Contagious equine metritis (CEM) is a type of metritis (uterine inflammation) in horses that is caused by a sexually transmitted infection. It is thus an equine venereal disease of the genital tract of horses, brought on by the "Taylorella equigenitalis" bacteria and spread through sexual contact. The disease was first reported in 1977, and has since been reported worldwide.

Equine venereal diseases are sexually transmitted infections in horses. They include contagious equine metritis (CEM) (caused by "Taylorella equigenitalis") and equine coital exanthema (caused by equine herpesvirus 3).

Signs in mares appear ten to fourteen days after breeding to an infected or carrier stallion. A gray to creamy vulvar discharge mats the hair of the buttocks and tail, although in many cases, the discharge is absent and the infection is not apparent. Most mares recover spontaneously, although many become carriers. Infected mares are usually infertile during the acute illness. However, the infertility only lasts a few weeks, after which pregnancy is possible.

Stallions do not show signs of infection. The first indication of the carrier state is lack of pregnancy in the mares covered by the stallion.

This disease affects the external genitalia, and is caused by equine herpesvirus 3. This disease remains with the horse for all its life. Equine coital exanthema is believed to only be transmitted during the acute phase of the disease through serous fluid from the blisters during sexual intercourse, and via breeding tools, handlers, etc.

Clinical signs include cute small lesions, no bigger than 2 mm in diameter around the vulva in mares, and on the sheath in stallions. The small bumps blister and then rupture, leaving raw, ulcerated, painful sores. While the majority of the symptoms are external, the presence of the virus can cause small and large plaque variants in tissues.

The U.S. Centers for Disease Control and Prevention (CDC) publishes a journal "Emerging Infectious Diseases" that identifies the following factors contributing to disease emergence:

- Microbial adaption; e.g. genetic drift and genetic shift in Influenza A

- Changing human susceptibility; e.g. mass immunocompromisation with HIV/AIDS

- Climate and weather; e.g. diseases with zoonotic vectors such as West Nile Disease (transmitted by mosquitoes) are moving further from the tropics as the climate warms

- Change in human demographics and trade; e.g. rapid travel enabled SARS to rapidly propagate around the globe

- Economic development; e.g. use of antibiotics to increase meat yield of farmed cows leads to antibiotic resistance

- Breakdown of public health; e.g. the current situation in Zimbabwe

- Poverty and social inequality; e.g. tuberculosis is primarily a problem in low-income areas

- War and famine

- Bioterrorism; e.g. 2001 Anthrax attacks

- Dam and irrigation system construction; e.g. malaria and other mosquito borne diseases

It is currently thought that it may be possible to eradicate yaws although it is not certain that humans are the only reservoir of infection. A single injection of long-acting penicillin or other beta lactam antibiotic cures the disease and is widely available; and the disease is believed to be highly localised.

In April 2012, WHO initiated a new global campaign for the eradication of yaws, which has been on the WHO eradication list since 2011. According to the official roadmap, elimination should be achieved by 2020.

Prior to the most recent WHO campaign, India launched its own national yaws elimination campaign which appears to have been successful.

Certification for disease-free status requires an absence of the disease for at least five years. In India this happened on 19 September 2011. In 1996 there were 3,571 yaws cases in India; in 1997 after a serious elimination effort began the number of cases fell to 735. By 2003 the number of cases was 46. The last clinical case in India was reported in 2003 and the last latent case in 2006. India is a country where yaws is now considered to have been eliminated

In March 2013, WHO convened a new meeting of yaws experts in Geneva to further discuss the strategy of the new eradication campaign. The meeting was significant, and representatives of most countries where yaws is endemic attended and described the epidemiological situation at the national level. The disease is currently known to be present in Indonesia and Timor-Leste in South-East Asia; Papua New Guinea, the Solomon Islands and Vanuatu in the Pacific region; and Benin, Cameroon, Central African Republic, Congo, Côte d'Ivoire, Democratic Republic of Congo, Ghana and Togo in Africa. As reported at the meeting, in several such countries, mapping of the disease is still patchy and will need to be completed before any serious eradication effort could be enforced.

About three quarters of people affected are children under 15 years of age, with the greatest incidence in children 6–10 years old. Therefore, children are the main reservoir of infection. Because "T. pallidum pertenue" is temperature- and humidity-dependent, yaws is found in humid tropical regions in South America, Africa, Asia and Oceania.

