There have been conflicting reports about the relationship between ABO blood groups, haemoglobin levels, haemoglobin genotypes and their susceptibility to falciparium malaria. A cross-sectional study of Plasmodium falciparium malaria in pregnant women in Uyo, South Eastern Nigeria was carried out to determine if there was any association between the disease and these genetic markers. Of the 540 women examined, 400 were pregnant, while 140 were non-pregnant healthy women (control). 164 (41.0%) of the pregnant women were positive for P. falciparum parasite. There was a significance difference (P<0.05) between the prevalence of malaria in the pregnant women and their controls. There was severe anaemia as revealed by the mean haemoglobin levels among the parasitaemic (9.80g/dl ± 2.11); a parasitaemic (11.40g/dl ± 1.33) pregnant women and control (12.45g/dl ± 1.82). It was statistically significant at P<0.05. There was no significant difference (P>0.001) in the frequency of the ABO antigens between the pregnant women with malaria and the expected. Parasitaemic pregnant women with sickle cell trait (Hb AS) had 39.8% prevalence rate, which was lower than 41.9% observed in those with normal haemoglobin (Hb AA), it was not significant (P>0.05). The need for a more practical approach in the treatment of falciparum malaria in pregnant women with different genetic markers is discussed.

In tropical Africa malaria is generally regarded to be hyperendemic or holoendemic unless special ecological and geographical features do not permit intensive transmission such as highland and semi-arid or arid areas (Wilson, 1949). About 93% of the 550 million people living in Africa are at risk of malaria infection (WHO, 1995). In the areas of stable hyperendemic or holoendemic malaria in tropical Africa, Anopheles gambiae, A. arabiensis or A. funestus are almost invariably the main vectors (McDonald, 1957; Bruce Chwatt 1971; Salako 1986). The prevailing parasite species is Plasmodium falciparum; with P. malariae and P. ovale in the second and third place (Wildling et al, 1995).

Falciparum malaria represents one of the major causes of mortality and morbidity throughout Nigeria, where it is holoendemic in status (Bruce-Chwatt 1952, Molineaux and Cramicia 1980, Aderoumu et al, 1980, Salako 1986, FMOH 1989). Falciparum malaria in pregnant versus non-pregnant women has a far more severe course with fairly frequent complications. It is generally agreed that during pregnancy women show an increased prevalence and intensity of malaria (Bruce-Chwatt 1957, Kortmann, 1972, Gilles and Warrel 1996). However it is not known if this increase relative to non-pregnant women remains unaltered with parity and/or age, (Bray and Anderson, 1979: Looareenswan et al, 1985). In hyperendemic areas both clinical symptoms and parasitaemia are worse in primigravid compared with multigravid women with malaria.

In Nigeria and other parts of the tropics were malaria is endemic the disease remains a major cause of maternal death, abortion, still birth, premature delivery, low birth weight and anaemia (Bruce-Chwatt, 1952, Fleming, 1986 and FMOH 1989). Since malaria in holoendemic or hyperendemic area is asymptomatic in pregnant women, there is often sudden and catastrophic fall in haemoglobin levels especially in the primigravid (Gilles et al, 1969). Haemoglobin level is known to be an important determinant of work capacity and is often used as a non-specific indicator of overall health status (Tracer, 1997).

There are documented reports about correlation between ABO blood groups and some infectious disease and evidence has been presented to indicate the presence or absence of relationships. Newman et al, (1961) reported a high incidence of gastric carcinoma and pernicious anaemia in people with blood group A. People with blood group A and B are known to be more susceptible to eosinophilia (Anand 1961). No correlation was found between the incidence of loiasis (Ogunba, 1970); bancroftian filariasis, (Ritaat et al, 1988; Romea et al, 1988) malaria and Schistosomiasis (Kazim and Ejezie (1982). Population, field and clinical studies have shown that where Plasmodium falciparum malaria is endemic, non-immune subjects who have sickle-cell trait Hb-AS have a survival advantage over subjects who have only normal adult haemoglobin (Hb-AA) as the presence of sickle-haemoglobin (Hb-S) in red cells limits the development and multiplication of the parasite (Luzzatto, 1979; Pasvol and Weatherall 1980).

