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


METHODS
Parasitemia (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/.


RESULTS
A 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.


CONCLUSIONS
This 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.
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Hoseah M
HM
Akala
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Angela O
AO
Achieng
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Fredrick L
FL
Eyase
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Dennis W
DW
Juma
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Luiser
L
Ingasia
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Agnes C
AC
Cheruiyot
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Charles
C
Okello
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Duke
D
Omariba
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Eunice A
EA
Owiti
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Catherine
C
Muriuki
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Redemptah
R
Yeda
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Ben
B
Andagalu
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Jacob D
JD
Johnson
Global Emerging Infections Surveillance Program, United States Army Medical Research Unit-Kenya, Kenya Medical Research Institute, Walter Reed Project, Kisumu and Nairobi, Kenya.
Edwin
E
Kamau
PfMDR1-N86Y; Pfcrt-K76T; parasitemia; polymorphism