While avian influenza (AI) is recognised to be an infectious disease primarily affecting birds, the European Food Safety Authority (EFSA) is continuously evaluating scientific evidence with respect to AI and food safety.
In this context, EFSA’s scientific panel on biological hazards (BIOHAZ) has just published a scientific report called Food as a possible source of infection with highly pathogenic avian influenza viruses for humans and other mammals.
This comprehensive scientific document analyses whether consuming food contaminated with highly pathogenic avian influenza (AI) virus could initiate infection in mammals via the digestive route. The paper examines in detail existing data on AI, and H5N1 in particular, studying various aspects of the virus’s transmission in relation to food and the gastrointestinal tract.
The report begins with a comprehensive background section in which the European Food Safety Authority (EFSA) points out that it is aware that there is no epidemiological information available to date suggesting that avian influenza (AI) – an infectious disease primarily affecting birds – can be transmitted to humans via food.
Constant review
Nevertheless, in view of the developing situation in relation to AI, EFSA’s BIOHAZ is keeping this issue under constant review. EFSA concurs with the advice of health authorities such as the World Health Organisation (WHO) and the European Centre for Disease Prevention and Control (ECDC) indicating that the most likely route of infection of the H5N1 bird flu virus in humans is through close contact with infected live poultry. The consumption of poultry products or eggs has not been implicated in the transmission of the H5N1 AI virus to humans. In the event of an H5N1 outbreak in poultry in Europe, stringent biosafety measures would immediately be put in place to limit the spread of infection by any means.
EFSA provided an initial statement on AI in January 2004 where it stated that there is no direct evidence to support the food chain as a possible route for transmission of the AI virus (www.efsa.eu.int). EFSA published a further statement on 12 September 2005 outlining its work in progress on the animal health and welfare aspects of AI and reiterating with respect to food safety the WHO recommendations on the safe handling and cooking of food in relation to AI.
On 20 September 2005 EFSA published an opinion and report on the animal health and welfare aspects of AI and provided information on the risks of AI entering the European Union and spreading amongst poultry. EFSA also made recommendations to prevent its introduction and spread amongst flocks in Europe. This report has provided the scientific basis for AI risk management measures already put into practice in Europe with respect to animal health.
Handling and preparation
Other organisations that have provided advice and information on the safe handling, preparation and cooking of foods are mainly food safety authorities, the World Health Organisation (WHO) (www.who.int) and the European Centre for Disease Prevention and Control (ECDC) which has provided advice regarding the public health aspects of avian influenza (www.ecdc.eu.int). EFSA has based its previous statements on the following scientific data:
- Scientific information on AI indicates that the AI virus can be present in the meat and eggs of poultry which are infected with the H5N1 form of AI.
- Documented cases of certain species of animals becoming infected to varying degrees through the consumption of raw poultry meat and eggs.
For example, one experimental study showed that cats became infected when fed on infected chickens. Further documentation also indicates that tigers may have contracted the infection in a similar way as a result of being fed fresh chicken carcasses from a local slaughterhouse.
Based on these reports, cats (felines) appear to be relatively susceptible to the H5N1 strain and may have become infected after consumption of carcasses of infected chicken.
Another example concerns the introduction of avian viruses to pigs, a not uncommon occurrence according to EFSA.
Pigs kept on farms where infected poultry had been detected during the Dutch avian influenza epidemic developed antibodies which were linked in one case to the feeding of broken eggs from infected poultry.
Likewise, the same EFSA scientific report also considers that there may be sufficient virus present in infected poultry meat to infect other birds if fed in the raw state. In effect, there is much circumstantial evidence of infection of certain animal species via food and consequently and as a precautionary principle this mode of transmission to animals cannot be ruled out.
- Among the reported human cases of H5N1, mainly in Asia, there are two reportedly related to the consumption of infected raw duck blood. However, as direct contact with infected live or undressed dead animals cannot be ruled out in these cases, epidemiological data are insufficient to confirm the consumption of infected product as the only transmission route.
- Among the 118 reported cases of human infection, most of the cases in Asia have been associated with direct exposure to live or dead infected poultry; however, in many instances, there is not sufficient epidemiological evidence to identify the source of infection (WHO) www.who.int
- While the level of acidity in the human stomach (pH value 1-3) does have the potential to eliminate the virus, as is widely believed to be the case for normal flu, this effect depends on several factors, such as the virus strain, quantity of virus present in the gastrointestinal tract and other local gastrointestinal factors (for example gastric transit time, acquired failure of the gastric acid barrier due to Helicobacter pylori infection, which is common among the healthy elderly) and the nature and composition of the gastric content. There are however few scientific data on this aspect today.
What is certain is that, in the hypothetical circumstance of infectious virus being present in the food, proper cooking of poultry meat and eggs will eliminate any virus present before consumption, thereby preventing even the theoretical possibility of the virus infection being acquired through food consumption.
The bulk of the 29-page report considers three main areas: the fate of avian influenza viruses (mainly H5 and H7 subtypes) in tissues of avian species; the infection of mammals with HPAI viruses; and viral and host factors possibly involved in AI infections in humans (with reference to the gastrointestinal tract).
Follow food safety advice
In conclusion, the report concurs with EFSA’s previously published advice on avian influenza in relation to food safety which said: “On present evidence, humans who have acquired the infection have been in direct contact with infected live or dead birds. There is no epidemiological evidence to date that avian influenza can be transmitted to humans through consumption of food, notably poultry and eggs. EFSA and other organisations such as the WHO generally support longstanding food safety advice that chicken and eggs be properly cooked in order to protect consumers from possible risks of food poisoning. Thoroughly cooking poultry meat and eggs also eliminates viruses, thereby providing further safety assurance in the unlikely event that H5N1 virus be present in raw poultry products entering the food chain.”
The full report is available at: www.efsa.eu.int
