Source: Wikimedia

Fonte: Wikimedia

ResearchBlogging.orgAlthough it is one of the most basic issues, Influenza virus transmission is still the target of much discussion. The role of contact contamination or through droplets and aerosols is considered a hot potato [1]. After a certain period without many experiments, nowadays we are aware that ferrets and guinea pigs may be infected by the Influenza A virus and that they may transmit it. These model animals make it possible for us to study flu transmission forms, although we are still far from completely clarifying this issue.

Model animals enable us to be in control of ethical problems instead of performing tests with human beings, but they are not the ideal solution. Their behavior is different from humans’, experimental conditions involve cages and closed environments, and it is very complicated to control the contact among the animals. Thus, every experiment involves more variables than what could be considered ideal. In addition to that, the ferrets’ humor is commented in several articles, although scientific articles are not a frequent target for catharsis.

Therefore, involuntary experiments with humans are highly valuable. We are going to check two tests and see what we can infer from them:

In 1977 one of the Alaska Airlines flight connections, an airplane with 54 passengers remained on the ground for 3 hours for repairs in the turbine. During these three hours, the air circulation system was off in order to save fuel and the passengers had to breathe the same air.

One of the passengers had Influenza A confirmed by a laboratory test. In 3 days, 39 out of the 54 passengers developed the flu. It was possible to isolate a similar virus strain in eight of these cases – the A/Texas/1/(H3N2) – and 20 other passengers had a positive test for antibodies of the same virus. Yes, 3 hours breathing the same air of a person who had the flu and 72% of the passengers caught the flu. The article also suggests that the contamination rate varied according to the time spent on board while the plane remained on the ground, for not all of the passengers stayed inside the aircraft all the time. Note that nothing was mentioned about the circulation of the passenger considered as the zero case inside the aircraft, so we cannot exclude contact contamination. [2]

The fact that the air circulation system was damaged in the Alaska flight may bring us a certain relief, but it is not an only case. More recently, in an American military flight 23 out of 50 passengers got sick after dividing the cabin with 11 colleagues who had the flu, although the aircraft had the air circulation system working perfectly well, renewing the air every 4 minutes, in a flow that was directed from the ceiling to the bottom of the plane. [3]

What does this tell us? Aerosols, very small particles of saliva containing the virus we exhale when we sneeze or even when we breathe if we have the flu, probably have an important role in the transmission of influenza. In addition to that we have public transportation, with a great number of people circulating in a place that may be closed and badly ventilated at times and we may have a notion of the importance of public campaigns that promote education and awareness of contaminated people to avoid leaving their homes when they have the flu and that they cover their mouth and nose with a disposable tissue when they sneeze and discard it right after that.

[1] Lemieux, C. (2007). Questioning Aerosol Transmission of Influenza Emerging Infectious Diseases, 13 (1), 173-175 DOI: 10.3201/eid1301.061202
[2] Moser MR, Bender TR, Margolis HS, Noble GR, Kendal AP, & Ritter DG (1979). An outbreak of influenza aboard a commercial airliner. American journal of epidemiology, 110 (1), 1-6 PMID: 463858
[3] Klontz KC, Hynes NA, Gunn RA, Wilder MH, Harmon MW, & Kendal AP (1989). An outbreak of influenza A/Taiwan/1/86 (H1N1) infections at a naval base and its association with airplane travel. American journal of epidemiology, 129 (2), 341-8 PMID: 2912044