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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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Border disease (BD) is caused by the Pestivirus border disease virus (BDV). BD is a viral disease of sheep and goats first reported in sheep in 1959 from the border region of England and Wales, and since recorded worldwide.
Prevalence rates in sheep vary from 5% to 50% between countries and from region to region within countries. Vertical transmission plays an important role in the epidemiology of the disease. Infection of fetuses can result in the birth of persistently infected (PI) lambs. These PI lambs are viraemic, antibody negative, and constantly excrete virus. The virus spreads from sheep to sheep, with PI animals being the most potent source of infection.
Infection in goats is less common, with abortion being the main presenting sign.
It is important to identify viraemic PI animals so that they will not be used for breeding or trading purposes.
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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 discharges 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
Common symptoms of Brucella infection are decreased milk production, weight loss, abortions, infertility, and lameness. Brucella uptake occurs orally, or via skin wounds or mucous membranes. Brucella bacteria are mainly excreted with aborted placentas and fetuses, 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 cheeses 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 usually not fatal, but if untreated it can last for many years.
The incubation period is usually 1 to 3 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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Epidemiology
CAE and maedi-visna are persistent viral infections caused by closely related lentiviruses belonging to the Retroviridae family. Although there are only a few documented cases of interspecific transmission, CAEV can infect sheep and maedi-visna can infect goats.
The infection is transmitted very early to the lamb or kid via the dam in colostrum or milk, or via the respiratory secretions of infected animals. Now a permanent carrier, the lamb or kid can transmit the virus to the rest of the flock throughout its life.
Signs
CAE is a disease that affects caprines, causing arthritis and mastitis in adults and encephalitis in younger animals. Maedi-visna is a disease of sheep, causing shortness of breath or respiratory distress, arthritis, and weight loss. In addition, some ovines develop lesions of variable severity in the lungs and on the udders. CAEV and maedi-visna are closely related viruses.
Prevalence
Although ovine lentiviruses have been identified in most countries where sheep are raised (apart from Australia and New Zealand), CAEV is more widespread in industrialized countries.
Disease-free status requires serological testing
Serological screening for both viruses is required for the certification of caprine and ovine breeding units. Symptoms only manifest in a fraction of seropositive animals (9%–38%, depending on the study).
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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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Overview
Foot and mouth disease (FMD) is a highly contagious 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 and 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 one of the 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 livestock industry, due to the culling of herds and the restriction on meat exports from affected areas.
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Overview
Maedi-visna (MV), ovine progressive pneumonia (OPP), and caprine arthritis-encephalitis (CAE) are chronic diseases of sheep and goats that are typically grouped together as small ruminant lentiviruses (SRLVs). Maedi-visna is an Icelandic name that describes two of the syndromes associated with the MV virus. “Maedi” translates to “labored breathing” and refers to the interstitial pneumonitis aspect of the disease; and “visna” translates to “wasting”, which is a sign associated with paralyzing meningoencephalitis.
Ovine lentiviruses have been identified in sheep-rearing countries throughout the world, with the exception of New Zealand and Australia, and CAEV is primarily found within industrialized countries, coinciding with the international transport of dairy goats (European breeds).
The virus affects all breeds of sheep and goats, but studies have shown that some breeds may have a greater resistance to the lentivirus infection. Transmission of MV and CAEV primarily occurs via the oral route by ingestion of infected colostrum or milk, or by inhalation of infected aerosol droplets.
Signs
The predominant signs in clinically affected sheep are emaciation and respiratory distress, whereas polyarthritis is the primary sign displayed in goats. Fever, coughing, and bronchial exudates are potential but seldom seen signs, unless secondary bacterial infection occurs. Circling, muscle tremors, and paralysis are typically associated with the encephalitic form of the virus.
Human health risk
It does not appear that MV presents a zoonotic risk.
