Infectious Diseases in Clinical Practice:
Plasmodium falciparum Malaria, Human Immunodeficiency Virus Infection, and Anemia During Pregnancy in Eastern Nigeria: The Public Health Implication
Uneke, Chigozie J. BSc, MSc*; Duhlinska, Dochka D. BSc, MSc, PhD†; Igbinedion, Esther B. BSc‡
*Department of Medical Microbiology/Parasitology, Faculty of Clinical Medicine, Ebonyi State University, Abakaliki; †Department of Zoology, Faculty of Natural Sciences, University of Jos; Jos and ‡Department of Applied Microbiology, Faculty of Applied and Natural Sciences, Ebonyi State University, Abakaliki, Nigeria.
Address correspondence and reprint requests to Chigozie J. Uneke, BSc, MSc, Department of Medical Microbiology, Faculty of Clinical Medicine, Ebonyi State University, P.M.B. 053 Abakaliki, Nigeria. E-mail: firstname.lastname@example.org.
Malaria, human immunodeficiency virus (HIV) infection, and anemia constitute major public health problems during pregnancy. These were assessed among pregnant women in southeastern Nigeria using standard techniques. Of the 480 women studied, 72 (15.0%, 95% confidence interval [CI], 11.8%-18.2%) had Plasmodium falciparum infection, and the prevalence was significantly higher among primigravidae than multigravidae (χ2 = 10.2, P < 0.05). Twenty-one (4.4%) of the women were HIV positive, and P. falciparum prevalence was significantly higher among them (38.1%, 95% CI, 17.3%-58.9%) than HIV-negative women (13.9%, 95% CI, 10.7%-17.1%; χ2 = 9.19, P < 0.05). P. falciparum prevalence was significantly associated with lower packed cell volume (χ2 = 14.20, P < 0.05). Prevalence of anemia (packed cell volume <33%) was significantly higher among women with P. falciparum (χ2 = 5.19, P < 0.05) and HIV infection (χ2 = 4.30, P < 0.05). Provision of sustainable and affordable integrated preventive maternal health services is crucial for reducing the burden of malaria, HIV infection, and anemia.
Infections by human Plasmodium parasites that cause malaria and human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome, represent major public health problems in many parts of the world. Both infections have been described as 2 of the greatest medical challenges facing developing nations today, particularly in the tropical and subtropical regions of the world.1 Together, malaria and HIV infection cause more than 4 million deaths per year, and both are scourges of nations of Africa, India, Southeast Asia, and South America.2,3
Malaria has been described as the disease of poverty and underdevelopment and remains the most complex and overwhelming health problem facing humanity in the vast majority of tropical and subtropical regions of the world, with 300 to 500 million cases and 2 to 3 million deaths per year.4 About 90% of all malaria deaths in the world today occur in the sub-Saharan Africa, and this is because most infections are caused by Plasmodium falciparum, the most dangerous of the 4 human malaria parasites, accounting for an estimated 1.4 to 2.6 million deaths per year in this region.5 In areas where malaria is highly endemic, a protective semiimmunity against P. falciparum is acquired during the first 10 to 15 years of life, and most of the malaria-related morbidity and mortality happen in young children.6 However, in contrast with low malaria prevalence in adults, pregnant women in endemic areas are highly susceptible to malaria, and both the frequency and the severity of disease are higher in pregnant than nonpregnant women.7 Malaria during pregnancy, therefore, is a serious problem in sub-Saharan Africa, affecting an estimated 24 million pregnant women.8 Each year, between 75,000 and 200,000 infant deaths are attributed to malaria infection in pregnancy globally.5,8 Pregnancies in women living in malaria-endemic regions particularly in sub-Saharan Africa are associated with a high frequency and density of P. falciparum parasitemia, with high rates of maternal morbidity including fever and severe anemia, with abortion and stillbirth, and with high rates of placental malaria, and consequently, low birth weight in newborns caused by both prematurity and intrauterine growth retardation.8,9
