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.

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.

Postpartum metritis, also known as puerperal sepsis, occurs within 21 days and is most common within 10 days of delivery. Metritis is characterized by an enlarged uterus and a watery red-brown fluid to viscous off-white purulent uterine discharge, which often has a bad smell. The severity of disease is categorized by the signs of health:

- Grade 1 metritis: An abnormally enlarged uterus and a purulent uterine discharge without any systemic signs of ill health.

- Grade 2 metritis: Animals with additional signs of systemic illness such as decreased milk yield, dullness, and fever >39.5°C.

- Grade 3 metritis: Animals with signs of toxemia such as inappetence, cold extremities, depression, and/or collapse.

Clinical endometritis is defined in cattle as the presence of a purulent uterine discharge detectable in the vagina 21 days or more postpartum. Simple grading systems for clinical disease are based on the character of the vaginal mucus and typical Grading schemes for clinical endometritis are widely used by veterinarians.

Subclinical endometritis is characterized by inflammation of the endometrium and the presence of neutrophils in cytology or biopsy histology, in the absence of signs of clinical endometritis.

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.

Metritis is inflammation of the wall of the uterus, whereas endometritis is inflammation of the functional lining of the uterus, called the endometrium The term pelvic inflammatory disease (PID) is often used for metritis.

External abscesses are the most common form of pigeon fever seen in horses. Abscesses develop on the body, usually in the pectoral region and along the ventral midline of the abdomen. However, abscesses can also develop on other areas of the body such as the prepuce, mammary gland, triceps, limbs and head. The fatality rate for this form infection is very low. The abscess is often drained once it has matured.

This is the least common form of pigeon fever seen in horses. It is characterized by severe limb swelling and cellulitis in one or both hind limbs and can lead to lameness, fever, lethargy and loss of appetite. Antimicrobial and anti-inflammatory treatments are required to prevent further complications such as limb edema, prolonged or recurrent infection, lameness, weakness and weight loss.

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).

Affected animals normally have generalised signs such as depression, dullness, weakness and lethargy, pyrexia and weight loss and decreased production. They will also have respiratory signs including bilateral nasal discharge, dyspnoea, tachypnoea and coughing. Occasionally the only sign seen is sudden death.

Typical pathological lesions are very suggestive of the disease - they are localised exclusively to the lung and pleura. Lungs are normally a port wine colour and abundant pleural exudate and pleuritis and adhesions are common. The pleural exudates may have solidified forming a gelatinous covering.

Histological examination of the lung tissues may show acute serofibrinous to chronic fibrino-necrotic pleuropneumonia with neutrophilic inflammation in the alveoli, bronchioles, interstitial septae and subpleural connective tissue.

In sheep, the disease is also called the "circling disease". The most obvious signs for the veterinarians are neurological, especially lateral deviation of the neck and head.

Caseous lymphadenitis (CLA) is an infectious disease caused by the bacterium "Corynebacterium pseudotuberculosis" found mostly in goats and sheep that at present has no cure. It manifests itself predominantly in the form of large, pus-filled cysts on the neck, sides and udders of goats and sheep. The disease is spread mostly from an animal coming in contact with pus from a burst cyst on an infected animal, but the disease is highly contagious and is thought to also be spread by coughing or even by flies. Studies have found CL incidence in commercial goat herds as high as 30%.

Listeriosis is an infectious but not contagious disease caused by the bacterium "Listeria monocytogenes", far more common in domestics animals (domestic mammals and poultry), especially ruminants, than in human beings. It can also occur in feral animals—among others, game animals—as well as in poultry and other birds.

The causative bacterium lives in the soil and in poorly made silage, and is acquired by ingestion. It is not contagious; over the course of a 30-year observation period of sheep disease in Morocco, the disease only appeared in the late 2000s (decade) when feeding bag-ensiled corn became common. In Iceland, the disease is called "silage sickness".

The disease is sporadic, but can occur as farm outbreaks in ruminants.

Three main forms are usually recognized throughout the affected species:

- encephalitis, the most common form in ruminants

- late abortion

- gastro-intestinal septicemia with liver damage, in monogastric species as well as in preruminant calves and lambs

Listeriosis in animals can sometimes be cured with antibiotics (tetracyclines, chloramphenicol and benzyl penicillin) when diagnosed early. Goats, for example, can be treated upon first noticing the disease's characteristic expression in the animal's face, but is generally fatal.

