Generalized Conditions

Actinobacillosis is caused by several species of gram-negative coccobacilli of the genus Actinobacillus. Clinical signs vary, depending on the specific bacteria and the animal species they infect. Diagnosis can be confirmed by culture, PCR, or ELISA of tissue samples to identify the bacteria. Antibiotics are the usual treatment in swine and horses. Sodium iodide is used in ruminants, although antibiotics or surgical debulking may be required in severe or refractory cases.

Actinomyces are gram-positive, anaerobic bacteria that cause disease primarily in cattle and swine but also occasionally in other animals. Lumpy jaw is a localized, chronic, progressive, granulomatous abscess that most frequently involves the mandible, the maxillae, or other bony tissues in the head. Presumptive diagnosis is often based on clinical signs. The diagnosis can be confirmed by culture of the organism from the lesion; however, this requires anaerobic conditions and is frequently negative. The goal of treatment for actinomycosis is to kill the bacteria and stop the spread of the lesion.

Amyloidosis is caused by deposition of insoluble proteins in tissue. Formation of the proteins is often associated with inflammation. Deposition can lead to organ dysfunction, which can be fatal if critical organs are affected. Diagnosis is based on tissue biopsy. There is no effective treatment once protein deposition has occurred, although reducing inflammation may slow the progression of the disorder.

Anthrax is a zoonotic disease caused by the sporeforming bacterium Bacillus anthracis. Anthrax is most common in wild and domestic herbivores (eg, cattle, sheep, goats, camels, antelopes) but can also be seen in people exposed to tissue from infected animals, to contaminated animal products, or directly to B anthracis spores under certain conditions. Depending on the route of infection, host factors, and potentially strain-specific factors, anthrax can have several different clinical presentations. In herbivores, anthrax commonly presents as an acute septicemia with a high fatality rate, often accompanied by hemorrhagic lymphadenitis. In dogs, people, horses, and pigs, it is usually less acute although still potentially fatal.

Besnoitiosis (originally named globidiosis) is a cyst-forming, usually nonfatal disease caused by a number of different species of the apicomplexan protozoa Besnoitia. Lesions are commonly seen in the dermis and in mucous and serous membranes, as well as in other tissues. These Besnoitia species tend to be confined to specific animal hosts that include large and small mammals, as well as reptiles.

Bacteria of the order Chlamydiales are ubiquitous, obligate intracellular gram-negative bacteria. Within the host cell, they replicate via a unique developmental cycle competing with the host for intracellular nutrient pools. Virtually any chlamydial organism can infect any eukaryotic host cell, resulting in various infections.

Clostridia are relatively large, anaerobic, sporeforming, rod-shaped, gram-positive organisms. They are found either as living cells (vegetative forms) or as dormant spores. Their natural habitats are soils and intestinal tracts of animals, including people. Dormant spores of several clostridial species have been found in healthy muscular tissue of horses and cows. The endospores are oval, sometimes spherical, and are located centrally, subterminally, or terminally. The vegetative forms of clostridia in tissue fluids of infected animals occur singly, in pairs, or rarely in chains. Differentiation of the various pathogenic and related species is based on cultural characteristics, spore shape and position, biochemical reactions, and the antigenic specificity of toxins or surface antigens. The genomes of many clostridia have been sequenced and are available online. Pathogenic strains or their toxins may be acquired by susceptible animals by either wound contamination or ingestion. Diseases thus produced are a constant threat to successful livestock production in many parts of the world.

Embryonic and fetal development are the result of a complex series of well orchestrated events. When properly accomplished, the outcome is a healthy neonate. Errors in the sequential steps of development may be followed by embryonic loss, fetal death, fetal mummification, abortion, stillbirth, birth of nonviable neonates, or birth of viable offspring with defects. When a developmental disruption results in a deviation from normal that is present or apparent at birth, the defect is said to be congenital. Other developmental defects may not become apparent until later in life, and although the disruptive event occurred before birth, the defect is not strictly classified as congenital. Although the event or agent resulting in disrupted development remains undefined for many recognizable congenital conditions, technologic advances in the field of teratology have identified an increasing number of specific genetic, environmental, and infectious agents as etiologic determinants of certain cases of defective fetal development.

Coxiellosis is a zoonotic bacterial infection associated primarily with parturient ruminants, although domestic animals such as cats and a variety of wild animals have been identified as sources of human infection. The zoonotic infection in people associated with Coxiella burnetii is widely known as Q fever. Coxiella is considered a potential agent of bioterrorism because of its low infectious dose, stability in the environment, and capability for aerosol dispersion.

