Bird flu (avian influenza) viruses belong to type A influenza viruses. Type B, C, and D viruses are also distinguished. Type A viruses can infect humans and animals. Viruses of this type are considered the most important from the point of view of public health because they can potentially cause a global influenza epidemic (pandemic).
Type A viruses are additionally separated into subtypes according to the combinations of their surface proteins – hemagglutinin (H) and neuraminidase (N). Some examples of subtypes that cause avian influenza include A/H5N1 (the most common) and A/H9N2. The natural reservoirs for most subtypes of influenza A viruses are waterfowl. Currently, known type A influenza viruses do not spread efficiently between humans.
Bird flu viruses pose two kinds of threats to humans.
The risk is that the bird flu virus could jump from birds to humans and cause severe disease in humans. The transmission risk is higher in locations where individuals and domestic birds live close to each other or in occupations exposed to contact with infected birds, e.g., during slaughter operations or veterinarians.
Influenza viruses evolve and may increase the risk of transmission to humans by acquiring mutations in the genome (or by exchanging genome segments between different subtypes of viruses also from different species (reassortment)) that favor adaptation to mammals.
Therefore, there are two forms of risk to human health posed by avian influenza viruses: infection with indigenous forms of avian influenza viruses and the possibility of new pandemic strains directly from avian viruses or their recombination with humans or other animal viruses.
Currently, no genetic changes enable species jumps of avian influenza viruses in the bird-mammal-human sequence. Still, the increasing number of A(H5N1) cases among mammals – biologically closer to humans than birds – raises concerns that some mammals will become suitable hosts for the reassortment of genetically variable zoonotic influenza viruses, which may lead to the emergence of new variants with epidemic and pandemic potential.
In humans, infection is most often transmitted by droplets, less frequently by contact with contaminated surfaces or objects or hands. People are relatively rarely infected with avian influenza.
People become infected with H5N1 by touching sick birds or coming into contact with their secretions and feces. Most human cases of illness have occurred in rural or suburban areas where many farms raise poultry. To reduce the likelihood of infection, you should:
Following these precautions can help reduce the risk of getting this condition.
High-risk groups include:
While human infection with bird flu is extremely rare, it can occur in specific situations. The disease can be transmitted through close contact with infected poultry or their droppings, as well as from surfaces contaminated by these materials. It's important to note that the virus can also spread through the air, meaning that direct physical contact is not always necessary for transmission.
The risk increases when individuals are within 1 meter of infected birds or contaminated environments. Most infections typically occur in rural areas, particularly on small farms where animals can roam, interact with wild birds, and enter homes or play areas where children are present.
In cases where bird flu is reported on large commercial farms, it is usually due to serious lapses in sanitary practices. However, no data indicates that properly cooked poultry or eggs pose a risk of illness.
The manifestations of bird flu in humans are often similar to those of a common viral infection, at least in the first phase.
Symptoms include:
However, in many patients, the disease develops uncontrollably, leading to viral pneumonia and then respiratory failure. This is already a direct danger to life and causes high mortality.
The treatment of bird flu is pharmacological and concerns the administration of antiviral medicaments. Patients can receive neuraminidase inhibitors, which are effective in infections with certain strains of influenza A and B viruses. They significantly improve the prognosis for survival, but the patient needs to start therapy as soon as possible.
Although this disease may be frightening, it should be remembered that the number of recorded cases worldwide is negligible when compared to the hundreds of millions of illnesses and deaths among animals.
According to data from the European Centre for Disease Prevention and Control (ECDC), from 2004 (when the first case was detected in humans) to June 2023, 876 people worldwide were infected with the H5N1 virus, mainly in Asia and Africa. It is, therefore, difficult to speak of an epidemic or the widespread nature of the phenomenon.
The ECDC information on the mortality rate of the disease is much more disturbing. 458 people died, which means the death rate was as high as 52 percent. Paradoxically, however, it is precisely the high virulence of the disease that is a factor protecting against its spread and the outbreak of a pandemic – patients are quickly isolated or die without spreading germs on a mass scale.
Experts emphasize that transmission of the virus typically transpires from animals to humans. However, there have been isolated cases of human-to-human transmission in 23 countries, indicating that it is theoretically possible.
In addition to H5N1, do other strains of bird flu pose a threat to humans? Until recently, the answer was undoubtedly negative. However, in 2021, the first isolated infections with the H5N8 and H10N3 strains were recorded.
Possible complications of bird flu infection in humans include:
The mortality rate of infections with the A/H5/ and A/H7N9/ subtypes in humans is much higher than that associated with seasonal flu.
If there is human exposure to a known outbreak of the influenza A virus in domestic poultry, wild birds, or other animals, or if there is an identified human case of this virus, enhanced surveillance of potentially exposed human populations becomes essential.
