STIs, or sexually transmitted infections, are diseases that are passed on through unprotected sex or genital contact. All animals, including humans, are vulnerable. More than 200 different STIs have been identified in animals which range from mammals to insects and even molluscs.
“Wild Animals don’t practise safe sex, of course they have STIs!” says Dr Barbara Natterson-Horowitz, a modern day Dr Dolittle and UCLA cardiologist consulting for the Los Angeles zoo. In fact, some of the major STIs in humans have come from animals. We know, for example, that HIV originated from contact with chimpanzees.
HIV came from Chimpanzees
AIDS (Acquired immunodeficiency syndrome) in humans is caused by two human immunodeficiency viruses (HIV-1 and HIV-2). Both are the result of multiple cross-species transmissions of the monkey version of the viruses, simian immunodeficiency viruses (SIVs), that infect African primates.
Old World monkeys are carriers of more than 40 different SIVs. HIV is thought to have resulted from the close contact of humans with the blood or other bodily fluids of apes or monkeys carrying SIV. Most monkey-to-human infections resulted in viruses that spread in humans only to a limited extent. However, one transmission event, involving SIVcpz from chimpanzees in south-eastern Cameroon, gave rise to HIV-1 — the principal cause of the AIDS pandemic. Another transmission of SIV from sooty mangabey monkeys gave rise to HIV-2.
Because of this relationship, the use of nonhuman primate models continues to be a mainstay of HIV-AIDS research. A number of key advances in HIV/AIDS research in the fields of HIV transmission, pathogenesis, prevention, and therapy have been made possible by the extensive use of animal models, including nonhuman primate models of SIV and SHIV infection of various monkey species such as macaques, sooty mangabeys, vervets, and others. Smaller animal models, such as mice, rabbits and cats have also been used to better understand the disease. In particular, the engineering of transgenic mice with a humanised immune system has helped bridge the gap between human and animal infections. However, humanised mice are not yet widely accepted as a testing platform for new therapeutics or vaccines, which are more likely to be tested in nonhuman primates prior to human trials.
Today, animal research continues to be a pillar of the fight against the AIDS pandemic. Advances in humanised mouse models, nonhuman primate immunogenetics and recombinant challenge viruses have greatly increased the number and sophistication of available mouse and simian models. And although the development of effective therapy has been a major triumph, the emergence of drug resistance requires active management of treatment regimens and the continued development of new antiretroviral drugs. Animal models allow for a more invasive investigation of the disease and for preclinical testing of drugs and vaccines.
More information on animal research and AIDS :
www.animalresearch.info/en/medical-advances/diseases-research/aids-hiv
www.animalresearch.info/en/medical-advances/diseases-research/hivaids-prophylaxis
Dolphins get genital warts
Just like humans, dolphins can get genital warts. The viruses behind these extrusions are called papillomaviruses, some of which can cause cancer. Several hundred species or types of papillomaviruses have been identified in mammals and other vertebrates such as birds, snakes and other reptiles, turtles and fish. However, they are thought to rarely be transmitted between species.
In humans alone, there are over 100 different types of Human papillomaviruses (HPVs), including 30 that are sexually transmitted. Co-infection, or infections of multiple papillomavirus types, is believed to be one of the biggest risk factors for the development of cervical cancer. Dolphins are the only species besides humans and nonhuman primates that are known to harbour these co-infections. Comparative genomics of human and dolphin papillomaviruses present a unique window to study the role of co-infections in the development of cancer.
To date nine classified papillomaviruses have been described as being associated with genital tumours in cetaceans (dolphins, porpoises and whales). Although papillomaviruses are species specific, understanding the natural history and carcinogenic potential of HPVs in one animal could benefit many others. Curative or preventative technologies could be transferable from one species to the next. For instance, vaccines developed to fight human papillomaviruses, could also be effective against the very similar horse or dog papillomaviruses.
Find out more about how papillomaviruses were first discovered in rabbits : www.animalresearch.info/en/medical-advances/diseases-research/human-papillomavirus-hpv
Discover which species can get infected with papillomaviruses : www.animalresearch.info/en/medical-advances/diseases-research/human-papillomavirus-hpv
Find out more about the role of papillomaviruses in cervical cancer : www.animalresearch.info/en/medical-advances/diseases-research/cervical-cancer
Baboons suffer from herpes
Herpesviruses can be found throughout the animal kingdom. They occur in all vertebrates from mice to elephants and also in birds, turtles, reptiles, fish and even oysters. Baboons are no exception.