Mass treatment campaigns in the 1950s reduced the worldwide prevalence from 50–150 million to fewer than 2.5 million; however during the 1970s there were outbreaks in South-East Asia and there have been continued sporadic cases in South America. It is unclear how many people worldwide are infected at present.

The global prevalence of this disease and the other endemic treponematoses, bejel and pinta, was reduced by the Global Control of Treponematoses (TCP) programme between 1952 and 1964 from about 50 to 150 million cases to about 2.5 million (a 95 percent reduction). Following the cessation of this program yaws surveillance and treatment became a part of primary health systems of the affected countries. However incomplete eradication led to a resurgence of yaws in the 1970s with the largest number of case found in the Western Africa region.

Following the development of orally administered azithromycin as a treatment, the WHO has targeted yaws for eradication by 2020.

Bejel, or endemic syphilis, is a chronic skin and tissue disease caused by infection by the "endemicum" subspecies of the spirochete "Treponema pallidum".

Bejel is also known by a variety of other names, including belesh, dichuchwa, endemic syphilis, nonvenereal syphilis, frenga, njovera, skerljevo, siti, or treponematosis-bejel type.

Specific age groups, persons who participate in risky sexual behavior, or those have certain health conditions may require screening. The CDC recommends that sexually active women under the age of 25 and those over 25 at risk should be screened for chlamydia and gonorrhea yearly. Appropriate times for screening are during regular pelvic examinations and preconception evaluations. Nucleic acid amplification tests are the recommended method of diagnosis for gonorrhea and chlamydia. This can be done on either urine in both men and women, vaginal or cervical swabs in women, or urethral swabs in men. Screening can be performed:

- to assess the presence of infection and prevent tubal infertility in women

- during the initial evaluation before infertility treatment

- to identify HIV infection

- for men who have sex with men

- for those who may have been exposed to hepatitis C

- for HCV

It is treatable with penicillin or other antibiotics, resulting in a complete recovery.

Many STIs are (more easily) transmitted through the mucous membranes of the penis, vulva, rectum, urinary tract and (less often—depending on type of infection) the mouth, throat, respiratory tract and eyes. The visible membrane covering the head of the penis is a mucous membrane, though it produces no mucus (similar to the lips of the mouth). Mucous membranes differ from skin in that they allow certain pathogens into the body. The amount of contact with infective sources which causes infection varies with each pathogen but in all cases a disease may result from even light contact from fluid carriers like venereal fluids onto a mucous membranes.

Some STIs such as HIV can be transmitted from mother to child either during pregnancy or breastfeeding.

Healthcare professionals suggest safer sex, such as the use of condoms, as a reliable way of decreasing the risk of contracting sexually transmitted diseases during sexual activity, but safer sex cannot be considered to provide complete protection from an STI. The transfer of and exposure to bodily fluids, such as blood transfusions and other blood products, sharing injection needles, needle-stick injuries (when medical staff are inadvertently jabbed or pricked with needles during medical procedures), sharing tattoo needles, and childbirth are other avenues of transmission. These different means put certain groups, such as medical workers, and haemophiliacs and drug users, particularly at risk.

It is possible to be an asymptomatic carrier of sexually transmitted diseases. In particular, sexually transmitted diseases in women often cause the serious condition of pelvic inflammatory disease.

There are many different forms on prevention of syphilis and other sexually transmitted diseases in general. Prevention of syphilis includes avoiding contact of bodily fluids with an infected person. This can be particularly difficult because syphilis is usually transmitted by people who are unaware that they have the disease because they do not have any visible sores or rashes that may denote having an infection in general. Being abstinent or having mutually monogamous sex with a person who is uninfected with any type of sexually transmitted disease is the greatest guarantee of not becoming infected with syphilis or any form of a sexually transmitted disease. Using latex condoms can however reduce the risk of obtaining syphilis. In order to prevent further contamination to other individuals, benzathine penicillin is given to any contacts. Washing, douching, or urinating cannot prevent the transmission of a sexually transmitted disease in general.

Individuals obtain syphilis through a variety of circumstances. In general, syphilis can be transmitted from individual to individual through direct contact with sores that are present on the external genitals, vagina, rectum, anus, lips, or mouth. Transmission can occur through any form of sexual contact, including vaginal, anal, and oral sex. In addition, women who are pregnant and infected with syphilis can transmit the disease onto their child as well. If transmission has occurred, it is important to check up immediately with a physician to avoid further damage.

