How does the human body respond during the latent period of an infection?

[mktsgm]

I have a few doubts regarding infection.

When a bacteria enters a human body, it doesn't give symptoms immediately. Usually there is a latent/incubation period during which we don't feel the infection.

But what happens during this incubation period? What is the body's response during this time?

Of the possibilities described below, what describes correctly the events during the incubation period?

1) Body identifies the moment any bacteria or germ invaded the body. But the body couldn't mobilize the immune soldiers immediately to make an attack. It always takes some time. This is incubation time.

2) Body cannot identify the miniscule number of bacteria. It identifies the invaders only when they're in significant numbers. So body waits for some time for the germs to grow in number to identify and then attack.

3) Is there any other explanation or state which I am missing?

Also some persons remain carriers (without disease manifestations) of some infection for too long a period. They don't display any symptoms but they're potential candidates for spread of the infection to others.

What happens in the carrier's body? While its immune cells are powerful enough to keep the invaders at bay, what is preventing them from completely eradicating the germs, so that they're no longer carriers also.

So, generally what triggers the immune system's attack on invaded germs and when it happens? And how long does this battle continue?

Can someone clear my doubts?

 

[jim mcnamara]

First off, the "delay" in symptom onset can be caused by bacteria waiting for a so-called quorum, by coordinating with one another chemically when to launch toxin output, toxins causing the symptoms. example:
https://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate?language=en

The delay in the immune response is a matter of the the time it takes to recognize bad guys, which can be a day or two, and then the time required to mobilize the cells that actually go after and destroy bad guys. Bacteria exhibit logarithmic growth, with doubling times a fast as 20 minutes, as an example. Viral pathogens can reproduce very fast.
Overview of the whole process:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5091071/

 

[mktsgm]

That Ted talk gave me something to munch on. Yet to read the article.

Thank you Jim.

 

[Drakkith]

Overview of the whole process:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5091071/

Very nice article! Thanks, Jim!

 

[Laroxe]

I think it might be important to recognise that the different bacteria that cause infections behave very differently from one another and as part of the evolutionary arms race have developed all sorts of tools to help them survive and in the same way, so have we. Even the idea of an incubation period is a bit misleading and the term tends to be used only in relation to specific diseases. For any bacteria to gain access to our internal environment it has already had to get through certain defences, there are physical barriers like the skin, mucus membranes and other surfaces these often contain chemicals to kill organisms. However quite a few do gain entry, the vast majority of these are rapidly eliminated, most bacteria simply can't become established enough to cause infections in humans.
If there is a breach in your skin and bacteria gain entry, there is no latent period as far as your body is concerned, there are cells constantly on patrol throughout all of your tissue, these rapidly identify proteins that are not you and start a whole cascade of responses that build up over time. Chemicals are released to attract other immune cells, blood flow is slowed and increased to help white cells move into the area and these first responders attack the bacteria directly using chemical toxins or engulfing the organism.The body doesn't wait for a certain number of bacteria to be present, that would be daft, and a white cell is perfectly capable of recognising a single bacteria. Really at this stage its a matter of how quickly the bacteria can reproduce vs how quickly the white cells can kill them, for the bacteria to win there will need to be a minimum number, the inoculum and they will normally have abilities that interfere with the white cells. This local battle escalates as the bacteria multiply and more immune cells enter the fray. The changes in the blood supply and tissue fluids lead to swelling and redness along with pain, the increasing number of dead cells can lead to pus formation and other white cells try to wall off the area and keep the infection to the local area, this is of course when you recognise you have an infection. The incubation period isn't everyone having a rest its the period between the bacteria gaining entry to the onset of obvious symptoms. Remember that fighting an infection requires you to invest a great many resources so generally we see an escalating response, we actually respond very quickly but we don't immediately switch to committing everything when it probably won't be needed. This just describes a simple infection like a boil, Jims article covers a lot more ways our body responds and methods are often combined.
Often the most complicated types of infections are the ones that originated in humans and have evolved along side us like TB and possibly syphilis, the most successful infections are long term infections, they can continue to live in the body and have plenty of opportunity to spread. Diseases like Ebola, which we caught from animals kills its victims at a very high rate and very quickly, but in doing that it interferes with its own ability to spread, that's why we have been able to contain it. If it was less deadly it would actually be more successful and in fact there is some evidence it may be evolving in that direction, and that's scary. I think its a fascinating subject but really its far to big, very general answers don't explain things very well. Try reading up on some specific diseases, you see how varied they can be, I'd go for TB, Syphilis, Pneumonia a couple of viral infections like Measles & Flu and maybe a parasite or two like Malaria. Even in the time of modern medicine there are around 6.4 million new cases of TB reported every year and around 1.6 million deaths worldwide, flu kills between 300,000 to 600,000 every year and malaria around 500,000.