs that quickly eliminate both asexual parasites and gametocytes are essential for halting transmission. Mosquito feeding tests may provide more accurate evidence of a drug's gametocytocidal activity than microscopy, which can sometimes miss transmissible infections.

Regular monitoring of antimalarial drug efficacy is crucial for making timely and informed treatment decisions (White, 2017). In addition, a deeper understanding of how rapidly the addition of PQ reduces malaria transmission can inform more effective use of the drug to lower both transmission rates and the overall malaria burden. This study aimed to assess whether adding a 14-day course of PQ to CQ reduces the transmission of P. vivax parasites to mosquitoes in symptomatic patients, compared to treatment with CQ alone. We also evaluated whether the addition of PQ accelerates the clearance of both asexual and sexual parasites in symptomatic individuals receiving CQ.

2. Materials and methods

2.1. Study patients involvement

The study included individuals who visited Woze Health Centre between February and June 2023 and were diagnosed with P. vivax mono-infection via light microscopy. Only patients who consented to participate in the study were considered. The final analysis was conducted solely on cases that were confirmed through polymerase chain reaction (PCR) testing.

2.2. Trial design

This was a randomized trial with two parallel groups in a 1:1 ratio: one received the PQ-CQ combination, and the other received CQ alone. Mosquito feeding experiments were conducted prior to the initial drug dose on day 0, and subsequently on days 1 and 3 following treatment. Microscopic blood samples and dried blood spots (DBS) were collected up to day 28 to measure the density and clearance of sexual parasites and gametocytes. Patients who missed only one follow-up appointment were allowed to continue in the study if they returned for the subsequent scheduled follow-up.

Patients who tested positive for P. vivax were asked to give 3 ml of venous blood on day 0, day 1, and day 3 for feeding experiments (Fig. 1). The blood sample was collected using lithium heparin (Vacutainer®) (for feeding assay) and ethylenediaminetetraacetic acid (EDTA) tubes (BD Vacutainer). The study utilized a long-established colony (> 920th generation) of An. arabiensis reared under controlled laboratory conditions (Mamai et al., 2018). The blood samples from P. vivax patients were placed in glass feeders (Coelen Glasstechniek in Arnemuiden, The Netherlands) maintained at 37 °C, covered with a parafilm membrane (Ouédraogo et al., 2013). Eighty starved mosquitoes aged 2 to 6 days were allowed to feed for 30 to 40 min in each experiment. Fully engorged mosquitoes were then retained for either 8 days (for midgut dissection by staining with 1.0% mercurochrome (Germa Products, LLC)) or 12 days (for CSP detection using enzyme-linked immunosorbent assay (ELISA)) (Wirtz et al., 1987), with a 10% sugar solution. All positive samples were retested and confirmed to verify the absence of false positive results.

Fig. 1.

Fig. 1

Open in a new tab

Conceptual framework of the study.

The blood in the EDTA tube was used to prepare DBS using Whatmann™ 3MM (VWR®) and slides. Three drops of blood sample, each containing 20 μl, were placed on the Whatman filter paper to prepare the DBS for the follow-up period. The DBS was air dried and stored in a −40 °C freezer in zip-locked plastic bags containing silica gel desiccant (Geejay Chemicals Ltd) for molecular analysis. Thick and thin blood films were prepared on a slide on days 0, 1, 3, 7, 14, 21, and 28. The thin smear was fixed with methanol. The thin and thick blood films were stained with a 10% fresh Giemsa (AppliChem GmbH, Germany) solution for 10 min.

2.3. Trial setting

The patients were recruited from Woze Health Centre in Arba Minch, South Ethiopia. The town has a warm and humid climate, with an average annual rainfall of 800–1000 mm and a temperature of 29.0 °C. It is located at an altitude of 1200–1400 m above sea level. Malaria is a common disease, with P. falciparum and P. vivax being the two common parasites (Getawen et al., 2018). The primary vector is Anopheles arabiensis (Akirso et al., 2024; Getawen et al., 2018), while An. pharoensis and An. stephensi are also documented (Akirso et al., 2024; Massebo et al., 2024).

Arba Minch has four government health facilities: Arba Minch General Hospital, Dilfana Primary Hospital, and the Secha and Woze Health Centres. Due to the high number of malaria cases reported at Woze Health Center, it was selected as the appropriate site for the study. More malaria cases were documented in villages near the Kulfo River (Getawen et al., 2018), likely due to the river creating an ideal breeding ground for mosquitoes.

2.4. Eligibility criteria

Patients aged 15 or older diagnosed with P. vivax mono-infection by microscopy were eligible to participate in the study. Individuals willing to provide written consent or assent and committed to attending the scheduled visits were eligible. The study excluded pregnant and breastfeeding women, individuals with illnesses other than malaria caused by P. vivax mono-infection, and those who had taken antimalarial drugs within two weeks before enrollment.

2.5. Intervention and comparator

The study aimed to evaluate the impact of adding PQ to CQ treatment of P. vivax, focusing on parasite transmission and clearance. One group received CQ phosphate at a dosage of 25 mg/kg of body weight, administered in three divided doses over three days (Medopharm Batch No. 23A057, expiry date: 12/2025). The other group received PQ phosphate at a dosage of 0.25 mg/kg daily for 14 days (Remedica Ltd., Batch No. 92728, expiry date: 02/2025), in addition to CQ, in accordance with national treatment guidelines (FMoH, 2018). The administration of the drugs was semi-supervised; patients were monitored until day three, after which they reported their adherence to PQ. PQ treatment was initiated simultaneously with CQ therapy.

