Paravaccinia virus originates from livestock infected with bovine papular stomatitis. When a human makes physical contact with the livestock's muzzle, udders, or an infected area, the area of contact will become infected. Livestock may not show symptoms of bovine papular stomatitis and still be infected and contagious. Paravaccinia can enter the body though all pathways including: skin contact by mechanical means, through the respiratory tract, or orally. Oral or respiratory contraction may be more likely to cause systemic symptoms such as lesions across the whole body

A person who has not previously been infected with paravaccinia virus should avoid contact with infected livestock to prevent contraction of disease. There is no commercially available vaccination for cattle or humans against paravaccinia. However, following infection, immunization has been noted in humans, making re-infection difficult. Unlike other pox viruses, there is no record of contracting paravaccinia virus from another human. Further, cattle only show a short immunization after initial infection, providing opportunity to continue to infect more livestock and new human hosts.

Currently, there is no proven, safe treatment for monkeypox. The people who have been infected can be vaccinated up to 14 days after exposure.

Variola caprina (goat pox) is a contagious viral disease caused by a pox virus that affects goats. The virus usually spreads via the respiratory system, and sometimes spreads through abraded skin. It is most likely to occur in crowded stock. Sources of the virus include cutaneous lesions, saliva, nasal secretions and faeces. There are two types of the disease: the papulo-vesicular form and the nodular form (stone pox). The incubation period is usually 8–13 days, but it may be as short as four days.

It is thought the same virus spreads sheep pox, to which European sheep breeds are highly susceptible. The virus may be present in dried scabs for up to six months.

In endemic areas the morbidity rate is 70–90% and the mortality rate is 5–10%. The mortality rate may reach nearly 100% in imported animals. Resistant animals may show only a mild form of the disease, which may be missed as only a few lesions are present, usually around the ears or the tail.

Vaccination against smallpox is assumed to provide protection against human monkeypox infection considering they are closely related viruses and the vaccine protects animals from experimental lethal monkeypox challenge. This has not been conclusively demonstrated in humans because routine smallpox vaccination was discontinued following the apparent eradication of smallpox and due to safety concerns with the vaccine.

Smallpox vaccine has been reported to reduce the risk of monkeypox among previously vaccinated persons in Africa. The decrease in immunity to poxviruses in exposed populations is a factor in the prevalence of monkeypox. It is attributed both to waning cross-protective immunity among those vaccinated before 1980 when mass smallpox vaccinations were discontinued, and to the gradually increasing proportion of unvaccinated individuals. The United States Centers for Disease Control and Prevention (CDC) recommends that persons investigating monkeypox outbreaks and involved in caring for infected individuals or animals should receive a smallpox vaccination to protect against monkeypox. Persons who have had close or intimate contact with individuals or animals confirmed to have monkeypox should also be vaccinated.

CDC does not recommend preexposure vaccination for unexposed veterinarians, veterinary staff, or animal control officers, unless such persons are involved in field investigations.

Paravaccinia is a member of the Parapoxvirus family. It has a cylindrical body about 140 X 310 nm in size, with convex ends covered in a criss-cross pattern of rope like structures. The virus is resistant to cold, dehydration, and temperatures up to 56 °C. Upon injecting a cell with its genome, the virus begins transcription in the cytoplasm using viral RNA polymerase. As the virus progresses through the cell, the host begins to replicate the viral genome between 140 minutes and 48 hours.

Goat pox is found in the part of Africa north of the equator, the Middle East, Central Asia and India. It may be spread between animals by:

- Direct contact

- Indirect transmission by contaminated implements, vehicles or products such as litter or fodder

- Indirect transmission by insects (mechanical vectors).

- Contamination by inhalation, intradermal or subcutaneous inoculation, or by respiratory, transcutaneous and transmucosal routes

It has been recorded since the late 19th century and has been reported from most sheep-or goat-raising areas including those in Europe, the Middle East, the United States, Africa, Asia, Alaska, South America, Canada, New Zealand and Australia. Orf is spread by fomites and direct contact. In some environments infection is injected by scratches from thistles of both growing and felled plants. Symptoms include papules and pustules on the lips and muzzle, and less commonly in the mouth of young lambs and on the eyelids, feet, and teats of ewes. The lesions progress to thick crusts which may bleed. Orf in the mouths of lambs may prevent suckling and cause weight loss, and can infect the udder of the mother ewe, thus potentially leading to mastitis. Sheep are prone to reinfection. Occasionally the infection can be extensive and persistent if the animal does not produce an immune response.

A live virus vaccine (ATCvet code: ) is made from scab material and usually given to ewes at the age of two months, but only to lambs when there is an outbreak. The vaccine can cause disease in humans.