Based on genetic and molecular biology, baboons harbour viruses that are homologues to human herpesviruses, causing similar symptoms. The first herpesvirus discovered in baboons, in the 1970s, is closely related to the Epstein Barr virus in humans. In 1995 a second herpesvirus was identified in baboons, resembling the human herpes simplex virus 1 (HSV-1). Shortly afterwards another virus, this time homologous to the human cytomegalovirus, was isolated from the saliva of baboons.
Baboons are not the only primate affected. Each primate species has its own strain of the herpes virus. Researchers believe that the herpes simplex virus 1 (HSV-1) infected hominids before their evolutionary split from chimpanzees 6 million years ago. The herpes simplex 2 (HSV-2) seems to have been transferred from ancient chimpanzees to human ancestors –probably Homo erectus –about 1.6 million years ago, long before the rise of early modern humans about 200,000 years ago.
The high concordance between the pathology of herpesvirus-associated disease in baboons and in humans, along with the data demonstrating the existence of closely related homologues of human herpesviruses, establish baboons as a valid animal model for the study of herpesvirus pathogenesis. However, the prevalence of herpesviruses in other species means that baboons are far from the only option. Rabbit infection models, for example, have been developed to study herpesvirus pathogenesis with a more exaggerated phenotype.
Rabbits can acquire a number of different herpesviruses, including HSV-1. Rabbits can host the herpes virus and infect humans the same way primate species do: through bites or scratches. It can also happen the other way around. The external lesions caused by the virus make it easily transmittable between species. One of the most common ways human HSV-1 can affect rabbits is by infecting the eyes. Just like in humans, it is a condition that can come and go as the virus re-emerges after periods of dormancy. Exposure of the HSV-1 strain to pet rabbits has also, on rare occasions, resulted in brain lesions, a condition that can lead to seizures, coma and death.
More information on STIs in animals : www.animalresearch.info/en/medical-advances/diseases-research/stis-sexually-transmitted-infections
www.understandinganimalresearch.org.uk/news/sti-day
Syphilis is common in rabbits
Just like humans, rabbits are susceptible to syphilis. Rabbits get syphilis from other infected rabbits through sexual contact, direct contact with the sores of an infected rabbit, or at birth during the vaginal passage. But be reassured, Treponema paraluis-cuniculi, the bacteria associated with syphilis in rabbits, is different from the one found in humans – the subspecies pallidum – and cannot be spread from rabbit to human.
In humans, syphilis remains a significant global health burden, with some 8 million people affected each year. Unfortunately, the bacterium that relies heavily on its host for nutrients, cannot survive outside of mammalian cells. Therefore, it cannot be grown in vitro, which limits opportunities for study. Many questions still remain unanswered, including regarding the biologic basis of the disease and the development of new tools for diagnosis, treatment and prevention. And for this, rabbits can help.
Although humans are the only natural host for the T. pallidum bacterium, rabbits are the only mammal to develop naturally occurring syphilis caused by a bacterium with antigenic cross-reactivity (similar surface antigens to the human bacterium, which means the immune system recognises both as the same), and similar symptoms to those experiences by humans. This unique property led to the use of rabbits as an in-vivo medium for the propagation of T. pallidum and a primary model for studying the pathogenesis and immune response of human syphilis. Because the rabbit model closely reflects human infection, it is frequently used to study disease pathogenesis, explore new therapies, and develop potential vaccines.
More information on STIs in animals : www.animalresearch.info/en/medical-advances/diseases-research/stis-sexually-transmitted-infections
www.understandinganimalresearch.org.uk/news/sti-day
Koalas get chlamydia
Another STD that humans share with other animals is chlamydia. This bacterial infection has been found in a wide variety of species including many mammals, birds, and reptiles. The disease can seriously damage the reproductive system, causing infertility, abortion, inflammation of the testicles, and sterility, as well as high fevers and problems in the respiratory and digestive systems. However, human and animal chlamydia are caused by different species of the bacterium Chlamydiapsittaci, so the disease can't be spread between humans and animals.
There is only one exception. Chlamydia can spread from birds to humans. When humans come into contact with infected birds the bacterium can mutate into a form that can be transmitted to humans in a condition called psittacosis. A similar thing happens between birds and cats and there have even been rare occurrences of bird-to-cat-to-human transmission.
Chlamydia has become a major threat for one animal in particular: koalas. The species has been in dramatic decline – in some places plummeting by 80% in just ten years. In 2022, the Australian Government listed the koala as endangered in several states due to habitat destruction, traffic strikes, dog attacks, and Chlamydia pecorum disease. Of the different infectious diseases that affect koalas, those involving chlamydia are by far of the most concern, as they are highly prevalent (up to 73% in some populations), and cause premature mortality, and chronic, painful conditions, such as blindness, and reproductive disease. Koalas are suspected to have first caught chlamydia from livestock – but the spread and intensity of the disease among the marsupials is unmatched.
