Plasmodium falciparum reinfection in children from a holoendemic area in relation to seroreactivities against oligopeptides from different malaria antigens.

The rate and densities of Plasmodium falciparum reinfections were investigated in children five to 14 years old from one village in Tanzania with a high transmission rate. Initial parasitemias were eradicated by a curative treatment with quinine, a drug with a short elimination half-life, to minimize the effects of residual drug on reinfection. The seroreactivities to seven oligopeptides, representing T and B cell epitopes from the ring erythrocyte surface antigen (Pf155/RESA), the clustered arginine-rich protein antigen (CARP), and the circumsporozoite (CS) proteins were determined in the children at the start of the study and after 28 days. All children were reinfected within 42 days (mean 27 days). The geometric mean maximum parasite density at reinfection was 308 parasites per microliter (range 4-13, 920). The antipeptide antibody levels showed high interindividual variation, with a significant mean decrease (16%) between days 0 and 28 for the blood stage antigens, but not for the (NANP)6 peptide from the CS protein. This suggests that the absence of blood stage antigenic stimulation had already influenced the antibody levels within this short period of time. The mean reinfection day was not influenced by the levels of antibodies to any of the peptides. However, the children with higher antibody levels to (EENVEHDA)2(EENV)2 developed significantly lower parasitemias than those with lower antibody levels (P less than 0.05). This suggests that this subunit of the Pf155/RESA molecule is an important B cell epitope for protective antiparasitic immunity.

Suppression of Plasmodium falciparum infections during concomitant measles or influenza but not during pertussis.

In tropical countries, concomitant infections are a continuous problem. In the Rufiji Delta, an area of Tanzania that is holoendemic for malaria, there were outbreaks of influenza A, measles, and pertussis in 1986 and 1987. Significantly lower parasitic prevalences and mean densities of malaria parasites were found in children up to nine years of age who had measles or influenza than in asymptomatic control children. In contrast, children with pertussis had a higher prevalence and mean density than controls. The clinical courses of measles, influenza, or pertussis infections did not appear to be significantly affected by concomitant malaria infections. The reasons for the suppression of Plasmodium falciparum parasitemia during these viral infections are unclear. This effect could not be explained by the presence of fever.

Daily dynamics of Plasmodium falciparum subpopulations in asymptomatic children in a holoendemic area.

Plasmodium falciparum is the major cause of malaria morbidity and mortality in the world. Biologic and antigenic diversity is a characteristic of this parasite and infections can consist of several genetically diverse parasites. The daily dynamics of these parasite subpopulations were investigated in asymptomatic children in rural Tanzania. Fingerprick blood samples were collected on 14 consecutive days from 20 children. Parasite densities were detected by light microscopy and genotyping of P. falciparum was done using a nested polymerase chain reaction (PCR) assay targeting polymorphic regions on the merozoite surface protein-1 (MSP-1), MSP-2, and glutamine-rich protein (GLURP) genes. In the eight children harboring P. falciparum throughout the study period, infections were found to be highly complex with daily changes in both parasite density and genotypic pattern. A nonrandom. 48-hr periodicity in these fluctuations suggests that P. falciparum infections consist of inherently synchronous subpopulations of parasites. These findings have important biologic and epidemiologic implications since one blood sample may only partly reflect the whole parasite population in an infected individual.

Fever episodes in a holoendemic malaria area of Tanzania: parasitological and clinical findings and diagnostic aspects related to malaria.

All episodes of acute illness, in children aged 0-9 years, were registered during 3 years in a health clinic in a village of about 500 inhabitants in a malaria holoendemic area on the Tanzanian coast. Of 668 clinical episodes, 395 were diagnosed as malaria. There was no death. Only 5% of the children with malaria episodes came to the clinic after more than 3 d of symptoms. All 11 severe anaemias occurred among these children. Fever was reported in 98%, vomiting in 15%, and diarrhoea in 8% of the malaria episodes. Intermittent fever was reported in 98% of the malaria patients with more than one day of fever, compared to 4% of those with other febrile illnesses. Parasite densities > or = 10,000/microliters were found in 48% of the malaria episodes. Densities > or = 400/microliters were found in 96% of the malaria episodes and in only 8% of the other febrile illnesses. The 16 malaria episodes (4%) with densities below that level were all in children under one year of age. The ability of the rural medical aid or the doctor to differentiate malaria episodes from other febrile illnesses without microscopical examination was limited. Although very few malaria episodes were missed, substantial over-diagnosis resulted in specificity values of only 13% and 52% for their respective malaria diagnoses. It is concluded that intermittent fever was strongly associated with malaria, but a high accuracy of malaria diagnosis in febrile children requires microscopical examination.(ABSTRACT TRUNCATED AT 250 WORDS)

Low seroprevalence of Toxoplasma gondii antibodies in a Tanzanian village.