Recent reports that Duffy blood group negative individuals are not susceptible to Plasmodium vivax infection (Miller et al, 1976), the conflicting report of Facer and Brown (1979) on Plasmodium falciparum and the doubt expressed by Carnevale et al (1981); Michel et al (1981) that sickle-cell trait confers any parasitological advantage on subjects Hb-AS, promoted us to investigate the relationship of these genetic markers with falciparum malaria in an area endemic for this disease. This is done with a view to recommending appropriate intervention strategies during pregnancy as one part of complete antenatal package designed to ensure optimal maternal and infant health.

The study was carried out in Uyo, South Eastern Nigeria. The town serves the dual purpose of a local government headquarters and state capital. It lies within the tropical rainforest belt of the country on Lat. 5⁰20, and 5⁰32, East of the Greenwich Moridian. There are two distinct seasons namely the wet season (March-October) and dry season (November – February). All over the town there are bushes and stagnant bodies of water that favours the breeding of mosquitoes. Uyo is relatively dense populated and the general sanitation standard is below average. Most of the inhabitants are of medium and low socio-economic status, who live in brick and mud houses with most of them not screened with nets. Majority of the women are housewives and peasant farmers whose husband’s wage income is generally below average. There are numerous privately owned hospitals that are being patronized by high-income earners due to their efficient services. However, due to the exorbitant cost of privately owned hospital most people in the town and surrounding rural communities visit the two Government owned tertiary health institutions where cases can be referred. These are the St. Luke’s Hospital Anua, Uyo and University of Uyo Teaching Hospital, Uyo (UUTH).

A total of 540 women were studied. Of this number 400 (74.07%) were pregnant and attending antenatal/clinic at St. Luke’s Hospital, Anua, Uyo, while 140 (24.93%) were healthy non-pregnant women of same age group, working at the hospital. This group served as control since they were afebrile, not on routine antimalaria prophylaxis and showed no parasites in their peripheral blood films.

Blood sample for parasite estimation, blood group and genotype assay, haemoglobin estimation were collected from both pregnant women and control subjects using standard venepuncture method as described by Cheesbrough (1993). About 4ml of blood was collected from each subject and dispensed into EDTA bottles.

A drop of the venous blood was placed on the slide and a thick film was made, air dried and read after application of the standard Giemsa staining method, using a light microscope with a x100 oil immersion lens and x10 eyepiece, infections of malaria species aside P. falciparum were excluded in this study

The haemoglobin concentration was measured spectrophotometrically by the cyanmethahemoglobin method of Hall and Malian (1991). 0.02ml of well mixed blood was added to 4ml of modified Drabkin solution. The mixture was allowed to stand for 3 minutes and the Hb concentration was read spectrophotometrically.

Blood groups were determined by the direct slide method using agglutinating A.,B and anti-D sera (Kazim and Ejezie, 1982).

Haemoglobin electrophoresis was performed on cellulase acetate as described by Lehmann and Huntsman (1975).

Of the 400 pregnant women examined 164 (41.00%) were infected with malaria parasite, while the blood films of the 140 control subjects were aparasitaemic. There was a significant difference (P<0.05) between the prevalence of malaria in pregnant women and their control (Table 1). The prevalence according to age showed that the age group of 21-25 years and 26-40 years had the highest percentage infection of 50%, followed by 31-35 years with 37.50% infection rate. The age bracket of 16-20 years had the least prevalence of 12.15% (Table 1).

Table 2, shows the haemoglobin concentration of pregnant women with and without falciparum malaria and their control. The mean haemoglobin values of 164 parasitaemic women was 9.84g/dl ± 2.11 (5.5 – 10.4g/dl) while the mean haemoglobin values of 236 pregnant women without malaria parasite was 11.40g/dl ± 1.33 (9.0 – 12.5g/dl). The control was 12.45g/dl ± 1.82 (10.2 – 13.4g/dl). These values were statistically significant with the expected at (P<0.05). The haemoglobin concentration of pregnant parasitaemic and aparasitaemic women were lower than those of the controls. The frequency of haemoglobin concentration in the 540 women is shown in figure 1. Table 3, show the distribution of ABO blood group in the subjects studied. The highest infection rate of 63.41% was recorded in blood group O, followed by blood group A with 24.39%. Chi-square analysis showed no statistical association (P<0.05) between the incidence of falciparum malaria and the population frequencies of the ABO blood group.

Table 4, gives the haemoglobin genotypes of the women. Parasitaemic pregnant women with sickle-cell trait (Hb AS) had a lower prevalence (40.24%) than infected pregnant women with normal haemoglobin Hb AA (59.76%). The prevalence between the two genotypes were not statistically significant (P<0.05).

