OVERVIEW

What is human infection with highly pathogenic avian influenza?

Human infection with highly pathogenic avian influenza, as the name suggests, can be broken down into three concepts for interpretation.

First, avian influenza is the abbreviation for avian flu, which is a poultry infectious disease caused by avian type A influenza viruses, primarily spreading among poultry such as chickens, ducks, and geese.

Avian type A influenza viruses have different subtypes, among which strains of the H5 and H7 subtypes (represented by H5N1, H7N7, and H7N9) cause diseases with strong pathogenicity and virulence, known as highly pathogenic avian influenza.

When these viruses infect humans, leading to acute respiratory infectious diseases primarily characterized by respiratory symptoms, it is referred to as "human infection with highly pathogenic avian influenza."

Is human infection with highly pathogenic avian influenza common?

Not very common.

Taking H5N1 as an example, since its discovery in 2003, sporadic transmissions have infected approximately 860 people. Meanwhile, H7N9 has recorded about 1,300 cases since its first report in 2013. Given the vast total population, human infection with highly pathogenic avian influenza is relatively rare.

However, it exhibits clear seasonal patterns and certain regional distribution. Additionally, based on studies of the virus's genetic characteristics, there is a need for high vigilance against potential pandemics.

SYMPTOMS

Will different viruses causing highly pathogenic avian influenza in humans lead to different symptoms?

Avian influenza viruses are essentially still "influenza," so even if infected with different virus subtypes, most symptoms remain similar.

The most common and primary symptoms are respiratory, including fever, runny nose, sore throat, cough, difficulty breathing, as well as systemic symptoms such as headache, muscle pain, and fatigue.

Specific subtypes may exhibit some distinctive symptoms, such as:

• H5N1 may involve gastrointestinal or central nervous system manifestations, such as diarrhea or encephalitis.
• H7N7 and H7N3 may present as simple conjunctivitis, among others.
• Among these, H5N1 infection is more likely to lead to severe illness and has a higher mortality rate.

What symptoms does H5N1 avian influenza cause in humans?

The most common symptoms of H5N1 avian influenza in humans are respiratory, but it may also present solely with gastrointestinal or central nervous system involvement, including: fever, cough, difficulty breathing, headache, muscle pain, diarrhea, encephalopathy, conjunctivitis, gum bleeding, etc..

What severe consequences can highly pathogenic avian influenza cause after infection in humans?

Severe cases of highly pathogenic avian influenza in humans progress rapidly, with a series of complications potentially arising in a short period, including: fulminant pneumonia, acute respiratory distress syndrome, respiratory failure, septic shock, disseminated intravascular coagulation, rhabdomyolysis, encephalopathy, and multiple organ failure. These can ultimately lead to death.

CAUSES

What is avian influenza virus?

Avian influenza virus belongs to the influenza A virus strain, primarily infecting poultry (such as chickens, ducks, geese) or wild birds, causing infectious diseases. Some strains can also infect humans.

Avian influenza viruses have different subtypes, with H5 and H7 being the most common. Representative strains include H5N1, H7N7, and H7N9, which are highly pathogenic and virulent and have been confirmed to infect humans, leading to respiratory diseases.

What types of highly pathogenic avian influenza viruses can infect humans?

The most common highly pathogenic avian influenza viruses are H5 and H7 subtypes, represented by H5N1, H7N7, and H7N9.

Is highly pathogenic avian influenza contagious in humans? How is it transmitted?

Humans can contract the disease through close contact with infected birds, including direct exposure to live infected poultry or their excreta, participating in culling poultry in epidemic areas without respiratory protection, or consuming undercooked poultry meat.

However, whether human-to-human transmission occurs remains inconclusive. Current research suggests that the H7N9 subtype shows no evidence of sustained human-to-human transmission, while the H5N1 subtype may have limited human-to-human transmission.

The primary transmission routes are close contact and droplet spread. Due to the higher severity and mortality rate of H5N1, patients diagnosed with H5N1 avian influenza are required to be isolated and treated as if the virus spreads via airborne transmission.

Who is more susceptible to highly pathogenic avian influenza?

