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Chlamydia sheep (lat. - Abortus enzootica ovis; English - Chlamydiosis of sheep; chlamydial abortion, enzootic abortion, viral abortion) - a contagious, enzootic flowing disease that manifests itself clinically mainly with abortions in the last week of dysfunction or premature lambing and the birth of the weak unviable lambs.
Historical background, distribution, degree of danger and damage. Greig (1936) for the first time described an unusual, not caused by well-known bacterial infections, enzootic abortion of sheep, identified by him in areas of Scotland. For the first time, Stemp (1950) isolated a pathogen from the vaginal mucus of an aborted sheep that was referred to the group of psittacosis-lymphogranulomatosis. Later, the identical nature of enzootic abortion of sheep was established in England, France, USA, Japan and other countries of the world. In our country, for the first time, chlamydia of sheep was established in 1965. In the study of RAC serum of aborted sheep, complement-binding antibodies to the chlamydial antigen were detected. Sheep abortions caused by chlamydia cause significant damage to sheep farms. The causative agent of enzootic abortion is pathogenic for humans.
The causative agent of the disease. The causative agent of chlamydia sheep - CMamydophila abortus ovis. All representatives of this genus are antigenically related, possess common cultural-morphological and tinctorial properties. Chlamydia are clearly visible under a light microscope. The diameter of the elementary bodies reaches 350 nm. C. abortus ovis is easily cultivated in the yolk sac of 6 ... 7-day-old chicken embryos, causing their death after 8 ... 12 days after infection. From laboratory animals, white mice, rats, guinea pigs, rabbits, which develop pneumonia during infection, are sensitive to the causative agent of abortion of sheep.
The resistance of the pathogen has been little studied. It is known that in the pathological material from aborted fetuses it remains in an active state at temperatures from below –20 ° C for many months. In the external environment it dies in a few days, at 100 ° C - instantly.
Epizootology. Sheep chlamydia usually occurs as an enzootic with the most common infection during the lambing period. The source of infection are sick and ill animals. With the initial appearance of infection in a safe flock in the first 2 ... 3 years, the number of abortions and premature lambing in sheep of all ages reaches 20 ... 30, even up to 60%. Sheep are most affected with the second degree. After abortions or premature lambing, most sheep develop immunity, and subsequently the incidence does not exceed 5 ... 10% per year. The main source of the pathogen is sick animals from a dysfunctional farm. Particularly dangerous hidden bacteria. The causative agent is excreted into the environment with milk, amniotic membranes, vaginal effusions, feces and urine. The vertical transmission path of the pathogen is not excluded. Lambs can become infected immediately after birth from mothers when sucking.
Mass infection of animals occurs when healthy sheep come in contact with patients during the period of suction, lambing and in the next 2 months after it. Contaminated feed, water, animal care items can serve as factors of transmission of the pathogen. A significant number of sheep become infected during this period. Under natural conditions, infection occurs by alimentary and during maceration. The producing rams easily become infected from sick sheep by contact, and they themselves can later transmit the pathogen to healthy ewes with their sperm, although the sexual way with chlamydia is minor. The infection spreads especially quickly under conditions of unsanitary placement of sheep, with insufficient control over mating, hunting, as well as over the condition of offspring.
Pathogenesis. In sugary sheep, chlamydia infects the placental tissue, causing necrosis of cotyledons, which, in turn, leads to the death of the fetus. Chlamydia, as well as the toxins secreted by them, enter the blood from the injection site and are spread to various organs and tissues, causing the body to respond, characterized by hyperthermia, deterioration of the general condition, cell proliferation of reticulohistiocytic and lymphoid types; neutrophilic reaction in the lymph nodes, parenchymal organs; liver necrosis. The main cause of fetal death is dystrophic-necrotic changes and hemodynamic disorder in the parenchymal organs and brain as a result of chlamydia penetrated into its organs.
Current and clinical manifestation. The incubation period in natural conditions lasts from several months to 1 year, and in some cases longer. The duration of the incubation period depends on the timing of the sheep, as well as the virulence, dose and method of administration of the pathogen. Infection can occur hidden and typical. The hidden course of the disease is detected only in the study of serum in the RAC. Okotki in latently sick sheep passes normally, but their membranes and secretions from the genital organs contain chlamydia, so these sheep have long been considered dangerous carriers of the causative agent of the disease. Lambs from such sheep are relatively poorly developed and are hidden carriers of chlamydia.
