Many infectious diseases affect multiple body systems and are discussed in individual chapters of this section. Several metabolic disorders that affect the body as a whole are also included.
Generalized Conditions Sections (A-Z)
Members of the genus Actinomyces are gram positive, anaerobic, non-acid-fast rods, many of which are filamentous or branching. Branches are <1 μm in diameter, as opposed to fungal filaments, which are >1 μm in diameter. Although they are normal flora of the oral and nasopharyngeal membranes, several species are associated with diseases in animals.
African Horse Sickness
African Swine Fever
African swine fever (ASF) is a highly contagious hemorrhagic disease of pigs that produces a wide range of clinical signs and lesions that closely resemble those of classical swine fever (see Classical Swine Fever). It is an economically important disease that is enzootic in many African countries and the Mediterranean island, Sardinia. In June 2007, ASF was confirmed for the first time in Georgia in the Caucasus region. Since its introduction into Georgia, African swine fever virus (ASFV) has spread rapidly into vast areas of western and southern Russia, where it is currently (2013) circulating out of control in domestic and wild pig populations. The virus has spread to the edges of Europe, with outbreaks reported in both the Ukraine and Belarus in 2013, putting at risk the very large pig populations present in Eastern Europe.
The amyloidoses are diseases that result from errors in protein folding. When new proteins are made, their peptide chains normally fold into the correct shape. Sometimes, however, the peptide chains fold incorrectly and form highly stable β-sheets that are insoluble and resistant to proteolytic digestion. When this insoluble protein is deposited in tissues, it is called amyloid. Amyloid proteins may be deposited in a localized fashion or widely distributed throughout the body. They cause damage by displacing normal cells. If critical organs such as the kidneys, liver, or heart are extensively disrupted, the disease may be fatal. Amyloidosis can affect all domestic mammals, and minor, asymptomatic deposition of amyloid proteins is common in aged animals.
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.
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
Bovine ephemeral fever is an insect-transmitted, noncontagious, viral disease of cattle and water buffalo that is seen in Africa, the Middle East, Australia, and Asia. Inapparent infections can develop in Cape buffalo, hartebeest, waterbuck, wildebeest, deer, and possibly goats. Low levels of antibody have been recorded in several other antelope species and giraffe, but the specificity has not been confirmed.
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
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.
Canine distemper is a highly contagious, systemic, viral disease of dogs seen worldwide. Clinically, it is characterized by a diphasic fever, leukopenia, GI and respiratory catarrh, and frequently pneumonic and neurologic complications. Its epidemiology is complicated by the large number of species susceptible to infection. The disease is seen in Canidae (dog, fox, wolf, raccoon dog), Mustelidae (ferret, mink, skunk, wolverine, marten, badger, otter), most Procyonidae (raccoon, coatimundi), some Viveridae (binturong, palm civet), Ailuridae (red panda), Ursidae (bear), Elephantidae (Asian elephant), primates (Japanese monkey), and large Felidae. Domestic dogs (including feral populations) are considered to be the reservoir species in most, if not all, locations. Antigenic drift and strain diversity is increasingly documented in association with outbreaks in wild species, domestic dogs, and exotic animals held in zoos and parks.
Canine Herpesviral Infection
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.
Caprine Arthritis and Encephalitis
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.
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.
Classical Swine Fever
Classical swine fever is a contagious, often fatal, disease of pigs clinically characterized by high body temperature, lethargy, yellowish diarrhea, vomiting, and a purple skin discoloration of the ears, lower abdomen, and legs. It was first described in the early 19th century in the USA. Later, a condition in Europe termed “swine fever” was recognized to be the same disease. Both names continue to be used, although in most of the world the disease is now called classical swine fever (CSF) to distinguish it from African swine fever (see African Swine Fever), which is a clinically indistinguishable disease but caused by an unrelated DNA virus. Because of the severe economic impact of CSF, outbreaks are notifiable to the OIE. CSF has the potential to cause devastating epidemics, particularly in countries free of the disease. In these countries, vaccination is allowed only under emergency circumstances. In case of a new outbreak, strict measures are enforced to control spread, eg, culling of infected and disease suspect herds and strict movement restrictions. This can have severe consequences for the swine industry, especially in densely populated livestock areas. Awareness and vigilance are essential, so that outbreaks are detected early and control measures instituted rapidly to prevent further spread of CSF. The “high risk period,” ie, the time between introduction of the virus and detection of the outbreak, must be kept as short as possible.
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.
Congenital and Inherited Anomalies
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.
Crimean-Congo Hemorrhagic Fever
Encephalomyocarditis Virus Infection
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.
