Malaria infection and morbidity in infants in relation to genetic polymorphisms in Tanzania

To investigate the effects of host polymorphisms on malaria morbidity and infection, the frequency distributions of TNF alpha promotor gene and sickle cell trait were studied in infants in an area highly endemic for Plasmodium falciparum transmission in Tanzania. Differences in parasite prevalence, density, febrile episodes with and without parasitaemia, PCV levels and the frequencies of different MSP-2 parasite infections were assessed by genotype. The frequency of the TNF alpha promotor allele 2 was 0.09, and the trait was in Hardy-Weinberg equilibrium. There were no differences in malariametric indices between infants with the normal TNF alpha promoter gene and those who were heterozygous for this trait. Infants heterozygous for the TNF alpha promotor gene appeared to have fewer febrile episodes when they were free of parasites. The two infants homozygous for the TNF alpha promoter allele 2 had both a much higher incidence of fever, independently of parasitaemia, than the average for the other genotypes. The frequency of the sickle cell allele S was 0.06 and the trait was also in Hardy-Weinberg equilibrium. Infants heterozygous for the sickle cell trait had significantly lower parasite densities, but similar prevalence, and MSP-2 infections compared to infants with normal haemoglobin. PCV levels, and the incidence of febrile episodes both with and without parasitaemia were also similar. In contrast to the sickle cell trait, the TNF alpha promotor polymorphism appeared not to have any protective effect on malaria in this study, and its importance in other unspecified fever-causing diseases in this population needs further investigation.     

Severe malaria in children in areas with low, moderate and high transmission intensity in Uganda

OBJECTIVES: Age and transmission intensity are known to influence the manifestations of severe falciparum malaria in African children. However, it is unclear how specific clinical features such as seizures, impairment of consciousness, or respiratory distress vary with the parasite load and transmission intensity. We examined how the peripheral parasite load varies with transmission intensity and how this influences the symptoms and manifestations of severe malaria in children under 5 years in three areas with different malaria transmission intensity across Uganda. METHODS: We consecutively recruited 617 children with severe malaria presenting to three hospitals in areas with very low (51), moderate (367) and very high (199) transmission intensities and compared the age, admission parasite density and proportions of patients with different manifestations of severe disease. RESULTS: The median age (months) was inversely proportional to transmission intensity and declined with rising transmission (26.4 in very low, 18.0 in moderate and 9.0 under very high transmission). The highest proportion of patients reporting previous malaria admissions came from the area with moderate transmission. The geometric mean parasite density (18,357, 32,508 and 95,433/microl) and the proportion of patients with seizures (13.7%, 36.8% and 45.7%, P < 0.001) from very low, moderate and very high transmission respectively, increased with rising transmission. A linear increase with transmission was also observed in the proportion of those with repeated seizures (9.8%, 13.4% and 30.2%, P < 0.001) or impaired consciousness (7.8%, 12.8% and 18.1%, P = 0.029) but not respiratory distress. The proportion of patients with severe anaemia (19.6%, 24.8% and 37.7%, P = 0.002) mirrored that of patients with seizures. CONCLUSIONS: These findings suggest that heavy Plasmodium falciparum parasitaemia may be important in development of seizures, severe malarial anaemia and impaired consciousness in children under 5 years of age but may not be important in the development of respiratory distress.     

Malaria in Nigeria: a revisit

The frequency of asymptomatic malaria parasitaemia was investigated in rural and urban school-children aged six to 12 years in southwestern Nigeria between January 1987 and October 1988. Asymptomatic parasitaemia was detected in the rural school-children all year round with the lowest parasite rate in January and the highest in July, corresponding to the mid-dry and wet seasons respectively. Asymptomatic parasitaemia was also common amongst urban school-children, but the frequency was lower than in the rural children. Parasite density was less than or equal to 1000 microliters-1 in 42% of parasite-positive asymptomatic children and was greater than 10,000 microliters-1 in only 20% of them. Mass treatment with chloroquine, to which the parasites were fully sensitive, was followed by the same rate of re-infection in the parasite-positive and parasite-negative groups. Of 7713 patients clinically diagnosed as having malaria 4425 were found to have parasitologically-proven malaria, and of these 4239 had pure Plasmodium falciparum malaria. Of the patients with falciparum malaria only 4.6% were below the age of one year. In 47% the parasite count was less than or equal to 1000 microliters-1, and it was over 10,000 microliters-1 in 37% and over 250,000 microliters-1 in 16%. There was no significant difference between the asymptomatic children and the acutely ill patients in the percentage with parasite densities less than or equal to 1000 microliters-1, but the percentage with parasite densities greater than 10,000 microliters-1 was significantly greater in the acute malaria patients than in those with asymptomatic parasitaemia.     