A typical disease is characterized by abortion and premature lambing with the appearance of weak, non-viable and poorly developing lambs. Such lambs, as a rule, die soon. The time when an abortion or premature lambing occurs in every sheep sheep depends on the intensity of placentitis and the degree of chlamydia of the membranes; this usually happens 2 ... 3 weeks before the end of the normal term of malice, less often - 6 ... 8 weeks.
A few days before abortions or premature lambing in sheep, symptoms such as fever, colic, and purulent discharge from the genitals often appear.
Discharges are also observed after an abortion or lambing. As a result of the addition of a secondary bacterial infection, the animal's body temperature rises again and purulent offensive discharge with an acidic reaction appears. Such secretions are observed in sheep for 3 ... 6 weeks. If an abortion does not occur, then the fruits continue to develop, lambs are born weak. They usually suffer from arthritis, partial or complete paralysis of the limbs, lack of coordination of movements, and in some cases conjunctivitis.
Ewes after the birth of the dead offspring are often in serious condition and may die suddenly or after a few days. If the fetus dies during an abortion, then the general condition of the sheep, as a rule, deteriorates slightly, but there is constantly a decrease in nutrition and fertility; complete infertility is rarely observed. Sometimes the disease can manifest interstitial pneumonia, polyarthritis and conjunctivitis.
Pathological signs. Pathological changes are determined by the development of placentitis and the defeat of the fetus without any specific features. In aborted fruits, bloody edema and hemorrhages in the subcutaneous and muscle tissues are usually found with varying intensity, as well as bloody-serous transudate in the thoracic and abdominal cavities. Often aborted fetus is mummified. In some cases, the entire chorion is affected, and in others, only its individual parts. The color of the affected chorion varies from dark red to slightly brown. Due to edema and hemorrhages on the chorion, limited thickenings are formed and its surface becomes hilly. Affected cotyledons lose the color of normal tissue, they become elastic, brown in color. Some cotyledons are significantly necrotized, the epithelium and vessels are often completely destroyed by inflammatory exudate.
In aborted fetuses, hemorrhages in the brain and its membranes, congestive blood supply and liver dystrophy are noted.
Diagnostics and differential diagnostics. The diagnosis of chlamydia abortion is established in a complex way, but the epizootological, clinical, and pathological changes cannot be regarded as strictly specific for this disease. From the laboratory methods for diagnosing chlamydial abortion of sheep, the following are mandatory: 1) microscopic detection of inclusions and elementary bodies of chlamydia in uteropaginaries and organs of aborted fetuses; 2) detection of specific antibodies in diagnostic titers in blood sera of aborted ewes in the RAC or RNA; 3) isolation of the pathogen in chick embryos, study of its morphological, tinctorial properties by staining preparations using the Stamp method and performing serological identification.
The most reliable method for diagnosing chlamydial abortion in sheep is the isolation of the pathogen in 6 ... 7-day chick embryos.
In the differential diagnosis exclude the disease of sheep brucellosis, salmonellosis, campylobacteriosis, lysterosis, leptospirosis, Q fever, toxoplasmosis. The results of laboratory studies are of decisive importance in the differential diagnosis.
Immunity, specific prevention. Although chlamydia has a weak immunogenic activity, they are nonetheless able to induce both humoral and cellular immune responses.
Vaccines have been developed for the specific prophylaxis of chlamydia, in particular, in Russia, an inactivated emulsin-vaccine against chlamydial abortion of sheep (VIEV) is used.
Prevention. In the prevention and elimination of chlamydial abortion of sheep perform the following set of veterinary and sanitary measures:
newly received sheep are allowed on the farm or in a flock of prosperous farms only if there are no abortions or premature lambing in the first lamb period, and special microscopic and serological studies do not reveal the hidden carriage of chlamydia;
spend lambing in isolated areas, strictly observing all veterinary and sanitary rules;
systematically examine sheep, apply artificial insemination of sheep and timely disinfect them in sheep farms.
Treatment. The use of antibiotics for prophylactic purposes during insemination or mating of females is economically justified, when there are isolated cases of abortion in sheep. The best results were obtained from the use of tetracycline, spiramycin, reverin and other tetracycline antibiotics.
Control measures. When a diagnosis of chlamydia is established, sheep farms are declared unfavorable and impose restrictions. A serological study of blood sera from positively reacting and aborted ewes is carried out; the bright and the rams are isolated, treated or sent for slaughter. Negatively reactive animals are vaccinated before insemination. In general, activities are carried out similarly to those for chlamydia in cattle (see the section “Chlamydia in cattle”).
Conducting these special veterinary and sanitary and therapeutic and preventive measures can eliminate the disease in sheep and remove restrictions from a dysfunctional economy 30 days after their completion.
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