Erysipelothrix rhusiopathiae is an opportunistic bacterial pathogen that primarily affects swine, turkeys, and sheep. In swine, it causes erysipelas, which takes forms ranging from acute septicemia to subacute cutaneous erythema—including classic, diamond-shaped lesions—to chronic arthritis or endocarditis. In turkeys, erysipelas also has a range of clinical signs but primarily manifests as cyanotic cutaneous lesions, including blue comb, and muscular petechiae. E rhusiopathiae infection in sheep is most commonly seen as nonsuppurative polyarthritis in growing lambs over a month of age. As a zoonosis, erysipeloid in humans is generally an occupational disease characterized by localized cutaneous lesions and rarely septicemia. The bacterium can infect a wide range of host species, and disease is newly emerging in wildlife. Diagnosis is based on clinical signs, isolation of the bacteria, and PCR. Treatment with antibiotics is generally effective in acute cases, and prevention through vaccination is effective at controlling outbreaks in swine.

Foot-and-mouth disease (FMD) is a highly communicable viral disease caused by an Aphthovirus of the family Picornaviridae. There are 7 serotypes: A, O, C, Asia 1, and SAT (Southern African Territories) 1, 2, and 3. Further diversity is found in strains within each serotype. It primarily affects cloven-hooved animals of the order Artiodactyla. Livestock hosts include cattle, pigs, sheep, goats, and experimental infections in alpacas and llamas. FMD virus has also been reported in >70 species of wild artiodactyls, including bison, giraffes, Indian elephants, and several species of deer and antelope. The disease is characterized by fever and vesicles in the mouth and on the muzzle, teats, and feet and is spread through direct contact or aerosolized virus via respiratory secretions, milk, semen, and ingestion of feed from infected animals (meat, offal, milk). In a susceptible population, morbidity reaches 100% with rare fatalities except in young animals. FMD was once distributed worldwide but has been eradicated in some regions, including North America and Western Europe. In endemic countries, FMD places economic constraints on the international livestock trade and can be easily reintroduced into disease-free areas unless strict precautions are in place. Outbreaks can severely disrupt livestock production and require significant resources to control, as in the 2001 UK outbreak.

Systemic mycoses are infections with fungal organisms that exist in the environment, enter the host from a single portal of entry, and disseminate within the host usually to multiple organ systems. The soil reservoir is the primary source of most infections, which can be acquired by inhalation, ingestion, or traumatic introduction of fungal elements. (Also see Dermatophilosis.)

Leptospirosis is a zoonotic disease with a worldwide distribution caused by infection with any of several pathogenic serovars of Leptospira. The disease affects virtually all mammals and has a broad range of clinical effects, from mild, subclinical infection to multiple-organ failure and death.

Injury or death from electrocution may be caused by lightning, fallen power lines, faulty electric circuits, or other causes. Death usually results from cardiac or respiratory arrest. Besides sudden death, signs can include singe marks, temporary loss of consciousness in mild cases, and fractures or muscle damage from severe contractions. Diagnosis may depend on circumstantial evidence, such as the location of groups of affected animals and lack of other signs of disease. For animals that survive the initial event, supportive care is indicated.

Listeriosis is a sporadic bacterial infection that affects a wide range of animals, including people and birds. It is seen worldwide, more frequently in temperate and colder climates. There is a high incidence of intestinal carriers. Encephalitis or meningoencephalitis in adult ruminants is the most frequently recognized form.

Lyme borreliosis is a bacterial, tick-transmitted disease of animals (dogs, horses, probably cats) and people. Many additional mammalian and avian species become infected but do not develop overt clinical signs. Areas of greatest incidence in the USA are regions in the northeast (particularly the New England states), the upper Midwest, and the Pacific coast. Lyme borreliosis also occurs in moderate climatic regions of Europe and Asia.

Melioidosis is a bacterial infection of animals and people. It is often associated with suppurative or caseous lesions, comprising a mixed purulent and granulomatous response that can occupy any body organ.

Neosporosis is a disease caused by infection with protozoal parasites in the genus Neospora, most often N caninum but also N hughesi in horses. The most commonly observed problems include bovine abortion and gradually progressive myositis with paraparesis in puppies. Diagnosis is based on a combination of clinical signs, histopathology, serology, and PCR. There are no approved treatments in cattle, but antibiotics may be helpful in dogs.

Nocardiosis is an opportunistic, noncontagious, pyogranulomatous to suppurative disease of domestic animals, wildlife, and people.

Peritonitis is the inflammation of the serous membranes of the peritoneal cavity. It may be primary or caused by infectious or noninfectious agents. Signs include localized pain, depression, fever, and anorexia. The clinical diagnosis may be supported by ultrasonography and laboratory analysis of blood or abdominal fluid. Treatment may include peritoneal lavage, surgery, antibiotics, and anti-inflammatory medications.

