Gert van der Hoek
In Memoriam - Editor, Senior Moderator
Low Pathogenicity Avian Influenzas and human health
Influenza Team (influenza@ecdc.europa.eu)
European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden
Human disease due to LPAIs
Influenza A/H7N2 virus, as seen in the poultry outbreak described above, is one of many Low Pathogenicity Avian Influenzas (LPAIs) [1]. These have a genotype associated with causing milder symptoms in birds than the rarer high pathogenicity viruses and are negative on in vivo test [2,3]. Outbreaks of LPAIs in birds, both wild and domestic poultry, occur regularly in Europe and are probably more common than recognised.
Serological surveys of domestic poultry have found evidence of outbreaks that seem to have been missed [4,5]. Occasionally, it seems that an LPAI transforms in birds to become a high pathogenicity avian influenza (HPAI) strain, but that is thought to be a rare event [4,6].
Human disease due to LPAIs
The fact that an avian influenza is highly pathogenic for birds does not necessarily mean it is pathogenic for humans. However, one notable influenza (type A/H5N1) is both highly pathogenic for birds and humans [7,8]. Influenza A/H7N2 virus infection in humans and all other human infections with LPAIs have only been associated with mild to moderate self-limiting disease, primarily conjunctivitis or flu like illness.
Some cases have ended up requiring hospitalisation, but all have recovered. In addition, it is likely that there are asymptomatic infections and infections with mild symptoms that are never diagnosed because LPAI is not suspected and tested for [5]. It is unclear whether or not there has ever been human-to-human transmission of an LPAI virus, although this has happened with some highly pathogenic viruses [9-11].
During case-finding in outbreaks, people are often found to have symptoms compatible with LPAI infection, but turn out not to be infected [6]. This was seen in an influenza A/H7N3 virus outbreak in the United Kingdom (UK) in 2006, when a single poultry worker presented with conjunctivitis and had confirmed infection, but others with similar symptoms were test-negative [12].
Who is at risk from LPAIs?
Following requests from European Union (EU) Member States and the European Commission, the European Centre for Disease Prevention and Control (ECDC) is undertaking a formal risk assessment for avian influenza viruses (excluding H5N1) in relation to human health. We also posted a document examining this outbreak and its implications on our website on 28 May [10],11.
After a thorough review of the literature, our assessment was that there is only limited public health risk from LPAIs, but that those who are at risk should nevertheless maintain vigilance and take precautions. The risk of infection with LPAIs is almost entirely confined to people who have close contact with domestic poultry (chickens, ducks etc) or their droppings. Human cases have almost entirely been in this category [11].
People with small domestic and pet flocks are probably most at risk, as they are less likely to be able to take precautions than those working in industry and may be less aware of the dangers. Other groups that have occasionally been infected are veterinarians and people involved in controlling outbreaks in birds (culling) and people who work on industrial poultry farms.
Most EU Member States have standard occupational guidance for the latter group, but there are others at theoretical risk who should follow basic precautions, as shown in the table below. However, no infections have been seen in these groups. For the vast majority of people, who have no direct contact with domestic birds or their droppings, the risk of acquiring LPAIs and the risk to health are almost non-existent.
Human infection with LPAIs from wild birds has never been reported.
What actions should those with domestic poultry take?
The advice from the ECDC has not changed and is the same as for reducing the risk of acquiring infection with HPAIs. People with small domestic flocks in Europe should always look out for ill-health in their birds and promptly report such to the authorities. They and their families should also maintain basic hygiene as this will minimise the risk of them catching LPAIs and the more dangerous pathogens that poultry may carry such as campylobacter and salmonellosis. The ECDC has produced model guidance on this for use by national authorities [12].
What is the risk of a pandemic resulting from an LPAI?
