There's a certain type of person in this town whom my children have labelled 'Mrs Dirty Dirty'. She's easily identified. She carries at least three spare T-shirts for her children, a carton-load of anti-bacterial wipes and shrinks in terror at the sight of any living thing not sanitised and plastic wrapped, especially large hairy dogs. Right now, she's enjoying a revival. Mothers who tell their children not to touch animals are being proven right by recent health warnings about four-footed or feathery friends. Even the mosquito is being sought and destroyed everywhere. And as a letter writer to the editorial page noted, if we continue to label every species on Earth a health hazard that needs to be destroyed, won't we be ruining our own ecosystem? This week, the creatures back on the hit list are birds. Chickens are being slaughtered in the millions by our neighbours north of the border, and the warnings not to let children feed or play with the birds are back in force. How real is the risk? Is Mrs Dirty Dirty well-advised to add a barrier suit to her equipment list when she takes the dog for a walk in the park? First, the birds that are carrying the various forms of bird flu - although H5N1 has got us all worried, there are plenty of others - are water birds. The migratory water birds that stop over at the Mai Po marshes carry wild strains of these viruses much of the time. They pass them on to ducks and geese, which don't seem to be affected. The trouble starts when they come into contact with chickens, either on farms, on the way to market, or crammed in at the wet markets. This mixing has been eliminated in Hong Kong by strict rules that enforce the separation of chickens from geese, ducks and other bird species. But does this mean humans need to be so obsessive? They should certainly be careful. Not handling birds, or their feathers, and making sure children don't handle them is wise. Bird feathers can carry flu viruses that pass through their gut. Regardless of whether an animal is listed as this week's danger, washing hands after handling birds or touching related equipment is basic hygiene. Training children to always wash their hands before they eat is giving them a basic survival skill. It's remarkable how many people start preparing food without washing their hands or eat food with unwashed hands. The Sars lessons haven't been learnt as well as we thought. What about a fear of pigeons - something encouraged by park curators? Pigeons haven't been identified as culprits so the warning is really only precautionary. Pigeons carry plenty of germs, so children who have been playing in areas full of pigeons should thoroughly wash their hands before they eat. But making them afraid of the birds is unhealthy. Given the anxiety about animal-borne diseases (even domestic cats were under threat at one point, but I'm happy to say they've been given a full clearance), should you consider having a pet? Pets are great for teaching children responsibility and how to care for someone dependent on you. But in Hong Kong, domestic helpers seem to do most of the pet care, so children don't learn very much. There have been plenty of studies showing that children exposed to pets early are healthier, suffer less from asthma and are more confident. But not all children benefit, because some have pet-hair allergy and get severe asthma if they're close to a hairy animal. But it's a personal decision, and since living in a flat isn't easy for any animal, if you have doubts don't get one. Mrs Dirty Dirty is wrong to fear animals, but she's right to be cautious.