Equine Granulocytic Ehrlichiosis
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
Equine infectious anemia (EIA) is a noncontagious, infectious disease of horses and other Equidae. It is caused by an RNA virus classified in the Lentivirus genus, family Retroviridae. EIA can present as an acute, subacute, or chronic infection. On occasion, the virus can be a cause of significant morbidity and mortality. The most frequently encountered form of the disease is the inapparent, chronically infected carrier.
Equine Viral Arteritis
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.
Erysipelothrix rhusiopathiae Infection
Erysipelothrix rhusiopathiae is a significant bacterial pathogen of swine, turkeys, and sheep. It is distributed worldwide and has also been isolated from cattle, horses, dogs, cats, mice, rats, fresh and saltwater fish, domestic poultry, and a variety of wild birds and mammals. Erysipeloid, a condition characterized by localized skin infections and cellulitis, may develop in people who work with infected animals, infected carcasses, or infected animal byproducts.
Feline Infectious Peritonitis
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 and Related Diseases
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 highly contagious, often fatal, viral disease of cats that is seen worldwide. Kittens are affected most severely. The causative parvovirus is very resistant; it can persist for 1 yr at room temperature in the environment, if protected in organic material. Feline panleukopenia is now diagnosed infrequently by veterinarians, presumably as a consequence of widespread vaccine use. However, infection rates remain high in some unvaccinated cat populations, and the disease occasionally is seen in vaccinated, pedigreed kittens that have been exposed to a high virus challenge.
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.)
Glanders is a contagious, acute or chronic, usually fatal disease of Equidae caused by Burkholderia mallei and characterized by serial development of ulcerating nodules that are most commonly found in the upper respiratory tract, lungs, and skin. Felidae and other species are susceptible, and infections are usually fatal. The organism is infectious for people, with a 95% fatality rate in untreated septicemia cases, and is considered a potential bioterrorism agent. Glanders is one of the oldest diseases known and once was prevalent worldwide. It has now been eradicated or effectively controlled in many countries, including the USA. In recent years, the disease has been reported in the Middle East, Pakistan, India, Mongolia, China, Brazil, and Africa.
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).
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.
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.
Hendra Virus Infection
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.
Histophilosis, or Histophilus somni–associated disease, is a common disease in North American cattle. It also has been reported to occur sporadically in beef and dairy cattle worldwide. H somni predominantly causes an acute, often fatal, septicemic disease that can involve the respiratory, cardiovascular, musculoskeletal, or nervous systems, either singly or together in confined cattle. The reproductive system is often affected without clinical signs or other systemic involvement; however, herd infertility has been reported to occur more frequently.
Infectious Canine Hepatitis
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.
Leishmaniosis is a disease caused by protozoan parasites of the genus Leishmania and transmitted through the bites of female phlebotomine sand flies. More than 23 species of Leishmania have been described, most of which are zoonotic. The most important Leishmania parasite to affect domestic animals is L infantum, also known as L chagasi in Latin America. Dogs are the main reservoir host for human visceral leishmaniosis caused by L infantum, and the disease is potentially fatal in dogs and people. Because the internal organs and skin of the dog are affected, the canine disease is termed viscerocutaneous or canine leishmaniosis. Cats, horses, and other mammals can be infected by L infantum or other Leishmania species. The disease in cats is rarer than in dogs and may manifest in cutaneous or visceral organs. L braziliensis, the cause of tegumentary canine leishmaniosis, is widespread in regions of South America and may geographically overlap with L chagasi.
Lightning Stroke and Electrocution
Injury or death of an animal due to high-voltage electrical currents may be the result of lightning, fallen transmission wires, faulty electrical circuits, or chewing on an electrical cord. Electrocution due to lightning stroke is seasonal and tends to be geographically restricted. Investigation of possible electrocution should always proceed with caution, because the electrification resulting from broken transmission wires, for example, may still be present. Once the site is clearly safe, the investigation should include the location of the dead animals, examination of all affected animals, and necropsy of those that died.
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.
Malignant Catarrhal Fever
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
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.
Neospora caninum is a microscopic protozoan parasite with worldwide distribution. Many domestic (eg, dogs, cattle, sheep, goats, water buffalo, horses, chickens) and wild and captive animals (eg, deer, rhinoceros, rodents, rabbits, coyotes, wolves, foxes) can be infected. Neosporosis is one of the most common causes of bovine abortion, especially in intensively farmed cows. Neosporosis abortion also occurs in sheep, goats, water buffalo, and camelids, although they may be less susceptible than cattle.
