Causes of disease
A disease can be caused by many things. Sometimes germs enter our body through food, water or air. A person can be infected by infectious agents like bacteria, viruses or fungus. Disease can also be caused by eating bad or old foods. There are small germs in old foods that can cause diseases. Sometimes the germs produce chemicals or toxins which causes the disease.
One of the most common causes of disease is poor sanitation and lack of clean water. Some deadly diseases like malaria in tropical parts of the world are spread by a mosquito. Animals that spread disease are called vectors. There are many vectors, including snails, ticks, and fleas.
Some people are born with 'genetic diseases'. These are diseases because of an error or mutation in a person's DNA. An example of a mutation is cancer. Living or working in an unhealthy environment can also be a cause for diseases. Diseases are more common in older people.