Absence of association between delayed type hypersensitivity to tuberculin and atopy in children in The Gambia

BACKGROUND

An inverse association between delayed type hypersensitivity to tuberculin and atopy has been observed in children, suggesting that exposure to mycobacteria may influence the immune response to allergens.

OBJECTIVE

To investigate the relationship between tuberculin responses and atopy in children living in three different environments in The Gambia.

METHODS

In this cross-sectional study a total of 507 school-aged children were recruited from rural, urban poor or urban affluent communities. They were assessed for skin responses to five common allergens and tuberculin, presence of bacille Calmette-Guérin (BCG) scar, presence of intestinal parasites, and total serum IgE. Atopy was defined as the presence of a skin prick test response > or = 3 x 3 mm to at least one allergen.

RESULTS

The overall prevalence of atopy was 33% but there was a significant variation among the three study groups. The prevalence of atopy was 22% in urban poor, 36% in urban affluent, and 43% in rural children. Controlling for potential confounding factors, children in the rural community had a significantly higher odds ratio, 3.3 (95% confidence interval 1.8-6.0) of being atopic than children from the urban poor community. No association between atopy and tuberculin response or BCG scar was observed in any of the three groups. Serum IgE levels were higher among children of the urban poor group but were not associated with tuberculin response or BCG scar in any of the groups.

CONCLUSION

Environmental factors have an important influence on the development of atopy in children in The Gambia but delayed type hypersensitivity to tuberculin is not a protective factor.

Changes in house design reduce exposure to malaria mosquitoes

House design may affect an individual's exposure to malaria parasites, and hence to disease. We conducted a randomized-controlled study using experimental huts in rural Gambia, to determine whether installing a ceiling or closing the eaves could protect people from malaria mosquitoes. Five treatments were tested against a control hut: plywood ceiling; synthetic-netting ceiling; insecticide-treated synthetic-netting ceiling (deltamethrin 12.5 mg/m2); plastic insect-screen ceiling; or the eaves closed with mud. The acceptability of such interventions was investigated by discussions with local communities. House entry by Anopheles gambiae, the principal African malaria vector, was reduced by the presence of a ceiling: plywood (59% reduction), synthetic-netting (79%), insecticide-treated synthetic-netting (78%), plastic insect-screen (80%, P < 0.001 in all cases) and closed eaves (37%, ns). Similar reductions were also seen with Mansonia spp., vectors of lymphatic filariasis and numerous arboviruses. Netting and insect-screen ceilings probably work as decoy traps attracting mosquitoes into the roof space, but not the room. Ceilings are likely to be well accepted and may be of greatest benefit in areas of low to moderate transmission and when used in combination with other malaria control strategies.

Increased risk for malaria in chronically malnourished children under 5 years of age in rural Gambia

Malaria and malnutrition cause high morbidity and mortality in rural sub-Saharan Africa. To explore the relationship between nutritional status and malaria, a cohort of Gambian children under 5 years of age was followed weekly during one malaria season. Anthropometric measurements were made at the beginning and at the end of the season. A total of 55/107 (51.4 per cent) children with baseline stunting, defined as having a height-for-age z-score below -2 standard deviations, subsequently experienced malaria episodes, compared to 145/380 (38.2 per cent) children who were not stunted (RR = 1.35; 95 per cent CI, 1.08-1.69; p value = 0.01). Neither wasting (weight-for-height z-score below -2 standard deviations) nor undernutrition (weight-for-age z-score below -2 standard deviations) influenced susceptibility to malaria. Adjustment for characteristics of age, sex, and ethnicity did not significantly change the risk ratios. Malaria had no effect on the nutritional status from the beginning to the end of the malaria season. Our findings suggest that chronically malnourished children may be at higher risk for developing malaria episodes.

Short-range attractiveness of pregnant women to Anopheles gambiae mosquitoes

Malaria is a major cause of illness and an indirect cause of mortality in pregnant women. It can also cause stillbirths and low-birthweight babies. We have shown previously that pregnant women attracted twice as many Anopheles gambiae mosquitoes, the principal African malaria vector, as their non-pregnant counterparts over distances of about 15 m. In the current study (in 1998/99) we compared the short-range attractiveness of both pregnant and non-pregnant women sleeping under untreated bednets in Gambian villages. First, we measured the rate of mosquito entry under bednets and, second, we calculated the proportion of mosquitoes biting mothers under each bednet compared to their children. The feeding preference of An. gambiae collected under nets was determined by DNA fingerprinting blood samples from human subjects sleeping under each bednet and comparing these to fingerprints obtained from mosquito bloodmeals. Pregnant women were more attractive to An. gambiae mosquitoes than non-pregnant women under an untreated bednet. The number of mosquitoes entering bednets each night was 1.7-4.5 times higher in the pregnant group (P = 0.02) and pregnant women also received a higher proportion of bites under the bednets than did non-pregnant women (70% vs 52%, P = 0.001). This study clearly demonstrates that pregnant women are more exposed to malaria parasites than other women, which contributes to the greater vulnerability of pregnant women to malaria.