Journal of Tropical Diseases & Public Health

H1N1 (Swine flu)

H1N1, commonly known as Swine Flu, is a strain of the influenza A virus that caused a global pandemic in 2009. It is named H1N1 based on the structure of its surface proteins: Hemagglutinin (H) and Neuraminidase (N). While it originated from pigs, this strain can infect humans and spread easily from person to person.

Virus Characteristics

• Type: H1N1 is a subtype of the Influenza A virus, which is part of the Orthomyxoviridae family.
• Origin: The 2009 H1N1 strain was a result of a mix (reassortment) of human, pig, and bird flu viruses.
• Naming: The "H" and "N" in the name refer to proteins on the virus's surface. There are 18 different Hemagglutinin (H) and 11 Neuraminidase (N) proteins, which can combine to form various flu strains.

Transmission

• Human-to-Human Transmission: The virus spreads mainly through droplets when an infected person coughs, sneezes, or talks. It can also spread by touching surfaces contaminated with the virus and then touching the nose, mouth, or eyes.
• Not Spread by Pork: Despite the name "swine flu," H1N1 is not spread through eating properly handled and cooked pork.

Symptoms

• Symptoms of H1N1 are similar to those of other strains of influenza and typically appear within 1-3 days after exposure.
• Common Symptoms:
  • Fever (usually above 38°C or 100.4°F)
  • Cough
  • Sore throat
  • Runny or stuffy nose
  • Body aches and muscle pain
  • Headache
  • Chills
  • Fatigue
  • Some people, especially children, may experience vomiting and diarrhea.
• Severe Cases: In more severe cases, H1N1 can lead to pneumonia, respiratory failure, and even death, particularly in high-risk groups.

High-Risk Groups

• Certain populations are at higher risk for complications from H1N1:
  • Pregnant women
  • Young children, especially those under 5
  • Elderly individuals (above 65 years)
  • People with chronic medical conditions (asthma, diabetes, heart disease)
  • Immunocompromised individuals
• Healthcare workers are also at increased risk due to potential exposure.

Diagnosis

• Clinical Diagnosis: Doctors may diagnose H1N1 based on symptoms and the presence of flu in the community.
• Laboratory Tests: Diagnostic tests include:
  • PCR (Polymerase Chain Reaction) testing to detect the virus.
  • Rapid influenza diagnostic tests (RIDTs) can give results in 10-15 minutes, but they are less accurate.

Treatment

• Antiviral Medications: Two main antiviral drugs are effective against H1N1:
  • Oseltamivir (Tamiflu)
  • Zanamivir (Relenza)
• These antivirals can reduce the severity and duration of symptoms if taken within 48 hours of onset.
• Supportive Care: Rest, fluids, and over-the-counter medications can help alleviate symptoms like fever and body aches.

Prevention

• Vaccination: The flu vaccine is the most effective way to prevent H1N1 and other influenza viruses. The annual flu vaccine typically includes protection against the H1N1 strain.
• Hygiene Practices:
  • Wash hands frequently with soap and water or use hand sanitizer.
  • Avoid touching the face, especially the mouth, nose, and eyes.
  • Cover the mouth and nose with a tissue or elbow when sneezing or coughing.
  • Stay home if feeling unwell to avoid spreading the virus.

Global Impact

• The 2009 H1N1 pandemic spread rapidly across the globe. The World Health Organization (WHO) declared it a pandemic in June 2009, as the virus caused widespread illness across continents.
• Morbidity and Mortality: Estimates suggest that between 151,700 and 575,400 people worldwide died from H1N1 during the first year of the pandemic.

Evolution and Current Status

• The H1N1 virus is now a regular human flu virus and circulates seasonally, typically included in the seasonal flu vaccine.
• Although the 2009 H1N1 pandemic strain has evolved, its descendants continue to cause illness each flu season.

Comparison with Other Influenza Strains

• H3N2: Another common strain that causes seasonal flu.
• Avian Influenza (H5N1): Mainly transmitted by birds, it poses a risk to humans but is less transmissible than H1N1.