Flu is a viral disease caused by different genres of influenza virus. In general, cases of infection tend to increase in winter. For what reason? Here we explain it.
In times of pandemic, COVID-19 has monopolized all media and investigations globally.
Even so, we continue to have other viruses in circulation that, even though they are less dangerous, cause discomfort and severe symptoms exceptionally.
This is the case of the flu, a disease that often spreads in winter.
Entering the month of May, with the increase in temperature that it entails.
you may be wondering: “Why does the flu peak in its prevalence in autumn and winter, practically disappear in spring?” In this discussion, we try to answer.
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Table of Contents
A Clinical Picture, Multiple Forms Of Flu
These are single-stranded RNA viruses, which are covered by an external lipid layer that gives them their characteristic rounded appearance.
According to the World Health Organization, there are 4 types of seasonal flu:
- Influenza A viruses are classified into subtypes based on combinations of two proteins on their surface—all known influenza pandemics caused by type A viruses.
- Type B viruses not classified into subtypes, but circulating viruses can currently be divide into two lineages.
- Type C viruses are detected less often and often cause mild infections. They are of no epidemiological importance.
- Type D viruses primarily affect livestock and do not appear to cause human illness or disease.
The global incidence calculated at 20%, that is, that 20% of the world population spends it at a certain point.
Besides, it is a selective pathology since, in certain population groups, it can reach a 50% incidence.
Due to its epidemiological importance, influenza has been the subject of multiple studies.
Flu is a viral disease whose cases increase, especially in winter.
Flu And Weather
A study published in the scientific journal Plos Pathogens explains the relationship of influenza with climatic factors:
- Twenty experimental replicas with guinea pigs used. In various habitats, there were several guinea pigs sick with the flu, in others adjacent to the sick, in air contact, functional groups.
- The different sample groups with healthy and diseased guinea pigs subjected to different relative humidity and temperature ranges.
- At constant temperature, relative humidity and flu transmission found inversely correlated. At a relative humidity of 20%, most healthy guinea pigs were infected by aerosols from the sick ones, while in 80%, no transmission observed.
- Guinea pigs infected in 5-degree temperature environments. Also found to expel more viral loads from their airborne particles, and for longer, than those infected in 20-degree environments.
It seems that the central hypothesis evidenced in this experiment: low temperatures, dryness promote the spread of the virus. Why?
Low Relative Humidity
Various assumptions try to explain why low relative humidity favors the spread of influenza:
- First, dry air could damage and deteriorate the host’s nasal mucosa, leaving it more unprotected against viral respiratory entry infections such as influenza.
- Second, the stability of the virus in aerosols appears to vary with humidity, with the virus remaining active longer in less humid environments.
- Third, the virus could lose its ability to spread at higher humidity.
At high relative humidities, the aerosols expelled by the patient could quickly adhere to water molecules in the medium.
Thus increasing their volume and precipitating earlier. This would decrease the speed, distance traveled by the virus.
Low temperatures provide an environment conducive to the transmission of influenza-causing viruses.
In this case, the explanation could be a little easier. At low temperatures, the nasal mucosa cools when taking the air.
This would create a micro environment more conducive to the virus, which could replicate better.
This would translate into a higher viral load with each sneeze, spray, thus favoring transmission.
A Justified Seasonality
Therefore, we have been able to see that the seasonality of influenza has a precise scientific meaning.
In the northern hemisphere, this virus begins to rebound in October, the peak observed between December, February.
These data agree with those observed in the exposed study since they are cold.dry months.
Luckily, the human being has an annual flu vaccine. Its problematic potential almost nullified.
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