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Prevention of infectious diseases in aquaculture

Infectious diseases remain one of the most important limitations to the successful propagation of aquatic animals. Most of the losses caused by pathogens in aquaculture could be prevented by health inspection, adequate environment and sound management practices. Effective control measures, mainly based upon 1) avoidance of pathogens 2) modification of the environment 3) improvement of host resistance 4) vaccination and 5) chemoprophylaxis are described.

Journal of Veterinary Medicine, Series B

Parsing the effects of demography, climate, and management on recurrent brucellosis outbreaks in elk

1. Zoonotic pathogens can harm human health and well-being directly or by impacting livestock. Pathogens that spillover from wildlife can also impair conservation efforts if humans perceive wildlife as pests. Brucellosis, caused by the bacterium Brucella abortus, circulates in elk and bison herds of the Greater Yellowstone Ecosystem and poses a risk to cattle and humans. Our goal was to understand the relative effects of climatic drivers, host demography, and management control programs on disease dynamics. 2. Using >20 years of serologic, demographic, and environmental data on brucellosis in elk, we built stochastic compartmental models to assess the influences of climate forcing, herd immunity, population turnover, and management interventions on pathogen transmission. Data were collected at feedgrounds visited in winter by free-ranging elk in Wyoming, USA. 3. Snowpack, hypothesized as a driver of elk aggregation and thus brucellosis transmission, was strongly correlated across feedgrounds. We expected this variable to drive synchronized disease dynamics across herds. Instead, we demonstrate asynchronous epizootics driven by variation in demographic rates. 4. We evaluated the effectiveness of test-and-slaughter of seropositive female elk at two feedgrounds. Test-and-slaughter temporarily reduced herd-level seroprevalence but likely reduced herd immunity while removing few infectious individuals, resulting in subsequent outbreaks once the intervention ceased. We simulated an alternative strategy of removing seronegative female elk and found it would increase herd immunity, yielding fewer infections. We evaluated a second experimental treatment wherein feeding density was reduced at one feedground, but we found no evidence for an effect despite a decade of implementation. 5. Synthesis and applications: Positive serostatus is often weakly correlated with infectiousness but is nevertheless used to make management decisions including lethal removal in wildlife disease systems. We show how this can have adverse consequences whereas efforts that maintain herd immunity can have longer-term protective effects. Climatic drivers may not result in synchronous disease dynamics across populations unless vital rates are also similar because demographic factors have a large influence on disease patterns.

Idaho, Montana, Wyoming

Control of infectious Hematopoietic Necrosis virus disease by elevating the water temperature

Studies were performed to determine if increasing water temperatures could control infectious hematopoietic necrosis virus (IHN) disease in sockeye salmon ( Oncorhynchus nerka ). Mortalities could be prevented if the water temperature was raised to at least 18 C within the first 24 hr after infection of the fish and if the fish were maintained at this temperature for 4–6 days. The disease did not recur after the elevated temperature treatment, but the fish would still contract the disease if they were reinfected. Reasons for the protecting action are discussed.