The effects of HIV on maternal health have been superimposed on that of malaria in the malaria-endemic regions, particularly the sub-Saharan Africa.9 Concerning the global HIV epidemic, the sub-Saharan Africa remains by far the worst affected region with 25.4 million people living with HIV (just less than two thirds, ie, 64% of all people living with HIV).10 The HIV/acquired immunodeficiency syndrome epidemic is affecting the women most severely, and because heterosexual transmission is predominant in the subregion, women of reproductive age make up almost 57% of adults living with HIV, accounting for up to 80% of the world's HIV-infected women, with HIV prevalence rates sometimes exceeding 40% among pregnant women.10,11 Because of the high prevalence of HIV and malaria in sub-Saharan Africa, coinfections are common. The 2 diseases have been identified to critically intersect in pregnancy and have serious consequences in pregnant women, their fetuses, and infants.9,12
Anemia in pregnancy has been described as an enormous medical challenge and a major public health problem in Africa and an important factor associated with increased risk for poor pregnancy outcomes, and maternal morbidity and mortality in developing countries.13 In the sub-Saharan Africa, anemia prevalence rate as high as 95.4% has been reported among pregnant women.14 Although the etiology of anemia in pregnancy in the sub-Saharan Africa is complex and multifactorial,15 apart from an iron- and folate-deficient diet and infections such as hookworm, it is well established that malaria and HIV infection are the major causes of anemia in pregnancy in the subregion.16,17
Despite the considerable number of scientific investigations on malaria in pregnancy in the sub-Saharan Africa, a comprehensive evaluation of malaria during pregnancy and its association with maternal anemia and HIV infection has not been conducted in Nigeria and many parts of West Africa. Because of the paucity of comprehensive population-based data, the formulation of policies that would transform into effective and sustainable malaria intervention/control programs for pregnant women is still an enormous challenge to health policy makers in this part of the globe. The present study was designed to provide scientific information that can be used to direct policy development and control program implementation and also provide a baseline measurement on which the impact of interventions can be evaluated.
MATERIALS AND METHODS
This investigation was conducted at the Ebonyi State University Teaching Hospital (EBSUTH), Abakaliki, the capital of Ebonyi State, eastern Nigeria from July 2005 to June 2006. Apart from being the largest health facility in the area, the choice of the hospital was because it serves as a referral center for gynecologic services and run the biggest antenatal clinic (ANC) in Ebonyi State. The study area is defined by longitude 8°6′6″E and latitude 6°22′28″N, elevated at 380 feet above sea level. The vegetation characteristic is that of the tropical rain forest, with an average annual rainfall of about 1600 mm and an average atmospheric temperature of 30°C. There are 2 distinct seasons, the wet and the dry seasons, the former takes place between April and October, whereas the latter occurs from November to March. Malaria transmission in the area is perennial but usually at the peak toward the end of the rainy season.
Ethical approval of this study was obtained from the Faculty of Clinical Medicine (Infectious Diseases Research Division, Department of Medical Microbiology), Ebonyi State University, Abakaliki, and from the ethical committee of the EBSUTH, Abakaliki. The approval was on the agreement that patient anonymity must be maintained, good laboratory practice/quality control ensured, and that every finding would be treated with utmost confidentiality and for the purpose of this research only. All work was performed according to the international guidelines for human experimentation in clinical research.18
Study Population/Sampling Technique
Pregnant women in their various pregnancy trimesters who visited the ANCs of the EBSUTH, Abakaliki, for routine pregnancy care at their first ANC booking since commencement of pregnancy were considered for the study. All the subjects were verbally notified before sample collection, and their informed consent was duly obtained. The age of each woman, parity, and pregnancy trimester were determined by interview. None of the women included in the study received malaria treatment at least 2 months before enrollment into the study. This was one of the study inclusion criteria. About 4 mL of blood sample was obtained by venipuncture from each patient for analysis. For the purpose of the research, no personal identifiers (names, identification number, address, etc) were used on the blood sample of the participants. Instead, bar-coded numbers were used to ensure anonymity of the donors to facilitate laboratory procedures and minimize the chances of errors during the handling of the blood specimens. All specimens were analyzed within 1 hour of collection.
