Anthrax is a severe and acute infectious disease caused by Bacillus anthracis. It can be infected by all kinds of animals, especially herbivores. Dairy cows can be infected with anthrax in any season of the year. The most common cause of anthrax is in summer, especially when there is more rain, washing dead cows bodies and causing the disease in one year. Distribution or epidemic within a certain range. Next, let's learn about the pathogenic characteristics of dairy cattle anthrax. Clinical symptoms and prevention and control measures of dairy cattle anthrax.
Bacillus anthracis is a Gram-positive bacterium and the largest pathogen with a length of 3-8 t_Lm and a width of 1-1.5 t_Lm. It can not move. The bacteria can appear in the blood in the form of a short chain, that is, one or several pairs arranged together, leading to the larger body, the flat ends of the bacteria, and the formation of obvious capsules. They can also be arranged in a long chain, like bamboo, which makes it difficult to form capsules. The bacterium has poor resistance. It will die immediately after boiling in a Petri dish for 2-5 minutes and within 24-96 hours if decay occurs in summer. Also, the bacteria can survive for 4 days under direct sunlight, 10 years under dry conditions and 30 years in the soil after sporulation. In the experiment, only a few spores could be detected by the boiling, and the bacteria could be completely killed by heating at 100 C for 2 hours. Also, the survival time of bacteria in different disinfection solutions is different after sporulation. For example, ethanol can not kill them. It can be killed in 3%-5% carbolic acid for 1-3 days, in 3%-5% Lysol for 12 or 24 hours, in 4% iodine tincture for 2 hours, in 0.1% mercury and 2% formalin for about 20 days. Min can be killed, especially in 0.1% mercury liter added with 0.5% hydrochloric acid, which takes only 1 to 5 minutes to kill.
The most acute type is characterized by a very short incubation period, usually after several minutes to several hours of infection will show symptoms, often in the grazing process of sudden fainting, dyspnea, and accompanied by natural hole bleeding and mucosal purple-blue symptoms, and then quickly fall to the ground to death. In acute type, the body temperature of diseased cattle is increased, which can exceed 41 °C. In the initial stage, shortness of breath, rapid heart rate, loss of appetite, slow reaction or no reaction. Rumen swelling occurs when symptoms are serious. If infected with pathogens in the neck, chest, and waist, it will cause excessive excitement, instability, and sway of the body. The course usually lasts for 1 to 2 days. Subacute type, cattle show local inflammatory edema in the skin, mouth or rectum, there is a certain degree of hard heat pain at the beginning, later will become cold, and no pain, and often appear anthrax carbuncle, the course of disease can last for several days, or even more than a week.
The blood of diseased cattle was collected and cultured under sterile conditions. The blood of diseased cattle was extracted by sterilized syringe and inoculated in a broth culture tube. The blood was cultured at 37 °C for 18-24 hours. The blood was inoculated on an agar plate and blood plate respectively. The blood was cultured at 37 °C for 18-24 hours. Gram staining was performed on a single colony and related identification tests were carried out.
Morphological examination. After staining, it was found that the pathogen was Gram-positive Escherichia coli with long chains like bamboo knots and slightly flat ends. The bacteria can form spores on the old culture medium, which is elliptical and located in the center of the bacteria body. It has strong refractive properties, does not cause the expansion of the bacteria body, nor does it cause the breakage of the bacterial chain. It can form a capsule on the culture medium containing bovine serum.
Culture characteristics. On the ordinary culture medium, grey-white opaque colonies with a diameter of 2-3 mm were grown, which had a flat appearance, dry and rough surface, lost luster and irregular edges. Under the magnifying glass, the edges were like curls. Mild hemolysis occurs gradually on the blood plate. In the broth tube, precipitation will occur due to the formation of long chains, while the upper part of the tube is relatively clear, the liquid surface will not form a bacterial film, nor will there be bacterial rings attached to the wall of the tube.
Identification test. Penicillin inhibition test can be carried out, that is to say, pure strains can be inoculated on agar plates of 50,000 IU/mL, 100,000 IU/mL and 1 million IU/mL penicillin respectively by line inoculation, and cultured at 37 ~C for 24 hours. The results show that the strains can grow on the penicillin medium of 50,000 IU/mL, but they can grow on the agar plates of 1,000 IU/mL penicillin. It could not grow on the penicillin medium with a concentration of 100,000 IU/mL and 1,000,000 IU/mL. Bead test can also be carried out, that is, inoculated in penicillin medium with a concentration of 0.05 million to 0.5 million IU/mL, the bacteria will grow large and round spherical bodies, if bead chain, and will become Gram-negative.
Immunoprophylaxis. The main measure to prevent anthrax in dairy cows is to immunize the herd regularly. The non-toxic anthrax spore vaccine can be inoculated regularly every year. Dairy cows older than 1-year-old are inoculated with 1 mL, while cows younger than 1-year-old are inoculated with 0.5 ml. Or use anthrax spore vaccine No. 2 and inoculate 1 mL at any age.
Emergency Management. For those areas where cattle are found dead or sick, the epidemic spot should be delimited immediately. Generally, the area extending 3000 m from the edge of the epidemic area is the epidemic area, while the area extending 5000 m from the epidemic area is the threatened area. Dead cattle and their contaminated bedding and feed must be treated harmlessly. Cattle calf contaminated with dead cattle should use 5% formalin for 3 spray disinfection and 20% bleach powder for spray disinfection. In general, use 200 ml per square meter for 2h.
Medication. In the early stage of onset, 100-300 ml anti-anthrax serum can be injected intraperitoneally, subcutaneously or intravenously into adult diseased cattle, and the therapeutic effect is good. If the body temperature remains unchanged after injection, it can be injected once again after 12-24 hours. Sulfadiazine is the most effective drug in the treatment of anthrax. The diseased cattle can be intravenously injected with 80-100 ml 20% sodium sulfadiazine twice a day, and continue to be injected for 1-2 days after body temperature drops.