Quarterly Wildlife Mortality Report
July 2015 to September 2015
Written and compiled by the U.S. Geological Survey National Wildlife Health Center Epidemiology Team members: Anne Ballmann, Barb Bodenstein, Bob Dusek, Dan Grear, and Jenny Chipault, with contributions from Michelle Magagna, visiting pathology extern.
Highly pathogenic avian influenza in North America - 2015 third quarter update
The USGS National Wildlife Health Center (NWHC) continues to play an active role in surveillance and research into the emergence of highly pathogenic avian influenza (HPAI) viruses in North America. In the third quarter of 2015 (July - September), the NWHC tested 391 bird carcasses (Table 1) submitted from mortality and morbidity investigations nationwide. The NWHC also tested 4,758 swab samples from live or hunter-harvested waterfowl, primarily from the Mississippi and Atlantic Flyways, as part of the Interagency Surveillance Plan for Highly Pathogenic Avian Influenza in Waterfowl in the United States.
Nationally, there were no detections of HPAI virus in the third quarter of 2015 through the NWHC's mortality testing or through national surveillance samples collected from live or hunter-harvested birds. Samples from two mallards (Anas platyrhynchos) tested PCR positive for the Eurasian lineage HPAI H5 gene, which was first detected in North America in late 2014; however, virus was not isolated or sequenced from either sample. One sample was from a live mallard in Davis County, Utah in July and the second sample was from a hunter-harvested mallard in Morrow County, Oregon in November.
The NWHC is continuing to accept mortality and morbidity event submissions for HPAI testing under our expanded submission criteria. To date, no humans or other mammals have shown signs of disease from these particular viruses but field personnel handling live or dead wild birds should take appropriate precautions. For more information, see the USGS Role and Response to Highly Pathogenic Avian Influenza fact sheet.
Table 1. NWHC avian influenza tests of birds submitted for mortality investigation were all negative, July 1 - September 30, 2015.
|Species group (Order)
|Ducks, Geese, Swans (Anseriformes)
|Shorebirds, Gulls, Terns, Auks (Charadriiformes)
|Raptors (Falconiformes, Strigiformes)
|Seabirds and other Waterbirds
(Ciconiiformes, Gaviiformes, Pelecaniformes, Procellariiformes, Podicidiformes)
|Passerines and others
(Passeriformes, Galliformes, Gruiformes, Coraciiformes, Columbimformes)
|Third quarter total
Batrachochytrium salamandrivorans (Bsal): an emerging threat to salamanders
A newly identified fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has caused mass mortality events and severe population declines in European fire salamanders (Salamandra salamandra). The fungus appears to be native to Asia and was likely introduced to naïve European salamanders via the pet trade. The host range and pathogenicity of Bsal in North American salamanders is largely unknown and it is likely that North American salamanders are at risk from imported pets. North America has the highest diversity of salamanders in the world and introduction of this pathogen could be devastating, not only to local populations but also to salamander biodiversity globally. The NWHC is working collaboratively with the USGS Amphibian Research and Monitoring Initiative (AMRI), zoological parks, resources management agencies, and researchers from around the world to understand the host and pathogen ecology; the epidemiology and pathogenesis of the fungus; diagnostic techniques for detection of the pathogen; the threats posed if Bsal is introduced into North America; and to create tools to prevent introduction and manage consequences, if introduced. The NWHC uses a molecular assay that can detect both Batrachochytrium dendrobatis (Bd) and Bsal in salamander species. The NWHC maintains a large collection of archived amphibian tissues and is in the process of screening these samples to determine if Bsal is already present (and previously undetected) in the United States. The assay will also be important for future surveillance efforts aimed at early detection of Bsal in the United States, should it be introduced. In addition, the NWHC recently completed a risk assessment to determine the likelihood of Bsal introduction and consequences of potential introduction for salamanders in the United States. For information on Bsal diagnostic and epidemiological activities at the NWHC, contact Dan Grear, NWHC Bsal Coordinator, firstname.lastname@example.org or C. LeAnn White, NWHC Wildlife Epidemiology and Emerging Diseases Branch Chief, email@example.com.
Brevetoxin detected in green tree frogs (Texas)
On September 16th 2015, a mortality event involving American green tree frogs (Hyla cinerea) at Padre Island National Seashore, Texas was reported by the National Park Service to the NWHC. An estimated 30 - 40 adult green tree frogs died, many after showing signs of neurologic impairment including tremors, weakness, and abnormal movements and postures. Two days previously, a red tide event (harmful algal bloom) began along the coastline of the park, roughly 1 km from where the frogs were found, and a storm accompanied by winds, surf, and high tides had occurred the morning of the observed mortality. There has since been no further green tree frog mortality, but increases in coyote (Canis latrans) and unspecified ground squirrel deaths at Padre Island National Seashore were noted in the following weeks.
Five green tree frog carcasses were submitted to and necropsied at the NHWC. All had adequate body fat reserves and food in their stomach, suggesting an acute death. Testing for ranavirus was negative. Due to the lack of necropsy findings, the clinical history of neurologic abnormalities, and the concurrent presence of the red tide, brevetoxin was considered as a possible cause of death. Samples sent to the Florida Fish and Wildlife Conservation Commission Fish and Wildlife Research Institute (St. Petersburg) for ELISA testing were preliminarily positive for brevetoxin. Testing performed by Texas A & M University on an additional six frogs and a ground squirrel from this mortality event were also positive for brevetoxin. Testing is on-going to further characterize this finding.
Brevetoxin is produced by Karenia brevis, the algal organism responsible for red tides. When present at high enough levels, this toxin can cause large fish die-offs. Mammals that ingest toxin can develop signs of neurological impairment followed by rapid death. The NWHC believes this to be the first documented incident of a harmful algal bloom associated with amphibian mortality. The route of exposure in this terrestrial, freshwater frog species whose diet consists of flies, mosquitos, and other small insects is unclear, but exposure may have resulted from absorption of the toxin through the skin.
Aquatic bird bornavirus in a Canada goose (Massachusetts)
In October, a wild Canada goose (Branta canadensis) observed having signs of neurological impairment while on the grounds of the Capron Park Zoo in Attleboro, Massachusetts was euthanized and submitted by the U.S. Department of Agriculture's Animal and Plant Health Inspection Service to the NWHC for diagnostic evaluation. Clinical signs included intermittent circling and loss of coordination. No other wild or captive birds were reported to be affected. The necropsy revealed that both the esophagus and the gastrointestinal tract were dilated. Brain tissue tested positive for aquatic bird bornavirus-1 (ABBV-1) via culture and sequencing of the M gene at Texas A&M University. Histopathology revealed a severe non-suppurative meningoencephalitis consistent with ABBV-1 infection. Testing for avian influenza, West Nile virus, bacterial infections, lead toxicosis, and pesticide exposure was negative.
ABBV-1 is known to cause neurologic disease in several goose, swan, and gull species. These birds also may carry the virus subclinically. A related bornavirus infection associated with proventricular dilatation disease in psittacines (parrots) causes a similar array of neurologic and gastrointestinal clinical signs and is often fatal. At this point it is unknown whether ABBV-1 is capable of causing clinical disease in psittacines, but it is an important consideration as zoological parks represent potential areas for transmission of ABBV-1 to resident psittacine birds from local wildlife.
To view, search, and download historic and ongoing wildlife morbidity and mortality event records nationwide visit the Wildlife Health Information Sharing Partnership event reporting system (WHISPers) online database: http://www.nwhc.usgs.gov/whispers/
To request diagnostic services or report wildlife mortality: http://www.nwhc.usgs.gov/services/