Childhood infections quite usual — they are the body gathering experience
‘ ELL doctor, I know it’s just a cold, but Jimmy’s had an awful lot of them this winter. Do you think there could be something wrong with his immune system?’’
The human immune system is extraordinarily complicated and absolutely essential to our survival and well-being. When you stop to think about it, it has a very difficult job to do. It has to quickly detect and identify foreign biological material, and then mount a rapid, lethal response. To do this it needs an arsenal of destructive weapons such as antibodies and various white blood cells — weapons which can be just as deadly to our own cells as they are to invading organism.
Most of the time the system is able to both discriminate our own (host) tissues from invading material, and mount an effective response with minimum collateral damage. Inevitably, things occasionally do go wrong. Broadly speaking, immunological diseases fall
Winto one of two categories. Auto-immune diseases, such as rheumatoid arthritis, occur when the body initiates a destructive immune response against its own tissues. Immunodeficiency diseases, such as AIDS, happen when the defensive capacity of the body is impaired.
Different components of the immune system tend to deal with different organisms. While there is always some co-ordination between different elements, as a broad generalisation the different types of white cells are primarily responsible for defending against viruses, fungi and mycobacteria (organisms such as TB). Deficient cellular immunity is the key problem in AIDS, and sufferers typically experience infections with these types of germs. Antibodies (special proteins manufactured by immune cells and released into the bloodstream) are particularly important in fighting bacterial infections, so antibody-deficient patients tend to get recurrent infections caused by germs such as staphylococcus.
The immune system, important as it is, is not the only defence our body has against infection. The integrity of physical barriers such as skin and mucosal surfaces is very important, as is the production and flow of body secretions — such as respiratory mucous — and the presence of normal bacteria on the skin and in the gut.
Babies are born functionally immunodeficient. Not having been exposed to any infections, they have no ‘‘ immune memory’’ to call on, and their cellular immunity is not yet mature. Maternal antibodies transferred during pregnancy and breastfeeding counteract this to some degree, but infections remain a serious threat in the first weeks of life.
Even when their immune system matures, it is still naive in that it has not built up a stock of antibodies against common organisms. Hence childhood is a period of frequent illness — half of all children experience nine or more infections between their third and fourth birthdays. These are more common in winter, so a lot of these kids seem constantly unwell.
The vast majority of children with frequent infections are experiencing multiple viral colds or flus and have perfectly normal immunity. There are, however, a few disorders which do leave children with significant immune deficiency.
Rather than frequent upper respiratory tract infections, these children have features such as multiple high-grade bacterial infections, infections with unusual organisms or common organisms at unusual sites, and recurrent or difficult-to-treat infections.
They are often associated with poor growth and development, and the more severe causes result in early death if untreated.
The most common recognised congenital immuniodeficiency syndrome is a lack of antibodies of the immunoglobulin A type, affecting about one in 600 people. Fortunately it is a mild disorder, often asymptomatic, though if combined with reduced levels of immunoglobulin G can cause recurrent sinus and chest infections.
In short, it’s highly likely Jimmy has an intact immune system and mum can be reassured. But if he had recurrent pneumonia or other serious infections and was not thriving as expected, investigation of his immune system might be warranted. Simon Cowap is a GP practising in Newtown, Sydney