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Sheep chlamydia (Latin - Abortus enzootica ovis; English - Chlamydiosis of sheep; chlamydial abortion, enzootic abortion, viral abortion) is a contagious, enzootically occurring disease, manifested clinically mainly by abortion in the last week of coagulation or premature lambing and the birth of the weak, non-viable lambs.
Historical background, distribution, hazard and damage. Greig (1936) first described the unusual, not caused by well-known bacterial infections, enzootic abortion of sheep, revealed by him in areas of Scotland. Stemp (1950) was the first to isolate a pathogen from the vaginal mucus of an aborted sheep, which was assigned to the psittacose-lymphogranulomatosis group. Later, the identical nature of enzootic sheep abortion was established in England, France, the USA, Japan and other countries of the world. In our country, for the first time, chlamydia of sheep was established in 1965. When examining the blood serum of aborted sheep in DSC, complement-binding antibodies to chlamydial antigen were found. Sheep abortions caused by chlamydia cause significant damage to sheep farms. The causative agent of enzootic sheep abortion is pathogenic to humans.
The causative agent of the disease. The causative agent of chlamydia in sheep is CMamydophila abortus ovis. All representatives of this genus are antigenically related, have common cultural, morphological and tinctorial properties. Chlamydia is clearly visible under a light microscope. The diameter of 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 8 ... 12 days after infection. From laboratory animals, white mice, rats, guinea pigs, rabbits, which develop pneumonia upon infection, are susceptible to the causative agent of sheep abortion.
The resistance of the pathogen has been little studied. It is known that in pathological material from aborted fetuses it remains in an active state at temperatures from below -20 ° C for many months. In the environment dies in a few days, at 100 ° C - instantly.
Epizootology. Chlamydia of sheep usually proceeds in the form of enzootia with the strongest spread of infection during lambing. The source of infection is sick and ill animals. With the initial occurrence 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%. The most affected sheep with a second coagulation. 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 causative agent of the infection is sick animals coming from a dysfunctional economy. Hidden bacteria carriers are especially dangerous. The causative agent is excreted into the environment with milk, amniotic membranes, vaginal outflows, feces and urine. The vertical path of transmission of the pathogen is not excluded. Lambs can become infected immediately after birth from their mothers by sucking.
Mass infection of animals occurs when healthy sheep come in contact with sick people during the period of coagulation, lambing, and in the next 2 months after it. Contaminated feeds, water, and animal care items can serve as transmission factors for the pathogen. A significant number of sheep become infected in a random period. In vivo, infection occurs alimentarily and with mating. Sheep-producers easily become infected from sick sheep by contact and can subsequently transfer the pathogen to healthy ewes with their sperm, although the genital tract during chlamydia is minor. The infection spreads especially quickly in conditions of unsanitary placement of sheep, with insufficient control over mating, hunting, and also the state of offspring.
Pathogenesis. Chlamydia affect placental tissue in placental sheep, causing cotyledon necrosis, which, in turn, leads to fetal death. Chlamydia, as well as the toxins secreted by them, enter the bloodstream and spread to various organs and tissues, causing an organism response characterized by hyperthermia, worsening of the general condition, and proliferation of cells of the reticulohistiocytic and lymphoid type; neutrophilic reaction in the lymph nodes, parenchymal organs; necrosis of the liver. The main cause of fetal death is dystrophic-necrotic changes and a hemodynamic disorder in parenchymal organs and the brain as a result of the action of chlamydia that has penetrated into its organs.
The course and clinical manifestation. The incubation period in vivo lasts from several months to 1 year, and in some cases longer. The duration of the incubation period depends on the timing of sheep cohesion, as well as on the virulence, dose and method of administration of the pathogen. Infection can occur covertly and typically. The latent course of the disease is detected only during the study of blood serum in CSC. Lambing in latently sick sheep passes normally, but their fetal membranes and excretions from the genital organs contain chlamydia, therefore, such sheep have long been considered dangerous carriers of the pathogen. Lambs from such sheep develop relatively poorly 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 usually die soon. The time when an abortion or premature lambing occurs in each coot sheep depends on the intensity of placentitis and the degree of chlamydia of the membranes; this usually occurs 2 ... 3 weeks before the end of the normal period of maturity, less often - 6 ... 8 weeks.
