Question

when a pathogen initially invades a new host such as when HIV first infected humans it is usually deadly. After some time, however, the pathogen usually evolves to become less deadly. Explain why natural selection would favor a less harmful pathogen

Answer 1

@aaronq

Answer 2

@dan815

Answer 3

Natural selection is when traits of an organism become more common or less common overtime as the animals choose to interact with the same enviornment. So once an organism adapts to a pathogen, it's offspring will have the same effect

Answer 4

i sill don't understand how natural selection would favor a less harmful pathogen

Answer 5

how does it evolve to become less deadly

Answer 6

"The risk of transmitting HIV to another individual, for example, is much higher if the infected person has lots of the virus in their body, so efficient viral replication mechanisms could be advantageous. However, these more virulent strains are also more likely to kill off the host before they have a chance to pass on the virus to someone else, meaning a trade-off exists. It’s therefore generally believed that over time, pathogens will evolve to become less deadly because natural selection favors those that cause minimal disease and are thus more likely to be transmitted."

read in depth...

http://www.iflscience.com/health-and-medicine/hiv-could-be-evolving-less-deadly-form

Answer 7

Too many usages of the same thing will cause people to adapt to it so they can stop it. It's kind of like playing a joke on someone, keep doing it, people catch on.

Answer 8

@Compassionate

Answer 9

@EclipsedStar

Answer 10

@prguan

Your not really explaining which part you don't get. The article I gave you is literally a whole page about the exact question your asking.

Answer 11

i don't get is why would natural selection favor a less harmful pathogen

Answer 12

generally a more harmful pathogen would be favored because they have a better chance of living.

Answer 13

Natural selection favors those who don't get the attention of things that can kill them.

Answer 14

i don't really understand that ^

Answer 15

Basically, think of it this way, if you go around breaking into people's houses, doing the exact same thing over and over, the cops will eventually catch on and go after you, and then they'll eliminate you, which is what a virus would do, if it goes and does the same thing over and over, it'll be eliminated by the things that assemble to take it out. If you went around breaking into the houses in an inconsistent and different manner, it'd take longer, and in this case, if a virus doesn't infect things often, people and the things that would bring it down won't have much time to assemble a defense.

Answer 16

ok i get it now.

Answer 17

with the disease HIV,how does killer T cells have to do with anything

Answer 18

T cells are among the more powerful anti-disease cells in the body, eliminating those paves the way for the other diseases to get in and kill a person.

Answer 19

so if HIV would only attack killer T cells then less damage would be done because killer T cells fight off the disease more?

Answer 20

No, they'd cause more damage.

Answer 21

how?

Answer 22

T cells help protect the body from infection, eliminating them basically creates an open season on the body.

Answer 23

oh ok that makes sense
thanks

Answer 24

You're welcome.

Answer 25

@prguan In fact, one of the first signs of the HIV/AIDS epidemic was adults with oral thrush (yeast infection of the mouth). Humans are incredibly resistant to fungal diseases, with the exceptions of vaginal yeast infection and infections of the hair or nails. Both of these are minor and are extremely benign. So, when HIV started killing off the immune cels of those infected, the less common fungal infections could occur.

@surana's explanation and analogy of the breaking into houses is good. However, it is not quite a true analogy. It has nothing to do with how often or how consistent the virus is in infecting the host, nor is it about having "enough time" to make a defense.

The issue is that there are many strains of the virus, just like there are different races of people that look different but are still all human. Some strains of the virus do not kill a host very quickly, or sometimes not at all. These viruses persist longer in the host and have many more opportunities to infect a second host than viruses that kill the host quickly.

Look at ebola. Ebola needs pretty direct contact to infect a person, and is very deadly. In ~6 to 16 days you'll be dead. Suppose we had two strains, one kills a person in 6. Imagine two people get infected on a camping trip, they notice they are sick and head back, but it will take 10 days. Well, the person infected with the 6 day strand will die before making it back to infect other people while the one with the slower killing strain will survive long enough to potentially infect others.

Answer 26

Natural selection has no foreknowledge or should not be treated as an agent knowing what it will produce. First, it is a mechanism that describes what is contributing to the variety of life and species around us today; second, whether it becomes less pathogenic or more pathogenic (deadly) is not something that natural selection would "try to accomplish." This view is dependent on the response of the environment including other species that will come to contact with. The survival point towards its capacity to survive and reproduce before it "dies."

Answer 27

@nincompoop Spot on. Far too often, explanations for certain aspects of Biology are discussed in a highly anthropomorphic way. The mechanisms and underpinning of Biology (and many other areas of study) are frequently treated as self aware.

In the short term, many find it helpful to have these topics anthropomorphized, but in the long run it causes issues.

To any others that read this, I would say that in Universities, professors usually come down pretty hard on students that ascribe a conscience to these non-entities.