Reconstrucción de la historia

In this study, the age group 0-9 years recorded the highest number of P. falciparum infections with 36.7 % of the total 169 positive individuals. This is consistent with the age-related patterns of prevalence of malaria for a typical endemic area (Ng’ong'a, 2012). The age categories 0-9, 30-39, 40-49 and 60-69 years were statistically significant suggesting that individuals within these age categories are more susceptible to P. falciparum than the other age categories. This implies that the individual’s age category may be a risk factor to acquiring P. falciparum infection.

Possible explanation for the significant association of age group 0-9 years is because young children are much more vulnerable to all forms of malaria (Malaria. www.malariaconsortium.org). The immune system of infants is not yet fully developed, while in children under five years they have not yet developed effective resistance to the disease. As the children grow and are bitten repeatedly by an infected mosquito they

gradually build up resistance to the malaria parasites. Therefore, older and stronger children of age above 15 years have a better chance of fighting the disease (Markell et al., 1998; Malaria. www.againstmalaria.com/faq_malaria).

The results of the current study revealed that age category between 30-49 years had high number of malaria infected individuals (21.9 %). Some of the women in this age group were pregnant and this could have accounted for high malaria infection at this age category. Pregnant women constitute a special group with specific symptoms not expected in an immune adult due to lowered immunity coupled with parasitization of the placenta. Studies have shown that infection rates are highest in first and second parity women with lower rates in later pregnancies (Duffy et al., 2005). This could have accounted for high malaria infections at age category 30-35 year. Pregnant women with malaria have an increased risk of abortion, stillbirth, premature delivery and low-birth weight infants (Guyatt et al., 2001; Steketee et al., 2001). Such children have reduced immunity and might succumb to malaria infection since children at age category 0-9 are at higher risk. The current study has also revealed that old people of age 60-69 were at risk since 14.2 % of the sampled populations were positive. This could be attributed to their reduced immunity due to old age.

Considering mean parasitaemia levels in individuals of different age sets (Table 4.5), it was observed that age 0-9 had high levels of mean parasitaemia followed by individuals of age category 60-69 year. Regression analysis revealed that there was a strong positive relationship between age category and parasitaemia levels. This supports that the individual’s age category may be a risk factor to acquiring complicated cases of P.

falciparum infection. The observed decline in parasite density from age groups 0-9 to 10- 19 and 20-29 is most likely to be due to the development of non-sterile clinical immunity over time. This background immunity regulates infection and is usually pronounced in children above 15 years and in adults (Markell et al., 1998). These are people who have been exposed to mosquito bites over the years, hence to malaria many more times. Such limited immunity enables the individuals to exhibit low parasitaemia levels in their blood and tolerate severe malaria infection though they may get malarial fever (Markell et al., 1998).

In a study done to determine levels of parasitaemia and changes in some liver enzymes among malaria infected patients in Edo-Delta Region of Nigeria, it was concluded that live enzyme activities correlated positively with age. Therefore, as age group increased, enzyme activities also increased and hence advancing age may worsen the effect of malarial infection on hepatic integrity (Onyesom et al., 2011) owing to the fact that the life cycle of P. falciparum involves exo-erythrocytic cycle which occurs in the liver where the ruptured schizonts are released into the blood circulation. This could also partly explain why individuals of age group 60-69 years had high levels of P. falciparum parasitaemia in the current study.

5.1.6 Rhesus factor and Plasmodium falciparum infections

The current study provides evidence that majority of the sampled individuals were Rhesus positive, 90.2 %, while few were Rhesus negative, 9.8 % (Table 4.8). This is in agreement with other studies done in Niger Delta, Nigeria by Emelike and Jeremiah, (2010) where they reported that Rhesus positive accounted for 91.3 % while Rhesus

negative was 8.7 %. Similarly, studies on the distribution of ABO and Rh blood groups among indigenes of Abuja, Nigeria reported high prevalence of Rhesus positive subjects compared to Rhesus negative subjects which were 95.7 % and 4.3 % respectively (Olaniyan et al., 2013).

Considering the infected individuals, a high proportion (90.5 %) were Rhesus positive while Rhesus negative individuals were 9.5 %. Chi-square revealed a positive association between Rhesus positive individuals and P. falciparum infections (χ2 _{= 80.6, df= 1, p=} 0.0001). On the other hand, Rhesus negative individuals showed lack of association with P. falciparum infections (χ2 _{= 445.2, df= 1, p= 0.067). The results from the current study} therefore suggest that Rhesus positive individuals are more likely to be infected with P. falciparum infections than Rhesus negative individuals living in the same malaria endemic area. In earlier studies done in Portuchuelo, Brazil, no significant associations were observed between rhesus factor and P. falciparum infections (χ2=8.943, df=1, P=0.257). Since Rh blood group system consists of different antigens (D, C, c, E and e), the researchers were further prompted to retest the association using the other phenotypes and they found that individuals with EE antigen exhibited a higher number of malaria episodes than individuals with ee antigens (Beiguelman et al., 2003).