Avian Influenza

Avian influenza is caused by influenza A viruses, which are classified based on the hemagglutinin (HA) and neuraminidase (NA) surface proteins. Notable subtypes affecting birds and humans include H5N1, H7N9, and H5N8. The virus primarily affects avian species, particularly domestic poultry such as chickens, ducks, and turkeys, but can also affect other wild and domestic animals. Wild birds, especially waterfowl, are natural reservoirs of the virus. Avian influenza viruses are classified into two categories based on their pathogenicity in birds: low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI).

Certain HPAI strains have zoonotic potential, meaning they can infect humans and cause severe respiratory illness. H5N1 and H7N9 can cause severe disease in birds, and are the most concerning due to their high case fatality rates in humans. These subtypes have been responsible for human outbreaks and deaths in Africa, Asia, Europe, the Middle East, and the Americas. 

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation. 

Suspected case: A case that is compatible with the clinical description and has an epidemiological link to confirmed or suspected animal cases or contaminated animal products. 

Probable case: A suspected case that has evidence of an acute pneumonia on chest radiograph plus evidence of respiratory failure (hypoxemia, severe tachypnea). 

Confirmed case: A suspected case that is laboratory-confirmed. 

WHO case definition source of information: https://iris.who.int/bitstream/handle/10665/205388/B0634.pdf   

Single case

• Children playing with infected poultry, particularly asymptomatic infected ducks.  
• Workers handling infected poultry or livestock including on farms and backyard flocks
• Poultry handlers in live animal markets / wet markets  
• Cullers without proper PPE  
• Persons hunting, plucking, butchering, and preparing infected wild birds and wild mammals.
• Consumption of undercooked poultry products  
• Hospital staff managing human cases of avian influenza without proper PPE 

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities. 

• Generally low and depends on the type of exposure. 

• People with weakened immune systems.
• People living with other respiratory issues such as pneumonia
• Immunosuppressed persons such as those receiving chemotherapy, transplant recipients or HIV carriers.
• People with chronic diseases such as renal disease, cancer, chronic lung or liver disease and diabetes. 

It is a complex disease is caused by a group of Influenza viruses divided into multiple subtypes (i.e. H5N1, H7N9, H5N3, H5N8 etc.) whose genetic characteristics rapidly evolve. 

Zoonotic disease: mostly found in domesticated poultry birds and wild migratory birds. While avian influenza primarily infects birds, it can also infect mammals, particularly those who consume birds or are exposed to heavily contaminated environments. 

• Direct contact: Individuals may be infected when they touch infected birds or other infected animals or when they are in close contact (within one metre) with a person (e.g. caring for, speaking with or touching) who is a suspected, probable or confirmed case.
• Environmental exposure: Humans can also get infected when they are in environments contaminated by their faeces in an area where infections in birds or humans have been suspected or confirmed in the last month.
• Vehicle-borne transmission: Birds may become infected by eating contaminated feedstuff. Humans may be infected by eating raw or poorly cooked poultry products from environments where the disease has been confirmed. 

Incubation period is usually 2-8 days after exposure to the causative virus from sick or dying wild or domestic birds or other mammals. 

Human to human transmission cases have been recorded but rarely happen.

https://www.cdc.gov/bird-flu/virus-transmission/avian-in-humans.html&nb…;

Onset similar to seasonal influenza;

• Fever >38.0C Cough  
• Difficulty in breathing after 5-7 days of onset  
• Conjunctivitis / eye inflammation
• Sore throat, muscle aches, runny nose
• Diarrhoea  
• Severe cases may progress to:
• Primary viral pneumonia  
• Rapid deterioration to acute respiratory distress syndrome (ARDS) and multi-organ failure  

Infrequent features:  

• Vomiting  
• Abdominal pain  
• Chest pain  
• Bleeding from nose and/or gums  
• Encephalopathy (rare) 

Community-Acquired Pneumonia (CAP), H1N1 Influenza (Swine Flu), Influenza, Middle East Respiratory Syndrome (MERS), Pneumococcal Infections (Streptococcus pneumoniae), Severe Acute Respiratory Syndrome (SARS) 

• Isolation of an H5N1 virus (or other known HPAI subtype)
• Positive H5 PCR results from tests using two different PCR targets, e.g. primers specific for influenza A and H5 HA;  
• A fourfold or greater rise in neutralisation antibody titer for H5N1 (or other HPAI subtype) based on testing of an acute serum specimen (collected 7 days or less after symptom onset) and a convalescent serum specimen. The convalescent neutralising antibody titer must also be 1:80 or higher.  
• A micro-neutralization antibody titer for H5N1 (or other HPAI subtype) of 1:80 or greater in a single serum specimen collected on Day 14 or later after symptom onset and a positive result using a different serological assay, for example, a horse red blood cell hemagglutination inhibition titer of 1:160 or greater or an H5-specific western blot positive result. 

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of a treatment or vaccine should be conducted by a health professional.  

• Avian Influenza cannot be treated with antibiotics. However, secondary bacterial infections that may arise can be treated with antibiotics.
• An antiviral (Oseltamivir) is the primary drug of choice for avian influenza.

Previous infections grant some level of immunity