Theoretically, all people are susceptible to highly pathogenic avian influenza. However, certain groups, such as children, pregnant women, the elderly, and those with chronic diseases, are more likely to develop severe illness if infected and thus require special preventive measures.

Additionally, some individuals are at higher risk due to their occupations, including those involved in poultry or wild bird breeding, sales, or processing; workers participating in culling poultry or handling epidemic sites; veterinarians; laboratory personnel handling avian influenza virus samples; and individuals in close contact with infected patients.

Besides humans, which other animals can be infected by highly pathogenic avian influenza?

Avian influenza primarily infects birds, with most domestic and wild birds being susceptible, such as chickens, ducks, geese, pigeons, parrots, peacocks, seagulls, swallows, herons, bar-headed geese, and quails. Apart from birds, animals like pigs and horses can also be infected by avian influenza viruses.

DIAGNOSIS

How do doctors diagnose highly pathogenic avian influenza in humans?

The diagnosis of all infectious diseases relies on identifying the pathogen.

For patients with a history of avian influenza exposure + typical symptoms, doctors will collect samples such as throat swabs, sputum, or bronchoalveolar lavage fluid and perform real-time RT-PCR testing to confirm the virus.

Additionally, viral culture or serological antibody testing may aid diagnosis, but the former requires highly specialized facilities, while the latter is mainly used for retrospective diagnosis and offers no help for acute infections, so they are not the first choice.

What tests are needed when highly pathogenic avian influenza infection is suspected?

When avian influenza infection is suspected, doctors first conduct pathogen tests for confirmation, as detailed in the previous section.

Depending on the patient’s symptoms, doctors may also perform:

• Routine lab tests: including complete blood count, C-reactive protein, arterial blood gas analysis, liver/kidney function tests, cardiac enzyme tests, and coagulation studies;
• Imaging tests: Chest X-ray or lung CT scan;
• Some patients may require lumbar puncture, cerebrospinal fluid analysis, stool tests, or blood cultures to assist diagnosis.

Which diseases can highly pathogenic avian influenza be confused with?

It can be mistaken for other acute respiratory illnesses, such as seasonal flu, respiratory syncytial virus infection, atypical pneumonia, severe acute respiratory syndrome (SARS), or Middle East respiratory syndrome (MERS). Rare cases may resemble infectious diarrhea, bacterial dysentery, or viral encephalitis.

TREATMENT

Which department should I visit for human infection with highly pathogenic avian influenza?

Respiratory medicine or infectious diseases department. Many patients may initially go to the fever clinic or emergency department due to their first symptoms.

Can human infection with H5N1 avian influenza resolve on its own?

Some young, otherwise healthy H5N1 patients without severe complications may recover on their own with proper nutrition and rest. However, early medical attention is still recommended to avoid delays in treatment if the condition worsens.

Does human infection with H5N1 avian influenza require hospitalization?

Not necessarily. Doctors will assess based on the patient's specific condition.

• Mild cases with no medical history or complications can be treated as outpatients.
• Severe cases, especially those with symptoms like difficulty breathing or low oxygen levels, as well as high-risk groups (children, pregnant women, the elderly, or those with immunosuppression or chronic lung diseases), require hospitalization.

How is human infection with H5N1 avian influenza treated?

• Antiviral therapy: Neuraminidase inhibitors (e.g., oseltamivir) are proven effective against H5N1. Early use is recommended. The standard adult dose is 75 mg twice daily for 5 days, though some patients may need extended or higher doses. Alternatives include zanamivir and peramivir.
• Supportive care: Bed rest, fever reduction, fluid replacement, and nutritional support.

Can human infection with H5N1 avian influenza be completely cured?

Recovery depends on factors like age, overall health, and complications.

• Mild cases often fully recover with prompt and effective treatment.
• H5N1, however, is a severe subtype with high mortality. It can rapidly progress to conditions like severe pneumonia, respiratory failure, or ARDS, requiring complex treatments such as ICU care, intubation, mechanical ventilation, blood purification, or ECMO. Some patients may experience long-term complications.

How long does recovery take for human infection with H5N1 avian influenza without complications?

If no complications occur, H5N1 infection behaves like typical influenza, peaking within a week. Most patients recover fully within about 2 weeks.

