Newcastle is a disease that can exist in several degrees of severity. The U.S. accepts the presence of the milder form of the virus, termed lentogenic, and that is why all commercial chicken flocks are vaccinated with live B-1 and LaSota Newcastle vaccines, and sometimes killed oil-emulsion vaccines for long-lived flocks, such as layers and breeders. These lentogenic viruses cause only mild respiratory symptoms and no mortality. Viruses of somewhat more virulence are termed mesogenic, and those cause some moderate symptoms, but little mortality. The most severe form of Newcastle is termed velogenic, and those viruses cause severe illness and high death losses.
Traditionally, those viruses have been further subdivided into VVND (viscerotropic velogenic Newcastle disease, meaning those involving mostly the internal organs) and NVND (neurotropic velogenic Newcastle disease, meaning those involving mostly the nervous system). Now, all velogenic viruses are classified together under the term, exotic Newcastle disease, or END. Viruses isolated from clinical cases are characterized by standardised bird inoculation tests and newer molecular methods to determine which of these three virulence types they represent.
Exotic Newcastle disease is caused by a virus that can infect and damage a wide variety of organs in the bird. While the mild viruses are more limited to the respiratory and digestive systems, the exotic viruses invade essentially the entire body, leading to severe multi-system illness and death. High rates of mortality are usually accompanied by symptoms involving the respiratory, digestive, and nervous systems. Respiratory distress (coughing, laboured breathing) and lesions of excess mucus and redness in the trachea could be confused with other common respiratory diseases, such as infectious bronchitis, mycoplasmosis (MG), infectious laryngotracheitis (ILT), influenza, or coryza.
Affected birds typically have a greenish diarrhea and the intestinal tract can show hemorrhagic or necrotic areas that could resemble coccidiosis or bacterial enteritis. Birds that survive longer can develop neurological symptoms such as twisted heads and inability to stand.
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Article made possible through the contribution of Hy-Line International.