_The preventive treatment_ consists in thoroughly draining pastures and yards where cattle run. This measure does not insure cattle against the disease. Cattle that die of "black leg" should be cremated. This should be done at the spot where the animal dies. If the carcass is moved or opened, the ground should be thoroughly wet with a four per cent water solution of a cresol disinfectant and covered with lime.
_Vaccination_ of the exposed or susceptible animals should be practised. On farms where the disease exists it may be necessary to vaccinate the young animals (less than two years of age) once or twice every year in order to prevent the disease. Medicinal treatment is unsatisfactory.
TEXAS OR TICK FEVER.--Tick fever is an infectious disease of cattle. It is caused by an animal organism that is present in the blood, and is conveyed from the animal that is host for the tick fever parasite to the non-infected animal by a tick (Figs. 120 and 121).
[Illustration: FIG. 120.--Cattle tick (male).]
[Illustration: FIG. 121.--Cattle tick (female).]
Tick fever was introduced into the southern portion of the United States through importation of cattle by the Spaniards. Previous to the establishing of a definite quarantine line between the permanently infected and the non-infected sections, heavy losses among northern cattle resulted through driving and shipping southern cattle through the northern States.
The specific cause and the part taken by the tick in its distribution were not discovered until 1889-'90. Smith recognized and discovered the specific cause of the disease, and Kilborn and Salmon proved by a series of experiments that the cattle tick was responsible for the transmission of the disease from animal to animal.
_The specific cause_ of tick fever is a protozoan parasite, _Piroplasma bigeminum_ (Fig. 122). It is present in the blood of cattle that are affected with this disease. The natural method of entrance into the body is through the bite of the cattle tick. The disease may be transmitted by inoculating blood containing the parasite into a susceptible animal.
There are two forms of the disease, the _acute_ and _chronic_.
_The symptoms of the acute form_ of the disease are a high fever, depression, loss of appetite, diarrhoea, dark or bloody urine, staggering gait and delirium. Death may occur within a few days from the time the first symptoms are manifested.
_The symptoms of the chronic form_ of the disease resemble the acute form, but are more mild. The animal is unthrifty and loses flesh rapidly. The bloodless condition of the body is manifested by the pale, visible mucous membrane. Death seldom occurs.
[Illustration: FIG. 122.--Blood-cells with _Piroplasma bigeminum_ in them.]
The most characteristic _diseased changes_ found on post-mortem examination occur in the liver and spleen. The liver is enlarged, and a yellowish, mahogany-brown color. The gallbladder is filled with a very thick bile. The spleen may be several times the normal size and dark colored. When it is cut into, the pulpy tissue may resemble thick, dark blood. The kidneys are pale and the bladder may contain dark or reddish-colored urine.
In the northern States and outside of the quarantined area, the direct or indirect exposure of the affected cattle to southern cattle, and the presence of the cattle tick, _Margarophus annulatus_, are sufficient evidence to confirm the diagnosis of this disease.
_The prevention and control_ depend on destruction of the cattle tick. In the early history of the disease, shipping and driving of southern cattle into and through the northern States caused outbreaks of tick fever and heavy losses among northern cattle. This finally resulted in the locating of the infected district, and the establishment of the Texas-fever quarantine line in 1891 by Dr. D. E. Salmon.
Previous to this time Kilborne and Salmon proved that the cattle tick was essential to the spread and production of the disease. A further study of the life history of the tick resulted in the discovery that it could not mature unless it became a parasite of horses, mules, or cattle. This has led to the eradication of the tick in certain sections of the South, by not allowing cattle access to a pasture or lot for a certain period, and by freeing the animals from ticks by hand-picking, dipping and smearing.
The immunization of cattle that are shipped into an infected district for breeding purposes is often practised. Immunity is obtained by introducing the P. bigeminun into the blood, either by placing a few virulent young ticks upon the animal, or by repeated inoculation with a very small quantity of virulent blood.
QUESTIONS
1. Give the cause and treatment of actinomycosis.
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.
_The treatment is both preventive and curative_. The preventive treatment consists in quarantining newly purchased birds until we are satisfied that they are free from disease. The occasional disinfection of the poultry houses and runs is highly important. Cleaning the poultry house by removing the floor, roosts, or any part of the house for the purpose of removing all filth, and spraying the interior with a three per cent water solution of a cresol disinfectant, should be practised. Lime should be scattered over the runs, or the yards immediately about the house. The above preventive measures form an important part of the care and management of the flock.