Plague, caused by Yersinia pestis, is an acute and sometimes fatal bacterial zoonosis transmitted primarily by the fleas of rats and other rodents. Enzootic foci of sylvatic plague exist in the western USA and throughout the world, including Eurasia, Africa, and North and South America. In addition to rodents, other mammalian species that have been naturally infected with Y pestis include lagomorphs, felids, canids, mustelids, and some ungulates. Domestic cats and dogs have been known to develop plague from oral mucous membrane exposure to infected rodent tissues, typically when they are allowed to roam and hunt in enzootic areas. Birds and other nonmammalian vertebrates appear to be resistant to plague. On average, 10 human plague cases are reported each year in the USA; most are from New Mexico, California, Colorado, and Arizona. Most human cases result from the bite of an infected flea, although direct contact with infected wild rabbits, rodents, and occasionally other wildlife and exposure to infected domestic cats are also risk factors.

Rhodococcosis is a pyogranulomatous disease of domestic animals, wildlife, and people. It is caused by Rhodococcus equi (formerly Corynebacterium equi), the pathogenicity of which has been mainly attributed to the presence of virulence-associated antigens and plasmids.

Sweating sickness is an acute, febrile, tickborne toxicosis characterized mainly by a profuse, moist eczema and hyperemia of the skin and visible mucous membranes. It is essentially a disease of young calves, although adult cattle are also susceptible. Sheep, pigs, goats, and a dog have been infected experimentally. It occurs in eastern, central, and southern Africa and probably in Sri Lanka and southern India.

Toxoplasma gondii is a protozoan parasite that infects people and other warm-blooded animals, including birds and marine mammals (see Toxoplasmosis). It has been found worldwide from Alaska to Australia.

Tuberculosis (TB) is considered a reemerging, infectious granulomatous disease in animals and people caused by acid-fast bacilli of the genus Mycobacterium. Although commonly defined as a chronic, debilitating disease, TB occasionally assumes an acute, rapidly progressive course. The disease affects practically all species of vertebrates. The widespread occurrence of multidrug-resistant (MDR) strains and extensively drug-resistant (XDR) strains of M tuberculosis is of concern to clinicians and public health and regulatory officials involved in the control of disease. Bovine TB is still a significant zoonosis in nonindustrialized countries of the world. Signs and lesions are generally similar in the various species.

Tularemia is a bacterial septicemia that infects >250 species of wild and domestic mammals, birds, reptiles, fish, and people. It is listed as a category A bioterrorism agent because of the potential for fatality, airborne dissemination, and societal disruption if released. Clinical signs depend on the host species, subspecies of bacteria, and route of infection. Diagnosis is confirmed by culture, serology, or PCR. Antibiotic treatment can be effective if begun early.

Vesicular stomatitis (VS) is a viral disease of livestock transmitted primarily by biting flies and midges. The disease results in characteristic vesicular lesions that can occur on the muzzle, lips, tongue, ears, sheath, udder, ventral abdomen, and/or coronary bands. The disease is generally self-limiting, with no specific treatment, but some animals may require supportive care. VS is a reportable disease in most countries, including the United States, with diagnostic confirmation by complement fixation test, PCR, and/or virus isolation at an approved reference laboratory. In ruminants and swine, the disease is clinically indistinguishable from foot-and-mouth disease, swine vesicular disease, and vesicular exanthema of swine, which must be ruled out first on diagnostic testing. Vesicular stomatitis virus is zoonotic and can be transmitted to humans through direct contact with lesioned animals, so personal protective measures should be used when handling infected livestock.

African horse sickness (AHS) is an insectborne, viral disease of equids that is endemic to sub-Saharan Africa. It can be acute, subacute, or subclinical and is characterized by clinical signs and lesions associated with respiratory and circulatory impairment.

Equine granulocytic ehrlichiosis is an infectious, noncontagious, seasonal disease, originally seen in the USA in northern California but now recognized in many states where the tick vector occurs; it is also seen in Europe, Africa, and South America. (Also see Potomac Horse Fever.)

Equine infectious anemia (EIA) is a noncontagious infectious disease of equids caused by a virus of the same name. Clinical outcomes range from subclinical to a range of signs of variable severity, including fever, depression, muscle weakness, thrombocytopenia, anemia, jaundice, increased heart and respiration rates, hemorrhages on mucous membranes, epistaxis, collapse, and death in a small percentage of cases. Diagnosis of EIA is based on serologic testing and demonstration of antibodies to the virus in blood. There are no treatments or vaccines.