Equine infectious anemia or equine infectious anaemia (EIA), also known by horsemen as swamp fever, is a horse disease caused by a retrovirus and transmitted by bloodsucking insects. The virus ("EIAV") is endemic in the Americas, parts of Europe, the Middle and Far East, Russia, and South Africa. The virus is a lentivirus, like human immunodeficiency virus (HIV). Like HIV, EIA can be transmitted through blood, milk, and body secretions.

Transmission is primarily through biting flies, such as the horse-fly and deer-fly. The virus survives up to 4 hours in the vector (epidemiology). Contaminated surgical equipment and recycled needles and syringes, and bits can transmit the disease. Mares can transmit the disease to their foals via the placenta.

The risk of transmitting the disease is greatest when an infected horse is ill, as the blood levels of the virus are then highest.

A vaccine is available, called "Chinese Live Attenuated EIA vaccine", developed in China and widely used there since 1983. Another attenuated live virus vaccine is in development in the United States.

Reuse of syringes and needles is a risk factor for transfer of the disease. Currently in the United States, all horses that test positive must be reported to federal authorities by the testing laboratory. EIA-positive horses are infected for life. Options for the horse include sending the horse to a recognized research facility, branding the horse and quarantining it at least 200 yards from other horses for the rest of its life, and euthanizing the horse. Very few quarantine facilities exist, which usually leads to the option of euthanizing the horse. The Florida Research Institute for Equine Nurturing, Development and Safety (a.k.a. F.R.I.E.N.D.S.) is one of the largest such quarantine facilities and is located in south Florida.

The horse industry and the veterinary industry strongly suggest that the risks posed by infected horses, even if they are not showing any clinical signs, are enough of a reason to impose such stringent rules. The precise impacts of the disease on the horse industry are unknown.

A vaccine is available in the UK and Europe, however in laboratory tests it is not possible to distinguish between antibodies produced as a result of vaccination and those produced in response to infection with the virus. Management also plays an important part in the prevention of EVA.

The most popular treatment forms for any type of syphilis uses penicillin, which has been an effective treatment used since the 1940s.

Other forms also include Benzathine penicillin, which is usually used for primary and secondary syphilis (it has no resistance to penicillin however). Benzathine penicillin is used for long acting form, and if conditions worsen, penicillin G is used for late syphilis.

Methicillin-resistant Staphylococcus aureus (MRSA) evolved from Methicillin-susceptible Staphylococcus aureus (MSSA) otherwise known as common "S. aureus". Many people are natural carriers of "S. aureus", without being affected in any way. MSSA was treatable with the antibiotic methicillin until it acquired the gene for antibiotic resistance. Though genetic mapping of various strains of MRSA, scientists have found that MSSA acquired the mecA gene in the 1960s, which accounts for its pathogenicity, before this it had a predominantly commensal relationship with humans. It is theorized that when this "S. aureus" strain that had acquired the mecA gene was introduced into hospitals, it came into contact with other hospital bacteria that had already been exposed to high levels of antibiotics. When exposed to such high levels of antibiotics, the hospital bacteria suddenly found themselves in an environment that had a high level of selection for antibiotic resistance, and thus resistance to multiple antibiotics formed within these hospital populations. When "S. aureus" came into contact with these populations, the multiple genes that code for antibiotic resistance to different drugs were then acquired by MRSA, making it nearly impossible to control. It is thought that MSSA acquired the resistance gene through the horizontal gene transfer, a method in which genetic information can be passed within a generation, and spread rapidly through its own population as was illustrated in multiple studies. Horizontal gene transfer speeds the process of genetic transfer since there is no need to wait an entire generation time for gene to be passed on. Since most antibiotics do not work on MRSA, physicians have to turn to alternative methods based in Darwinian medicine. However prevention is the most preferred method of avoiding antibiotic resistance. By reducing unnecessary antibiotic use in human and animal populations, antibiotics resistance can be slowed.