2.6. Outcomes

The primary outcome of this study was the percentage of mosquitoes infected with oocysts in the two groups. The secondary outcomes included the density of oocysts, the CSP infection rates in mosquitoes, and the clearance rates of gametocytes and asexual parasites in patients in the two groups. Oocyst density was determined using a microscope, while CSP detection was performed using an ELISA. The densities of asexual parasites and gametocytes were also assessed using a microscope, following the procedures outlined by the World Health Organization (WHO, 2016). Nested polymerase chain reaction (PCR) was employed to monitor the clearance of asexual parasites in the patients over 28 days by targeting the 18S ribosomal RNA (rRNA) gene (Singh et al., 1999).

2.7. Harms

The patients were recruited without testing for glucose-6-phosphate dehydrogenase (G6PD) deficiency; hence, the addition of PQ may cause potential harm, particularly PQ-induced hemolysis.

2.8. Sample size determination

The trial's sample size was determined using OpenEpi software. The following assumptions were considered to estimate the sample size: a power of 80%, a 50% more reduction in the prevalence of oocyst-positive mosquitoes in the combination group in 24 h post-treatment, and a 17% reduction in the CQ-alone group. This estimation was conducted with a 95% confidence level. Hence, the calculated total sample size was 64, with 32 in each group.

2.9. Randomization

2.9.1. Sequence generation

The participants in the study were randomly assigned to the CQ-PQ and CQ alone groups using a lottery method based on even and odd numbers.

2.9.2. Allocation concealment and implementation

Patients were assigned to the CQ treatment group if the sequential number was odd, while they were assigned the CQ-PQ combination when the number was even. Consistent procedures were followed in sequential order throughout the study period.

2.9.3. Blinding

The molecular biology teams who conducted the nested PCR assays for asexual parasites were blinded to the microscopy results to minimize bias in their analysis, judgment, or interpretation. The laboratory technicians who conducted the ELISA tests for circumsporozoite protein (CSP) were not informed about the patients' microscopic/nested PCR results. Additionally, the slide readers were unaware of the health facility results.

2.10. Statistical methods

Data analysis was performed using R software (version 4.4.1), with visualizations created using the ggplot2 package. Descriptive statistics summarized the number of mosquitoes exposed, fed, dissected, infected, tested for CSP, and CSP-positive. Baseline differences in median asexual parasite and gametocyte densities between treatment groups were assessed using the Mann-Whitney test. Independent two-sample t-tests were used to compare log-transformed parasite and gametocyte densities. A two-sample proportion test compared sporozoite infection rates between groups. Fisher's exact test assessed asexual parasite clearance, mosquito infectivity, and percentage reduction. A zero-inflated Poisson regression model evaluated predictors of oocyst count. Binary logistic regression with generalized estimating equations was used to model the proportion of sporozoite-positive mosquitoes over follow-up, accounting for treatment and patient sex. Two-tailed tests were used, with significance set at P < 0.05.

2.11. Ethical approval

This study received review and approval from the Institutional Review Board of Arba Minch University (IRB/1260/2022). All participants volunteered to take part in the study. Individuals between the ages of 15 and 17 were required to provide written assent in the presence of their parents or guardians, while participants aged 18 and older were asked to give written consent.

3. Results

3.1. Patient enrollment and follow-up

64 patients were enrolled in the study- 33 in the CQ alone group and 31 in the CQ-PQ combination group (Fig. 2). Among the 64 patients, 56 (28 in each group) were eligible after PCR correction. Eight patients (8/64 = 12.5%) were excluded from the analysis: five from the CQ group and three from the combination group. Seven patients were lost to follow-up after day three, with three in the group receiving only CQ and four in the CQ-PQ combination group. However, the data from the mosquito-feeding assay of these patients were still analyzed.

Fig. 2.

Fig. 2

Open in a new tab

Flow chart of patient enrollment and follow-up.

The median (IQR) age of the study participants was 18 (5.5) in the group that received CQ alone and 20 (5.3) in the CQ-PQ group. The median gametocyte density was 1380 in the CQ alone group and 2260 in the CQ-PQ combination group. Among the participants, 57% (16/28) were infectious to mosquitoes in the CQ group, while it was 82% (23/28) in the CQ-PQ combination group (Table 1).

Table 1.

Baseline characteristics of PCR-confirmed P. vivax mono-infection cases in CQ alone and CQ-PQ groups in Arba Minch, Ethiopia.

Characteristics CQ CQ + PQ Test statistics (P value)
Participants, n 28 28
Male/female, n 10/18 16/12
Median age (IQR) 18 (5.5) 20 (5.3) 283.5 (0.08)
Infectious to mosquitoes, n (%) 16 (57) 23 (82)
Infectious to mosquitoes; male/female, n 8/8 13/10
Median gametocyte density/μl (IQR) 1380 (2490) 2260 (3510) 324 (0.27)
Median parasites density/μl (IQR) 700 (760) 1200 (3860) 318 (0.23)
Gametocyte prevalence n; (% positive) 28 (100) 28 (100)
Open in a new tab

3.2. Feeding efficiency

During three rounds of infectivity experiments conducted on Day 0, Day 1, and Day 3, blood samples from P. vivax patients in the CQ group were exposed to 6625 mosquitoes, while samples from the CQ-PQ group were exposed to 6720 mosquitoes (Table 2). The overall mean feeding efficiency was 80.2% (5316/6625; 95% CI: 79.3–81.2) in the CQ group and 77.4% (5202/6720; 95% CI: 76.4–78.4) in the CQ-PQ group. The two groups had no significant difference in mosquito feeding efficiency (P = 0.11). The mean age of mosquitoes that feed on blood samples from patients in the CQ group was 4.6 (95% CI: 4.3–5.0), and similar to the age in the CQ-PQ group (4.7 days; 95% CI: 4.3–5.0 (P = 0.88).

