Newcastle disease has for several years been recognized as a leading cause of loss to poultry farmers, it’s deadly to birds. In laying birds, Newcastle disease may cause a temporary stoppage of egg production lasting 4-6weeks.
It is one of the major diseases of poultry, present in almost every country in the world and causing economic losses because of high levels of mortality, decreased production and trading embargos.
Newcastle Disease is a highly contagious viral infection that affects many species of domestic and wild birds to varying degrees. Domestic fowl, turkeys, pigeons and parrots are most susceptible while a mild form of the disease affects ducks, geese, pheasants, quail and guinea fowl.
The disease can result in digestive, respiratory and/or nervous clinical signs, which range from a mild, almost inapparent respiratory disease to very severe depression, drop in egg production, increased respiration, profuse diarrhoea followed by collapse, or long-term nervous signs (such as twisted necks), if the birds survive. Severe forms of the disease are highly fatal.
Newcastle disease is a highly contagious disease of birds caused by a para-myxo virus. Birds affected by this disease are fowls, turkeys, geese, ducks, pheasants, partridges, guinea fowl and other wild and captive birds, including ratites such ostriches, emus and rhea.
Humans aren’t normally affected, but people in direct contact with infected birds may develop a very short-term eye infection, which passes without treatment.
Causes of Newcastle Disease
Newcastle Disease is caused by a paramyxovirus that can vary in pathogenicity from mild to highly pathogenic. Spread is usually by direct physical contact with infected or diseased birds. The virus is present in manure and is breathed out into the air.
Other sources of infection are contaminated equipment, carcasses, water, food and clothing. People can easily carry the virus from one shed or farm to another. Newcastle Disease virus does not affect humans in the same way that it does birds but it can cause conjunctivitis in humans.
Mode of transmission
It is airborne and spread by inhalation or ingestion of virus. Free-flying birds maybe infected with lentogenic viruses and can spread them readily. Exotic birds and backyard birds from tropical areas are also commonly infected with velogenic viruses.
The disease is transmitted through infected birds’ droppings and secretions from the nose, mouth and eyes. The disease is spread primarily through direct contact between healthy birds and the bodily discharges of infected birds. Virus-bearing material can also be picked up on shoes and clothing and carried from an infected flock to a healthy one.
Possible routes of transmission therefore include contact between poultry and also through movements of contaminated vehicles, equipment, manure, feed and water.
The virus can survive for several weeks in a warm and humid environment on birds’ feathers, manure, and other materials.
The disease is spread by direct contact with bodily fluids of infected birds, especially their faeces and aerosol contact.
Symptoms of Newcastle Disease
These symptoms are usual in chicks and adult birds for instance: gasping, coughing and rattling in the windpipe, followed in 1 or 2days by characteristic nervous symptoms such as paralysis of legs or wings, twisting of head and neck.
On post mortem examination, there is nothing to differentiate Newcastle disease form other respiratory disease because the windpipe may contain excessive mucus, except the presence of hemorrhage in the proventriculus and cecal tonsils.
The three forms of Newcastle disease are categorized on the basis of the severity of their clinical signs.
- The lentogenic form is mildly pathogenic.
- The mesogenic form is moderately pathogenic.
- The velogenic form, or VVND, is highly pathogenic.
Mortality can range from 10% to 80% depending on the virus strain.
Newcastle disease is characterized by a sudden onset of symptoms, which include hoarse chirps (in chicks), watery discharge from the nostrils, labored breathing (gasping), facial swelling, paralysis, trembling, and twisting of the neck.
The twisting of the neck, or torticollis, is a sign that the central nervous system is affected. In adult laying birds, symptoms also include decreased feed and water consumption and a dramatic drop in egg production.
The clinical signs in affected birds can vary. The disease can be present in a very acute form with sudden onset and high mortality or as a mild disease with respiratory distress or a drop in egg production as the only detectable clinical signs.