Giemsa-stained thick and thin blood films were performed and the Plus System was used for the determination of parasite density as previously outlined.19 All the films were double checked blindly by experienced parasitologists, and if there were differences, an additional assessment was made by another observer, and the average of the 2 agreeing counts using the Plus System was recorded. The packed cell volume (PCV) of each subject was determined using the hematocrit centrifugation technique and was expressed in percentage.20 The World Health Organization definition of anemia in pregnancy, that is, hemoglobin concentration of less than 11 g/dL corresponding to PCV of less than 33% by applying the constant factor of 0.321 was adopted in this investigation. The HIV Tri Line Test kits, commercially available (Biosystem INC, Vienna, Austria) were first used to screen each subject's serum sample, which was separated from the blood to detect antibodies to HIV-1 and HIV-2. Thereafter, the HIV-seropositive samples were confirmed by immunoblot analysis using the Bio-Rad New Lav Blot kits, commercially available (Bio-Rad, Novapath Diagnostic Group, Hercules, Calif). Manufacturer's instructions were strictly followed to determine the serostatus of the samples.
Differences in proportion were evaluated using the χ2 test. Statistical significant was achieved if P < 0.05.
A total of 480 women in their various pregnancy trimesters were sampled for the study. The average age was 28.0 years and ranged from 15 to 40 years. According to the criteria of this investigation, malaria parasites were found in the peripheral blood of 72 (15.0%, 95% confidence interval [CI], 11.8%-18.2%) women. Of the infected individuals, 44 (61.1%) had 1 to 10 parasites per 100 thick film fields (+), 26 (36.1%) had 11 to 100 parasites per 100 thick film fields (++), whereas 2 (2.8%) had above 100 parasites per 100 thick film fields (+++). P. falciparum was identified in all the infected cases.
Of the 480 women enrolled, the PCV was determined for 394 of them. When the prevalence of malaria parasite infection was associated with maternal age, individuals of age group 20 to 24 years old had the highest prevalence of positive smears (20.5%, 95% CI, 16.8%-24.2%), whereas the lowest prevalence was recorded among those aged 15 to 19 years old (10.9%, 95% CI, 8.0%-14.0%), but there was no significant difference in the trend (χ12 = 4.52, P > 0.05; Table 1). Relating malaria prevalence to obstetrics history such as parity and pregnancy trimester, it was observed that the prevalence of positive malaria smears was higher among the primigravidae (24.5%, 95% CI, 21.0%-28.9%) than the multigravidae (12.2%, 95% CI, 9.1%-14.9%), and the difference was statistically significant (χ12 = 10.2, P < 0.05). Although individuals in their second pregnancy trimester had more malaria parasite-positive smears (18.4%, 95% CI, 14.5%-21.5%) than those in their third (13.8%, 95% CI, 10.9%-17.1%) and first (10.0%, 95% CI, 7.3%-12.7%) trimester, there was no statistically significant difference in the trend (χ22 = 2.02, P > 0.05; Table 1).
A total of 21 (4.4%) of the women were HIV positive (Table 1). Malaria prevalence was significantly higher among the HIV-positive (38.1%, 95% CI, 17.3%-58.9%) than the HIV-negative (13.9%, 95% CI, 10.7%-17.1%) women (χ12 = 9.19, P < 0.05; relative risk, 2.74; 95% CI, 1.28-4.20; odds ratio, 0.37; 95% CI, 0.17-0.91; Table 1). Results indicated that the highest prevalence of malaria (25%, 95% CI, 21.1%-30.6%), was observed among the individuals with PCV 24% or less, followed by those with PCV 25% to 29% (23.4%, 95% CI, 18.8%-27.2%). The lowest malaria prevalence of 9.7% (95% CI, 11.5%-18.5%) was recorded among individuals with PCV 30% to 34%. Statistical analysis indicated a significant difference in the trend (χ32 = 14.2, P < 0.05; Table 1).
