Exotic Newcastle Disease

Last updated September 19, 2003

Agent
Hosts
Epidemiology
Newcastle Disease As a Biological Weapon
Clinical Features
Differential Diagnosis
Laboratory Diagnosis
Treatment
Prevention
Outbreak Control
Public Health Issues
References

Agent

Newcastle disease derives its name from an outbreak near Newcastle upon Tyne, England, in 1927, which is the first recorded instance of the disease (see References: Alexander 1992). It is caused by a fatal, contagious virus that affects all species of birds and is one of the most infectious diseases of poultry in the world. Infected birds usually experience symptoms of the nervous, respiratory, and digestive systems (see References: USDA/APHIS).

The virus occurs as three pathotypes: lentogenic, mesogenic, and velogenic. The velogenic isolates can be divided into neurotropic and viscerotropic types. Velogenic isolates are considered to be exotic to the United States and are often referred to as exotic Newcastle disease (END) (see References: Beard 1998). Lentogenic and mesogenic isolates are more commonly found in the United States. END is considered an important potential bioterrorism agent.

Key features of the virus are outlined below:

RNA virus with helical capsid symmetry and nonsegmented, single-stranded genomes of negative-sense (see References: Pringle 1990)
Virus family Paramyxoviridae, genus Rubulavirus (see References: Beard 1998)

The hemagglutinin/neuroaminidase (HN) surface protein is important for serologic indentification. At least nine known types of avian paramyxoviridae exist. Type differences are based on genetic differences in the hemagglutinin.
The fusion (F) surface protein is important in pathogenesis of the disease.

Inactivated in 3 hours at 56°C or in 30 minutes at 60°C
Ether-sensitive and inactivated by formalin, phenol, and acid pH (see References: OIE: Newcastle disease: Technical disease card database)
Survival for several weeks in a warm, humid environment, such as on birds' feathers, manure, and other materials
Indefinite survival in frozen material
Destroyed rapidly by dehydration and ultraviolet rays (see References: ISDA/APHIS)
Minimum core temperature of 80°C for 1 minute will destroy the virus in meat products (see References: Queensland DPI)

Hosts

Newcastle disease can affect many species of birds, both domestic and wild:

It is most severe in chickens, peafowl, guineas, pheasant, quail, and pigeons.
It can be found in a more mild form in turkeys.
Finches and canaries may not show clinical disease (see References: Beard 1998)
Carrier states can exist in psittacine and other wild birds (see References: OIE: Newcastle disease: Technical disease card database).

Epidemiology

Transmission

Occurs through direct contact between healthy birds and the bodily discharges of infected birds, specifically feces and secretions from the nose, mouth, and eyes
Spreads rapidly among birds in confinement, such as commercially raised chickens
Can be spread by mechanical means, including contaminated shoes and clothing, from an infected flock to a healthy one
Often is spread by vaccination and debeaking crews, manure haulers, rendering-truck drivers, feed-delivery personnel, poultry buyers, egg- service workers, and poultry farm owners and employees (see References: USDA/APHIS)
Contamination of such items as feed, water, tools, premises, human clothing (see References: OIE: Newcastle disease: Technical disease card database)

Sources

Smuggled pet birds, specifically Amazon parrots from Latin America, are sometimes carriers of the disease. Carriers do not show clinical signs but are capable of shedding the Newcastle virus for more than 400 days (see References: USDA/APHIS).

In infected birds, the virus can be found in respiratory discharges and feces as well as all parts of the carcass (see References: OIE: Newcastle disease: Technical disease card database).

Occurrence

END is endemic in many countries of Asia, the Middle East, Africa, and Central and South Asia. It has also been found in Europe, Canada, and the United States (see References: Beard 1998) as well as Australia (see References: Queensland DPI). Information on specific outbreaks follows:

