The epidemiology of malaria in adults in a rural area of southern Mozambique

Background: Epidemiological studies of malaria in adults who live in malaria endemic areas are scarce. More attention to the natural history of malaria affecting adults is needed to understand the dynamics of malaria infection and its interaction with the immune system. The present study was undertaken to investigate the clinical; parasitological and haematological status of adults exposed to malaria; and to characterize parasites in these individuals who progressively acquire protective immunity. Methods: A cross-sectional survey of 249 adults was conducted in a malaria endemic area of Mozambique. Clinical; parasitological and haematological status of the study population was recorded. Sub-microscopic infections and multiplicity of infections were investigated using polymerase chain reaction (PCR) and restriction fragment length polymorphism of Plasmodium falciparum merozoite surface protein 2 (msp2). Results: Prevalence of P. falciparum infection by microscopy (14) and PCR (42) decreased progressively during adulthood; in parallel with an increase in the prevalence of sub-microscopic infections. Anaemia was only related to parasitaemia as detected by PCR. Multiplicity of infection decreased with age and was higher in subjects with high P. falciparum densities; highlighting density-dependent constraints upon the PCR technique. Conclusions: Adults of Manhica progressively develop non-sterile; protective immunity against P. falciparum malaria. The method of parasite detection has a significant effect on the observed natural history of malaria infections. A more sensitive definition of malaria in adults should be formulated; considering symptoms such as diarrhoea; shivering and headache; combined with the presence of parasitaemia

Community incidences of respiratory infections in an actively followed cohort of children <1 year of age in Manhiça, a rural area of southern Mozambique.

OBJECTIVE: To estimate the community incidence-rates of respiratory infections among infants in Manhiça, southern Mozambique, and to determine risk factors associated with these infections. METHODS: A cohort of children <1 year of age were visited at home every week until they turned one. During the visits, field workers recorded signs/symptoms of respiratory infections and tested the children for malaria parasites when they had fever. RESULTS: Between 1 July 1998 and 30 June 1999, 1,044 children contributed with 23,726 weeks at risk. Children met the criteria for acute respiratory infection in 19.2% of the visits, for lower respiratory infection in 0.9% and for severe lower respiratory infection in 0.2%. The crude incidence rate measured for acute respiratory infections was 23.0, that for lower respiratory infection was 0.9 and that for severe lower respiratory infection was 0.2 per 100-person-week-at-risk. The risk of acute and lower respiratory infection was inversely related to age. Females were at significantly lower risk for all three conditions than males. A trend of increased risk of severe lower respiratory infection was noted among children born during the rainy season (adjusted rate ratio = 1.95, P = 0.122 in only 47 episodes). Malaria was strongly associated with an increased risk of all three respiratory infections [rate ratio of 2.35, 10.90 and 13.82 (P < 0.001) in the adjusted analysis, respectively]. Thirty-five children died during the follow-up period; 20% of them from lower respiratory infection. Conclusions Respiratory infections are a major cause of morbidity and mortality among infants in rural Mozambique. Our study provides a better understanding of the associated determinants.

Plasmodium species mixed infections in two areas of Manhiça district, Mozambique.

We compared the distribution patterns of individual Plasmodium species and mixed-species infections in two geographically close endemic areas, but showing environmental differences. Comparisons concerned circulating Plasmodium infections in both human and mosquito vector populations in the dry and wet seasons, at a micro-epidemiological level (households). Both areas revealed a very high overall prevalence of infection, all year-round and in all age groups. Plasmodium falciparum was the predominant species, being found in the vast majority of infected individuals regardless of the presence of other species. Plasmodium malariae and Plasmodium ovale occurred almost exclusively in mixed infections. Seasonal variation in P. malariae prevalence was observed in one area but not in the other. A decrease in P. malariae prevalence concurred with a marked increase of P. falciparum prevalence. However this was strongly dependent on age and when analysing infections at the individual level, a different pattern between co-infecting species was unveiled. Regarding transmission patterns, in both areas, P. falciparum gametocytes predominated in single infections regardless of age and P. malariae gametocyte carriage increased when its overall prevalence decreased.

Entomological characteristics of malaria transmission in Manhiça, a rural area in southern Mozambique.

From October 1997 to September 1998, an entomological survey was carried out in Manhiça, Mozambique, to describe the anopheline population and intensity of malaria transmission. Ten different huts were randomly selected for entomological surveillance throughout the year. CDC light trap collections were conducted during three nights each month. Additional knockdown spraying catches were carried out in the morning, after the last catch. A total of 17,245 Culicinae and 1,251 Anophelinae were collected during the study. There was substantial house to house variation and seasonality in the distribution of Anophelinae population, with a peak in April towards the end of the warm and rainy season. Four species of genus Anopheles (Diptera: Culicidae) were described: Anopheles funestus Giles, Anopheles tenebrosus Dönitz, Anopheles arabiensis Patton, and Anopheles merus Dönitz. An. funestus constitutes 72.3% of the anopheline population. The estimated sporozoite rate was 1.2% and the average entomological inoculation rate for the area was 15 infective bites per person per year.

Ankle clonus and thiocyanate, linamarin, and inorganic sulphate excretion in school children in communities with Konzo, Mozambique.

We examined 397 school children for ankle clonus in five communities in three districts affected by konzo, spastic paraparesis associated with cassava consumption. From a subsample of 131 children, we analysed urine specimens for urinary thiocyanate, linamarin, and inorganic sulphate. The proportion of children with clonus varied between sites, ranging from 4 to 22 per cent. Geometric mean thiocyanate, linamarin, and inorganic sulphate concentrations were 163 and 60 mumol/l and 4.4 mmol/l, respectively. Children with ankle clonus had higher urinary thiocyanate concentrations. We recommend prevention to reduce cyanide exposure and further monitoring of cyanide exposure and neurological damage in these communities.

Konzo associated with war in Mozambique.

We report an epidemic of konzo, symmetric spastic paraparesis associated with cassava consumption and cyanide exposure: 384 patients were treated in rehabilitation centres; the prevalence rate in a badly affected area was 30/1000. Most patients were children over 3 and women. Owing to war, communities turned to bitter cassava as their staple and took shortcuts in its processing. When the war ended, they continued to depend on inadequately processed bitter cassava. The epidemic lasted 2 years (the last year of war and the first of peace) with peaks each year during the cassava harvest. Although most cases were reported from rural inland areas, patients also came from small towns and the coast. School children had raised urinary thiocyanate and linamarin and low inorganic sulphate concentrations. Urinary thiocyanate values were lower than those previously reported in konzo epidemics, probably because we collected specimens before the cassava harvest and epidemic peak. The necessary conditions for konzo were present: intensive cultivation of bitter casava, insufficient processing, a probable high cyanide intake, and a low intake of protein-rich foods.