Economic impact
Control programs have helped to decrease MV incidence in some countries, but the disease is still widespread in various parts of the world. For example, within the US infection rates of sheep can exceed 50% in some areas, with midwestern and western states reporting some of the highest rates. Infections are typically asymptomatic, but once clinical signs emerge MV is typically progressive and fatal.
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Epidemiology
Diarrhea is a major cause of death in calves and other young ruminants. This form of neonatal gastroenteritis is caused by ingested microorganisms that reach the gut. Many different microorganisms can cause neonatal diarrhea, including viruses (rotavirus, coronavirus), bacteria (Salmonella, enterotoxinogenic Escherichia coli K99), and protozoa (Cryptosporidium parvum, coccidia).
Signs
Viral infection often paves the way for bacterial superinfection, which exacerbates the problem and prejudices the outcome. The first signs of diarrhea are loss of appetite, abdominal retraction and tightness, and lethargy. In animals, diarrhea can quickly lead to dehydration followed by paralysis, circulatory failure, and death.
Laboratory testing needed for diagnosis
The causative agent of calf diarrhea cannot be identified on the basis of the symptoms alone; laboratory testing is required. The best prophylaxis against neonatal diarrhea is to ensure that the calf is given an adequate dose of colostrum as soon as possible after delivery.
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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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Overview
Paratuberculosis, also known as Johne ’s disease, is caused by the presence of the Myobacterium avium subspecies paratuberculosis 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 subsp. paratuberculosis, in feces or intestinal tissues post-mortem. 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
The 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 subsp. 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, causing economic losses to producers. Consequently, a 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 impact of Johne’s disease. It is a cooperative program involving the Australian livestock industries, government, and veterinary profession. Animal Health Australia manages the program on behalf of these key stakeholders.
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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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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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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).
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Overview
Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii, which belongs to the family Sarcocystidae. Toxoplasma infections are widespread in humans and many other species of warm-blooded animals, including pigs, sheep, and goats. Occurrence is worldwide; however, the prevalence in human and animal populations varies greatly among countries.
Infections occur as a result of consuming raw or undercooked meat that contains tissue cysts, and tachyzoites, or by food or water contaminated with oocysts. Toxoplasma-infected meat and meat products are considered to be an important source for human infection.
Signs
The clinical signs include fever, diarrhea, cough, dyspnea, icterus, seizures, and death. T gondii is also an important cause of abortion and stillbirth in sheep and goats, and sometimes in pigs. After infection of a pregnant ewe, tachyzoites spread via the bloodstream to placental cotyledons, causing necrosis. Tachyzoites may also spread to the fetus, causing necrosis in multiple organs.
Human health risk
In humans, toxoplasma infections are also mostly asymptomatic. Clinical signs are mostly known to appear in immunosuppressed individuals, where an infection can cause severe neurological disease. Recent studies have shown, however, that immunocompetent people may develop clinical toxoplasmosis more frequently than previously thought. The Panel of Biological Hazards considers toxoplasmosis to be an under-detected and under-reported disease in the European Union (The EFSA Journal 2007; 583: 1-64), and has recently ranked “Toxoplasma gondii and pathogenic verocytotoxin-producing Escherichia coli (VTEC) as the most relevant biological hazards for meat inspection of sheep and goats” (The EFSA Journal 2013; 11(6): 3265).
The Emerging Pathogens Institute of the University of Florida ranks toxoplasmosis as the number 2 public health burden among food-borne infections, in its publication “Ranking the Risks: The 10 Pathogen-Food Combinations with the Greatest Burden on Public Health.”
Economic impact
Because of the risk of human infection, the meat production industry can be severely affected when a toxoplasma infection occurs. Surveillance and diagnosis of infected pig, sheep, and goat herds can be easily achieved by testing for Toxoplasma antibodies in the animals’ serum, plasma, or meat juice.
Toxoplasma in small ruminants causes losses to herds due to abortions, stillbirths, or the birth of weak lambs. The implementation of appropriate measures—based on the test results—can significantly improve the health status of a herd.
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