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INFECTIVITY OF PLASMODIUM FALCIPARUM GAMETOCYTES IN PATIENTS ATTENDING RURAL HEALTH CENTRES IN WESTERN KENYA
Abstract
ABSTRACT
Background: Experimentally studying the transmission of the malaria parasite and its
regulating factors requires availability of human blood donors carrying infectious gametocytes.
The difficulty of identifying gametocyte carriers from the community is often limited due
to financial and human resources constraints. The available alternative is rural health
centres where malaria patients go for treatment. In this study, the potential of recruiting
volunteers and acquiring infectious blood for experimental infections from rural health
centers in malaria endemic area was examined through routine patient diagnosis.
Objective: To examine the patients presenting at rural health centers for the potential to
carry sexual stage malaria parasite and test their infectivity to Anopheles gambiae
mosquitoes.
Setting: Mbita Health Centre, Mbita Town Ship, Suba District, western Kenya.
Methodology: Routine survey of all patients attending Mbita Health Centre with suspected
malaria. Patients were examined for Plasmodium falciparum trophozoites and gametocytes.
Gametocyte-positive volunteers were recruited for their potential to infect Anopheles
mosquitoes via membrane feeding.
Results: Three thousand nine hundred and eighty seven patients were screened between
May 2000 and April 2001. Plasmodium falciparum was the predominant parasite species
and P. malariae being the only minor species, accounting for 0.9% of malaria cases. Clinical
malaria varied with age and prevailed throughout the year with a slight seasonality.
Gametocyte prevalence was low (0.9-6.6%), and gametocyte densities were generally very
low with a geometric mean of 39 gametocytes per μl blood. Children aged >5 years
constituted 67% of all gametocyte carriers. Only 22 volunteers with mean gametocytes
density of 39.62 per μl blood (range: 16-112) were recruited for study of parasite
infectiousness to laboratory-reared mosquitoes. Only two patients infected 1% of 1099
mosquitoes with one or two oocysts.
Conclusion: The low gametocyte densities or other possible host and vector related factors
regulating infectivity of gametocyte carriers to mosquitoes may have caused the poor
infections of mosquitoes. This study indicates that rural health centers in malaria-endemic
areas may not be suitable for recruiting infectious gametocyte donors for studies of vector
competence. They are suitable for passive clinical case surveillance and for evaluation of
the effects of control measures.
Background: Experimentally studying the transmission of the malaria parasite and its
regulating factors requires availability of human blood donors carrying infectious gametocytes.
The difficulty of identifying gametocyte carriers from the community is often limited due
to financial and human resources constraints. The available alternative is rural health
centres where malaria patients go for treatment. In this study, the potential of recruiting
volunteers and acquiring infectious blood for experimental infections from rural health
centers in malaria endemic area was examined through routine patient diagnosis.
Objective: To examine the patients presenting at rural health centers for the potential to
carry sexual stage malaria parasite and test their infectivity to Anopheles gambiae
mosquitoes.
Setting: Mbita Health Centre, Mbita Town Ship, Suba District, western Kenya.
Methodology: Routine survey of all patients attending Mbita Health Centre with suspected
malaria. Patients were examined for Plasmodium falciparum trophozoites and gametocytes.
Gametocyte-positive volunteers were recruited for their potential to infect Anopheles
mosquitoes via membrane feeding.
Results: Three thousand nine hundred and eighty seven patients were screened between
May 2000 and April 2001. Plasmodium falciparum was the predominant parasite species
and P. malariae being the only minor species, accounting for 0.9% of malaria cases. Clinical
malaria varied with age and prevailed throughout the year with a slight seasonality.
Gametocyte prevalence was low (0.9-6.6%), and gametocyte densities were generally very
low with a geometric mean of 39 gametocytes per μl blood. Children aged >5 years
constituted 67% of all gametocyte carriers. Only 22 volunteers with mean gametocytes
density of 39.62 per μl blood (range: 16-112) were recruited for study of parasite
infectiousness to laboratory-reared mosquitoes. Only two patients infected 1% of 1099
mosquitoes with one or two oocysts.
Conclusion: The low gametocyte densities or other possible host and vector related factors
regulating infectivity of gametocyte carriers to mosquitoes may have caused the poor
infections of mosquitoes. This study indicates that rural health centers in malaria-endemic
areas may not be suitable for recruiting infectious gametocyte donors for studies of vector
competence. They are suitable for passive clinical case surveillance and for evaluation of
the effects of control measures.
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