In 2008, a Texas man with HIV was sentenced to 35 years in prison for spitting at a police officer — after his saliva was deemed a deadly weapon due to his HIV status.

Texas isn't the only state that would send an HIV-positive person to prison for spitting. Thirty-seven states criminalize certain acts if someone has HIV, and five more have prosecuted people for HIV exposure or transmission. More than a dozen states penalize spitting and biting even though they rarely, if ever, transmit the disease. And several of these states, from Maryland to Colorado, have filed criminal charges against HIV-positive people for biting and spitting on others in recent years.

The Movement Advancement Project mapped states' HIV laws:

(Movement Advancement Project)

As the Center for HIV Law and Policy notes, there's no evidence these laws actually reduce risky behavior that spreads HIV. But the laws might discourage some people from seeking testing and treatment, since coming out as HIV-positive could elevate previous non-criminal offenses to criminal acts.

Only certain bodily fluids — blood, semen, rectal fluids, vaginal fluids, and breast milk — can transmit HIV. These fluids must be directly injected into the bloodstream or come in direct contact with a mucous membrane or damaged tissue for transmission to occur, according to the Centers for Disease Control and Prevention.

Receptive anal sex poses the greatest risk of HIV transmission, followed by insertive anal sex, vaginal sex, and shared needles. Oral sex poses a very small risk as well.

Biting can very rarely transmit HIV if the skin is broken, which is quite rare since it requires so much force. Saliva can't transmit HIV.

Further reading: This is what it's like to have HIV in 2014.