Avian influenza in humans
Links between human and avian influenza
Influenza viruses are classified as types A, B and C, and they are found in various birds and mammals, including humans. In addition to man, influenza A viruses cause natural infections in birds while influenza B and C types usually affect humans. Influenza A viruses are also frequently isolated from pigs and horses. Wild birds are thought to be the reservoir of influenza A viruses.
Avian Influenza (AI) is a serious disease of poultry occuring more and more frequently all over the world. The recent spread in bird populations in Asia is unprecedented. Two groups of viruses are recognised on the basis of their ability to cause disease in poultry: Highly Pathogenic Avian Influenza (HPAI) and Low Pathogenic Avian Influenza (LPAI).
Influenza A viruses have a segmented genome allowing for genetic re-assortment. As a result, circulating influenza viruses show a high level of genetic variations and may develop the capability of crossing the species barrier. Animal husbandry systems where humans live in close cohabitation with poultry and pigs are considered as potential sources of new strains capable to cross the species barrier from animal to man. Avian influenza viruses able to infect humans and to spread easily from person to person may cause an influenza pandemic.
The reported symptoms of avian influenza in humans range from typical influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.
Humans are not commonly affected by avian influenza. However, the large epidemics of highly pathogenic avian influenza that currently affect poultry in Asia, and the widespread presence of the virus in the environment increase opportunities for human exposure and infection. In fact, over the past years, avian influenza infections in humans have been repeatedly reported from Asia. Stringent measures such as large scale culling of affected poultry are believed to have prevented the evolution of these outbreaks towards a pandemic. The Office International des Epizooties OIE and the Food and Agricultural Organisation FAO maintain rapid alert and notification systems on animal health and food safety that cover influenza.
Analysis of the evidence available during past outbreaks indicates that:
- the majority of human infections is caused by HPAI viruses following direct exposure to infected birds.
- direct contact with infected poultry appears to be the favourite way of transmission from poultry to humans.
- human to human transmission is very limited;
- only HPAI viruses are fatal to humans.
- considering the massive exposure, there are very few human infections resulting from HPAI.
Firstly, legislation adopted by the EU to prevent the spread of avian influenza amongst birds and poultry (control measures to be applied, preventive vaccination) has a direct impact on human health. These measures contribute to reduce the opportunities for human exposure and infection.
In addition, according to the terms of the Decision No 2119 of the European Parliament and of the Council, the EU took some measures to watch over the disease and to facilitate communication between Community health services and Member States concerning avian influenza :
- Since the first human cases have been notified by Viet Nam, the Commission services have facilitated communication at community level. Through the activation of the EU Early Warning and Response System, Member States, EEA/EFTA and acceding countries are sharing information on measures that they have undertaken or that they have planned to implement.
- A restricted web-based portal Health Emergency & Diseases Information System (HEDIS) has been developed. The site is designed to support Community services and Member States during disease outbreaks and health emergencies. It is currently used to provide a central point of access to all information concerning avian influenza derived from various sources available: news, press releases, updated situational maps, online questionnaires, activity logbook, virtual meetings, access to relevant documents, discussion forums, etc.
- At global level, the European Commission contributes to the assistance offered to affected countries. International cooperation has been set up to assist these countries to control and eradicate the disease in poultry. The Commission closely cooperates with the WHO to follow the evolution of the disease.
- Furthermore, avian influenza in humans may be a potential source of pandemic influenza. Concerning this issue, the Commission actively collaborates with Member States and the WHO to develop influenza pandemic preparedness planning at EU level.
The European Centre for Disease Prevention and Control (ECDC), an EU Agency created in 2004 to help strengthen Europe's defences against infectious diseases, has taken over the task to provide scientific advice on risk assessment and to coordinate influenza surveillance at EU level. The ECDC has issued several documents:
- The Public Health Risk from Highly Pathogenic Avian Influenza Viruses Emerging in Europe with Specific Reference to type A/H5N1 (Version June 1st 2006)
- Guidelines to minimise the Risk of Humans Acquiring Highly Pathogenic Avian Influenza from Exposure to Infected Birds or Animals (Version December 21th 2005)
- Guidance for National Authorities to Produce Messages for the Public Concerning the Protection of Vulnerable Groups (Version February 2006)
- Health advice for people living in or travelling to countries where the A/H5N1 virus has been detected (Version April 2006)
The European Food Safety Authority (EFSA), the EU Agency providing scientific advice on all matters on nutrition in relation to community legislation, issued a report on avian influenza and food safety.