A marked seasonality of malaria transmission in two rural sites in eastern Sudan

The ecology of Anopheles arabiensis and its relationship to malaria transmission was investigated in two villages in eastern Sudan. Seasonal malaria case incidence was compared with the number of vectors detected and with climatic variables. Following the end of the short rainy season in October the number of A. arabiensis detected dropped gradually until February when neither outdoor human bait trapping nor indoor spray catches revealed any mosquitoes. Vectors re-appeared in June as humidity rose with the onset of rain. Despite the apparent absence of the vector at the height of the long, hot dry season between February and May, sporadic asymptomatic malaria infections were detected in the two villages. The low endemicity of malaria in the area was reflected by the relatively low total September-December parasite and sporozoite rates (15 and 1.4%, respectively) measured in the villages. The entomological inoculation rate (EIR) was estimated to be around two to three infective bites per person per year, although heterogeneity in the transmission indices of malaria between the two villages was observed. The implications of these patterns of anopheline population dynamics for the epidemiology and control of malaria in eastern Sudan are considered.     

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.     

Maternal responses to childhood febrile illnesses in an area of seasonal malaria transmission in rural Ethiopia

Although malaria is the leading cause of illness and death among children less than 5 years of age, there is limited information on mother's response and experience about diagnosis and treatment of the disease in children in rural areas of Ethiopia. The objective of this study was to assess maternal responses and treatment seeking behaviour for children reported to have malaria. A community-based cross-sectional study was conducted between October and November 2003 in Adami Tulu District, south-central Ethiopia. Mothers/caretakers of children less than 5 years of age were interviewed about history of febrile illness suspected to be malaria for all under-five children and the actions taken in the 2 weeks prior to the survey. Of 3872 children identified in 2372 households, 817 (21.1%) had febrile illness reported to be malaria according to the mothers/caretakers. The main symptoms included fever (99%), shivering/chills (92.2%), vomiting (55.1%), sleeplessness/restlessness (12.9%) and refusal to feed (21.3%). Of the total febrile children, 27.3% sought the first care from a public health facility, 27% visited community health workers (CHWs), 25.7% taken to private clinics, 6.4% received home treatment, and 13.3% did not get any care. Among 710 children who reported to receive any type of anti-malarial treatment, 78.8% got it from one source, 19.4% visited two sources and 1.8% sought three sources. Only 28% of the children received any form of treatment within 24h of the onset of illness. Public facilities, private clinics and CHWs were the main sources of care sought by febrile children. Strengthening peripheral health services and community-based interventions using CHWs at village levels would improve the early diagnosis and treatment of malaria among children.     

Molecular epidemiology of malaria in Cameroon. XXIV. Trends of in vitro antimalarial drug responses in Yaounde, Cameroon

In vitro response to chloroquine, monodesethylamodiaquine, mefloquine, lumefantrine, and dihydroartemisinin was assessed by the radioisotopic microtest in Yaoundé, Cameroon, during 2000-2004 and compared with our previous data obtained during 1996-1999. Based on the cut-off value of 100 nmol/L, 36.3% of isolates were chloroquine-susceptible (N = 175; geometric mean IC(50), 40.3 nmol/L) and 63.7% were chloroquine-resistant (N = 307; geometric mean IC(50), 211 nmol/L). There was no significant difference (P > 0.05) in the mean IC(50)s from 1996 to 2004, but a significant linear trend (P < 0.05) toward an increased proportion of chloroquine-resistant isolates was observed from 1996 (49%) to 2004 (69%). All chloroquine-susceptible isolates and most chloroquine-resistant isolates were susceptible to monodesethylamodiaquine (i.e., IC(50) < 60 nmol/L). Despite the positive correlation between chloroquine and monodesethylamodiaquine (r = 0.739, P < 0.05), the IC(50)s for monodesethylamodiaquine remained stable during 1997-2004, with no increase in the proportion of monodesethylamodiaquine-resistant isolates. Mefloquine, lumefantrine, and dihydroartemisinin were equally active against the chloroquine-susceptible and chloroquine-resistant parasites. The responses to these three drugs were positively correlated, and a significant decrease (P < 0.05) in the mean IC(50)s was observed during the study period compared with our earlier data in 1997-1999, probably because of their inverse relationship with chloroquine response. The in vitro results were in general agreement with the in vivo response to chloroquine and amodiaquine. In vitro drug susceptibility assay is a useful, complementary laboratory tool for determining the trend of response to drugs for which there is still no established molecular marker and may serve as an early warning system for emerging drug resistance.     

