The incrimination of Aedes (stegomyia) aegypti as the vector of Dirofilaria repens in Nigeria

Six local species of culicides were identified as the common mosquitoes in Zaria, out of 15 species captured using various adult and larval collection methods. These common culicides are Culex pipiens fatigans, Anopheles gamb iae grp., Mansonia africana, Culex pipiens pipiens, Aedes (stegomyia) aegyp ti and Aedes vittatus. They were each fed directly on a local dog naturally infected with Dirofilaria repens to evaluate their refractoriness/suscepti bility to dirofilarial infection. In a number of donor-feeding trials, 39.4 % Culex pipiens fatigans; 58.9% An gambiae grp.; 60.5% Mansonia africana; 1 .8% of Culex pipiens pipiens; 23.4% Ae aegypti and 3.3% of Ae vittatus succ essfully fed on the microfilaraemic host. Only Aedes aegypti was susceptibl e to the infection as all 40 (100%) Ae aegypti reaching 10-14 day post-bloo d meal had infective (L-3) larvae of D. repens. The remaining five species were refractory. The microfilariae in the five non-susceptible mosquitoes w ere always found trapped in the blood meal in the insects midgut (stomach). These trapped microfilaria were dead by the 2nd day in the insect' s midgu t. However, in the susceptible Ae aegypti, the microfilariae were set free from the blood meal in the midgut and within 24 h migrated to the malpighia n tubules (MT) of the mosquitoes. All Ae aegypti dissected 5-7 day post-inf ective blood meal showed the typical quiescent sausage stage (L-2) larvae i n the malpighian tubules. At day-10 post-blood meal, relatively active infe ctive (L3) larvae of D. repens were found in the MT; and by day 12-14, high ly motile infective larvae had reached the insect's head and proboscis, wit h infective larvae occasionally oozing out during dissection through the ti p of the proboscis. The rate of development of D. repens to infective larva e was faster in mosquitoes infected in July when the environmental temperat ure was 24.5 degrees C than those infected in November when the temperature was 22-.5 degrees C. The latter were delayed for 4 days. The breeding sour ces of Ae aegypti, the local vector implicated were also identified. As no particular Vector of this zoonotic filaria has been identified previously i n Nigeria, these findings could make any control programme more focussed an d easier. (C) 2000 Elsevier Science B.V. All rights reserved.