Table 2.

The feeding efficiency of mosquitoes in blood samples from P. vivax mono-infections in CQ and CQ-PQ groups using membrane feeding apparatus in Arba Minch, Ethiopia.

Variables Study groups and the respective mosquito feeding experiment days
CQ
 CQ + PQ
Day 0 Day 1 Day 3 Day 0 Day 1 Day 3
Number of exposed mosquitoes 2265 2270 2090 2240 2240 2240
Number of fed mosquitoes 1886 1829 1601 1751 1692 1759
Median (IQR) feeding efficiency ±± 86 (18) 81 (9) 76 (20) 80 (16) 75 (17) 79 (21)
Mean age of mosquitoes 4.6 ± 1.6 4.6 ± 1.5 4.8 ± 1.7 4.8 ± 1.6 4.3 ± 1.5 4.9 ± 1.6
Open in a new tab

Day 0 = before treatment; Day 1 and Day 3 = post treatment follow-up days.

3.3. Mid-gut dissection for oocyst detection

After eight days of feeding on the patient's blood sample, mosquitoes were dissected. In the CQ alone group, 10% (250/2469; 95% CI: 8.9–11.4) were positive for P. vivax oocysts. In the CQ-PQ group, 2541 mosquitoes, 18% (456/2541; 95% CI: 16.5–19.5) were infected with P. vivax oocysts. The difference in the proportion of infection between the two groups was significant (P < 0.001).

At baseline (Day 0), 23.1% (199/861) of mosquitoes in the group treated with CQ alone tested positive for oocysts, compared to 47.7% (406/850) in the CQ-PQ group. The infection rate in the CQ-PQ group was significantly higher than that of the CQ-alone group (χ2 = 113.7; P < 0.001). After one day, the infection rate dropped to 6.1% in the CQ group and 5.4% in the CQ-PQ group (χ2 = 0.45; P = 0.5). The CQ group showed a 73.5% reduction in mid-gut oocyst infection rate, while the CQ-PQ group showed an 88.6% reduction compared to the baseline (P = 0.005). No mosquitoes tested positive for oocysts after day three of treatment, except for a single case that infected four mosquitoes in the CQ-PQ group (Table 3).

Table 3.

The oocyst infection rate of mosquitoes exposed to blood samples of P. vivax patients in CQ alone and CQ-PQ groups using membrane feeding apparatus in Arba Minch, Ethiopia.

Variables
 Study groups and mosquito feeding experiment days
CQ
 CQ + PQ
Day 0 Day 1 Day 3 Day 0 Day 1 Day 3
Number of mosquitoes dissected 861 834 774 850 855 836
Infected out of dissected 199 51 0 406 46 4
Oocyst infection rate 23.1 6.1 0 47.7 5.4 0.5
Median oocyst number (IQR) 6 (18) 3 (5) 0 11 (28) 4.5 (8.8) 4.5 (1.8)
Min – Max oocyst number 1–170 1–53 0 1–344 1–34 2–6
Open in a new tab

Day 0 = before treatment; Day 1and Day 3 = post-treatment follow-up days.

The median number of oocysts per infected mosquito in the CQ-PQ group was 11 (IQR: 28), whereas, in the CQ-alone group, it was 6 oocysts per infected mosquito (IQR: 18). The distribution of oocyst numbers was significantly different between the two treatments at baseline (W = 32,819, p-value = 0.0001). After one day of treatment, the median number of oocysts per infected mosquito was 3 (IQR: 5) in the group that received only CQ and 4.5 (IQR: 8.75) in the group that received a combination of CQ-PQ. There was no statistically significant difference between the treatments after one day (W = 929, p-value = 0.075) (Table 3).

The oocyst number per infected mosquitoes ranged from (1–344) in the CQ-PQ group before treatment. However, after one day of treatment, the range declined to (1–34). On the other hand, in the CQ alone group, the oocyst number per infected mosquitoes ranged from (1–170) before treatment and declined to (1–53) after one day of treatment. Although the number of infected mosquitoes and oocyst density reduced after one day of treatment, a substantial number of mosquitoes tested positive for oocyst stages (Fig. 3).

Fig. 3.

Fig. 3

Open in a new tab

The oocyst number in mosquitoes exposed to blood samples of P. vivax patients before and after treatment of CQ-PQ and CQ alone in Arba Minch, Ethiopia.

3.4. Effect of treatment on the infectiousness of the patient's blood to mosquitoes

At the baseline, the blood samples from 57% (16/28) patients in the CQ-alone group and 82% (23/28) patients in the CQ-PQ group were infectious to mosquitoes. The two groups had no significant difference in the number of infectious patients (Fisher's exact, P = 0.08). After one day of the first dose of treatment, the number of infectious patients decreased to 36% (10/28) in the CQ-alone group and to 21% (6/28) in the CQ-PQ group. It was observed that using CQ alone resulted in a 37% reduction in infectious patients, while using a combination of CQ-PQ resulted in a 74% reduction after one day of treatment. The percentage reduction in the number of infectious patients was significantly higher in patients treated with CQ-PQ compared to CQ alone (Fisher's exact, P < 0.001). All patients, except one in the CQ-PQ group, were not infectious to mosquitoes at day three of treatment (Fig. 4).

Fig. 4.

Fig. 4

Open in a new tab

The number of infectious patients to mosquitoes in the CQ alone and CQ-PQ groups during the follow-up days in Arba Minch, Ethiopia.