Living conditions and occurrence of malaria in a rural community

Results of a prospective study of the association between environmental factors and malaria occurrence among 1461 individuals in an Indian rural community are reported. A multiplicative model was fitted by relating malaria positivity with different environmental risk factors as categorical variables. The risk of acquiring malaria infections varied significantly within a village stratified by proximity of breeding sources to human dwellings (chi 2 = 19.87, df = 5, p = 0.0000) and different types of houses (chi 2 = 11.32, df = 2, p = 0.0035). People residing in thatched houses with [Relative Risk (RR) = 6.72] and without false ceiling (RR = 11.27) are exposed to greater risk of contracting malaria infections when compared to tiled houses (RR = 1.00). However, malaria infection was not significantly associated with proximity of cattlesheds to human dwellings (chi 2 = 1.54, df = 2, p = 0.46). A significantly high risk was observed in zones where the cattle to man ratio was very low and vice versa (chi 2 = 15.32, df = 6, p = 0.018). These data suggest and corroborate with earlier studies that transmission is a local problem and it varies within a village according to the microepidemiological factors.     

Eosinophilic esophagitis in children and adolescents: epidemiology, clinical presentation and seasonal variation

Background

Eosinophilic esophagitis (EoE) is defined by infiltration of eosinophils in the esophageal mucosa (>20 eosinophils/hpf). The epidemiology and seasonal variation have not been well studied in children and adolescents.

Methods

Review of all esophageal biopsies performed from January 2001 to December 2006 on patients younger than 21 year of age, focusing on demographics, onset and duration of presenting symptoms, history of allergies and endoscopic findings.

Results

A total of 753 upper endoscopies were performed, 44 of which showed histologic evidence of EoE (5.8 %). Fifty percent of all EoE endoscopies were grossly normal. Onset of symptoms was 23 % in the spring, 29 % in the summer, 23 % in the fall and 25 % in the winter. More cases (36 %) were diagnosed in the fall. Time between onset of symptoms and diagnosis was 115 ± 145 days (mean ± SD). The most common presenting symptoms were vomiting (61 %), dysphagia (39 %), abdominal pain (34 %), feeding disorders (14 %), heartburn (14 %), food impaction (7 %), vague chest pain (5 %) and diarrhea (5 %). Children presenting with vomiting and feeding disorders were younger (p < 0.02), whereas children presenting with heartburn and dysphagia were older (p < 0.02).

Conclusions

The incidence of EoE did not increase between 2001 and 2006. Onset of symptoms did not vary by season, indicating that allergens triggering EoE are present all year around. Vomiting and feeding disorders are seen in young children, while dysphagia and heartburn are seen in older children. As endoscopic findings were normal in 50 % of cases, an esophageal biopsy should be performed in all patients with suspected EoE.     

Echinococcosis, toxocarosis and toxoplasmosis screening in a rural community in eastern Kazakhstan

Objective To determine the extent of carnivore‐transmitted parasitic zoonoses in a community in eastern Kazakhstan, a region where cystic echinococcosis (CE) re‐emerged in recent years. Methods Cross sectional ultrasound study of 3126 human subjects to determine the extent of human cystic and alveolar echinococcosis (AE). Blood samples were taken from each subject and analysed for antibodies against Echinococcus, Toxocara and Toxoplasma spp. Each subject was questioned about possible risk factors that might be associated with zoonotic transmission. Analysis employed a mixed modelling approach based on the results of the ultrasound study, the serological results and the results of the questionnaire. Bayesian techniques were employed to estimate diagnostic performance. A helminthological study of the local dog population was also undertaken. Results A total of 23 subjects tested positive for CE on ultrasound and a further three individuals had strong serological evidence of infection. Another 24 reported treatment for CE. Ultrasound lesions or treatment for CE were associated with poverty. No ultrasound evidence of AE was found, but one individual had strong serological evidence of exposure to Echinococcus multilocularis. Toxoplasma seropositivity (16%; 504 individuals) increased with age. Household level Toxoplasma‐seropositivity was associated with unsafe drinking water. Toxocara seropositivity (11%; 349 individuals) was more frequent in children and in individuals who disposed of dog faeces on the vegetable garden. A purgation study of dogs indicated that 13% of dogs in the community were infected with Echinococcus granulosus, 5% with E. multilocularis and 2% with Toxocara canis respectively. Conclusions There is significant transmission of E. granulosus to humans in this community. Transmission may be associated with poverty. There is little evidence of E. multilocularis transmission to humans, despite the presence in the parasite in the domestic dog population. Toxoplasma is actively transmitted and there is evidence for transmission by the water supply. Children are at highest risk of exposure to Toxocara.     