In this investigation, anemia was described as PCV of less than 33%. A total of 330 (83.8%) of the women had PCV values less than 33% (Table 2). The primigravidae were significantly more anemic than the multigravidae (91.0% vs. 81.9%; χ12 = 3.93, P < 0.05). Furthermore, women in their second pregnancy trimester had a comparatively higher proportion of anemia than their counterparts in their first and third trimesters, and the difference was statistically significant (χ22 = 6.5, P < 0.05; Table 2). The prevalence of anemia was significantly higher among women with malaria (94.4%) than those without malaria (5.6%) (χ12 = 7.17, P < 0.05). All the HIV-infected women were anemic, and the difference was statistically significant (χ12 = 4.30, P < 0.05; Table 2).
In the present investigation, the maternal malaria prevalence rate of 15.0%, referring to prevalence of parasitemia found during the first prenatal visit, was obtained. This was comparable to findings of recent studies from other malarious areas of the sub-Saharan Africa including eastern Sudan, where the prevalence of malaria among pregnant women was 17.4%,22 in Bamako, Mali, where the prevalence was 11.0%,23 13.6% in Rwanda,24 14.7% in Zimbabwe, and 13.7% in another study in Sudan.25 The relatively lower prevalence rates of malaria infection among ANC attendees in recent times (from year 2003) may not necessarily be the consequence of the development of higher levels of acquired antimalaria immunity among pregnant women in the subregion. A more plausible explanation to this reduction in maternal malaria prevalence in recent times could be a result of an increase of malaria awareness among women of childbearing age in many endemic areas of the sub-Saharan Africa and the intensified efforts of various health authorities at regional, national, and local levels in the control and prevention of malaria in pregnancy. Currently, the World Health Organization recommendation that women in areas of high transmission in Africa receive intermittent preventive treatment with an effective antimalarial drug at regularly scheduled ANC visits after "quickening," that is, when the pregnant woman feels fetal movement for the first time,26 is being implemented in many malarious areas.
In relation to parity, the prevalence of malaria in our investigation was significantly higher among the primigravidae (24.5%) than the multigravidae (12.2%) (P < 0.05). These results were in general accordance with findings from similar studies conducted in many other malarious areas of the tropics, indicating that gravidity and premunition (ie, partial immunity in which parasitemia is better tolerated) influence susceptibility to malaria infection with the parasite rate and density significantly higher in primigravidae than in the multigravidae.27-30 These reports indicate a strong relationship between parity and malaria infection with mean parasite density levels decreasing as the number of gestation increased, thus confirming that the African primigravidae remain unquestionably the most susceptible and are a high-risk group whose protection should be a priority. Primigravidae have been reported to experience deleterious effects of malaria (particularly during the second trimester), whereas complications are less frequent in women who have had multiple pregnancies (multigravidae), indicating that the protective immunity in pregnancy is a function of parity.6 The reason for this is unclear; immune suppression is probably more marked in primigravidae, but it is also possible that protective immunity may be acquired in the reproductive tract through malaria infection during the first pregnancy, reducing susceptibility in later pregnancies.28,29,31
Our result showed that prevalence of maternal malaria and the parasite density was highest among women in their second pregnancy trimester followed by those in their third trimester, but there was no statistically significant difference in the trend (P > 0.05). This finding is consistent with a number of previous studies28-30 but contrasts with studies conducted in Bandiagara, Mali, where the risk of malaria infection among pregnant women was significantly higher among individuals in their first trimester of gestation32 and in eastern Sudan, where the third trimester was significantly associated with malaria infection.25 However, it is established that maternal immunosuppression is evident during the second half of pregnancy, and this results possibly from the presence in the blood of high adrenal steroid levels, as well as placental chorionic gonadotrophin and α-fetoprotein; there may also be depression of lymphocyte activity.33 This may have accounted for the higher susceptibility to malaria by women in their second trimester pregnancy, as recorded in most of the studies including this present one. The higher rate of the infection and increase in malariometric parameters in the second trimester compared with the first and third confirmed an earlier report, which had indicated that resistance to malaria by African pregnant women falls sharply in the second trimester of pregnancy, especially first trimester pregnancy during which parasitemias become denser and more frequent with hemolysis after and leading to anemia, which is normocytic and normochromic and accompanied with reticulocytosis.34
