Knowledge Nugget | Why is H1N1 spreading? Understand swine flu and how influenza viruses evolve

Influenza H1N1, commonly known as swine flu, has been spreading rapidly in Delhi, with 1,449 reported cases as of August 12 this year, surpassing the 229 infections recorded during the same period last year. The virus, a type of influenza A, has the H1 and N1 subtypes and was responsible for a global pandemic in 2009.

The first case of H1N1 was reported in Hyderabad on May 16, 2009, and by May 24, 2010, India had recorded 10,193 cases and 1,035 deaths. In June 2009, the World Health Organization declared H1N1 a global pandemic, affecting over 74 countries.

Influenza viruses belong to the Orthomyxoviridae family and have proteins called hemagglutinin (H) and neuraminidase (N) that help infect cells in the human respiratory and gastrointestinal tract. There are at least 18 H subtypes and 11 N subtypes, with combinations of these subtypes denoting the type of strain. Swine flu, or H1N1, is a type A virus that spreads from pigs to people.

Symptoms of swine flu include fever, cough, headache, muscle aches, tiredness, sweating, and chills. Influenza B, mainly infecting humans, is less common and mutates slowly. The virus spreads from pigs to people, and common symptoms include fever, cough, headache, muscle aches, tiredness, sweating, and chills.

The current rise in H1N1 cases in Delhi may be due to the virus mutating or increased human contact. Seasonal changes may also affect overall immune responses, increasing susceptibility to flu viruses. Influenza viruses typically peak during monsoon seasons.

Dr. S Chatterjee, an internal medicine specialist at Apollo Hospital, stated that only a genetic study of the virus would determine the exact reason for the current rise. Dr. Amit Gupta, a senior neonatologist and paediatrician at Motherhood Hospitals, Noida, noted that flu usually occurs from January to March and reaches its peak during the rainy season, which peaks around August, September, and October. Urban centers often report higher rates of infection compared to more rural areas.