The effect of infection with Dirofilaria immitis (dog heartworm) on fluid secretion rates in the Malpighian tubules of the mosquitoes Aedes taeniorhynchus and Anopheles quadrimaculatus

Dirofilaria immitis, the parasitic nematode causing the disease dog heartworm, is transmitted by female mosquitoes. During their development, larval nematodes reside in the cells of the Malpighian tubules of these mosquitoes for approx 13 days. We have examined the effect of the presence of these large intracellular parasites on the main physiological function of the Malpighian tubules, i.e. fluid secretion. Rates of fluid secretion were examined in vitro using both normal and infected tubules of the mosquito species Aedes taeniorhynchus and Anopheles quadrimaculatus. Tubules of A. quadrimaculatus show changes in trasport rate during the reproductive cycle. Those of A. taeniorhynchus do not. Infection with larvae of D. immitis had no effect on the rate of fluid secretion in tubules of A. quadrimaculatus. In A. taeniorhynchus by contrast, the tubules show decline in transport with time following infection. The reduction in transport capacity is proportional to the number of worms infecting the tubule. The present paper and separate ultrastructural studies demonstrate that parallel changes in microvillar ultrastructure and epithelial transport rates occur in response to infection by the parasite. In both species examined, the survival of the mosquitoes and their vector potential are determined by factors other than the transport capacities of the infected Malpighian tubules.