The workers and engineers still viewed miasma theory (‘bad air’), foul tropical soils, and direct contact with infected persons as the causes of the disease. This lack of knowledge of its entomological transmission route in fact resulted in many disastrous decisions facilitating the disease to spread[3]. For instance, hospital wards in which the afflicted were treated were routinely kept with wide open windows, meaning mosquitos were free to enter, feast upon infected inpatients, and disperse freely to blight the healthy. Even worse, potted plants brought in to improve aesthetics provided females with pools of standing water: a perfect habitat in which to lay their eggs. The French were effectively culturing the disease in the very rooms in which the sick were being treated!
It was US army physician Major Walter Reed who finally demonstrated unequivocally thatAedes aegypti was the vector of the virus, building on the ‘mosquito hypothesis’ proposed by Cuban scientist Carlos Finlay in 1881. This was achieved through an ethically questionable, but simple experiment[5]. A newly emerged A. aegypti mosquito was taken by Reed, allowed to feed on a suffering patient, and then transferred – voluntarily – to his friends and co-workers. When they became sick with Yellow Fever days later (but thankfully surviving) the breakthrough had been made[5]. The Americans now knew how to succeed where the French had failed.