Species variation in mosquito flight-muscle damage resulting from a single filarial infection and its repercussions on a second infection.

Serial sections of females of two highly filaria-susceptible mosquitoes, Aedes togoi and Ae. aegypti, were examined by light microscopy. Following a single Brugia pahangi infection, the predominant reaction of flight muscles of Ae. aegypti was degeneration, whereas that in Ae. togoi was nuclear enlargement, a putative repair response. This also holds true following mechanical injury (Beckett 1990), suggesting an inherent species difference in flight-muscle response to injury. The filariae of a second B. pahangi infection, initiated after muscle damage had been established, usually avoided degenerate muscle fibres (which cannot support larval development) but entered similar proportions of normal fibres and those with enlarged nuclei. Filariae of a second infection, initiated whilst first-infection larvae were still within the muscle fibres, entered similar proportions of already-parasitized and non-parasitized fibres. The sole change in muscle fibres detectable by filarial larvae is therefore degeneration.