Dr Fred Kavalier: A Question of Health

"What are the risks of getting an infection from a dog? Our toddler is frequently being licked around the face by a dog that is brought into his nursery by one of the other mothers."

"What are the risks of getting an infection from a dog? Our toddler is frequently being licked around the face by a dog that is brought into his nursery by one of the other mothers."

The greatest potential risk to children from dogs in this country is an infection with a worm called toxicara. Toxicara worms live in the intestines of dogs, and eggs from the worms get into the soil and environment from dogs' faeces. If the eggs get on to a child's hands, they can end up in the child's mouth and cause an infection. There are two types of human infection from toxicara, but the more serious one occurs when the worm gets into the eyes. Left untreated, it can cause blindness or permanent eye damage. The best protection against toxicara is regular worm treatment for dogs. "Scooping the poop" is also important, and dog owners who let their animals foul the pavements and parks are often unaware of the disease risks they are causing. Luckily, toxicara is rare ­ there are only about 100 cases a year in the UK. The only way to diagnose it is with a special blood test.

"In a recent article about alternative medicine, I read that there were concerns about possible side effects of St John's Wort. As I have taken this recently and may continue to do so, I wondered if you would advise me of what these side effects are."

St John's Wort is a herbal preparation that is used to treat depression. In this country it is considered to be an "alternative" medicine, but in Germany it is much more widely used than drugs like Prozac. It is not completely free of side effects, but they do seem to be uncommon and relatively mild. The most widely quoted side effects are dryness of the mouth, dizziness, fatigue and stomach and intestinal upsets. St John's Wort can also increase your sensitivity to sunlight, so a mild tan could turn into a bad sunburn much more quickly than you expect. It can interact with other drugs, including prescribed antidepressants, drugs used to treat epilepsy and migraine, and even the contraceptive pill. Last year the Department of Health issued a warning that women who take the pill should not take St John's Wort, due to an increased risk of unintended pregnancy.

"My daughter's period, which often makes her take to her bed for at least one day a month, is due right in the middle of her A-level exams. Is there any safe way of delaying it until after the exams are over?"

It's relatively easy to delay a menstrual period, but it takes a little forward planning. Your daughter could start taking the contraceptive pill a month before her exams begin, and take it continuously until the exams are over. This would almost certainly abolish her periods without causing any side effects that are going to affect her exam performance. When the exams are over, she could stop the pill without any problems and her cycle would return to normal. There is another method of delaying periods that involves taking the hormone norethisterone, but this is less reliable and more unpredictable.

Please send your questions to A Question of Health, 'The Independent', Independent House, 191 Marsh Wall, London E14 9RS; fax 020-7005 2182 or e-mail health@independent.co.uk. Dr Kavalier regrets that he is unable to respond personally to questions