Essentially this risk is unknown and unknowable. It is thought that each of the three pandemics of the 20th century had a link with avian influenza, as some avian genes seem to have appeared in the resulting human pandemic strain. Although there is particular concern about avian influenza H5N1 because of its high pathogenicity in humans and its stability over time in bird populations, there is no prima facie reason to imagine that the next pandemic strain will contain genes from a HPAI rather than an LPAI [13,14].
http://www.eurosurveillance.org/ew/2007/070531.asp#2
Influenza Team (influenza@ecdc.europa.eu)
European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden
Human disease due to LPAIs
Influenza A/H7N2 virus, as seen in the poultry outbreak described above, is one of many Low Pathogenicity Avian Influenzas (LPAIs) [1]. These have a genotype associated with causing milder symptoms in birds than the rarer high pathogenicity viruses and are negative on in vivo test [2,3]. Outbreaks of LPAIs in birds, both wild and domestic poultry, occur regularly in Europe and are probably more common than recognised.
Serological surveys of domestic poultry have found evidence of outbreaks that seem to have been missed [4,5]. Occasionally, it seems that an LPAI transforms in birds to become a high pathogenicity avian influenza (HPAI) strain, but that is thought to be a rare event [4,6].
Human disease due to LPAIs
The fact that an avian influenza is highly pathogenic for birds does not necessarily mean it is pathogenic for humans. However, one notable influenza (type A/H5N1) is both highly pathogenic for birds and humans [7,8]. Influenza A/H7N2 virus infection in humans and all other human infections with LPAIs have only been associated with mild to moderate self-limiting disease, primarily conjunctivitis or flu like illness.
Some cases have ended up requiring hospitalisation, but all have recovered. In addition, it is likely that there are asymptomatic infections and infections with mild symptoms that are never diagnosed because LPAI is not suspected and tested for [5]. It is unclear whether or not there has ever been human-to-human transmission of an LPAI virus, although this has happened with some highly pathogenic viruses [9-11].
During case-finding in outbreaks, people are often found to have symptoms compatible with LPAI infection, but turn out not to be infected [6]. This was seen in an influenza A/H7N3 virus outbreak in the United Kingdom (UK) in 2006, when a single poultry worker presented with conjunctivitis and had confirmed infection, but others with similar symptoms were test-negative [12].
Who is at risk from LPAIs?
Following requests from European Union (EU) Member States and the European Commission, the European Centre for Disease Prevention and Control (ECDC) is undertaking a formal risk assessment for avian influenza viruses (excluding H5N1) in relation to human health. We also posted a document examining this outbreak and its implications on our website on 28 May [10],11.
After a thorough review of the literature, our assessment was that there is only limited public health risk from LPAIs, but that those who are at risk should nevertheless maintain vigilance and take precautions. The risk of infection with LPAIs is almost entirely confined to people who have close contact with domestic poultry (chickens, ducks etc) or their droppings. Human cases have almost entirely been in this category [11].
People with small domestic and pet flocks are probably most at risk, as they are less likely to be able to take precautions than those working in industry and may be less aware of the dangers. Other groups that have occasionally been infected are veterinarians and people involved in controlling outbreaks in birds (culling) and people who work on industrial poultry farms.
Most EU Member States have standard occupational guidance for the latter group, but there are others at theoretical risk who should follow basic precautions, as shown in the table below. However, no infections have been seen in these groups. For the vast majority of people, who have no direct contact with domestic birds or their droppings, the risk of acquiring LPAIs and the risk to health are almost non-existent.
Human infection with LPAIs from wild birds has never been reported.
What actions should those with domestic poultry take?
The advice from the ECDC has not changed and is the same as for reducing the risk of acquiring infection with HPAIs. People with small domestic flocks in Europe should always look out for ill-health in their birds and promptly report such to the authorities. They and their families should also maintain basic hygiene as this will minimise the risk of them catching LPAIs and the more dangerous pathogens that poultry may carry such as campylobacter and salmonellosis. The ECDC has produced model guidance on this for use by national authorities [12].
What is the risk of a pandemic resulting from an LPAI?
Essentially this risk is unknown and unknowable. It is thought that each of the three pandemics of the 20th century had a link with avian influenza, as some avian genes seem to have appeared in the resulting human pandemic strain. Although there is particular concern about avian influenza H5N1 because of its high pathogenicity in humans and its stability over time in bird populations, there is no prima facie reason to imagine that the next pandemic strain will contain genes from a HPAI rather than an LPAI [13,14].
http://www.eurosurveillance.org/ew/2007/070531.asp#2
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