Incubation period is usually two to three weeks. The most common manifestation is flu-like symptoms with abrupt onset of fever, malaise, profuse perspiration, severe headache, muscle pain, joint pain, loss of appetite, upper respiratory problems, dry cough, pleuritic pain, chills, confusion, and gastrointestinal symptoms, such as nausea, vomiting, and diarrhea. About half of infected individuals exhibit no symptoms.

During its course, the disease can progress to an atypical pneumonia, which can result in a life-threatening acute respiratory distress syndrome, whereby such symptoms usually occur during the first four to five days of infection.

Less often, Q fever causes (granulomatous) hepatitis, which may be asymptomatic or becomes symptomatic with malaise, fever, liver enlargement, and pain in the right upper quadrant of the abdomen. Whereas transaminase values are often elevated, jaundice is uncommon. Retinal vasculitis is a rare manifestation of Q fever.

The chronic form of Q fever is virtually identical to inflammation of the inner lining of the heart (endocarditis), which can occur months or decades following the infection. It is usually fatal if untreated. However, with appropriate treatment, the mortality falls to around 10%.

After an incubation period of up to seven days, the signs associated with swine vesicular disease occur. The first sign is a transient mild fever. Other signs include:

- Vesicles in the mouth and on the snout and feet

- Lameness and an unsteady gait, shivering and jerking–type leg movements

- Ruptured vesicles can cause ulcers on limbs and feet, and foot pads may be loosened.

Young animals are more severely affected. Recovery often occurs within a week. There is no mortality.

Swine vesicular disease has the same clinical signs as foot-and-mouth disease, and can only be diagnosed by laboratory testing.

Q fever is a disease caused by infection with "Coxiella burnetii", a bacterium that affects humans and other animals. This organism is uncommon, but may be found in cattle, sheep, goats, and other domestic mammals, including cats and dogs. The infection results from inhalation of a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period is 9–40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.

Contagious caprine pleuropneumonia (CCPP) is a cause of major economic losses to goat producers in Africa, Asia and the Middle East.

Disease is caused by members of the Mycoplasma genus - usually "Mycoplasma capricolum subsp. capricolum" but sometimes by "M. mycoides" subsp. "capri" or "M. mycoides" subsp. "mycoides". It is extremely contagious with very high morbidity and mortality rates, causing an interstitial fibrinous pleuropneumonia in infected goats. Infection is spread by close-contact aerosol, therefore overcrowding and confinement increases disease incidence. Stress factors such as malnutrition and long transport can also predispose animals to disease.

Goats are the only species affected, therefore the disease is not a zoonosis. There is no age breed or sex predilection, but clinical signs are often worse in younger animals.

Aleutian disease, also known as mink plasmacytosis, is a disease which causes spontaneous abortion and death in minks and ferrets. It is caused by "Carnivore amdoparvovirus 1" (also known as "Aleution diease virus", ADV), a highly contagious parvovirus in the genus "Amdoparvovirus".

The virus has been found as a natural infection in the "Mustelidae" family within mink, ferrets, otters, polecats, stone and pine martens and within other varying carnivores such as skunks, genets, foxes and raccoons. This is most commonly explained as because they all share resources and habitats.

A lethal infection in mink, the Aleutian disease virus lies dormant in ferrets until stress or injury allows it to surface. While the parvovirus itself causes little or no harm to the ferret host, the large number of antibodies produced in response to the presence of the virus results in a systemic vasculitis, resulting in eventual renal failure, bone marrow suppression and death.

The symptoms are chronic, progressive weight loss, lethargy, splenomegaly (enlarged spleen), anemia, rear leg weakness, seizures and black tarry stool. Additional symptoms include poor reproduction and/or oral bleeding/gastrointestinal bleeding. Lesions can also be found within the pelt depending on the severity of the disease. This virus can unfortunately reduce fitness of wild mink especially, by disturbing both the productivity within adult females and the overall survivor rates of both juveniles and adults. Likewise, in the mink kits that survive, it infects the alveolar cells and ultimately causes respiratory distress, possibly leading to death.