The implementation of community participation in the control of malaria in rural Tanjung Pinang, Indonesia

A study was undertaken to involve a hyperendemic community in Berakit village near Tanjung Pinang to participate actively in the control of malaria. Weekly chemoprophylaxis with chloroquine was given to all villagers of RK I with a population of about 700 for a period of one year. Nine cadres were selected from the community by the villagers for the distribution of the drug and coordinated by the head of the village. About 14-19 families were supervised by one cadre who was responsible for the weekly distribution of the drug to these families. The weekly dosage of the drug was adjusted according to age. The drug was taken in the presence of the cadres to assure the intake, and recorded by each cadre. The results showed that 93.7% of the villagers have taken the drug regularly. The remaining 6.3% of them showed refusal and irregular intake, or moved to another village during the period of prophylaxis. Although the drug has a bitter taste, most of the children were able to tolerate it. In general, mild side effects were reported and infrequently observed. Implementation of community participation to control malaria in this village showed good results which was reflected in the results of the malariometric surveys carried out before and after one year chemoprophylaxis. The spleen rate of about 600 villagers of RK I examined was 54.3% and the parasite rate 13.2% before the drug intervention. After one year chemoprophylaxis the spleen rate decreased to 21.7% and the parasite rate to 4.5% showing a significant difference.     

Molecular epidemiology of malaria in Cameroon. XXVII. Clinical and parasitological response to sulfadoxine-pyrimethamine treatment and Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase alleles in Cameroonian children

The rapidly changing epidemiology of antifolate-resistant Plasmodium falciparum in Africa requires monitoring. The present study was designed to assess the degree of association between the clinical and parasitological response to sulfadoxine-pyrimethamine and allelic combinations of dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes. Of 357 children who completed the 14-day follow-up, an adequate clinical and parasitological response was observed in 316 patients (88.5%) and early and late failures occurred in 18 (5%) and 23 (6.4%, mostly due to recrudescence) patients, respectively. The majority of clinical isolates were characterized as "quadruple" (n=196, 55.2%; N51I-C59R-S108N in DHFR and A437G in DHPS) or "triple" mutants (n=97, 27.3%; N51I-C59R-S108N in DHFR and wild-type DHPS; S108N+N51I or C59R in DHFR and A437G in DHPS). Wild-type, single mutation, and double mutation were observed in 29, 20, and 13 parasites, respectively. The comparison of different sets of mutations and early or late failures did not reveal any molecular marker associated with treatment outcome when the follow-up period was limited to 14 days (P>0.05). In this study, the determination of dhfr-dhps genotypes was of limited value to predict the treatment outcome in individual patients, mostly due to few treatment failures and few wild-type haplotypes. Further monitoring will be required to define the relationship between clinical response to SP therapy and parasite genotypes in our epidemiological setting.     

