Animal Diseases –
Bovine / Cattle

Adenovirus 3

Overview 
Adenoviruses are divided into 10 serotypes, such as Bovine adenovirus type 3 (BAV-3), which belong to the Mastadenovirus genus of the family Adenoviridae. Bovine adenoviral infections primarily target the respiratory and digestive tracts of cattle, which usually results in cell lysis and virus shedding.

Fecal and respiratory shedding will usually last for 10 days, while excretion of the virus in urine can transpire over 10 weeks.

BAV is particularly widespread in Africa and Central America, but instances of the disease have been reported worldwide.

Signs
BAV-infected animals can display a number of general clinical signs including fever, lethargy, reduced appetite, abdominal distension, diarrhea, tarry stools, and weight loss. Respiratory signs may initially encompass nasal discharge, coughing (with or without blood), shortness of breath (dyspnea), or rapid breathing (tachypnea), and may progress to bronchopneumonia in the presence of a secondary bacterial infection.

Human health risk
It does not appear that BAV presents a zoonotic risk.

BesnoitiosisTop

Overview
Bovine besnoitiosis is a vector-transmitted disease caused by the protozoan parasite Besnoitia besnoiti. The disease spreads from one animal to another by insect vectors—specifically, biting flies such as Tabanus and Stomoxys. All cattle breeds, independent of sex or age, can be infected.

Signs
Cattle can show severe clinical signs of the disease, whereas infected sheep are often asymptomatic. Affected cattle can experience different stages of the disease with a range of symptoms including skin thickening and swelling, hair loss, and skin necrosis; bulls can become infertile. In severe cases, the disease can lead to the animal’s death.

Cysts (200–600 µm in diameter) are found in the subcutaneous tissue, fascia, and mucosa of infected animals and can survive for over 10 years in the host animal.

Human health risk
It does not appear that besnoitiosis presents a zoonotic risk.

Economic impact
Besnoitia besnoiti infections cause substantial economic losses, especially among cattle breeds, due to high morbidity and mortality rates.

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Bluetongue Virus (BTV)Top

Epidemiology
Bluetongue, or catarrhal fever, is caused by a double-stranded RNA virus of the genus Orbivirus and family Reoviridae. It is a noncontagious disease transmitted by insects to wild and domesticated ruminants, especially sheep.

Signs
Seven or eight days after infection, sheep develop acute signs—high temperature, lethargy, and self-isolation from the herd. Shortly after the rise in temperature, the buccal mucosa becomes red and swollen, and large volumes of foamy saliva are produced. The tongue swells up and in some cases turns blue (hence the name of the disease). The crown of the unguis becomes red and painful. Affected animals can limp and ewes may abort. In most cases, growth is retarded and there is coat loss. Severely affected sheep may die eight to 10 days into the infection.

In cattle and goats, the infection is usually asymptomatic. When there are signs in cattle, the most common are hyperthermia, abortion towards the end of gestation (in the eighth month), edema (of the udders, teats, vulva, and hocks), and erythema (mucosa, teats, and udders).

The spread of BTV
Bluetongue was first reported in 1876 in South Africa. While it used to be believed that is was confined to Africa, over the last 10 years the disease has spread to Asia, the southern United States, Australia, and southern Europe. A total of 24 different serotypes of the bluetongue virus are known, of which eight have been reported in Europe (serotypes 1, 2, 4, 6, 8, 9, 11, and 16).

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Bovine respiratory syncytial virus (BRSV/RSV)Top

Epidemiology
Ovine respiratory syncytial virus is a pneumovirus belonging to the Paramyxoviridae family. It is closely related to human RSV, which often infects the airways of children. Both are single-stranded RNA enveloped viruses. In bovines, RSV causes respiratory infections in young animals and dairy cows. The virus is mainly present in the lower airways (the lobes of the lungs), where it damages ciliated epithelial cells that normally protect the lung against microbial invasion. RSV infection often leads to secondary bacterial infection, notably with Pasteurella haemolytica and Corynebacterium pyogenes.

Signs
The signs of the disease are hyperthermia, coughing, nasal and ocular discharge, anorexia, and dyspnea (if the disease is progressing towards fatal pneumonia). In dairy cows, milk production falls off.

Transmission
RSV is transmitted by direct contact through nasal secretions, and its spread is favored by proximity, for example in winter stabling, and as a result of licking in the milking room.

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Bovine viral diarrhea (BVD)Top

Epidemiology
The BVD virus is a small, single-stranded RNA virus belonging to the genus Pestivirus. Two other animal viruses belong to this genus, namely the viruses that cause border disease (BD) in sheep and classical swine fever (CSF) in pigs.The virus that causes bovine viral diarrhea (BVD) was first identified in 1946. The disease is found throughout the world and its prevalence among animals exposed to the virus ranges from 30–80% in different countries and regions.

