Avian flu and other forms of zoonotic flu
- Humans can be infected with avian influenza viruses and other zoonotic influenza viruses such as bird influenza subtypes A (H5N1), A (H7N9), and A (H9N2), and the two subtypes of swine flu viruses A (H1N1) and H3N2.
- Human infections occur mainly through direct contact with infected animals or contaminated environments, but these infections do not lead to the effective transmission of these viruses in humans. There is no evidence of human susceptibility to bird or zoonotic influenza viruses through adequately cooked foods.
- The majority of human infections with A (H5N1) and A (H7N9) viruses have been associated with direct or indirect contact with live or dead poultry infected with the infection. The control of the disease at the animal source level is critical to reducing people's vulnerability to infection.
- It is impossible to eliminate influenza viruses because there is a large silent virus repository in water birds. Infections with zoonotic influenza can continue to occur in humans. The minimize public health risks, it is essential to ensure quality animal and human monitoring, comprehensive investigation of each human infection, and risk-based pandemic planning.
There are three types of influenza viruses: A, B, and C. Humans and many different animals are infected with A-style influenza viruses. B-type influenza viruses apply only to humans and cause seasonal epidemics. Humans and pigs can be infected with type C influenza viruses, but infections are generally mild and rarely reported.
Type A influenza viruses are classified into two subtypes depending on the combinations of different proteins found on the surface of the viruses, namely the agglutinin (H) protein and the neuraminidase (N) protein. There are 18 different subtypes of proteins (H) and 11 different subtypes of proteins (N). Type A influenza viruses can be classified as bird flu, swine flu, or other animal flu viruses by their original host. Examples include subtypes of bird influenza A (H5N1), A (H9N2), or subtypes of swine flu A (H1N1) and A (H3N2). All these Type A animal influenza viruses differ from human influenza viruses and are not easily transmitted to humans.
Water birds are the primary natural repository of most of the subtypes of influenza A viruses. Most of these viruses cause asymptomatic or mild infections in birds, and the range of symptoms depends on the virus's characteristics. Viruses that cause severe diseases in birds and lead to high mortality rates are called highly pathogenic avian influenza viruses. Viruses that cause poultry outbreaks but are not generally associated with severe diseases are called low-pathogenic bird flu viruses.
Human infection with avian and zoonotic influenza viruses
Human infections with avian and zoonotic influenza viruses were reported. Human infections occur mainly through direct contact with infected animals or contaminated environments but do not lead to the effective transmission of these viruses in humans.
In 1997, human infections of the highly pathogenic avian influenza A (H5N1) were reported at the time of an outbreak among poultry in China's Hong Kong Special Administrative Region. Since 2003, this avian influenza virus has spread from Asia to Europe and Africa and has taken hold in poultry in some countries. Outbreaks have resulted in millions of poultry infections, hundreds of human cases, and many human deaths. Poultry outbreaks have had a serious impact on the affected countries' livelihoods, economies, and international trade. Other bird influenza subtype A (H5) viruses also caused poultry outbreaks and human infections.
In 2013, cases of human infection with the low-morbidity avian influenza A (H7N9) virus were reported in China. Since then, the virus has spread to poultry swarms nationwide, causing hundreds of human infections and many human deaths.
Other avian influenza viruses, including those from A (H7N7) and A (H9N2), have caused sporadic human infections. Some countries have also reported sporadic cases of swine flu viruses in humans, especially with viruses of subtypes A (H1) and A (H3).
Clinical features of bird flu infections and other forms of zoonotic flu
Infections with bird flu and other forms of zoonotic influenza in humans may cause diseases ranging from mild conjunctivitis to severe pneumonia and even death. The characteristics of the disease, such as the incubation period, severity of the symptoms, and clinicadependetype ofethe subtype of the virus causing the infection.
For human infections of the avian influenza A (H5N1) virus, current data indicate an incubation period of two to five days on average, ranging up to 17 days (1). For cases of human infection of A (H7N9), the incubation period varies from one to 10 days and averages 5 days (2). The average incubation period for these two viruses is longer than that for seasonal influenza (within two days) (2). An incof days period ofhuman for human infections with swine has beenrrespondedeen reported. (2)
The disease has a violent clinical pathway in many patients infected with avian influenza A (H5) or A (H7N9) viruses. High fever (38 °C or higher) and cough are common primary symptoms. Signs and symptoms of lower respiratory tract injury, including shortness of breath or dyspnea, have been reported. Upper respirinjuriestract injuries symptoms such as a sore throat or a cold, are less common. Other symptoms such as diarrhea, vomiting, abdominal pain, nostril or gingival bleeding, and chest pain were also reported in some patients' clinical pathways. The complications of the infection include hypoxia, multiple-organ dysfunction, microbial infections, and secondary fungal infections. The mortality rate of viral infections from subtypes A (H5) and A (H7N9) in humans is significantly higher than that of seasonal influenza infections.