Covering sickness, or dourine (French, from the Arabic "darina", meaning mangy (said of a female camel), feminine of "darin", meaning dirty), is a disease of horses and other members of the family Equidae. The disease is caused by "Trypanosoma equiperdum", which belongs to an important genus of parasitic protozoa, and is the only member of the genus that is spread through sexual intercourse. The occurrence of dourine is notifiable in the European Union under legislation from the OIE. There currently is no vaccine and although clinical signs can be treated, there is no cure.

Only 8% of infected horses have this form of pigeon fever, however, it has a 30-40% fatality rate. Organs that are commonly affected are the liver, spleen, and lungs. For a successful recovery, long-term antimicrobial therapy is essential.

Because this disease is highly durable in its equine host, it has proved very difficult to develop a vaccine for it. There are four main drugs on the market that are used to treat the clinical signs of dourine: Suramin, Diminazen, Cymerlarsan, and Quinapyramin. However, none of the listed drugs are a cure and even the individual animals that are treated will experience relapses. Although this disease is not fatal in all cases and spontaneous recovery can occur, the death rate is relatively high and listed at a mortality rate of over fifty percent.

This lack of a cure or vaccine is a definite problem in the equine industry, especially in developing countries where equines are highly valuable for both agriculture and transportation. Dourine is considered an endemic problem in developing countries, where over sixty percent of equines in the world are located. The protocol for this disease, as stated by OIE, currently stands at slaughter of seropositive animals. This is not an economically feasible option for many people who depend on horses for their livelihood. Therefore, it is crucial to continue research in this field and develop a viable vaccine.

The disease can be prevented in horses with the use of vaccinations. These vaccinations are usually given together with vaccinations for other diseases, most commonly WEE, VEE, and tetanus. Most vaccinations for EEE consist of the killed virus. For humans there is no vaccine for EEE so prevention involves reducing the risk of exposure. Using repellent, wearing protective clothing, and reducing the amount of standing water is the best means for prevention

While a vaccine is available for PHF, it does not cover all strains of the bacterium, and recent vaccine failures seem to be on the rise. Additionally, the vaccine usually produces a very weak immune response, which may only lessen the severity of the disease rather than prevent it. The vaccine is administered twice a year, in early spring and in early summer, with the first one inoculation given before the mayflies emerge and the second administered as a booster.

Some veterinarians have started making recommendations for farm management to try to prevent this disease:

- Maintaining riparian barriers along bodies of water may encourage aquatic insects to stay near their places of origin

- Turning off outside lights around the barn will prevent insects from being attracted

- Cleaning water buckets and feed areas frequently and keeping food covered will reduce the chance that the horse will accidentally ingest infected insects

Babesiosis is a vector-borne illness usually transmitted by "Ixodes scapularis" ticks. "B. microti" uses the same tick vector as Lyme disease, and may occur in conjunction with Lyme. The organism can also be transmitted by blood transfusion. Ticks of domestic animals, especially "Rhipicephalus (Boophilus) microplus" and "R. (B.) decoloratus" transmit several species of "Babesia" to livestock, causing considerable economic losses to farmers in tropical and subtropical regions.

In the United States, the majority of babesiosis cases are caused by "B. microti", and occur in the Northeast and northern Midwest from May through October. Areas with especially high rates include eastern Long Island, Fire Island, Nantucket Island, and Martha's Vineyard.

In Europe, "B. divergens" is the primary cause of infectious babesiosis and is transmitted by "I. ricinus".

Babesiosis has emerged in Lower Hudson Valley, New York, since 2001.

In Australia, babesiosis of types "B. duncani" and "B. microti" has recently been found in symptomatic patients along the eastern coastline of the continent. A similar disease in cattle, commonly known as tick fever, is spread by "Babesia bovis" and "B. bigemina" in the introduced cattle tick "Rhipicephalus microplus". This disease is found in eastern and northern Australia.

A table of isolated cases of babesiosis, which may be underestimated given how widely distributed the tick vectors are in temperate latitudes.

EVA is caused by an arterivirus called equine arteritis virus (EAV). Arteriviruses are small, enveloped, animal viruses with an icosahedral core containing a positive-sense RNA genome. As well as equine arteritis virus the Arterivirus family includes porcine reproductive and respiratory syndrome virus (PRRSV), lactate dehydrogenase elevating virus (LDV) of mice and simian haemorrhagic fever virus (SHFV).

There are a number of routes of transmission of the virus. The most frequent is the respiratory route. The virus can also be spread by the venereal route, including by artificial insemination. Stallions may become carriers.