Virology and Immunology

By Thomas Sim, 14 April 2004

Virology is the study of viruses. Immunology is the study of our immune system. Immune system is the primary defense against foreign invader in our body. This article is about the common myths and misunderstanding of these subjects.

Viruses are once classified as organisms like bacteria but now it is vastly recognized as non-living things which only become 'active living' in a host organism. If you say a bacterium is like an orange, then viruses are the size of beans. Some viruses live in bacteria as their host. Therefore, for the sack of comparison, viruses can live in our body cells, just like they live in a bacterium (which is a single cell).

Immunity is our defense against foreign organism. We can acquire this immunity by recognising the invader (be a bacterium or a virus). If we develop some form of immunity (defense) against this organism, generally we refer to have some antibody against it.

Therefore, we develop vaccine to prevent certain infection from virus or bacteria. There are many diseases and infections that we can get vaccinated against. In simple languages, we teach our body to defense against a particular invader by giving mock attack to our immune system. This is largely carried out by government in all strata of population in a national vaccination programme. For example, new borns are vaccinated against Hepatitis B virus in a 3 doses vaccination programme.

However, the interesting part of the viro-immunology is that antibody to the virus does not indicate defense. In many instances, it is taken as indication of infection and thus does not render a person protected against the virus. This is the most misunderstood part of the science by any lay person.

Just to give two examples: HIV and HBV

A patient is diagnosed of HIV (Human Immunodeficiency Virus) by antibody screening. In fact, by checking whether a person develops antibody to the HIV becomes the means to determine whether a person is infected by the virus. In conventional thinking, a person who develop antibody to virus is considered immune to the virus. Just compare the distinction of the difference! By misunderstanding the antibody, a person separates himself from heaven and hell! Hence, when a doctor tests for HIV antibody, in fact it is not a great news. If found positive, it is sentencing a patient to HIV positive! This means the patient is infected by HIV and going to need HIV treatment.

Next it is Hepatitis B Virus (HBV). In recent years, advances in immunology and in particular, Polymerase Chain Reaction (PCR) technology have revolutionalised the thinking of monitoring HBV viral load. A patient who has acquired antibody to the surface antigen (HBsAg ) - Anti-HBs, doesn't necessarily render the patient free from the harm of the virus. There is still trace of the virus DNA in the blood for as long as 7 years after patient had seroconverted from HBsAg+ve to Anti-HBs+ve. There is still question for blood product on this group of donors as no conclusive data is available to rule out danger of virus transmission from blood of the recovered HBV patient.