Infectious Diseases

Weather and Infectious Diseases

As if toxic pollution isn’t enough, every breath you take fills your lungs with a multitude of dangerous germs. The sneeze of the person next to you, or the gases from animal housing nearby propels bacteria, viruses and fungi into the atmosphere. Natural or man-made turbulence lifts germs off the ground and into the breeze. Their survival depends largely on temperature, humidity and UV radiation.

Bacteria are the dominant life form on earth and adapt to almost all habitats. In the air they like to attach to other substances, thus increasing their chances of survival. Bacteria are present high in the atmosphere and drift long distances in the prevailing winds. Food and water are also likely carriers of bacteria. Most bacteria are harmless but others cause diseases such as cholera, pneumonia, leprosy, diphtheria, scarlet fever and tetanus.

Viruses don’t feel as comfortable in the air as bacteria do. They require a host to multiply and most don’t defend well against climatic variations and UV radiation. There are always exceptions, of course, such as the polio virus, which can live long enough to travel several kilometres. Some animal viral diseases can cause outbreaks from some distance away. Nevertheless, close contact is still the major means of spreading viral diseases such as chickenpox, influenza, measles and the common cold.

A major fungal disease dispersed by the air is histoplasmosis, also known as ‘bird fever.’ The fungus grows in bird and bat droppings. Dry droppings readily release the fungus into the air when they are disturbed, and then an unsuspecting person downwind inhales the microscopic organism and gets infected. While the lungs are the primary targets, the fungus can also invade other parts of the body. A mild attack has symptoms that are almost indistinguishable from those of the common cold, while a more serious form infects the liver and the eye.

The skin and the linings of nose, throat and airways are the first line of defence against any dangerous organism. When the immune system is impaired or the mucus layer is dry, the invaders break through the barrier and infect the tissue or enter the bloodstream. A bodily reaction to the invasion can occur at the point of entry or at a distant organ.

Common Cold and Influenza

Fellow travellers on the train cough and sneeze behind their newspapers. At the office, the first empty chairs forewarn of the start of a flu epidemic. Yes, it is winter – the season of coughs, wheezes and sniffs, of common cold and influenza.

Historians describe several devastating influenza epidemics. An estimated 20 million people lost their lives during the ‘Spanish flu’ in 1918. Since then, medical advances contained major outbreaks so that today ‘only’ thousands become victims. The US experienced an epidemic in 1957 that killed an estimated 70,000 people, followed by another outbreak in 1968 with 34,000 victims.

For New Zealand, the Ministry of Health reports:

“Influenza is a significant public health issue in New Zealand. Each year it has a large impact on our community, with 10-20% of New Zealanders infected. Some of these people become so ill they need hospital care, and a small number die.”

girl_with_influenzaApproximately 200 different kinds of viruses cause symptoms of the common cold. Several others lead to influenza. Often, the first signs are sneezing and a sore throat, followed by the inflammation of the sinuses (sinusitis) and the lungs (bronchitis). Fever generally occurs with influenza only. A third kind of virus (Herpes simplex) attacks the weakened body and causes a cold sore.

Whenever the person next to you sneezes or coughs, he or she dislodges tiny droplets that contain a large number of viruses. In summer, the fresh air outdoors rapidly dilutes the density of the viruses and the risk of catching the germ is lower – not so in winter. During winter people tend to spend more time indoors with the windows closed to save energy. The virus concentration is high, and with it comes the risk of inhaling a few. Winter’s low level of ultraviolet sunlight also plays a part. Sufficient ultraviolet rays during the summer period help kill the viruses.

The skin and the linings of nose, throat and airways are the first line of defence against any dangerous organism. When the immune system is impaired or the mucus layer is dry, the invaders break through the barrier and infect the tissue or enter the bloodstream. A bodily reaction to the invasion can occur at the point of entry or at a distant organ.

Viruses don’t survive the cold very well and multiply more readily in warm conditions. This contradicts the high number of cold or influenza cases in winter. Only recently scientist found the explanation for this contradiction: the viruses protect themselves against the cold. In warm conditions, viruses are covered by a liquid membrane, which becomes gel-like when the temperature drops. This protective coat melts once it enters your warm airways and the virus begins to multiply and infect your body.

With every exposure to any of the viruses’ strains, the body develops immunity and protects the person against that particular germ when it appears the next time. The children’s immune system, however, hasn’t had much experience with viruses. It is still learning how to recognize the different strains. Until their body develops the relevant immunities, they will be sick more often. Vaccines induce the body to produce such immunities.

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