infectious diseases

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bionewbie
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infectious diseases

Post by bionewbie » Thu Apr 13, 2006 2:27 am

Why are measles so contagious?
I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit nature and more time tasting her sweetness and respecting her seniority. ~ E. B. White

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Linn
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Post by Linn » Sun Apr 16, 2006 4:20 pm

akwap "the disease of the wind"
"How far you go in life depends on your being tender with the young, compassionate with the aged, sympathetic with the striving and tolerant of the weak and strong. Because someday in life you will have been all of these".

~ George washington Carver

bionewbie
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Post by bionewbie » Thu Apr 20, 2006 1:27 pm

On a separate note, but related to infectious diseases ... you know it's that time of year when colds and flus are prevalent (especially if you are sitting in an exam with all the coughers, snifflers, nose-blowers etc - you guys know what I mean), so anyways, why do humans "catch" a cold year after year?
I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit nature and more time tasting her sweetness and respecting her seniority. ~ E. B. White

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Post by pdavis68 » Fri Apr 21, 2006 5:27 pm

There are a variety of reasons why colds and flus tend to propagate in the colder months. Exposure to cold or flu doesn't guarantee one will get it. One generally gets it when the immune system is compromised.

A study was recently done where some subjects had their feet placed in very cold water for 20 minutes (causing their body temperature to drop slightly) and others didn't. They were then exposed to cold-causing agents (there are many virus and bacterial causes of the common cold).

The ones who had their feet in the water were far more likely to catch cold. So the part where people say to "wrap up or you'll catch a cold", appears to be based in fact.

I lived in tropical Mexico for a while. My first 6 months there (starting at early summer), I caught 4 colds and 2 flus. So it wasn't caused by cold temperature, but simply a compromised immune system due to the extreme change in environment (and possibly diet as well).

Hope that helps.

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Post by Khaiy » Fri Apr 21, 2006 6:57 pm

There's also the issue of resistance. If you've caught one strain of a cold for example, your body will be pretty good at fighting off an identical infection later on. But colds and flus changes very rapidly, and every year or so there is a new strain that is prevalent in an area. That's why some people get flu shots every year, to protect them from the newest strain of the flu. Pdavis is right about the compromised immune system accounting for the high rates of contraction during the winter months.

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Post by pdavis68 » Fri Apr 21, 2006 7:36 pm

Khaiy,

You too are correct. My answer was incomplete, I should have stressed that compromised immune system was simply one aspect. There are many variations of the flu virus and they mutate rapidly.

In regards to the flu shot, the flu shot is actually a vaccine against several varieties of flu that are believed will be the prevalent strains for a given year.

I'd like to go off on a bit of a tangent and mention the hot topic of avian flu. Avian flus are normally not contagious to people, at least not easily. The concern now is that the current strain of avian flu, which is spreading, but is not easily contagious, may mutate and become easily contagious. These types of flus are extremely dangerous and cause flu pandemics.

It's interesting to note that these flus are more dangerous for people with a healthy immune system, as what tends to kill people is a very powerful immune system response that ends up destroying the lungs.

There were 3 flu pandemics in the 20th century. The first (Spanish Flu) was in 1918, killing between 25 & 50 million people. The second (Asian Flu) in 1957, killing between 1 & 4 million people. The third (Hong Kong Flu) in 1968, killing between 750,000 and 2 million people.

What's really scary about the current avian flu is that it is currently far deadlier than any of those varieties, with an almost 50% mortality rate. The Spanish Flu was considered extremely bad with a mortality rate of 2.5-5%. It's quite possible that with a mutation that would cause the current avian flu to be easily transmissible, that this mortality rate would drop, possibly significantly, but it's quite likely that it would be far deadlier than the Spanish Flu and we would likely be looking at hundreds of millions dead within 2 years.

Sorry, I don't really know why I went off on that tangent. Just something I was reading about recently and thought I'd share it.

Pete

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Post by Khaiy » Fri Apr 21, 2006 7:42 pm

Sorry bionewbie, your thread got hijacked!!

All that I know about measles is that it's a pathogen that can be spread through respiration, including aerosol transmission, which makes it easier to spread. As to why it spreads so aggressively, I'm not sure. But 90% of people without immunity who live in a house with an infected person will catch it.

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Post by pdavis68 » Fri Apr 21, 2006 8:06 pm

You are right, we've gone a bit afield of the original question. Measles is a virus. Why a given virus is more or less contagious than another can be induced by a number of factors. Different viruses can operate in different ways.

A virus is, at it's most basic level, simply a string of nucleic acid that's injected into a cell. There are a couple of ways it might operate at that point.

The key thing, though is the structure of the nucliec acid. Viruses are varied, just as people, animals, and plants are varied. Some are simply more contagious than others because of that variation.

When the body is attacked by a virus, it often (but not always) creates antibodies that will protect it from future infestations of the same virus. Sometimes the antibodies can protect against similar, but different viruses.

In the case of measles, there isn't really anything similar that would give you antibodies, other than the vaccination. Because of this, there's simply no defense in the body against the virus.

With flu on the other hand, most people have had flus and develop some antibody resistance. In this case, being attacked by a flu that's similar enough to one you've previously had, may prevent you from becoming infected.

Sorry, not really sure how much information you want on the topic. molecular virology is a very complex subject, but that's sort of a bit of the basics.

So, in summary, the primary reasons why measles is so contagious (among people who haven't been vaccinated) is largely due to the fact that there are no natural defenses in the body against it and because of its particular genetic makeup.

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Post by bionewbie » Tue Apr 25, 2006 1:53 am

Khaiy wrote:Sorry bionewbie, your thread got hijacked!!


pdavis68 wrote: You are right, we've gone a bit afield of the original question.


no prob, i'm learning a lot from you both. i just pose the question just because i thought it would be interesting. also, it *is* very practical to everyday life.
I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit nature and more time tasting her sweetness and respecting her seniority. ~ E. B. White

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