What are the prevention and treatment methods for bovine blackleg?
Blackleg, commonly known as "black leg disease", is an acute septicemic infectious disease of cattle, characterized mainly by black gas swelling in well-muscled areas (especially the thigh), with crepitation on pressure, hence it is also called black leg disease or bellowing gangrene. The pathogen is Clostridium chauvoei, an obligate anaerobe, which can survive in the body for as long as 5 years.
In recent years, the climate in the Bayanbulak area of Hejing County has been changeable, with frequent rain throughout the year, humid air and relatively low temperatures. The low-temperature climate conditions and the humid valley pasture environment provide livestock with excellent forage, but at the same time, cases of bovine blackleg that had not been seen for many years have also appeared.
Bovine blackleg mainly affects yellow cattle, with yellow cattle being the most susceptible, and it mostly occurs in herds of calves under 3 years of age. The main source of infection is sick cattle, followed by sheep and water buffalo, while reports of this disease in dairy cattle are rare.
1. Case investigation
In August 2003, 3 cattle in a herd in Gongnaisi Township, Hejing County suddenly fell ill, with body temperature rising to 41-42°C, loss of appetite and rumination, and lameness. Among them, 2 dairy cows developed swelling of the thigh muscles, which was painful when pressed. One sick cow died on the morning of the second day after onset.
2. Clinical symptoms
The cattle fell ill suddenly, with body temperature rising to 41°C, loss of appetite and rumination, and the sick cattle showed lameness. Among them, 2 dairy cows developed swelling of the thigh muscles, which was painful when pressed. One dairy cow with more severe illness could not stand up, and swelling appeared in well-muscled areas, with severe edema of the muscles and subcutaneous tissue, blackened skin, and crepitation on pressure. When the swollen area was cut open, a dark red, foamy liquid with a sour, foul odor flowed from the incision. The local lymph nodes were enlarged, and the animal had difficulty breathing and died the next morning.
3. Necropsy changes
The carcass of the dead dairy cow rapidly decomposed and bloated, with dark red foamy liquid flowing from the mouth, nose, and anus. The affected muscles were black, and the cross-section was spongy and contained liquid with air bubbles. The liver and kidneys were slightly enlarged, and the liver was mildly swollen, with brownish-red necrotic lesions of varying sizes on the cut surface. After the lesions were cut open, large amounts of blood and air bubbles flowed out.
4. Laboratory examination
Under strictly disinfected conditions, smears were made from the muscles and edema fluid of the swollen lesions, stained with alkaline blue, and examined under a microscope.
Microscopic findings: large bacilli were seen arranged singly or in pairs, not forming long chains, with bluntly rounded ends joined together, and without capsules. The spore-bearing Clostridium chauvoei was located at one end or in the center of the bacterial cell, causing the cell to swell into a spindle shape, with peripheral flagella.
5. Diagnosis
Based on the case investigation, clinical symptoms, necropsy changes, and laboratory examination, it was determined to be blackleg.
6. Clinical diagnosis and treatment
1. Prevention
The affected cattle herd was examined one by one, sick cattle and suspected cattle were isolated and treated on site, and other cattle were immediately vaccinated with blackleg vaccine. It was strictly forbidden to eat dead cattle, and contaminated feces, urine, bedding, etc. were buried deeply together with the carcasses. Contaminated sites were thoroughly disinfected with 25% bleaching powder solution and 3% formalin solution to prevent the formation of a blackleg epidemic focus.
2. Treatment
① This disease has an acute onset and a short course. After sick animals are found, large doses of antibacterial drugs should be used immediately for systemic treatment in order to control the progression of the disease. We used intramuscular injection of penicillin and Kelinshuang, while also administering 5% glucose and sulfadiazine sodium intravenously. The purpose was to strengthen the heart and replenish fluids while coordinating treatment, so as to improve the therapeutic effect.
② In the early stage, oil-based procaine penicillin was injected intramuscularly into the swollen areas of sick cattle. In the middle and late stages, the swollen areas of sick cattle were cut open, necrotic tissue was removed, and the area was thoroughly flushed with 2% PP solution or 3% hydrogen peroxide. The purpose was antisepsis and the production of carbon dioxide, and injections were made at multiple points around the swelling (the swollen area should not be cut open or punctured).
③ Because the toxic symptoms of this disease are relatively severe, treatment such as cardiac support and detoxification should also be carried out according to the overall condition.
7. Prevention measures
1. In recent years, animal husbandry has brought considerable economic benefits to farmers and herders. Many breeders only focus on raising livestock while neglecting the epidemic prevention work for livestock diseases, causing some epidemics that had not appeared for many years to resurface. The occurrence of this case fully demonstrates that "veterinary prevention and control work should focus on prevention". The prevention of epidemic diseases is the most critical and effective measure for controlling and even eliminating livestock diseases.
2. Sick animals are the main source of this disease. Therefore, when this disease occurs, the affected herd should immediately be quarantined, and isolated for treatment. Other herds should also be immediately vaccinated with blackleg vaccine to prevent the spread of the pathogen.
3. Clostridium chauvoei is an obligate anaerobe and mainly exists in the tissues and edema fluid of dead cattle. It can form highly resistant spores in the tissues of sick cattle. According to the pathological characteristics of this disease, spores can survive for 10 minutes in 0.2% mercury solution, 15 minutes in 3.0% formalin solution, and more than 5 years in soil. In particular, after the tissues of dead cattle decay and edema fluid flows out of the body and contaminates the environment, healthy cattle become infected and fall ill after consuming soil, forage, or drinking water containing large amounts of Clostridium chauvoei (spores). At the same time, the disease can also be transmitted through wounds and the bites of blood-sucking insects and mosquitoes. Therefore, if this disease becomes epidemic in one place, the pasture should be moved immediately, strict disinfection and sterilization should be implemented, and other cattle herds should also be compulsorily vaccinated to prevent an epidemic.
4. It is not permitted to arbitrarily dissect the carcasses of cattle that die from this disease, and eating them is strictly forbidden, so as to avoid causing greater contamination. Dead animals should be deeply buried or incinerated outside the pasture in places with a low groundwater level.
5. After the occurrence of this case, the source of infection must be controlled and eliminated within a short period. Therefore, the animal husbandry and veterinary epidemic prevention department of our county adopted active treatment and preventive measures against the occurrence of bovine blackleg, and vaccinated all cattle herds with blackleg vaccine. The specific method was: vaccinate with blackleg vaccine in spring and autumn every year, with all large and small cattle individuals receiving a subcutaneous injection of 5 milliliters, and continue vaccine injections for 3 consecutive years. Calves that have reached 6 months of age must receive 1 additional booster immunization injection. For cattle herds in marginal areas where the epidemic occurs, preventive vaccination must also be guaranteed continuously for 3 years to establish an immune belt, and this must never be taken lightly.
6. The local swelling of blackleg is very similar to malignant edema, and veterinary personnel are prone to misjudgment during diagnosis and may overlook the existence of blackleg, thus causing sudden outbreaks of this disease. Therefore, effective funding input should be used to strengthen the capacity for disease prevention at the grassroots level and ensure that veterinary technicians can make correct judgments through advanced laboratory testing.