Risk factors for presentation to hospital with severe anaemia in Tanzanian children: a case-control study

In malaria endemic areas anaemia is a usually silent condition that nevertheless places a considerable burden on health services. Cases of severe anaemia often require hospitalization and blood transfusions. The objective of this study was to assess risk factors for admission with anaemia to facilitate the design of anaemia control programmes. We conducted a prospective case-control study of children aged 2-59 months admitted to a district hospital in southern Tanzania. There were 216 cases of severe anaemia [packed cell volume (PCV) < 25%] and 234 age-matched controls (PCV > or = 25%). Most cases [55.6% (n = 120)] were < 1 year of age. Anaemia was significantly associated with the educational level of parents, type of accommodation, health-seeking behaviour, the child's nutritional status and recent and current medical history. Of these, the single most important factor was Plasmodium falciparum parasitaemia [OR 4.3, 95% confidence interval (CI) 2.9-6.5, P < 0.001]. Multivariate analysis showed that increased recent health expenditure [OR 2.2 (95% CI 1.3-3.9), P = 0.005], malnutrition [OR 2.4 (95%CI 1.3-4.3), P < 0.001], living > 10 km from the hospital [OR 3.0 (95% CI 1.9-4.9), P < 0.001], a history of previous blood transfusion [OR 3.8 (95% CI 1.7-9.1), P < 0.001] and P. falciparum parasitaemia [OR 9.5 (95% CI 4.3-21.3), P < 0.001] were independently related to risk of being admitted with anaemia. These findings are considered in terms of the pathophysiological pathway leading to anaemia. The concentration of anaemia in infants and problems of access to health services and adequate case management underline the need for targeted preventive strategies for anaemia control.     

Seasonal profiles of malaria infection,anaemia, and bednet use among age groups and communities in northern Ghana

We conducted all-age point prevalence surveys to profile the severity and seasonality of malaria and anaemia in Kassena-Nankana District of northern Ghana. Random cross-sectional surveys were timed to coincide with the end of low (May 2001) and high (November 2001) malaria transmission seasons and to yield information as to the potential value of haemoglobin (Hb) levels and parasitaemia as markers of malaria morbidity and/or malaria vaccine effect. Parasitaemia was found in 22% (515 of 2286) screened in May (dry-low transmission), and in 61% of the general population (1026 of 1676) screened in November (wet-high transmission). Malaria prevalence in May ranged from 4% (infants <6 months and adults 50-60 years) to 54% (children 5-10 years). Age-specific malaria prevalence in November ranged from 38% (adults 50-60 years) to 82% (children 5-10 years). Differences between low- and high-transmission periods in the prevalence of severe anaemia (SA) among young children (6-24 months) were unexpectedly comparable (low, 3.9%vs. high, 5.4%; P = 0.52) and greatly reduced from levels measured in this same community and age group in November 2000 (12.5%) and November 1996 (22.0%). Despite the lower frequency of anaemia/SA in young children surveyed in 2001, it was still clear that this condition was strongly associated with parasitaemia and that children under 5 years of age experienced a significant drop in their mean Hb levels by the end of the high transmission season. Prevalence of parasitaemia was significantly lower (P < 0.01) among infants and young children (<2 years) whose parents reported the use of bednets. There was a significantly lower risk of parasitaemia among infants [odds ratio (OR) 6-8] and young children (OR 3-4) living in the central, more urbanized sector of the study area.     