Review: Intermittent preventive treatment--a new approach to the prevention of malaria in children in areas with seasonal malaria transmission

Intermittent preventive treatment, the administration of a full course of an anti-malarial treatment to a population at risk at specified time points regardless of whether or not they are known to be infected, is now a recommended approach to the prevention of malaria in pregnancy and is being explored as a potential way of preventing malaria in infants. However, in many malaria endemic areas, the main burden of malaria is in older children and increasing use of insecticide treated bednets is likely to increase further the proportion of episodes of malaria that occur in older children. Recently, it has been shown in Senegal and in Mali that intermittent preventive treatment given to older children during the malaria transmission season can be remarkably effective in preventing malaria. This approach to malaria control is likely to be most effective in areas with a high level of malaria transmission concentrated in a short period of the year. However, several issues need to be addressed before intermittent preventive treatment in children can be advocated for use in malaria control programmes. These include: (1) determination of whether intermittent preventive treatment adds to the protection afforded by other control measures such as insecticide-treated bednets; (2) whether an effective and sustainable delivery system can be found; (3) choice of drug to be used; (4) optimum timing of drug administration; (5) the requisite interval between treatments. The potential benefits of intermittent preventive treatment in children are substantial; more research is needed to determine if this is a practical approach to malaria control.     

The changed pattern of malaria endemicity and transmission at Amani in the eastern Usambara mountains, north-eastern Tanzania

Parasitological and entomological studies on malaria were conducted between 1980 and 1982 on the Amani hills in the eastern Usambara mountains of north-eastern Tanzania. Malaria vectors were scarce on the Amani hills until the late 1960s and it was generally presumed that any cases of malaria transmission must have been contracted by people while visiting lower altitudes where malaria is holoendemic. However, the malaria vectors Anopheles funestus and An. gambiae have both become more abundant during the 1970s and 1980s and sporozoite-positive specimens of both have been found. Malaria asexual parasite rates have been shown to have increased, for instance from 52.7% in 1980 to 53.8% and 63.7% in 1981 and 1982, respectively. The percentage of parasitized children aged below 1 year whose parents report that they have not visited lowland localities away from the Amani hills has increased, from 71.4% in 1980 to 80.0% and 91.0% in 1981 and 1982, respectively, suggesting possible local malaria acquisition. These parameters have been confirmed by increasing sporozoite rates from 0.0% in 1967-1971 to 0.09% in May-June 1973 and 11.1% in August and December 1980. Various factors including climatological changes and increased agricultural activities are attributable to this changed malaria endemicity and transmission.     

Molecular epidemiology of malaria in Yaounde, Cameroon. VII. Analysis of recrudescence and reinfection in patients with uncomplicated falciparum malaria.

In an endemic area where malaria transmission is intense and continuous, reappearance of asexual parasites may be ascribed to either recrudescence or reinfection. To distinguish between recrudescence and reinfection after oral treatment with chloroquine, amodiaquine, pyronaridine, sulfadoxine-pyrimethamine, halofantrine, or artesunate, three polymorphic markers (circumsporozoite protein, merozoite surface antigens 1 and 2) from pre-treatment and post-treatment samples were amplified by the polymerase chain reaction, and the in vitro response to chloroquine was determined for comparison. Of 52 paired samples, 22 (42%) were reinfections. Recrudescence occurred more frequently on or before Day 14 (22 of 30 cases, 73%). Except for one case, all reinfections were observed beyond Day 14. The phenotype determination was not sufficiently precise to distinguish between recrudescence and reinfection. Our results suggest that beyond Day 14 (and until Day 42), recrudescence and reinfection cannot be distinguished at our study site unless molecular techniques are used and that some results derived from the polymerase chain reaction need to be compared with the microscopic examination of thick blood smear to exclude gametocyte carriers without asexual parasites after treatment.     

Wuchereria bancrofti in a community with seasonal transmission: stability of microfilaraemia, antigenaemia and filarial-specific antibody concentrations

The effect of seasonal transmission on microfilaraemia, antigenaemia and filarial-specific antibody levels in individuals infected with Wuchereria bancrofti was investigated in a follow-up study in an endemic community in north-eastern Tanzania. The subjects were 37 adult male residents who were found to be positive for circulating filarial antigen (CFA) at the beginning of the study (26 of whom were also found microfilaraemic with W. bancrofti at this time). Blood samples were collected from each subject in July 1998, January 1999 and July 1999, during the seasons when transmission intensity was high, low and high, respectively. The mean intensities of microfilaraemia and the mean concentrations of CFA were each slightly higher during the low-transmission season than during the two high-transmission seasons but the differences were not statistically significant (P > 0.05). Similarly, the mean levels of filarial-specific IgG1, IgG2, IgG3, IgG4 or IgE did not differ to a statistically significant degree between the three examination times. Microfilaraemias and the levels of CFA and filarial-specific antibodies all therefore appeared to be remarkably stable and largely unaffected by the seasonal variation in transmission. That no variation in the mean IgG4/IgE ratio was observed over the study period may indicate that the level of resistance to W. bancrofti infection in the study subjects was also unaffected by the transmission season.     

