Epidemiologic and Genomic Evidence for Zoonotic Transmission of SARS-CoV-2 among People and Animals on a Michigan Mink Farm, United States, 2020.

Farmed mink are one of few animals in which infection with SARS-CoV-2 has resulted in sustained transmission among a population and spillback from mink to people. In September 2020, mink on a Michigan farm exhibited increased morbidity and mortality rates due to confirmed SARS-CoV-2 infection. We conducted an epidemiologic investigation to identify the source of initial mink exposure, assess the degree of spread within the facility's overall mink population, and evaluate the risk of further viral spread on the farm and in surrounding wildlife habitats. Three farm employees reported symptoms consistent with COVID-19 the same day that increased mortality rates were observed among the mink herd. One of these individuals, and another asymptomatic employee, tested positive for SARS-CoV-2 by real-time reverse transcription PCR (RT-qPCR) 9 days later. All but one mink sampled on the farm were positive for SARS-CoV-2 based on nucleic acid detection from at least one oral, nasal, or rectal swab tested by RT-qPCR (99%). Sequence analysis showed high degrees of similarity between sequences from mink and the two positive farm employees. Epidemiologic and genomic data, including the presence of F486L and N501T mutations believed to arise through mink adaptation, support the hypothesis that the two employees with SARS-CoV-2 nucleic acid detection contracted COVID-19 from mink. However, the specific source of virus introduction onto the farm was not identified. Three companion animals living with mink farm employees and 31 wild animals of six species sampled in the surrounding area were negative for SARS-CoV-2 by RT-qPCR. Results from this investigation support the necessity of a One Health approach to manage the zoonotic spread of SARS-CoV-2 and underscores the critical need for multifaceted public health approaches to prevent the introduction and spread of respiratory viruses on mink farms.

Short report: Antibody prevalence of select arboviruses in mute swans (Cygnus olor) in the Great Lakes region and Atlantic coast of the United States.

Mute swans (Cygnus olor) are an invasive species in the United States. The dramatic increase in their populations in localized areas has led to various problems, among them competition with native species and attacks on humans by aggressive swans. However, very little is known about the ability of these swans to transmit pathogens to humans, domestic birds, or wildlife or participate in enzootic maintenance. To learn more about select pathogens that mute swans may harbor, a survey was conducted from April of 2011 to August of 2012 in the Great Lakes region and localized areas of the Atlantic coast, which revealed serologic evidence of arbovirus exposure in mute swans. Of 497 mute swans tested, antibodies were detected for eastern equine encephalitis (4.8%), St. Louis encephalitis (1.4%), West Nile (1.2%), and Turlock (0.6%) viruses. Samples were also tested for evidence of antibodies to La Crosse virus, but none were positive.

Avian paramyxovirus serotype 1 (Newcastle disease virus), avian influenza virus, and Salmonella spp. in mute swans (Cygnus olor) in the Great Lakes region and Atlantic Coast of the United States.

Since their introduction to the United States in the late 19th century, mute swans (Cygnus olor) have become a nuisance species by causing damage to aquatic habitats, acting aggressively toward humans, competing with native waterfowl, and potentially transmitting or serving as a reservoir of infectious diseases to humans and poultry. In an effort to investigate their potential role as a disease reservoir and to establish avian health baselines for pathogens that threaten agricultural species or human health, we collected samples from 858 mute swans and tested them for avian paramyxovirus serotype 1 (APMV-1), avian influenza virus (AIV), and Salmonella spp. when possible. Our results indicate that exposure to APMV-1 and AIV is common (60%, n = 771, and 45%, n = 344, antibody prevalence, respectively) in mute swans, but detection of active viral shedding is less common (8.7%, n = 414, and 0.8%, n = 390, respectively). Salmonella was isolated from three mute swans (0.6%, n = 459), and although the serovars identified have been implicated in previous human outbreaks, it does not appear that Salmonella is commonly carried by mute swans.

Influence of body condition on influenza A virus infection in mallard ducks: experimental infection data.

Migrating waterfowl are implicated in the global spread of influenza A viruses (IAVs), and mallards (Anas platyrhynchos) are considered a particularly important IAV reservoir. Prevalence of IAV infection in waterfowl peaks during autumn pre-migration staging and then declines as birds reach wintering areas. Migration is energetically costly and birds often experience declines in body condition that may suppress immune function. We assessed how body condition affects susceptibility to infection, viral shedding and antibody production in wild-caught and captive-bred juvenile mallards challenged with low pathogenic avian influenza virus (LPAIV) H5N9. Wild mallards (n = 30) were separated into three experimental groups; each manipulated through food availability to a different condition level (-20%, -10%, and normal ±5% original body condition), and captive-bred mallards (n = 10) were maintained at normal condition. We found that wild mallards in normal condition were more susceptible to LPAIV infection, shed higher peak viral loads and shed viral RNA more frequently compared to birds in poor condition. Antibody production did not differ according to condition. We found that wild mallards did not differ from captive-bred mallards in viral intensity and duration of infection, but they did exhibit lower antibody titers and greater variation in viral load. Our findings suggest that reduced body condition negatively influences waterfowl host competence to LPAIV infection. This observation is contradictory to the recently proposed condition-dependent hypothesis, according to which birds in reduced condition would be more susceptible to IAV infection. The mechanisms responsible for reducing host competency among birds in poor condition remain unknown. Our research indicates body condition may influence the maintenance and spread of LPAIV by migrating waterfowl.