Promoting health and stopping the spread of disease requires education and access to health care, both of which are hard to come by in some developing countries. The social mores and customs of a society sometimes make it difficult for such things to take place effectively or even easily.
For example, HIV drugs have been made available to some degree in developing African countries, but in many societies there, time is a different concept than it is in the West. The idea that such drugs that must be taken regularly, and on time, is a foreign concept to people who do not tend to carry watches or cellphones. In other cultures, the persistent myth that, if an HIV-infect man has sex with a virgin, then he can be cured of the disease. In some countries, they are very resistant to immunization simply because they do not understand how the body works. Promoting safer health habits, then, is very much a social problem as well as a health issue as one must work to counter the social customs and misinformation that exists in a society.
In other societies, female health care workers are rare, countercultural, or may only work on female patients. Taking the social and religious customs of a society into account when trying to promote health is therefore essential. Having medical professionals who are culturally (and hopefully linguistically) fluent in the area they are sent to help is also critical.