Newcastle Disease

O. L. OSTEEN.

NEWCASTLE DISEASE is a specific, highly contagious disease primarily of chickens and turkeys. Other domestic poultry, various species of wild birds, and people are susceptible to it, but in man it is usually mild and is characterized by inflammation of one eye, seldom both.

Among young chickens the loss may be as high as 100 percent. The average is usually 30 to 40 percent. The death losses may vary greatly from one outbreak to another. Chicks that survive an outbreak are retarded in growth and efficiency of feed utilization. It requires at least 2 extra weeks to finish birds in affected broiler flocks.

Turkey poults are somewhat less severely affected, but the loss among them may be 15 to 20 percent of the brood.

The death loss among laying birds usually is quite low but occasionally may be as high as 80 percent of the flock. Production and quality of eggs usually drop sharply. The disease in breeding flocks also results in lower fertility and hatchability of the eggs.

Additional losses to the poultry industry arise from the restriction on exportation of live and dressed fowl from the United States to other countries.

Dr. T. M. Doyle of England first recognized Newcastle disease as a distinct and separate disease of chickens in 1926. He discovered that the disease in a flock near Newcastle upon Tyne, England, was a virus disease, which differed from fowl pest. He named it after the town.

The disease apparently reached California about 1940, but because of its unusual nature it went unrecognized until 1944. Then the virus of the new respiratory-nervous disorder, which research workers in California called pneumo-encephalitis, was shown to be identical with the virus of Newcastle disease.

Newcastle disease was found in 1945 on the eastern seaboard first in New Jersey and New York. By 1947 the infection had been reported in 30 States. Within a year or two it had spread to every State reached by traffic in poultry and poultry products.

After Newcastle disease was first recognized as a disease of chickens, other species of poultry and birds and certain mammals were found to be susceptible to it by natural exposure.

Turkeys usually are less severely affected than are chickens. Pheasants, guinea fowls, geese, ducks, pigeons, swans, quail, sparrows, parrots, doves, owls, gannets, starlings, and martins are reported to have become infected under natural conditions. Thus these birds, as well as people, dogs, and cats, may be unrecognized or mechanical carriers and spreaders of the virus of Newcastle disease because they often show little or no evidence of the disease.

THE VIRUS that causes Newcastle disease is present in actively infected individuals and in apparently healthy carriers. It is too small to be seen except through an electron microscope. It appears to be shaped like a tadpole. About 250 thousand of them measure an inch.

Nasal secretions, saliva, and droppings of infected birds contain the virus 1 or 2 days after they are exposed to the infection. Birds that survive attacks of the disease seldom give off the virus for more than 3 or 4 weeks, but the virus has been recovered from the lungs of a few chickens 2 or 3 months after recovery.

The portion of healthy, recovered carriers of the virus is ordinarily quite low, but the persistence for a month or more of only a small percentage of carrier cases often is enough to set up new centers of infection and thus to favor spread of the disease.

The possibility of transmission of the virus from an infected hen through her egg to the hatched chick is not important in the spread of the disease few, if any, infected eggs hatch.

Conditions outside the living bird are usually unfavorable for the survival of the virus for any great length of time. When the virus is protected against heat, light, moisture, and other factors that destroy it, however, its livability may be prolonged for months.

The virus is extremely hardy at low temperatures. It can live in frozen poultry carcasses for more than 2 years. Quite resistant to heat, it can withstand a temperature of 132 F. for at least 30 minutes. On ordinary farm materials feedbags, egg flats, feathers, eggshells and such it may survive at the usual temperatures for 2 to 8 weeks.

Boiling water destroys it instantly. The usual coal tar disinfectants quickly destroy the virus.

One-percent saponified cresol, 1-percent Lysol, and 10-percent quaternary ammonium compounds are effective in 5 to 10 minutes, but are ineffective when the virus is protected by dirt, droppings, body secretions, or tissues.

Fumigation of cleaned incubators with formaldehyde as it is used against pullorum disease destroys the virus.

THE SYMPTOMS vary with the age of the bird. In chicks a few days to a few weeks old, the first symptom usually is difficulty in breathing. The birds are depressed and weak. Sometimes a marked stupor develops. Twitching of the head and neck, marked weakness, and paralysis may occur within a few days. Generally the symptoms subside rapidly, or the chicks die in a few days.

The symptoms in broilers resemble those in chicks. Apparently broilers have a greater tendency to a more lasting illness and paralysis.

The disease usually begins in older or adult birds with a drop in feed consumption and with respiratory symptoms. A characteristic symptom in laying flocks is an abrupt and almost complete interruption of egg production. Soft-shelled or rough-shelled eggs are found on the henhouse floor. Eggshells are often off color. The loss in egg production may last 4 to 8 weeks. The birds may go into a molt, which is usually much heavier than that normally observed. Paralysis is less frequent generally and the mortality is much lower in laying birds than in other groups.

The symptoms in turkeys are quite similar to those seen in chickens but generally are less severe.

Postmortem findings are variable and inconsistent. Hemorrhages are found in acute infections in the body membranes, heart, stomach, and intestine, but infrequently in less severe outbreaks. Often there is a thickening and clouding of the abdominal and thoracic air sacs, which are covered with slimy exudate. The trachea contains an inflammatory mucous exudate, but the lungs are not seriously affected. Clouding of the eyes occurs in a few birds. The spleen may be mottled, pale, and small.