Science - November 10, 2005

‘Vaccinating hobby poultry dangerous’

Preventive vaccination of poultry kept as pets is unwise and may present a risk to humans, says veterinary epidemiologist Professor Mart de Jong. Nevertheless, the Dutch ministry of agriculture has announced that it wants to make vaccination of ‘hobby birds’ possible.

De Jong, chair of Quantitative Veterinary Epidemiology and researcher at the Animal Sciences Group (ASG), fears that vaccination might make the virus go ‘underground’. Experiments performed by ASG and CIDC-Lelystad have indicated that vaccinated golden pheasants do not develop symptoms of avian influenza, but are capable of transmitting the virus. ‘Vaccination can therefore create a false sense of security,’ says De Jong. ‘The last thing we want is poultry that remains healthy but passes the virus on to humans.’

The ministry of agriculture therefore needs to think very carefully about preventive vaccination. According to De Jong there are too many species of birds that are kept by enthusiasts in the Netherlands to be able to predict what the effects of vaccination will be. ‘The research that has been done on golden pheasants and ringed teals makes it clear that the effects of vaccination of one kind of bird will not necessarily be the same for another type of bird.’

Dr Guus Koch, a virologist at CIDC-Lelystad, has his doubts about how realistic preventive vaccination is. ‘Vaccination is an option, but only if it can be carried out in an optimal fashion. In some cases it will be necessary to vaccinate more than once to ensure a good response, and it is by no means certain that this is feasible.’ According to Koch there are even strong indications that suboptimal vaccination of chickens in Indonesia led to influenza infection in humans.

Stephanie Wiessenhaan of the Food Quality and Animal Health directorate at the ministry of agriculture confirmed that the decision has been made to request permission to vaccinate ‘hobby poultry’ from the European Union. A definitive vaccination plan has not yet been drawn up. ‘One of the points for discussion is the target animals. We still need to gather expert advice on this.’ She points out though that non-vaccination also carries risks. ‘In the end it’s about the risks we are prepared to live with.’ / GvM