Equine viral arteritis (EVA) is an acute, contagious, viral disease of equids caused by equine arteritis virus (EAV). Typical cases are characterized by fever, depression, anorexia, leukopenia, dependent edema (especially of the lower hind extremities, scrotum, and prepuce in the stallion), conjunctivitis, supra- or periorbital edema, nasal discharge, respiratory distress, skin rash, temporary subfertility in affected stallions, abortion, and infrequently, illness and death in young foals. A variable percentage of postpubertal colts and stallions become carriers and semen shedders after infection with EAV.

Glanders, an often fatal contagious disease of solipeds, now found in remote areas of the world, is caused by Burkholderia mallei. The disease is characterized by purulent nasal discharge, nasal mucosal ulceration, lung lesions, and ulcerating nodules along the subcutaneous lymphatics. Diagnosis is based on presence of nasal ulcers, complement fixation test reaction, positive mallein test, and culture and PCR. Control is based on isolation and culling of affected animals.

Hendra virus was first described in 1994 after an outbreak of acute respiratory disease in a Thoroughbred training stable in Australia in which horses and one person were fatally infected. Sporadic cases continue to occur in eastern Australia, typically presenting as an acute febrile illness and rapidly progressing with variable system involvement, notably acute respiratory and/or severe neurologic disease. Fruit bats (suborder Megachiroptera) are the natural reservoir of the virus. Hendra virus is classified as a biosafety Level 4 agent (defined as posing a high risk of life-threatening disease in people), and the use of safe work practices and personal protective equipment is essential to manage the risk of human exposure. The earlier names of equine morbillivirus and acute equine respiratory syndrome are no longer appropriate.

African swine fever (ASF) is a highly infectious and severe hemorrhagic disease of pigs that produces a wide range of clinical signs and lesions that can closely resemble those of classical swine fever. African swine fever virus (ASFV) has a case fatality rate of up to 100% in domestic pigs and wild boar. The virus is enzootic in many African countries, where it is maintained in the environment through a sylvatic cycle involving warthogs and Ornithodoros (soft) ticks. In 2007, ASFV spread from Africa to Georgia and has since spread to many countries across Northern and Eastern Europe, Russia, and Asia, including China, which produces over half of the world's pork. This outbreak has resulted in the death and slaughter of millions of pigs, posing a massive threat to the global pig industry. There is currently no effective vaccine.

Classical swine fever (CSF) is a highly contagious and often fatal viral disease of swine. Infected pigs develop fever, hemorrhages, lethargy, yellowish diarrhea, vomiting, and a purple skin discoloration of the ears, lower abdomen, and legs. Neurologic signs, reproductive failures, and abortion may also be observed. Diagnostic tests for CSFV detection include RT-qPCR, virus isolation, immunofluorescence assay, and detection of antibodies by serologic tests such as ELISA and virus neutralization. There are no treatments for CSFV. Instead, vaccination against CSFV is used to prevent the disease and is usually applied in regions of the world where CSF is endemic. Countries considered free of the disease do not apply vaccination (eg, USA, Canada, and Europe).

Edema disease is a peracute toxemia caused by specific pathotypes of Escherichia coli that affect primarily healthy, rapidly growing nursery pigs. Other names for edema disease include “gut edema” or “bowel edema” because of the prominent edema of the submucosa of the stomach and mesocolon.

Encephalomyocarditis (EMC) is a significant viral infection of swine and zoologic mammals. It is caused by members of the genus Cardiovirus in the family Picornaviridae and recognized in many parts of the world. Although EMC virus (EMCV) isolates from various regions and countries have differed in pathogenicity and virulence, until recently all EMC viruses were considered to exist as a single serotype (EMCV-1). A cardiovirus isolated from a wood mouse in Germany in 2012 was distinguished from EMCV-1 by serologic and molecular means and has been designated EMCV-2. Although EMCV-1 infects a wide variety of hosts, the host range and pathogenicity of EMCV-2 remains to be determined.

Pigs can be colonized by different microorganisms before weaning, but some of those early colonizing agents are potentially pathogenic. This is the case with Haemophilus parasuis, a commensal organism of the upper respiratory tract of swine that causes severe systemic disease characterized by fibrinous polyserositis, arthritis, and meningitis. Disease has a sudden onset, short course, and high morbidity and mortality. Young animals (4–8 wk old) are primarily affected, although sporadic disease can be seen in adults (eg, introduction of a naive adult to a healthy herd). Survivors can develop severe fibrosis in the abdominal and thoracic cavities, which can result in reduced growth rate and carcass condemnation at slaughter. Glässer’s disease is seen worldwide, and its incidence appears to have increased since the introduction of porcine reproductive and respiratory syndrome (see Porcine Reproductive and Respiratory Syndrome).

