Communicable & Non- Communicable Diseases

Pathogens

A pathogen is a microorganism that causes a disease. There are four main types of pathogen:

All types of pathogen have a simple life cycle. They infect a host, reproduce themselves or replicate if it is a virus, spread from their host and infect other organisms. They also all have structural adaptations that make them successful at completing their life cycles, which enable them to cause further disease.
Diseases caused by pathogens are called communicable diseases. This means they can be transferred from one person to another.

There are other types of disease which cannot be caught:

• Inherited genetic disorders like cystic fibrosis.
• Deficiency diseases which are caused by a lack of essential vitamins or minerals, such as scurvy which occurs when an individual has insufficient vitamin C.
• Diseases like cancer that develop as a result of exposure to carcinogens or develop naturally as cell division occurs incorrectly.

All organisms are affected by pathogens. Even bacteria are infected by certain types of virus. Some of these infections can be transferred to organisms of a different species.

Transmission

Transmission can occur in a number of important ways, as shown in the table below.

Non-communicable diseases

Cancer

Cancers are non-communicable diseases, which means they cannot be caught from another source. Instead they naturally develop in the body. Cancers occur when cell division goes wrong. This causes cells to grow out of control, which form a tumour. There are two types of tumour:

• malignant - these tumours are cancerous and can break apart, move around the body and start new instances of the same cancers in a process called metastasis
• benign - these tumours are less serious because they are not cancerous, and do not spread

Cancers are looked for by doctors in a process called screening. This can be in an x-ray, in blood or urine tests, or by using monoclonal antibodies.
Many cancers are caused by smoking or drinking excessive quantities of alcohol. Others are caused by infections such as the HPV virus. Other reasons include the Sun's UV rays and some environmental pollutants. The risk of cancer also increases as we get older.
The most frequent cancers in the UK are breast, lung and bowel cancers, and prostate cancer in men. A quick diagnosis is essential for treating all cancers. Treatment can be:

• chemotherapy, by using chemicals to kill cancerous cells
• radiotherapy, by using x-rays to kill cancerous cells
• palliative, which helps a person who has terminal cancer to die as comfortably as possible

Many cancers are less likely to develop if people lead healthy lifestyles, such as not smoking, exercising regularly and eating a healthy diet.

Other non-communicable diseases

• Anything that increases a chance of developing a disease is called a risk factor. Risk factors can be part of a person's lifestyle, or substances that a person consumes or their environment. Some diseases are caused by an interaction between risk factors.
• Some risk factors have been proved to cause a disease. We know that smoking causes lung cancer. Other risk factors are linked but not proved. The risk factor physical inactivity is linked to increased levels of breast cancer but this has not been proved.
• Some diseases, their effects and their risk factors are shown in the table below.