A few days before abortion or premature lambing, sheep often experience symptoms such as fever, colic, and mucopurulent discharge from the genitals.
Discharge is also observed after abortion or lambing. Due to the attachment of a secondary bacterial infection in the animal, the body temperature rises again and purulent fetid discharge with an acid reaction appears. Such secretions are observed in sheep for 3 ... 6 weeks. If the abortion does not occur, then the fruits continue to develop, the lambs are born weakened. Usually they suffer from arthritis, partial or complete paralysis of the limbs, uncoordinated movements and, in some cases, conjunctivitis.
Ewe after the birth of a dead offspring are often in serious condition and may die suddenly or in a few days. If the fetus dies during an abortion, then the general condition of the sheep, as a rule, worsens slightly, but a decrease in fatness and fecundity is constantly observed; complete infertility is rare. Sometimes the disease can manifest itself as interstitial pneumonia, polyarthritis, and conjunctivitis.
Pathological signs. Pathological changes are determined by the development of placentitis and fetal damage without any specific features. In aborted fetuses, bloody edema and hemorrhage in the subcutaneous and muscle tissues, as well as blood-serous transudate in the chest and abdominal cavities are usually found of varying intensity. Often an aborted fetus is mummified. In some cases, the entire chorion is affected, and in others - only its individual parts. The color of the affected areas of the chorion varies from dark red to light brown. Due to edema and hemorrhages on the chorion, limited thickenings form and its surface becomes tuberous. Affected cotyledons lose the color of normal tissue, they become elastic, brown. Some cotyledons are significantly necrotic, epithelium and blood 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 chlamydial abortion of sheep is established in a comprehensive manner, but epizootological, clinical and pathological changes cannot be considered as strictly specific for this disease. Of the laboratory methods for diagnosing chlamydial abortion of sheep, the following are mandatory: 1) microscopic detection of inclusions and elementary bodies of chlamydia in uterine-vaginal outflows and in organs of aborted fetuses; 2) detection of specific antibodies in RSK or RNGA in diagnostic titers in blood serum of aborted ewes; 3) the selection of the pathogen in chicken embryos, the study of its morphological, tinctorial properties by staining the drugs according to the Stamp method and conducting serological identification.
The most reliable method for diagnosing chlamydial abortion in sheep is to isolate the pathogen in 6 ... 7-day-old chicken embryos.
Differential diagnosis excludes sheep disease with brucellosis, salmonellosis, campylobacteriosis, listeriosis, leptospirosis, Q fever, toxoplasmosis. Crucial in the differential diagnosis are the results of laboratory tests.
Immunity, specific prevention. Although chlamydia have weak immunogenic activity, nevertheless they are able to induce both a humoral and a cellular immune response.
Vaccines have been developed for the specific prevention of chlamydia, in particular, inactivated emulsin vaccine against chlamydial abortion of sheep (VIEV) is used in Russia.
Prevention In the prevention and eradication of chlamydial abortion, sheep perform the following set of veterinary and sanitary measures:
newly obtained sheep are allowed on a farm or in a flock of prosperous farms only if there are no abortions or premature lambing in the first lambing season and hidden carriage of chlamydia is not revealed with special microscopic and serological studies;
lambing in isolated rooms, strictly observing all veterinary and sanitary rules;
sheep are systematically examined, artificial insemination of sheep is used, and disinfection at sheep farms is carried out in a timely manner.
Treatment. It is economically justified to use antibiotics for prophylactic purposes during the period of insemination or mating of the uterus, when individual cases of abortion in sheep are observed on the farm. The best results are obtained from the use of tetracycline, spiramycin, reverin and other tetracycline antibiotics.
Control measures. When establishing a diagnosis of chlamydia, sheep farms are declared dysfunctional and impose restrictions. A complete serological examination of the blood serum of a positively reacting and aborting ewes, bright and sheep is carried out, isolated, treated or sent for slaughter. Negatively reacting animals are vaccinated before insemination. In general, events are carried out similarly to those for cattle chlamydia (see the section "Cattle Chlamydia").
The implementation of these special veterinary-sanitary and medical-preventive measures allows to eliminate the disease in sheep and remove restrictions from a dysfunctional farm 30 days after their completion.
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