BVD impacts fertility in the herd
The infection compromises the herd's fertility and induces the return of heat following death of the embryo when the cow is infected between the first and second months of gestation. Abortion and birth defects are possible throughout gestation.

BVD-PI animals serve as a reservoir of infection
A common consequence of prenatal infection by members of this viral genus is the birth of infected offspring that are permanently immunotolerant (BVD-persistent infection (BVD-PI)), which disseminate the virus throughout the herd. BVD-PI animals (i.e., those infected between the second and the fourth months of gestation) carry the virus throughout their lifetime and constantly secrete large numbers of viral particles. This group therefore constitutes a major source of infection for the rest of the herd. In addition, BVD-PI animals sooner or later develop the fatal form of BVD called mucosal disease (MD). The number of BVD-PI animals in an infected herd is of the order of 1% (although the percentage can be as high as 27%) and detecting them is primordial in the control of Pestivirus disease.

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Infectious bovine rhinotracheitis (IBR)/Bovine herpes virus (BHV)Top

Epidemiology
IBR is caused by a herpesvirus (BHV-1) that infects the airways, causing respiratory tract problems (tracheitis and rhinitis), fever, abortion, and infertility. It can lead to death when the disease rapidly spreads through a herd. IBR is transmitted through direct contact via respiratory, ocular, and genital secretions.

The IBR virus has an immunosuppressive effect, and infection can predispose the host to secondary bacterial infection. Infection can also be latent: although the primary infection may appear to be cleared, the virus is still present in the lymph nodes and can be reactivated to spread throughout the body.

Incidence and prevalence
Although the incidence and prevalence of the disease varies on different continents, it is present throughout the world and nearly 50% of all adult bovine herds have already been exposed.

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BrucellosisTop

Overview
Brucellosis is an infectious disease caused by Brucella bacteria. Brucella species of major concern are B. abortus, primarily affecting cattle; B. melitensis, primarily affecting sheep and goats; and B. suis, primarily affecting pigs. All these Brucella species are non–host-specific and may be transmitted to other animal species or humans under appropriate conditions.

Brucellosis is commonly transmitted to susceptible animals by direct contact with infected animals or in an environment that has been contaminated with discharge from infected animals. Brucellosis is thus a herd or flock problem.

Brucellosis is a notifiable disease, and any occurrence of it has to be reported to the local health authority. Depending on the species and the infection rate, different eradication programs are effective. Where incidence rates are high, vaccination programs are necessary to lower the infection rate. Once this has been achieved, surveillance programs linked to slaughter of infected animals are introduced. These programs lead to "Brucellosis-Free" and "Officially Brucellosis-Free" status for specified regions or whole countries. In Europe, surveillance is regulated in the EU Directive 2003/99/EC on monitoring of zoonoses.

Signs
Symptoms of a Brucella infection are often decreased milk production, weight loss, abortion, infertility, and lameness. Brucella uptake occurs orally and via skin wounds or mucus membranes. Brucella bacteria are mainly excreted with aborted fetal tissue and placenta, and with semen and milk.

Occasionally, animals may recover after a period of time. More commonly, however, the symptoms disappear but the disease prevails. Such asymptomatic animals are dangerous sources of infection.

Human health risk
Raw milk and unpasteurized cheese represent the most frequent sources of human infection. Farmers and veterinary staff run an increased risk of infection due to direct exposure to aborted infected materials. In humans, the disease is not usually fatal, but if untreated, it can last for many years.

The incubation period is usually one to three weeks, but can sometimes be as long as several months. Patients show nonspecific symptoms such as undulating fever, chills, malaise, and headache.

Economic impact
Brucellosis is a major public and animal health problem in many regions of the world. Although it rarely kills infected animals, considering the economic damage the disease can cause, brucellosis is one of the most serious livestock diseases worldwide.

This zoonosis has been or is close to being eradicated from a number of countries, but it is still prevalent in the Mediterranean region, Africa, Asia, and South America.

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ChlamydiosisTop

In ruminants, chlamydiosis is a contagious disease caused by a bacterium that also infects birds and humans. It can cause abortion, premature delivery, pneumonia, conjunctivitis, and arthritis in ruminants. The infection can be transmitted to the newborn, young, or adult ruminant by the large numbers of bacteria excreted in fetal envelopes and fluids, feces, urine, and milk, although the main route of infection is via the inhalation of contaminated aerosols. Chlamydia taxonomy was revised by Everett in 1999. In the new classification, the species are divided between two main genera:

  • The genus Chlamydia, which includes C. trachomatis (humans), C. suis (pigs), and C. muridarum (mice and hamsters)
  • The genus Chlamydophila, which consists of six species, namely Cp. abortus (mammals), Cp. psittaci (birds), Cp. felis (cats), Cp. caviae (guinea pigs), Cp. pecorum (mammals), and Cp. pneumoniae (humans)

In ruminants, two species have been identified: Cp. abortus (which causes abortion) and Cp. pecorum (which causes asymptomatic gut infection, pneumonia, conjunctivitis, arthritis, abortion, and infertility). In pregnant women, C. abortus can also induce abortion with serious complications.