Journal of the Fisheries Research Board of Canada

The Amphibian Research and Monitoring Initiative (ARMI): 5-year report

The Amphibian Research and Monitoring Initiative (ARMI) is an innovative, multidisciplinary program that began in 2000 in response to a congressional directive for the Department of the Interior to address the issue of amphibian declines in the United States. ARMI’s formulation was cross-disciplinary, integrating U.S. Geological Survey scientists from Biology, Water, and Geography to develop a course of action (Corn and others, 2005a). The result has been an effective program with diverse, yet complementary, expertise. ARMI’s approach to research and monitoring is multiscale. Detailed investigations focus on a few species at selected local sites throughout the country; monitoring addresses a larger number of species over broader areas (typically, National Parks and National Wildlife Refuges); and inventories to document species occurrence are conducted more extensively across the landscape. Where monitoring is conducted, the emphasis is on an ability to draw statistically defensible conclusions about the status of amphibians. To achieve this objective, ARMI has instituted a monitoring response variable that has nationwide applicability. At research sites, ARMI focuses on studying species/environment interactions, determining causes of observed declines, and developing new techniques to sample populations and analyze data. Results from activities at all scales are provided to scientists, land managers, and policymakers, as appropriate. The ARMI program and the scientists involved contribute significantly to understanding amphibian declines at local, regional, national, and international levels. Within National Parks and National Wildlife Refuges, findings help land managers make decisions applicable to amphibian conservation. For example, the National Park Service (NPS) selected amphibians as a vital sign for several of their monitoring networks, and ARMI scientists provide information and assistance in developing monitoring methods for this NPS effort. At the national level, ARMI has had major exposure at a variety of meetings, including a dedicated symposium at the 2004 joint meetings of the Herpetologists’ League, the American Society of Ichthyologists and Herpetologists, and the Society for the Study of Amphibians and Reptiles. Several principal investigators have brought international exposure to ARMI through venues such as the World Congress of Herpetology in South Africa in 2005 (invited presentation by Dr. Gary Fellers), the Global Amphibian Summit, sponsored by the International Union for Conservation of Nature (IUCN) and Wildlife Conservation International, in Washington, D.C., 2005 (invited participation by Dr. P.S. Corn), and a special issue of the international herpetological journal Alytes focused on ARMI in 2004 (edited by Dr. C.K. Dodd, Jr.). ARMI research and monitoring efforts have addressed at least 7 of the 21 Threatened and Endangered Species listed by the U.S. Fish and Wildlife Service (California red-legged frog [Rana draytonii], Chiricahua leopard frog [R. chiricahuensis], arroyo toad [Bufo californicus], dusky gopher frog [Rana sevosa], mountain yellow-legged frog [R. muscosa], flatwoods salamander [Ambystoma cingulatum], and the golden coqui [Eleutherodactylus jasperi]), and 9 additional species of concern recognized by the IUCN. ARMI investigations have addressed time-sensitive research, such as emerging infectious diseases and effects on amphibians related to natural disasters like wildfire, hurricanes, and debris flows, and the effects of more constant, environmental change, like urban expansion, road development, and the use of pesticides. Over the last 5 years, ARMI has partnered with an extensive list of government, academic, and private entities. These partnerships have been fruitful and have assisted ARMI in developing new field protocols and analytic tools, in using and refining emerging technologies to improve accuracy and efficiency of data handling, in conducting amphibian disease, malformation, and environmental effects research, and in implementing a network of monitoring and research sites. Accomplishments from these endeavors include more than 40 publications on amphibian status and trends, nearly 100 publications on amphibian ecology and causes of declines, and over 30 methodological publications. Several databases have emerged as a result of ARMI and its partnerships; one, a digital atlas of ranges for all U.S. amphibian species, was used by the IUCN to display amphibian distribution maps in the Global Amphibian Assessment Project. Given the scope of ARMI and the panoply of projects, findings have had implications for policy. Investigations that demonstrate amphibian declines or illuminate causes of declines provide valuable information about habitat management, environmental effects, mechanisms for the spread of disease, and human/amphibian interfaces. This information has been made available to land managers, scientists, educators, Congress and other policymakers, and the public. The support afforded ARMI by Congress has been influential in the program’s development and success. The value of ARMI’s efforts will continue to increase as we are able to extend our studies spatially and temporally to answer critical questions with more confidence. We are using ARMI’s resources efficiently and continuing to develop innovative mechanisms for leveraging resources for maximum effectiveness during challenging financial times. This report is a 5-year retrospective of the structure, methodology, progress, and contributions to the broader scientific community that have resulted from this national USGS program. We evaluate ARMI’s success to date, with regard to the challenges faced by the program and the strengths that have emerged. We chart objectives for the next 5 years that build on current accomplishments, highlight areas meriting further research, and direct efforts to overcome existing weaknesses.

Scientific Investigations Report

Cause of death, pathology, and chronic wasting disease status of white-tailed deer (Odocoileus virginianus) mortalities in Wisconsin

White-tailed deer (WTD; Odocoileus virginianus ) are a critical species for ecosystem function and wildlife management. As such, studies of cause-specific mortality among WTD have long been used to understand population dynamics. However, detailed pathological information is rarely documented for free-ranging WTD, especially in regions with a high prevalence of chronic wasting disease (CWD). This leaves a significant gap in understanding how CWD is associated with disease processes or comorbidities which may subsequently alter broader population dynamics. In this study, we investigated unknown mortalities among collared WTD in southwestern Wisconsin, an area of high CWD prevalence. We tested for associations between CWD and other disease processes and used a network approach to test for co-occurring disease processes. Predation and infectious disease were top suspected causes of death, with high prevalence of CWD (42.4%; of 245 evaluated) and pneumonia (51.2%; of 168 evaluated) in our sample. CWD prevalence increased with age, before decreasing among older individuals, with more older females than males in our sample. Females were more likely to be CWD positive, and while this was not statistically significant when accounting for age, females were significantly more likely to die with end-stage CWD than were males and may consequently be an underrecognized source of CWD transmission. Presence of CWD was associated with emaciation, atrophy of marrow fat and hematopoietic cells, and ectoparasitism (i.e., lice, ticks). Occurrences of severe infectious disease pathologies clustered together (e.g., pneumonia, CWD), as compared to non-infectious or low severity processes (e.g., sarcocystosis). However, pneumonia cases were not fully explained by CWD status. With the prevalence of CWD increasing across North America, our results highlight the critical importance of understanding the potential role of CWD in favoring or maintaining disease processes of importance for deer population health and dynamics.