If caught early enough, treatment is an option. But the use of antibiotics isn’t without risk. It destroys the gut bacteria which allow koalas to digest otherwise toxic eucalyptus leaves – their main food source. Moreover, treatment does not prevent future infection. Fortunately, considerable effort over the past 20 years has been focused on the development of a koala chlamydia vaccine. There have been 14 separate koala vaccine trials conducted within South East Queensland, assessing different antigens, adjuvants, modes of delivery, and immunological responses.
Safety and effectiveness of a single-shot vaccine, which has been designed specifically for koalas, has been confirmed. Today, scientists are evaluating the use of vaccines in wildlife populations to determine among other things what percentage of koalas need to be vaccinated to meaningfully reduce infection and disease.
While the strain of chlamydia in koalas is quite different from that in humans, the possibility of a vaccine for koalas could be helpful for the development of a model to vaccinate humans.
More information on STIs in animals: www.animalresearch.info/en/medical-advances/diseases-research/stis-sexually-transmitted-infections
www.understandinganimalresearch.org.uk/news/sti-day
Deer catch brucellosis
One of the most common sexually transmitted diseases in the animal kingdom is brucellosis, or undulant fever. It is common among domestic livestock and occurs in mammals. Cows, goats, sheep, pigs, caribou, bison, camels, elk, cetaceans, seals and dogs, can all be affected by different bacteria of the Brucella family. The disease is usually sexually transmitted, but it can be shared between species by coming into contact with an infected animal or meat. Symptoms of the disease include miscarriage, inflammation of the testes, and uterine infections.
This disease is thought to have existed since ancient times. First evidence of brucellosis was revealed in ancient archeological solid residue of Egyptian cheese found in the tomb of Ptahmes, mayor of Memphis and high-ranking official under the Pharaohs Sethi I and Ramses II (1290–1213 B.C.) of the XIX dynasty.
Brucellosis is dangerous to animals due to its prevalence, but it also poses a threat to humans with possible long-term effects. Humans can contract brucellosis through drinking contaminated milk or through direct contact with infected animals. Although few cases of brucellosis are spread from human to human through sexual contact, individuals who have had sexual intercourse before realising they’ve contracted the illness are more likely to spread it to their partners.
Brucellosis remains a neglected human zoonosis that is emerging or reemerging in many parts of the world. It places significant burdens on human healthcare systems. Millions of people are at risk from the disease, especially in developing countries where the infection in animals has not been brought under control, where heat treatment is not routinely applied to dairy and where consumption of raw milk and poor hygienic conditions encourage human infection.
Brucellosis can be prevented in people by controlling and eliminating the disease in animals through vaccination or other control methods such as testing herds and killing the infected animals, and by avoiding the consumption of raw milk. In endemic areas, vaccination is often used to reduce the incidence of infection. Several vaccines are available that use modified live bacteria. The WOAH Manual of Diagnostic Test and Vaccines for Terrestrial Animals provides detailed guidance. However, no secure and effective vaccine for human beings has been developed against brucellosis, for which antibiotics remain the frontline therapy. Novel treatment protocols and preventative measures are still much needed and being explored.
For more information on Brucellosis : hwww.animalresearch.info/en/medical-advances/veterinary-medicine/brucellosis-or-undulant-fever
IIV-6 infection affects cold-blooded insects, mostly crickets
Insect iridescent virus 6 (IIV-6) is part of a large and diverse group of viruses that infect insects and other invertebrates. This sexually transmitted disease is known for its unique ability to cause iridescence in infected insects, resulting in a striking blue or green coloration of the insect's body. It has become a particularly bad problem for cricket colonies.
Infection renders the males and females infertile. Although they are unable to breed, infected male hosts experience an increased need to mate, which increases the spread of the infection from partner to partner. While the disease has been known for around a decade, the rate of infection has recently increased in different colonies of crickets, spreading in a way that may start to affect other invertebrates.
Equine viral arteritis in horses can be spread sexually
Equine viral arteritis (EVA) is an economically important, contagious, viral disease of equids caused by equine arteritis virus (EAV). The virus which causes EVA was first isolated in 1953, but the disease has afflicted equine animals worldwide for centuries.
Symptoms of equine viral arteritis vary considerably among individual horses and among outbreaks, from simple fever, to conjunctivitis, stiffness of gait, ataxia, abortion, diarrhoea, and subfertility. The frequency and severity of clinical illness associated with EAV infection tend to be greater in very young, old, or debilitated individuals and under adverse climatic conditions.
