Short answers, pulled from the story.
A sexually transmitted infection, also known as a sexually transmitted disease or venereal disease, is an infection spread by sexual activity, especially vaginal intercourse, anal sex, oral sex, or sometimes manual sex. The term sexually transmitted infection is generally preferred because it includes cases with no symptomatic disease.
Bacterial sexually transmitted infections include chlamydia, gonorrhea, and syphilis. Viral ones include genital warts, genital herpes, and HIV/AIDS, while trichomoniasis is caused by a parasite. Some, such as syphilis, gonorrhea, chlamydia, and trichomoniasis, are curable, while HIV/AIDS and genital herpes are not.
In 2015, about 1.1 billion people had sexually transmitted infections other than HIV/AIDS, and these infections resulted in 108,000 deaths worldwide that year. About 500 million had syphilis, gonorrhea, chlamydia, or trichomoniasis, at least 530 million more had genital herpes, and 290 million women carried human papillomavirus.
Using condoms, having fewer sexual partners, mutual monogamy, abstinence, and vaccination all reduce the risk of sexually transmitted infections. Vaccines protect against hepatitis A, hepatitis B, and some types of HPV, and proper condom use reduces contact, though it does not provide complete protection.
The first recorded syphilis outbreak in Europe occurred in 1494, when it broke out among French troops besieging Naples in the Italian War of 1494-98. It was commonly called the French Disease, though the French called it the mal de Naples.
Sexually transmitted infection is preferred because it includes cases with no symptomatic disease. Venereal disease, a euphemism from the Latin venereus relating to Venus, lost its euphemistic effect and came to hold only negative connotations, and the World Health Organization has recommended the term sexually transmitted infection since 1999.