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Clostridium perfringensTop

Overview
A spore-forming anaerobic bacterium, Clostridium perfringens is commonly found in the soil and digestive tract of various domestic animals, and is categorized under six unique types (A, B, C, D, E, and F), with types B, C, and D being the most common form of the disease.

It is not uncommon for small amounts of C. perfringens to inhabit, and pass through, the digestive tract of an animal without causing disease. But in instances where an animal is exposed to a sudden increase in carbohydrates (milk, supplementary concentrates, etc.) C. perfringens bacteria can rapidly increase in numbers, producing large amounts of toxin that often cause rapid death.

Type-B, also known as lamb dysentery, presents a high mortality rate in young lambs and is also linked to disease in young calves.

Type-C typically affects cattle, small ruminants, and pigs, where it can contribute to hemorrhagic and necrotic enteritis.

Type-D, also known as pulpy kidney disease or overeating disease, is associated with small ruminants and cattle. C. perfringens Type-A and -C can also cause enterocolitis (swelling of the small and large intestines) in foals, with stock horse breeds such as quarter horses more susceptible.

Signs
Because of the aggressive nature of the disease, and rapid onset of death, it can be challenging to observe clinical signs in an infected animal. Upon closer examination of an animal prior to death, C. perfringens infection may present a variety of signs such as excitement, circling, head pressing, convulsions, listlessness, diarrhea, colic, or a disinterest in nursing.

Human health risk
It does not appear that C. perfringens presents a zoonotic risk.

Bovine coronavirus (BCV)Top

Overview
BCV is an enveloped, single-stranded, positive-sense RNA virus belonging to the Coronaviridae family that causes intestinal and respiratory infections in ruminants worldwide. Infection can cause winter dysentery in adult animals, as well as calf enteritis and enzootic pneumonia complex in calves. Bovine coronavirus is transmitted via the oral-fecal or respiratory routes, and infected animals will typically shed the virus in their feces, particularly during parturition.

BCV may also reproduce in the upper respiratory tract, causing reoccurring respiratory or gastrointestinal infection in an animal. Infected wild ruminants have the potential to transmit the disease to domestic ruminants.

Signs
BCV signs may include diarrhea, tarry stool, indigestion, reduced appetite, weight loss, anorexia, weight loss depression, and dehydration. Additionally, BCV may present various respiratory signs such as nasal discharge, coughing, shortness of breath (dyspnea), and rapid breathing (tachypnea).

Human health risk
It does not appear that BCV presents a zoonotic risk.

Economic impact
Bovine respiratory complex in feedlot cattle, as well as acute intestinal disease in dairy cows, can contribute to financial losses and significant economic consequences.

Coxiella burnetii/Q feverTop

Epidemiology
Q (Query) fever is an ubiquitous zoonosis that is found throughout the world (apart from New Zealand). It is caused by Coxiella burnetii, an obligate intracellular bacterium that can infect many different animal species, including ruminants, dogs, cats, birds, and arthropods as well as humans. In ruminants (which are believed to be the main reservoir for human infection), the disease is mainly associated with reproductive dysfunction. It usually remains asymptomatic and is not usually screened for unless an animal has aborted several times or shows reproductive problems. Coxiella burnetii colonizes the placenta and causes premature delivery, low birth weight, and abortion.

Impact of Q fever on humans
The main route of infection in humans is through the inhalation of contaminated aerosols, but pregnant women should not drink unpasteurized milk or consume dairy products made with untreated milk. Q fever often goes unnoticed because it can be mistaken for an influenza-like syndrome. The consequences can be dramatic in pregnant women (abortion or premature delivery) and in immunodeficient subjects or patients with valvular heart disease.

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CryptosporidiosisTop

Overview
Cryptosporidiosis is caused by microscopic intestinal parasites that are excreted through the feces of an infected animal. Found throughout the world, the parasites commonly interact with other enteropathogens to produce diarrhea and intestinal injury in neonatal farm animals such as piglets, kids, lambs, and foals.

Studies have shown that concurrent infections with other pathogens such as coronavirus and rotavirus can result in more severe diarrhea. While mortality rates in cryptosporidiosis are usually low, it can be fatal when complicated by other factors such as an animal experiencing energy deficit as a result of low colostrum or milk intake, concurrent infections, or chilling caused by adverse weather conditions.

Transmission of the disease may occur directly from animal to animal, or indirectly from environmental contamination, fecal contamination of the water or feed supply, or human transmission. Infection in calves can be detected as early as 5 days of age, with diarrhea occurring between 5 and 15 days of age.

