Islands are choice settings for experimental studies of vector control strategies based on transgenic insects. Before considering this approach, knowledge of the population structure of the vector is essential. Genetic variation at 12 microsatellite loci was therefore studied in samples of the malaria vector Anopheles gambiae s.s., collected from six localities of Sã o Tomé island (West Africa). The objectives were (i) to assess the demographic stability and effective population size of A. gambiae from these sites, (ii) to determine population differentiation and (iii) to relate the observed patterns of population structure with geographic, ecological and historical aspects of the vector on the island.Significant population differentiation, revealed by F ST and R ST statistics, was found between the southernmost site, Porto Alegre, and northern localities. The observed patterns of population substructure are probably a result of restrictions to gene flow in the less inhabited, more densely forested and mountainous south. In all localities surveyed, A. gambiae appeared to be experiencing a demographic expansion, consistent with a relatively recent (ca. 500 years) founder effect. The results are discussed with respect to current and future prospects of malaria vector control.
BackgroundThe status of Toxoplasma gondii infection among primary schoolchildren (PSC) of the Democratic Republic of São Tomé and Príncipe (DRSTP), West Africa, remains unknown to date.MethodsA serologic survey and risk factors associated T. gondii infection among PSC in the DRSTP was assessed by the latex agglutination (LA) test and a questionnaire interview including parents’ occupation, various uncomfortable symptoms, histories of eating raw or undercooked food, drinking unboiled water, and raising pets, was conducted in October 2010. Schoolchildren from 4 primary schools located in the capital areas were selected, in total 255 serum samples were obtained by venipuncture, of which 123 serum samples were obtained from boys (9.8 ± 1.4 yrs) and 132 serum samples were obtained from girls (9.7 ± 1.3 yrs).ResultsThe overall seroprevalence of T. gondii infection was 63.1% (161/255). No significant gender difference in seroprevalence was found between boys (62.6%, 77/123) and girls (63.6%, 84/132) (p = 0.9). The older age group of 10 years had insignificantly higher seroprevalence (69.9%, 58/83) than that of the younger age group of 8 year olds (67.7%, 21/31) (p = 0.8). It was noteworthy that the majority of seropositive PSC (75.8%, 122/161) had high LA titers of ≥1: 1024, indirectly indicating acute or repeated Toxoplasma infection. Parents whose jobs were non-skilled workers (73.1%) showed significantly higher seroprevalence than that of semiskilled- (53.9%) or skilled workers (48.8%) (p < 0.05). Children who had a history of raising cats also showed significantly higher seroprevalence than those who did not (p < 0.001).Children who claimed to have had recent ocular manifestation or headache, i.e. within 1 month, seemed to have insignificantly higher seroprevalence than those who did not (p > 0.05).ConclusionsParents’ educational level and cats kept indoors seemed to be the high risk factors for PSC in acquisition of T. gondii infection. While, ocular manifestation and/or headache of PSC should be checked for the possibility of being T. gondii elicited. Measures such as improving environmental hygiene and intensive educational intervention to both PSC and their parents should be performed immediately so as to reduce T. gondii infection of DRSTP inhabitants including PSC and adults.
The impact of a vector eradication programme, conducted in the 1980s, on Anopheles gambiae populations from the islands of São Tomé and Príncipe, was evaluated by microsatellite DNA analysis. Significant genetic differentiation was observed within and between the two islands and between the islands and a population from Gabon, suggesting a degree of isolation between them. Large estimates of long-term N(e) suggested that the control programme did not affect the effective population size of the vector. Heterozygosity tests were also not consistent with a recent bottleneck.
The seroprevalence of Toxoplasma gondii infection among pregnant women in the Democratic Republic of Sao Tome and Principe (DRSTP) from November 2003 to March 2004 was determined by detection of serum anti-T. gondii antibodies. A short questionnaire interview for pregnant women was performed to investigate risk factors associated with T. gondii infection, including consumption of raw meat or unwashed vegetables, drinking unboiled water and keeping pets (cats and dogs). The overall seroprevalence of T. gondii infection was high (75.2%; 375/499). The older age group of > or =35 years had a significantly higher seroprevalence (85.7%; 54/63) than that of the younger age group of 15-25 years (70.4%; 178/253) (odds ratio 2.5, 95% CI 1.2-5.4; P=0.01). No significant difference in the seroprevalence of T. gondii infection was found between the pregnant women with and without exposure to the risk factors studied. However, among pregnant women with high antibody titers of > or =1:1024, it seemed likely that continual contact with pets and consumption of oocyst-contaminated water or raw unwashed vegetables rather than tissue cysts in meat was the primary route of infection. The incidence of congenital toxoplasmosis in unborn babies should be intensively monitored in the DRSTP.
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