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About H1N1
This illness is referred as "Swine Flu" because the genes of this virus strain were found to be similar to influenza virus occurring in pigs in North America. But, further studies have indicated that the virus is very different from the virus affecting North American pigs. It consists of two genes similar to that found in flu viruses affecting pigs in Europe and Asia, avian and human genes.
Molecular Markers of Pathogenicity:
H1N1 is a new hybrid strain of virus, the surface hemagglutinin antigen sequences of which are derived from swine, human, and avian flu sources. 7 PB1-F2 coding sequence, the smallest protein in the influenza virus is known to be the molecular marker of pathogenicity which is exclusively absent in human influenza viruses. The degree of identity between the viral hemagglutinin molecules of new strain and other human flu viruses is the second marker of virulence that can be assessed by sequences alone. Low identity of hemagglutinin structures indicates that degree of “herd” immunity resulting from exposure to similar viruses does not blunt the transmission from one human to another. A third molecular marker, polybasic cleavage site which is a protease site in the viral hemagglutinin plays a role in the pathogenicity of avian influenza viruses. These host proteases enables virus fusion with a host cell by activating the hemagglutinin molecule.
Reassortment event:
Influenza A virus lacks PB1-F2 which indicates a milder disease compared to the other major pandemic viruses. However, mutations resulting in altered expression of PB1-F2 might affect this status. Genes shuffling with other influenza viruses known as reassortment event may lead to incorporation of a gene responsible for PB1-F2 production.
RNA genomes of Influenza A viruses encode up to 11 proteins including the surface glycoproteins, hemagglutinin, neuraminidase, NS1 virulence factors (host interferon antagonist) and PB1-F2 (proapoptotic factor). The presence of a functional hemagglutinin molecule and host cell receptor expression for hemagglutinin, sialic acid decides the entry of viruses into cells.
Swine tissues express two forms of sialic acid which enables swine infections to mediate virus reassortment resulting in cells coinfected with avian and human viruses. Swine viruses combine with human and avian viruses to produce triple reassortants, thus acquiring the ability to produce human infections, i.e. Influenza A. It is a typical example of a triple reassortant including segments from swine, avian, and human influenza viruses. 8
Pathogenesis & Pathology
Pigs carry the virus and spread it to young animals. However, there is no evidence that they remain in true long term carrier state. After inhalation, the virus gets deposited on the surface of the lower respiratory tract. 9
Incubation Period:
The estimated incubation period in humans is unknown and could range from 1-7 days, and more likely 1-4 days. Patient may be contagious from one day before they develop symptoms to up to 7 days after they get sick. Younger children might potentially be contagious for longer periods. 10
Uncomplicated infections might cause changes in the cranial ventral lung lobes. Bronchial and mediastinal lymph nodes get enlarged. The pathological changes that can be seen as follows:
- Sharp line of demarcation between normal and affected lung tissue can be identified with the affected tissue being purple and firm.
- Interlobular edema can be found in few cases.
- Airways get filled up with blood-tinged fibrinous exudates with peribronchial and perivascular cellular infiltration.
- Fibrinous pleuritis is seen in severe cases.
- Microscopically lesions show airways filled with exudate, with extensive alveolar atelectasis, interstitial pneumonia and emphysema.
- Research revealed that widespread interstitial pneumonia prevails up to 21 days after infection and causes hemorrhagic lymph nodes. 11
Transmission of H1N1
- Large-particle respiratory droplet transmission: When an infected person coughs or sneezes near a susceptible person, airborne transmission occurs. It requires close contact between the infected and recipient persons because droplets do not remain suspended in the air and travel short distances not more than 6 feet.
- Respiratory secretions and bodily fluids (diarrheal stool) of infected cases are potentially infectious. However, susceptibility of ocular, conjunctival, or gastrointestinal infection is not yet known.
- Contact with contaminated surface: Sometimes people may become infected by touching something with flu viruses on it and then touching their mouth or nose. Studies have shown that virus can survive on environmental surfaces for nearly 2-8 hours after being deposited on the surface and have the potential for infecting a person.12
What works against the transmission?
- Influenza A virus can be destroyed by heat at 167-212°F [75-100°C].
- Detergents (Soap), chemical germicides including chlorine, hydrogen peroxide, iodophors (iodine-based antiseptics), and alcohols are also effective against human influenza viruses, if used in proper concentration for a sufficient length of time.
For example- wipes or gels with alcohol in them can be used to clean hands. The gels should be rubbed into hands until they are dry. 13
Myths and Facts
- People get infected from eating or preparing pork.
Fact - This virus does not spread by food or from eating pork or pork products, if properly handled and cooked.
- There is a risk of virus transmission from drinking water.
Fact - Research on susceptibility of this virus to conventional drinking water treatment processes is not yet completed. However, recent studies have demonstrated that highly pathogenic H5N1 avian influenza gets inactivated by free chlorine levels normally used in drinking water treatment. So, it is believed that other influenza viruses like novel H1N1 can also be inactivated by chlorination. No human case was documented as caused by exposure to influenza-contaminated drinking water, till date.
- It can spread through water in swimming pools, water parks, spas, interactive fountains, and other recreational water venues.
Fact - Till now, no case of influenza virus infection has been documented as caused by water exposure. Recreational water treated with disinfectant at CDC recommended levels (1–3 parts per million [ppm or mg/L] for pools and 2–5 ppm for spas) does not cause transmission of influenza viruses like avian influenza A (H5N1) virus. No research is completed on the susceptibility of novel H1N1 virus to chlorine and other disinfectants used in swimming pools, water parks, spas, interactive fountains etc. So, it is believed that novel H1N1 might be disinfected similarly.
- There is a risk of spread at recreational water venues outside of the water!
Fact - Recreational water venues are not different from other common group setting. 14
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