Dengue, Zika, and chikungunya are transmitted by the same mosquito genus (Aedes). The age distribution of reported cases for all three diseases is remarkably consistent — across different countries, different outbreak sizes, and different years. The shape of who gets sick, as a function of age, doesn’t change.

This is surprising because social behavior varies enormously between populations. Children in Brazil and adults in Thailand have very different daily routines, housing conditions, and outdoor exposure patterns. If human behavior determined infection risk, the age distributions should differ between populations. They don’t.

The invariance points to ecology, not sociology. The mosquito’s biting behavior — when it feeds, where it rests, how far it flies — creates a characteristic age-dependent exposure profile that is approximately universal across human populations. The mosquito doesn’t care about your culture. It cares about your skin surface area, your CO2 output, and your presence during its active hours. These biological features scale with age in the same way everywhere.

The implication for public health: the target population for intervention is determined by the vector’s ecology, not the human population’s structure. Changing human behavior might reduce overall transmission, but it won’t change which ages are most affected. That’s set by the mosquito-human interface, which is biological, not cultural.