In this study, the prevalence of maternal malaria was significantly higher among individuals with comparatively lower PCV (P < 0.05). These findings were in conformity with results of several studies conducted in various malarious areas of the sub-Saharan Africa.25,28-30 In addition, a number of studies have indicated that the prevalence of severe anemia was consistently higher among pregnant women infected with malaria than those uninfected.8,29,32 It is therefore obvious that malaria clearly contributes to anemia during pregnancy. In a review of studies of P. falciparum-related anemia in pregnant women, it was suggested that up to 400,000 pregnant women develop moderate or severe anemia (hemoglobin level <8.0 g/dL or hematocrit <25%) each year in sub-Saharan Africa as a result of malaria infection.16 Although the specific biologic processes are not clearly delineated, the contribution of moderate and severe anemia to poor oxygen transport to the developing fetus is a likely mode of action for anemia's adverse effect on fetal growth. In addition, malaria-associated anemia in the mother likely has important consequences on her outcome, whereby already anemic women are at an increased risk of severe consequences (eg, hypotension, shock, death) even with a moderate antepartum or postpartum hemorrhage.35
The HIV infection prevalence of 4.4% was obtained from this present investigation. The prevalence of maternal HIV infection in areas where maternal malaria studies have been reported has ranged from 3% to 27%.8 Our result showed that malaria prevalence was significantly higher among the HIV-positive than the HIV-negative women (P < 0.05). In line with the findings of this present investigation, higher prevalence of malaria infection in HIV-positive than HIV-negative pregnant women was also reported in Malawi,36 Zimbabwe,12 Kenya,37 and Rwanda.38
The mechanisms of the association between malaria and maternal HIV infection are potentially numerous, and many aspects are yet to be fully understood. A meta-analysis of studies on coinfection in pregnancy demonstrates that HIV infection impairs the ability of pregnant women to control P. falciparum infection.9 Impaired cell-mediated immunity in HIV-infected women could influence the frequency and course of malaria infection, as HIV infection interferes with the maintenance of immune recognition of malaria.39 It is already well established that P. falciparum malaria during pregnancy can lead to parasite sequestration in the maternal placental vascular space, with consequent maternal anemia, abortion, stillbirth, fetal distress, prematurity, low birth weight, congenital malaria, and neonatal or maternal death.2,7,16 The risk of these adverse pregnancy outcomes is further increased with HIV coinfection.12 As a result, a considerable proportion of infants exposed in utero to both placental malaria and maternal HIV infection have an increased risk for postneonatal death 3- to 8-fold higher than infants born to mothers with either infection alone.40 However, whether the dual infection with placental malaria and HIV increases the risk of mother-to-child transmission of HIV (perinatal HIV transmission) or congenital malaria is yet to be unequivocally established, as studies examining these relationships have inconsistent findings and a wide range of unanswered questions.
In conclusion, our inability to conduct a comprehensive evaluation of other possible factors that may contribute to anemia during pregnancy and the lack of information on the HIV disease stage of infected women in the present study population were major drawbacks of this investigation. These limitations may have affected the adequate assessment of the contributory role of malaria and HIV infection on the anemia observed among the subjects. The high rate of anemia among the women studied (83.8%) is an indication that factors other than malaria and HIV infection are playing a considerable role in the development of anemia among pregnant women in this part of the globe. Future research incorporating these aspects is therefore advocated. The high frequency of malaria and HIV infection in the sub-Saharan Africa necessitates the provision of integrated preventive health services that are sustainable and affordable, this is crucial for reducing the burden of the 2 diseases. In most parts of the developing world, maternal and child health services are the most accessible health services in many communities, thus, antenatal care services, in particular, could serve as the pivotal entry point for simultaneous delivery of interventions for the prevention and control of malaria and HIV in pregnant women and their neonates with linkages to the community, child health, HIV counseling and testing, treatment, care and support services, family planning, and other services.
