Infectivity of asymptomatic Plasmodium-infected human populations to Anopheles dirus mosquitoes in western Thailand.
The infectivity of Plasmodium-infected humans in western Thailand was estimated by feeding laboratory-reared Anopheles dirus Peyton and Harrison mosquitoes on venous blood placed in a membrane-feeding apparatus. Between May 2000 and November 2001, a total of 6,494 blood films collected during an active malaria surveillance program were checked by microscopy for the presence of Plasmodium parasites: 3.3, 4.5, and 0.1% of slides were P. falciparum- (Pf), P. vivax- (Pv), and P. malariae (Pm)-positive. Venous blood was collected from 70, 52, 6, and 4 individuals infected with Pf, Pv, Pm, and mixed Pf/Pv, respectively, with 167 uninfected individuals serving as negative controls. Only 10% (7/70), 13% (7/52), and 0% (0/6) of membrane feeds conducted on Pf-, Pv-, and Pm-infected blood yielded infected mosquitoes. One percent (2/167) of microscope-negative samples infected mosquitoes; however, both samples were subsequently determined to be Pf-positive by polymerase chain reaction. Gametocytes were observed in only 29% (4/14) of the infectious samples. All infections resulted in low oocyst loads (average of 1.2 oocysts per positive mosquito). Only 4.5% (10/222) of mosquitoes fed on the seven infectious Pf samples developed oocysts, whereas 2.9% (9/311) of mosquitoes fed on the seven infectious Pv samples developed oocysts. The probability of a mosquito becoming infected with Pf or Pv after a blood meal on a member of the human population in Kong Mong Tha was estimated to be 1 in 6,700 and 1 in 5,700, respectively. The implications toward malaria transmission in western Thailand are discussed.
Coleman
Russell E
RE
Department of Entomology, U.S. Army Medical Component, Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
Kumpitak
Chalermpon
C
Ponlawat
Alongkot
A
Maneechai
Nongnuj
N
Phunkitchar
Vichit
V
Rachapaew
Nattawan
N
Zollner
Gabriella
G
Sattabongkot
Jetsumon
J
D000293:Adolescent; D000328:Adult; D000818:Animals; D000852:Anopheles / Q000469:parasitology*; D002648:Child; D002675:Child, Preschool; D005843:Geography; D006801:Humans; D007113:Immunity, Innate; D007223:Infant; D008288:Malaria / Q000453:epidemiology* / Q000276:immunology*; D008875:Middle Aged; D010961:Plasmodium / Q000472:pathogenicity*; D010963:Plasmodium falciparum; D010966:Plasmodium vivax; D011156:Population Density; D013785:Thailand / Q000453:epidemiology