Wisconsin

Infectious canine hepatitis in a brown bear (Ursus arctos horribilis) from Alaska.

We diagnosed infectious canine hepatitis in a free-ranging brown bear ( Ursus arctos horribilis ) cub from Alaska, US, found dead in October 2015. Intranuclear inclusion bodies were present in hepatocytes, and immunohistochemistry showed reactivity to adenoviral antigens. Sequencing of the hexon protein of adenovirus showed 100% identity to canine adenovirus 1.

Journal of Wildlife Diseases

Diagnostic histological findings in Yosemite toads (Bufo canorus) from die-off in the 1970s

Twelve adult and 25 larval Yosemite toad ( Bufo canorus ) specimens from the eastern Sierra Nevada of California were examined histologically for evidence of infectious, toxicological, and degenerative diseases. The preserved toads were selected from 21 that had been salvaged or collected during a die-off in 1976-1979 that immediately preceded a population decline. Causes of death of four toads were determined histologically; clinical signs and field observations suggested causes of death of three more. Four toads died of infectious diseases, including chytridiomycosis of the skin ( N = 1), bacillary septicemia ( N = 2), and combined chytridiomycosis and bacterial septicemia ( N = 1). Infections by a funguslike organism ( Dermosporidium penneri ), renal myxozoa ( Leptotheca ohlmacheri ), larval Rhabdias, various gastrointestinal nematodes, urinary bladder flukes, and lung flukes were detected in five specimens. No evidence of degenerative diseases, virus infections, or intoxications was found. The variety of lethal diseases and our inability to determine the causes of death of five specimens suggests that one or more histologically undetectable diseases or intoxications may have also contributed to the deaths and population decline.

California

Fish viruses: A double-stranded RNA icosahedral virus from a North American cyprinid

A previously unreported virus disease of cultured golden shiners ( Notemigonus crysoleucas ) is described. The condition is called golden shiner virus (GSV) disease. The virus is icosahedral, measures approximately 70 nm, is ether and heat resistant, stable at pH 3, 7, and 10, and appears to have a double stranded RNA core. It was not neutralized by infectious pancreatic necrosis virus specific antiserum. GSV causes syncytial like cytopathic effect in fathead minnow cells but not brown bullhead, rainbow trout gonad (RTG-2) or channel catfish ovary cells. Severe mortalities in golden shiner culture ponds do not appear to be associated with GSV infections.

Journal of the Fisheries Research Board of Canada

Mortality trends in northern sea otters (Enhydra lutris kenyoni) collected from the coasts of Washington and Oregon (2002–15)

During 2002−15 we examined the causes of mortality in a population of northern sea otters ( Enhydra lutris kenyoni ). Beachcast sea otters were collected primarily from the coast of Washington. Although there are no permanent sea otter residents in Oregon, several beachcast otters were collected from the Oregon coast. Infectious diseases were the primary cause of death (56%) for otters we examined. Sarcocystosis was the leading infectious cause of death (54%) and was observed throughout the study period. Some infectious diseases, such as morbilliviral encephalitis and leptospirosis, were documented for a limited number of years and then not detected again despite continued testing for these pathogens in necropsied animals. Trauma was the second most common cause of death (14%) during the study period. The continued stable growth of the Washington population of otters suggests they are able to tolerate current mortality rates.

