The HIV virus is spread mostly by ______________.

The HIV virus is primarily spread through sharing intravenous drug needles. This is because the virus is present in the blood of an infected person, and when needles are shared among individuals who inject drugs, contaminated blood can easily be transferred from one person to another. This mode of transmission highlights the importance of safety practices in the use of needles, especially among high-risk populations.

Other forms of transmission do not pose as significant a risk for spreading HIV. For example, airborne particles are not a means of HIV transmission, as the virus does not survive well in the environment outside of the human body. Contaminated water is also not a vector for HIV, as the virus does not thrive in water. Additionally, insect bites do not transmit HIV; although some viruses can be spread by insects, HIV is not one of them. This distinction is critical in understanding how to prevent the spread of the virus effectively.