3.5. Efficacy of treatment on oocyst development to CSP

Among the mosquitoes fed on P. vivax-positive blood samples during the first three days of the experiment (D0, D1, and D3), a total of 2846 were tested for CSP via ELISA in both groups. In the group that only received CQ, 1390 mosquitoes were tested, and 8.6% (119/1390; 95% CI: 7.1–10.2) tested positive for CSP. In the CQ-PQ group, 1456 mosquitoes were tested, and 14.3% (209/1456; 95% CI: 12.6–16.3) were positive for CSP.

At baseline, the mosquito CSP rate was 17.5% (100/539; 95% CI: 15.4–22.1) in the CQ group and 39.8% (193/484; 95% CI: 35.5–44.4) in the CQ-PQ group. The proportion of CSP-positive mosquitoes in the CQ-PQ group was significantly higher than in the CQ-only group (P < 0.001) (Fig. 6).

Fig. 6.

Fig. 6

Open in a new tab

Microscopy-based P. vivax asexual parasite and gametocyte clearance rate in patients receiving CQ alone and CQ-PQ combination in Arba Minch, Ethiopia.

After one day of treatment, patients who received the CQ-PQ combination experienced a 92.5% reduction in the CSP rate. In comparison, patients receiving only CQ treatment had a 78.4% reduction. The decrease in the CSP rate was significantly higher in the group receiving the CQ-PQ combination than in the group receiving only CQ treatment (χ2 = 9.2; P = 0.002). None of the mosquitoes that fed on the patients' blood samples on day three tested positive for CSP in both groups (Fig. 5).

Fig. 5.

Fig. 5

Open in a new tab

The proportion of CSP-positive mosquitoes across follow-up days by treatment groups in Arba Minch, Ethiopia.

Of the patients who were initially infectious to mosquitoes (positive for oocysts) in the CQ-PQ group, 95.6% (22/23) were positive for CSP at the baseline. In comparison, only 13% (3/23) were positive after day 1 of treatment. In the CQ alone group, 88% (14/16) of patients with positive oocysts were also positive for CSP at baseline, while 43.7% (7/16) of patients were still positive for CSP one day after treatment. The sporozoite infection rate declines significantly across follow-up days (from day 0 to day 3) in both groups.

3.6. Efficacy of treatment on gametocyte clearance rate

Before treatment, all patients in both groups had gametocytes, and there was no statistically significant difference in gametocyte density. Gametocyte density showed a positive correlation with both the prevalence of oocyst-positive mosquitoes and the CSP infection rate (Supplementary Fig. 1).

The median gametocyte density at baseline was 1380 (IQR: 480–3060) for patients receiving CQ alone and 2020 (IQR: 700–4000) for patients in the CQ-PQ group. After day one of treatment, 14% (4/28) of patients in the CQ alone group had gametocytes, and the median gametocyte density for those who tested positive was 680 (IQR: 320–1260). In contrast, in the CQ-PQ group, only 3.5% (1/28) had gametocytes after one day of treatment. The percentage reduction in the number of patients with gametocytes one day after treatment was 96.4% in the CQ-PQ group, higher than 85.7% in the CQ-alone group (χ2 = 6.4; P = 0.02). By the third day, both treatment groups had completely cleared gametocytes (Fig. 6).

3.7. Efficacy of treatment on asexual parasite clearance

The two treatment groups had no statistically significant difference in asexual parasite density before treatment (P = 0.099). On day 1 after treatment, all asexual parasites were cleared under the microscope, except for two patients who received the CQ-PQ treatment (Fig. 6).

After one day of treatment, the PCR results showed that only 5% (3/56) of patients had cleared asexual parasites: 4% (1/28) in the group receiving only CQ and 7% (2/28) in the group receiving both CQ and PQ. However, by the third day post-treatment, 83.9% (47/56) of patients had cleared all asexual parasites, while 12.5% (7/56) still had detectable parasites: five in the CQ group and two in the CQ-PQ group. There was no significant difference in the clearance rate between the two groups three days post-treatment (P = 0.42). By day seven, all patients in both groups had cleared all asexual parasites (Fig. 7).

Fig. 7.

Fig. 7

Open in a new tab

Polymerase chain reaction-based asexual parasite clearance rate in patients receiving CQ alone and CQ-PQ combination in Arba Minch, Ethiopia.

4. Discussion

Our findings indicate that the addition of PQ to the treatment for P. vivax cases reduces the transmission of the parasite to mosquitoes. After one day, both groups showed a decrease in the number of patients infectious to mosquitoes, with a steeper decline observed in the CQ-PQ group. The infection rate of sporozoites significantly decreased from day 0 to day 3 in both groups, with a greater reduction in the CQ-PQ combination group. Likewise, the reduction in gametocyte prevalence one day after treatment was higher in the CQ-PQ group, while asexual parasite clearance rates remained similar in both groups.

The CQ-PQ combination reduced the prevalence of oocyst-positive mosquitoes within one day of treatment, overcoming its initially higher baseline compared to CQ alone. The addition of PQ enhanced transmission-blocking by targeting and eliminating mature gametocytes in the bloodstream, thereby reducing malaria parasite transmission from humans to mosquitoes (Angrisano and Robinson, 2022; Chu and White, 2021). PQ rapidly eliminates gametocytes, alters their sex ratio, and induces oxidative damage to malaria parasites, thereby effectively preventing transmission to mosquitoes. Although the CQ shows limited capability against mature gametocytes (Andrade et al., 2023; Chaumeau et al., 2024), its quick response to asexual parasites helps reduce transmission by lowering the likelihood of mosquitoes ingesting gametocytes. Moreover, CQ can inhibit the growth of immature gametocytes by interfering with hemoglobin digestion, but it does not act as a sterilizing agent on mature-stage gametocytes (Klein et al., 1991). Gametocyte circulation duration is affected by natural decay, immune response, and gametocytocidal drugs (Bousema and Drakeley, 2011).

