Understanding Avian Flu – Key Facts
The European Commission has recently adopted protective measures to try to contain a bird flu outbreak after new cases were reported in the UK and the Netherlands. The measures include killing animals in infected areas and banning sales of poultry products from those areas. The Dutch government has reported the “highly contagious” H5N8 strain at a poultry farm there, and the UK reported a case at a duck farm in East Yorkshire, of which the Commission said was “probably identical”.
On 17 November 2014 the Commission adopted interim protective measures for the Netherlands and for the United Kingdom which will be published on 19 November 2014 in the Official Journal of the European Union
The press release issued on 17 November gives more details on the events:
As regards the HPAI H5N8 outbreak detected in Germany on 5 November first interim EU measures were adopted on 6 November and published on 8 November as Commission Implementing Decision 2014/778/EU. The measures have already been reviewed and confirmed at the meeting of the Standing Committee on Plants, Animals, Food and Feed on 13 November 2014.
Epidemiological investigations are ongoing to identify the possible source of virus. The fact that the three recent outbreaks in Germany, The Netherlands and the United Kingdom have occurred in proximity of humid areas with wild birds and the absence of any other epidemiological link between them, point towards wild migratory birds as the likely source of virus. Member States concerned are evaluating their wild bird surveillance data and are enhancing monitoring. Consequently, the Commission has asked all EU Member States to increase biosecurity on poultry farms.
- Avian influenza (AI), commonly called bird flu, is an infectious viral disease of birds.
- Most avian influenza viruses do not infect humans; however some, such as A(H5N1) and A(H7N9), have caused serious infections in people.
- Outbreaks of AI in poultry may raise global public health concerns due to their effect on poultry populations, their potential to cause serious disease in people, and their pandemic potential.
- Reports of highly pathogenic AI epidemics in poultry, such as A(H5N1), can seriously impact local and global economies and international trade.
- The majority of human cases of A(H5N1) and A(H7N9) infection have been associated with direct or indirect contact with infected live or dead poultry. There is no evidence that the disease can be spread to people through properly cooked food.
- Controlling the disease in animals is the first step in decreasing risks to humans.
Influenza at the Human-Animal Interface
Influenza viruses circulating in animals pose threats to human health. Humans can be exposed to these viruses, such as avian influenza virus subtypes H5N1 and H9N2 and swine influenza virus subtypes H1N1 and H3N2, in many ways, such as:
- when people’s work brings them in contact with infected animals.
- when people contact infected animals during their everyday lives, such as when visiting live animal markets or when these animals are kept as part of the household.
- when people handle or slaughter infected animals, or work with raw meat and by-products from infected animals.
- when people contact things around them, such as animal housing areas and equipment, ponds and other water sources, feces, and feathers, if these things are contaminated with influenza viruses.
In some cases these zoonotic infections (infections in humans acquired from an animal source) result in severe disease or even death in humans, but often these infections result in only a mild illness or appear to cause no illness at all. All human infections with animal influenza viruses are of concern, not only because of the cases of disease and deaths in individual people, but also because if these viruses become able to spread from human to human they could spark a pandemic. All of the past four pandemic influenza viruses have contained gene components originating in animals.
The actual public health risks posed by influenza viruses circulating in bird, swine, and other animal populations are not completely understood. Recent findings suggest that influenza viruses in animals and humans increasingly behave like a pool of genes circulating among multiple hosts, and that the potential exists for novel influenza viruses to be generated in swine and other animals. This situation reinforces the need for close monitoring and close collaboration between public health and veterinary authorities.
Avian influenza (AI) is an infectious viral disease of birds (especially wild water fowl such as ducks and geese), often causing no apparent signs of illness. AI viruses can sometimes spread to domestic poultry and cause large-scale outbreaks of serious disease. Some of these AI viruses have also been reported to cross the species barrier and cause disease or subclinical infections in humans and other mammals.
AI viruses are divided into 2 groups based on their ability to cause disease in poultry: high pathogenicity or low pathogenicity. Highly pathogenic viruses result in high death rates (up to 100% mortality within 48 hours) in some poultry species. Low pathogenicity viruses also cause outbreaks in poultry but are not generally associated with severe disease.
Avian influenza A(H5N1) and A(H7N9) background
The A(H5N1) virus subtype, a highly pathogenic AI virus, first infected humans in 1997 during a poultry outbreak in Hong Kong SAR, China. Since its widespread re-emergence in 2003 and 2004, this avian virus has spread from Asia to Europe and Africa and has become entrenched in poultry in some countries, resulting in millions of poultry infections, several hundred human cases, and many human deaths. Outbreaks in poultry have seriously impacted livelihoods, the economy and international trade in affected countries.
The A(H7N9) virus subtype, a low pathogenic AI virus, first infected 3 humans – 2 residents of the city of Shanghai and 1 resident of Anhui province – in March 2013. No cases of A(H7N9) outside of China have been reported. Containment measures, including the closure of live bird markets for several months, have impacted the agriculture sectors of affected countries and international trade. Continued surveillance for A(H7N9) will be necessary to detect and control the spread of the virus.