Anaemia in pregnancy: Plasmodium falciparum infection is an important cause in primigravidae in Hoima district, western Uganda

Infection with Plasmodium falciparum is a major cause of anaemia in pregnancy, especially in primigravidae. Of 853 primigravidae visiting an antenatal clinic in Hoima district, western Uganda, for the first time, 530 (62.1%) were found to have P. falciparum parasitaemias and 305 (57.5%) of these had at least 1000 parasites/microliter blood. Plasmodium falciparum parasitaemia was significantly associated with anaemia (relative risk = 0.84, with 95% confidence limits = 0.74-0.96; P = 0.01). Malarial parasites were detected in > 80% of the women who had severe anaemia (P = 0.0008) and haemoglobin concentrations decreased with increasing intensity of infection (P = 0.03). Malarial hyper-reactive splenomegaly was associated with high parasite density (P = 0.01) and low haemoglobin level (P < 0.0001). Effective measures aimed at prevention of malaria and anaemia in pregnancy, especially in primigravidae, would significantly reduce anaemia and its deleterious effects on both the mother and the baby.     

Malaria and asymptomatic parasitaemia in Gabonese infants under the age of 3 months

We determined the incidence of both malaria and asymptomatic parasitaemia in infants under the age of 3 months within the framework of a longitudinal cohort study in Lambaréné, Gabon, between December 2002 and July 2004. Of 878 infants who were included at birth, we identified malaria in three infants and, additionally, asymptomatic parasitaemia in six infants. The malaria incidence density was 1.1/1000 person-months or 0.1% of observations. Our findings underpin the notion that the incidence of malaria and parasitaemia in infants below the age of 3 months is very low.     

Risk associated with asymptomatic parasitaemia occurring post-antimalarial treatment

Objective  Parasites may recur asymptomatically after initial clearance by antimalarial treatment. Current guidelines recommend treatment only when patients develop symptoms or at the end of follow-up. We wanted to assess prospectively the probability of becoming symptomatic and the risks of this practice.
Methods  We analysed data collected in 13 trials of uncomplicated paediatric malaria conducted in eight sub-Saharan African countries. These studies followed all cases of post-treatment asymptomatic parasitaemia until they developed symptoms or to the end of the 28-day follow-up period, at which time parasite genotypes were compared to pre-treatment isolates to distinguish between recrudescences and new infections.
Results  There were 425 asymptomatic recurrences after 2576 treatments with either chloroquine, sulfadoxine/pyrimethamine or amodiaquine, of which 225 occurred by day 14 and 200 between day 15 and day 28. By day 28, 42% developed fever (median time to fever = 5 days) and 30% remained parasitaemic but afebrile, while 23% cleared their parasites (outcome unknown in 4%). Young age, parasitaemia ≥500 parasites/μl; onset of parasitaemia after day 14, and treatment with amodiaquine were the main variables associated with higher risk of developing fever.
Conclusion  In areas of moderate to intense transmission, asymptomatic recurrences of malaria after treatment carry a substantial risk of becoming ill within a few days and should be treated as discovered. Young children are at higher risk. The higher risk carried by cases occurring in the second half of follow-up may be explained by falling residual drug levels.     

Socially marketed insecticide-treated nets improve malaria and anaemia in pregnancy in southern Tanzania

OBJECTIVES: To study the uptake of socially marketed insecticide-treated nets (ITNs) and their impact on malaria and anaemia in pregnancy; and to report on a discount voucher system which aimed to increase coverage in pregnancy. METHODS: A 12-month cross-sectional study of women in the second or third trimester of pregnancy. ITN use and other factors were assessed by questionnaire and a blood sample taken for malaria parasitaemia and anaemia. 'Non-users' of ITNs included both women not using any net and women using untreated nets. RESULTS: Fifty three per cent of pregnant women used ITNs. Women aged 15-19, primigravidae, unmarried women, and those with no access to cash had the lowest ITN use. Fewer ITN users were positive for malaria than ITN non-users (25 vs. 33%: P=0.06), and the protective efficacy (PE) for parasitaemia was 23% (CI 2-41). Multiparous ITN users had a twofold decrease in parasite density compared with multiparous non-ITN users (625 parasites/microl vs. 1173 parasited/microl: P=0.01). Fewer ITN users were anaemic (Hb < 11 g/dl) than ITN non-users (72 vs. 82%: P=0.01). ITNs had a PE of 12% (CI 2-21) against mild anaemia and a PE of 38% (CI 4-60) against severe anaemia (Hb < 8 g/dl). There was a trend in the prevalence of severe, mild and no anaemia, and of high density, low density and no malaria infection by ITN status. Recently treated nets were most effective at preventing malaria and anaemia (prevalence of mild anaemia was 68% compared with 82% for those without nets (P=0.002); prevalence of malaria was 22% compared with 33% for those without nets (P=0.02). Knowledge and reported use of the discount voucher system were low. Further qualitative research is ongoing. CONCLUSIONS: A modest impact of ITNs on pregnancy malaria and anaemia was shown in our high malaria transmission setting. The development of ITN programmes for malaria control should include pregnant women as a specific target group.     

