Plasmodial Prevalence with Respect to Gender in 6 Villages Around Balombo Town, Benguela Province, Angola, before Malaria Vector Control Implementation

Background: The different susceptibility of gender to infectious diseases is still a matter of concern and several studies were devoted to these issues; for malaria, recent studies reported a comparable “Force of Infection” in both gender while women could have a faster elimination of parasite than men.

Study Area and duration Period of the Research: The study was done in villages around Balombo town, Benguela Municipality, Angola and initially scheduled for 5 years since year 2007 with 2 years before vector control implementation and 3 years after.

Objectives of the research. The village scale malaria vector control program was planned and implemented to compare 4 methods of vector control with comprehensive entomological and parasitological evaluation, focusing on symptomless randomly selected patients, and noticing age and gender during each field survey for further analysis.

Study Design: To check an eventual gender difference, we decided to analyze the parasitological data gained during the 56 cross sectional surveys (CSS) done during 2 consecutive years in the 6 villages used as “control” i.e. before implementation of vector control operations (VCO) considering the gender of symptomless patients (≤15 years old) surveyed. We considered 2 indicators: Plasmodial Prevalence (PP) and Parasite Load (PL).

Main Results: 6727 thick blood smears (TBS) were prepared during these 56 CSS, and microscopically examined; the sex ratio of this total sample was well balanced with 3406 TBS (=50.6%) from men (“M”) and 3321 TBS (49.4%) from women (W”). The overall Plasmodial prevalence (all Plasmodium sp gathered because P. falciparum infections, as already noticed, are largely preponderant) were similar 41.02% for M and 40.1% for W.

The overall plasmodial prevalence significantly decreased from Year 2007 to Year 2008: respectively 47.8% (n= 2686) and 35.7% (n= 4041); but the plasmodial prevalence were similar each year between gender: in year 2007: PP= 48.9% (n=1338) for M and 46.7% (n= 1348) for W and in year 2008: 35.9% (n=2068) for Men and 35.6% (n=1973) for Women.

In Year 2007 the PP of Men and Women were similar in each village; in Year 2008 the PP were similar in 5 villages, but in Libata PP was significantly higher in Men than in Women.

The trends of change from year to year appeared similar for gender excepted in Capango where the PP remained similar in W and significantly decreased for M.

In term of Parasite Load the comparison of median of parasitaemia with the non-parametric Mann-Whitney test showed similar distribution between gender each year in each village and their evolution from year to year appeared also similar in each gender excepted for Men in Libata.

Conclusion: These possibilities of changes of plasmodial infections according to gender with time and villages must be taken into consideration when planning, implementing and analyzing parasitological data of symptomless carriers before, and after, a vector control program which must be implemented on a long term basis. They show that an “only one” CSS could lead to wrong information and conclusion of malaria and gender and the recommendation to carry on longitudinal regular field studies for relevant conclusion on malaria infections among communities.

The next step will be to analyze the plasmodial infection in both gender after vector control implementation.