Ongoing circulation of A(H5N1) and A(H7N9) viruses in poultry, especially where endemic, continues to pose threats to public health, as these viruses have both the potential to cause serious disease in people and may have the potential to change into a form that is more transmissible among humans. Other influenza virus subtypes also circulate in poultry and other animals, and may also pose potential threats to public health.
Avian influenza A(H5N1) and A(H7N9) infections and clinical features in humans
The case fatality rate for A(H5N1) and A(H7N9) virus infections in people is much higher compared to that of seasonal influenza infections. The A(H7N9) virus particularly affects people with underlying medical conditions.
In many patients, the disease caused by the A(H5N1) virus follows an unusually aggressive clinical course, with rapid deterioration and high fatality. Like most emerging disease, A(H5N1) influenza in humans is not well understood.
The incubation period for A(H5N1) avian influenza may be longer than that for normal seasonal influenza, which is around 2 to 3 days. Current data for A(H5N1) infection indicate an incubation period ranging from 2 to 8 days and possibly as long as 17 days. Current data for A(H7N9) infection indicate an incubation period ranging from 2 to 8 days, with an average of five days.1 WHO currently recommends that an incubation period of 7 days be used for field investigations and the monitoring of patient contacts.
Initial symptoms include high fever, usually with a temperature higher than 38°C, and other influenza-like symptoms (cough or sore throat). Diarrhea, vomiting, abdominal pain, chest pain, and bleeding from the nose and gums have also been reported as early symptoms in some patients.
One feature seen in many patients is the development of lower respiratory tract early in the illness. Respiratory distress, a hoarse voice, and a crackling sound when inhaling are commonly seen. Sputum production is variable and sometimes bloody.2 Complications of A(H5N1) and A(H7N9) infection include hypoxemia, multiple organ dysfunction, and secondary bacterial and fungal infections.3
Evidence suggests that some antiviral drugs, notably oseltamivir, can reduce the duration of viral replication and improve prospects of survival.
In suspected cases, oseltamivir should be prescribed as soon as possible (ideally, within 48 hours following symptom onset) to maximize its therapeutic benefits. However, given the significant mortality currently associated with A(H5N1) and A(H7N9) infection and evidence of prolonged viral replication in this disease, administration of the drug should also be considered in patients presenting later in the course of illness. The use of corticosteroids is not recommended.
In cases of severe infection with the A(H5N1) or A(H7N9) virus, clinicians may need to consider increasing the recommended daily dose or/and the duration of treatment.
In severely ill A(H5N1) or A(H7N9) patients or in patients with severe gastrointestinal symptoms, drug absorption may be impaired. This possibility should be considered when managing these patients.4 Moreover, most A(H5N1) and A(H7N9) viruses are predicated to be resistant to adamantine antiviral drugs, which are therefore not recommended for use.
Risk factors for human infection
The primary risk factor for human infection appears to be direct or indirect exposure to infected live or dead poultry or contaminated environments, such as live bird markets. Controlling circulation of the A(H5N1) and A(H7N9) viruses in poultry is essential to reducing the risk of human infection. Given the persistence of the A(H5N1) and A(H7N9) viruses in some poultry populations, control will require long-term commitments from countries and strong coordination between animal and public health authorities.
There is no evidence to suggest that the A(H5N1)and A(H7N9) viruses can be transmitted to humans through properly prepared poultry or eggs. A few A(H5N1) human cases have been linked to consumption of dishes made of raw, contaminated poultry blood. However, slaughter, defeathering, handling carcasses of infected poultry, and preparing poultry for consumption, especially in household settings, are likely to be risk factors.
Human pandemic potential
Influenza pandemics (outbreaks that affect a large proportion of the world due to a novel virus) are unpredictable but recurring events that can have health, economic and social consequences worldwide. An influenza pandemic occurs when key factors converge: an influenza virus emerges with the ability to cause sustained human-to-human transmission, and the human population has little to no immunity against the virus. With the growth of global trade and travel, a localized epidemic can transform into a pandemic rapidly, with little time to prepare a public health response.
The A(H5N1) and A(H7N9) AI viruses remain two of the influenza viruses with pandemic potential, because they continue to circulate widely in some poultry populations, most humans likely have no immunity to them, and they can cause severe disease and death in humans.
However, whether the influenza A(H7N9) virus could actually cause a pandemic is unknown. Experience has shown that some animal influenza viruses that have been found to occasionally infect people have not gone on to cause a pandemic while others have done so. Surveillance and the investigations now underway will provide some of the information needed to make this determination.
In addition to A(H5N1) and A(H7N9), other animal influenza virus subtypes reported to have infected people include avian H9, and swine H1 and H3 viruses. H2 viruses may also pose a pandemic threat. Therefore, pandemic planning should consider risks of emergence of a variety of influenza subtypes from a variety of sources.
Sources: World Health Organization, EUROPA, European Centre for Disease Control