Virus Influenza A (H1N1) pdm09: Features predisposed to aggressive forms groups, children and youth, pregnant. Molecular diagnosis (real time PCR) detection of specific antibodies, antiviral susceptibility.

15-06-2009 information.

The new influenza pandemic is caused by an influenza A virus (H1N1), which only differs from the virus Influenza A (H1N1) seasonal flu in the antigenic profile. Viruses from pandemic have been sequenced so far lack markers aggressiveness known for influenza virus highly pathogenic, such as the presence of multiple basic amino acids in its hemagglutinin and structure of the PB2 proteins and PB1 . In these strains, the hemagglutinin is similar to that of seasonal influenza virus PB2 protein has in position 627 glutamic acid rather than lysine and position 701 aspartic instead of arginine, and PB1 protein in position 66 possesses arginine instead serine, typical of the usual influenza viruses. Therefore, we can not speak, at least for now, the virus has increased its aggressiveness.

Groups predisposed to aggressive forms

At the moment, there is no justification to think about it even though they have been serious cases. The kind of evolution of viral infections depends on three key elements: the organic status of the infected individual, the amount of inoculum of the infecting virus and the immune response against the virus. Organic status of the infected individual, discussed below are the most likely people to suffer serious infections, justified by their poor organic situation hinders the elimination of the organism virus, while basic life functions decompensate, primarily respiratory are and circulatory.

As for the virus, the current (June 2009), so far, has shown no change in respect of which began to be detected in April 2009. An important element is the amount of virus inhale. Logically , when inhale few virions from infecting these cells only the upper respiratory tract (nasal epithelium, pharynx and upper respiratory tract), causing a mild and short evolution symptoms; whereas if we inhale a lot of virus, they would reach the deepest parts of the respiratory system affecting cells found where oxygen exchange occurs, the alveoli, so you will have major clinical consequences and worse outcomes. The third element to consider is the immune response of the infected patient, whose ultimate aim is to eliminate the virus. To achieve attacks the virus - infected cells, releasing molecules communication and cellular damage. Communication molecules attract phagocytic cells to the site of infection, and activated to achieve its goal; other molecules cause vasodilation and increased permeability of blood vessels, so they allow the exit of plasma molecules with antiviral effect. Molecules released causing injury aim to eliminate cells infected by the virus. This immune action should be beneficial to the infected individual but may become harmful when overproduced, triggering inflammation in the lung serious consequences due to severe lung inflammation, as is observed in patients who do severe pneumonia.


Infections in pregnant

We know that there have been serious cases in pregnant women. This increased susceptibility is not surprising because generally viral infections usually cause pronounced symptoms and a longer evolution in them. Even this fact has been noted in previous pandemics. The explanation is simple and is based on the reduction of cellular immunity that occurs naturally during pregnancy, to allow the embryo or fetus are not rejected by the mother. Several studies since the 70s, have demonstrated the decline in cellular immune mechanisms during gestation. This transient partial deficiency of cellular immunity explains that viral infections such as influenza, among others, pursue more intensely, have a longer course, and may be more serious.


Infections in children and youth

Since the beginning of the pandemic, it was observed that most affected children and young individuals. This could only be explained by the existence of a pre - existing immunity in the elderly. Indeed, there have been studies that have shown the existence of reactive antibodies against the new virus in 33% of those over 60 years at 6 and 9% of individuals aged 18 to 60 years and 0% of the children, justifying the highest incidence in children and young adults. The presence of these antibodies indicates prior exposure to a virus with similar antigenic characteristics that must have circulated in the human population for years.


Infections in people with organic disorders

This new virus, like seasonal flu virus, affects more people with chronic respiratory impairment chronic -bronquíticos, asthma, cystic fibrosis affections, ...-, cardiac disorders, endocrine diseases -diabéticos, ...- , immunodeficient, fact motivated by the reduced ability of organic defense and the ease with which these patients suffer from a general functional imbalance.

Sensitivity / resistance to antiviral

All isolates of the novel virus Influenza A (H1N1) were sensitive to neuraminidase inhibitors (oseltamivir -Tamiflú R - and zanamivir -Relenza R), and resistant to adamantane (amantadine and rimantadine). Recently described three isolated in the world resistant to oseltamivir (Japan, Hong Kong and Denmark). These isolates remain sensitive to zanamivir (WHO statement of July 8, 2009, after testing the sensitivity to about 1,000 isolates of this virus). Patients in these resistant strains were isolated evolved well, and no resistant isolates found in their contagions.

Tests in IVAMI:

Regarding the new epidemiological situation, this laboratory provides diagnostic tests listed below, we said if they were of interest at some point:

  • Molecular rapid detection with Real Time RT-PCR (RT-PCR Real Time) following the protocol recommended by the CDC, to detect the presence of the virus genome. This test includes four RT-PCR reactions: one for Influenza A -gen M-, one for Influenza A porcine -gen NP-, one for new virus Influenza A (H1N1) -gene HA- and one for human DNA as internal control presence of inhibitors of PCR tests.
  • Type-specific detection of antibodies against influenza A (H1N1) pdm09, virus using tests hemagglutination inhibition (HAI), or microneutralization (MN). Enzyme immunoassay tests (ELISA) or complement fixation usual, type - specific antibodies not detected. These tests type-specific antibodies, to diagnose past infections through the presence of these antibodies, or the status of protection by antibodies acquired by having prior contact with the virus for a symptomatic or asymptomatic process, or because they have been immunized by vaccination when the vaccine is available.
  • Culture isolation of virus by inoculation of cell cultures type shell vial, necessary to have strains of virus, if necessary. Isolation results in culture may be available at 48 hours of receiving the sample.
  • Detection of resistance to neuraminidase inhibitors (oseltamivir -Tamiflu R - and zanamivir -Relenza R -), by sequencing the neuraminidase gene.
    Our laboratory supplies needed for sample collection and shipment to the laboratory (collection containers and containers for refrigerated transport) with corresponding messaging service.
  • Direct sequencing of PCR products of RT-isolates of new virus Influenza A (H1N1), or positive samples by RT-PCR for this virus.

Samples recommended:  

  • Deep ooze, or should not be obtainable respiratory, nasopharyngeal.  

Preservation and shipment of sample:


  • Refrigerated (preferred) for less than 2 days.
  • Frozen: over 2 days.  

Delivery times:

  • Molecular rapid detection with Real Time RT-PCR (RT-PCR Real Time): less than 24 hours.
  • Virus isolation in culture 5 to 7 days.
  • Type-specific detection of antibodies against influenza A virus (H1N1) pdm09: 3-4 days.
  • Detection of resistance to neuraminidase inhibitors: 3 - 4 days.
  • Direct sequencing of PCR products of the RT-new virus isolates: 4 - 4 days.

Cost of testing: