Mosquito aging modulates the development, virulence and transmission potential of pathogens

Host age variation is a striking source of heterogeneity that can shape
the evolution and transmission dynamic of pathogens. Compared to
vertebrate systems, our understanding of the impact of host age on
invertebrate-pathogen interactions remains limited. We examined the
influence of mosquito age on key life-history traits driving human malaria
transmission. Females of Anopheles coluzzii, a major malaria vector,
belonging to three age classes (4, 8, and 12 day-old), were experimentally
infected with Plasmodium falciparum field isolates. Our findings revealed
reduced competence in 12-day-old mosquitoes, characterized by lower
oocyst/sporozoite rates and intensities compared to younger mosquitoes.
Despite shorter median longevities in older age classes, infected
12-day-old mosquitoes exhibited improved survival, suggesting that the
infection might act as a fountain of youth for older mosquitoes
specifically. The timing of sporozoite appearance in the salivary glands
remained consistent across mosquito age classes, with an extrinsic
incubation period of approximately 13 days. Integrating these results into
an epidemiological model revealed a lower vectorial capacity for older
mosquitoes compared to younger ones, albeit still substantial due to
extended longevity in the presence of infection. Considering age
heterogeneity provides valuable insights for ecological and
epidemiological studies, informing targeted control strategies to mitigate
pathogen transmission.