CQ-PQ greatly reduces infectious patients and sporozoite infection rates. CQ alone also shows promise. PQ rapidly targets the mature sexual stages of the malaria parasite, which are crucial for mosquito transmission, thereby enhancing its efficacy (Baird and Hoffman, 2004). This finding is consistent with previous studies conducted in different parts of the world. For example, two days after the initial dose of CQ, all mosquitoes that fed on patients were found to be negative for oocysts when administered alone (Klein et al., 1991) or in combination with PQ (Klein et al., 1992). However, a recent small study (4 patients) found that individuals treated with CQ-PQ were non-infectious to mosquitoes by day one (Andrade et al., 2023).

The administration of CQ-PQ was more effective than CQ alone in reducing the number of patients with detectable gametocytes after the first day of treatment. However, complete gametocyte clearance was observed by day three in both treatment groups. These findings are consistent with a recent study in Ethiopia, which also reported full gametocyte clearance within three days following CQ-PQ treatment (Mekonnen et al., 2023). There was also another study in Ethiopia, which indicated that gametocyte clearance occurred within two days of post-treatment with CQ alone (Belay et al., 2023). Studies have documented that P. vivax gametocytes exhibit a delayed response to treatment with PQ (Salazar and Louzada, 2024).

The current study found a correlation between the rate at which gametocytes are cleared from human hosts and the mosquito's infectivity in transmitting the parasite. The speed at which asexual parasites are eliminated will determine how quickly gametocyte production is disrupted after treatment (White, 2017). CQ destroys the asexual parasite, thus preventing the formation of new gametocytes and PQ targets mature gametocytes, further reducing their presence (Commons et al., 2018; Douglas et al., 2013). This underscores that evaluating a drug's effect on transmission should not depend exclusively on gametocyte counts, as these are prone to human error and may fail to detect submicroscopic infections. Instead, it is essential to include direct mosquito infection studies, such as counting oocysts through microscopy (Churcher et al., 2013) and infectiousness of patients to mosquitoes (Goncąlves and Hunziker, 2016; Reader et al., 2021).

The study finds no significant difference in the clearance rate of asexual parasites between treatment with CQ alone and a combination of CQ and PQ. While PQ has gametocytocidal and anti-relapse effects (Ashley et al., 2014), CQ is highly effective in eliminating the blood-stage parasite (Pukrittayakamee et al., 2014). Similar findings have been reported in Ethiopia, where CQ was found to be effective against asexual stages of P. vivax for up to 28 days after treatment (Belay et al., 2023). However, longer follow-up periods are required to detect recurrent infections.

The study evaluated the efficacy of CQ alone compared to CQ combined with PQ in reducing the transmission of P. vivax and improving treatment outcomes. CQ alone efficiently clears the asexual parasite. Combining PQ with CQ effectively lowers P. vivax transmission. However, current practices often delay the administration of PQ until after completing the full CQ course, which may still allow for parasite transmission despite CQ treatment. To enhance effectiveness, it is recommended to initiate both medications simultaneously from the first day of treatment.

The study had some limitations. First, patient enrollment was based on microscopy results, leading to exclusions after PCR confirmation due to initial misdiagnoses. These misdiagnoses were likely attributable to microscopy's lower sensitivity, possibly influenced by human skill, ultimately reducing the final sample size and underpowering the study. Secondly, baseline gametocyte load was not measured in the two treatment groups, which could have influenced mosquito infectivity and led to differences in baseline infection rates between the groups. Another limitation was that the infectivity test was conducted using colony-maintained Anopheles mosquitoes that had been maintained in the laboratory for generations, so they may not accurately reflect the genetic makeup of a wild population. The extended follow-up period would have been more effective in evaluating the prolonged impact of antimalarial drugs on preventing relapse and reinfections.

5. Conclusions

Combining PQ with CQ effectively reduces the proportion of infectious patients and lowers transmission rates. Although CQ eliminates asexual parasites, some patients may remain infectious to mosquitoes for up to 24 h. To minimize transmission promptly, PQ should be administered with CQ starting on day 0.

CRediT authorship contribution statement

Mesay Melaku: Writing – review & editing, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Biniam Wondale: Writing – review & editing, Methodology, Conceptualization. Girum Tamiru: Writing – review & editing, Methodology, Formal analysis. Ribka Getu: Writing – review & editing, Methodology, Data curation. Tinsae Kumsa: Writing – review & editing, Data curation. Yilikal Tesfaye: Writing – review & editing, Visualization, Validation, Formal analysis, Data curation. Bernt Lindtjørn: Writing – review & editing, Validation, Supervision, Resources, Project administration, Funding acquisition. Fekadu Massebo: Writing – review & editing, Writing – original draft, Supervision, Resources, Project administration, Methodology, Funding acquisition, Formal analysis.

Declaration of competing interest

We wish to submit an original research article entitled “Impact of the combination of primaquine and chloroquine on parasite transmission to mosquitoes and clearance in Plasmodium vivax patients in Ethiopia” for consideration by Parasite epidemiology and control. We confirm that this work is original and has not been published elsewhere, nor is it currently under consideration for publication elsewhere.

