B. Malignant Edema

The first symptoms of malignant edema are usually observed in 12 to 36 hours after the infection enters the body. There are hot, painful swellings at the points of infection, high fever and loss of appetite, a drop in milk secretion, severe depression, difficult breathing, and convulsions before death. Most affected animals die 1 or 2 days after the symptoms appear. Malignant edema is diagnosed with difficulty because it may be mistaken for blackleg, anthrax, haemorrhagic septicemia, or other types of gas edema.

Laboratory tests are the only conclusive method of distingui­shing malignant edema from similar types of infection. The following points of difference between malignant edema and blackleg may be of some help in making a tentative diagnosis. Malignant edema affects cattle of all ages. It generally starts from a wound. The gangrenous swellings appear at the point of injury. The swellings, which develop rapidly, are usually extensive and doughy; they pit when they are pressed and discharge a reddish, gelatin like substance mixed with gas bubbles when they are opened.

Blackleg affects young animals. It is rare in animals more than 2 years old. It is caused by minute, invisible puncture wounds. The swellings appear mostly over the muscles of the hind or front quarters, and emit a crackling sound on pressure. They discharge a frothy, dark-red exudate with an odor like that of rancid butter, when they are incised.