In 1971, a major outbreak occurred in California, infecting 1,341 flocks and resulting in the destruction of 12 million birds. Eradicating the virus cost taxpayers $56 million and took 3 years. The loss also resulted in increased costs for poultry consumers.
An outbreak occurred in Northern Ireland in 1973 affecting 26 locations in all but one county. This resulted in a policy of compulsory vaccination (see References: Leslie).
In 1999-2000, Newcastle disease swept through northern and central Italy. There were 254 outbreaks there noted through December 31, 2000, resulting in the culling of over 13 million birds. The most susceptible birds were chickens and guinea fowl, followed by pheasants, turkeys, and ostriches (see References: Capua).
Beginning in late 2002, END again invaded California. The outbreak lasted until September 2003, when the last areas of quarantine were released. More than 3.5 million birds at over 2,100 sites, including 22 commercial poultry farms (see References: OIE: Disease information update; California Department of Food and Agriculture). The expense of controlling the outbreak cost $160 million.
In early 2003, outbreaks occurred in Nevada and Arizona. The disease was quickly contained, with minimal loss of birds. Quarantines were lifted in August 2003.
In April 2003, five counties in Texas and New Mexico were quarantined by the US Department of Agriculture (USDA) after END was confirmed in a backyard flock near El Paso. By the end of April, about 1,900 birds in 31 flocks had been destroyed to contain spread of the disease (see References: Texas Animal Health Commission). The outbreak was considered well contained by early May 2003 (see References: OIE: Disease Information Update), and the quarantine was lifted in June for New Mexico and all areas of Texas by August.

Newcastle Disease As a Biological Weapon

END is of concern as a biological weapon for the following reasons:

Extremely high morbidity and mortality rates, especially in chickens (100% and 90%, respectively)
No effective treatment
Vaccination not fully effective

Clinical Features

Newcastle disease has several strains with varying pathogenicity in chickens. As such, they have been divided into five main groups:

Viscerotropic velogenic (END): Often exhibit hemorrhagic intestinal lesions; highly pathogenic
Neurotropic velogenic (END): High rate of mortality following respiratory and nervous symptoms
Mesogenic: Respiratory signs, rare nervous signs, low mortality
Lentogenic or respiratory: Subclinical respiratory infection
Asymptomatic enteric: Subclinical enteric infection

Unfortunately, birds are often simultaneously infected with multiple strains (see References: OIE: Manual of standards for diagnostic tests and vaccines). Therefore, all signs must be taken into account. In young pullets, the symptoms are often more severe and the birds are more likely to die than are older birds (see References: Manitoba Agriculture and Food). Also, the milder versions will produce severe respiratory and systemic disease in chickens already infected with infectious bursal disease, which impairs the immune system through destruction of the bursa of Fabricius (see References: Pringle 1990). The clinical features of Newcastle disease are outlined in the table below.

Clinical Features of Newcastle Disease
*Feature*	*Characteristics*
Incubation period	Usually 5-6 days, but can vary from 2-15 days
Clinical signs	—Respiratory: sneezing, gasping for air, nasal discharge, coughing, increased respiration —Digestive: greenish, watery diarrhea 2-3 days after onset of illness —Nervous: depression, muscular tremors, drooping wings, dragging legs, lack of appetite, twisting of head and neck, circling, complete paralysis, survivors often exhibit permanent neurologic signs —Egg changes: Partial to complete drop in production; eggs produced are thin-shelled, misshapen, rough-shelled and contain water albumen; in those that survive, production may never reach its former capacity —Swelling of tissues around eyes and in neck (see Gray Book figure [References: Beard 1998]) —Sudden death within 24-48 hr —Increased death loss in flock
Compiled from USDA/APHIS; OIE: Newcastle disease: Technical disease card database; OIE: Manual of standards for diagnostic tests and vaccines; Beard 1998; Queensland DPI, DEFRA (see References).

Morbidity and mortality depend on the virulence of the virus strain, the degree of immunity from previous vaccinations, environmental conditions, and the condition of the flock.

There are no pathognomonic gross lesions seen on necropsy of affected birds. However, some characteristic lesions may be seen. These usually consist of the following:

Petechial and small ecchymotic hemorrhages on the mucosa of the proventriculus, usually near the base of the papillae around the posterior and anterior orifices (see Gray Book figure [References: Beard 1998]
Edematous, hemorrhagic, necrotic, and ulcerative areas on Peyer's patches, cecal tonsils, and other aggregations of lymphoid tissue in the gut wall (see Gray Book figure [References: Beard 1998])
Edematous, hemorrhagic, or degenerated ovaries

In birds other than chickens, the clinical signs can vary. For example, older turkeys and waterfowl tend to be more resistant to the disease than chickens (see References: Manitoba Agriculture and Food). Specific examples are given below (see References: Capua):