Molecular epidemiology of malaria in Yaounde, Cameroon IV. Evolution of pyrimethamine resistance between 1994 and 1998

Pyrimethamine, in combination with sulfadoxine, is currently one of the major alternative drugs used for the treatment of chloroquine-resistant Plasmodium falciparum malaria infections in Africa. The mechanism of pyrimethamine resistance has been strongly associated with a single, key point mutation in the dihydrofolate reductase-thymidylate synthase gene, resulting in the substitution of the wild-type allele Ser-108 by either Asn-108 or Thr-108. The pyrimethamine-resistant phenotype and/or genotype were determined in 273 Cameroonian clinical isolates obtained in Yaounde by in vitro assays and polymerase chain reaction-restriction fragment length polymorphism over a 5-year period. The in vitro assays showed that 42% (18 of 43) and 63% (69 of 110) of the isolates obtained in 1994-1995 and 1997-1998, respectively, were resistant to pyrimethamine (50% inhibitory concentration [IC50] > 100 nM). The polymerase chain reaction showed that 43% (55 of 127) and 59% (50 of 85) of the isolates in 1994-1995 and 1997-1998, respectively, had the mutant Asn-108 allele. The pyrimethamine-resistant genotype (Asn-108) corresponded with the pyrimethamine-resistant phenotype (IC50 > or = 100 nM) in a large majority (> 95%) of the isolates. The results of our study suggest an increasing prevalence of pyrimethamine resistance in Yaounde. Our study further suggests that pyrimethamine resistance can be monitored by a technique that can be adopted by malaria research centers in Africa.     

High seasonal variation in entomologic inoculation rates in Eritrea, a semi-arid region of unstable malaria in Africa

Entomologic studies were conducted in eight villages to investigate the patterns of malaria transmission in different ecologic zones in Eritrea. Mosquito collections were conducted for 24 months between September 1999 and January 2002. The biting rates of Anopheles arabiensis were highly seasonal, with activity concentrated in the wet season between June and October in the highlands and western lowlands, and between December and March in the coastal region. The biting rates in the western lowlands were twice as high as in the western escarpment and 20 times higher than in the coastal region. Sporozoite rates were not significantly different among villages. The risk of infection ranged from zero on the coast to 70.6 infective bites per year in the western lowlands. The number of days it would take for an individual to receive an infective bite from an infected An. arabiensis was variable among villages (range = 2.8-203.1 days). The data revealed the presence of only one main malaria transmission period between July and October for the highlands and western lowlands. Peak inoculation rates were recorded in August and September (range = 0.29-43.6 infective bits/person/month) at all sites over the two-year period. The annual entomologic inoculation rates (EIRs) varied greatly depending on year. The EIR profiles indicated that the risk of exposure to infected mosquitoes is highly heterogeneous and seasonal, with high inoculation rates during the rainy season, and with little or no transmission during the dry season. This study demonstrates the need to generate spatial and temporal data on transmission intensity on smaller scales to guide targeted control of malaria operations in semi-arid regions. Furthermore, EIR estimates derived in the present study provide a means of quantifying levels of exposure to infected mosquitoes in different regions of the country and could be important for evaluating the efficacy of vector control measures, since Eritrea has made significant steps in reducing the burden of malaria based on the Roll Back Malaria initiative of the World Health Organization.     

