Child­hood in­fec­tions quite usual — they are the body gath­er­ing ex­pe­ri­ence

The Weekend Australian - Travel - - Health - SI­MON COWAP

‘ 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

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