Can astrology be used to predict if there is a probability of acquiring any disease? Yes it can predict to some extent but there is still a lot of research required and findings to be authenticated before giving a final verdict. Astrology can accurately predict common diseases quite accurately. Its not that difficult. For example if you are born in a water ascendant like Cancer, Scorpio or Pisces than chances of catching cough, cold, jaundice and other water-born disease rise quite drastically. 

     Sexually Transmitted Disease(STD) send shivers down the spine of most people. Problem with STD is its not a result of unprotected sex all the time. In some cases it could be bad blood transfusion, unsterilized needles and medical equipments, unhygeinic tatoo's and other body works and sometimes hereditary. In STD's there has got to be Venus involved in one form of another. If you have Venus in sixth house, seventh house or eight house than you should definitely try not to do bravado of engaging in unprotected sex with multiple partners. All these houses deal with lower body parts. Again its not necessary that everyone who has Venus in those houses catches STD. Its just high probability. 

     Another is when Venus is with Mercury in a problematic location. Mercury rules over skin. In these cases if you try getting unhygeinic tatoo's or try other body works which do not use sterilized equipments than chances of catching STD increase. As long as Venus is involved with Mercury or placed in a Mercury sign or nakshatra you got to be careful somewhat of catching STD. Mercury is a prince and royalty who loves experimentation and Venus is romance, sex and lust personified. Both of them influencing each other is bound to create a personality which loves sexual experimentation. 

     One more place is when Venus is with Mars or occupies a sign or nakshatra of Mars. At that time one could catch STD via blood transfusion but also via unnatural sex. Venus as stated loves sex while Mars is aggressive and intense. With Venus and Mars together, exchanging signs and causing Parivartana Yoga, being placed in each others nakshatra the native is sure to go for love marriage. More importantly native is driven by lust and perfection. There is bound to be physical relationship with lots and lots of forbidden activities. That is what Mars+Venus association is known for. But Mars also rules over blood. So if Venus or Mars are somehow associated and if there is blood transfusion done than there could be STD encountered. 

     Ofcourse this is general hypothesis derived. There is not yet enough data to accurately describe what causes STD and when are the chances of getting STD the maximum. Its better to be left to medical department to determine if one has STD or not. Astrology is only meant to study and research probability of catching STD's. The bottomline is to be safe irrelevant of whether your horoscope says you would get STD or not. And by safe its not just about sex. Its also when getting tatoo or other body works. Also patients should be careful when getting blood transfusion and ensuring sterilized medical equpments are used to treat you.