In most cases of human infection with avian influenza A (H7N7) and A (H9N2) viruses, the disease is mild or non-clinical. Only one case of the deadly human infection influenza A (H7N7) has been reported in the Netherlands (3). The majority of human infections with swine flu viruses were mild, with a small number of people being hospitalized and very few deaths reported as a result of the infection (2).
Evidence suggests that some antiviral drugs, especially oseltamivir can reduce the period of HIV replication and improve potential survival chances (1).
Oseltamivir should be prescribed in suspected cases as soon as possible (within 48 hours following symptoms in optimal condition) for maximum therapeutic benefits. However, consideration should also be given to administering the drug to patients seeking treatment at a late stage in the course of the disease due to the high mortality rate currently associated with viral infections of subtypes A (H5) and A (H7N9) and evidence of prolonged viral replication in these diseases. Corticosteroids are not recommended. In cases of severe infection with the virus A (H5) or A (H7N9), doctors may have to consider increasing the recommended daily dose or extending the treatment period.
Absorption of the drug may be hampered in patients with severe cases of HIV infection A (H5), A (H7N9), or with severe gastrointestinal symptoms. That possibility should be taken into account in the treatment measures for those patients. Most viruses A (H5) and A (H7N9) are resistant to adamantine-type antiviral drugs that are therefore not recommended for use.
Risk factors for infection
The primary risk factor for infection with avian influenza viruses in humans appears to be direct or indirect exposure to live or dead poultry in infected or contaminated environments, such as live bird markets. Potential risk factors also include the slaughter, feathering, handling, and preparation of infected poultry for consumption, particularly in the domestic context.
There is no evidence to suggest that HIV (A (H5), A (H7N9), or other avian influenza viruses can be transmitted to humans through poultry meat or properly prepared eggs. A few cases of human infection with influenza A (H5N1) have been associated with the consumption of dishes prepared using raw and contaminated poultry blood. It is essential to combat the application of avian influenza viruses in poultry to reduce the risk of human infection. Given the persistence of viruses A (H5) and A (H7N9) in some poultry swarms, control will require countries' long-term commitment and firm coordination between animal health and public health authorities.
For swine flu viruses, most human cases are reported to be attributed to the close proximity of infected pigs or to visiting sites where pigs are exposed, but in some limited cases, human transmission has occurred.
Influenza pandemics (outbreaks affecting a large proportion of the world's people because of a new virus) are phenomena that can only be expected to recur and can have global health, economic, and social consequences. The influenza pandemic occurs when key factors come together as follows: A virus of avian or zoonotihahasntenuouslytransmit continuously in humans, reducing or eliminating people's immunity to the virus. Given the growth of global trade and travel, a domestic pandemic could rapidly become a pandemic, making time for a public health response.
The continued application of certain subtypes of avian influenza viruses, such as A (H5) or A (H7N9), in poultry raises public health concerns because these viruses generally cause severe diseases in humans and can undergo mutations that make them more transmissible in humans. To date, the human transmission of these viruses is considered to have occurred in some rare cases when there has been prolonged and very close contact between a very sick person and his or her caregivers, such as family members, but human transmission has not been continuous. If these viruses adapt or acquire virus genes, they can cause a pandemic.
It is not known whether the avian flu viruses and other zoonotic influenza viruses currently in force will cause a future pandemic, but the diversity of avian flu viruses and other zoonotic influenza viruses that have caused human infections entails continued animal and human monitoring, detailed surveillance of each human infection, and risk-based pandemic planning.
As part of its leadership role on global health issues, FAO is closely monitoring avian and other zoonotic influenza viruses through its Global Network for Flu Monitoring and Response. Specifically, FAO, OIE, and WHO are collaborating to track and assess risks from avian influenza viruses and other zoonotic influenza viruses of public health concern.
Based on the results of the risk assessment, the organization develops and adapts appropriate interventions in collaboration with its partners, including animal health agencies and national veterinary authorities responsible for the control and prevention of animal diseases, including influenza.
Member States apromptlyimely manner of the latest risk assessment findings and recommendations for interventions aimed at enhancing preparedness and response.