Nipah Virus Infection
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.
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.
Pasteurellosis of Sheep and Goats
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.
Peritonitis is an inflammation of the serous membranes of the peritoneal cavity. It may be a primary disease or secondary to other pathologic conditions. Different infectious and noninfectious agents may cause peritonitis, which may result in a variety of clinical manifestations, disease progression, and outcome. Peritonitis may be acute or chronic, septic or nonseptic, local or diffuse, or adhesive or exudative. The term “tertiary peritonitis,” used in human medicine for particular cases of chronic peritonitis with a small number of bacteria or fungi, is not used in veterinary medicine.
Peste des Petits Ruminants
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.
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.
Porcine Circovirus Diseases
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
Porcine hemagglutinating encephalomyelitis, a viral disease of young pigs, is characterized by vomiting, constipation, and anorexia and results either in rapid death or chronic emaciation (vomiting and wasting). Also, motor disorders due to acute encephalomyelitis (hemagglutinating encephalomyelitis) are often seen during field outbreaks.
Porcine Reproductive and Respiratory Syndrome
In the past, a number of obligate intracellular organisms that infect eukaryotic cells were classified in the genus Ehrlichia on morphologic and ecologic grounds. With newer genetic analyses, these agents have been reclassified into the genera of Ehrlichia, Anaplasma, and Neorickettsia, all of which are in the family Anaplasmataceae. However, usage of the term “ehrlichiosis” to broadly describe these infections may still persist.
Rift Valley Fever
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.
Historically, rinderpest virus was a scourge that wrought economic havoc throughout Africa, Asia, and Europe. The need to combat rinderpest provided the impetus for the establishment of the first modern veterinary school in Lyon (France) in 1762. After several decades of success in eradicating rinderpest from Europe, the disease recurred unexpectedly in Belgium in 1920, and renewed efforts to eradicate it resulted in the creation of the World Organization for Animal Health (OIE) in 1924. Shortly after the creation of the Food and Agriculture Organization (FAO) of the United Nations in 1946, the OIE and FAO signed a cooperation agreement in 1952. Since then, the two organizations (FAO and OIE) have been major participants in several global campaigns to combat rinderpest, which culminated in global eradication of the disease in 2011. In fact, the last reported rinderpest outbreak occurred in Kenya in 2001, but a 10-yr active surveillance period was necessary before global eradication could be declared. Rinderpest is only the second viral disease, after smallpox, to have been successfully eradicated worldwide.
Streptococcal Infections in Pigs
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 α-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. Streptococcus dysgalactiae equisimilis is considered the most important β-hemolytic Streptococcus involved in lesions in pigs, and it has been judged to be of etiologic significance in autopsy reports. S porcinus, another β-hemolytic Streptococcus, has been associated particularly in the USA with a contagious clinical entity in growing pigs known as streptococcal lymphadenitis, jowl abscesses, or cervical abscesses. Enterococci reside in the intestinal tract and may cause disease in multiple species. In pigs, the E faecium species group, mainly E durans and E hirae, are especially associated with enteritis and diarrhea.
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.
Swine Vesicular Disease
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.
Tick pyemia affects lambs 2–12 wk old and is characterized by debility, crippling lameness, and paralysis. Pyemic abscesses are common in joints but may be found in virtually any organ. The disease causes significant economic loss through debilitation and death. The disease is enzootic in many regions of the UK and Ireland where the tick Ixodes ricinus is common, and it is likely to be present in other parts of Europe where the same tick is found.
Tickborne fever is a febrile disease of domestic and free-living ruminants in the temperate regions of Europe. It is prevalent in sheep and cattle in the UK, Ireland, Norway, Finland, The Netherlands, Austria, and Spain. Disease is transmitted by the hard tick Ixodes ricinus. A similar disease transmitted by other ticks has been described in India and South Africa. The main hosts are sheep and cattle, but goats and deer are also susceptible.
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.
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.
Tuberculosis and other Mycobacterial Infections
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.
Vesicular Exanthema of Swine
Vesicular stomatitis is a viral disease caused by two distinct serotypes of vesicular stomatitis virus—New Jersey and Indiana. Vesiculation, ulceration, and erosion of the oral and nasal mucosa and epithelial surface of the tongue, coronary bands, and teats are typically seen in clinical cases, along with crusting lesions of the muzzle, ventral abdomen, and sheath. Clinical disease has been seen in cattle, horses, and pigs and very rarely in sheep, goats, and llamas. Serologic evidence of exposure has been found in many species, including cervids, nonhuman primates, rodents, birds, dogs, antelope, and bats.
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.