Oregon, Washington

Gross and microscopic pathology of lesions in Pocillopora spp. from the subtropical eastern Pacific

Coral reefs are threatened by a variety of factors including diseases that have caused significant damage in some regions such as in the Caribbean. At present, no data are available on coral diseases in the Mexican Pacific where Pocillopora spp. is a dominant component of coral communities. Here, we describe gross and microscopic morphology of lesions found in pocilloporids at four sites in the Mexican Pacific. Corals were identified and their lesions photographed and quantified in the field. Tissue samples were collected from healthy and affected colonies for histopathology. We recorded seven species of pocilloporids at the study sites with Isla Isabel being the location with the highest coral diversity ( H ′ = 1.27). Lesions were present in 42% of the colonies and included discoloration (32%), predation-induced tissue loss (30%), unexplained tissue loss (3%) and overgrowth by sponges or algae (35%). The most affected species, P . damicornis (50%), was also one of the most common in the region. No species was more prone to a particular lesion, but there was a significant association between location and the presence of lesions. Northern Islas Marietas (61%) and Isla Isabel (41%) had the highest prevalence of lesions, followed by Manzanillo (37%) and Bahías de Huatulco (23%). Histological changes included atrophy of the surface body wall with depletion of zooxanthellae (91%) in corals with discoloration (bleaching). Ablation of tissue from mesoglea (18%) was also observed. Colonies with unexplained tissue loss showed atrophy and thinning of the epidermis (89%), characterized by cuboidal instead of pseudocolumnar cells normally found in healthy pseudocolumnar ciliated epithelium. Bacterial aggregates between the mesoglea and gastrodermis (11%) were very conspicuous in healthy and diseased corals. Lesions produced by fish bites and gastropods were associated with tissue atrophy (40%) and, in some cases, algal overgrowth near the lesion (20%). No infectious agents associated with cell pathology were detected microscopically. Bleaching and overgrowth by algae and sponges, as well as unexplained tissue loss, are common in Pocillopora . These lesions and anatomical changes warrant further study since their incidence is potentially indicative of reef degradation.

Mexican Pacific

Causes of owl mortality in Hawaii, 1992 to 1994

Eighty-one barn owls ( Tyto alba ) and five Hawaiian owls or pueo ( Asio flammeus sandwichensis ) from Kauai, Oahu, Lanai, Molokai, Maui and Hawaii (USA) were evaluated for cause of death, November 1992 through August 1994. The most common cause of death in barn owls was trauma (50%) followed by infectious disease (28%) and emaciation (22%). Most traumas apparently resulted from vehicular collisions. Trichomoniasis was the predominant infectious disease and appeared to be a significant cause of death in barn owls in Hawaii. Pasteurellosis and aspergillosis were encountered less commonly. No predisposing cause of emaciation was detected. Stomach contents from 28 barn owls contained mainly insects (64%) of the family Tetigoniidae and Gryllidae, and rodents (18%); the remainder had mixtures of rodents and insects or grass. Three pueo died from trauma and one each died from emaciation and pasteurellosis. We found no evidence of organochlorine, organophosphorus, or carbamate pesticides as causes of death in pueo or barn owls.

Hawaii

Poisoning of Canada geese in Texas by parathion sprayed for control of Russian wheat aphid

Approximately 200 Canada geese ( Branta canadensis ) died at a playa lake in the Texas Panhandle shortly after a winter wheat field in the basin adjacent to the lake was treated with parathion to control newly invading Russian wheat aphids ( Diuraphis noxia ). No evidence of infectious disease was diagnosed during necropsies of geese. Brain ChE activities were depressed up to 77% below normal. Parathion residues in GI tract contents of geese ranged from 4 to 34 ppm. Based on this evidence, parathion was responsible for the goose mortalities. Parathion applications to winter wheat will undoubtedly increase if parathion is applied for control of both Russian wheat aphids and greenbugs ( Schizaphis graminum ). Geese may potentially be exposed to widespread applications of parathion from fall to spring, essentially their entire wintering period.

Texas

Fish viruses: Isolation and identification of infectious hematopoietic necrosis in eastern North America

Infectious hematopoietic necrosis virus (IHNV) was isolated from diseased fingerling rainbow trout ( Salmo gairdneri ) from a hatchery in West Virginia. Clinical signs, histopathologic findings, and origin of eggs provided a basis for diagnosis, and virus was isolated and presumptively identified by plaque characteristics. Serum neutralization tests provided positive identification of the agent as IHNV, and electronmicroscopy showed its rhabdovirus morphology. Experimental infections resulted in signs of IHNV and death; test fish had characteristic histopathologic alterations and appropriate virus titers. This is the first completely documented occurrence of IHNV beyond the Pacific Northwest.

