Filariasis transmission in Samoa. I. Relation between density of microfilariae and larval density in laboratory-bred and wild-caught Aedes (Stegomyia) polynesiensis (Marks) and wild-caught Aedes (Finlaya) samoanus (Gruenberg).

Transmission experiments of laboratory-bred and wild-caught Aedes polynesiensis and wild-caught Ae. samoanus on carriers with different levels of microfilaraemia showed that the percentage of mosquitoes infected, the average number and range of larvae found in each infected mosquito were directly proportional to the microfilarial densities in the carrier at the time of feeding. There was no difference between the results for laboratory-bred and wild-caught mosquitoes. Aedes polynesiensis fed on low carriers (around 20 Mf ml-1 and less) gave an average infection rate of 4.9%. Each infected mosquito harboured only one larva. A plot of the probit of percentage Ae. polynesiensis positive against the logarithm of microfilarial density showed a linear relationship. Using the regression line, at 95% confidence interval, a microfilarial density of 1 ml-1 would give an infection rate of 0.22-2.51%, a density of 0.1 Mf ml-1 an infection rate of 0.01-1.0%. The concentrating capacity of Ae. polynesiensis ranged from 0.70 to 4.74. As microfilaria densities decreased, concentration increased. The microfilarial intake, the subsequent worm burden and concentrating capacity were less in Ae. samoanus than Ae. polynesiensis. There was no evidence of any association between microfilarial density and concentration in Ae. samoanus.