1.1 Acute infections
The life-cycle shown earlier in Video 2 is typical of an acute virus infection, such as influenza or COVID-19. An acute infection is one where a person becomes infected, and the immune system then reacts to destroy the virus and virus-infected cells. In the end, the immune system prevails and there is no longer any of the virus left in that host – this is referred to as sterile immunity. Usually, an acute infection will last for a few weeks, at most.
However, some virus infections can evade the immune system and lie low within cells of the host for months or years, producing no symptoms. Such infections are said to be latent. In addition, they may reactivate or stay continuously active over this period; in this case they are responsible for a chronic infection.
Activity 1 Acute and chronic viral infections
Look at Table 1 below, which lists some viruses that produce disease in humans. From your previous knowledge or experience try to decide which of these viruses produce an acute infection and which produce a latent or chronic infection. Write your answers in the boxes provided in the last column. Then click on ‘Reveal feedback’ to see the answers. The first box has been filled in for you.
| Virus | Disease | Acute or latent/chronic infection |
|---|---|---|
| SARS-CoV2 | COVID-19 | Acute |
| Rubella virus | German measles | |
| Ebola virus | Ebola | |
| Human immunodeficiency virus (HIV) | Acquired immune deficiency syndrome (AIDS) | |
| Norovirus | Gastroenteritis (vomiting, diarrhoea) |
|
| Rhinovirus | Common cold | |
| Epstein Barr virus | Glandular fever | |
| Herpes simplex virus | Cold sores | |
| Poliovirus | Poliomyelitis (Infantile paralysis) |
|
| Varicella zoster virus | Chicken pox, shingles | |
| Mumps virus | Mumps |
Comment
Here is the completed table:
| Virus | Disease | Acute or latent/chronic infection |
|---|---|---|
| SARS-CoV2 | COVID-19 | Acute |
| Rubella virus | German measles | Acute |
| Ebola virus | Ebola | Acute |
| Human immunodeficiency virus (HIV) | Acquired immune deficiency syndrome (AIDS) | Chronic |
| Norovirus | Gastroenteritis (vomiting, diarrhoea) |
Acute |
| Rhinovirus | Common cold | Acute |
| Epstein Barr virus | Glandular fever | Acute/Chronic |
| Herpes simplex virus | Cold sores | Latent |
| Poliovirus | Poliomyelitis (Infantile paralysis) |
Acute |
| Varicella zoster virus | Chicken pox, shingles | Acute/Latent |
| Mumps virus | Mumps | Acute |
Rubella virus, Ebola virus, Norovirus, Rhinovirus, Poliovirus and Mumps virus cause acute infections. Notice that acute infections can still cause very serious diseases and in some cases (eg polio) the damage lasts for a lifetime, even if the viral infection is relatively short. HIV causes a persistent chronic infection. Epstein Barr virus causes glandular fever, an acute infection, but usually persists as a symptomless chronic infection for years. Herpes simplex can remain latent for many years and sporadically reactivate to produce cold sores. Varicella zoster produces chicken pox as an acute illness, but becomes latent in some people and reactivates to produce shingles. As you may have deduced, chronic and latent infections are persistent infections that continue after the initial acute infection with that virus.
Don’t worry if you did not get all of these. In reality, the outcome in any individual may be different from the usual course of infection. For example, in people who are immunosuppressed or immunodeficient, acute viral infections are often slower to clear and are more likely to become chronic infections.