Binocular compound microscopes aid veterinarians in identifying and diagnosing the animals they are taking care of.

In Caseus Lymphadenitis of sheep, caseous abscesses filled with greenish yellow pus occur chiefly in lymph nodes and to a lesser extent in internal organs. In the early stages the pus is soft and pasty but in the later stages it is firm and dry and has a characteristic laminated appearance. Diffuse bronchopneumonia, with more fluid pus of a similar color, may also be present.

Diagnosis

Palpable enlargements of peripheral lymph nodes as a flock problem in sheep are usually due to this disease. The caseous greenish pus is diagnostic. Caseous lymphadenitis runs a much more chronic course than that of melioidosis although the lesions in the two diseases have a superficial similarity. Suppurative lymphadenitis in lambs has been found to be caused by infection with microscopic Past. multocida (identified using a binocular compound microscope) and a disease characterized by the presence of yellow-green pus in abscesses situated in close proximity to the lymph nodes of sheep is caused by a Gram-positive micrococcus. The latter disease occurs in France and Kenya and is referred to as Morel’s disease.

Treatment

Veterinarians do not usually attempt treatment although the microscopic pathogenic organism is susceptible to penicillin. The local for¬mation of abscesses is unlikely to respond to other than surgical treatment and the usual non-progressive nature of this disease makes treatment unnecessary in most cases.

Control

Attempts at producing an effective vaccine against caseous lymphadenitis have been largely unsuccessful. The most that can be achieved is protection against the lethal effects of the bacterial toxin without restriction of abscess development. Control must depend upon elimination of the source of infection by culling all sheep with enlarged lymph nodes, preferably at shearing time when palpation is easier. Although this is a logical procedure it is worth noting that it is not capable of detecting early lesions, especially in the prescapular lymph node. Lambing and docking should be carried out in clean surroundings or in fresh fields. All docking implements, shears and other veterinary instruments used for the operation should be dipped in strong disinfectant before each use. Similar attention should be given to shears at shearing time and pus spilled on the shearing floor should be cleaned up and all shearing cuts dis¬infected. The younger age groups should be shorn first as the chance of infection is less among the lambs. All efforts must also be directed to avoid contaminating dipping fluid; one discharging abscess is capable of con¬taminating an entire tank of fluid. Dipping after shear¬ing may be undesirable in badly affected flocks. The addition of an efficient bactericidal agent to the dipping fluid is worthy of consideration.

Ulcerative Lymphangitis of Horses and Cattle Ulcerative lymphangitis is a mildly contagious disease of horses and cattle characterized by lymphangitis of the lower limbs.

Etiology

Corynebacterium pseudotuberculosis causes the classical disease but similar lesions may be due to infection with other pyogenic organisms including streptococci, staphylococci, Corynebacterium equi, and Pseudomonas aeruginosa. These bacteria can be identified with the use of microscopes such as a binocular compound microscope.

Epidemiology

Infection occurs through abrasions on the lower limbs and is more likely when horses are grouped together in dirty, unhygienic quarters. As a rule only sporadic cases occur in a stable.

The disease was of considerable importance and widely distributed during the horse era. The mortality rate was negligible but among affected horses there was interference with their ability to perform. Ulcerative lymphangitis has also been recorded in cattle.

Pathogenesis

Infection of skin wounds is followed by invasion of lymphatic vessels and the development of abscesses along their course, as seen when samples are studied under a binocular compound microscope. Lymph node involvement is un¬usual.

In horses the initial wound infection is followed by swelling and pain of the pastern, often sufficient to cause severe lameness. Nodules develop in the sub¬cutaneous tissue particularly around the fetlock. These may enlarge to 5-7 cm in diameter and rupture to discharge creamy green pus. The resulting ulcer has ragged edges and a necrotic base. Lymphatics draining the area become enlarged and hard and secondary ulcers may develop along them. Lesions heal in 1-2 weeks but fresh crops may occur and cause persistence of the disease for up to 12 months. In rare cases there is a slight systemic reaction and a bacteremia may result in localization in other organs. The lesions in cattle are similar to those in horses except that there may be lymph node enlargement and the ulcers discharge a gelatinous clear exudate.

Clinical Pathology

The isolation of Corynebacterium pseudotuberculosis from dis¬charging lesions and identifying them with the aid of a binocular compound microscope such as a veterinary microscope is necessary to confirm the diagnosis.

Diagnosis

Differentiation of ulcerative lymphangitis from the other diseases causing similar lesions is important because of the serious nature of such diseases as glanders and epizootic lymphangitis in horses. Restric¬tion of the lesion to the lower limbs and absence of lymph node involvement are important features although these are shared by sporotrichosis.

Treatment

Local treatment of ulcers is usually sufficient although parenteral injections of penicillin may be necessary in severe cases. In the early stages an autogenous bacterin may have value as treatment.

Control
Good hygiene in stables and careful disinfection of injuries to the lower limbs usually afford adequate protection against the disease. Read more on this subject