Containing an Outbreak in the Age of Social Media
In mid-May 2018, virulent Newcastle disease (vND) was detected in Los Angeles County, California when a sick exhibition chicken was brought to a local veterinary clinic. Newcastle disease is an infectious disease of domestic poultry and wild birds that is caused by Newcastle disease virus (NDV), a paramyxovirus1. Other well-known paramyxoviruses include parainfluenza, respiratory syncytial virus, and measles2. NDV is classified into virulent, and low virulent strains, with virulent strains being endemic in Asia, Africa, South America, and certain countries in North America3. There had been 2 outbreaks of vND in California prior to this; one in 1971 and the other in 2002. These previous outbreaks cost many millions of dollars to contain and resulted in the destruction of over 15 million birds4. However, due to the effective response to these outbreaks, the United States was classified as vND free by the World Organization for Animal Health (WOAH) prior to the 2018 outbreak5.
Maintaining vND-free status is important because the United States produces over $40 billion of poultry products annually; with roughly 10% of this production going to exports6,7. However, the diagnosis of vND in California suddenly caused the U.S. to lose their vND free status; jeopardizing billions of dollars of export revenue. For this reason, the 2018 outbreak of vND in California constituted a regulatory emergency that needed to be contained as soon as possible; both to mitigate immediate economic losses to the affected farms, and to prevent future losses to the industry at large from mortality and loss of WOAH status.
As soon as the diagnosis of vND was confirmed, a unified command was formed between the California Department of Food and Agriculture (CDFA) and the United States Department of Agriculture (USDA). The incident command system (ICS) was used to organize and manage the response. Many of the responders in the unified command had been involved in the previous vND outbreak, including Dr. Annette Jones, the California state veterinarian who was an incident commander during the 2002 response. The CDFA’s first action was to invoke their quarantine authority and manage movement via permitting. They created a 3-km control area around the premises associated with the index case, and began targeted surveillance at locations where chicken owners were likely to be (e.g. feed stores and known exhibition bird premises). This control area would later be expanded into county-based quarantine areas that prohibited the movement of non-CDFA certified poultry and eggs within and between affected counties8.
Despite these early actions, shortly after the index case, the number of known affected premises grew rapidly. By May 26th, there were 5 affected premises in San Bernardino County and 2 in Los Angeles County. To get a handle on the outbreak, epidemiologists from CDFA and USDA used disease spread and control simulations to develop a strategy for containing vND. These models showed that the most effective means of containing the spread of the virus were
1) rapid and targeted surveillance
2) depopulation and
3) disposal of carcasses.
However, the geography of the outbreak and ecology of the virus presented several challenges to implementing these control strategies. In contrast to typical agricultural incidents, this outbreak occurred in a dense, urban environment. Roughly ¾ of infected premises were found to be within 250 m of another infected premises, with over 95% of infected premises occurring within 1.5 km of another infected premises. Spatial and spatiotemporal patterns indicated that the highest risk areas were located within Riverside and San Bernardino counties8.
In addition, the majority of the premises in the affected area were small, non-commercial operations that were not registered in any industry or government database (i.e. no premises identification numbers or tax information that could identify them as bird owners). Because most of the affected premises were not registered, it was difficult to determine where non-commercial flocks were located. To help overcome this issue, a Bayesian hierarchical model was used to estimate the probability of backyard flocks existing in the affected area based on previously identified socioeconomic and demographic variables found to be associated with urban poultry ownership. Surveys were also conducted at case and control premises, including premises with an epidemiologic link or proximity to infected premises (a.k.a. dangerous contacts). These studies identified flock size, ownership of exhibition birds, high proportions of roosters in flocks, and the use of housing that allows contact with wild birds as risk factors for vND in the target population8.
Many of these operations used their chickens for personal and cottage-industry egg and meat production. However, some of the birds, including the index case, were classified as exhibition animals. No doubt many of these were used for legitimate exhibition purposes like poultry shows and 4H. However, a certain proportion of these exhibition operations were flocks with >50% roosters; in other words, some of these birds may have been used for cockfighting. Aside from the obvious biosecurity and biocontainment obstacles these stakeholder characteristics presented, they also posed several obstacles to surveillance, depopulation, and disposal. Because cockfighting is illegal in all 50 states, and can be prosecuted as a felony in California, the owners and purveyors of fighting roosters had an incentive to avoid contact with local, state, and federal authorities. Furthermore, the actual cockfights created a high potential for spread of the virus in underground and difficult to trace venues, and may have played a role in prolonging the outbreak8,9.
