Iron supplementation increases small intestine permeability in primary schoolchildren in Lusaka, Zambia.

Elevated intestinal permeability, measured as an increased lactulose:mannitol (L:M) ratio, indicates injury of the small intestinal mucosa. As part of a randomized iron and multi-micronutrient (without iron) supplementation trial (Nchito et al., 2004), we determined intestinal permeability in a subgroup of schoolchildren at 10 months' follow-up to assess the effect of the interventions. Among 153 children (mean age 10.2 years and 53.6% girls) iron supplementation resulted in a higher L:M ratio compared with placebo (0.29 vs. 0.21, P=0.025). There was no effect of multi-micronutrient supplementation, and no interaction between the interventions. The finding could be one of the mechanisms explaining the negative effects of medicinal iron supplementation on morbidity found in some other studies.

Phylogeography of Biomphalaria glabrata and B. pfeifferi, important intermediate hosts of Schistosoma mansoni in the New and Old World tropics.

The historical phylogeography of the two most important intermediate host species of the human blood fluke Schistosoma mansoni, B. glabrata in the New World, and B. pfeifferi in the Old World, was investigated using partial 16S and ND1 sequences from the mitochondrial genome. Nuclear sequences of an actin intron and internal transcribed spacer (ITS)-1 were also obtained, but they were uninformative for the relationships among populations. Phylogenetic analyses based on mtDNA revealed six well-differentiated clades within B. glabrata: the Greater Antilles, Venezuela and the Lesser Antilles, and four geographically overlapping Brazilian clades. Application of a Biomphalaria-specific mutation rate gives an estimate of the early Pleistocene for their divergence. The Brazilian clades were inferred to be the result of fragmentation, due possibly to climate oscillations, with subsequent range expansion producing the overlapping ranges. Within the Venezuela and Lesser Antilles clade, lineages from each of these areas were estimated to have separated approximately 740 000 years ago. Compared to B. glabrata, mitochondrial sequences of B. pfeifferi are about 4x lower in diversity, reflecting a much younger age for the species, with the most recent common ancestor of all haplotypes estimated to have existed 880 000 years ago. The oldest B. pfeifferi haplotypes occurred in southern Africa, suggesting it may have been a refugium during dry periods. A recent range expansion was inferred for eastern Africa less than 100 000 years ago. Several putative species and subspecies, B. arabica, B. gaudi, B. rhodesiensis and B. stanleyi, are shown to be undifferentiated from other B. pfeifferi populations.

Transmission of schistosomiasis in Kariba, Zimbabwe, and a cross-sectional comparison of schistosomiasis prevalences and intensities in the town with those in Siavonga in Zambia.

Given that the two communities lie only 10 km apart, on the northern shore of Lake Kariba, it is surprising that human schistosomiasis now appears to be a much less important health problem in Kariba town (Zimbabwe) than in Siavonga town (Zambia). In an attempt to explain this difference, the level and sites of Schistosoma haematobium and S. mansoni transmission in Kariba, and the prevalences and intensities of human infection with these parasites in both communities, have now been investigated. In a longitudinal study, a cohort of 378 schoolchildren, 150 subsistence fishermen and 42 commercial fishermen from Kariba town was screened three times for schistosome infection, at 6-month intervals. Sixteen human-water contact sites in or near the town were surveyed for intermediate host snails every month for 1 year. Finally, the results of screening 660 Kariba schoolchildren (in January 2001) and 527 Siavonga schoolchildren (in July 2002) were compared. In the longitudinal study, 9.0% of the schoolchildren, 7.3% of the subsistence fishermen and 0% of the commercial fishermen were each found positive for S. haematobium at least once. The corresponding values for S. mansoni were 2.5%, 12.5% and 26.3%, respectively. The results indicated that, each year in Kariba, 2.4% and 2.0% of schoolchildren and 18.2% and 5.2% of fishermen were infected with S. haematobium and S. mansoni, respectively. Although both Bulinus globosus and Biomphalaria pfeifferi were found at 14 of the 16 water-contact sites, snails infected with schistosomes that could infect mammals were only found at three of the sites. The problem of schistosomiasis in Kariba town appears to be greater among fishermen than schoolchildren, all transmission probably occurring in Lake Kariba. As expected, the overall prevalences of S. haematobium and S. mansoni infection among Siavonga schoolchildren (19.4% and 33.5%, respectively) were far higher than the corresponding values for Kariba schoolchildren (7.1% and 2.1%, respectively). The marked differences in the prevalence of human schistosomiasis between Kariba and Siavonga appear to be attributable to the better water and sanitation facilities and a history of schistosomiasis-control activities in Kariba town.

Snail-parasite compatibility and prevalence of Schistosoma haematobium on the shores of Lake Kariba, Zambia.

Reduced snail-parasite compatibility might be at least partially responsible for the decrease observed, over the last three decades, in the prevalence of urinary schistosomiasis on the shores of Lake Kariba, Zambia. To explore this possibility, the prevalences of urinary schistosomiasis in schoolchildren were investigated in three disparate areas of Zambia (Lake Kariba, Lake Bangweulu and Lusaka), and attempts were made to infect the snails that developed from the eggs of snails collected from each of these sites with Schistosoma haematobium from each of the sites. The prevalence of S. haematobium infection in schoolchildren ranged from 0% around Lake Bangweulu to 76% around Lake Kariba. The F1 progeny of Siavonga (Lake Kariba) snails showed good compatibility with the local parasite but were also susceptible to all of the geographical strains of S. haematobium tested. The interaction between the S. haematobium and S. mansoni found along the shores of Lake Kariba may favour S. mansoni, since prevalences of urinary schistosomiasis tend to be relatively high where S. mansoni is absent. Although Lake Bangweulu was confirmed to be an area of very low endemicity for urinary schistosomiasis, the snails bred from snails collected in this area were compatible with isolates of S. haematobium from the same region and also those from the other regions. In general, sympatric snail-parasite combinations were the most successful. All the snails were identified as Bulinus globosus, on the basis of common enzyme profiles, although polymorphism was evident for malate dehydrogenase (MDH): two samples had type-1 MDH and the rest were of type 3. Isoenzyme patterns for both acid phosphatase (AcP) and MDH could be used to distinguish between infected and uninfected snails.