Key Technical Points for the Prevention and Treatment of Necrobacillosis in Deer

Necrobacillosis in deer is a common chronic infectious disease of deer, characterized by damage to the hooves and necrosis of the skin, subcutaneous tissue, oral and digestive tract mucosa, and internal organs.

1. Pathogen The pathogen of this disease is Fusobacterium necrophorum, a pleomorphic Gram-negative bacterium, with small forms appearing spherical and large forms appearing as long filaments. This bacterium is widely distributed in nature and can be found in animal yards, swamps, and soil, and is also commonly present in the oral cavity, intestinal tract, and external genital tract of healthy animals. It is a strictly anaerobic bacterium. This bacterium can produce exotoxins, which can cause tissue edema, and its endotoxins can cause tissue necrosis. This bacterium has weak resistance to physical and chemical factors. Heat and common disinfectants can kill it.

2. Epidemiological characteristics Under natural conditions, a variety of livestock, poultry, and wild animals are susceptible. Among wild animals, sika deer, red deer, sambar deer, moose, and musk deer are all susceptible, with fawns being especially more susceptible. This disease occurs sporadically in autumn and winter, and less frequently in spring and summer. Infection occurs mainly through skin injuries. In fawns during the birthing and rearing period, it occurs as an endemic, especially when the ground is hard and infection occurs due to abrasions at the carpal and tarsal joints. After young deer are separated and transferred, infection may occur due to injuries from restlessness and violent jumping, or infection may occur due to oral injuries during the teething period or from eating coarse, hard feed.

3. Clinical symptoms At the beginning of the disease, hot, painful swelling occurs at the heel and coronary band of the hoof, and in some cases laminitis may be seen. Later, suppuration, ulceration, and necrosis appear and spread to deeper tissues, with many small openings on the swollen coronary band discharging cloudy, foul-smelling pus resembling millet gruel. Sometimes the necrosis extends to ligaments, joints, bones, and the hoof capsule, and in severe cases the hoof capsule may slough off and the pedal bone may fracture, causing lameness. At the same time, lesions may also be found at the base of the tongue and on the palate, and in some cases begin on the lips; the affected area has yellowish-white necrotic material firmly attached to healthy tissue. Sometimes fissures occur, and the necrotic appearance is grayish-green or filthy gray, with the necrotic foci gradually extending deeper, reaching as far as the bone. When the lesions spread to the internal organs, systemic symptoms appear, including depression, drooping ears, poor appetite, a tendency to lie down, and elevated body temperature. With secondary infection, appetite is completely lost, the animal rapidly becomes emaciated, breathing becomes short and rapid, and death may follow. In fawns infected through the umbilical wound, the course is somewhat longer, with symptoms including arching of the back during urination, lethargy, and rough hair coat. There is a cord-like induration at the umbilicus or swelling as large as a fist, with foul-smelling pus resembling millet gruel discharging from multiple openings at the umbilicus. When infection occurs in fawns through abrasions on the front of the carpal joint and the side of the tarsal joint, if not treated promptly it often becomes chronic, causing bone hyperplasia, and even after recovery it leaves sequelae such as "big joints" or "lameness."

4. Anatomical and pathological changes These vary with the species and age of the deer. Most carcasses of affected deer are highly emaciated. The necrotic foci in the liver vary in size and number, ranging from as small as a walnut to involving the entire liver. Necrotic foci of varying sizes are commonly seen on the mucosa of the first three stomachs, in the pleural cavity, and in the lungs, and in some cases suppurative pleuritis and suppurative fibrinous pneumonia occur. One side of the lung may be affected, or even most of the lung may be rotten, with a special foul odor. External lesions consist of firm swelling, ulceration, and necrosis of the affected area. The subcutaneous blood vessels of the affected limb are engorged, resembling ropes, and feel firm when pressed; in severe cases there is swelling and filling with foul-smelling pus, while in mild cases the skin of the coronary band and fetlock opens and ulcerates. The subcutaneous tissue shows gelatinous infiltration or a rubber-like leg. Fusobacterium necrophorum dies and disintegrates rapidly in dead tissue, and radially arranged bacterial bodies can be seen only at the junction between diseased and healthy tissue.

5. Diagnosis A preliminary diagnosis can be made based on symptoms, epidemiological characteristics, and lesions. A thick saliva smear from the mouth of the affected deer, or a smear made from material scraped from the junction between diseased and healthy tissue around the lesion and examined microscopically, may reveal unevenly stained long filamentous bacilli. In addition, animal inoculation and isolation culture can be used for confirmation.

6. Prevention and treatment (1) Prevention: Avoid injury to the skin and mucosa, and carry out safety checks on deer sheds and restraint chutes. Keep the ground level at all times, and keep the pens and surrounding environment clean and dry. Disinfect regularly to prevent contamination of feeding and management equipment. From 3 to 5 days after birth, fawns should be examined at the umbilicus, and if infection is found, treatment should be given immediately. Affected deer should be isolated immediately and treated. It is strictly forbidden to use equipment from isolation pens interchangeably with that for healthy animals. (2) Treatment 1) Local treatment. Thoroughly remove necrotic tissue from the affected area, drain the pus completely, and expose the wound surface to create aerobic conditions so as to inhibit the development of Fusobacterium necrophorum. Wash the affected area with 3% hydrogen peroxide or 1% potassium permanganate solution, and dust with iodoform and boric acid; for those with severe inflammatory swelling, apply ichthammol ointment externally, and perform regional block of the affected limb with 500,000 to 1,000,000 units of streptomycin and 10 to 20 mL of 0.25% procaine. If the necrotic area is large, deep tissues are involved, or a fistula has formed, after removing necrotic tissue and thoroughly washing, 10% formalin alcohol or 10% to 20% iodine tincture may be infused. For excessive granulation tissue, halide powder may be dusted on. When necrotic stomatitis occurs, rinse the oral cavity with 0.1% potassium permanganate solution, then apply iodine glycerin, twice daily until recovery. For deer with sloughed hoof capsules, protect against freezing in winter, bandage, and put on deer shoes. 2) Systemic treatment. Along with local treatment, combine with systemic therapy to control secondary infection and prevent the primary lesions from spreading to the internal organs. According to the drug sensitivity test of the isolated pathogen, select antibiotics, and at the same time combine with symptomatic treatment.