Abstract
The period prevalence rates for asthma and rhinitis were studied in a Sudanese village close to the Nile (Kalakla), where the inhabitants are seasonally exposed to very large numbers of nonbiting midges (the “green nimitti” midge,
Cladotanytarsus lewisi [Diptera: Chironomidae]). The results were compared with those in a control village some distance from the river, where this midge nuisance does not occur. Of the 5262 persons enumerated in Kalakla, 4.9% suffered from asthma compared with 3.2% of the 2634 in the control area. For allergic rhinitis the rates were 6.7% for Kalakla and 1.5% in the control town. The percentage of patients with the combination of asthma and allergic rhinitis was four times greater in the affected area. These differences were all highly statistically significant. Asthma and rhinitis appeared to affect all occupational classes in both locations with an unexplained high prevalence in civil servants. In both areas the majority with asthma developed their disease by young adulthood, with a predominance in males in almost all age groups. In Kalakla the rates for both asthma and rhinitis increased with age. In the control town there was a similar trend for rhinitis, but the prevalence rates for asthma did not vary appreciably with age. The patient's own subjective assessment of provoking agents and the higher incidence of symptoms during the winter months (the “green nimitti” season) indicated that seasonal exposure to chironomids was a major etiologic factor in asthma and rhinitis in Kalakla. These epidemiologic findings support previous immunologic data which indicated that the “green nimitti” midge is a potent seasonal allergen and that repeated exposure results in a very high incidence of allergic rhinitis as well as a significant increase in the indigenous asthmatic population.