A thorough epidemiological investigation should be conducted if there is confirmed or suspected human infection with a novel influenza A virus with pandemic potential, including avian influenza. This investigation should begin even while awaiting laboratory confirmation and must include a review of individuals' exposure history to animals and/or travel, as well as contact tracing. The investigation should focus on identifying distinctive circumstances that could indicate person-to-person transmission of the novel virus. Clinical specimens from suspected human cases should be collected and sent to the WHO Collaborating Centre for further evaluation.
According to the World Health Organization (WHO), antiviral drugs from the neuraminidase inhibitor group are useful in treating bird flu in humans. However, cases of virus resistance to the latter have been reported. The available evidence suggests that these drugs can shorten the pathogen's time to reproduce and improve the patient's survival prospects, but further research is needed. To maximize the therapeutic benefits, these drugs should be administered within 48 hours of the beginning of symptoms. Nevertheless, the WHO recommends considering their use later in the disease.
The treatment of bird flu is the same as that of typical flu. In the initial period, antiviral drugs can be used. This is a neuraminidase inhibitor that works by inhibiting the replication and multiplication of the influenza virus, which shortens the time of flu symptoms.
For this drug to be effective, it should be administered within two days of the first symptoms of the disease appearing. This drug is administered orally at a dose of 75 mg twice daily for five days. It is also used to prevent influenza – in patients after contact with a person infected with the influenza virus. This drug can be used in adults and children (from 1 year of age).
Symptom treatment primarily involves the use of antipyretics and anti-inflammatory drugs. Paracetamol (analgesic and antipyretic effects) and ibuprofen (antipyretic, anti-inflammatory, and analgesic effects) should be mentioned here.
In advanced cases, when hospitalization is necessary, the following are used:
When discussing issues related to bird flu, it is also worth noting what symptoms may indicate infection with the virus above in poultry. These include:
Some animals may also experience symptoms from the nervous system, such as:
Sometimes, sick poultry (e.g., geese) may have no eggshell. The birds are usually also lethargic and have fluffed-up feathers.
Deaths from avian influenza can occur suddenly, often without any visible symptoms indicating an infection. The mortality rate can even reach 100%. In infection with a low-virulence strain of the influenza virus, birds may exhibit mild symptoms primarily affecting the respiratory system, including signs of depression, diarrhea, and reduced egg production, which can lead to a complete cessation of laying. Other symptoms may include weakness, fluffing of feathers, and fever. Infected birds shed large amounts of the virus through their feces and secretions from their eyes and respiratory tract.
Prolonged illness can lead to increased congestion, particularly in the throat, trachea, stomach, and surrounding heart fat, along with subcutaneous swelling in the head and legs of the affected birds.
Chickens and turkeys are highly susceptible to the avian influenza virus infection and are prone to developing clinical forms of the disease. Guinea fowl, quail, pheasants, and partridges are also susceptible, though slightly lesser. Ducks and geese can be infected by all strains of the avian influenza virus, but only certain highly pathogenic strains lead to noticeable disease symptoms in them. Ostriches are the most resistant to bird flu, with mortality rates ranging from 20% to 30% in infected populations. In contrast, emus exhibit virtually no clinical symptoms or mortality when infected.
Contrary to appearances, preventing bird flu in humans is relatively simple because few people have direct access to infected birds. Today, it is not yet known whether the situation will be complicated by infections reported in cats. On the one hand, these animals commonly live in some countries; on the other hand, most do not have contact with other individuals, so the virus transmission paths are very limited. Nevertheless, it is worth following numerous rules that help reduce the risk.
As part of bird flu prevention, you should:
In addition, it is worth familiarizing yourself with the guidelines regarding contact with birds, both farm and wild. These recommendations are addressed primarily to employees of farms and companies involved in meat processing, but the principles contained therein may also be useful in everyday life.
Therefore, you should:
Travelers to countries experiencing avian influenza outbreaks should take precautions by avoiding farms, live animal markets, areas where animals may be slaughtered, and any surfaces that could be contaminated with animal feces. It is important for travelers to wash their hands frequently with soap and water and to follow good food safety and hygiene practices.
If individuals infected with the virus from affected areas travel abroad, their infection may be identified in another country during their travel or upon arrival. However, the likelihood of further community spread is considered low, as the virus has not yet developed the ability to spread easily between people.
All human infections caused by the new influenza A virus subtype must be reported under the International Health Regulations (IHR). Member States must promptly notify the World Health Organization (WHO) of any laboratory-confirmed recent human infections with influenza A virus that could potentially lead to a pandemic.
The WHO does not recommend implementing special checks on travelers at entry points or imposing restrictions on the current situation concerning influenza viruses at the human-animal interface.
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