We believe that this manuscript is suitable for publication in the Parasite epidemiology and control. The manuscript explains how adding primaquine to treat P. vivax malaria reduces transmission and sexual and asexual parasite clearance. Primaquine has been introduced in the treatment region of P. vivax to clear the hypnozoite stage and reduce transmission to mosquitoes by targeting mature gametocytes. Although little is known, the current increase in malaria cases raises questions about whether the drug performs as expected and how quickly it halts transmission. Lastly, while adding PQ reduced the number of infectious patients, some remained infectious to mosquitoes for up to 24 h. The two treatment groups showed no significant difference in clearing the asexual parasites. It is recommended to start administering PQ with CQ from day 0 to minimize transmission as quickly as possible.

The authors confirm that we have no conflicts of interest to disclose.

Acknowledgements

This work received support from the Norwegian Programme for Capacity Development in Higher Education and Research for Development (QZA-21/0162). The funders did not participate in the design of the study, data collection and analysis, decision to publish, or preparation of the manuscript. We are very grateful to the study participants for their active involvement and willingness to contribute to this research.

Footnotes

Appendix A

Supplementary data to this article can be found online at https://doi.org/10.1016/j.parepi.2026.e00484.

Appendix A. Supplementary data

Figures

mmc1.docx (507.5KB, docx)