Nipah virus disease is a relatively newly discovered disease of swine and people associated with infection with a novel paramyxovirus named Nipah virus. This disease emerged in Malaysia in 1998 and 1999. It was linked to severe encephalitis among people occupationally exposed to infected pigs in Malaysia and Singapore. The disease was eradicated from the national commercial swine population by control efforts. Fruit bats of the genus Pteropus appear to be reservoirs of the virus.

A novel, noncytopathogenic, picornavirus-like contaminant in the porcine kidney cell line PK-15 (ATCC-CCL33) was described in 1974. This agent was later shown to be a small, nonenveloped virus containing a single-stranded, circular DNA genome; it was named porcine circovirus (PCV). PCV antibodies in swine were found to be widespread, and experimental infections with this virus in pigs did not result in clinical disease, suggesting that PCV was nonpathogenic.

Porcine hemagglutinating encephalomyelitis is a viral disease of piglets, characterized by a vomiting and wasting syndrome and/or encephalomyelitis. Although the virus is widespread, outbreaks are rare because sows pass protective antibodies during nursing. Diagnosis is suspected based on clinical signs and can be confirmed by viral isolation, immunofluorescence staining of tissues, or PCR. There is no treatment or vaccine. Control is focused on building immunity among breeding sows.

Porcine reproductive and respiratory syndrome (PRRS) was first reported in the USA in 1987. Since then, outbreaks of PRRS and successful isolation of the virus have been confirmed throughout North America and Europe.

Of the bacterial group of gram-positive cocci comprising the genera Streptococcus, Enterococcus, and Peptostreptococcus, streptococci constitute the most significant pathogens of swine. Streptococci are also associated with infectious conditions of people, cattle, sheep, goats, and horses. Relative to pigs, S suis (an alpha-hemolytic Streptococcus) is by far the most important agent of infectious diseases in this group, affecting mainly nursing and recently weaned pigs. Septicemia, meningitis, polyserositis, polyarthritis, and bronchopneumonia are associated with S suis infections.

Swine vesicular disease (SVD) is typically a transient disease of pigs in which vesicular lesions appear on the feet and snout and in the mouth. SVD is usually mild in nature and may infect pigs subclinically. However, the disease is of major economic importance, because it must be differentiated from foot-and-mouth disease, eradication is costly, and embargoes on export of pigs and pork products are often imposed on nations not free of SVD.

Trichinellosis is a parasitic disease of public health importance caused by the nematode Trichinella spiralis. Human infections are established by consumption of insufficiently cooked infected meat, usually pork or bear, although other species have been implicated. Natural infections are found in wild carnivores; trichinellosis has also been found in horses, rats, beavers, opossums, walruses, whales, and meat-eating birds. Most mammals are susceptible. The number of human cases has declined in the past 50 years due in part to the move to modern production facilities (confinement) that reduces or eliminates exposure to rodents and other wildlife.

Vesicular exanthema of swine (VES) is an acute, highly infectious disease characterized by fever and formation of vesicles on the snout, oral mucosa, soles of the feet, coronary band, and between the toes.

Bluetongue is an infectious arthropod-borne viral disease primarily of domestic and wild ruminants. Infection with bluetongue virus (BTV) is common in a broad band across the world, which until recently stretched from ~35°S to 40°–50°N. Since the 1990s, BTV has extended considerably north of the 40th and even the 50th parallel in some parts of the world (eg, Europe). The geographic restriction is in part related to the climatic and environmental conditions necessary to support the Culicoides vectors. Most infections with BTV in wild ruminants and cattle are subclinical. Bluetongue (the disease caused by BTV) is usually considered to be a disease of improved breeds of sheep, particularly the fine-wool and mutton breeds, although it has also been recorded in cattle and some wild ruminant species, including white-tailed deer (Odocoileus virginianus), pronghorn antelope (Antilocapra americana), and desert bighorn sheep (Ovis canadensis) in North America, and European bison (Bison bonasus) and captive yak (Bos grunniens grunniens) in Europe.

Bovine ephemeral fever is an arthropod-borne viral disease of cattle and water buffalo that causes milk production losses, recumbency, and sometimes death. Diagnosis is mostly performed by PCR. Treatment includes administration of NSAIDs, accompanied by supportive care to recumbent cows. Vaccine effectiveness varies.

Lymphosarcoma in cattle may be sporadic or result from infection with bovine leukemia virus (BLV); the latter is often referred to as an enzootic bovine leukosis. Sporadic lymphosarcoma in cattle is unrelated to infection with BLV. Despite the lack of association, animals with sporadic lymphosarcoma may possibly be infected with the virus. Sporadic lymphosarcoma manifests in three main forms: juvenile, thymic, and cutaneous. Juvenile lymphosarcoma occurs most often in animals <6 mo old, thymic lymphosarcoma affects cattle 6–24 mo old, and cutaneous lymphosarcoma is most common in cattle 1–3 yr old.