Molecular epidemiology of HIV type 1 in a rural community in southwest Uganda

The molecular epidemiology of a population-based cohort in a cluster of 15 villages in southwestern Uganda was investigated by sequencing part of the p24 gag gene and performing heteroduplex mobility assays (HMAs) of the V3 region of the env gene. Sequence and HMA data, obtained for 69 and 88 proviruses, respectively, showed that the clade A and D viruses were present at a ratio of about 0.67:1. No other clades were detected. Thirteen (22%) of 59 proviruses for which both gag and env data were obtained appeared to be recombinants. Although both clade A and D viruses were present in 13 of the villages, their distribution was unequal: for example, from env data 59% of clade A viruses were found in the eastern villages, compared with only 27% of clade D viruses. Phylogenetic (maximum likelihood) analysis of the p24 gag sequences showed a total of five clusters supported by bootstrap resampling values above or close to 75%. Four clusters were sexual partners, but there was no known sexual contact between the persons in the other cluster. The DNA sequences showed between 0.5 and 8.3% divergence from the cohort clade A or D consensus sequences. The sequences were not closely related to those published for other clade A or D proviruses.     

Lymphocyte proliferation and antibody responses to Plasmodium falciparum liver-stage antigen-1 in a highland area of Kenya with seasonal variation in malaria transmission

Lymphocyte proliferation and antibody responses to five peptides corresponding to the N- and C-terminal non-repeat and central repeat regions of Plasmodium falciparum liver-stage antigen-1 (LSA-1) were examined in residents of a highland area of Kenya where malaria transmission is episodic and varies with rainfall. The frequency of lymphocyte proliferation responses (stimulation index > 2) by children (persons > or = 6 years old) and adults (persons > or = 18 years old) was similar and did not differ significantly across seasons. In contrast, the proportion of individuals with IgG antibodies to LSA-1 peptides was higher in the rainy than dry season, and the frequency of these responses was greater for adults than children (39.4% versus 18.7% during the period of high transmission; P = 0.009). Antibodies to LSA-1 were primarily of the IgG1 and IgG3 subclasses, and these also varied with season (30.1% and 32.5% of individuals had IgG1 and IgG3 in the rainy season versus none and 10.9% in the dry season). There was no significant difference in the time to re-infection between groups of persons with or without IgG antibody or lymphocyte proliferation responses to LSA-1 peptides. These data indicate that age and transmission intensity independently affect IgG antibody responses to LSA-1 but do not influence lymphocyte proliferation in this highland area where malaria transmission is highly variable.     

Molecular epidemiology of malaria in Yaounde, Cameroon. VIII. Multiple Plasmodium falciparum infections in symptomatic patients.

The extent of genetically distinct parasite populations coinfecting individual human hosts (i.e., multiplicity) was studied by polymerase chain reaction amplification of 3 polymorphic genetic markers, circumsporozoite protein and merozoite surface antigens (MSA) 1 and 2, in symptomatic children and adults and analyzed in relation with age and initial parasitemia. Of the total of 177 DNA samples analyzed (of which 115 were paired pre- and posttreatment samples), 101 (57%) were composed of multiclonal infections, with up to 7 distinguishable parasite populations. Among the 3 polymorphic markers, msa-2 yielded the highest proportion of clinical isolates with multiclonal populations. Patients with multiclonal infections before treatment had, on average, 2.9 genetically distinct parasite populations. The extent of multiplicity decreased significantly (P < 0.05) in recrudescent parasites, but not with reinfections, as compared with the pretreatment samples. Neither age (5-60 years) nor initial parasitemia was correlated with multiplicity. Further studies in different epidemiological settings are required to understand the role of multiclonal Plasmodium falciparum infections in influencing malaria transmission.     

Multiple modes of transmission of giardiasis in primary schoolchildren of a rural community, Thailand

In February 2005, we conducted a cross-sectional study to determine the prevalence and the risk factors of giardiasis in 531 primary schoolchildren of a rural community, Chacheongsao province, Thailand. Using both sedimentation and flotation techniques to detect Giardia duodenalis, the prevalence of giardiasis was 6.2%. Assemblage A, subgenotype II and assemblage B, subgenotype IV were identified by PCR-RFLP of glutamate dehydrogenase gene. Our data might indicate that, in this population, only assemblage A, subgenotype II of G. duodenalis was transmitted via water. Using multivariate analysis, significant risk factors for giardiasis were children of age 5-9 years, households with > or = 3 children under the age of 12 years, low parental educational level, drinking bottled water, and living in close contact with dogs. Washing hands before meals had a protective effect. From these significant risk factors, multiple modes of transmission of G. duodenalis were suggested in this population.