Definition

Infectious diseases - designed to spread

Infectious diseases are caused through the spread of a micro-organism such as a bacterium or virus. They spread from person to person, often via the skin, saliva, blood or other bodily fluids.

Roche works to diagnose and treat several infectious diseases.

Influenza
One of the most common and contagious viruses is influenza. This infects the lungs and upper airways, causing a sudden high temperature and symptoms including aches and pains, headache, coughing and sore throat.

By changing their profile slightly every year, influenza viruses make it difficult forour immune system to fight them off. In the UK, about 600 people a year die from flu and this can reach more than 12,000 during an epidemic year (Source:NHS Choices).

The influenza virus is spread in droplets of saliva coughed or sneezed into the air by an infected person. It can also be picked up from hard surfaces, such as door handles that have been touched by someone with the virus. 

Hepatitis B & C
Hepatitis B & C are viral infections that cause inflammation of the liver. They are similar in their causes and symptoms, however they have different effects on the liver.

Hepatitis B can cause the liver to swell, and sometimes cause significant liver damage. The vast majority of people who are infected with hepatitis B are able to fight off the virus and fully recover from the infection within a couple of months. However, hepatitis B can go on to cause chronic illness, where it lasts for longer than six months. This is very common in babies and young children, but it can also occur in 2-10% of infected adults (Source:NHS Choices).

Hepatitis C can lead to scarring of the liver, liver cancer or liver failure and is potentially life threatening.
It is estimated that around 200,000 people in the UK have long-term (chronic) hepatitis C infection and around half of those are undiagnosed (Source:NHS Choices).

Symptoms of hepatitis C can include a short, flu-like illness, fatigue, nausea, vomiting, diarrhoea, loss of appetite, weight loss, jaundice or itchy skin. Others may be infected for years without knowing.

Hepatitis C is mainly spread through contact with the blood of an infected person. Sharing contaminated needles or other equipment for injecting drugs poses the biggest risk. Anyone who received a blood transfusion or blood products in the UK before screening was introduced could also be at risk.

Less commonly, the virus can also be transmitted through unsterilised tattoo, acupuncture or body piercing equipment or by having unprotected sex with a person with the virus. It is also possible for the virus to be passed from an infected mother to her baby or via contaminated razors or toothbrushes.

Human Immunodeficiency Virus (HIV)
The HIV infects and destroys blood cells called CD4 cells. These cells help fight infection and their destruction stops the immune system working. Someone with HIV is therefore at a high risk of developing a serious infection or disease, such as cancer.

HIV is transmitted through the exchange of bodily fluids, such as semen or blood. It can spread through sexual intercourse, by sharing needles for injecting drugs, from a mother to her unborn child and through infected blood transfusions.

Sepsis
Sepsis occurs when infection has spread through the blood. This leads to widespread inflammation which can damage organs and interfere with the flow of blood. It is estimated that there are 31,000 cases of severe sepsis in England and Wales every year, with 30 to 50 per cent of those affected dying from the condition (Source:NHS Choices).

Sepsis begins either as a result of an infection confined to a particular part of the body, such as pneumonia or appendicitis, or as a result of a severe injury. If the immune system is weakened or the infection or injury is very severe, the infection then spreads through the blood. The immune system reacts by releasing a high number of proteins called cytokines. Instead of fighting the infection, the proteins cause damage to the organs of the body and affect blood circulation.

Chlamydia
Chlamydia is now the most commonly diagnosed sexually transmitted infection (STI) in the UK with almost 207,000 confirmed cases in England in 2012 (Source:NHS Choices). It often has no symptoms, but, if left untreated, can lead to complications including pelvic pain in women. If the infection spreads, it can cause pelvic inflammatory disease in women, which can cause infertility, ectopic pregnancy and miscarriage.

Chlamydia is caused by a bacterium called chlamydia trachomatis. It is transmitted through sex, with incidence higher in young people under 25.

Gonorrhoea
Another STI is gonorrhoea, which is also passed on by sex. It is caused by a bacterium called neisseria gonorrhoea. Symptoms include changes in discharge from the vagina or penis, pain or burning sensation when urinating in women and inflammation of the testicles and prostate gland in men. If left untreated, gonorrhoea can lead to pelvic inflammatory disease in women and can also affect fertility in men.

Human Papilloma Virus (HPV)
Also sexually transmitted are a group of more than 100 viruses that are known collectively as human papilloma virus (HPV). HPV affects the skin and the moist membranes that line parts of the body. Some types of HPV are known to increase the risk of developing particular types of cancer whilst others can cause warts and verrucas.

The HPV virus is spread through skin contact. It is often transmitted during sex but it is thought that there may be other ways of spreading the virus that are yet to be identified.

Understanding all these infectious diseases at a molecular level helps our scientists to develop tests and medicines to detect, treat and monitor them.