Newcastle Disease

Newcastle disease, a serious disease of poultry in many other countries, has been identified in several widely separated areas in the United States. Fortunately the disease has thus far caused relatively light losses here, although extremely heavy losses have been suffered in the Dutch East Indies, Korea, the Philippines, Ceylon, India, Kenya, the Middle Congo, parts of the European Continent, and Palestine. England and Australia have twice succeeded in eradicating the disease through rigid quarantines, prompt slaughtering of infected birds, and thorough cleaning of infected premises. In other countries the disease has spread alarmingly.

In 1944, a comparatively mild disease in California that caused symptoms resembling infectious bronchitis and laryngotracheitis, but was frequently complicated by nervous symptoms such as paralysis, proved to be a form of Newcastle disease. It spread rapidly and caused the greatest mortality in chicks, but it affected birds of all ages, including turkeys. Egg production in previously thrifty laying flocks suddenly dropped to low levels.

The disease, referred to earlier as a "respiratory nervous disease," or pneumoencephalitis, had apparently been present in California for several years. Its true nature remained unidentified until samples of the virus causing it were examined at Harvard University in 1944 by a group of specialists working under the direction of a War Department commission. Shortly thereafter the disease was identified in New Jersey and New York. It is known to have occurred in about 27 States, and there are strong suspicions of its existence elsewhere in the country. It cannot be said with certainty that any section of the country has escaped.

The apparent spread of the disease, and its potential hazard to the Poultry industry led to several regional conferences of animal-disease specialists, and a conference of poultry pathologists, State livestock sanitary authorities, and poultrymen from all parts of the country with Department officials in 1946. We decided to collect all the information we could about the disease and methods for its control. Poultrymen, veterinarians, and regulatory officials were warned to be on the alert.

Because of its similarity to other diseases, there may be considerable difficulty in making an exact diagnosis, which is possible only by technical examinations in the laboratory. Newcastle disease has certain aspects, however, that should arouse the poultryman's suspicions and lead him to report the facts promptly to a poultry pathologist and State veterinary authorities.

The incubation period may vary up to 2 weeks and sometimes longer. The average is generally placed at 5 days. The onset of the disease is usually sudden, and it spreads rapidly in the flock. In rare instances, death may occur before symptoms are observed. In the United States, the mortality rate has been less than 20 percent in most outbreaks, but in some instances the death rate, especially among young birds, has been alarming.

Respiratory symptoms, quite similar to those of infectious bronchitis and laryngotracheitis, are seen in Newcastle disease as it has occurred in the United States. Affected birds generally exhibit dullness, droopiness, weakness, slowness, lack of appetite, ruffled feathers, coughing, sneezing, rattling sounds in breathing, sleepiness, diarrhea, and fever. There may be a discharge of mucus from the nostrils; the accumulations lead to frequent swallowing and shaking of the head. A dark discoloration and swelling of the head may occur. Chicks usually emit a rapid, low, cheeping sound.

Egg production is sharply reduced. Affected flocks that survive generally seem to improve markedly after a week or 10 days, but decreased egg production continues for 4 to 8 weeks or longer. It has been reported that during this interval the laying of abnormal eggs, including some with soft shells, inferior quality of albumin, or bubbly contents, is not uncommon. At the same time, the birds are apt to go into a heavy moult. Younger birds, even though they appear to have recovered from the disease, are apt to develop poorly.

The nervous symptoms vary considerably. Sometimes they are absent. Weakness, progressing to paralysis, involves the legs and wings. Attacks like epilepsy may occur. Distortions of the neck, either downward, upward, or lateral, appear. Periodic shivering, twitching, incoordination, convulsive seizures, circling, backing up, and curling of the toes are common evidences of involvement of the nervous system. Such signs may develop abruptly or occur secondarily in birds that are apparently recovering. Paralyzed birds may live for several weeks, but most of them eventually die.

Post-mortem examination may reveal various changes, usually of little diagnostic significance. A catarrhal condition of the trachea, with accumulations of clear or yellowish mucus, or cheeselike material, occurs frequently. Cloudiness of the air sacs is common in chicks. Birds dying of the nervous type of the disease generally have no distinctive lesions.

Years have elapsed since Newcastle disease was last identified in either England or Australia. The procedure followed was the radical one of destruction of all affected birds, followed by thorough cleaning and disinfection of all infected premises before restocking was permitted. Rigid quarantines and control of all movements of chickens and other barnyard fowl were imposed. These means have also been used successfully in the United States in the eradication of European fowl plague. Such measures have been applied successfully with other highly contagious maladies when the diseases have been recognized early after their first appearance and before they have spread materially. The present situation is somewhat different in that the infection has been prevalent for a number of years and has apparently become widespread. Sanitary authorities have been reluctant to adopt the slaughter program as a general procedure, although they agree it may be the best procedure in isolated outbreaks.

Vaccination against Newcastle disease is still in the experimental stage, although rather extensive field trials have been carried out in California. Limited commercial production of vaccine was begun in 1945.