Bovine petechial fever is a rickettsiosis of cattle characterized by high fever, hemorrhages, and edema. Its occurrence has been confirmed in the highlands of Kenya and Tanzania at altitudes >5,000 ft (1,500 m), although it is considered likely to occur in neighboring countries with similar topography. The importance of bovine petechial fever lies in its threat to dairy development in the highlands of eastern Africa, but no outbreak has been reported for more than a decade.

Caprine arthritis and encephalitis (CAE) virus infection is manifested clinically as polysynovitis-arthritis in adult goats and less commonly as progressive paresis (leukoencephalomyelitis) in kids. Subclinical or clinical interstitial pneumonia, indurative mastitis ("hard udder”), and chronic wasting have also been attributed to infection with this virus. Most CAE virus infections, however, are subclinical. Infection with the CAE virus decreases the lifetime productivity of dairy goats and is a barrier to exportation of goats from North America.

Colisepticemia is characterized by invasion of the blood stream by coliform bacteria and is primarily observed in neonates and immune-compromised animals. Affected animals show pronounced signs of systemic disease and tend to deteriorate rapidly. A presumptive diagnosis is made based on clinical signs in combination with hematologic and blood biochemical results. Blood cultures are considered a diagnostic gold standard, but they lack sensitivity, and results are not readily available. Therapy consists of immediate, thorough antimicrobial, anti-inflammatory, and fluid therapy.

Crimean-Congo hemorrhagic fever (CCHF) is a severe hemorrhagic viral disease of people acquired from infected ticks, tissues of infected wild or domestic animals, and from human patients with the disease.

Heartwater is an infectious, noncontagious, tickborne rickettsial disease of ruminants. The disease is seen only in areas infested by ticks of the genus Amblyomma. These include regions of Africa south of the Sahara and the islands of the Comores, Zanzibar, Madagascar, Sao Tomé, Réunion, and Mauritius. Heartwater was introduced to the Caribbean, and it and its vector (A variegatum) are endemic on the islands of Guadeloupe and Antigua. A variegatum, but not the rickettsia, has since spread to several other islands despite attempts at eradication. Possible spread to the mainland threatens the livestock industry of regions from northern South America to Central America and the southern USA. In heartwater endemic areas in southern Africa, it is estimated that mortalities due to the disease are more than double those due to bacillary hemoglobinuria (red water, see Bacillary Hemoglobinuria) and anaplasmosis (see Anaplasmosis) combined. Cattle, sheep, goats, and some antelope species are susceptible to heartwater. In endemic areas, some animals and tortoises may become subclinically infected and act as reservoirs. Indigenous African cattle breeds (Bos indicus), especially those with years of natural selection, appear more resistant to clinical heartwater than B taurus breeds.

Infection by Histophilus somni is common in North American cattle and sporadic in other locations worldwide. Sudden death, or a variety of clinical signs dependent on the system affected, may be observed. Diagnosis is based on histopathology, bacterial isolation, and PCR. Because identification of infected animals is difficult early in the course of the disease, antibiotic treatment may not be successful. Multivalent bacterins may help reduce morbidity and mortality.

Hemorrhagic septicemia (HS) is an acute, highly fatal form of pasteurellosis that affects mainly water buffalo, cattle, and bison. It is considered the most economically important bacterial disease of water buffalo and cattle in tropical areas of Asia, particularly in southeast Asia, where water buffalo populations are high. Disease is most devastating to smallholder farmers where husbandry and preventive practices are poor and free-range management is common. HS is also an important disease in Africa and the Middle East, with sporadic outbreaks occurring in southern Europe. The only confirmed outbreaks of HS in the Americas occurred in bison in Yellowstone National Park, most recently from 1965–1967. Natural disease occurs infrequently in pigs, sheep, and goats and has been reported in camels, elephants, horses, donkeys, yaks, and various species of deer and other wild ruminants.

Malignant catarrhal fever (MCF) is an infectious systemic disease that presents as a variable complex of lesions affecting mainly ruminants and rarely swine. It is principally a disease of domestic cattle, water buffalo, Bali cattle (banteng), American bison, and deer. In addition to these farmed animals, MCF has been described in a variety of captive ruminants in mixed zoologic collections. In some species, such as bison and some deer, MCF is acute and highly lethal, capable of affecting large numbers of animals. With occasional exceptions, the disease in cattle normally is seen sporadically and affects single animals. MCF is typically fatal; however, there are outbreaks in which several animals are affected, with evidence of recovery and mild or inapparent infections in some cases. It also occasionally presents as chronic alopecia and weight loss. Its distribution is essentially worldwide, mirroring that of the principal carriers, domestic sheep and wildebeest. MCF has long been a major problem in farmed deer operations, and in recent years has emerged as a severe threat to the commercial bison industry.

