The pathogen depends only on the tick for survival. The organism causing Rocky Mountain Spotted Fever needs only the tick population to sustain the life cycle. It is not clear which ticks can transmit which diseases. The dog tick has also been shown to harbor the organism responsible for Lyme disease. Theoretically, one tick could transmit as many as three diseases.
More work needs to be done to determine what diseases each tick can transmit.
Studies have shown that the longer a tick stays on the more likely it is to transmit disease. If a deer tick is attached for less than 36 hours the risk of transmitting Lyme disease is pretty low. Other diseases transmitted by different ticks can occur more quickly. The efficiency by which ticks transmit disease needs further study. Common sense suggests that the sooner you remove a tick the better.