Ten cases of virulent Newcastle disease (vND) have been confirmed by the United States Department of Agriculture (USDA) in backyard chickens in California. The disease has not infected commercial poultry in the United States since an outbreak occurred in 2003. The vND viruses attack the respiratory, nervous and digestive systems of birds and poultry, oftentimes killing the birds prior to the presentation of visible clinical effects.1 The disease is primarily transmitted among birds and poultry via inhalation and ingestion of the virus shed, therefore entire flocks of birds and poultry may become infected with the virus and subsequently die, potentially leading to serious economic impacts. Humans in close contact with birds and poultry may also contract the virus and experience mild symptoms. The implementation and execution of strong biosecurity practices are critically important in preventing and containing vND.2,3
vND, formerly referred to as avian avulavirus2 and exotic Newcastle disease,1 was reportedly discovered about 90 years ago when outbreaks occurred in Indonesia, England and, possibly, Korea in 1926.3 Since then epizootic outbreaks have occurred on five of the six continents in the world, including North America.2 There are multiple strains of ND viruses, which consist of single-stranded, non-segmented, negative sense RNA viruses, differentiated by mean death time observed in chicken embyros (i.e., lentogenic, mesogenic, and velogenic).2 If a velogenic or mesogenic outbreak occurs, it must be reported to The World Organisation for Animal Health (OIE) to allow for trading partners to consider any necessary actions that may be necessary to limit the spread of the disease.3 Velogenic ND often infects the intestines of birds causing hemorrhagic lesions, which is referred to as viscerotropic velogenic ND, or it may cause respiratory and nueorological infections and is referred to as neurotropic velogenic ND. Birds that are partially immune to velogenic infections typically develop a chronic infection but may develop neurological effects, such as tremors, ataxia, torticollis, and paresis or paralysis in the wings and or legs within days of contracting the disease. Mesogenic viruses impact birds and poultry differently in that animals develop respiratory and neurological effects, but the infection is self-limiting, therefore animals typically survive. However, lesions have been reported in the central nervous system, alimentary tract, and renal and respiratory system in birds and poultry with velogenic and mesogenic ND viruses. In 2003, a velogenic ND virus was confirmed in domestic chickens in California, Nevada, Arizona and Texas, which also ended up infecting commercial poultry in California, reportedly “resulting in the culling of 3.16 million birds at a cost of $121 million”.2
The ND viruses are primarily transmitted among birds and poultry via inhalation and ingestion of the virus shed, and they are reportedly stable in the environment, surviving from seven to 30 days, depending on environmental conditions. Due to the viruses’ stability in the environment, the virus may spread via formite transmission or in contaminated animal feed and/or water.2 Wild birds (e.g., double-crested cormorants and rock doves in the United States) may also spread the disease to domestic birds and vice versa.
According to the USDA’s Animal and Plant Health Inspection Service (APHIS), humans have not been reported to contract the disease from eating poultry products which have been infected with vND and indicated that meat is safe to eat, provided it has been cooked properly. However, humans may contract the disease when in contact with infected birds and poultry. Unlike the severe effects observed in birds and poultry, humans typically only experience mild symptoms which may include flu-like effects and conjunctivitis.1,3
To prevent the spread of vND, APHIS has recommended that all bird owners have strong biosecurity practices in place, including good hygienic practices such as washing hands before and after entering areas with birds. Scrubbing boots and cleaning and disinfecting tires and other equipment before moving them off the property is also important. Isolating birds for 30 days prior to introducing them into a flock of birds is also recommended.1 Because wild birds are able to transmit the disease, limiting their access to food and water sources for domestic poultry may also serve as an effective biosecurity practice.2 A variety of vaccinations have also been reported as a method to limit and/or prevent ND viruses from infecting flocks of birds and poultry, however, there is still a potential for vaccinated birds to contract the disease and shed the virus.2,3 The APHIS encourages any bird owners to report birds that appear to be sick or die unexpectedly.1
With confirmed reports of virulent NDV in the United States,1 it is important for bird and poultry owners to have strong biosecurity practices in place to minimize the risk of infection of birds and poultry as well as humans. They should also be aware of the potential clinical effects that present when birds and poultry become infected with vND, in order to identify the presence of and contain the disease.
- Virulent Newcastle Disease, USDA APHIS, Site visited on June 4, 2018.
- Brown, V.R., and Devins S.N., 2017, A review of virulent Newcastle disease viruses in the United States and the role of wild birds in viral persistence and spread, Veterinary Research 48: 68.
- Dimitrov K.M., Afonso, C.L., Yu, Q., and Miller, P.J., 2017, Newcastle disease vaccines – a solved problem or a continuous challenge? Veterinary Microbiology 206: 126-136.