Blackleg : is an acute, febrile, highly fatal disease of cattle and sheep caused by Clostridium chauvoei .It is found worldwide. usually affecting cattle, sheep, and goats

In cattle, blackleg infection is endogenous. Lesions develop without any history of wounds, Commonly, the animals that contract blackleg are of the beef breeds, in excellent health, and gaining weight . Age of infection : -cattle are between the ages of six months and two years . - calves as young as 6 wk and cattle as old as 10–12 yr may be affected.

in sheep, the disease is almost always the result of a wound infection and often follows some form of injury such as shearing cuts, docking, crutching, or castration . *The disease usually occurs in summer and fall and is uncommon during the winter

EtiologyC .chauvoei is found naturally in the intestinal tract of animals. Spores remain viable in the soil for years and are purported to be a source of infection. Outbreaks of blackleg have occurred in cattle on farms in which recent excavations have occurred or after flooding. The organisms probably are ingested, pass through the wall of the GI tract, and after gaining access to the bloodstream, are deposited in muscle and other tissues (spleen, liver, and alimentary tract) and may remain dormant indefinitely.

pathogenesisIngestion of spores

intestine

circulation

Localization in skeletal muscle

germination multiplication exotoxines

Muscle necrosis , pigment and toxemia

clinical signs :1-the animal may develop a fever. 2-The limb usually swells significantly3- the animal can develop lameness on the affected leg. 4- Crepitation (the sensation of air under the skin) can be noticed in the hip, shoulder, chest, back, neck.5- as the area seems to crackle under pressure-The animal can live about 12-48 hours.

cattle succumb to the disease without showing any symptoms, and only a necropsy reveals the cause.

During a necropsy, a diagnosis is usually made very quickly, as the affected muscle is usually mottled with

black patches, which are dead tissue, killed by the toxins the bacteria release when they infect live

tissue. If viewed under a microscope, small rod-like bacteria can be seen to confirm the diagnosis. In

some cattle, the lesions are restricted to the myocardium and the diaphragm.

Gross finding :Subcutaneous and muscular emphysema throughout the animal. There was moderate to severe retroperitoneal and mediastinal edema. The hind-limb skeletal muscles had multiple dark red areas and were emphysematous. They had a prominent odor of rancid butter.

Microscopical appearance:1. Necrotizing emphysematous myositis and myocarditis, multifocal, severe, with intralesional bacteria.2. Fibrinous epicarditis3.Skeletal muscle: The majority of myocytes are diffusely devoid of nuclei but retain their cross-striations. There are multifocal hemorrhages within the muscle, and scattered foci of edema. Some sections have large clear spaces between myofibers (emphysema), and other sections have small numbers of degenerate neutrophils. There are rare nuclei present.

PM lesion

Early or wet stage :Muscle are necrosis

, appear dark red seperated by

serohemorrhagic exudate .

Late or dry stage : 1- muscles are dark red to nearly black ( due to the

formation of iron sulphate )with information of gases.

2-signs of toxemia ( as in septicemia).

Control: In cattle:A multivalent vaccine containing C chauvoei, C septicum and, where needed, C novyi antigens is safe and reliable for cattle and sheep. Calves 3–6 mo of age should be vaccinated twice, 4 wk apart. In an outbreak, all susceptible cattle should be vaccinated and treated prophylactically with penicillin (10,000 IU/kg, IM) to prevent new cases for as long as 14 days. Cattle should be moved from affected pastures. .

Control :In sheep:ewes should be vaccinated twice 1 mo before lambing and then with yearly boosters. -In outbreaks in flocks of ewes, prophylactic penicillin and antiserum treatments are recommended.-Young sheep should be vaccinated before going to pasture. Immunity in young sheep is relatively short. --Clostridial vaccines are reported to create a weaker immune response in sheep and goats than in cattle.- Carcasses should be destroyed by burning or buried deeply in a fenced-off area to limit heavy spore contamination of the soil

Made by :

رنا رأفت محمد-1 115692- 11580إسراء خميس عبد الباسط

Under supervision of: Prof./Sherein Saeid Abdelgayed