Nairobi sheep disease (NSD) is a tickborne viral disease of sheep and goats characterized by fever and hemorrhagic gastroenteritis, abortion, and high mortality. The disease was first identified near Nairobi, Kenya, in 1910, and NSD virus was shown to be the causative agent in 1917. The disease is endemic in Kenya, Uganda, Tanzania, Somalia, Ethiopia, Botswana, Mozambique, and Republic of Congo. Human infections are rare; however, accidental infections have been reported among laboratory workers, resulting in fever, joint aches, and general malaise. The African field rat (Arvicathus abysinicus nubilans) is a potential reservoir host. NSD is a reportable disease in the USA and is one of the OIE listed diseases.

Paratuberculosis is a chronic, contagious granulomatous enteritis characterized in cattle by persistent diarrhea, progressive weight loss, debilitation, and eventually death. It is considered a listed disease by the OIE, meaning it is a priority disease for international trade. The etiologic agent, Mycobacterium paratuberculosis, also known as Mycobacterium avium subsp paratuberculosis, is believed capable of infecting and causing disease in all other ruminants (eg, sheep, goats, llamas, deer) and in captive and free-ranging wildlife. The infection has also been recognized in omnivores and carnivores such as wild rabbits, foxes, weasels, pigs, and nonhuman primates. Distribution is worldwide. National control programs include those established in Australia, Norway, Iceland, Japan, The Netherlands, Denmark, Ontario, Canada, and the USA. The highest published prevalence is in dairy cattle, with 20%–80% of herds infected in many of the major dairy-producing countries. Limited information is available about the prevalence in other species. The disease is of economic importance for the goat industry in Spain and the sheep industry in Australia.

Pasteurella and Mannheimia organisms are β-hemolytic, gram-negative, aerobic, nonmotile, nonsporeforming coccobacilli in the family Pasteurellaceae. This family tends to inhabit the mucosal surfaces of the GI, respiratory, and genital tract of mammals. Many are known as opportunistic secondary invaders. Some species show preferences for specific surfaces and hosts. Updating of phylogenetic data has resulted in renaming based on gene sequence analysis. As a result, P haemolytica biotypes A and T were reclassified as M haemolytica (biotype A) and P trehalosi (biotype T). More recently, P trehalosi has been reclassified as Bibersteinia trehalosi. Each isolate of M haemolytica and B trehalosi is designated with a biotype and serotype. M haemolytica A2 is the most common strain isolated from sheep and goat respiratory pasteurellosis, although A6, A13, and Ant have been reported in sheep and Ant in goats. M haemolytica A2 is routinely reported from cases of mastitis in sheep. B trehalosi T3, T4, T10, and T15 have been most often associated with the systemic or septicemic form of pasteurellosis affecting lambs. These serotypes have been regrouped to B trehalosi biotype 2, and a new biotype 4 has been added. B trehalosi is often isolated from the lungs of sheep, goats, and cattle, but pathogenicity is variable and may be incidental. P multocida has also been reported as a cause of pneumonic pasteurellosis in sheep and goats and has been isolated in herd outbreaks of septic arthritis. M haemolytica is the most commonly isolated bacteria in clinical cases, followed closely by B trehalosi, with P multocida seen less frequently.

Peste des petits ruminants (PPR) is an acute or subacute viral disease of goats and sheep characterized by fever, necrotic stomatitis, gastroenteritis, pneumonia, and sometimes death. It was first reported in Cote d’Ivoire (the Ivory Coast) in 1942 and subsequently in other parts of West Africa. Goats and sheep appear to be equally susceptible to the virus, but goats exhibit more severe clinical disease. The virus also affects several wild small ruminant species. Cattle, buffalo, and pigs are only subclinically infected. People are not at risk.

Rift Valley fever (RVF) is a peracute or acute, mosquito-borne, zoonotic disease of domestic and wild ruminants in Africa, Madagascar, and the Arabian Peninsula. Large outbreaks of clinical disease are usually associated with heavy rainfall and localized flooding. During epidemics, the occurrence of abortions in livestock and deaths among young animals, particularly lambs, together with an influenza-like disease in people, is characteristic. However, infections are frequently subclinical or mild.

Rinderpest was the first animal disease to be globally eradicated. Because it was such a scourge and re-emergence remains a possibility, it is vital to maintain current information. Rinderpest was a viral disease of cattle and other ruminants (domestic and wild) characterized by fever, erosive stomatitis, diarrhea, and high morbidity and mortality. In the post-eradication era, testing for rinderpest, preferably using molecular methods, should be considered when an etiologic agent cannot be determined for an infectious disease with characteristic signs of rinderpest.

