What is the difference between active and latent tuberculosis?
Latent TB infection (LTBI) means a person has been infected with the M. tuberculosis bacteria but their immune system was able to contain the bacteria so it does not cause illness. TST and IGRA tests are used to screen for exposure of this form of TB. If, due to certain factors, (genetics, immunocompetency etc) the person's immune system isn't able to contain the bacteria, the infection then becomes active and the person becomes ill. This person will test positive with TST or IGRA and will also begin to exhibit signs and symptoms of active infection (they will be ill!)
Why is the following statement grammatically incorrect? I have visited Canada last weekend.
In English, the Present Perfect (has/have + past participle) is used to state that an action happened at a time before now but the time it happened is NOT SPECIFIC. The exact time is not important. Therefore, you CANNOT use the Present Perfect with specific time expressions such as: yesterday, one year ago, last weekend etc. You CAN use it for general, NON-SPECIFIC periods of time such as: once, before, several times, long ago, already, yet et cetera...
What is anthropology?
Simply put, anthropology is the study of mankind. There are various sub-disciplines within anthropology, all involve examining and working towards understanding man and our relationship to the environment, to nature, and to each other. Anthropology often examines various human groups or cultures from the past and the present, and by looking in a holistic, multi-variable manner at the context in which they were exposed to, we are able to gain a greater understanding of why humans do what we do - as individuals, as groups, and as a species in general.