They most definitely do, especially tick borne encephalitis, but not influenza (or at least it is several magnitudes more likely that a fellow human will give it to you than a tick), including the recent "Swine Flu". They are also vectors (this is the proper biological term for the carrier animals of different human diseases) for several other sicknesses. These ugly bugs are found even in the middle of all-concrete cities and are around for over 70 million years now. See related links below for more information on tick-borne diseases.
none
Yes, any animal with fur can.
Yes.
Yes. If you are sitting next to someone, a tick can jump off of you onto that person. This is most common when pets transfer ticks to people though.
Normally not, they prefer grasses and shades... but I have seen hundreds of ticks stuck to concrete walls and see they were just waiting for a tasty host to pass by and "jump" on them...
Parasites are any organism that lives off another organism. They can be anything from ticks and fleas to microscopic bacteria and viruses.
They can but don't always.
A virus can enter through many portals (doorways): nose, mouth, bites by dogs, ticks or mosquitoes through the skin or sexual contact.
Rickettsial disease covers a group of diseases caused by the microorganisms. Rickettsiae occupy a position between bacteria and viruses. Most rickettsial diseases are spread to humans by arthropods such as ticks, lice, mites and fleas.
Oxygen, Nitrogen, Carbon dioxide, Nutritions and alcohol can pass. And only one type of antibodies can pass which is the IgG. Viruses can pass like HIV and HBV (Hepatitis B virus) that's why the affected mothers usually have affected babies.
dread
A group of ticks is called a "cluster" or a "pack."