Five-year tracking of Plasmodium falciparum allele frequencies in a holoendemic area with indistinct seasonal transitions

Abstract

BackgroundThe renewed malaria eradication efforts require an understanding of the seasonal patterns of frequency of polymorphic variants in order to focus limited funds productively. Although cross-sectional studies in holoendemic areas spanning a single year could be useful in describing parasite genotype status at a given point, such information is inadequate in describing temporal trends in genotype polymorphisms. For Plasmodium falciparum isolates from Kisumu District Hospital, Plasmodium falciparum chloroquine-resistance transporter gene (Pfcrt-K76T) and P. falciparum multidrug resistance gene 1 (PfMDR1-N86Y), were analyzed for polymorphisms and parasitemia changes in the 53 months from March 2008 to August 2012. Observations were compared with prevailing climatic factors, including humidity, rainfall, and temperature.MethodsParasitemia (the percentage of infected red blood cells per total red blood cells) was established by microscopy for P. falciparum malaria-positive samples. P. falciparum DNA was extracted from whole blood using a Qiagen DNA Blood Mini Kit. Single nucleotide polymorphism identification at positions Pfcrt-K76T and PfMDR1-N86Y was performed using real-time polymerase chain reaction and/or sequencing. Data on climatic variables were obtained from http://www.tutiempo.net/en/.ResultsA total of 895 field isolates from 2008 (n=169), 2009 (n=161), 2010 (n=216), 2011 (n=223), and 2012 (n=126) showed large variations in monthly frequency of PfMDR1-N86Y and Pfcrt-K76T as the mutant genotypes decreased from 68.4%±15% and 38.1%±13% to 29.8%±18% and 13.3%±9%, respectively. The mean percentage of parasitemia was 2.61%±1.01% (coefficient of variation 115.86%; n=895). There was no correlation between genotype or parasitemia and climatic factors.ConclusionThis study shows variability in the frequency of Pfcrt-K76T and PfMDR1-N86Y polymorphisms during the study period, bringing into focus the role of cross-sectional studies in describing temporal genotype trends. The lack of correlation between genotypes and climatic changes, especially precipitation, emphasizes the cost of investment in genotype change.

Persistence of chloroquine resistance alleles in malaria endemic countries: a systematic review of burden and risk factors

“…of 76T CQR allele AF PCTrends in prev. of 86Y CQR allele AF PCAndriantsoanirina et al [37]18.7 nM (95% CI 14.7–23.7 nM)Madagascar2005NRNRAchieng et al [19]NRKenya19992008–2014: 28.5%, 2014: 2.3%2008–2014: 14.9%Hemming-Schroeder et al [20]NRKenya1999Kakamega2003: 80%2005: 61%2008: 60%2015: 2.7%Kombewa2003: 71%2005: 91.9%2008: 90%2015: 11.8%Kakamega2003: 59.2%2005: 59.1%2008: 40%2015: 4.2%Kombewa2003: 57.1%2005: 40%2008: 45%2015: 5%Akala et al [46]NRKenya19992008: 68.4%2009: 55.4%2010: 47.8%2011: 12.4%2012: 29.8%2008: 38.1%2009: 24.3%2010: 19.7%2011: 7.8%2012: 13.3%Lucchi et al [22]2010: 31.77 nM2011: 23.42 nM2012: 21.09 nM2013: 19.85 nMKenya19992010: 38.8%2011: 28.6%2012: 18.7%2013: 7%2010: 2%2011: 1.5%2012: 0%2013: 0%Okombo et al [18]NRKenya19992006: 49.5%2013: 17.2%2006: 57.5%2013: 2.1%Mwai et al [21]63 ± 90 nM (5-150 nM)Kenya19991993–2006: 94% to 63%1993–2006: 75%Bo Huang et al [35]NRGrande Comore Island20042006–2014: 72.2–19.5%2006–2007: 87%2013–2014: 40.2%Das et al [28]Kolkata2013: 238.6 nM, (95% CI 121–321 nM)Purulia2013: 247.42 nM, (95% CI 126–316 nM)India1982Kolkata2012: 94.64%Purulia2012: 96.15%K...…”

“…A high proportion, 65.8% (25/38) of the studies reported occurrence of mixed genotype infections. Six studies reported mixed 76T/86Y infections (Indonesia: [ 45 ]; India: [ 41 ]; Kenya: [ 46 ]; Benin: [ 23 ]; Mozambique: [ 16 ]). Thirteen studies reported presence of 76T/K and 86Y/N genotype in P. falciparum infections.…”

Peer Review #1 of "A seven-year surveillance of epidemiology of malaria reveals travel and gender are the key drivers of dispersion of drug resistant genotypes in Kenya (v0.1)"

“…Since effective vaccines for malaria are still way off, and drugs are most relied upon, success of malaria control strategies are dependent on understanding factors that influence dispersion of malaria drug resistance genotypes. Most studies on CQR appear inconclusive on methods of containing it's spread due to insufficient demographic and clinical information (Akala et al, 2014;Angira, Otieno, Muga, & Abong'o, 2010;Zhong et al, 2008). This study showed that travel, gender and clinical factors were associated with chloroquine resistance among symptomatic malaria cases in four of the five malaria epidemic zones in Kenya.…”

“…However, in endemic regions, males may delay seeking treatment and risk accumulating super infection. Research has shown that mutant strains that develop drug resistance enhance virulence (Shahinas, Folefoc, & Pillai, 2013) wanton utilization of resources and therefore eliciting symptoms that distorts the host/parasite balance that would allow wild type parasites to remain asymptomatic (Akala et al, 2014;Deroost, Pham, Opdenakker, & Van den Steen, 2016).…”

The Genotypic and Phenotypic Stability of Plasmodium falciparum Field Isolates in Continuous In Vitro Culture

“…The division of experimental therapeutics of the WRAIR supplied the following drugs: chloroquine diphosphate (CQ), dihydroartemisinin (DHA), artemether (AT), mefloquine (MQ) and lumefantrine (LU). SYBR green I assay technique [ 18 ] with additional modification [ 19 ] was used for drug susceptibility testing of the parasites. Drugs were dissolves in dimethyl sulfoxide before performing a 2-fold serial dilution in tissue culture media to dose ranges of DHA (700 nM to 0.69 nM), LU (378 nM to 0.37 nM), MQ (1200 nM to 1.1 nM), AT (670 nM to 0.65 nM) and CQ (883 nM to 3.79 nM); 3.2 μL of the drug diluents were aliquoted into 384-well plates.…”