Final answer:
In the 19th century, tropical regions were considered unhealthy zones that led to increased disease, partially due to European colonial expansion and the environmental conditions that favored disease vectors. The use of quinine as a prophylactic against malaria marked a significant improvement in the health conditions of these regions. Bacteriological advances further contributed to disease management in the tropics.
Step-by-step explanation:
In what century were the tropics considered 'unhealthy' zones leading to increased disease? The answer lies primarily in the 19th century, during the time of European imperialism and the expansion of colonial empires. Tropics were often labeled as zones rampant with diseases such as malaria, dysentery, and yellow fever, which were significant barriers to European imperial ambitions. One turning point came in 1841 when British expeditions discovered that daily doses of quinine could serve as a preventive measure against malaria. Colonization and the infrastructure changes it brought, like irrigation and transportation networks, often exacerbated the spread of disease. However, knowledge in bacteriology and medical advancements later allowed for more effective disease management in tropical regions.
Throughout the 19th century, tropical regions were stigmatized as sources of infectious diseases due to their hot and humid climate, which is conducive to the proliferation of vectors like mosquitoes, triggering a surge in diseases such as malaria and yellow fever. This perception of the tropics as an unhealthy zone influenced the imperial and colonial policies of European nations. The health conditions in the tropics were only marginally improved upon the introduction of modern medicine and increased understanding of disease transmission.