Newcastle Disease in Poultry

Newcastle disease virus, synonymous with avian paramyxovirus type 1 (APMV-1) (current taxonomic name: Orthoavulavirus javaense), is an RNA virus. As a pathogen for poultry, APMV-1 is the most important of the 28 known APMV serotypes.

The original classification of NDV isolates into one of three pathotype groups based on their pathogenicity in chickens—as virulent (velogenic), moderately virulent (mesogenic), or of low virulence (lentogenic)—has been abbreviated for regulatory purposes. Velogens and mesogens are now classified as virulent NDVs (vNDVs), the cause of Newcastle disease and reportable infection. Infections with lentogens (low-virulence NDVs, or loNDVs), some of which are widely used as live vaccines, are not reportable.

The severity of NDV infection depends on virus virulence; virus tropism; and age, immune status, and susceptibility of the host species. External factors such as stress, environmental temperature, and season have a lesser impact on the course of Newcastle disease.

Of domestic poultry, chickens are the most susceptible to NDV infection, and waterfowl are the least susceptible; however, some differences might be observed if the NDV strain is adapted to a particular species. NDV infects susceptible birds through the respiratory or digestive tract when they inhale contaminated dust or aerosolized virus, or when they ingest contaminated materials.

In field outbreaks of Newcastle disease, the incubation period varies from 4 to 6 days; however, clinical signs can appear as early as 2 days and as late as 15 days after infection.

Virulent Newcastle disease strains are endemic in poultry in most of Asia, Africa, Mexico, and some countries of South America. Other countries, including the US and Canada, are free of those strains in poultry and maintain that status with import restrictions, active surveillance and monitoring, and culling of infected poultry and susceptible birds within infected premises or zones. Outbreaks of Newcastle disease in Europe occur occasionally and are handled similarly to the way the US and Canada handle them.

Cormorants, pigeons, and psittacine species can be infected with vNDV and occasionally have also been sources of vNDV infections in poultry. Low-virulence NDV strains are prevalent in free-living wild birds, live bird markets, and poultry, especially waterfowl.

Migratory waterfowl and Charadriiformes (shorebirds) can be infected with loNDV and vNDV and can shed NDV without any apparent clinical signs of Newcastle disease. Infection of domestic poultry with naturally circulating loNDV can contribute to respiratory distress in young naive birds and to lower productivity in adult birds.

Birds infected with Newcastle disease virus shed the virus in exhaled air, respiratory discharge, and feces. Virus is shed during the incubation period, during the clinical stage, and for a varying, but limited, period during convalescence. NDV can also be present in all parts of the carcass and in eggs laid during acute vNDV infections.

The role of vertical NDV transmission is unclear and disputable because hatchlings can become infected via contaminated feces, eggshells, or environment. Chickens are readily infected by inhaling aerosols and by ingesting contaminated water or feed. Infected chickens and other domestic and wild birds can be sources of NDV.

NDV is transmitted mainly via the following modes:

• movement of infected birds (poultry; wild, exotic, and companion birds; racing and show birds)

• movement of poultry products

• movement of people and contaminated equipment or litter (the main mode of virus transmission between poultry flocks and farms)

Movement of contaminated feed and vehicles plays a lesser role in NDV transmission but has been documented (1).

There are no pathognomonic clinical signs for Newcastle disease. Onset in unvaccinated birds is rapid, and signs appear throughout the flock as early as 2 days (average 4–6) after aerosol exposure to Newcastle disease virus. Transmission of the disease is slower if the fecal-oral route is the primary means of transmission, particularly for caged birds. Young birds are the most susceptible.

Observed clinical signs of Newcastle disease depend on whether the infecting virus has a predilection for the respiratory and digestive systems (viscerotropic) or for the nervous system (neurotropic).

Clinical signs of infection with viscerotropic velogenic NDV in chickens include the following:

• lethargy

• inappetence (anorexia)

• respiratory distress (sometimes birds make a whistling sound; refer to whistling sound recording)

• clear mucus discharge from the mouth

• prostration

• sudden death (sometimes the only finding)

• up to 100% morbidity and mortality rates, especially in naive populations

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Newcastle disease, respiratory distress, whistling sound, adult chicken

In some Newcastle disease cases, periorbital and head edema develop (see typical signs image). The comb can become blue as a result of hypoxia, and some NDV strains cause hemorrhage. Birds that do not die within several days after infection might have watery greenish diarrhea and show neurological signs including tremor, torticollis, and opisthotonos (especially in vaccinated poultry).