Age-dependent effect of plasma nitric oxide on parasite density in Ghanaian children with severe malaria

Nitric oxide (NO) has toxic properties against Plasmodium falciparum. While high blood levels have been associated with protection against severe malarial disease, they may also contribute to the pathophysiology of cerebral malaria and severe anaemia. Promoter variants in the inducible nitric oxide synthase (iNOS) gene have been shown to influence NO concentrations and disease manifestation. However, findings are conflicting. We examined associations of plasma NO metabolites (NOx) with symptoms of severe malaria, particularly malarial anaemia and cerebral malaria, and with iNOS promoter variants. In 210 Ghanaian children with severe malaria, we measured plasma nitrite, nitrate, and S-nitrosothiol, and genotyped the iNOS promoter variants -954G-->C, -1173C-->T, and the -2.5 kb (CCTTT)(n) microsatellite. NOx levels decreased with age. In young children (<24 months), high NOx was associated with reduced parasite density. This was not seen in patients of 24-48 months of age and reversed in older children. Subgroup analysis revealed that in children with severe anaemia but without cerebral involvement (prostration, impaired consciousness, convulsions), high NOx levels correlated with low parasitaemia (P = 0.02). In these children, elevated NOx levels were also associated with the iNOS-954C-->T/(CCTTT)(8) haplotype (P = 0.03). No association between NOx or iNOS genotypes and cerebral malaria was observed. Our findings suggest that in young children with severe malaria NOx reduces parasitaemia. This effect wanes at higher ages and may reflect a predominance of unspecific immune responses to infection in early childhood. This finding may have importance for the understanding of associations between iNOS variants and severe malaria in regions of differing disease manifestation.     

The effect of altitude on parasite density case definitions for malaria in northeastern Tanzania

OBJECTIVES: Malaria clinical trials need precise endpoints to measure efficacy. In endemic areas where asymptomatic parasitaemia is common, 'fever plus parasitaemia' may not differentiate between malaria cases and non-cases. Case definitions based on parasite cut-off densities may be more appropriate but may vary with age and transmission intensity. This study examines appropriate case definitions from parasitological surveys conducted over a broad range of transmission intensities, using altitude as a proxy for transmission intensity. METHODS: Cross-sectional data collected from 24 villages at different altitudes in an endemic area of northeastern Tanzania were used to calculate malaria-attributable fractions using a modified Poisson regression method. We modelled fever as a function of parasite density and determined the optimum cut-off densities of parasites to cause fever using sensitivity and specificity analyses. RESULTS: The optimum cut-off density varied by altitude in children aged under 5 years: a case definition of 4,000 parasites per mul at altitudes <600 m (high transmission intensity) was most appropriate, compared with 1,000 parasites per mul at altitudes >600 m (low transmission intensity). In children aged over 5 years and adults, there was little variation by altitude and a case definition of any parasites plus fever was the most appropriate. CONCLUSIONS: Locally appropriate case definitions of malaria should be used for research purposes. In our setting, these varied independently with age and transmission intensity.     