In small ruminants, infection can be associated with severe outbreaks of diarrhea, resulting in high mortality rates in lambs 4–10 days of age, and goat kids 5–21 days of age.

Although cryptosporidiosis is not generally regarded as an important enteric pathogen in pigs, infections can be seen over a broader age range (1 week of age to market age), and can contribute to postweaning malabsorptive diarrhea in infected pigs.

Cryptosporidiosis is less prevalent in foals, but when infections do occur, it is typically at 5–8 weeks of age.

Signs
Signs of cryptosporidiosis can include diarrhea that persists for several days, significant weight loss, emaciation, apathy, anorexia, and dehydration.

Human health risk
Cryptosporidium can be a common nonviral cause of diarrhea in immunocompetent persons (e.g., children) and can have a severe health impact on immunocompromised persons. Infected animals can transmit the disease directly to humans, and there is also a risk of cryptosporidiosis being transmitted through surface and drinking water that has been contaminated with the feces of an infected animal.

E. coli F5 (K99)Top

Overview
Escherichia coli is a bacterial cause of diarrhea in calves, and there are at least two distinct types of diarrheal disease associated with different strains of the organism. One type has two virulence factors associated with the production of diarrhea, and fimbrial antigens such as K99 or F41 enable them to colonize villi of the small intestine.

These enteropathogens, also known as attaching and effacing E. coli, may produce verotoxins that contribute to more severe hemorrhagic diarrhea. The infection can reside in the colon, cecum, and distal small intestine, with severe infections causing edema, mucosal erosions, and ulceration.

Transmission routes include respiratory aerosol, fecal aerosol, and oral–fecal. Healthy carrier cattle may periodically excrete the organism in feces, and under the stress of parturition, excretion may increase. These conditions can lead to infection of the udder and perineum of the dam, along with contaminated calving environments. Alternately, the presence of several scouring calves can severely contaminate a calf-rearing area.

Signs
K99-bearing E. coli can cause the sudden onset of profuse diarrhea in calves that are typically <5 days old, resulting in calves becoming depressed and recumbent. Calves may experience significant weight loss (>12% of body weight), and potentially hypovolemic shock and death within 24 hours.

Human health risk
Cattle can be a reservoir for verotoxic E. coli serotypes associated with human hemolytic uremic syndrome and hemorrhagic colitis. Infection can occur through the consumption of contaminated food, but enteric livestock pathogens can also be transmitted to humans via direct contact that may occur during visits to petting zoos, farm tours, or livestock fairs.

Enzootic bovine leukosis (EBL)Top

Overview
EBL is a chronic disease of cattle caused by the retrovirus Bovine leukemia virus (BLV). The disease is transmitted either directly by transmission of lymphocytes via blood, semen, or milk, or indirectly via insects. The disease does not spread rapidly, but in infected herds the number of seropositive animals may be 80%.

The disease occurs worldwide, though its prevalence varies from country to country.

Signs
Clinical signs of EBL appear in a small proportion of infected animals and are usually apparent in cattle between 4 and 8 years of age, but only rarely in animals under 2 years old. Clinical signs are loss of body condition, persistent lymphocytosis, and swelling of the spleen and liver.

Diseases of the immune complex may occur later; only 1 to 10% of infected animals develop lymphatic sarcoma. Clinically affected animals will lose condition and eventually die.

As with other retrovirus infections, infected animals remain infected for life. BLV has serious implications for animal health and welfare. In many countries, EBL is a notifiable disease.

Human health risk
It does not appear that EBL presents a zoonotic risk.

Economic impact
This disease is economically significant to the producer because of premature culling or death as a result of lymphosarcoma, as well as the condemnation of carcasses at slaughter, which significantly impacts the dairy and cattle industries.

Losses from export restrictions are another economic concern of the disease.

Epizootic hemorrhagic disease (EHD)Top

Epidemiology
EHD is a vector-borne infectious disease caused by a virus belonging to the Orbivirus genus of the Reoviridae family (like the bluetongue virus). Between eight and 10 different serotypes have been identified.

Transmission
The virus is more-or-less exclusively transmitted by the bite of a small hematophagous dipteran of the genus Culicoides in the Ceratopogonidae family. The vector becomes infected when it feeds on an infected animal and then the virus replicates until it reaches the density necessary for transmission to another susceptible animal.

Signs
The EHD virus can infect bovines and cause signs similar to those of bluetongue (i.e., fever, erosive lesions and ulcers of the oropharyngeal mucosae, stiffness, collapse, and cutaneous edema). In gestating cows, infection can induce abortion or hydranencephaly if the infection appears between 70 and 120 days of gestation.