In sheep and goats the lesions mostly appear on or near the hairline and elsewhere on the lips and muzzle. In some cases the lesions appear on and in the nostrils, around the eyes, on the thigh, coronet, vulva, udder and axilla. In rare cases, mostly involving young lambs, lesions are found on the tongue, gums, roof of the mouth and the oesophagus. It has also been reported a number of times to cause lesions in the rumen. In one case it was shown that a severe form of orf virus caused an outbreak involving the gastrointestinal tract, lungs, heart, as well as the buccal cavity, cheeks, tongue and lips. Another severe case was reported pharyngitis, genital lesions and infection of the hooves which led to lameness and, in some cases, sloughing of the hoof.

More typically sheep will become free of orf within a week or so as the disease runs its course. Sheep custodians can assist by ensuring infected lambs receive sufficient milk and separating out the infected stock to slow down cross-transmission to healthy animals. It is advisable for those handling infected animals to wear disposable gloves to prevent cross-infection and self-infection. A veterinarian needs to be contacted if there is a risk of misdiagnosis with other, more serious conditions.

Primarily, orf is a disease of sheep and goats although it has been reported as a natural disease in the following: humans, steenbok and alpacas, chamois and thar, reindeer, musk ox, dog, cat, mountain goat, bighorn sheep, dall sheep, and the red squirrel .

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

Cowpox originates on the udders or teats of cows. It is classified as a zoonotic disease, which means it can be transferred from animals to humans and vice versa. Cowpox is an infectious disease. So, the disease can manifest on cows in environments where bacteria thrive, due to unsanitary conditions, or randomly. Cowpox symptoms are similar in whichever host they infect: cow, cat, human. Cowpox symptoms include round, pus filled lesions on the skin at the site of infection. In most cases of humans, the lesions develop on the inner and outer parts of the hand and fingers. In some cases, the infected person can develop a mild fever or inflammation around the lesions. Cowpox can be transferred from human to human by contact of the infected site to another individual. It is very similar in pathology and structure in contrast to small pox. However, cowpox has increased activity in between the ectoderm and endoderm layers of the human skin. Cowpox includes both A type bodies and B type inclusion bodies which largely impacts the pathology of the disease.

Alastrim, also known as variola minor, was the milder strain of the variola virus that caused smallpox. The last known case of variola minor was in Somalia, Africa in 1977. Smallpox was formally declared eradicated in May 1980.

Variola minor is of the genus orthopoxvirus, which are DNA viruses that replicate in the cytoplasm of the affected cell, rather than in its nucleus. Like variola major, alastrim was spread through inhalation of the virus in the air, which could occur through face-to-face contact or through fomites. Infection with variola minor conferred immunity against the more dangerous variola major.

Variola minor was a less common form of the virus, and much less deadly. Although alastrim had the same incubation period and pathogenetic stages as smallpox, alastrim is believed to have had a mortality rate of less than 1%, as compared to smallpox's 30%.

Because alastrim was a less debilitating disease than smallpox, patients were more frequently ambulant and thus able to infect others more rapidly. As such, variola minor swept through the USA, Great Britain, and South Africa in the early 20th century, becoming the dominant form of the disease in those areas and thus rapidly decreasing mortality rates.

Alastrim was also called white pox, kaffir pox, Cuban itch, West Indian pox, milk pox, and pseudovariola.

Like smallpox, alastrim has now been totally eradicated from the globe thanks to the 1960s Global Smallpox Eradication campaign. The last case of indigenous variola minor was reported in a Somalian cook, Ali Maow Maalin, in October 1977, and smallpox was officially declared eradicated worldwide in May 1980.

Pigeon pox is a viral disease to which pigeons are susceptible. There is a live viral vaccine available (ATCvet code: ). Pigeon pox is caused by a virus that is spread by mosquitoes and dirty water but not in droppings.

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.

Cowpox is an infectious disease caused by the cowpox virus. The virus, part of the orthopoxvirus family, is closely related to the "vaccinia" virus. The virus is zoonotic, meaning that it is transferable between species, such as from animal to human. The transferral of the disease was first observed in dairymaids who touched the udders of infected cows and consequently developed the signature pustules on their hands. Cowpox is more commonly found in animals other than bovines, such as rodents. Cowpox is similar to, but much milder than, the highly contagious and often deadly smallpox disease. Its close resemblance to the mild form of smallpox and the observation that dairymaids were immune from smallpox inspired the first smallpox vaccine, created and administered by English physician Edward Jenner.