Development of immunity against Plasmodium falciparum malaria: clinical and parasitologic immunity cannot be separated

A total of 1622 individuals of all ages living under conditions of continuous malarial transmission in Liberia were enrolled in a cross-sectional study of parasite rates, positive parasite densities, and body temperatures. The age-specific Plasmodium falciparum-positive parasite densities were greatest at ages 0.5-1.0 year, then slowly declined into adulthood. The age-specific mean body temperature at parasite isodensity showed a steady decline even in the oldest age group. The results do not support the hypothesis that adults have higher body temperatures at a given parasite density than do children with the same parasite density. The age-specific P. falciparum parasite density for specific isotemperatures showed that a subgroup of children in the age group 0.5-1.0 year had low temperatures (less than 36.5 degrees C) despite high parasite densities. This indicates that low body temperature should be investigated further as a possible indicator of serious malaria in young children. Parasitologic and clinical immunity develops concomitantly and cannot be separated. The findings do not support the hypothesis that a special "anti-disease" immunity exists independently of parasitologic immunity.     

Malaria parasitaemia in relation to HIV status and vitamin A supplementation among pre-school children

OBJECTIVES: To ascertain whether malaria parasitaemia in children is associated with HIV status. To examine the effect of vitamin A supplementation on malaria parasitaemia in children. METHODS: We studied the cross-sectional associations between HIV status and malaria parasitaemia among 546 children 6-60 months of age who participated in a double-blind, randomized clinical trial of vitamin A supplementation. Prevalence ratios and 95% confidence intervals (CI) were estimated for the presence of malaria parasites at baseline by HIV status in uni- and multivariate models that adjusted for sociodemographic and environmental variables. Among children with malaria, correlates of high parasite loads were identified. Next, we examined the effect of vitamin A supplementation on the risk of malaria parasitaemia and high parasite density at 4-8 months of the first dose in a subset of children. RESULTS: The prevalence of malaria parasitaemia was 11.4% among HIV-infected children, compared with 27.6% among uninfected. After adjusting for season, anaemia, use of bednets, maternal education and indicators of socioeconomic status, we found some evidence for lower prevalence of parasitaemia among HIV positive compared with HIV-negative children (prevalence ratio=0.56; 95% CI=0.29, 1.09; P=0.09). Other important correlates of malaria parasitaemia at baseline included low level of maternal education, poor quality of water supply, and the presence of animals at home. Vitamin A supplementation did not have a significant effect on malaria parasitaemia at 4-8 months of follow-up, overall or within levels of potential effect modifiers. CONCLUSION: HIV infection appears to be negatively correlated with malaria parasitaemia in this group of children. Investing in women's education is likely to decrease the prevalence of malaria parasitaemia in children. Vitamin A supplementation does not seem to have an effect on malaria parasitaemia in this population; possible benefits against clinical episodes and severe malaria deserve further examination.     

Severe anaemia in children living in a malaria endemic area of Kenya

Severe anaemia is an important cause of morbidity and mortality in African children, but the causes, particularly falciparum malaria, are difficult to determine. We assessed the contribution of falciparum malaria to anaemia in Kenyan children by clinical examination and measurement of parasitaemia and haemoglobin (Hb) concentration in 559 children in the community and in 2412 children admitted to Kilifi district hospital during a 2‐year period. We also attempted to characterize severe malarial anaemia by examining the causes and pathophysiology of anaemia in 101 children admitted with Hb concentration 50 g/l during a 1‐year period. Plasmodium falciparum infection was associated with reduced Hb concentration in children in the community and in those admitted to hospital irrespective of diagnosis. Falciparum malaria was the primary cause in 46 cases (46%) of severe anaemia admitted to hospital. There was no difference in the frequency of haemolysis or dyserythropoiesis in the children with malarial anaemia and those with anaemia from other causes, such as iron deficiency or sickle cell disease. The mortality rate in the children with severe malarial anaemia was 8.6% compared with 3.6% in children with severe anaemia due to other causes. Falciparum malaria does not present with a characteristic clinical or haematological picture, but is a major cause of the morbidity and mortality in children with severe anaemia who live on the Kenyan coast, a malaria endemic area.     