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Fasciola hepaticaTop

Overview
Fasciola hepatica is seen in a broad range of hosts worldwide, including cattle and sheep, where the infection will present itself in three forms: chronic, which contributes to a high mortality rate in sheep but few fatalities in cattle; acute, which is often fatal in sheep; and in combination with a secondary infection such as infectious necrotic hepatitis, which yields frequent fatalities in sheep.

The disease is transmitted through the ingestion of aquatic vegetation containing encysted cercariae that have emerged from infected lymnaeid snails. After ingestion, young flukes are released into the animal’s duodenum, travel to the liver, and eventually reside in the parenchyma for several weeks, where they grow and destroy tissue.

While most flukes are shed by cattle in <6 months, adult flukes can live within the bile duct of sheep for several years.

Signs
In cases of acute fasciolosis, signs can include distended abdomen, anemia, and sudden death, usually within 6 weeks of infection. Subacute signs of the disease are typically anemia and hemorrhage, and result in death 7–10 weeks after infection.

Chronic fasciolosis signs may involve anemia, edema, and reduced milk secretion.

Human health risk
Fasciolosis can be transmitted to humans through the ingestion of contaminated drinking water and freshwater plants in endemic areas, or the consumption of poorly cooked sheep liver. After infected material has been ingested, cercariae encyst in the duodenum, develop into larvae, and eventually penetrate through liver tissue into the biliary tract.

Economic impact
Liver flukes can cause significant economic consequences by greatly impairing feed efficiency, growth, and fertility in both cattle and sheep.

Foot and mouth disease (FMD)Top

Overview
FMD is a highly contagious viral disease that affects all cloven-hoofed animals, and is widespread throughout the world. FMD cannot be differentiated clinically from other vesicular diseases such as swine vesicular disease (SVD).

The virus is a member of the genus Apthovirus in the family Picornaviridae. There are seven serotypes of FMD virus: O, A, C, SAT 1, SAT 2, SAT 3, and Asia 1. Infection with any one serotype does not confer immunity against other serotypes.

Of the domesticated species, cattle, pigs, sheep, and goats are susceptible to FMD.

Signs
Clinical signs of FMD are the appearance of vesicles (small blisters) on the feet, in and around the oral cavity, and on the mammary glands of females. Vesicles can also occur inside the nostrils and at pressure points on the limbs, especially in pigs.

Transmission generally occurs through contact between infected and susceptible animals. The virus can be excreted into the air during the acute phase of infection.

Human health risk
It does not appear that FMD presents a zoonotic risk.

Economic impact
The presence of FMD is a very important economic threat to the livelihood of the livestock industry due to the culling of herds and the restriction on meat exports from affected areas.

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LeptospirosisTop

Overview
Leptospirosis occurs worldwide, and while the disease is typically reported in tropical climates, it can also be found in temperate climates during periods of rainfall. Leptospirosis most commonly affects pigs, cattle, and horses, and displays a variety of clinical effects ranging from mild infection to organ failure to death.

The disease is prevalent in wild mammals, but is often only noticed when the wildlife serve as an infection source for domestic animals and livestock. Leptospirosis can be transmitted transplacentally or venereally, but most often through direct contact with infected milk, urine, or placental fluids.

Signs
The signs of leptospirosis can vary greatly depending upon a herd’s immunity, age of an infected animal, and the infecting serovar. In respect to infecting serovars, there are >220 pathogenic serovars of Leptospira that can cause leptospirosis.

As an example, cattle are the maintenance host for Leptospira hardjo-bovis, which can affect an animal’s kidneys, resulting in long-term urinary shedding. L. hardjo-bovis is also associated with persistent reproductive tract infections that can cause infertility in cattle.

For other Leptospira serovars such as grippotyphosa, icterohaemorrhagiae, or pomona, cattle become incidental hosts for the disease and may display various clinical signs such as lethargy, jaundice, fever, anemia, and red urine. While adult cattle do not usually die from leptospirosis, the disease can be fatal to calves and may affect pregnant cows, causing abortion, stillbirth, and the birth of weak calves.

Human health risk
Leptospirosis is considered to be zoonotic, and can be transmitted to humans if a person comes in contact with water or soil that has been contaminated by urine or body fluids of an infected animal.

Economic impact
The infertility that can result from persistent reproductive tract infections is perhaps the most economically damaging aspect of leptospirosis.

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Bovine MycoplasmosisTop

Epidemiology
Mycoplasmas—most of which are host-specific—cause chronic diseases that progress slowly in humans and animals. The bacterium Mycoplasma agalactiae is a common pathogen of small ruminants and is of major importance in veterinary medicine. In ovines this disease is always due to M. agalactiae, but other Mycoplasma species, M. mycoides and M. capricolum, can cause a similar disease in goats.

