Illness and Diseases

The four drying regimens were also statistically compared on individual net brand. For PermaNetR and TNT, overall there were no significant differences observed between the four drying regimens on these nets (p = 0.7944 and 0.4703) respectively). For BASF nets that were dried hanging under the shade performed better compared to nets dried using other regimens p < 0.001. For Olyset, nets that were dried spread on the ground under the shade, performed worse compared to nets that were dried using the other three regimens. All the three drying regimens (sun/ground, sun/hang and shade/hang were statistically significant on Olyset p > 0.0001 The rate of insecticide loss after the above LLINs were repeatedly washed using the three washing procedures were also evaluated. Overall, nets which were washed by machine significantly retained more insecticide after each wash (p < 0.001) compared to nets washed by the two local washing methods. Further analysis on mean values of individual nets, showed that nets washed using WHO protocol, retained more insecticides than when washed by hand rubbing. When the two methods (washing by hand and machine washing) were compared: Olyset retained 89.7% and 84% when washed by machine and hand respectively. Permanet retained 40.9% and 35% when washed by machine and hand respectively. BASF retained 64.9% of the original insecticide and 57.5% when washed by machine and hand respectively, while TNT retained 87.3% compared to 60.9% when washed by machine and hand respectively. These results were statistically significant for Olyest and TNT (p = 0.037) and (0.018) respectively while for PermaNet and BASF the results were not statistically insignificant (0.09 and 0.083 respectively), Further, the effectiveness of the above LLINs were also evaluated per drying regimen and after repeated washing using three washing procedures. In general, it was observed that the mortalities of An. gambiae s.s. recorded 24 hrs after three minutes exposure varied with net type, drying regimen and number of washes.
For example on PermaNet the mortality reduced from 100 at zero washing to 30% at the 20th washing. For Olyset mortality reduced from 100% to 0%, BASF 100% to 20 and TNT 100 to 15% for the same washing period. Nets washed and air-dried by hanging under the shade showed overall higher percentage mortality than nets which were air-dried hanging or lying on the ground in direct sunlight 100 – 15.8% and 100- 31.3% respectively. The loss in efficacy followed the same trend of insecticide loss. The first five washes were most critical since all the nets except Olyset, exponentially lost up to 50% of their initial efficacy. Between the 5th and 15th washing the loss in efficacy was very gradual while the loss declined from 60 – 40% for nets that were air-dried while hanging under the shade. Similarly, it was observed that, the loss in efficacy corresponded to the reduction in residual insecticide contents for all the nets except for Olyset. Nets that were washed and air-dried while hanging under the shade generally recorded higher percentage mortality, compared to nets which were washed and dried using other regimens. Results of probit analysis modelling for mortalities of mosquitoes showed that there significant differences [p < 0.001]. Nets that were washed and air-dried spread on the ground in direct sunlight were the least effective.