Newcastle Disease

Additional scientific description

Human

Newcastle disease virus (NDV) is capable of infecting humans, causing a mild transient conjunctivitis which is self-limiting with no permanent effect, however, no human-to-human transmission has been reported. Conjunctival infection usually occurs due to physical introduction into the eye by operatives manipulating vaccines prior to vaccination of birds, usually with a finger or by splashing vaccine (WOAH, no date).

Animal

Newcastle Disease (ND) is a highly impactful poultry disease that affects livelihoods and food security and has zoonotic potential (WOAH, 2024a; WOAH, 2024b; WOAH, 2024c). Outbreaks can severely impact village chickens in developing countries, where poultry serves as a vital protein source and ND remains endemic (FAO, 2004). However, it is preventable through control measures, including vaccination. A wide range of ND vaccines is available worldwide, including both live and inactivated (killed) vaccines. Most countries maintain a list of approved veterinary vaccines for use. For specific regulations, consult the country's veterinary authorities.

Newcastle disease (ND) is one of the most important diseases in poultry worldwide and is endemic in many parts of the world. It causes devastating losses to the poultry industry, whilst impacting food security in many countries. It is caused by the Newcastle disease virus (NDV), which belongs to the avian orthoavulavirus type 1 (AOAV-1) serotype and is a member of the Paramyxoviridae family.

Although chickens appear to be the most susceptible domestic species to NDV, the virus is capable of infecting a wide range of avian species, such as ducks and other species can act as reservoir hosts, such as Columbiformes (including pigeons and doves) which may be significant in the spread and transmission of disease. NDV is capable of infecting humans, causing a mild transient conjunctivitis which is self-limiting with no permanent effect, however, no human-to-human transmission has been reported. Conjunctival infection usually occurs due to physical introduction into the eye by operatives manipulating vaccines prior to vaccination of birds, usually with a finger or by splashing the vaccine.

The disease is exhibited in five forms; highly virulent infection with haemorrhagic lesions in the intestinal tract; neurotropic causing high mortality following nervous signs; respiratory and sometimes nervous signs with low to moderate mortality; mild respiratory and/or unapparent enteric infection and avirulent asymptomatic. The mode of transmission from bird to bird is dependent on the tropism of the virus, with birds that show respiratory disease, shedding the virus in droplets and aerosolised mucus which may be inhaled by susceptible birds. Viruses restricted to replication in the gastrointestinal tract may be transferred by ingestion of contaminated faeces either directly or in contaminated food or water or by the inhalation of small infective particles produced in dried faeces. The clinical signs vary from loss of appetite, coughing, gasping, nasal discharge, watery eyes, bright green diarrhoea and nervous signs such as paralysis and convulsions. Combs and wattles may look swollen, enlarged and discoloured (purple or blue), reduced egg production with the few eggs that produced being soft-shelled and malformed.

Humans have a central role in the spread of NDV, mainly through the movement of live birds, fomites, personnel and poultry. It is important to note that NDV is capable of infecting humans, causing a mild transient conjunctivitis which is self-limiting with no permanent effect, however, no human-to-human transmission has been reported. Conjunctival infection usually occurs due to physical introduction into the eye by operatives manipulating vaccines prior to vaccination of birds, usually with a finger or by splashing the vaccine.

For these reasons, control and eradication of the disease presents significant challenges to the poultry industry worldwide, and therefore the use of vaccination has been applied for many decades as an important control tool.

The commercial vaccines can be broadly divided into live attenuated vaccines and inactivated vaccines. Live attenuated vaccines vary in their relative tropism for respiratory, enteric and nervous systems, they are controlled however to prevent adverse clinical side effects. There are many aspects of vaccine specification that should be considered in the context of the epidemiological situation where it will be used. A detailed account of all aspects of ND vaccines, including their production and use has been published (Allan, Lancaster, & Toth 1978). The fundamental considerations should be for safety, quality and efficacy.

Metrics and numeric limits

FAO considers that, in many respects, it is extremely difficult to assess the prevalence of NDV in the world at any given time. In some countries or areas disease is not reported at all or only if it occurs in commercial poultry, while its presence in village chickens or backyard flocks is ignored (FAO, no date).