Animal Diseases –
Ovine / Sheep

Bluetounge Virus (BTV)

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)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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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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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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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

Epidemiology
Paratuberculosis (paraTB) is a chronic, contagious infection caused by Mycobacterium avium sub. paratuberculosis (MAP), which belongs to the same family as the causative agent of tuberculosis. This incurable disease affects bovines, caprines, and other wild and domesticated ruminants.

Mycobacterium paratuberculosis is particularly hardy and is excreted in great numbers in the feces of infected animals. Infection occurs early in life through the ingestion of feed, water, or maternal milk contaminated with fecal material. The disease is highly complex and depends on many factors. How the disease will progress depends on the resistance of the bacillus, the rate of its excretion into the environment, latent phases, and antibody responses (which are sometimes delayed).

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

Removing infected animals is key to controlling the spread
Control of paraTB depends on identifying and removing infected animals: the main diagnostic tools are PCR and ELISA tests, as well as stool culture.

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Maedi-visna VirusTop

Epidemiology
Caprine arthritis-encephalitis virus (CAEV) and maedi-visna are lentiviruses belonging to the Retroviridae family. These viruses lead to persistent infections.

CAEV and maedi-visna are closely related viruses. Although documented cases of interspecies transmission are rare, CAEV can infect sheep and maedi-visna–infected goats. Young animals (lambs or kids) become infected at a very early age, through colostrum or milk during suckling, and respiratory secretions from infected animals. As permanent carriers, they are then capable of transmitting the virus to the rest of the flock or herd throughout their lives.

Signs
CAEV is a disease of goats and is associated with the following clinical signs: arthritis and mastitis in adults, and encephalitis in young animals. Maedi-visna is a disease of sheep associated with the following clinical signs: respiratory difficulties or dyspnea, arthritis, and emaciation. In addition, some sheep develop lesions of varying severity in the lungs and udder.

Prevalence
Whereas ovine lentiviruses have been identified in the majority of sheep-farming countries in the world (with the exception of Australia and New Zealand), CAEV is more widespread in industrialized countries.

Disease-free status requires serological testing
Clinical signs are expressed in only a proportion of the animals testing seropositive (9–38%, according to published studies).To certify sheep and goat farms are free of these diseases, confirmation by serological testing is necessary.

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Neonatal GastroenteritisTop

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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Ovine Herpesvirus Type 2 (Gangrenous Coryza)Top

Epidemiology
Gangrenous coryza is a disease of large ruminants and pigs, characterized by high fever and usually fatal. Gangrenous coryza is caused by a virus belonging to the genus Rhadinovirus (of the Herpesviridae family), specifically, one of two different gamma-herpesviruses. The natural host of Alcelaphine herpesvirus 1 (AIHV-1) is the wildebeest, in which the infection is silent. The disease appears in various parts of Africa and in a wide variety of ruminant species in zoological parks. Ovine herpesvirus 2 (OvHV-2) is prevalent in all races of domesticated sheep, in which it causes a subclinical infection.

Signs
Found in most parts of the world, the disease's clinical manifestations can vary enormously, from an acute form with mild symptoms to a more typical form with high fever, erosive ulceration of the gastrointestinal mucosa, keratoconjunctivitis with corneal opacity, and copious ocular and nasal discharge.

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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).

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