The result from pregnant women reported here shows that despite the complete package of antenatal care, falciparum malaria is still prevalent among pregnant women in Nigeria. Malaria prevalence was significantly more in pregnant women than non-pregnant women. This report is similar to those documented by Gilles et al (1969) and McGregor (1984).

According to Bruce-Chwatt (1952); Kortmann (1972); Gilles and Warell (1993), who stated that during pregnancy women show an increase prevalence and intensity of malaria, because pregnancy is known to attenuate acquired immunity. Furthermore, during pregnancy there is increased production of many hormones, some of which notably cortisone can exert immune suppresant effect on pregnant women thereby predisposing them to malaria and other infectious diseases (McGregor et al, 1983).

The highest prevalence rate of 50% was observed in age group 21-25 years and 26-30 years. This finding is not unexpected because in Nigeria and other African countries this age groups are the child bearing group, with most of them in their first pregnancy (Primigravid). Reports by Brabin (1983), McGregor (1984), Gilles and Warrel (1973) have implicated the primigravidae as having a higher prevalence of malaria than the multigravidae. It is generally agreed that there is a decreased level of IgG specific for P. falciparum during early pregnancy.

The World Health Organisation cut-off for classifying a non-pregnant, non-lactating woman as anaemic is 12g/dl and for a pregnant woman is 11g/dl (WHO, 1972). The level of haemoglobin reported in this study is within the anaemic level classification of WHO. Several cases of severe anaemia were encountered in this study. The mean level of 9.8g/dl recorded in parasitaemic pregnant women is due to the fact that women with falciparum malaria haemolyse quickly resulting in a rapid fall of haemoglobin (Shulman & Dorman, 2000). The results agrees with the findings of Fleming (1985), Brabin (1990), Obi and Chukudebelu (1981), who worked on pregnant women in Nigeria and New Guinea. The low level of haemoglobin concentration found among pregnant women and their controls are likely to be multifactorial in origin resulting from chronic holoendemic malaria and hookworm infection (Jackson & Jackson, 1987) and inadequate intake of iron-rich foods especially animal protein (Jandl, 1987). Inadequate protein intake has also been found to interfere with iron utilization even in cases where iron intake is sufficient (Bruchanan, 1975). Fleming (1989) reported anaemia, specifically folate deficiency and megaloblastic anaemic to be a well described complication of malaria in pregnancy in Northern Nigeria. Apart from the effect of malaria casuing anaemia in pregnant women, the result also show that non-pregnant healthy women are also anaemic with mean haemoglobin of 12.45g/dl. The poor nutritional status resulting from poor economy of the country might have accounted for this observation, since most of the subjects attending the clinic, are low-income earners who might not be able to afford the high cost of proteinous foods.

The blood group distributions found in this study are similar to those previously reported for the same Nigeria population by Worlledge et al (1974); Gilles (1965); Araba (1975); Kazim and Ejezie (1982). The ABO blood group system has no relationship to the prevalence of falciparum malaria. The frequency distributions of the ABO blood group antigen in pregnant women with malaria were not significantly different from those of controls. Similar results have been obtained by Kazim and Ejezie (1982); Martins et al (1979); Facer and Brown (1979). However, this finding contrasts with that of Agbonlahor et al (1993) who reported the existence of an association between ABO blood group and malaria infection. It has been reported that Anopheles gambiae recognises ABO blood group variation with a preference for blood group O (Wood & Harrison, 1972) this observation might have accounted for the high percentage (64.41%) of blood group O infected with malaria. The preponderance of blood group O in the population may also be a factor for the high prevalence.

The prevalence of Plasmodium falciparum was less prevalent among pregnant women with Hb-AS than among those with Hb-AA, but differences in prevalence was statistically not significant (P>0.05). This confirms the report of Brabin and Pervin (1985); Bernstein et al. (1980) and contrast that of Fleming (1984) and Luzzatto (1979).

In view of the chronic anaemia observed in this study, it therefore becomes imperative that the administration of antimalaria drugs prophylatically during pregnancy should be one of the antenatal packages, since in holoendemic areas, malaria in pregnancy is often asymptomatic, so may go unsuspected and undetected. The campaign by public health workers on the need for good proteinous food during pregnancy should be enhanced.

The technical and professional assistance of Mr. Frank Asuquo and Mrs. Akpan of St. Luke’s Hospital Laboratory, Anua (Pathology Department) is highly appreciated.