Sexually transmitted diseases are on the rise in the U.S. Even senior citizens are seeing an increase in infections. But STDs also occur in the animal kingdom, from mammals to insects to birds. And recent progress on a chlamydia vaccine for koalas may even lead to breakthroughs in vaccinating humans against sexually transmited infections.
STDs in animals and humans have a historical relationship. "Two or three of the major STDs have come from animals," says Alonso Aguirre, a veterinarian and vice president for conservation medicine at Wildlife Trust. "We know, for example, that gonorrhea came from cattle to humans. Syphilis also came to humans from cattle or sheep many centuries ago, possibly sexually." The most recent, as well as the deadliest, STD to migrate to humans is HIV, which hunters acquired from the blood of chimpanzees, says Aguirre.
The most common sexually transmitted disease among animals today is brucellosis, or undulant fever, which is common among domestic livestock and occurs in mammals including dogs, goats, deer, and rats. A bacterial infection that can be treated with antibiotics, the disease can be transmitted sexually or otherwise; for example, groups of cattle often eat the placenta of a spontaneously aborted fetus, and they can acquire the disease that way. Humans can contract brucellosis through drinking contaminated milk or through direct contact with infected animals.
Another STD that humans and other animals share is chlamydia, a bacterial infection that has been found in a wide variety of species including many mammals, birds, and reptiles. The human and animal STDs are spread by different species of Chlamydia (C. psittaci and C.trachomatis, respectively), so the disease can't be spread between humans and animals. Unfortunately for animals, Chlamydiapsittaci can also be transmitted through mucous membranes such as the eyes and urogenital tract, so mothers can give it to newborns and males can become infected through fighting.
In Australia, researchers have been working on a chlamydia vaccine for koalas, which may also be a step towards development of a human vaccine. Peter Timms and Ken Beagley from Queensland University of Technology's Institute of Healthand Biomedical Innovation spent years developing a vaccine for humans; when they saw a widespread chlamydia outbreak among the local koala population, the researchers turned their efforts to protecting the animals. Timms says that while the disease has also been reported in other animals in the region, including bandicoots and possums, koalas have been the most affected. The marsupials are known for their active sex lives, and as many as 50 percent of the koalas treated at the university have shown signs of the sexually transmitted disease.
So far, tests of the koala vaccine have brought encouraging results: Eighteen females treated with it are showing improvement.