More houses need to be built to accommodate the growing population, and forests and ecosystems are being destroyed to do so. This destruction of ecosystems on which to build land, as well as the need for wood to build houses, greatly affects the home environments of wildlife and plant life and, consequently, the entire ecology of the world. The overall health of the world's population is severely affected by population growth. When a population significantly increases in size, the need to build more hospitals and the need for more doctors also increases. This need for hospitals forces governments to raise taxes to finance the construction of these necessary facilities. Unfortunately, many third world countries cannot afford to build all the necessary hospitals and have inadequate sanitation available to their populations, making their large, densely populated areas very susceptible to spreading viruses..