References

  1. Akirso A., Tamiru G., Eligo N., Lindtjørn B., Massebo F. High human blood meal index of mosquitoes in Arba Minch town, Southwest Ethiopia: an implication for urban mosquito-borne disease transmission. Parasitol. Res. 2024;123:102. doi: 10.1007/s00436-024-08121-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Andrade A.O., Santos N.A.C., Bastos A.S., Silva A.M.V., Martinez L.N., Lima A.A. Transmission-blocking activity of antimalarials for Plasmodium vivax malaria in Anopheles darling. PLoS Negl. Trop. Dis. 2023;17 doi: 10.1371/journal.pntd.0011425. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Angrisano F., Robinson L.J. Plasmodium vivax – how hidden reservoirs hinder global malaria elimination. Parasitol. Int. 2022;87 doi: 10.1016/j.parint.2021.102526. [DOI] [PubMed] [Google Scholar]
  4. Ashley E.A., Recht J., White N.J. Primaquine: the risks and the benefits. Malar. J. 2014;13:418. doi: 10.1186/1475-2875-13-418. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Assefa A., Ali A., Deressa W., Tsegaye W., Abebe G., Sime H., Kebede A., Jima D., Kassa M., Abreha T., Teka H., Solomon H., Malone J., Shi Y.P., Zhou Z., Reithinger R., Hwang J. Glucose-6-phosphate dehydrogenase (G6PD) deficiency in Ethiopia: absence of common African and Mediterranean allelic variants in a nationwide study. Malar. J. 2018;17:388. doi: 10.1186/s12936-018-2538-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Baird J.K., Hoffman S.L. Primaquine therapy for malaria. Clin. Infect. Dis. 2004;39:1336–1345. doi: 10.1086/424663. [DOI] [PubMed] [Google Scholar]
  7. Bantuchai S., Imad H., Nguitragool W. Plasmodium vivax gametocytes and transmission. Parasitol. Int. 2022;87 doi: 10.1016/j.parint.2021.102497. [DOI] [PubMed] [Google Scholar]
  8. Battle K.E., Lucas T.C.D., Nguyen M., Howes R.E., Nandi A.K., Twohig K.A., Pfeffer D.A., Cameron E., Rao P.C., Casey D., Gibson H.S., Rozier J.A., Dalrymple U., Keddie S.H., Collins E.L., Harris J.R., Guerra C.A., Thorn M.P., Bisanzio D., Fullman N., Huynh C.K., Kulikoff X., Kutz M.J., Lopez A.D., Mokdad A.H., Naghavi M., Nguyen G., Shackelford K.A., Vos T., Wang H., Lim S.S., Murray C.J.L., Price R.N., Baird J.K., Smith D.L., Bhatt S., Weiss D.J., Hay S.I., Gething P.W. Mapping the global endemicity and clinical burden of Plasmodium vivax, 2000–17: a spatial and temporal modelling study. Lancet. 2019;394:332–343. doi: 10.1016/S0140-6736(19)31096-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Belay H., Alemu M., Hailu T., Mohammed H., Sime H., Hailegeorgies H., Gidey B., Haile M., Assefa G., Bekele W., Reta M.A., Tamene A.A., Tasew G., Assefa A. Therapeutic efficacy of chloroquine for the treatment of uncomplicated Plasmodium vivax infection in Shewa Robit, Northeast Ethiopia. PLoS One. 2023;18 doi: 10.1371/journal.pone.0277362. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Bousema T., Drakeley C. Epidemiology and infectivity of Plasmodium falciparum and Plasmodium vivax gametocytes in relation to malaria control and elimination. Clin. Microbiol. Rev. 2011;24:377–410. doi: 10.1128/CMR.00051-10. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Bradley J., Stone W., Da D.F., Morlais I., Dicko A., Cohuet A., Guelbeogo W.M., Mahamar A., Nsango S., Soumaré H.M., Diawara H., Lanke K., Graumans W., Siebelink-Stoter R., van de Vegte-Bolmer M., Chen I., Tiono A., Gonçalves B.P., Gosling R., Sauerwein R.W., Drakeley C., Churcher T.S., Bousema T. Predicting the likelihood and intensity of mosquito infection from sex specific Plasmodium falciparum gametocyte density. Elife. 2018;7 doi: 10.7554/eLife.34463. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Chaumeau V., Kittiphanakul P., Watson J.A., Oo T. Transmission-blocking activity of artesunate, chloroquine and methylene blue on Plasmodium vivax gametocytes. Antimicrob. Agents Chemother. 2024;68 doi: 10.1128/aac.00853-24. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Chu C.S., White N.J. Management of relapsing Plasmodium vivax malaria. Expert Rev. Anti Infect. Ther. 2016;14:885–900. doi: 10.1080/14787210.2016.1220304. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Chu C.S., White N.J. The prevention and treatment of Plasmodium vivax malaria. PLoS Med. 2021;18 doi: 10.1371/journal.pmed.1003561. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Churcher T.S., Bousema T., Walker M., Drakeley C., Schneider P., Ouédraogo A.L., Basáñez M.G. Predicting mosquito infection from Plasmodium falciparum gametocyte density and estimating the reservoir of infection. Elife. 2013;2 doi: 10.7554/eLife.00626. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Commons R.J., Simpson J.A., Thriemer K., Humphreys G.S., Abreha T., Alemu S.G., Añez A., Anstey N.M., Awab G.R., Baird J.K., Barber B.E., Borghini-Fuhrer I., Chu C.S., D’Alessandro U., Dahal P., Daher A., de Vries P.J., Erhart A., Gomes M.S.M., Gonzalez-Ceron L., Grigg M.J., Heidari A., Hwang J., Kager P.A., Ketema T., Khan W.A., Lacerda M.V.G., Leslie T., Ley B., Lidia K., Monteiro W.M., Nosten F., Pereira D.B., Phan G.T., Phyo A.P., Rowland M., Saravu K., Sibley C.H., Siqueira A.M., Stepniewska K., Sutanto I., Taylor W.R.J., Thwaites G., Tran B.Q., Tran H.T., Valecha N., Vieira J.L.F., Wangchuk S., William T., Woodrow C.J., Zuluaga-Idarraga L., Guerin P.J., White N.J., Price R.N. The effect of chloroquine dose and primaquine on Plasmodium vivax recurrence: a WorldWide antimalarial resistance network systematic review and individual patient pooled meta-analysis. Lancet Infect. Dis. 2018;18:1025–1034. doi: 10.1016/S1473-3099(18)30348-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. de Pina-Costa A., Silvino A.C.R., dos Santos E.M., Pedro R.S., Moreira J., Umana G.L., da Silva A.D.T., da Rosa Santos O.H.L., de Deus Henriques K.M., Daniel-Ribeiro C.T., Brasil P., Sousa T.N., Siqueira A.M. Increased primaquine total dose prevents Plasmodium vivax relapses in patients with impaired CYP2D6 activity: report of three cases. Malar. J. 2021;20:341. doi: 10.1186/s12936-021-03869-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Douglas N.M., Simpson J.A., Phyo A.P., Siswantoro H., Hasugian A.R., Kenangalem E., Poespoprodjo J.R., Singhasivanon P., Anstey N.M., White N.J., Tjitra E., Nosten F., Price R.N. Gametocyte dynamics and the role of drugs in reducing the transmission potential of Plasmodium vivax. J Infect Dis. 2013;208:801–812. doi: 10.1093/infdis/jit261. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Fernando D., Rodrigo C., Rajapakse S. Primaquine in vivax malaria: an update and review on management issues. Malar. J. 2011;10:351. doi: 10.1186/1475-2875-10-351. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. FMoH . 2018. National Malaria Control and elimination program. Dis. Prev. Control Dir. 43–57. [Google Scholar]
  21. Getawen S.K., Ashine T., Massebo F., Woldeyes D., Lindtjørn B. Exploring the impact of house screening intervention on entomological indices and incidence of malaria in Arba Minch town, Southwest Ethiopia: a randomized control trial. Acta Trop. 2018;181:84–94. doi: 10.1016/j.actatropica.2018.02.009. [DOI] [PubMed] [Google Scholar]