Signs
Mycoplasma agalactiae is the causative agent of contagious agalaxia, the main form of mycoplasmosis in European ovines and caprines that has a serious impact on the dairy industry. Antibiotics often fail to eradicate these infections, and in food animals mycoplasmosis is responsible for substantial economic losses.

Transmission
Infection is often oral or mammary, with an incubation period ranging from two weeks to two months.

Closely Related to M. agalactiae
M. bovis, which is closely related to M. agalactiae, causes respiratory and mammary pathology in bovines and is also important in economic terms (causing calf pneumonia, mastitis, and arthritis). These two pathogens induce similar signs in their respective hosts, and they are difficult to differentiate using conventional diagnostic methods because they are so closely related.

NeosporosisTop

Epidemiology
Neospora caninum is a protozoan parasite first observed in dogs, in which it causes myositis and encephalitis. However, in the 1990s it was observed that Neospora was a major cause of abortion in cows, usually between the fourth and seventh months of gestation. Depending on the number of infected cows in the herd, the abortion rate ranges from 5–30%; the higher rates are characterized by serial abortions occurring in less than a month.

Transmission
It is not fully understood how the parasite is transmitted, but the main route seems to be from mother to offspring, with at least 80% of the calves born to seropositive cows infected. In addition, it has been suggested that dogs may be involved in the transmission of Neospora to bovines. This infection is known on all continents and is the leading cause of bovine abortion in some countries (ahead of BVD and IBR).

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Paratuberculosis (Johne’s disease)Top

Overview
Paratuberculosis, also known as Johne’s disease, is caused by the presence of Myobacterium avium spp. paratuberculosis (sometimes abbreviated MAP) in the small intestine of ruminants. It is a worldwide animal health problem, especially affecting beef and dairy herds.

Paratuberculosis is a chronic debilitating enteritis, and its presence in an animal herd can have serious effects on production.

Diagnosis of clinical infection is usually confirmed by the demonstration of the causal organism, M. avium ssp. paratuberculosis, in feces or in intestinal tissues postmortem. The identification of subclinical disease in animals, which can shed the organism over long periods and thus be the source of infection for other members of a herd, is more difficult. The prevalence of bovine paratuberculosis in Europe varies from country to country, ranging from 7% to 55%.

Signs
Chronic inflammation of the intestine, mesenteric lymph node lesions, diarrhea, weight loss, and edema usually appear in animals of over 2 years of age with an advanced stage of the disease.

Human health risk
The causative bacterium of paratuberculosis, M. avium ssp. paratuberculosis, is known to survive pasteurization of milk and other dairy products, and therefore could be a risk to human health. Increasing scientific evidence indicates that there is a link between paratuberculosis in dairy herds and Crohn's disease in humans. Crohn's disease is an incurable chronic inflammatory bowel disease.

Economic impact
Paratuberculosis in domestic livestock may entail significant economic losses due to several factors, such as reduced production, premature culling, and veterinary costs. In the United States, paratuberculosis is of growing concern to the cattle industry because the presence of the disease impacts international marketing of cattle and cattle products, which causes economic losses to producers. Consequently, the Voluntary Johne's Disease Herd Status Program for Cattle (VJDHSP) has been established. In April of 2002, USDA-APHIS-Veterinary Service incorporated parts of this program into its national program standards.

Within the European Union, there are no official programs in place; however, country-specific policies apply. Australia has a National Johne’s Disease Control Program (NJDCP) that aims to reduce the spread and the impact of Johne’s disease. It is a cooperative program involving Australian livestock industries, government, and the veterinary profession. Animal Health Australia manages the program on behalf of these key stakeholders.

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Rift valley fever (RVF)Top

Overview
RVF is categorized as caused by a bunyavirus, and is an acute zoonotic disease that affects ruminants throughout the Arabian Peninsula, Africa, and Madagascar. During periods of epidemic, high abortion and mortality rates can occur among young animals, and humans will often experience an influenza-like disease.

RVF may be transmitted by the movement of animals infected with the virus or by various species of wind-borne mosquitoes. Instances of RVF generally reach their peak during summer, and at the sign of first frost, insect vectors and the disease will typically disappear. In warmer regions, the disease and vectors may be present year-round.

Signs
Common signs of RVF may include lethargy, fever, unwillingness to feed, abdominal pains, jaundice, and diarrhea. In some cases, abortion may be the only sign of infection that an animal displays.

Human health risk
It is possible for humans to be infected with RVF via contact with infected animal tissue or aborted fetuses, mosquito bites, or blood aerosols during the slaughter of an infected animal.

RotavirusTop

Overview
Bovine rotavirus is categorized within the Reoviridae viral family, and along with coronavirus, contributes to >50% of the diarrhea problems in calves. While rotavirus is common in cattle herds, other animals such as pigs, chickens, sheep, horses, and rabbits are also susceptible to the disease.