To mitigate the added challenges, the incident command instituted policies and strategies designed specifically to reach out to these producers. First, they did not track the specific use of exhibition birds, and made it clear that their job was to contain the outbreak, not track down and prosecute cockfighting rings. This approach helped to engender trust and lower the hazard of exhibition flock owners cooperating with the response team. Second, they performed outreach activities that informed producers of the dangers of vND, and provided educational resources to help these owners protect their flocks. Any serious purveyor of exhibition birds would have invested large amounts of time and resources into developing their flocks. In other words, they were financially and emotionally invested in their birds and had a vested interest in keeping them healthy. Being aware of the dangers and having tools for protecting themselves made them more likely to cooperate with response efforts10.
On the other end of the spectrum were producers who viewed their birds more as pets, or even members of the family, than as units of production or exhibition. These other non-commercial flocks presented unique challenges, as the presence of an enhanced human-animal bond between the producers and their birds, coupled with the amplifying effect of social media, would prove to be a hinderance to depopulation efforts11.
Newcastle Disease in Poultry. Merck Veterinary Manual. Patti J. Miller. 2016. https://www.merckvetmanual.com/poultry/newcastle-disease-and-other-paramyxovirus-infections/newcastle-disease-in-poultry?query=virulent%20newcastle%20disease
Chapter 59. Medical Microbiology 4th edition. 1996 https://www.ncbi.nlm.nih.gov/books/NBK8461/
Newcastle Disease Standard Operating Procedures: 1. Overview of Etiology and Ecology. United States Department of Agriculture. 2013. https://www.aphis.usda.gov/animal_health/emergency_management/downloads/sop/sop_nd_e-e.pdf
Virulent Newcastle Disease. California Department of Agriculture. 2022. https://www.cdfa.ca.gov/ahfss/Animal_Health/Newcastle_Disease_Info.html#:~:text=1971%20Exotic%20Newcastle%20Disease%20Outbreak,12%20million%20birds%20were%20destroyed
Virulent Newcastle Disease (vND). Animal and Plant Health Inspection Service. United States Department of Agriculture. 2021. https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/avian/virulent-newcastle/vnd
Poultry – Production and Value 2021 Summary. National Agricultural Statistics Service. United States Department of Agriculture. 2022. https://www.uspoultry.org/economic-data/docs/broiler-production-and-value-2021.pdf
S. Dairy, Livestock and Poultry Exports in 2021. Foreign Agricultural Service. United States Department of Agriculture. 2022. https://www.fas.usda.gov/commodities/dairy-livestock-and-poultry
Epidemiologic Analyses of Virulent Newcastle Disease in Poultry in California. Animal and Plant Health Inspection Service. United States Department of Agriculture. 2021. https://www.aphis.usda.gov/animal_health/downloads/animal_diseases/ai/epi-analy-vnd-poultry-calif.pdf
Cockfighting Laws. National Conference of State Legislatures. Jonathan Griffin. 2014. https://www.ncsl.org/research/agriculture-and-rural-development/cockfighting-laws.aspx#:~:text=State%20Action,and%20the%20U.S.%20Virgin%20Islands
Personal Communication with CDFA. 2022.
To stop a virus, California has euthanized more than 1.2 million birds. Is it reckless or necessary? Los Angeles Times. Jaclyn Cosgrove. 2019. https://www.latimes.com/local/lanow/la-me-ln-virulent-newcastle-disease-outbreak-in-southern-california-20190607-story.html
California’s Defeat of Newcastle Disease Offers Lessons for Poultry Industry. Lancaster Farming. Philip Gruber. 2021. https://www.lancasterfarming.com/news/main_edition/california-s-defeat-of-newcastle-disease-offers-lessons-for-poultry-industry/article_20c2a0a8-157b-11ec-9945-3b2d61b62862.html
History they don’t teach you: A tradition of cockfighting. White River Valley Historical Quarterly. Lynn Morrow. 1995. https://thelibrary.org/lochist/periodicals/wrv/v35/n2/f95d.htm