Infections can be viral, bacterial, fungal and protozoal. Sports people catch infections just like anyone else, however, sometimes they are more exposed, particularly in team situations or travelling. Training hard can also weaken the immune system which can make athletes more susceptible to illness. Here we explain some of the more common infections and viruses affecting athletes.


Viral illnesses are usually simply referred to as a virus or viral infection. They occur when a microscopic infectious agent enters the body. Here the virus attacks the body, causing an immune response and illness. When training hard, athletes could be at increased risk of viral infections as their immune system is weakened. Viral infections can be mild or severe, with a range of symptoms.

Viruses can take many forms, some cause a feeling of fatigue for a few days, some cause vomiting and diarrhea or infections (most commonly to the respiratory system) or more serious forms, include ebola, AIDs, cancer and avian influenza (bird flu).

In the case of the athlete, training hard for prolonged periods results in a weakened immune system and increased susceptibility to viruses.

Once a virus has been diagnosed, a decision must be made regarding training and sometimes competition. Those suffering symptoms of vomiting and diarrhea and with a raised temperature are ruled out due to the potential for serious illness developing. Training in the presence of systemic symptoms (such as muscle aching, hot flushes etc) is also contraindicated.

Those with a mild (or no) temperature the athlete may be able to complete a light training session, keeping below 70% of maximum heart rate. This has previously been demonstrated to have positive effects. Competing with a viral illness will in the vast majority of cases result in impaired performance.

Bacterial infections

Bacteria are tiny sorganisms made of a single cell. They are particularly resilient and can survive in the harshest of conditions.  Some bacteria are beneficial to us, especially in the gut but some can be very harmful (called pathogenic bacteria).

Fungal infections

Fungi can live in our bodies quite happily without causing any problems. Common fungal infections include Candid (thrush) and Tinea Pedis (athletes foot). Less common fungal infections include aspergillosis which causes a chest infection and pneumocystis can result in Pneumonia.

Protozoal infections

Protozoa are the smallest animals known. Toxoplasmosis is an infection caused by protozoa, causing mild illness in healthy people, but those with weakened immune systems can get more serious infections that can spread to the brain.