Does human infection with highly pathogenic avian influenza leave sequelae?

Mild cases generally leave no lasting effects. However, severe cases, especially in patients with pre-existing heart/lung conditions or immunodeficiency, may result in sequelae such as impaired cardiopulmonary function or irreversible kidney failure.

Is the mortality risk high for human infection with highly pathogenic avian influenza?

Mortality varies by subtype. H5N1 has the highest severity and mortality, with an overall rate around 53%. High-risk groups (pregnant women, the elderly, or those with chronic conditions like asthma, diabetes, or cancer) are more prone to severe outcomes and higher mortality.

DIET & LIFESTYLE

What should one eat during the treatment of highly pathogenic avian influenza in humans?

For mild cases of highly pathogenic avian influenza in humans, a normal diet is sufficient. Maintain regular meals, increase the intake of fresh vegetables and fruits, and consume high-quality protein such as fish and shrimp, while avoiding greasy and spicy foods. Increase fluid intake appropriately, especially if fever is present.

Severe cases, particularly those with serious complications, may be unable to eat orally. In such cases, enteral nutrition should be provided via a nasoenteric tube, or fluids and parenteral nutrition should be administered intravenously. Oral feeding should resume as soon as the condition improves.

What lifestyle precautions should be taken during the treatment of highly pathogenic avian influenza in humans?

During the acute phase of highly pathogenic avian influenza infection, rest is recommended. Ensure adequate sleep, avoid fatigue and exercise, pay attention to diet, and refrain from smoking and alcohol.

Additionally, practice frequent handwashing, wear masks correctly, follow medical guidance for strict self-isolation, and prevent disease transmission.

Do patients with highly pathogenic avian influenza require isolation?

Yes. Although human-to-human transmission of highly pathogenic avian influenza is limited, isolation is still implemented based on airborne precautions.

• Outpatients should self-isolate at home, wear N95 masks, stay in a separate room, avoid close contact with family members, wash hands frequently, and ensure proper ventilation.
• Hospitalized patients should be placed in negative-pressure isolation rooms, and healthcare providers should wear N95 masks and protective clothing.

PREVENTION

How to Prevent Highly Pathogenic Avian Influenza in Humans?

General Public:

• Avoid smoking and exposure to secondhand smoke.
• Maintain a healthy diet and exercise regularly—3 to 5 times per week for 30 minutes each session, combining aerobic and strength training at moderate intensity without overexertion.
• Develop good hygiene habits, wash hands frequently, and ensure proper ventilation at home.
• During disease outbreaks, stay warm, avoid crowded places, wear masks when in contact with infected individuals, and disinfect clothing promptly after returning home.
• Avoid contact with live poultry, wild animals, or their consumption.

Children, Pregnant Women, and Elderly with Underlying Conditions:

• Annual vaccination against influenza and pneumonia is recommended to prevent infections caused by certain pathogens.
• However, self-administering "preventive medications" (especially traditional Chinese medicines or immunity-boosting supplements) without symptoms is not advised.

High-Risk Groups:

• For individuals at occupational risk, additional protective measures are necessary, such as wearing masks, gloves, and protective gear when handling, slaughtering, or processing poultry.
• Strict adherence to laboratory protocols and standard precautions when working with viruses is essential.

Are There Vaccines to Prevent Highly Pathogenic Avian Influenza in Humans?

Currently, the U.S. and EU have approved two H5N1 avian influenza vaccines. However, production challenges and limited immunogenicity (requiring multiple doses for seroprotection) restrict their widespread use.

For the general public, annual influenza and pneumonia vaccinations before peak seasons are recommended to reduce infection risks and prevent co-infections.

Why Is Highly Pathogenic Avian Influenza (a Category B Infectious Disease) Managed as Category A?

China classifies pathogens based on transmissibility and severity. Under the Law on the Prevention and Treatment of Infectious Diseases, Category A diseases (e.g., plague, cholera) entail stricter reporting and control measures than Category B.

Although avian influenza is classified as Category B, certain high-mortality subtypes pose significant public health threats and pandemic risks. Thus, Category A management ensures enhanced surveillance and containment to mitigate severe outcomes.