Avian Influenza

 Key Points to Remember

• Avian influenza (bird flu) is a viral respiratory disease mainly affecting birds but can infect humans through contact with infected poultry.
• The H5N1 and H7N9 subtypes cause severe illness and high fatality rates in humans.
• Human-to-human transmission is rare, with most cases linked to direct or indirect contact with infected birds.
• There is no specific vaccine for humans; antiviral drugs like oseltamivir can reduce severity if given early.
• Prevention involves culling infected birds, strict farm hygiene, and avoiding contact with live poultry.

Keywords

Avian influenza, Bird flu, H5N1, H7N9, Influenza A virus, Zoonotic influenza, WHO response.

Avian Influenza (Bird Flu)

Introduction

Avian influenza, commonly known as bird flu, is a contagious viral respiratory disease that primarily affects poultry and other bird species, including migratory waterfowl, pet birds, and ostriches. The virus can occasionally infect humans, often leading to severe illness.

The first human cases were identified in Hong Kong in 1997, when the H5N1 subtype caused infection in 18 people, resulting in six deaths. Since then, several avian influenza subtypes have been detected worldwide, making bird flu a persistent public health concern.

The Pathogen: Types of Influenza Viruses

Influenza viruses can be categorized into four main types: A, B, C, and D.

1. Influenza A

• Infects humans and various animals (birds, pigs, horses, etc.).
• Responsible for pandemics when a new strain emerges capable of human-to-human transmission.
• Subtyped based on two surface proteins: Hemagglutinin (HA) and Neuraminidase (NA) — for example, H5N1, H7N9, and H9N2.

2. Influenza B

• Circulates mainly among humans and causes seasonal epidemics.
• Occasionally detected in marine animals like seals.

3. Influenza C

• Infects humans and pigs, but usually causes mild illness.
• Rarely associated with outbreaks.

4. Influenza D

• Affects cattle and is not known to infect humans.
• Among these, Influenza A viruses are the most significant due to their ability to mutate and cause pandemics.

Natural Reservoirs and Classification

• Wild aquatic birds are the primary natural hosts of most Influenza A viruses.
• Highly Pathogenic Avian Influenza (HPAI): Causes severe illness and high death rates in poultry.
• Low Pathogenic Avian Influenza (LPAI): Results in mild or no symptoms.
• The most common avian influenza viruses that infect humans are H5N1, H7N9, H7N7, and H9N2

Transmission

Humans typically contract bird flu through direct or indirect contact with infected birds or contaminated environments.

Common risk activities include:

• Handling live or dead poultry
• Slaughtering, defeathering, or preparing infected birds for food
• Exposure to live bird markets
• Person-to-person transmission is rare and usually limited to close contact cases.

There is no evidence that properly cooked poultry or eggs spread the infection.

Epidemiology

• Since the 1997 Hong Kong outbreak, avian influenza has spread across Asia, Europe, and Africa.
• H5N1: Endemic in some countries, with hundreds of human cases and high mortality rates.
• H7N9: First detected in China in 2013; over 1,500 human cases reported since.
• H9N2 and H7N7: Cause sporadic, usually mild, human infections.
• Global poultry outbreaks have led to economic losses and trade restrictions, highlighting the link between animal and human health.

Signs and Symptoms in Humans

Avian influenza infections can range from mild respiratory illness to severe pneumonia and death.

Common symptoms include:

• High fever (≥38°C)
• Cough and sore throat
• Shortness of breath or difficulty breathing
• Fatigue and muscle pain
• Headache and malaise
• Severe or additional symptoms:
• Diarrhea, vomiting, and abdominal pain
• Bleeding gums or nose
• Chest pain or confusion
• Multi-organ failure in advanced cases

The incubation period ranges from 2 to 10 days, sometimes extending up to 17 days, depending on the viral strain.

Diagnosis

Laboratory confirmation is essential for diagnosing avian influenza.

Diagnostic methods include:

• RT-PCR (Reverse Transcriptase Polymerase Chain Reaction): Detects viral RNA.
• Serological tests: Identify antibodies against avian influenza.
• Rapid Influenza Diagnostic Tests (RIDTs): Used in clinical settings but less accurate for subtyping.
• Samples should be collected from respiratory secretions and processed according to WHO guidelines.

Treatment

• Currently, no specific vaccine is available for avian influenza in humans.
• However, antiviral medications can improve survival chances when given early.

Recommended treatment:

Neuraminidase inhibitors:

• Oseltamivir (Tamiflu)
• Zanamivir (Relenza)

Best results occur when treatment starts within 48 hours of symptom onset.

Duration: at least 5 days or longer until clinical improvement.

Not recommended:

• Corticosteroids (unless required for other conditions)
• Adamantanes (Amantadine, Rimantadine): Most strains are resistant

Supportive care:

• Oxygen therapy
• Hydration
• Management of secondary bacterial or fungal infections

Prevention and Control

Preventing avian influenza involves strict biosecurity and public health measures.

1. Poultry control

• Culling infected or exposed birds to prevent spread
• Disinfection of equipment, clothing, and facilities using formalin or iodine solutions
• Heat inactivation: Virus dies at 56°C for 3 hours or 60°C for 30 minutes

2. Farm and market management

• Restrict movement of live birds within and between countries
• Maintain quarantine and surveillance in affected areas

3. Personal protection

• Avoid contact with live poultry or open-air bird markets
• Avoid consuming raw eggs or undercooked poultry
• Wash hands frequently or use alcohol-based sanitizers
• Travelers to affected areas should take extra precautions and get a flu shot to prevent co-infection with human influenza.

Pandemic Potential

Avian influenza has the potential to cause a global pandemic if a virus mutates to allow sustained human-to-human transmission. While occasional limited transmission has occurred, no sustained outbreak among humans has been confirmed to date. Global surveillance and preparedness are crucial to prevent future pandemics.

WHO Response

• The World Health Organization (WHO) monitors avian influenza through the Global Influenza Surveillance and Response System (GISRS).
• In coordination with FAO (Food and Agriculture Organization) and WOAH (World Organisation for Animal Health), WHO:
• Tracks avian and zoonotic influenza outbreaks
• Assesses global risk
• Provides guidance and preparedness plans for affected countries
• International cooperation between animal and human health sectors remains essential for preventing and controlling future outbreaks.

Conclusion

Avian influenza continues to pose a serious threat to global health due to its ability to cross species barriers and cause severe disease in humans. While human infections are rare, high fatality rates and the potential for mutation demand continued surveillance, vaccination research, and public awareness. Practicing safe poultry handling, improving farm hygiene, and following international control measures are vital steps in preventing bird flu outbreaks.