Guinea fowl

Peracute disease
Initial depression followed by rapid increase in mortality
Possibility of 100% mortality
Few clinical signs, which may include dark green diarrhea, nasal discharge, and death preceded by paddling movement while in recumbency
Few postmortem lesions, including catarrhal tracheitis with petechial hemorrhages on the trachea and pharynx; and pinpoint hemorrhages on the proventriculus and hemorrhagic duodenitis

Pheasants

Nervous and enteric signs
High mortality rates in unvaccinated birds
Postmortem lesions including hemorrhages on the proventriculus, intestinal mucosa, and respiratory tract

Differential Diagnosis

Newcastle disease may be confused with the following diseases (see References: Newcastle disease: Technical disease card database; Beard 1998):

Highly pathogenic avian influenza
Fowl cholera
Infectious laryngotracheitis
Fowl pox (diphtheritic form)
Coryza
Psittacosis (chlamydiosis) (psittacine birds)
Mycoplasmosis
Infectious bronchitis
Pacheco's parrot disease (psittacine birds)
Management errors such as deprivation of water, air, feed

Laboratory Diagnosis

Sample Collection

The samples below should be taken in the early stages of the disease and placed in isotonic phosphate-buffered saline-containing antibiotics.

Live birds

Tracheal swabs
Cloacal swabs (or feces)

Dead birds

Pooled organ samples, including oronasal swabs and samples from the lung, kidneys, intestine (including contents), spleen, brain, liver, and heart tissues
Feces

Diagnostic Tests

In the laboratory, a series of diagnostic tests are necessary to isolate the virus and determine which pathotype is present.

Virus isolation is attempted by inoculating 9- to 11-day-old embryonating chicken eggs.
Chorioallantoic fluid (CAF) is collected from all embryos that die after 24 hours.
CAF is tested for hemagglutination (HA) activity.
Positive results are then tested with an hemagglutination-inhibition (HI) test to confirm the presence of Newcastle disease.
The pathotype is determined by inoculating 4- to 6-week-old Newcastle disease–free chicks with CAF.
If END is present, the chicks usually die in 3 to 7 days and have characteristic postmortem lesions. If no chicks die within 10 days, the virus is not considered to be velogenic.

Treatment

There is no effective treatment for Newcastle disease (see References: OIE: Newcastle disease: Technical disease card database).

Prevention

The easiest way to prevent the virus is to import birds only from disease-free flocks (see References: Alexander 1992). Newcastle disease can infect and cause death even in vaccinated poultry (see References: USDA/APHIS).

Vaccination

In general, birds are either vaccinated at 2 to 4 weeks of age when they become susceptible, or at 1 day of age via conjunctival instillation. The latter birds are revaccinated 3 to 4 weeks later. The duration of immunity depends on the vaccination program. Regardless of the initial treatment, however, vaccinations must be continued throughout the life of the bird to maintain efficacy (see References: OIE: Newcastle disease: Manual of standards for diagnostic tests and vaccines). Both live and inactivated vaccines are available:

Live vaccine

Administered via ingestion from drinking water, as well as intranasally or intraocularly by aerosol (see References: Alexander 1992)

Inactivated vaccine

Considerably more expensive than live vaccine, since each bird must be handled individually for intramuscular or subcutaneous injection (see References: OIE: Newcastle disease: Manual of standards for diagnostic tests and vaccines)
The inactivated vaccine is prepared from allantoic fluid that has been treated with formalin or beta-propiolactone to eliminate infectivity. It is then incorporated into an emulsion made with mineral salts. It can be given after the live vaccine to provide higher immunity (see References: Pringle 1990).

In May 2003, a proprietary virus–antibody complex vaccine called Newplex received marketing approval from the USDA. The vaccine is delivered into eggs before chicks hatch and can be administered automatically by machines.

Biosecurity

Because vaccines are not 100% effective in preventing Newcastle disease, vaccinated poultry can serve as reservoirs for the disease. Therefore, good management principles and biosecurity measures in commercial poultry flocks are vital.