Transmission of the virus can occur by many means. The most frequent is the respiratory route. Viral particles can also be shed into the semen, and the disease has been spread by artificial insemination. Carrier stallions are the primary reservoir of equine arteritis virus. Although EAV infection is restricted almost exclusively to equids (horses, donkeys, mules, and zebras), limited data suggest the host range may also extend to alpacas and llamas.
EVA is a manageable and preventable disease that can be controlled by observation of sound management practices together with a targeted vaccination program. Attenuated live and inactivated vaccines are available in North America and Europe, respectively, for prevention and control. Although these two vaccines are available, the vaccination coverage of the equine population is largely insufficient to prevent new EAV outbreaks around the world. Testing effective candidate antiviral molecules is still underway in vitro on equine cells and also in animal models. It remains important to enhance our understanding of the EAV carrier state in stallions to mitigate disease spread.
Moreover, EAV persistence provides a powerful natural animal model to study RNA virus persistence in the male reproductive tract.
Tasmanian devils transmit tumours
Tasmanian devils can transmit cancer. Tasmanian devil facial tumour disease (DFTD) is spread by direct transfer of living cancer cells between individuals, most likely through biting inflicted during certain interactions such as feeding and mating. DFTD was first observed in 1996, and within three years caused a 30% decline in the Tasmanian devil population growth rate. The disease poses a direct threat to the survival of Tasmanian devils as a species as the disease is almost universally fatal. In the two decades since the disease was first spotted, the population of devils declined by 80% (locally exceeding 90%), as the condition spread through virtually all of Tasmania.
Unfortunately, there is no cure for the cancer so far. Trial studies of three different chemotherapy medications (vincristine, doxorubicin and carboplatin) found they were not successful in treating devils with DFTD. Surgical resection has been successful in treating a very small number of experimentally infected animals. In the meantime, there has been extensive research around why DFTD cells are not rejected by the host’s immune response.
Vaccination offers some promise in the fight, but researchers have not found a suitable candidate yet. Research and trials into an effective vaccine against DFTD are ongoing. A number of vaccination studies have been undertaken, producing variable results. A 2017 vaccine trial found that only one in five devils could resist DFTD. A DFT1 oral vaccine candidate is currently being tested in the captive devil population.
While on the search for a DFTD vaccine, a second cancer lineage, DFT2, was detected in 2014– 2015. Although the two cancer lineages produce very similar clinical signs, DFT2 is histologically and genetically distinct from DFT1. These two strains are two of four transmissible cancers – three of which are transmitted through sexual intercourse in the animal kingdom.
The third venereal tumour is found in dogs. Canine transmissible venereal tumour (CTVT or Sticker’s sarcoma) affects both males and females equally and occurs naturally. CTVT has developed a way to adapt dogs’ genes to survive in an almost parasitic form. Even though this disease has several mutations, each variation includes the same gene from the original dog that was first infected. CTVT can be treated with chemotherapy.
Rodents carry monkeypox
Monkeypox is a zoonotic virus, meaning it can pass from animals to humans. It has been found in a wide range of animals including rope squirrels, tree squirrels, Gambian pouched rats, dormice, and some species of monkeys. Despite its name, which suggests that monkeys are the original host of the virus, scientists have yet to pinpoint the specific animal reservoir of monkeypox.
The monkeypox virus was first documented in Denmark in 1958 during an outbreak among research monkeys (cynomolgus macaques) that were being used for polio-vaccine related research. It is believed that these monkeys caught the virus from a source in Africa before being transported to Denmark. The first recorded case of monkeypox in humans was in the Democratic Republic of the Congo (then Zaire) in 1970, and all subsequent cases to date have been linked to the virus spilling over from animals in Africa. The first time the virus was found in a wild animal was in 1985 when a squirrel (Funiscirurs anerythrus) with mpox symptoms was captured in then-Zaire.
Evidence about the virus and the spread of disease has offered clues as to which animals may be a reservoir of the mpox virus. In the DRC, 43 species of animals, including primates, have shown positive evidence of exposure to orthopoxvirus. At least one species of terrestrial rodent, and more prominently squirrels, have shown antibodies specific to the virus that causes mpox – in other words they have been exposed to the virus.
Overall, three genera of African rodent, Graphiurus (African dormice), Cricetomys (giant pouched rat) and Funisciurus (African striped squirrel), have been named as likely reservoirs of the mpox virus.
Due to the zoonotic nature of monkeypox, research has been carried out in captive and wild populations of animals.
More information on monkeypox: www.understandinganimalresearch.org.uk/human-diseases/monkeypox
Last edited: 13 May 2025 10:17
