Multiple genetic backgrounds of the amplified Plasmodium falciparum multidrug resistance (pfmdr1) gene and selective sweep of 184F mutation in Cambodia.

BACKGROUND: The emergence of artesunate-mefloquine (AS+MQ)-resistant Plasmodium falciparum in the Thailand-Cambodia region is a major concern for malaria control. Studies indicate that copy number increase and key alleles in the pfmdr1 gene are associated with AS+MQ resistance. In the present study, we investigated evidence for a selective sweep around pfmdr1 because of the spread of adaptive mutation and/or multiple copies of this gene in the P. falciparum population in Cambodia. METHODS: We characterized 13 microsatellite loci flanking (+/-99 kb) pfmdr1 in 93 single-clone P. falciparum infections, of which 31 had multiple copies and 62 had a single copy of the pfmdr1 gene. RESULTS: Genetic analysis revealed no difference in the mean (+/- standard deviation) expected heterozygosity (H(e)) at loci around single (0.75+/-0.03) and multiple (0.76+/-0.04) copies of pfmdr1. Evidence of genetic hitchhiking with the selective sweep of certain haplotypes was seen around mutant (184F) pfmdr1 allele, irrespective of the copy number. There was an overall reduction of 28% in mean H(e) (+/-SD) around mutant allele (0.56+/-0.05), compared with wild-type allele (0.84+/-0.02). Significant linkage disequilibrium was also observed between the loci flanking mutant pfmdr1 allele. CONCLUSION: The 184F mutant allele is under selection, whereas amplification of pfmdr1 gene in this population occurs on multiple genetic backgrounds.

Active case detection, treatment of falciparum malaria with combined chloroquine and sulphadoxine/pyrimethamine and vivax malaria with chloroquine and molecular markers of anti-malarial resistance in the Republic of Vanuatu.

BACKGROUND: Chloroquine-resistant Plasmodium falciparum was first described in the Republic of Vanuatu in the early 1980s. In 1991, the Vanuatu Ministry of Health instituted new treatment guidelines for uncomplicated P. falciparum infection consisting of chloroquine/sulphadoxine-pyrimethamine combination therapy. Chloroquine remains the recommended treatment for Plasmodium vivax. METHODS: In 2005, cross-sectional blood surveys at 45 sites on Malo Island were conducted and 4,060 adults and children screened for malaria. Of those screened, 203 volunteer study subjects without malaria at the time of screening were followed for 13 weeks to observe peak seasonal incidence of infection. Another 54 subjects with malaria were followed over a 28-day period to determine efficacy of anti-malarial therapy; chloroquine alone for P. vivax and chloroquine/sulphadoxine-pyrimethamine for P. falciparum infections. RESULTS: The overall prevalence of parasitaemia by mass blood screening was 6%, equally divided between P. falciparum and P. vivax. Twenty percent and 23% of participants with patent P. vivax and P. falciparum parasitaemia, respectively, were febrile at the time of screening. In the incidence study cohort, after 2,303 person-weeks of follow-up, the incidence density of malaria was 1.3 cases per person-year with P. vivax predominating. Among individuals participating in the clinical trial, the 28-day chloroquine P. vivax cure rate was 100%. The 28-day chloroquine/sulphadoxine-pyrimethamine P. falciparum cure rate was 97%. The single treatment failure, confirmed by merozoite surface protein-2 genotyping, was classified as a day 28 late parasitological treatment failure. All P. falciparum isolates carried the Thr-76 pfcrt mutant allele and the double Asn-108 + Arg-59 dhfr mutant alleles. Dhps mutant alleles were not detected in the study sample. CONCLUSION: Peak seasonal malaria prevalence on Malo Island reached hypoendemic levels during the study observation period. The only in vivo malaria drug efficacy trial thus far published from the Republic of Vanuatu showed chloroquine/sulphadoxine-pyrimethamine combination therapy for P. falciparum and chloroquine alone for P. vivax to be highly efficacious. Although the chloroquine-resistant pfcrt allele was present in all P. falciparum isolates, mutant alleles in the dhfr and dhps genes do not yet occur to the extent required to confer sulphadoxine-pyrimethamine resistance in this population.

Seasonal prevalence of malaria in West Sumba district, Indonesia.

BACKGROUND: Accurate information about the burden of malaria infection at the district or provincial level is required both to plan and assess local malaria control efforts. Although many studies of malaria epidemiology, immunology, and drug resistance have been conducted at many sites in Indonesia, there is little published literature describing malaria prevalence at the district, provincial, or national level. METHODS: Two stage cluster sampling malaria prevalence surveys were conducted in the wet season and dry season across West Sumba, Nusa Tenggara Province, Indonesia. RESULTS: Eight thousand eight hundred seventy samples were collected from 45 sub-villages in the surveys. The overall prevalence of malaria infection in the West Sumba District was 6.83% (95% CI, 4.40, 9.26) in the wet season and 4.95% (95% CI, 3.01, 6.90) in the dry. In the wet season Plasmodium falciparum accounted for 70% of infections; in the dry season P. falciparum and Plasmodium vivax were present in equal proportion. Malaria prevalence varied substantially across the district; prevalences in individual sub-villages ranged from 0-34%. The greatest malaria prevalence was in children and teenagers; the geometric mean parasitaemia in infected individuals decreased with age. Malaria infection was clearly associated with decreased haemoglobin concentration in children under 10 years of age, but it is not clear whether this association is causal. CONCLUSION: Malaria is hypoendemic to mesoendemic in West Sumba, Indonesia. The age distribution of parasitaemia suggests that transmission has been stable enough to induce some clinical immunity. These prevalence data will aid the design of future malaria control efforts and will serve as a baseline against which the results of current and future control efforts can be assessed.

Plasmodium vivax-associated acute respiratory distress syndrome after extended travel in Afghanistan.

A 21-year-old soldier developed anorexia, vomiting, diarrhea and fever 10 days after returning to the United States from an 8-month deployment in Afghanistan. His symptoms persisted over the next 5 days until he presented in respiratory failure with a partial pressure oxygen: concentration of inspired oxygen (PaO(2):FiO(2)) ratio of 63, requiring urgent intubation and ventilator support. Chest roentgenogram revealed diffuse bilateral alveolar opacities consistent with acute respiratory distress syndrome. Although sputum and blood cultures did not reveal a causative agent, Giemsa-stained blood smears were positive for Plasmodium vivax alone, which was later confirmed by small subunit ribosomal RNA polymerase chain reaction amplification. After a tenuous course marked by splenic rupture and prolonged requirement for ventilator support, the patient ultimately recovered. Although generally considered benign, this and other recent reports of vivax malaria-associated lung injury emphasize the need for persistent pursuit of the diagnosis in febrile travelers returning from vivax endemic locations as well as aggressive monitoring for and management of life-threatening complications.

Nephrotic syndrome and unrecognized Plasmodium malariae infection in a US Navy sailor 14 years after departing Nigeria.

A 34-year-old Nigerian man presented with nephrotic syndrome. Renal biopsy revealed chronic membranous glomerulopathy with focal segmental sclerosis. Blood Giemsa smear contained rare Plasmodium sp. trophozoites and small subunit ribosomal RNA polymerase chain reaction amplification confirmed the presence of Plasmodium malariae. This case highlights the importance of obtaining even remote travel histories from ill immigrants and considering occult quartan malaria in patients from endemic locations with nephrotic syndrome.