Association of the sickle cell trait and the ABO blood group with clinical severity of malaria in southwest Nigeria

In regions of high Plasmodium falciparum malaria endemicity, certain erythrocyte polymorphisms confer resistance to severe disease. In this study, we evaluate the role of the sickle cell trait (HbS) and ABO blood groups in the clinical manifestations of childhood malaria in Southwest Nigeria. The subjects comprised 3100 children (53% males, median age 39 months), including 1400 children with uncomplicated malaria, 1000 children with asymptomatic malaria and 700 with severe malaria. Haemoglobin (Hb) types were determined using electrophoresis and serum agglutination techniques were used to determine ABO blood groups. Blood group O was the commonest ABO blood group (47.7%) in the study population, the others were A (22.5%), B (25.2%) and AB (4.6%). The frequencies of the HbAS and HbAC were 14.4% and 5.8%, respectively. In regression models adjusting for age, gender, parasite density and blood group, HbAS was associated with a reduced risk of severe malaria OR=0.46 (CI(95%): 0.273-0.773). Among severe malaria subjects, HbAS was associated with significantly lower parasite densities. The protective effect of blood group O was demonstrated with a decreased risk of severe malaria OR=0.743 (CI(95%): 0.566-0.976) after adjusting for age, gender and parasite density and Hb genotype. Blood group B was associated with increased risk of severe malaria OR=1.638 (CI(95%): 1.128-2.380) after adjusting for age, gender, packed cell volume, parasite density and Hb genotype. We have confirmed from this large study of Nigerian children the major protective effective of the sickle cell heterozygous state against both cerebral malaria and severe malarial anaemia. We also show that the B blood group is associated with an increased risk of severe malaria. In conclusion, the sickle cell haemoglobin type and ABO groups modulate the risk of severe malaria in Nigerian children.     

Spatial effects of the social marketing of insecticide-treated nets on malaria morbidity

Randomized controlled trials have shown that insecticide-treated nets (ITNs) have an impact on both malaria morbidity and mortality. Uniformly high coverage of ITNs characterized these trials and this resulted in some protection of nearby non-users of ITNs. We have now assessed the coverage, distribution pattern and resultant spatial effects in one village in Tanzania where ITNs were distributed in a social marketing programme. The prevalence of parasitaemia, mild anaemia (Hb <11 g/dl) and moderate/severe anaemia (Hb <8 g/dl) in children under five was assessed cross-sectionally. Data on ownership of ITNs were collected and inhabitants' houses were mapped. One year after the start of the social marketing programme, 52% of the children were using a net which had been treated at least once. The ITNs were rather homogeneously distributed throughout the village at an average density of about 118 ITNs per thousand population. There was no evidence of a pattern in the distribution of parasitaemia and anaemia cases, but children living in areas of moderately high ITN coverage were about half as likely to have moderate/severe anaemia (OR 0.5, 95% CI: 0.2, 0.9) and had lower prevalence of splenomegaly, irrespective of their net use. No protective effects of coverage were found for prevalence of mild anaemia nor for parasitaemia. The use of untreated nets had neither coverage nor short distance effects. More efforts should be made to ensure high coverage in ITNs programmes to achieve maximum benefit.     

不同密度间日疟原虫对中华按蚊的感染性观察

目的观察不同密度间日疟原虫对中华按蚊的感染性。方法：对蚊传人工感染滇南间日疟原虫的３８例志愿者，于原虫出现日及各次临床发作时抽取病人静脉血，用离体吸血法感染中华按蚊，以显微镜下在蚊胃壁查见卵囊为感染阳性。结果：虫现期原虫不能使按蚊获得感染。原虫密度高于１００／μｌ以上的初发病例，对按蚊的感染率和感染程度随病程的延长和原虫密度的增高而上升；复发期间日疟原虫对按蚊的感染率和感染程度远远高于初发病例，其原虫密度只要在１／μｌ以上即可使按蚊获得感染；原虫密度大于１０００／μｌ的初发病例和大于１００／μｌ的各组复发病例均能使按蚊获得较高的感染率、蚊胃阳性率及卵囊指数。结论：间日疟临床发作期是传播疟疾最危险的时期，复发病例是疟疾扩散过程中危险性较大的传染源；选择实验感染病例时，初发病例以虫数高于１０００／μｌ、复发病例高于１００／μｌ者为佳。     

Genetic aspects of control of anaemia development in trypanotolerant N'Dama cattle.