Tickborne fever is a rickettsial disease of domestic and free-living ruminants in the temperate regions of Europe. Disease is transmitted by the hard tick Ixodes ricinus. The main clinical signs are sudden fever in sheep and depression, weight loss and decreased milk yield in cattle. Diagnosis is by PCR. Oxytetracyclines are the most effective treatment. There is no vaccine.

Tick pyemia is mainly a staphylococcal superinfection of lambs already infected with Anaplasma phagocytophilum,the causative agent of tickborne fever. This results in the formation of crippling abscesses in joints and other parts of the body. Diagnosis is based on clinical signs, isolation of bacteria from lesions, and PCR. Penicillin or tetracycline can be used for treatment.

Wesselsbron disease is an acute, arthropod-borne flavivirus infection of mainly sheep, cattle, and goats in sub-Saharan Africa. Infection is common, but clinical disease is infrequent although likely under-reported. Newborn lambs and goat kids are most susceptible, and mortality may occur. Infection in adult sheep, cattle, and goats is usually subclinical, but disease may be severe in sheep with preexisting liver pathology. Occasional abortion in ewes, together with congenital malformation of the CNS with arthrogryposis of the ovine (and also the bovine) fetus and hydrops amnii in ewes, is seen. Incidental spillover occurs to people, causing a nonfatal, influenza-like disease.

Canine distemper is a highly contagious, systemic, viral disease of dogs seen worldwide.

Canine herpesvirus is best known as a severe viral infection of puppies worldwide, which often has a 100% mortality rate in affected litters. Increasingly sensitive molecular diagnostics have enabled its recognition in adult dogs with upper respiratory infection, ocular disease, vesicular vaginitis or posthitis, and in dogs with no clinical signs. As is typical of herpesviruses, recovery from clinical disease is associated with lifelong latent infection. Only canids (dogs, wolves, coyotes) are known to be susceptible. The seroprevalence in dog populations worldwide ranges from 20% to 98% depending on the region. Because latently infected animals may transiently convert to seronegative status, any seroprevalence study likely underestimates the true rate of exposure and carriage.

Feline infectious peritonitis (FIP) is an immune-mediated disease triggered by infection with a feline coronavirus (FCoV). FCoV belongs to the family Coronaviridae, a group of enveloped, positive-stranded RNA viruses frequently found in cats. Coronavirus-specific antibodies are present in as many as 90% of cats in catteries and in as many as 50% of those in single-cat households. However, <5% of FCoV-infected cats develop FIP in multicat households.

Feline leukemia virus (FeLV) remains one of the most important infectious diseases of cats globally. It manifests primarily through profound anemia, malignancies, and immunosuppression and infects domestic cats and other species of Felidae. In the laboratory, cells from a much wider range of species can be infected by some strains of the virus.

Feline panleukopenia is a parvoviral infectious disease of kittens typically characterized by depression, anorexia, high fever, vomiting, diarrhea, and consequent severe dehydration. Adult cats are much less often affected. Diagnosis is usually based on clinical signs, severe neutropenia and lymphopenia, and fecal viral antigen or PCR testing. Treatment includes intensive fluid therapy, glucose and potassium supplementation, antimicrobial, anthelmintic, and antiemetic therapy, and sometimes immunotherapy.

Infectious canine hepatitis (ICH) is a worldwide, contagious disease of dogs with signs that vary from a slight fever and congestion of the mucous membranes to severe depression, marked leukopenia, and coagulation disorders. It also is seen in foxes, wolves, coyotes, bears, lynx, and some pinnipeds; other carnivores may become infected without developing clinical illness. In recent years, the disease has become uncommon in areas where routine immunization is done, but periodic outbreaks, which may reflect maintenance of the disease in wild and feral hosts, reinforce the need for continued vaccination.

The leishmaniases are spectral diseases caused by protozoan parasites of the genus Leishmania. Key signs range from localized cutaneous lesions to lymphadenopathy and renal failure for visceral disease. Diagnosis is often made via serology, with quantitative serologic tests such as immunofluorescence assays or ELISA as confirmation. Treatment options are limited by World Health Organization guidelines in human disease endemic areas and by drugs that are FDA-approved within the USA, but include combination use of allopurinol with miltefosine, or liposomal amphotericin B within the USA, and glucantime internationally.

Ehrlichiosis is a tick-transmitted disease that infects blood cells and can cause a variety of signs from none to fever and generalized achiness to possible fatality. Several species of bacteria cause ehrlichiosis, and some of the species infect humans as well as animals such as dogs. Diagnosis is based on signs, serology, and PCR. Doxycycline is the treatment of choice.