You’re an infant teacher, helping a child with her reading. The child trusts you implicitly. When she rests her head on your shoulder, and reaches out to touch your cheek, as if to convince herself you’re real, you’re moved to believe you have the most worthwhile job going.

It’s a strong and abiding feeling. It has to be to survive the evenings you spend combing livestock out of your hair, or the sick days you have to take waiting for conjunctivitis to clear or impetigo scabs to disappear.

It’s important not to exaggerate the rate at which teachers catch illnesses and parasites from pupils. But happen it does, particularly in key stage 1, when children are more likely to be physically close and less aware of what they might be carrying. One infant school deputy head - let’s call her Sally - reels off a litany of unpleasantness that’s enough to put anyone off their school dinner.

“In my first term I caught mumps from a child,” she says. (Mumps is usually little more than uncomfortable in childhood - although there are some rare complications. It’s more serious and painful for adults, especially men, because their testicles can be affected.) “I was off school for half of the term. It really knocked me back for the whole of the year at the start of my career. I never really got to know the children as I should have done.”

Not long afterwards, when Sally was pregnant with her first child, there was an outbreak of rubella in the school. This is a nightmare for many female teachers, as contracting rubella in the first four months of pregnancy can cause the baby to be born with congenital rubella syndrome (CRS), which can bring blindness, deafness and heart defects. It can be severe enough to prompt some women to terminate their pregnancy.

Sally thought she might have caught rubella, and had to go to hospital for tests. The condition is difficult to diagnose - which adds to the anxiety - and to this day Sally doesn’t know whether she had it or not. What she does know is that she had an anxious pregnancy before giving birth to a healthy girl who later became a teacher herself.

Rubella is becoming increasingly rare now it’s included in the infant MMR immunisation programme and in the pre-school booster. Women teachers should make sure of their own immunisation status, though, because the disease won’t be eliminated as long as some parents exercise their right not to have children immunised. One headteacher recalls when rubella was much more common in schools. “It was never just a matter of saying, ‘Oh, none of us is pregnant’. We had to bear in mind the people who might have been pregnant and didn’t know.”

In the years that followed, Sally had the full house. As well as endless coughs and colds, there was scabies (an itchy, scabby condition, usually around the hands and fingers, caused by a microscopic, burrowing mite). Then she had more than one bout of impetigo - another scabby skin condition, bacterial and highly contagious. A recurrent problem, which afflicts many infant teachers, was conjunctivitis, an eye infection that can be easily spread by sharing towels as well as by direct contact.

The most common affliction, though, is humanity’s old companion (they’ve been spotted on Egyptian mummies), the common head louse, Pediculus humanus capitis.

Sally has suffered from regular attacks of head lice and become adept at minimising the discomfort. Her secret? “Use plenty of hairspray. It seems to stop them getting a foothold. Only today my headteacher plucked off a louse that was stuck in my spray.”

Sally’s sanguine attitude is not shared by every adult, even though, unlike many parasites, head lice do not transmit diseases. In the Seventies, so great was the concern that health officials launched a campaign to eradicate head lice altogether. It was a brave effort - and it failed.

Pauline Archer, a senior school health officer in Warwickshire, says: “It’s surprising the amount of hysteria that’s generated over this insect the size of a grain of rice, when there are much more important and dangerous things to worry about, such as meningitis.”

Many medical experts oppose the use of pesticides on head lice, on the grounds that the problem isn’t serious enough to warrant anointing yourself with poisonous substances. Sally employs a back-to-basics approach. “Most of us try not to use chemicals,” she says. “Some swear by a mixture of tea tree oil and vodka, but even that’s a bit strong for your hair and scalp. I use a fine tooth comb, and a conditioner that makes it easier to get the comb through your hair. You just persevere with it until they’ve gone.”

The combs are fine enough to let individual strands of hair through but too narrow for the lice. Some, like Sally’s, have a battery pack that sends a small electric charge strong enough to kill or stun unwelcome visitors. Whatever comb you use, make sure you soak it in hot water afterwards. If you don’t, you could put the lice back where they came from.

Lubricating the hair to make combing easier is a good idea. In southern Europe, olive oil is commonly used, but it tends to leave a sticky residue. Some of the “essential oil” treatments for head lice may well be useful as much for easing the combing as for any anti-louse properties. One such treatment is Nitmix, which was developed by a qualified nurse and her husband. They claim their product can even prevent re-infestation. Worth a try, and certainly harmless.

Sally has never allowed the occasional infection - aside from that early brush with rubella - to worry her too much. She’s a dedicated, long-serving key stage 1 teacher, and it seems likely that her love of the job and of children have actually brought about some of her problems. She’s careful about washing her hands, tying her hair back, avoiding contact where possible and being aware of the implications of an itchy spot or a rash. In the end, though, she’s still going to be invaded by nasties from time to time.

“This sort of thing is much more prevalent in nursery and infant departments,” she says. “We do have guidelines about touching and cuddling now, but that doesn’t stop children coming close to you when you’re sitting down, perhaps putting their hands on your face. It’s a spontaneous thing to do.”

Teachers working with older children are no more prone to catching coughs, colds and rashes than other workers. There are occasional outbreaks of meningitis - potentially lethal enough to undermine reassurances to parents about its rarityJ- and teachers are regularly reminded of the need to be aware of the danger signs. If it does appear in a school, the health authorities rapidly set up immunisation programmes, which are usually effective.

In the late Eighties, schools faced growing concern about the possibility of HIV transmission, and in 1988 the Medical Officers of Schools Association produced a set of guidelines that changed the way teachers and other staff deal with first aid. The traditional sports field bucket and sponge, for example, was replaced by pre-packed sterile sponges and sterile water, all handled with protective gloves. We now know that the risk of infection through this route is virtually non-existent, but the precautions are sensible in general health terms - and they work against hepatitis, too.

The good news for new teachers, who traditionally catch a series of colds and sore throats in the first term, is that there may well be some substance in the idea that immunity grows. Bridget Lawder, school nurse at Edgarley Hill School in Somerset, and a contributor to the excellent Handbook of School Health produced by the Medical Officers of Schools Association, says: “On the whole, teachers and nurses develop immunity because they’re subjected to low levels of infection all the time. But general personal hygiene is very important.”

The Handbook of School Health is available from Trentham Books, pound;22. Tel: 01782 745567 Nitmix: PO Box 5605, Loughborough LE12 6ZD www.nitmix.com SOMETHING IN THE HAIR

* Pediculus humanus capitis (pictured opposite) has legs adapted to grasping the hairs of the human head, and lives on daily meals of human blood. It won’t live on your pets, and it won’t survive anywhere else for more than a day.

* It’s passed on by direct head-to-head contact. Only rarely is it caught in any other way - furniture, hats and so on.

* About 3mm long when fully grown, the female louse lays about 100 eggs at the rate of six a day. She attaches them to the hair, and they hatch after eight days.

* The newly hatched louse - “nymph” - is less than one millimetre long and takes one to two weeks to grow fully.

* They’ve been with us since ancient times, indifferent to class, social status and level of cleanliness, and are well programmed to survive.

* An infested person might have only a dozen live lice (but hundreds of eggs - “nits”). Yet it’s the live lice you have to target.

* They can be difficult to spot - especially at the nymph stage, when they can be too small even for a fine comb - and they run for cover. That’s why you have to repeat the combing, to get the ones you’ve missed and to catch the growing nymphs.

* Most frustrating of all, the victim is frequently reinfested by contact with the same carrier. Adults are usually more careful than children, but even teachers can be caught out in this way.