Love Sickness

Love Sickness (恋の病) is a particular disease that seems to be contracted by the empresses of the Kuja tribe.

About
This happens when they fall in love with a man. If they suppress their emotions, then it weakens them and eventually leads them to death. This disease killed many Kuja empresses in the past. It is unknown if the illness can be contracted by normal Kuja citizens.

In order to cure the disease, the empresses must accept their emotions and follow the loved one. This means that leaving Amazon Lily seems to be a prerequisite for the survival of the recipient, since only the former Empress Gloriosa is currently the only known survivor, and was known to have left the island at some point prior to returning. She also implied that if Hancock, another sufferer of the disease, follows her beloved Luffy (which means leaving the island), she wouldn't die. Outside of this cure, it is unknown if this disease can be cured by other means or if there is a cure specifically intended for it.

Symptoms
The disease basically develops as an exceptionally extreme version of the emotions that lovers would suffer while courting each other.

According to Elder Nyon, the feelings of emotion are "like a hurricane" hitting when least expected. The victim suffers unbearable pain in their heart when their love attempts to leave the island and even mentioning the date of leaving is enough to cause agony. However, once their love is present, the victim may display usual strength when needed be, or possibly be rendered powerless. As seen with Hancock they can become a completely different person, possibly even blinded by their love for the person so much that they don't acknowledge anyone one else around them (or even their love for that matter as Hancock demonstrated). No one matters more to them and every action their love does is interpreted incorrectly by the sufferer.

People Known to be Afflicted

 * Many empresses of the past: died because of their suppressed emotions.
 * Elder Nyon: she somehow survived the illness after falling in love with a man, even though their relationship was unknown.
 * Boa Hancock: having fallen in love with Monkey D. Luffy, she contracted the disease. However, she managed to hold it off when she accepted her feelings and decided to go with Luffy. Slight symptoms have resurfaced, such as barely eating or sleeping while she was unsure of Luffy's condition, so she is most likely not cured. Sometime later, she collapsed when her heart was pounding so much. When she finally part ways with Luffy, she asked him not to say the word "goodbye", but mistook Luffy's word of meeting again as proposal for marriage.

Trivia

 * The term, "love is a hurricane," was actually first used by Sanji back in the Arlong Arc, which may indeed mean that this saying originated in the East Blue.