Once symptoms show themselves, the disease progresses rapidly, usually to death within a few months.

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.

Strangles (equine distemper) is a contagious upper respiratory tract infection of horses and other equines caused by a gram-positive bacterium, "Streptococcus equi". As a result the lymph nodes swell, compressing the pharynx, larynx and trachea and can cause airway obstruction leading to death, hence the name Strangles. Strangles is enzootic in domesticated horses worldwide. The contagious nature of the infection has at times led to limitations on sporting events.

Signs and symptoms of PHF include acute-onset fever, depression (sometimes profound), inappetance, mild colic-like symptoms, decreased manure production, profuse watery non-fetid diarrhea endotoxemia, edema due to protein imbalances, abortion by pregnant mares, and acute laminitis (20 to 40 percent of cases). Infected horses founder usually within three days of the initial symptoms, thought to be secondary to endotoxemia. Death may occur and is usually due to severe laminitis leading to founder.

Horses may not always display any other symptoms beyond a fever.

Swine vesicular disease is most commonly brought into a herd by the introduction of a subclinically infected pig.

The disease can be transmitted in feed containing infected meat scraps, or by direct contact with infected feces (such as in an improperly cleaned truck).

Acute: The acute form is a sudden onset of the disease at full-force. Symptoms include high fever, anemia (due to the breakdown of red blood cells), weakness, swelling of the lower abdomen and legs, weak pulse, and irregular heartbeat. The horse may die suddenly.

Subacute: A slower, less severe progression of the disease. Symptoms include recurrent fever, weight loss, an enlarged spleen (felt during a rectal examination), anemia, and swelling of the lower chest, abdominal wall, penile sheath, scrotum, and legs.

Chronic: The horse tires easily and is unsuitable for work. The horse may have a recurrent fever and anemia, and may relapse to the subacute or acute form even several years after the original attack.

A horse may also not appear to have any symptoms, yet still tests positive for EIA antibodies. Such a horse can still pass on the disease. According to most veterinarians, horses diagnosed EIA positive usually do not show any sign of sickness or disease.

EIA may cause abortion in pregnant mares. This may occur at any time during the pregnancy if there is a relapse when the virus enters the blood. Most infected mares will abort, however some give birth to healthy foals. Foals are not necessarily infected.

Studies indicate that there are breeds with a tolerance to EIA.

Recent studies in Brazil on living wild horses have shown that in the Pantanal, about 30% of domesticated and about 5.5% of the wild horses are chronically infected with EIA.

An emerging infectious disease (EID) is an infectious disease whose incidence has increased in the past 20 years and could increase in the near future. Emerging infections account for at least 12% of all human pathogens. EIDs are caused by newly identified species or strains (e.g. Severe acute respiratory syndrome, HIV/AIDS) that may have evolved from a known infection (e.g. influenza) or spread to a new population (e.g. West Nile fever) or to an area undergoing ecologic transformation (e.g. Lyme disease), or be "reemerging" infections, like drug resistant tuberculosis. Nosocomial (hospital-acquired) infections, such as methicillin-resistant Staphylococcus aureus are emerging in hospitals, and extremely problematic in that they are resistant to many antibiotics. Of growing concern are adverse synergistic interactions between emerging diseases and other infectious and non-infectious conditions leading to the development of novel syndemics. Many emerging diseases are zoonotic - an animal reservoir incubates the organism, with only occasional transmission into human populations.

A contagious disease is a subset category of transmissible diseases, which are transmitted to other persons, either by physical contact with the person suffering the disease, or by casual contact with their secretions or objects touched by them or airborne route among other routes.

Non-contagious infections, by contrast, usually require a special mode of transmission between persons or hosts. These include need for intermediate vector species (mosquitoes that carry malaria) or by non-casual transfer of bodily fluid (such as transfusions, needle sharing or sexual contact).

The boundary between contagious and non-contagious infectious diseases is not perfectly drawn, as illustrated classically by tuberculosis, which is clearly transmissible from person to person, but was not classically considered a contagious disease. In the present day, most sexually transmitted diseases are considered contagious, but only some of them are subject to medical isolation.