  22. Goncąlves D., Hunziker P. Transmission-blocking strategies: the roadmap from laboratory bench to the community. Malar. J. 2016;15:95. doi: 10.1186/s12936-016-1163-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Gunalan K., Niangaly A., Thera M.A., Doumbo O.K., Miller L.H. Plasmodium vivax infections of duffy-negative erythrocytes: historically undetected or a recent adaptation? Trends Parasitol. 2018;34:420–429. doi: 10.1016/j.pt.2018.02.006. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Howes R.E., Reiner R.C., Battle K.E., Longbottom J., Mappin B., Ordanovich D., Tatem A.J., Drakeley C., Gething P.W., Zimmerman P.A., Smith D.L., Hay S.I. Plasmodium vivax transmission in Africa. PLoS Negl. Trop. Dis. 2015;9 doi: 10.1371/journal.pntd.0004222. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Howes R.E., Battle K.E., Mendis K.N., Smith D.L., Cibulskis R.E., Baird J.K., Hay S.I. Global epidemiology of Plasmodium vivax. Am. J. Trop. Med. Hyg. 2016;95:15–34. doi: 10.4269/ajtmh.16-0141. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Ketema T., Bacha K., Getahun K., Del Portillo H.A., Bassat Q. Plasmodium vivax epidemiology in Ethiopia 2000-2020: a systematic review and meta-analysis. PLoS Negl. Trop. Dis. 2021;15 doi: 10.1371/journal.pntd.0009781. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Kiszewski A.E. Blocking Plasmodium falciparum malaria transmission with drugs: the gametocytocidal and sporontocidal properties of current and prospective antimalarials. Pharmaceuticals. 2011;4:44–68. [Google Scholar]
  28. Klein T.A., Tada M.S., Lima J.B.P., Katsuragawa T.H. Infection of Anopheles darlingi fed on patients infected with Plasmodium vivax before and during treatment with chloroquine in Costa marques, Rondonia, Brazil. Am. J. Trop. Med. Hyg. 1991;45:471–478. doi: 10.4269/ajtmh.1991.45.471. [DOI] [PubMed] [Google Scholar]
  29. Klein T.A., Lima J.B., Toda Tang A. Vector incrimination and effects of antimalarial drugs on malaria transmission and control in the Amazon basin of Brazil. Mem. Inst. Oswaldo Cruz. 1992;3:393–397. doi: 10.1590/s0074-02761992000700066. [DOI] [PubMed] [Google Scholar]
  30. Mamai W., Lobb L.N., Bimbilé Somda N.S., Maiga H., Yamada H., Lees R.S., Bouyer J., Gilles J.R.L. Optimization of mass-rearing methods for anopheles arabiensis larval stages: effects of rearing water temperature and larval density on mosquito life-history traits. J. Econ. Entomol. 2018;111:2383–2390. doi: 10.1093/jee/toy213. [DOI] [PubMed] [Google Scholar]
  31. Massebo F., Ashine T., Demeke N.N., Eligo N., Hailemeskel E., Minda T.T., Lindtjorn B., Gadisa E. The expansion of an invasive malaria vector: Anopheles stephensi emergence in Arba Minch town in the southern Rift Valley of Ethiopia. Parasitol. Res. 2024;123:333. doi: 10.1007/s00436-024-08356-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Mekonnen D.A., Abadura G.S., Behaksra S.W., Taffese H.S., Bayissa G.A., Bulto M.G., Tessema T.S., Tadesse F.G., Gadisa E. Treatment of uncomplicated Plasmodium vivax with chloroquine plus radical cure with primaquine without G6PDd testing is safe in Arba Minch, Ethiopia: assessment of clinical and parasitological response. Malar. J. 2023;22:135. doi: 10.1186/s12936-023-04562-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Ouédraogo A.L., Guelbéogo W.M., Cohuet A., Morlais I., King J.G., Gonçalves B.P., Bastiaens G.J.H., Vaanhold M., Sattabongkot J., Wu Y., Coulibaly M., Ibrahima B., Jones S., Morin M., Drakeley C., Dinglasan R.R., Bousema T. A protocol for membrane feeding assays to determine the infectiousness of P. falciparum naturally infected individuals to Anopheles gambiae. MalarWorld J. 2013;4 doi: 10.5281/zenodo.10926272. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Pukrittayakamee S., Tarning J., Jittamala P., Charunwatthana P., Lawpoolsri S., Lee S.J., Hanpithakpong W., Hanboonkunupakarn B., Day N.P.J., Ashley E.A., White N.J. Pharmacokinetic interactions between primaquine and chloroquine. Antimicrob. Agents Chemother. 2014;58:3354–3359. doi: 10.1128/AAC.02794-13. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Reader J., van der Watt M.E., Taylor D., Le Manach C., Mittal N., Ottilie S., Theron A., Moyo P., Erlank E., Nardini L., Venter N., Lauterbach S., Bezuidenhout B., Horatscheck A., van Heerden A., Spillman N.J., Cowell A.N., Connacher J., Opperman D., Orchard L.M., Llinás M., Istvan E.S., Goldberg D.E., Boyle G.A., Calvo D., Mancama D., Coetzer T.L., Winzeler E.A., Duffy J., Koekemoer L.L., Basarab G., Chibale K., Birkholtz L.M. Multistage and transmission-blocking targeted antimalarials discovered from the open-source MMV pandemic response box. Nat. Commun. 2021;12:269. doi: 10.1038/s41467-020-20629-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Salazar Y.E.A.R., Louzada J., Puça M.C.S.D.B., Guimarães L.F.F., Vieira J.L.F., Siqueira A.M.D., Gil J.P., Brito C.F.A.D., Sousa T.N.D. Delayed gametocyte clearance in plasmodium vivax malaria is associated with polymorphisms in the cytochrome P450 reductase (CPR) Antimicrob. Agents Chemother. 2024;68 doi: 10.1128/aac.01204-23. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Sharp P.M., Plenderleith L.J., Culleton R.L., Hahn B.H. Origin of the human malaria parasite Plasmodium vivax. Trends Parasitol. 2024;40:562–572. doi: 10.1016/j.pt.2024.05.001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Singh B., Bobogare A., Cox-Singh J., Snounou G., Abdullah M.S., Rahman H.A. A genus- and species-specific nested polymerase chain reaction malaria detection assay for epidemiologic studies. Am. J. Trop. Med. Hyg. 1999;60:687–692. doi: 10.4269/ajtmh.1999.60.687. [DOI] [PubMed] [Google Scholar]
  39. von Seidlein L., White N.J. Taking on Plasmodium vivax malaria: a timely and important challenge. PLoS Med. 2021;18 doi: 10.1371/journal.pmed.1003593. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. White N.J. Determinants of relapse periodicity in Plasmodium vivax malaria. Malar. J. 2011;10:297. doi: 10.1186/1475-2875-10-297. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. White N.J. Malaria parasite clearance. Malar. J. 2017;16:88. doi: 10.1186/s12936-017-1731-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. WHO . 2016. Malaria Parasite Counting: Malaria microscopy standard operating procedures; pp. 1–5. [Google Scholar]
  43. WHO . World Health Organization; Geneva: 2022. World Malaria Report 2022. [Google Scholar]
  44. Wirtz R.A., Burkot T.R., Graves P.M., Andre R.G. Field evaluation of enzyme-linked immuosorbent assays for Plasmodium falciparum and Plasmodium vivax sporozoites in mosquitoes (Diptera: Culicidae) from Papua New Guinea. J. Med. Entomol. 1987;24:433–437. doi: 10.1093/jmedent/24.4.433. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Figures

mmc1.docx (507.5KB, docx)

Articles from Parasite Epidemiology and Control are provided here courtesy of Elsevier

RESOURCES