# Urgent Viruses

1. May 23, 2005

### Craps

I just recieved another problem that was faxed from the lady i mentioned in my other thread in this forum. She is urgently asking for help with virus attacks in a day. Supposing that a patient is infected with N(large number) viruses, under what condition that should be established can I say the patient's IS (immune system) is able to get over the disease caused by these viruses ?
Thanks a lot

2. May 23, 2005

### iansmith

Staff Emeritus
The peak immune response usually appears between 7 to 14 days when it is the first encounter with the virus. For subsequet encouter, the peak immune reponse is reached between 48 hours and 5 days.

If the number of viruse/invaders is to large, the organisms will kill the patient before the proper immune response if mounted.

3. May 23, 2005

### Craps

So, do you know how can people find out the infection rate of a given virus ?
What methods available out there ?

4. May 23, 2005

### iansmith

Staff Emeritus
Usually the infection rate is calculate in animal models because the dosage and the initial infection time is known. This is often extrapollated to human. The infection is usually calculate as a lethal dose (number of pathogen that is required to kill x% of animal). People also collect sample from blood, other body fluid and tissues to measure the amount of infectious agent and to measure the immune response. This can give a good time frame of the infection and the immune response.

Human volonteer are also used as model for infections. A person would be infected with a given amount of pathogen via the common route of infection. The onset of the disease and the recovery period would be recorded.

You can also calculate the infection rate in epidiomological studies. However, this is approximate because the time of the initial exposure is often approximate and the amount of invading viruses is unknown.

5. May 23, 2005

### Monique

Staff Emeritus
You mean the viral load? If you take HIV or Hepatitis B/C as an example, you can measure the virus' RNA/DNA from a blood sample. Viral load is analyzed by doing a polymerase chain reaction (PCR), which amplifies the RNA/DNA to levels so that you can detect it. You can also measure antigens of the virus, such as the viral capsid by antibodies. The test that is used here is ELISA.

You can also measure the specific immune cells that are made by the body against a virus, this is done by synthetic MHCI tetramers containing certain viral peptides. Tetramers were first used to determine that during a virus infection ~70% of the activated CD8+ T cells are specific for the virus.