148 one-year-old N'Dama cattle, progeny of 29 sires, were exposed for 92 days to a medium natural tsetse-trypanosome challenge in Gabon, Central Africa. Matching health and performance data were recorded on 11 occasions. Average packed red cell volume percent (PCV) and lowest PCV reached during the period were evaluated as measures of ability to control the development of anaemia. Attempts were made to systematically control other possible causes of anaemia. In animals detected as parasitaemic, those with above average average PCV values or above average lowest PCV reached had 34% and 35% respectively higher daily weight gains than those with below average. Even when not detected as parasitaemic, those with above average average PCV values or above average lowest PCV reached had 14% and 12% respectively higher gain indicating that a proportion of these animals actually were parasitaemic. When all environmental and parasitaemia information was taken into account, the heritability of growth, average PCV and lowest PCV reached was 0.39 +/- 0.31, 0.64 +/- 0.33 and 0.50 +/- 0.32 respectively. The genetic correlation between average PCV and growth was 0.70 +/- 0.42 and between lowest PCV reached and growth was 0.28 +/- 0.55. While the standard errors are large, the higher heritabilities of PCV measures compared to animal growth and the positive genetic correlations between PCV and growth do indicate an opportunity for selection on PCV when animals can be detected as parasitaemic. All heritabilities and genetic correlations increased in size when parasitaemia information was utilized in the analysis.(ABSTRACT TRUNCATED AT 250 WORDS)     

The epidemiology of malaria among pregnant women attending antenatal clinics in an area with intense and highly seasonal malaria transmission in northern Ghana

Objective  To describe the factors associated with malaria infection and anaemia in pregnancy in northern Ghana.
Method  We studied 3642 pregnant women of all gravidities and gestational age of 18–32 weeks who attended an antenatal clinic in the Kassena-Nankana district of Ghana between June 2004 and July 2006. Blood samples were examined for haemoglobin concentrations and parasitaemia, and we obtained socio-demographic data, an obstetric history, information on their past and current state of health and bed net use.
Results  The overall prevalence of malaria parasitaemia during pregnancy was 47%. Older age [adjusted odds ratio (AOR) 0.65, 95% CI 0.54–0.78], multigravidity (AOR 0.51, 95% CI 0.42–0.61) and third trimester of pregnancy (AOR 0.85, 95% CI 0.73–0.99) were associated with a decreased risk of parasitaemia. Enrolment during the rainy or post-rainy season was associated with an increased risk of parasitaemia (AOR 2.59, 95% CI 2.20–3.04 and AOR 3.12, 95% CI, 2.60–3.74 respectively). Malaria infection was associated with an increased risk of anaemia among young women. The prevalences of anaemia (Hb<11.0 g/dl) and severe anaemia (Hb<7.0 g/dl) during pregnancy were 72% and 2% respectively. The risk of anaemia was lower in older women (AOR 0.79, 95% CI, 0.64–0.97), multigravidae (AOR 0.67, 95% CI 0.55–0.83) and in educated women (AOR 0.81, 0.68–0.98).
Conclusion  The prevalence of malaria parasitaemia and anaemia among pregnant women in Kassena-Nankana district is high with marked seasonal variation. Targeting of interventions to the high transmission season and to paucigravidae may be appropriate in this setting.     

Blood and bone marrow changes in malaria.

A variety of abnormalities in the number, morphology and function of blood and bone marrow cells may be found in Plasmodium falciparum and P. vivax malaria. In a non-immune individual, the nature of such abnormalities depends on the time after infection. In others it is determined by the pattern and intensity of malaria transmission in the area and the extent of host immunity. Severe anaemia may occur in children with chronic falciparum malaria and low parasitaemia as well as in patients with complicated acute falciparum malaria with high parasitaemia. However, the mechanisms underlying the anaemia in these two situations appear to be different. The possible roles of parasite products, T-cell-derived cytokines produced in response to the infection, macrophage activation and hyperplasia, macrophage-derived factors such as tumour necrosis factor-alpha, and macrophage dysfunction in the pathogenesis of the haematological abnormalities are discussed.