2. Give the cause and treatment of emphysematous anthrax.
3. Give the cause of tick fever; distribution of the disease and methods of control.
CHAPTER XXXI
INFECTIOUS DISEASES OF POULTRY
FOWL CHOLERA.—This is a highly infectious disease of all species of poultry, that is characterized by weakness, depression and yellowish colored excrement.
The specific cause of fowl cholera is the Bacillus avisepticus (Fig. 123). This microorganism is transmitted to the healthy birds by the feed, or water becoming contaminated with the discharges from the diseased birds. According to Salmon, the period of incubating varies from four to twenty days.
The early symptoms are a falling off in appetite, high fever, dulness, diarrhoea and weakness. The affected bird becomes drowsy, the head is drawn toward the body, and it may remain asleep for long periods at a time. Salmon states that the general outline of the sick bird becomes spherical or ball-shaped.
[Illustration: FIG. 123.—Bacillus avisepticus.]
The disease is usually highly fatal. In the acute form the larger portion of the flock may die off within a week. In the subacute and chronic forms, the birds become greatly emaciated, and a few die off weekly through a period of a month or longer.
The tissue changes occurring in the disease are inflammation of all or a few of the internal organs. Ward states that the most characteristic lesion of fowl cholera is the severe inflammation of that portion of the small intestine nearest to the gizzard. Small hemorrhagic spots may be found on the heart and other organs.