The authors thank the management of Ebonyi State University Teaching Hospital, Abakaliki, for logistic support.
1. Chandramohan D, Greenwood BM. Is there an interaction between human immunodeficiency virus and Plasmodium falciparum? Int J Epidemiol. 1998;27:296-301.
2. World Health Organization (WHO). Malaria and HIV Interactions and Their Implications for Public Health Policy. Report of a Technical Consultation on Malaria and HIV Interactions and Public Health Policy Implications 2004. Geneva, Switzerland: WHO; 2005.
3. Huff B. HIV and malaria: two intertwining epidemics. Am Found AIDS Res. 2000;6:1-5.
4. World Health Organization (WHO). Expert Committee on Malaria. WHO Technical Report Series 892, i-v. Geneva, Switzerland: WHO; 2000.
5. World Health Organization (WHO). The African Malaria Report 2003. Geneva, Switzerland: WHO; 2003.
6. Riley EM, Hviid L, Theander TG. Malaria. In: Kierszenbaum F, ed. Parasitic Infections and the Immune System. New York, NY: Academic Press; 1994:119-143.
7. Brabin BJ. An analysis of malaria in pregnancy in Africa. Bull World Health Organ. 1983;61:1005-1016.
8. Steketee RW, Nahlen BL, Parise ME, et al. The burden of malaria in pregnancy in malaria-endemic areas. Am J Trop Med Hyg. 2001;64:28-35.
9. ter Kuile FO, Parise ME, Verhoeff FH, et al. The burden of co-infection with human immunodeficiency virus type 1 and malaria in pregnant women in sub-Saharan Africa. Am J Trop Med Hyg. 2004;71:41-54.
10. World Health Organization (WHO). AIDS Epidemic Update. Geneva, Switzerland: UNAIDS/WHO; 2004.
11. De Cock KM, Fowler MG, Mercier E, et al. Prevention of mother-to-child HIV transmission in resource-poor countries: translating research into policy and practice. JAMA. 2000;283:1175-1182.
12. Ticconi C, Mapfumo M, Dorrucci M, et al. Effect of maternal HIV and malaria infection on pregnancy and perinatal outcome in Zimbabwe. J Acquir Immune Defic Syndr. 2003;34:289-294.
13. World Health Organization (WHO). WHO Report of the African Regional Consultation on Control of Anaemia in Pregnancy. Document AFR/MCH/86, AFR/NUT/104. Brazzaville, Congo: World Health Organization; 1989.
14. Parise ME, Lewis LS, Ayisi JG, et al. A rapid assessment approach for public health decision-making related to the prevention of malaria during pregnancy. Bull World Health Organ. 2003;81:316-323.
15. Fleming AF. Joint meeting of the Royal College of Obstetricians and Gynaecologists and the Royal Society of Tropical Medicine and Hygiene Manson House, London, 10 November 1988, Tropical obstetrics and gynaecology. 1. Anaemia in pregnancy in tropical Africa. Trans R Soc Trop Med Hyg. 1989;83:441-448.
16. Guyatt HL, Snow RW. The epidemiology and burden of Plasmodium falciparum-related anemia among pregnant women in sub-Saharan Africa. Am J Trop Med Hyg. 2001;64:36-44.
17. Antelman G, Msamanga GI, Spiegelman D, et al. Nutritional factors and infectious disease contribute to anemia among pregnant women with human immunodeficiency virus in Tanzania. J Nutr. 2000;130:1950-1957.
18. World Medical Association Declaration of Helsinki. Ethical principles for medical research involving human subjects. World Medical Association, 2000. Available at: http://www.wma.net/e/policy/b3.htm
. Accessed June 15, 2005.
