Plasmodium diversity in non-malaria individuals from the Bioko Island in Equatorial Guinea (West Central-Africa).
BACKGROUND
In this paper we analyse the Plasmodium sp. prevalence in three villages with different isolation status on the island of Bioko (Equatorial Guinea) where malaria is a hyper-endemic disease. We also describe the genetic diversity of P. falciparum, using several plasmodia proteins as markers which show a high degree of polymorphism (MSP-1 and MSP-2). The results obtained from three different populations are compared in order to establish the impact of human movements and interventions.


METHODS
Plasmodium sp. were analysed in three villages on Bioko Island (Equatorial Guinea), one of which (Southern) is isolated by geographical barriers. The semi-nested multiplex polymerase chain reaction (PCR) technique was used to determine the prevalence of the four human plasmodia species. The genotyping and frequency of P. falciparum populations were determined by PCR assay target polymorphism regions of the merozoite surface proteins 1 and 2 genes (MSP-1 and MSP-2).


RESULTS
The data obtained show that there are no differences in plasmodia population flow between the Northwest and Eastern regions as regards the prevalence of the different Plasmodium species. The Southern population, on the other hand, shows a minor presence of P. malariae and a higher prevalence of P. ovale, suggesting some kind of transmission isolated from the other two. The P. falciparum genotyping in the different regions points to a considerable allelic diversity in the parasite population on Bioko Island, although this is somewhat higher in the Southern region than the others. There was a correlation between parasitaemia levels and the age of the individual with the multiplicity of infection (MOI).


CONCLUSIONS
Results could be explained by the selection of particular MSP alleles. This would tend to limit diversity in the parasite population and leading up to the extinction of rare alleles. On the other hand, the parasite population in the isolated village has less outside influence and the diversity of P. falciparum is maintained higher. The knowledge of parasite populations and their relationships is necessary to study their implications for control intervention.
Guerra-Neira
Ana
A
Centro de Referencia para el Control de Endemias, Centro Nacional de Medicina Tropical. Instituto de Salud Carlos III, Malabo, Bioko, Equatorial Guinea. lahullaguerra@hotmail.com
Rubio
José M
JM
Royo
Jesús Roche
JR
Ortega
Jorge Cano
JC
Auñón
Antonio Sarrión
AS
Diaz
Pedro Berzosa
PB
Llanes
Agustín Benito
AB
D000483:Alleles; D000818:Animals; D002648:Child; D002675:Child, Preschool; D016703:Equatorial Guinea / Q000453:epidemiology; D014644:Genetic Variation; D006801:Humans; D018512:Parasitemia / Q000145:classification / Q000453:epidemiology*; D010963:Plasmodium falciparum / Q000235:genetics* / Q000302:isolation & purification; D016133:Polymerase Chain Reaction; D015995:Prevalence; D013045:Species Specificity