The virus enters through the small intestine, attacking villi and making it difficult for material to be effectively absorbed into the animal’s body. This condition leads to water loss from the epithelial cells and body, causing dehydration and potentially death if there is significant dehydration and emaciation.

Transmission generally occurs when an unaffected animal has oral contact with infected feces and contaminated feed, or if they are exposed to living quarters with poor hygiene characteristics. Cows displaying signs and symptoms may shed the virus for as long as a week, while some cows can become reinfected and shed the virus throughout their life and remain asymptomatic.

Signs
The primary sign of rotavirus is a runny, often yellow diarrhea that contains mucous, blood, or both. Additionally, the animal may become lethargic and have a disinterest in drinking or feeding, which could result in mild to severe dehydration, depending on the animal and the circumstances.

Human health risk
Bovine and human rotavirus strains are specific to their hosts and are not considered a transmission risk from one species to another.

Economic impact
Significant economic loss may occur due to increased morbidity and mortality in neonatal ruminants, treatment costs, and reduced growth rates.

SalmonellosisTop

Overview
Salmonellosis is an infection caused by Salmonella bacteria. The presence of salmonellosis has been identified in countries throughout the world, but it appears to be most prevalent in areas of intensive animal husbandry, especially occurring in pigs, calves, and some types of poultry.

The disease can affect all domestic animals; however, young animals and pregnant or lactating animals are the most susceptible to the disease. The clinical signs that may be seen are abortion, arthritis, respiratory disease, and acute septicemia. Enteric disease, often presenting as a bloody, watery diarrhea with pyrexia, is the most common clinical manifestation.

Many animals, especially pigs, cattle and poultry, may also be infected but show no clinical illness. Such animals may be important in relation to the spread of infection between flocks and herds and also as a source of food contamination and human infections.

Signs
Typical clinical signs can include fever and severe watery diarrhea with subsequent rapid onset of dehydration. The diarrhea is usually putrid and may contain blood and mucus. Salmonellae produce toxins that can contribute to gut damage and have systemic effects. If sufficient damage occurs to the intestinal lining, the bacteria may enter the bloodstream, resulting in septicemia, and the bacteria can spread to the brain, lungs, joints, uterus (causing abortion in pregnant cows), and other organs.

Human health risk
Salmonellosis is one of the most important zoonotic diseases that can cause serious clinical symptoms in humans. Pigs, cattle, poultry, and eggs have been recognized as important sources of these Salmonella infections. The existence of this disease presents great risks for human health. Salmonella infections of animals intended for the food industry play an important role in public health, as these animals are considered to be the major source of human Salmonella infections.

Economic impact
Salmonellosis has a serious economic impact on the cattle industry worldwide. Livestock mortality, treatment costs, abortion, reduced production, discarded milk, and reduced consumer confidence all contribute to the cost of Salmonella to cattle industries.

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Schmallenberg VirusTop

Epidemiology
The Schmallenberg virus belongs to the Bunyaviridae family, genus Orthobunyaviridae and is closely related to Akabane, Aino, and Shamonda viruses. This virus was first identified in November 2011 in Germany. It was found in several samples coming from bovine and ovine hosts showing atypical symptoms, not characteristic of known diseases at the time.

Signs
This virus induces weak clinical symptoms affecting the global health of the animal, such as hyperthermia, loss of appetite, decreased milk production, and in some cases, diarrhea. Infection of female ruminants during gestation can also result in the birth of malformed animals (e.g., hydrocephalus).

Diagnostics
Virus detection is optimally performed using the brain of an aborted fetus, but the virus can also be detected in blood, serum, and the spleen (FLI—German National Reference Laboratory).

Transmissible spongiform encephalopathy (TSE)Top

Overview
TSEs are infectious diseases of the brain that affect animal species in various forms, such as bovine spongiform encephalopathy (BSE, affecting cattle), scrapie (affecting goats and sheep) and chronic wasting disease (CWD, affecting deer). The diseases are caused by altered prion proteins that are resistant to chemicals and heat, and are very difficult to decompose biologically, often surviving in soil for several years.

The diseases are reported worldwide, with BSE found most frequently in Europe and CWD being most prevalent in North America. TSEs cause a slow degeneration of the central nervous system that ultimately leads to the death of an animal, and there is often a significant lapse of time between an animal becoming infected with the disease and displaying the first symptoms. As an example, at the point of infection, cattle may not show clinical symptoms for up to 6 years, and sheep may not show signs for up to 4 years.

Transmission of BSE in cattle occurs through ingestion of feed containing contaminated bone and meat meal. Transmission does not appear to occur naturally between cattle, though some evidence suggests there may be a maternally associated risk for calves born to infected cows. While pathogenesis details are unknown, studies have shown that after the agent enters the animal through oral exposure, it replicates in the Peyer's patches of the ileum and migrates to the central nervous system via peripheral nerves.