A sub-clinical (asymptomatic) form of Newcastle disease and many intermediate forms of the disease can also occur. The main signs are:
- Nasal discharge
- Greenish, watery diarrhoea
- Muscular tremors
- Drooping wings
- Complete paralysis
- Swelling of the tissues around the eyes and in the neck
- Sudden death
- Increased death loss in a flock
- In laying birds there can be partial to complete drop in egg production; and production of thin-shelled eggs
Prevention Measures of Newcastle Disease
Poultry farmers should give their baby chicks “Intra Ocular: (i/o) vaccines between “Day Old” to 10 days, before taking them into the farm and must increase sanitary procedures.
There is no treatment for Newcastle Disease, although treatment with antibiotics to control secondary infections may assist. The virus can remain alive in manure for up to 2 months and in dead carcasses for up to 12 months, however it is easily killed by disinfectants, fumigants and direct sunlight. Prevention relies on good quarantine and biosecurity procedures and vaccination.
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Newcastle disease is a contagious bird disease affecting many domestic and wild avian species. It is a zoonotic disease with widespread distribution. It is caused by avian Paramyxovirus serotype 1 virus which, with viruses of the other eight serotypes (avian paramyxovirus1-9), has been placed in the genus Avulavirus, sub-family Paramyxovirinae, family Paramyxoviridae.
Virulent ND virus strains are endemic in poultry in most of Asia, Africa, and some countries of North and South America. Other countries, including the United States of America and Canada, are free of those strains in poultry.
The strain of Newcastle pathogenicity can be classified into five pathotype: Asymptomatic enteric strain; Lentogenic strain; Mesogenic strain; Viscerotropic velogenic strain and Neurotropic velogenic strain.
Clinical signs are extremely variable depending on the strain of virus, species and age of bird, management, concurrent disease, and pre-existing immunity caused by Paramixovirus with worldwide distribution affecting chickens of all age groups.
The transmission of ND occurs through respiratory aerosols, exposure to fecal and other excretions from infected birds, through newly introduced birds, selling and giving away sick birds and contacts with contaminated feed, water, equipment, cannibalism and clothing.
Gasping, coughing, sneezing, rales, tremors, paralyzed wings and legs, twisted necks, circling; colonic spasms and complete paralysis are the clinical pictures of the disease. Newcastle disease may cause conjunctivitis in humans, when a person has been exposed to large quantities of the virus.
The objective of this review is, therefore, to understand the epidemiology, clinical signs, diagnosis, prevent and control of Newcastle disease in poultry.
Read Also: Vaccination Program for Poultry Chickens
The Newcastle virus is a member of the family Paramyxoviridae, genus Avulavirus. There are ten serotypes, but only serotype 1 causes Newcastle disease (APMV-1). Below is a representation of the virus.
Live vaccines are very important for the control and prevention of Newcastle disease, to provide local protection and prime for the inactivated vaccine. When choosing the live vaccine strain, we face a dilemma, reaction versus protection.
Normally the best protection comes with undesirable post-vaccine reactions, whilst the vaccines with a reduced post-vaccine reaction provide more limited protection.
To analyse the protection of the vaccine and the reaction, it is important to understand a few points:
- The method of vaccination: Ideally, the best method of vaccination for Newcastle vaccines are spray or eye drop. It is very important to check the size of the droplets, as fine drops can cause reactions. The ideal droplet size is between 160 – 180 μ
- The performance of the vaccination: Regardless of the method of vaccination chosen, it is important to carry it out correctly. In the case of poor performance of the vaccination, it is possible for a “rolling effect” to occur: if the vaccination does not reach all the birds at the same time, some of the birds will have contact with the vaccine virus later on, causing a reaction.
- Maternal antibodies: In the case of Newcastle vaccination, maternal antibodies are important in order to minimise any vaccine reaction and to give the birds humoral protection until the inactivated vaccine takes effect.
- Choice of strain: As mentioned before, the less reactive strains will confer limited protection and strains that are more reactive will provide better protection. The process of choosing will have to take account of the pressure of infection in the region. Normally the LaSota strain is one of the most popular, as it provides good protection.
- The vaccine titre: The titre will influence control of the disease and the shedding of the virus, 10 being the minimum titre for control of clinical signs (Cornax et al., 2012), however control of clinical signs is not enough, it is important to reduce the shedding of the virus.
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