With no doubt illiteracy is a crucial problem of the world, and it is a pervasive phenomenon in poor countries.
There are many causes for the problem, and I think poverty is the most important one. In many undeveloped or developing countries, many people can't afford their basic living needs: food, water,etc. For this reason, the they may not care about if they are illiteracy, and how illiteracy can influence their lives. In these countries, many people are illiteracy, they may have many children in one family, not for other reasons, but to have more labour to get enough food, so they will not send their children to school. It is not suprising that in some poor countries, all generations in a family are illiteracy.
Besides, traditional concept also can be one of the causes. In some countries, such as China,differece among girls and boys is large. In the past decades, girls were not allowed for school,and had to stay at home for housework while boys could go to school for education. Nowadays this phenomenon seems being eased, however, this traditional concept still existed in some countries.
The effects of illiteracy? It leads to a more serious poor-rich gap, not only within a country, but worldwide. Many countries have been developing with their knowledge and technology in different aspects, such as sience, medical fesilities,etc., however those countries with serious illiteracy problem without such knowledge or technologies, this hinders them to make steps forward for improvement. Serious poor-rich gap causes serious society problem(this topic is not discussed here).
Solving illiteracy problem needs long-term policies, it may takes a very long time to ease this problem. Developed countries can donate materials to those which are undeveloped, helping them settle the problems of living needs, then enable the children going to school.
The governments of the countries can also help, by encouraging or enforcing the parents to send their childre to school, letting them know the iffluence of seriousness of illiteracy problem; but the most important is, the illiteracy should keep open-minded, try to learn more, should not only stay in their little world.