Signs
Clinical signs of TSEs are often subtle and may include nervousness, aggression, low head carriage, ataxia, tremors and increased sensitivity to touch (hyperesthesia). Animals may also have a reluctance to be milked and experience weight loss and diminished milk production.

Human health risk
Humans can develop a form of TSE known as Creutzfeldt-Jakob disease (CJD) by consuming food products that have been contaminated with BSE. Initiatives are in place to remove high-risk bovine tissue from the human food chain, and for products containing bovine proteins (cosmetics, pharmaceuticals, etc.), measures have been instituted to help ensure that raw materials are sourced from BSE-free regions.

Economic impact
TSEs can contribute to significant economic losses, whether it be culling of animals linked to BSE or scrapie cases, the destruction of Specified Risk Material (SRM) derived from ruminants (cattle, sheep, and goats), or the impact that export restrictions in affected areas may have on the meat industry as a whole.

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TrichomoniasisTop

Overview
Trichomoniasis (Trich) is a venereal disease that occurs in cattle worlwide and is typically characterized by infertility and abortions in cows and heifers, which contributes to extended calving intervals.

The disease is caused by Tritrichomonas foetus (T foetus) a small, motile protozoan that lives in the reproductive tract of cows and the penis sheath of bulls. The disease organism is transferred to a cow's vagina from the bull during breeding and causes infection as it migrates to the uterus resulting in a white sticky discharge from the vulva of the infected cows.

When an infected bull is naturally bread with cows, 30%–90% become infected, which may suggest the existence of strain differences as well as a variation in breed susceptibility to the disease. Bulls of any age can remain infected for an indefinite period of time, but in younger males this scenario is less likely to occur. In contrast, cows are typically free of infection within 3 months of breeding, though they are still susceptible to reinfection. T foetus may also be transmitted when the semen from infected bulls is used during artificial insemination.

Signs
The primary sign is infertility caused by embryonic death, which contributes to repeat breeding and scenarios where cows are in heat when they should be pregnant. In addition to reduced calving rates and calf crops being extended over 3-6 months and increased number of cows may be associated with nonpregnant abnormal reproductive diagnosis such as endometritis and pyometra. Bulls will display no signs of the T foetus but can shed the organism for an indefinite period of time. Diagnosis of the disease in bulls requires the collection and testing of a preputial fluid sample taken from the sheath of the bull's penis.

Human health risk
It does not appear that Trichomoniasis presents a zoonotic risk.

Economic impact
The economic losses associated with affected herds are primarily the result of smaller, less uniform calf crops, as well as increased culling, testing and prevention costs. Various studies and models have estimated income reduction anywhere between 20%-40% when trichomoniasis is present in a herd.

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Bovine Tuberculosis (TB)Top

Overview
Bovine tuberculosis is a respiratory disease caused by the bacterium Mycobacterium bovis. It is a major infectious disease found worldwide in domestic animals, particularly cattle, as well as in certain wildlife populations.

Airborne transmission is the primary pathway for infection of M. bovis within and between species; however, animals may also become infected if they ingest large quantities of the bacterium.

Signs
Bovine tuberculosis is predominantly a respiratory disease affecting the lungs and associated lymph nodes. Infection is often subclinical, while clinical signs, when present, are not specifically distinctive of the disease. Symptoms may include physical weakness, anorexia, emaciation, enlargement of lymph nodes, and coughing, particularly in advanced cases of bovine tuberculosis.

Human health risk
Bovine tuberculosis is a significant zoonosis and presents a serious health risk to humans. The bacterium can be spread from animals to humans through aerosols, or through the consumption of unpasteurized milk or dairy products from infected cows.

Economic impact
An outbreak of bovine tuberculosis may have a significant negative impact on the farming industry as a result of reduced milk yields, culling of herds, and restrictions on meat exports from affected areas.

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Parainfluenza 3 (PI3)Top

Epidemiology
Parainfluenza virus type 3 (PI3) is an RNA virus belonging to the Paramyxoviridae family, which is extremely common in livestock throughout the world. PI3 has been detected in both respiratory and digestive conditions, and it causes respiratory problems in young bovines. PI3 is also considered a cofactor in conditions associated with infection by certain bacteria (Mycoplasma bovis and Pasteurella haemolytica), and other viruses (including those that cause BVD and IBR).

Signs
The signs of the disease are hyperthermia, coughing, ocular and nasal discharge, anorexia, dyspnea, and diarrhea. PI3 is also immunosuppressive, and infected animals are predisposed to secondary infections.

Transmission
PI3 is usually transmitted in nasal secretions, and its transmission is favored by animal transport (direct contact, poor ventilation, and a stagnant atmosphere). To confirm PI3 infection, serological testing is strongly recommended.

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