West Nile Virus Infections in an Urban Colony of American White Ibises (Eudocimus albus) in South Florida, USA.

West Nile virus (WNV) is pathogenic in a wide range of avian hosts and is endemic in much of North America. This virus is responsible for population declines of some Passeriformes. We describe a WNV-associated mortality event in American White Ibis (Eudocimus albus) nestlings. This is a species, inherent to the Everglades ecosystem, which has recently begun nesting in urban areas. An urban colony in south Florida was monitored from March-July in 2020 as part of an ongoing study. Nestling carcasses were collected opportunistically and sent to the Southeastern Cooperative Wildlife Disease Study, University of Georgia within 24 h for diagnosis. Three ibis nestling deaths were confirmed to be caused by WNV infection based on histopathology, immunohistochemistry, and reverse transcription PCR. Serial plasma samples collected weekly from 36 healthy chicks of the same urban rookery were tested for WNV-neutralizing antibodies via plaque reduction neutralization test; four chicks were seropositive. Antibody titers in three seropositive chicks from which serial samples were collected waned over time, suggesting maternal antibody transfer. Ibis mortalities were consistent with a spike of WNV activity in this region of Florida. West Nile virus infection may be an important seasonal cause of mortality for wading bird nestlings.

Avian Influenza Virus Status and Maternal Antibodies in Nestling White Ibis (Eudocimus albus).

The White Ibis (Eudocimus albus), a nomadic wading bird, has increased its exploitation of urban habitats in South Florida, United States, and has recently established several urban breeding colonies. Certain characteristics of ibis ecology could position them in the natural cycle of the avian influenza virus (AIV). In fact, experimentally infected ibises were shown to be competent hosts for multiple AIV subtypes, and seroconversion to AIV has been documented in adult ibises in natural populations. However, the mechanisms of transmission and the timing of infection are unclear as we have yet to isolate AIV from a free-living ibis. To investigate the age-specific AIV dynamics of ibis, we captured nestlings (n = 115) weekly for 1-4 weeks from urban and natural settings in 2020 and 2021. We collected choanal/cloacal swabs for rRT-PCR and virus isolation, and plasma to screen for maternal AIV antibodies. AIV was not detected in any individual by virus isolation; however, maternal antibodies to AIV were detected in 95% of nestlings, with varying rates of catabolism. These results confirm that nestlings are afforded maternal antibodies from adults at rates reflective of higher adult seroprevalence than previously documented and that nestlings in breeding colonies may have some degree of protection and are unlikely to become infected with AIV.

Assessment of a Commercially Available Serum Pregnancy-specific Protein B Test in Free-ranging Elk (Cervus canadensis) in Pennsylvania, USA.

Uterine examinations provide an inexpensive and reliable postmortem alternative to monitor pregnancy rates in free-ranging elk (Cervus canadensis). However, this technique may be insensitive during early pregnancies (i.e., <20 d postconception), relies on proper collection of tissues, and may not be comparable to antemortem approaches used throughout the rest of the year. To circumvent some of these issues, the sensitivity and specificity of a commercially available serum pregnancy-specific protein B (PSPB) enzyme-linked immunosorbent assay (ELISA) was determined relative to uterine examination. From 2013 to 2017, paired serum samples and uteri were collected from 245 harvested free-ranging cow elk in Pennsylvania, US in November. Uteri were examined to determine whether the cow was pregnant, and, if so, gestation age was estimated based on embryo crown-rump (CR) length. The serum PSPB ELISA testing was then performed. Since harvested elk could not be retested, samples with optical densities close to the threshold for pregnancy determination (i.e., high-recheck samples) were considered as both not pregnant and pregnant, and analyses were performed separately under each scenario. Overall, the PSPB ELISA had a sensitivity of 95% (high-recheck considered pregnant) and 93% (high-recheck considered not pregnant), and a specificity of 91% (high-recheck considered pregnant) and 93% (high-recheck considered not pregnant) relative to uterine examinations. Based on CR length, gestation age was <14 to 55 d. Our results indicated the PSPB ELISA was an accurate serum-based pregnancy test for elk.