1. Animal welfare and husbandry
The farm is located 800 metres southeast of Zabitui village, Alarsky district, Irkutsk region. As of March 16, 2019, the following animals were present: 108 cattle, 45 horses, and 250 sheep. Different species of animals were kept separate from each other on permanent flooring. The animals did not graze because there was a lot of snow on the pastures.
The animals were fed locally produced hay and crushed grains. Water for household needs and animal consumption was supplied from a borehole. The territory of the farm was established by a solid wooden fence and metal gates. The territory was used for logging and other economic activities. The territory was full of wooden rubbish and metal objects.
We conducted a study that excluded alimentary causes and poisoning with toxins.
2. Epidemiological data
Official reports from the past 10 years yielded no records of blackleg in Zabitui village. This outbreak was the first to be registered in the area.
The outbreak started on March 17, 2019, with sudden death of three cattle on the second day after vaccination against blackleg. The animal carcasses were disposed of the same day by cremation in a specifically designated are.
The epidemic involved pregnant cows, cows with calves and young cattle (n=43). They were vaccinated against blackleg and anthrax two days before the outbreak (15 March). Infections in other species, such as sheep, horses and buffaloes, that were vaccinated against blackleg in December 2018 were not observed.
The outbreak lasted two weeks, from March 17 to April 04, 2019. During this period, 43 head of cattle died (Figure 1).
3. Clinical signs
The following clinical signs were observed in all affected animals: depression-like behaviour, anorexia, and a high body temperature reaching 38.0-39.5 °С. Gross swelling was present on the surfaces of the body, although no crepitus was palpable. In different animals, the oedema was localized to the limbs (Figure 2a), chest, abdomen (Figure 2b), and back (Figure 2c). Paracentesis of the oedema revealed fluid accumulation and haemorrhage. During abdominal auscultation, there were signs of increased gas formation in the intestine.
Several animals showed signs of papillomatosis on the muzzle and vulva, as well as birth trauma. The papilloma and birth trauma were accompanied by the subsequent formation of oedema and compaction of the surrounding subcutaneous tissue and muscles with the formation of dense nodes (Figure 2d).
Abortions and stillbirths were reported in pregnant cows. A total of 3 cows aborted, and all of them subsequently died.
4. Autopsy
Immediately after death, the bodies of the animals released foamy, bloody fluid from the mouth, nose and eyes (Figure 3a).
Necropsies were performed on all the carcasses of the cows and calves, and the following distinct changes were observed at the sites of oedema: haemorrhagic-necrotic myositis with gas formation and serous haemorrhagic infiltration of the loose subcutaneous tissue adjacent to muscles (Figure 3b).
Some animals had serous haemorrhagic lymphadenitis of the pulmonary lymph nodes (48.0%), cardiac haemorrhage (26.5%) (Figure 3c), ruminal tympany with abdominal anaemia and thoracic hyperaemia (11.1%), haemorrhage in the serous membrane of a scar (26.5%) (Figure 3d), and haemorrhage in the subcutaneous tissue in the area of ribs 5-8 and 10-12 on the left side of the body (2.3%).
One animal had connective tissue adhesions between the peritoneum and the serous membrane of the intestine and between the pulmonary and bone pleura and haemorrhages on the abdominal wall. In the region of the lumbar spine on the abdominal side, there was a haematoma with coagulated blood that was approximately 25 cm long (along the spine) and approximately 13 cm wide. Yellow gelatinous infiltration was found in the muscular tissue of the right hind limb.
The necropsy of the stillborn calves revealed haemorrhages on the spleen, gross haemorrhages in the heart and a lack of any border between the cortical and medulla matter in the kidneys.
5. Laboratory research
During testing, a large amount of gas on the Kitt-Tarozzi medium was observed only on the first day. There was no mortality among the guinea pigs when the bioassay was carried out.
In the preparations of bacterial cultures on the Kitt-Tarozzi medium, gram-positive rods with subterminally located spores were detected (Figures 4a). We confirmed the presence of bacteria in the samples by multiplex PCR.
In a microscopic examination of a blood smear obtained from a haematoma of the scapular shoulder joint that had been present for a week, erythrocytes with basophilic granularity were detected (Figure 4b). At the same time, inclusion bodies were observed in almost 100% of the cells.