The Challenge of Animal STDs
By: A. S. Deller
Tags: Animals, Science, Disease, Ecology, Environment

Prior to the horrible outbreak of bushfires that began in September of 2019 in Australia — the worst bushfire season on record — koalas were facing another kind of outbreak that was already threatening them with extinction.

On May 6, 2018, John Oliver announced on his “Last Week Tonight” HBO show that he had helped fund (very indirectly, through an amazing back and forth with Russell Crowe) a koala chlamydia ward at the Australia Zoo Wildlife Hospital. The crowd chuckled, but the threat posed by the disease to the koala is very real and very serious.

Over 50% of koala have the disease, which is passed between adults through sexual transmission as well as to baby koala.

Surveys have shown that some wild populations demonstrate a 100 percent rate of infection, which frequently leads to blindness, severe bladder inflammation, infertility and death. And treatment with antibiotics could create further problems for the marsupials, upsetting their gut microbes and making it difficult for them to digest the eucalyptus leaves that are a staple of their diet. — Mindy Weisberger, LiveScience

Chlamydia isn’t all most of these koala are infected with. Their immune systems are also weakened by koala retrovirus-B (KoRV-B), an HIV-like virus which makes them more susceptible to other infection.

Transmission of KoRV-B was found at a rate of 3% via adult-to-adult contact per year, while there was a 100% rate of KoRV-B-positive mothers transmitting the virus to their joeys…We can now link KoRV-B to neoplasia and chlamydial disease in both wild and captive koalas, making it an imminent threat to this already vulnerable species. — Bonnie L. Quigley, et al., Journal of Virology

It’s actually a 3-pronged attack that the koala are under. While the chlamydia itself causes severe bladder infection, infertility, blindness and death in many cases, the KoRV-B allows lowers the koala’s ability to fight general bacterial and fungal disease, and the antibiotics that animal caregivers use to treat the chlamydia have a side effect that damages the koala gut flora and their ability to digest the eucalyptus that is their only source of nourishment.

Over the past twenty years, some koala populations in Australia have diminished by as much as 80%, with 3/4ths of the causes being disease-based. Of those disease causes, most could be explained as symptoms with roots in the KoRV-B and chlamydia STDs.

Koala may be the latest animal in the news to be linked to an STD, but they are far from the only animal in dire straits due to such disease. Some such diseases are even scarier.

The IIV-6 virus found in Texas crickets operates in a very strange manner, increasing the insects’ desire to mate while also making them infertile: a perfect recipe for extinction as the virus spreads while preventing new population growth.

Affecting ladybugs in the UK is a parasitic mite called Coccipolipus Hippodamie, which is passed between mating ladybugs. These mites accumulate into small colonies on the insect and live on their blood, and also reduce the insects’ fertility.

STDs are also found widely among housepets. Syphilis in rabbits, also known as “vent disease”, is a very common STD found worldwide, and results in lowered fertility. FIV (feline immunodeficiency virus) affects cats and reduces their immune system capabilities in much the same way that HIV does for humans. Pet owners need to educate themselves on these diseases, fix their animals and refrain from ever letting any of them go into the wild or live as “outdoor cats”.

Another Australian native marsupial, the Tasmanian devil is victim to a particularly malicious STD that takes the form of cancerous facial tumors. Called, rather fiendishly, Devil Facial Tumour Disease (DFTD), the disease is transmissible via blood contact, which often occurs during Tasmanian devils’ mating practice. Though the cause is not yet proven, a retrovirus is likely at the root of this disease, which has claimed nearly 95% of the devil population in Australia since its discovery in 1996.

Humans have never faced an existential threat from STDs (as far as we know), but our ability to combat them with medicine has increased in tune with our population. Despite this, we are always capable of becoming breeding grounds for new pathogens: Gonorrhea, syphilis and AIDs were all originally transmitted to humans from animals — gonorrhea from cattle, syphilis from sheep (or cattle), and HIV from chimpanzees.

With the human population as large as it is today, the medical responses available and advanced fertility technology, it is highly unlikely that Homo sapiens will ever be at risk as a species from a sexually transmitted infection. But wild animal populations, which — due directly to human engineering of the environment — are more and more likely to exist in reduced numbers contained in smaller and smaller geographic areas, are at great risk from such diseases. Scientists and conservationists need to remain highly aware of this and work toward funding research, cures and vaccines that can prevent STDs from exacting such large tolls on already vulnerable creatures such as koala and Tasmanian devils.