19. World Health Organization (WHO). Basic Malaria Microscopy. Learner's Guide. Geneva, Switzerland: WHO; 1991.
20. Dacie JV, Lewis SM. Practical Haematology. 8th ed. Edinburgh, Scotland: Churchill Livingstone; 1994.
21. World Health Organization (WHO). The Prevalence of Anaemia in Women: A Tabulation of Available Information. WHO/MCH/MSM/92.2. Geneva, Switzerland: WHO; 1992.
22. Elghazali G, Adam I, Hamad A, et al. Plasmodium falciparum infection during pregnancy in an unstable transmission area in eastern Sudan. East Mediterr Health J. 2003;9:570-580.
23. Ayoya MA, Spiekermann-Brouwer GM, Traore AK, et al. Determinants of anemia among pregnant women in Mali. Food Nutr Bull. 2006;27:3-11.
24. Van Geertruyden JP, Ntakirutimana D, Erhart A, et al. Malaria infection among pregnant women attending antenatal clinics in six Rwandan districts. Trop Med Int Health. 2005;10:681-688.
25. Adam I, Khamis AH, Elbashir MI. Prevalence and risk factors for Plasmodium falciparum malaria in pregnant women of eastern Sudan. Malar J. 2005;4:18.
26. World Health Organization (WHO). Strategic Framework for Malaria Control During Pregnancy in the WHO African Region. Geneva, Switzerland: WHO; 2002.
27. Mockenhaupt FP, Rong B, Gunther M, et al. Anaemia in pregnant Ghanaian women: importance of malaria, iron deficiency and haemoglobinopathies. Trans R Soc Trop Med Hyg. 2000;94:477-483.
28. Nair LS, Nair AS. Effects of malaria infection on pregnancy. Indian J Malariol. 1993;30:207-214.
29. Rogerson SJ, Van den Broek NR, Chaluluka E, et al. Malaria and anemia in antenatal women in Blantyre, Malawi: a twelve-month survey. Am J Trop Med Hyg. 2000;62:335-340.
30. Anorlu RI, Odum CU, Essien EE. Asymptomatic malaria parasitaemia in pregnant women at booking in a primary health care facility in a periurban community in Lagos, Nigeria. Afr J Med Sci. 2001;30:39-41.
31. Fried M, Nossten F, et al. Maternal antibodies block malaria. Nature. 1998;395:851-852.
32. Dicko A, Mantel C, Aly Thera M, et al. Risk factors for malaria infection and anemia for pregnant women in the Sahel area of Bandiagara, Mali. Acta Trop. 2003;89:17-23.
33. Bruce-Chwatt LT. Essential Malariology. London, UK: William Heinemann Medical Books Ltd; 1980.
34. Parry EHO. Principles of Medicine in Africa. London, UK: Oxford University Press; 1978.
35. Steketee RW. Pregnancy, nutrition and parasitic diseases. J Nutr. 2003;133:1661S-1667S.
36. Steketee RW, Wirima JJ, Bloland PB, et al. Impairment of a pregnant woman's acquired ability to limit Plasmodium falciparum by infection with human immunodeficiency virus type-1. Am J Trop Med Hyg. 1996;55:42-49.
37. van Eijk AM, Ayisi JG, ter Kuile FO, et al. HIV increases the risk of malaria in women of all gravidities in Kisumu, Kenya. AIDS. 2003;17:595-603.
38. Ladner J, Leroy V, Simonon A, et al. Pregnancy and HIV Study Group (EGE). HIV infection, malaria, and pregnancy: a prospective cohort study in Kigali, Rwanda. Am J Trop Med Hyg. 2002;66:56-60.
39. Wabwire-Mangen F, Shiff CJ, Vlahov D, et al. Immunological effects of HIV-1 infection on the humoral response to malaria in an African population. Am J Trop Med Hyg. 1989;41:504-511.
40. Bloland PB, Wirima JJ, Steketee RW, et al. Maternal HIV infection and infant mortality in Malawi: evidence for increased mortality due to placental malaria infection. AIDS. 1995;9:721-726.
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