Only allow essential workers and vehicles on premises.
Clean clothing and disinfection facilities should be provided for employees.
Vehicles entering and leaving premises must be disinfected.
Other poultry operations should not be visited.
Clean poultry houses between each lot of birds.
Do not keep pet birds on the premises or hire employees with pet birds.
Protect flock from wild birds by cleaning up spilled feed and removing wetlands near the barn.
Have only one age-group per farm ("all-in all-out" policy).
Take diseased birds to a diagnostic laboratory for examination (see References: USDA/APHIS).
Keep the tops of feed bins closed.
Chlorinate water taken from dugouts or ponds (see References: Manitoba Agriculture and Food).

Pet bird enthusiasts and backyard hobbyists can also affect the spread of Newcastle disease. These owners should:

Ensure their birds are legally imported, requesting documentation of the bird's health and safe transportation.
Isolate new purchases for 30 days, including the restriction of personnel movement between new and old birds (see References: USDA/APHIS).

Outbreak Control

Surveillance

Because vaccinated birds can be infected with END without showing severe clinical signs, infected carriers can be difficult to identify. Two systems are used to detect carrier birds.

In the first system, all birds dying during a 24-hour period are collected twice a week.

Cloacal swabs and brains are collected and cultured for the presence of VND virus using routine diagnostic procedures.

In the second virus detection system, sentinel birds are placed in vaccinated flocks. The sentinel birds have not been vaccinated for Newcastle Disease.

If virus is present in the flock, sentinel animals usually die within a week of placement.

Source: (References: Beard 1998).

Eradication

Strict quarantine and destruction of all birds infected with END is necessary to eradicate the virus from an area. Because the virus can survive well in some environmental conditions, special precautions need to be taken during the destruction of birds and subsequent environmental cleanup:

After cleaning and disinfection is complete, no birds should be reintroduced into depopulated facilities for at least 30 days.
Contaminated manure must be safely removed by:

Burying it at least 5 feet deep
Composting it

Any insects or mice that could act as potential vectors need to be destroyed prior to the destruction of birds.
Cresylics or phenolic disinfectants should be used after thorough cleaning of all surfaces and equipment.
Extremely cold temperatures can make disinfection and cleaning much more difficult.

Public Health Issues

Humans can be infected with Newcastle virus and infection generally causes conjunctivitis (see References: Pringle 1990). Most often, those affected are workers in the poultry industry or laboratory technicians who handle the virus (see References: Alexander 1992).

No instance is known of transmission to humans through handling or consumption of poultry products (see References: Beard 1998).

References

Alexander D. Paramyxoviridae,, Infection, and Immunity. In: Roitt, IM, DeWes PJ. eds. Encyclopedia of immunology. Vol 3. London: Academic Press, 1992:1203-5

Beard CW. Velogenic Newcastle disease. In: Foreign animal diseases: the gray book. Ed 6. Part IV. Richmond, VA: US Animal Health Association, 1998 [Full text]

Capua I, Dalla Pozza M, Mutinelli F, Marangon S, Terregino C. Newcastle disease outbreaks in Italy during 2000. Vet Rec 2002 May 4;150(18):565-8 [Abstract]

California Department of Food and Agriculture. Exotic Newcastle disease [Web page]

DEFRA (Department for Environment, Food & Rural Affairs). Newcastle disease [Web page]

Leslie J. Newcastle disease: outbreak losses and control policy costs. Vet Rec 2000 May 20;146(21):603-6 [Abstract]

Manitoba Agriculture and Food. Newcastle disease in laying hen flocks. May 2001 [Web page]

OIE (Office International des Epizooties/World Organization for Animal Health). Disease information update [Web page]

OIE (Office International des Epizooties/World Organization for Animal Health). Newcastle disease. In: Manual of standards for diagnostic tests and vaccines 2000. Chap 2.1.15 [Full text]

OIE (Office International des Epizooties/World Organization for Animal Health). Newcastle disease. Technical disease card database [Web page]

Pringle CR, Health RB. Paramyxoviridae. In: Collier LH, Timbury MC.Topley and Wilson's principles of bacteriology, virology, and immunity. Vol 4. Chap 4.14. Kent, England: Edward Arnold, Hodder & Sloughton, 1990:286-7

Texas Animal Health Commission. Team continues search for sick birds near El Paso; quarantines remain on five counties. Press release. Apr 17, 2003 [Full text]

USDA/APHIS (US Department of Agriculture/Animal and Plant Health Inspection Service). Exotic Newcastle disease. Jan 2003 [Fact Sheet—Note: may open slowly]


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