The word “vaccination,” coined by Jenner in 1796, is derived from the Latin root "vaccinus", meaning of or from the cow. Once vaccinated, a patient develops antibodies that make them immune to cowpox, but they also develop immunity to the smallpox virus, or "Variola virus". The cowpox vaccinations and later incarnations proved so successful that in 1980, the World Health Organization announced that smallpox was the first disease to be eradicated by vaccination efforts worldwide. Other orthopox viruses remain prevalent in certain communities and continue to infect humans, such as the cowpox virus (CPXV) in Europe, vaccinia in Brazil, and monkeypox virus in Central and West Africa.

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.

In an endemic herd, only a minority of the animals develops clinical signs; most animals either eliminate the infection or become asymptomatic carriers. The mortality rate is about 1%, but up to 50% of the animals in the herd can be asymptomatically infected, resulting in losses in production. Once the symptoms appear, paratuberculosis is progressive and affected animals eventually die. The percentage of asymptomatic carriers that develop overt disease is unknown.

MAP is capable of causing Johne's-like symptoms in humans, though difficulty in testing for MAP infection presents a diagnostic hurdle.

Clinical similarities are seen between Johne's disease in ruminants and inflammatory bowel disease in humans, and because of this, some researchers contend the organism is a cause of Crohn's disease. However, epidemiologic studies have provided variable results; in certain studies, the organism (or an immune response directed against it) has been much more frequently found in patients with Crohn's disease than asymptomatic people.

Key measures to prevent outbreaks of the disease are maintaining hygiene standards and using screening to exclude persons with suspicious infections from engaging in contact sports. A skin check performed before practice or competition takes place can identify individuals who should be evaluated, and if necessary treated by a healthcare professional. In certain situations, i.e. participating in wrestling camps, consider placing participants on valacyclovir 1GM daily for the duration of camp. 10-year study has shown 89.5% reduction in outbreaks and probable prevention of contracting the virus. Medication must be started 5 days before participation to ensure proper concentrations exist.

Herpes gladiatorum is transmitted by direct contact with skin lesions caused by a herpes simplex virus. This is the main reason why the condition is often found in wrestlers. It is believed that the virus may be transmitted through infected wrestlers' mats, but this is still subject of research since the virus cannot live long enough outside the body in order to be able to cause an infection. Direct contact with an infected person or infected secretions is undoubtedly the main way in which this virus may be transmitted.

It is also believed that wearing abrasive clothing may increase the chances to get infected with this type of virus. Shirts made of polyester and cotton may cause frictions that lead to small breaks in the skin which makes it easier to contract the infection. Studies in which athletes were wearing 100% cotton shirts showed a decrease in the number of herpes gladiatorum cases.

The spread is facilitated when a sore is present but it can happen in its absence as well. The patients may know that the virus is present on the skin when they experience the so-called "prodromal symptoms". These include itching or tingling on the skin, right before the blisters or lesions appear. The virus may spread since the first symptoms appear until lesions are completely healed.

The incubation period is situated between 3 and 14 days. This means that a person will experience the symptoms within 14 days after he or she contracted the infection. This type of virus may be transmitted even if the symptoms are not yet present. Some individuals can have very mild symptoms that may not be taken as herpes symptoms and the patient may not recognize them. The asymptomatic transmission occurs when the infection is spread between outbreaks.

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%.

The duration of the visible blistering caused by varicella zoster virus varies in children usually from 4 to 7 days, and the appearance of new blisters begins to subside after the fifth day. Chickenpox infection is milder in young children, and symptomatic treatment, with sodium bicarbonate baths or antihistamine medication may ease itching. It is recommended to keep new infants from birth up to age 6 months away from an infected person for 10 to 21 days because their immune systems are not developed enough to handle the stress it can bring on. Paracetamol (acetaminophen) is widely used to reduce fever. Aspirin, or products containing aspirin, should not be given to children with chickenpox, as it can cause Reye's Syndrome.

In adults, the disease is more severe, though the incidence is much less common. Infection in adults is associated with greater morbidity and mortality due to pneumonia (either direct viral pneumonia or secondary bacterial pneumonia), bronchitis (either viral bronchitis or secondary bacterial bronchitis), hepatitis, and encephalitis. In particular, up to 10% of pregnant women with chickenpox develop pneumonia, the severity of which increases with onset later in gestation. In England and Wales, 75% of deaths due to chickenpox are in adults. Inflammation of the brain, or encephalitis, can occur in immunocompromised individuals, although the risk is higher with herpes zoster. Necrotizing fasciitis is also a rare complication.

Varicella can be lethal to adults with impaired immunity. The number of people in this high-risk group has increased, due to the HIV epidemic and the increased use of immunosuppressive therapies. Varicella is a particular problem in hospitals, when there are patients with immune systems weakened by drugs (e.g., high-dose steroids) or HIV.

