Influenza (Flu): Causes

Pathogenesis (development of disease)

Seasonal influenza can be distinguished from pandemic influenza (H1N1). Seasonal influenza is caused by type A, B, or C influenza viruses. These are orthomyxoviruses (RNA viruses). Type A influenza viruses in particular are responsible for epidemics. Since 1972, more than 20 variants of the type A virus have been found. This virus can infect both humans and animals. Type B of the virus is more likely to be responsible for individual human illnesses, while type C is of little importance.

Influenza viruses are classified according to the number of proteins found on their surface. A distinction is made between hemagglutinin (H) and neuraminidase (N). Both proteins are known to have several subtypes; hemagglutinin has about 15 different types, and neuraminidase has about nine, which can occur in different combinations. Note: Neuraminidase is the major pathogenicity factor for virus entry into the host cell. The count begins with the aggressive strain of the 1918 Spanish flu, which consequently holds the classification H1N1. After an influenza virus with two other proteins appeared in the 1957 flu epidemic, for example, it was given the name H2N2. Because of the great genetic variability and minute genetic changes in viruses (antigenic drift or antigenic shift), once an infection is contracted, it does not provide immune protection. Influenza is transmitted by droplet infection. The new influenza (swine flu; H1N1/2009) contains gene segments of viruses that are found in humans, pigs and birds. In avian flu (avian influenza), the dangerous form of the virus carries the classification H5N1. But this virus, in turn, has several strains that are pathogenic to varying degrees. Avian influenza is transmitted through contact with infected poultry.

Etiology (causes)

Biographic causes.

Genetic exposure through parents, grandparents

  • Genetic risk depending on gene polymorphisms:
    • Genes/SNPs (single nucleotide polymorphism; English : single nucleotide polymorphism):
      • Genes: IFITM3
      • SNP: rs12252 in the gene IFITM3
        • Allele constellation: CC (much higher influenza susceptibility (“susceptibility”); 6-fold higher risk of developing a severe form of influenza than CT genotype)Note: 6% of Caucasians carry the C allele; 25-50% of East Asian populations carry the C allele.
        • Allele constellation: TT (more resistant to influenza).
  • Hormonal factors – pregnant or postpartum women.
  • Occupations – Medical staff and employees in facilities with high traffic.

Behavioral causes

  • Nutrition
    • Micronutrient deficiency (vital substances) – see Prevention with micronutrients.
  • Consumption of stimulants
    • Tobacco (smoking) – increases oxidative stress, weakens the immune system, and damages the respiratory system
  • Avoid contact with sick people in the phase of infection. This phase begins shortly before the appearance of the first symptoms and usually persists for up to five days. Transmission is usually by droplet infection, less frequently by direct contact with the virus, for example, through hand contact.

Disease-related causes (below diseases that may be associated with increased influenza complications).