Situation in Austria
Newcastle disease last occurred in Austria in poultry in 1997, but is observed sporadically in wild pigeons.
Newcastle disease is a notifiable disease. The occurrence of clinically suspicious symptoms must be reported to the official veterinarian, who takes the samples and sends them for diagnosis. Only highly pathogenic virus types are notified as disease if the virus has a pathogenicity index (ICPI) of 0.7 or higher and if a velogenic (highly pathogenic) pathotype of the virus strain is detected by sequencing.
After Newcastle disease is detected, all birds in the affected holding are killed in accordance with the Animal Health Law (AHL).
The causative agent of Newcastle disease is the Newcastle disease virus (Avian Avulavirus 1, APMV-1), a single-stranded RNA virus of the family Paramyxoviridae. NDV is classified in the genus Avulavirus. Apathogenic, lentogenic (low virulence), mesogenic (low virulence), and velogenic (high virulence) virus types are distinguished. The symptoms depend on the virulence of the pathogen.
In bone marrow and muscle of slaughter poultry, NCD virus remains infectious for 6 months at -20 ⁰C and up to 134 days at 1 ⁰C. In contaminated houses, the virus remains infectious for 30-25 days depending on the ambient temperature. Drying can preserve the infectivity of the virus for years.
Transmission can be airborne, direct or via objects. The spread of the disease is favoured by the high tenacity of the virus as well as the broad host spectrum. Sources of infection are often clinically inapparent infected, diseased animals or animals in the incubation period.
NDV is excreted in large quantities via faeces, eye, nasal and pharyngeal secretions and all other body fluids. Excretion takes approximately 26 days; in vaccinated animals, approximately 40 days. The pathogens are spread directly from animal to animal as well as indirectly via all equipment, stable dust and air, shoes, and vehicles. Transovarial virus transmission plays a major role, whereby infected chicks hatch from NCD virus-contaminated eggs.
Trade in live or slaughtered poultry or their products plays a role in the introduction of the disease into disease-free regions (introduction also via frozen poultry!). Virus transmission is also possible through the feeding of kitchen waste, litter, feed, housing equipment and transport containers. In comparison, the probability of transmission via wild birds is low. With respect to wild birds, waterfowl and wild fowl are a natural reservoir for epidemics.
Newcastle disease has a worldwide distribution. Control measures have made the disease less important in recent years. In July 2018, an outbreak was reported in Belgium in domestic chickens.
Laboratory diagnosis is made by pathogen detection from tracheal/oropharyngeal swabs (throat) and cloacal swabs as well as from animal carcasses (CNS, lung, liver, kidney, heart, intestine) by specific molecular biological methods (RT-qPCR, RT-PCR and additional pathotyping) as well as by virus cultivation in egg culture followed by haemagglutination test (HA) and haemagglutination inhibition test (HAH). Detection of antibodies by ELISA and HAH is possible, but should be evaluated depending on the situation if vaccination is permitted.
Differential diagnostic in question are all diseases with:
- acutely increasing mortality
- respiratory disorders
- CNS disorders
- decrease in laying performance
- reduction of weight gain
- petechial haemorrhages on seroses
e.g. infectious bronchitis, infectious laryngitis, avian influenza, Marek's disease, fowl cholera, mycoplasmosis, deficiency symptoms. In case of the slightest suspicion, the responsible official veterinarian must send the legally required samples to the National Reference Laboratory after contacting them by telephone (+43 50555 38112, 0664 9670940). Sample type for sampling:
- Throat and cloacal swabs (no bacteriological swab transport medium).
Samples from dead animals:
- Organ material especially brain, lung, liver, kidney, heart, intestine.
- Specimen transport and short-term storage: at +4 °C
Detection methods according to OIE
Direct pathogen detection:
- Rapid diagnosis: quantitative RT PCR, conventional RT PCR.
- Pathotyping by sequencing: determines whether the virus is highly pathogenic or low pathogenic
- Virus detection by egg culture and haemagglutination: pathogen detection is performed by inoculating organ suspensions from the brain, lungs, liver, kidney and heart of diseased animals into the allantoic cavity of 9-11 day-old chicken embryos
Indirect virus detection (antibody detection):
- Antibodies can be detected in chronic forms of disease; however, the vaccination status of the animals must be considered.
- Hemagglutination inhibition