Friday, September 04, 2009
H1N1 and severe respiratory failure
Scientists are ferreting out clues to the ferocity with which this new swinish flu attacks the lower airways in some of its victims. Ferrets demonstrate a susceptibility to influenza A very similar to humans and therefore are used as an animal model in flu investigations.
The above picture(1) shows microscopic sections of ferret airways (that is not a goose!), comparing seasonal H1N1 flu (the usual variety that circulates each winter season) on the left to tissue infected by the 2009 A/H1N1 flu on the right. Violet coloration indicates affected surface cells, and both varieties make a mess out of noses with sloughing sheets of dead nasal tissue full of violet-colored intruders as seen in the top pair of slides.
Moving on down to the trachea (which is the largest central airway lined with rings of cartilage that you can feel in the front of your neck), the ferret with seasonal flu middle picture on left is free of viral invasion but the swine-flu ferret victim on the right has dots of violet flu violation throughout its trachea. Finally, and of importance to this discussion, slides from the bronchioles of both ferrets are pictured at the bottom. This tissue was obtained from the smallest airways that go directly into the alveolae or air sacs that hook up oxygen with blood. Seasonal Flu Ferret has normal bronchioles, flu bug free, but Swine Flu Ferret's tiny air passages are teeming with the little buggers.
What's this got to do with the upcoming flu season? One of my patients, an ICU nurse, shared a disturbing report with me yesterday. She said that her unit has been busy this entire spring to summer with youngish patients suffering from severe swine flu-related bronchiolities (inflammation filling these airways with fluid) requiring ventilator support until the infection started to clear. Her information jibed with an August report from the World Health Organization entitled "Preparing for the second wave: lessons from current outbreaks." Per the WHO document:
"Clinicians from around the world are reporting a very severe form of disease, also in young and otherwise healthy people, which is rarely seen during seasonal influenza infections. In these patients, the virus directly infects the lung, causing severe respiratory failure. Saving these lives depends on highly specialized and demanding care in intensive care units, usually with long and costly stays."
This information highlights not only the importance of widespread immunization against the 2009 A/H1N1 flu (which creates so-called herd immunity, slowing down or preventing the lateral spread of flu from person-to-person due to the large number of vaccine-protected people) but also the paramount importance of immunizations for persons with underlying illnesses, particularly asthma, cardiovascular disease, diabetes, and immunosuppression.
(1) Munster, VJ, et al. "Pathogenesis and Transmission of Swine-Origin 2009 A(H1N1) Influenza Virus in Ferrets." Science 24 July 2009: Vol. 325. no. 5939, pp. 481 - 483.