Newcastle disease

Newcastle disease is a highly contagious viral disease that affects a wide variety of bird species, both domestic and wild. The disease is caused by the Newcastle disease virus (NDV), a member of the genus Avulavirus within the family Paramyxoviridae.

Etiology

The causative agent, NDV, is an enveloped, single-stranded, negative-sense RNA virus. The virus is classified into three pathotypes based on the severity of the disease: lentogenic (low virulence), mesogenic (moderate virulence), and velogenic (high virulence). The velogenic strains cause the most severe form of the disease and are further divided into neurotropic (causing neurological signs) and viscerotropic (causing intestinal lesions).

Clinical Signs

The clinical signs of Newcastle disease vary widely and depend on factors such as the strain of the virus, the age and species of the bird, and the bird's immune status. Signs can range from mild respiratory symptoms to severe neurological signs and sudden death. In chickens, the disease often presents with respiratory signs such as gasping, coughing, and nasal discharge, as well as neurological signs like tremors, paralysis, and twisted necks.

Diagnosis

Diagnosis of Newcastle disease is based on the clinical signs, post-mortem lesions, and laboratory testing. The virus can be isolated from the bird's tissues and identified using virus isolation and serological testing. Molecular techniques such as polymerase chain reaction (PCR) can also be used for rapid detection of the virus.

Prevention and Control

Prevention and control of Newcastle disease involve strict biosecurity measures, vaccination, and culling of infected birds. Vaccination is widely used in commercial poultry, but it does not prevent infection; it only reduces the severity of the disease.

Economic Impact

Newcastle disease has a significant economic impact on the poultry industry worldwide due to high mortality rates and decreased egg production in infected flocks. The disease is listed by the World Organisation for Animal Health (OIE) due to its potential for transboundary spread and significant socio-economic and public health consequences.