The carcasses of the dead birds should be burned. It is advisable to kill all birds that are fatally sick.
All of the flock should be given antiseptics with the feed and water. Four ounces of a water solution of copper sulfate, made by dissolving one-quarter pound of this drug in one gallon of hot water, may be added to each gallon of drinking water. Frequent disinfection of the drinking fountains, feeding places and houses should be practised.
DISEASES RESEMBLING FOWL CHOLERA.--There are a few diseases, such as septicaemia, limber neck and infectious enteritis, that are sometimes mistaken for fowl cholera. These diseases are caused by different microorganisms that may be found in the digestive tract and air-passages of healthy birds, insanitary conditions and decomposed feed, especially meat.
It seems that under certain conditions, such as insanitary quarters and birds that are low in constitutional vigor and weakened from other causes, certain germs may become disease-producers. The death rate from mixed infections is very heavy in poultry.
_The symptoms_ vary in the different cases. The disease may be highly acute, as in limber neck, or chronic, extending over a period of a week or more. Diarrhoea is not a prominent symptom in the majority of cases.
The post-mortem lesions vary from a hemorrhagic to a chronic inflammation of the different body organs and serous membranes.
_The treatment_ is preventive. A frequent cleaning and disinfecting of the poultry house and surroundings, avoiding the feeding of spoiled feed, or allowing the drinking fountains and feeding places to become filthy, are effective preventive measures. Sick birds should be either isolated and quarantined, or destroyed. Antiseptics may be given with the feed and drinking water.
AVIAN DIPHTHERIA (ROUP).--This infectious disease of poultry is especially common in chickens. It is characterized by a catarrhal and diphtheritic inflammation of the mucous membranes of the head.
_The specific cause of roup_ has not been determined. The disease-producing germs are present in the discharges from the nostrils, eyes and mouth, and the body excretions of sick birds. Birds having a mild form of roup, or that have recently recovered from it, are common carriers of the disease.
The disease is usually introduced into the flock by allowing birds exposed at poultry shows, or recently purchased breeding stock from an infected flock, to mix with the healthy birds.
_The predisposing causes_ are very important factors in the development of roup. Cold, damp, draughty, poorly ventilated poultry houses cause the disease to spread rapidly and become highly acute.
_The symptoms_ differ in character in the different outbreaks of the disease. Usually the first symptoms noticed are sneezing, dulness, diminished appetite and a watery discharge from the nostrils and eyes.
Later the eyelids may become swollen and the nostrils plugged by the discharge from the inflamed membranes. If the mouth is examined at this time, an accumulation of mucus and patches of diphtheritic or false membranes are found. In the acute form of roup the false membranes and yellowish, cheesy-like material accumulate on the different mucous membranes, and interfere with vision, breathing and digestion. The affected bird becomes thin and weak. The death rate is very high in this form of the disease.
_The preventive treatment_ consists in quarantining birds that have been purchased from other flocks, and that have been exhibited, for a period of three weeks. A careful examination of the mouth should be made. If a catarrhal discharge from the nostrils and false membranes is present, prompt treatment should be used. A sick bird should be held in quarantine for several weeks after it has recovered, and receive a thorough washing in a two per cent water solution of a cresol disinfectant before allowing it to mix with the healthy birds.
The medicinal treatment consists in removing the discharges from the nostrils and eyes with pledgets of absorbent cotton that are soaked with a four per cent water solution of boric acid. Among the common treatments mentioned are boric acid and calomel, equal parts by weight, blown into the nostrils and eyes with a powder blower. Water solutions of boric acid, potassium permanganate and hydrogen peroxide are recommended. Liquid preparations are applied with pledgets of cotton, oil cans, or atomizers.
Many recoveries can be obtained with careful treatment. It is usually most economical to kill the severely affected birds. Many poultrymen dispose of the entire flock as soon as the disease makes its appearance, and clean and disinfect the premises before restocking.
CHICKENPOX.--In some sections the disease appears in another form, known as _chickenpox_ (contagious epithelioma), in which nodules form on the skin along the base of the comb and other parts of the head, or both forms may be met with in the same flock. The nodules should be treated with vaseline, or glycerine ointments containing two per cent of any of the common antiseptics or disinfectants.
ENTERO-HEPATITIS. "BLACKHEAD."--This is a very fatal disease of young turkeys. Grown turkeys and other fowls are not so susceptible to the disease. It is characterized by an inflammation of the liver and intestines, especially the caeca.
_The specific cause_ is a protozoan microorganism, _Amoeba meleagridis_.