EMERGENCE AND CLEARANCE OF GAMETOCYTES IN UNCOMPLICATED PLASMODIUM FALCIPARUM MALARIA

WATCHARAPONG PIYAPHANEE 0 1 SRIVICHA KRUDSOOD 0 1 NOPPADON TANGPUKDEE 0 1 WIPA THANACHARTWET 0 1 UDOMSAK SILACHAMROON 0 1 NANTAPORN PHOPHAK 0 1 CHATNAPRA DUANGDEE 0 1 ORATHAI HAOHARN 0 1 SUPARAT FAITHONG 0 1 POLRAT WILAIRATANA 0 1 WATTANA LEOWATTANA 0 1 SORNCHAI LOOAREESUWAN 0 1 0 ment of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University , Bangkok 10400 , Thailand 1 Department of Clinical Tropical Medicine and Hospital for Tropical Diseases, and Department of Tropical Hygiene, Faculty of Tropical Medicine, Mahidol University , Bangkok , Thailand We reviewed the records of 1,175 patients with uncomplicated Plasmodium falciparum malaria to determine the prevalence of gametocytemia. All patients were admitted and received artemisinin combination therapy. Blood films were checked daily until discharge. Circulating gametocytes were observed in 240 (20.2%) of patients and in most cases (222 of 240, 92.5%) gametocytemia was detected during the first 24 hours after admission. Gametocytes were first seen in 174 cases on admission, in 24 cases at 12 hours, and in 24 cases at 24 hours. The longest interval between admission and first appearance of gametocytes was 192 hours. The median gametocyte clearance time was 163 hours (range 12-806) in the 219 patients in whom gametocytemia resolved. However, 21 patients (9.8%) still had gametocytemia on discharge. Gametocytemia generally is present within the first 24 hours after admission, and emerges in only 1.9% of patients later on during treatment with artemisinin. - The gametocyte plays a key role in malaria transmission. When transmitted from infected humans to the mosquito, this stage of the malaria parasite completes the life cycle. The precise mechanism of gametocytogenesis is unknown,1,2 but several factors influencing gametocyte emergence have been identified, including parasite genetics,3 stress to the parasite,4 host immunologic factors,57 and even seasonal change.8 Without treatment, most patients with falciparum malaria will develop gametocytemia within 1040 days after the onset of parasitemia.9 Gametocytes have been reported to survive as long as 21 days in peripheral blood.10 Mature gametocytes are relatively resistant to most antimalarial compounds, and primaquine is the only drug with proven gametocidal activity.11,12 In some areas, it is recommended that primaquine be given to patients with P. falciparum malaria with gametocytemia to prevent transmission. In Thailand, it is recommended that primaquine be given with artesunate and mefloquine to all newly diagnosed patients with P. falciparum malaria whether or not gametocytes are present. The rationale is that even if there is no gametocytemia at the time malaria is diagnosed, it is possible that gametocytes will emerge during treatment. However, the prevalence of gametocytemia during malaria infection is not well defined. Here, we retrospectively review data from patients with uncomplicated P. falciparum malaria enrolled in treatment trials to gather information on the emergence and clearance of gametocytes during therapy. PATIENTS AND METHODS We retrospectively reviewed charts from patients with uncomplicated P. falciparum malaria enrolled in nine separate trials of artemisinin combination therapy. All trials were conducted at Hospital for Tropical Diseases in Bangkok, Thailand between 1999 and 2004. Four trials are published1316 and five trials are unpublished. Details of all trials are shown in Table 1. Most patients in our study were from Thailands western border with Myanmar, where malaria epidemiology has been previously described in detail.17,18 Transmission of malaria is low and seasonal. On average, each person has one P. vivax and one P. falciparum malaria infection every two years. Nearly all P. falciparum malaria infection is symptomatic. Patients. Studies were reviewed and approved by the Ethics Committee of the Faculty of Tropical Medicine of Mahidol University and informed consent was obtained from each subject. All patients had slide-confirmed P. falciparum malaria, with no signs or symptoms of severe malaria.19 All patients received artemisinin combination therapy and remained in hospital for 28 days. Laboratory methods. Thick and thin blood films were examined for asexual blood stage parasites and gametocytes every 12 hours until asexual blood stage parasites were no longer present and then daily thereafter until day 28 or until discharge. Parasite and gametocyte counts per microliter of blood were calculated per 1,000 red blood cells in a thin film or per 200 white blood cells in a thick film. Time to gametocyte detection was the number of hours from admission to the first peripheral smear positive for gametocytes. Gametocyte clearance time was the interval between the first and last positive smears for gametocytes. The parasite clearance time was the interval between starting treatment and the first peripheral blood smear with no demonstrable asexual parasites. Statistical analysis. All statistical analyses were performed with the statistical computing package SPSS version 11 for Windows (SPSS Inc., Chicago, IL). Arithmetic means were generally used, except that initial parasite counts and maximum gametocyte counts were expressed as geometric means. Gametocyte clearance times were evaluated by Kaplan-Meier analysis. Data from 1,175 patients with uncomplicated P. falciparum malaria studied between May 1999 and September 2004 and whose treatment did not include primaquine were analyzed. All patients receive artemisinin combination therapy regimen. Gametocytemia was found in 240 of these 1,175 patients Published drug tiral 1. DHA (4 mg/kg/day 3 days) + mefloquine (8 mg/kg/day 3 days)13 2. Artecom (DHA 32 mg, piperaquine 320 mg, trimethoprim 90 mg) 2 tablets orally bid 2 days14 3. Artesunate (200 mg od 3 days) + mefloquine (250 mg) 1.5 tablets od 3 days15 4. Artesunate (200 mg od 3 days) + mefloquine (250 mg) 1.5 tablets od 3 days16 Unpublished drug trial 5. Artekin (DHA 40 mg + piperaquine 320 mg) 2 tablets od on D1 + D2 (total 8 tablets) 6. Artekin 2 tablets bid D0, 2 tablets bid on D1 (total 8 tablets) 7. Artepie (artemisinin 250 mg + piperaquine 1,500 mg) 1 tablet od 2 days 8. Artekin 2 tablets bid D0, 2 tablets bid on D1 (total 8 tablets) 9. Artequick (artemisinin 62.5 mg + piperaquine base 375 mg) 2 tablets bid * DHA dihydroartemisinin; bid twice a day; od once a day; D1 day 1, D2 day 2; D0 day 0. (20.2%), and it is these individuals who are the main focus of our investigation. One hundred seventy-nine patients (74.6%) were male, the median age was 21 years (range 262), and slightly more than half (57.9%) were having their first episode of malaria. The median duration of fever prior to admission was 5.0 days (range 060) and the median admission parasite count was 5,363/ L (range 17156,240). The admission characteristics of the 240 patients are summarized in Table 2. First detection of gametocyte (...truncated)