Newcastle disease, typical signs, chickens

Image

Typical signs of Newcastle disease in chickens. A. Lethargy in a young chicken. B. Necrotic/hemorrhagic areas of comb in a young chicken. C. Lethargy with periorbital edema in an adult hen. D. Head swelling in an adult hen.

Courtesy of Southeast Poultry Research Laboratory of the USDA Agricultural Research Service. Images by Dr. Kiril M. Dimitrov.

Newcastle disease can cause egg production to be interrupted or to stop completely. Eggs might be abnormal in color, shape, or surface and have watery albumen (which might be the only clinical sign in fully vaccinated hens).

Birds well vaccinated against Newcastle disease might appear clinically normal aside from decreased egg production; however, these birds shed virus in saliva and feces. Poorly and suboptimally vaccinated birds might develop neurological signs 10–14 days after infection and might recover.

Clinical findings of infection with neurotropic velogenic NDV in chickens include respiratory distress with sneezing, coughing, and nasal discharge. Respiratory signs might accompany neurological signs but usually come after neurological signs, which include the following:

• tremors and seizures

• paralysis of wings and legs

• torticollis

• circling with clonic spasms

• complete paralysis

• up to 100% morbidity and 50% mortality (up to 90% in young birds)

Clinical signs of mesogenic NDV infection of chickens include the following:

• respiratory signs with gasping, coughing, sneezing, and rales in young birds

• decrease in egg production, which returns to normal in a few weeks

• neurological signs in protracted cases

• low mortality rate (which might be higher in young birds)

Infections with loNDVs vary from subclinical to mild respiratory signs at onset; however, secondary infections can exacerbate the clinical presentation. Although adult birds commonly are subclinically affected, young birds might show gasping, coughing, sneezing, and rales.

Clinical signs of Newcastle disease in turkeys largely resemble those in chickens but often are milder. A decrease in egg production is typical, and eggs have soft shells and abnormal shape (see abnormally shaped eggs image).

Newcastle disease, abnormally shaped eggs, chickens

Image

Chicken eggs with abnormal shape—an asymmetrical teardrop shape with irregular contours. This shape is not pathognomonic; eggs from chickens with Newcastle disease show a variety of shell shape and texture abnormalities.

Courtesy of Southeast Poultry Research Laboratory of the USDA Agricultural Research Service.

Conjunctivitis, rhinitis, dyspnea, diarrhea, and neurological signs (tremors, ataxia, and torticollis) are typical in pigeons infected with vNDVs (see torticollis image).

Newcastle disease, torticollis, pigeon

Image

A pigeon with torticollis, which often occurs with virulent Newcastle disease virus infection.

Courtesy of Dr. Kiril M. Dimitrov.

The mortality rate due to NDV infection in pigeons is commonly 40%, but 80–90% has been reported from experimental studies (2). Infection in cormorants and exotic birds (particularly psittacines) is characterized by leg and wing paralysis and an inability to fly. Infection of chickens with some pigeon- or cormorant-adapted NDV strains can lead to neurological clinical signs but is subclinical in most cases.

Lesions of Newcastle Disease in Poultry

Remarkable Newcastle disease gross lesions typically are present only in infections with viscerotropic velogenic NDVs. Petechiae can occur on the serous membranes; hemorrhages of the proventricular mucosa and intestinal serosa are accompanied by multifocal necrotic hemorrhagic areas on the mucosal surface of the intestine, especially at lymphoid foci such as cecal tonsils and Peyer's patches. Splenic and thymic necrosis, hemorrhages, and edema can also occur. Hyperemia and mild multifocal petechial hemorrhages can be observed in the meninges of the encephalon in chickens infected with cormorant-adapted NDV strains (see VNDV infection images).