The prevalence of antibodies against Toxoplasma gondii was studied in the population of Nyamisati village in Tanzania using the direct agglutination test, indirect immunofluorescence test, and immunosorbent agglutination test. All positive sera were positive by both direct agglutination and indirect immunofluorescence tests and were confirmed by the dye test. The seropositivity was confirmed by immunoblotting showing a distinct 32 kDa band in all the seropositive samples. The seropositivity rate was 4% (19/450) among the subjects of Nyamisati origin and 47% (15/32) among immigrants from other areas of Tanzania. Most of the infections appeared to have occurred between 5 and 15 years of age. The generally low transmission in this mainly Muslim village appeared to be related to sparse consumption of contaminated food and low prevalence of oocysts due to scarcity of felines.

Proguanil daily or chlorproguanil twice weekly are efficacious against falciparum malaria in a holoendemic area of Tanzania.

The prophylactic efficacy of proguanil 100 mg (Paludrine) daily was compared to that of chlorproguanil 20 mg (Lapudrine) twice weekly in school children from Nyamisathi village, in a coastal area of Tanzania, 160 km south of Dar es Salaam. A total of 80 children were randomly allocated to three groups after radical treatment with a curative dose of mefloquine (Lariam). Seventy-six children were then followed up with daily prophylaxis and/or placebo for 13 weeks. All children in the group taking placebo prophylaxis were reinfected within 10 weeks whereas no parasites were detected in the children taking proguanil or chlorproguanil for prophylaxis. We conclude that both regimens were efficacious and that chlorproguanil represents an important alternative for chemoprophylaxis if taken at least twice weekly instead of the recommended once weekly regimen.

A study on malaria infection during the acute stage of measles infection.

The recognized high mortality from measles in Africa is considered to be partly due to the flare-up of concomitant malaria infection. In 1987 there was a measles epidemic in the Rufiji Delta, Tanzania, in spite of recent vaccination campaigns. A comparative study was therefore conducted on the densities of malaria parasites in children during the acute stage of measles (67 consecutive cases, aged 5 months-19 years). The period of study was March-June, the peak season for malaria transmission. For each measles patient, a blood film was concomitantly taken from an asymptomatic age-matched child from the same village. Of 67 children with measles, 17 (25%) had parasitaemia ranging from 8 to 2480 parasites microliter-1 blood. Out of 67 asymptomatic control children 59 (88%) had parasitaemia ranging from 8 to 3400 parasites microliter-1 blood. This study indicates that malaria densities were lower during the acute stage of measles than in healthy children. The contribution of malaria to mortality in children with acute measles may be questioned.

Complexity of Plasmodium falciparum infections is consistent over time and protects against clinical disease in Tanzanian children.

The complexity of Plasmodium falciparum populations in 21 children was studied in repetitive samples over 4 years in an area of Tanzania where the organism is holoendemic. Genotyping was done by a polymerase chain reaction method that targets three highly polymorphic regions of the merozoite surface protein (MSP) 1 block 2, MSP 2, and the glutamine-rich protein. Eight children were repeatedly parasitemic, 5 had scanty parasitemias, and 8 were consistently nonparasitemic. Varying numbers of genotypes were detected in the parasitemic children, but the multiplicity of infection was significantly constant within each child. The children with frequent parasitemias experienced fewer clinical episodes during the study period than those without parasitemias. There was also a tendency for children with more complex infections to experience fewer episodes. The children had consistent parasitologic profiles over the 4 years. Although few subjects were studied and the results will require confirmation, the results suggest that asymptomatic (especially polyclonal) P. falciparum infection protects against clinical disease from new infections.