Secondary bacterial infection of skin lesions, manifesting as impetigo, cellulitis, and erysipelas, is the most common complication in healthy children. Disseminated primary varicella infection usually seen in the immunocompromised may have high morbidity. Ninety percent of cases of varicella pneumonia occur in the adult population. Rarer complications of disseminated chickenpox include myocarditis, hepatitis, and glomerulonephritis.

Hemorrhagic complications are more common in the immunocompromised or immunosuppressed populations, although healthy children and adults have been affected. Five major clinical syndromes have been described: febrile purpura, malignant chickenpox with purpura, postinfectious purpura, purpura fulminans, and anaphylactoid purpura. These syndromes have variable courses, with febrile purpura being the most benign of the syndromes and having an uncomplicated outcome. In contrast, malignant chickenpox with purpura is a grave clinical condition that has a mortality rate of greater than 70%. The cause of these hemorrhagic chickenpox syndromes is not known.

Hemorrhagic smallpox, sometimes called bloody pox, fulminant smallpox, and blackpox, is a severe and rare form of smallpox and is usually fatal. Like all forms of smallpox it is caused by the variola virus. It is characterized by an incubation period of 7 to 14 days. It has two stages, the first begins with fever, headache, chills, nausea, vomiting and severe muscle aches. The skin flushes in a deep-purple, uneven pattern across the face. The early stage is often mistaken for measles. The late stage is characterized by the appearance of small blisters resembling a severe form of chickenpox. These small blisters then flatten until they are even with the skin, and change into reddish lesions similar to those seen in measles. The skin then turns a deep purple. Lesions appear inside the mouth and active bleeding from oral and nasal mucous membranes is common. This is followed by active bleeding in the gastrointestinal tract, and blood appears in the stool and urine. Blood studies resemble the clinical values of disseminated intravascular coagulation.

The spores are able to survive in harsh conditions for decades or even centuries. Such spores can be found on all continents, including Antarctica. Disturbed grave sites of infected animals have been known to cause infection after 70 years.

Occupational exposure to infected animals or their products (such as skin, wool, and meat) is the usual pathway of exposure for humans. Workers who are exposed to dead animals and animal products are at the highest risk, especially in countries where anthrax is more common. Anthrax in livestock grazing on open range where they mix with wild animals still occasionally occurs in the United States and elsewhere. Many workers who deal with wool and animal hides are routinely exposed to low levels of anthrax spores, but most exposure levels are not sufficient to develop anthrax infections. A lethal infection is reported to result from inhalation of about 10,000–20,000 spores, though this dose varies among host species. Little documented evidence is available to verify the exact or average number of spores needed for infection.

Historically, inhalational anthrax was called woolsorters' disease because it was an occupational hazard for people who sorted wool. Today, this form of infection is extremely rare in advanced nations, as almost no infected animals remain.

Anthrax can enter the human body through the intestines (ingestion), lungs (inhalation), or skin (cutaneous) and causes distinct clinical symptoms based on its site of entry. In general, an infected human will be quarantined. However, anthrax does not usually spread from an infected human to a noninfected human. But, if the disease is fatal to the person's body, its mass of anthrax bacilli becomes a potential source of infection to others and special precautions should be used to prevent further contamination. Inhalational anthrax, if left untreated until obvious symptoms occur, is usually fatal.

Anthrax can be contracted in laboratory accidents or by handling infected animals or their wool or hides. It has also been used in biological warfare agents and by terrorists to intentionally infect as exemplified by the 2001 anthrax attacks.

The overall case-fatality rate for ordinary-type smallpox is about 30 percent, but varies by pock distribution: ordinary type-confluent is fatal about 50–75 percent of the time, ordinary-type semi-confluent about 25–50 percent of the time, in cases where the rash is discrete the case-fatality rate is less than 10 percent. The overall fatality rate for children younger than 1 year of age is 40–50 percent. Hemorrhagic and flat types have the highest fatality rates. The fatality rate for flat-type is 90 percent or greater and nearly 100 percent is observed in cases of hemorrhagic smallpox. The case-fatality rate for variola minor is 1 percent or less. There is no evidence of chronic or recurrent infection with variola virus.

In fatal cases of ordinary smallpox, death usually occurs between the tenth and sixteenth days of the illness. The cause of death from smallpox is not clear, but the infection is now known to involve multiple organs. Circulating immune complexes, overwhelming viremia, or an uncontrolled immune response may be contributing factors. In early hemorrhagic smallpox, death occurs suddenly about six days after the fever develops. Cause of death in hemorrhagic cases involved heart failure, sometimes accompanied by pulmonary edema. In late hemorrhagic cases, high and sustained viremia, severe platelet loss and poor immune response were often cited as causes of death. In flat smallpox modes of death are similar to those in burns, with loss of fluid, protein and electrolytes beyond the capacity of the body to replace or acquire, and fulminating sepsis.