Virulent Newcastle disease virus infection, lesions, chickens

Image

Necropsy photographs of tissues from chickens infected with virulent Newcastle disease virus (vNDV). A. Hemorrhages and necrosis of intestines (longitudinal section). B. Hemorrhages in proventricular mucosa. C. Intact small intestine with hemorrhages. D. Enlarged, mottled spleen with multifocal necrosis. E. Necrotic, hemorrhagic cecal tonsils. F. Hyperemia and mild multifocal petechial hemorrhages in the meninges of a chicken's encephalon due to infection with cormorant-adapted vNDV.

Courtesy of Southeast Poultry Research Laboratory of the USDA Agricultural Research Service. Images by Dr. Kiril M. Dimitrov.

In chickens, congestion and hemorrhage of the trachea and lung can occur with velogenic viscerotropic NDV infection. Egg yolk peritonitis with atrophied follicles can occur in laying birds. In contrast, lesions in birds infected with loNDV strains might be limited to congestion and mucoid exudates present in the respiratory tract, with opacity and thickening of the air sacs. Secondary bacterial infections increase the severity of respiratory lesions.

• Isolation of Newcastle disease virus

• Detection of virulent virus RNA

• Detection of virus-specific antibodies

The clinical signs and gross lesions due to infection with virulent Newcastle disease virus are not pathognomonic and therefore cannot be used alone for diagnosis of Newcastle disease. Laboratory confirmation is required.

NDV can be isolated from oropharyngeal or cloacal swabs or from tissues from infected birds by inoculation of the allantoic cavity in specific-pathogen-free (SPF) embryonated chicken eggs 9–11 days old.

NDV infection is confirmed by recovery of a hemagglutinating virus that is inhibited with NDV antiserum or by detection of NDV RNA by real-time RT-PCR assay. Real-time RT-PCR can be used to detect viral RNA directly from clinical samples (swabs, tissues, feces, and discharges), and the assay can discriminate vNDV from loNDV.

In the absence of recent vaccination, an increase in NDV antibody titer detected by hemagglutination inhibition or by ELISA of paired serum samples indicates NDV infection. To confirm diagnosis, identification of an isolate as vNDV is established by how quickly day-old SPF chicks inoculated via the intracerebral route die, by the intracerebral pathogenicity index, or by genomic sequencing and identification of a specific amino acid motif at the cleavage site of the fusion protein precursor.

Reference laboratories use nucleotide sequence analysis to detect genetic differences (genotypes) for comparison of isolates from different Newcastle disease outbreaks and to identify the source of those infections.

The acute form of Newcastle disease should be differentiated from other diseases known to cause high mortality rates with sudden death, or lethargy and respiratory signs, such as highly pathogenic avian influenza.

Among suboptimally vaccinated birds in which the onset of clinical signs is not rapid and the mortality rate is not very high, the mild forms of NDV and infections need to be differentiated from the following diseases:

• infectious bronchitis

• infectious laryngotracheitis

• avian metapneumovirus

• infectious coryza

• mycoplasmosis

• fowl cholera

• aspergillosis

• Biosecurity

• Vaccination

No medication has been shown to affect the course of virulent Newcastle disease virus infection, and treatment with antivirals is not recommended. In cases of poultry flocks affected by loNDV, supportive care with antimicrobials against secondary infections can alleviate clinical signs and decrease morbidity and mortality rates.

Prevention of Newcastle disease is achieved through biosecurity and vaccination.

All Newcastle disease virus strains can produce transitory conjunctivitis in humans; however, the condition has been limited primarily to laboratory workers and vaccination teams exposed to large quantities of virus.

Before poultry vaccination was widely practiced, conjunctivitis from NDV infection occurred in crews eviscerating poultry in processing plants. The disease has not been reported in people who rear poultry or consume poultry products.

• Newcastle Disease. Center for Food Security & Public Health. Last updated January 2016.

• Virulent Newcastle Disease. Animal and Plant Health Inspection Service, USDA. Last modified July 30, 2025.

• Virulent Newcastle Disease Emergency Response. Animal and Plant Health Inspection Service, USDA. Last modified December 21, 2025.

• Suarez DL, Miller PJ, Koch G, Mundt E, Rautenschlein S. Newcastle disease, other avian paramyxoviruses, and avian metapneumovirus infections. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald CR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020;111-166.

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