Investigating Salmonella and Wild Songbirds: A One Health Approach
During 2020, epidemiologists in Oregon contacted CDC about a peculiar finding—a strain of Salmonella causing human illnesses matched a strain of Salmonella isolated from a wild songbird, specifically a pine siskin. Additionally, in late 2020, the Wildlife Health Laboratory in California received an increased number of reports from the public and other agencies about Salmonella in wild songbirds. This gave investigators a clue that the two events may be related.
Although birds can be exposed to and even die from Salmonella when migrating to find food in the winter, the number of reports coming in was worrisome. Like California, several other states were reporting increased numbers of sick birds, which was concerning because of the potential for infection in people and other animals that may have contact with birds and bird feeders. People can get sick when they touch their mouth with unwashed hands after touching wild birds, bird feeders, bird baths, or pets that have contact with wild birds. Pets can also get sick if they hunt and catch sick birds or have contact with bird droppings.
“The salmonellosis outbreak in migratory songbirds during winter 2020–21 was the largest event on record for California. We received nearly three times more reports from the public than the previous large event during winter 2015–16. We also confirmed infection in six different bird species, including three for the first time.”
– Krysta Rogers, senior environmental scientist, California Department of Fish & Wildlife
To learn more about the illnesses in people and pets and the die-offs of songbirds, CDC worked with state and local health departments, wildlife departments, and wildlife research laboratory networks to identify and sequence Salmonella isolates. Public health departments interviewed people infected with Salmonella Typhimurium to see if they had contact with wild birds before their illness started. CDC’s role was unique because of the agency’s ability to bring together partners from multiple states and agencies to collaborate on addressing this problem. Creating the advice for CDC’s investigation notice was also a collaborative effort—CDC scientists reviewed existing scientific literature and consulted subject matter experts to compile recommendations for safe interaction with wild birds and bird feeders. The advice included ways to clean and disinfect bird feeders and bird baths, as well as what to do with dead birds and when it is appropriate to remove bird feeders completely. The advice, developed using a One Health approach, was shared by partners to help prevent further illnesses among people, pets, and wildlife, and to reduce environmental contamination with Salmonella from bird feeders.
This was the first time Salmonella in wild birds was linked to an outbreak of human illnesses. This investigation led to better understanding of the occurrence and relationship of Salmonella infections in people, pets, and wildlife. Investigation partners noted that collaborating with CDC and other health agencies was beneficial because of the different perspectives brought to this issue at the intersection of human and animal health. For example, those working in wildlife were considering human health aspects of this outbreak, in addition to the die-offs in songbirds. By working together, CDC and state health and wildlife partners were able to identify links between sick people and wild birds, such as contact with bird feeders, which may have led to the spread of illness. For wildlife officials, having CDC involved increased the reach of health messaging to a national level and helped raise awareness of steps that could be taken to prevent Salmonella infections among people, pets, and wild birds.
“We are very enthusiastic about the prospect of CDC investigating Salmonella cases in humans that are related to birds and bird feeders. We have suspected for years that this was a public health concern, and a previous study we conducted showed the relationship between bird and human isolates (from the PulseNet database maintained by CDC), yet the epidemiological investigation that CDC’s resources bring to bear will go a long way in raising this to the national attention it deserves. We hope to continue to collaborate on this issue to better educate people on ways to safely feed and observe birds.”
– Sonia M. Hernandez, professor of ecology and wildlife disease, University of Georgia