Journal of the Fisheries Research Board of Canada

Avian influenza shedding patterns in waterfowl: implications for surveillance, environmental transmission, and disease spread

Despite the recognized importance of fecal/oral transmission of low pathogenic avian influenza (LPAI) via contaminated wetlands, little is known about the length, quantity, or route of AI virus shed by wild waterfowl. We used published laboratory challenge studies to evaluate the length and quantity of low pathogenic (LP) and highly pathogenic (HP) virus shed via oral and cloacal routes by AI-infected ducks and geese, and how these factors might influence AI epidemiology and virus detection. We used survival analysis to estimate the duration of infection (from virus inoculation to the last day virus was shed) and nonlinear models to evaluate temporal patterns in virus shedding. We found higher mean virus titer and longer median infectious period for LPAI-infected ducks (10–11.5 days in oral and cloacal swabs) than HPAI-infected ducks (5 days) and geese (7.5 days). Based on the median bird infectious dose, we found that environmental contamination is two times higher for LPAI- than HPAI-infectious ducks, which implies that susceptible birds may have a higher probability of infection during LPAI than HPAI outbreaks. Less environmental contamination during the course of infection and previously documented shorter environmental persistence for HPAI than LPAI suggest that the environment is a less favorable reservoir for HPAI. The longer infectious period, higher virus titers, and subclinical infections with LPAI viruses favor the spread of these viruses by migratory birds in comparison to HPAI. Given the lack of detection of HPAI viruses through worldwide surveillance, we suggest monitoring for AI should aim at improving our understanding of AI dynamics (in particular, the role of the environment and immunity) using long-term comprehensive live bird, serologic, and environmental sampling at targeted areas. Our findings on LPAI and HPAI shedding patterns over time provide essential information to parameterize environmental transmission and virus spread in predictive epizootiologic models of disease risks.

Journal of Wildlife Diseases

Detection and transmission of infectious hematopoietic necrosis virus in rainbow trout

Detection and transmission of Infectious Hematopoietic Necrosis Virus in rainbow trout ( Salmo gairdneri ) was studied at a commercial trout hatchery. Transmission of virus was demonstrated via water, feed and contaminated eggs. If eggs from carrier females were incubated several weeks in virus-free water, the resulting fry did not become infected. However, if fry subsequently became infected they were lifetime carriers. Infectious virus was readily detectable in most tissues of moribund fish; in carriers it was detected in sex products of spawning fish, and in samples from the intestine of post-spawning fish, but not in samples from blood, feces, kidney, or liver. The carrier rate was not significantly different between sexes. It was concluded that adult carriers are the reservoir of infection and that transmission occurs primarily when carriers shed virus and expose susceptible fish or eggs.

Journal of Wildlife Diseases

Pathophysiology of infectious hematopoietic necrosis virus disease in rainbow trout (Salmo gairdneri): early changes in blood and aspects of the immune Response after Injection of IHN Virus

Juvenile rainbow trout ( Salmo gairdneri ) were injected with infectious hematopoietic necrosis (IHN) virus and various hematological and blood chemical changes were monitored over 9 days. The packed cell volume, hemoglobin, red blood cell count, and plasma bicarbonate were significantly depressed by day 4. Plasma chloride, calcium, phosphorus, total protein, and blood cell types did not change during the 9 days. Furthermore, plasma LDH isozyme was significantly increased by the fourth day, and fish infected with infectious pancreatic necrosis virus, Vibrio anguillarum , Aeromonas salmonicida , and redmouth bacterium did not show specific LDH isozyme alterations. Acid-base alterations occurred at 10 C but not at 18 C. The acid-base imbalance and elevation of the LDH isozyme were consistently associated with the early development of the disease.The immune response after injection of IHN virus was determined and protection from disease was tested by passive immunization. Actively immunized fish developed IHN-neutralizing antibodies within 54 days after injection of virus, and the antibodies were protective when juvenile fish were passively immunized and experimentally challenged with IHN virus.

Journal of the Fisheries Research Board of Canada

Titre distribution patterns of infectious haematopoietic necrosis virus in ovarian fluids of hatchery and feral salmon populations

Infectious haematopoietic mecrosis virus (IHNV) is enzootic in virtually all populations of sockeye salmon, Oncorhynchus nerka (Walbaum), and in populations of chinook salmon, O. tshawytscha (Walbaum), of the Sacramento River drainage in California. This disease is an obstacle in hatcheries using brood stocks from these populations. However, naturally spawning sockeye salmon are highly successful and are the most important commercially fished salmon species in the United States. Most of the commercial landings of sockeye salmon are of feral fish originating in Alaska. The success of natural populations of salmon in which IHNV is enzootic, and the recurrent outbreaks of the disease in hatchery fish, led us to compare IHNW prevalence rates in hatchery and feral salmon populations.

Journal of Fish Diseases

Experimental challenge of a peridomestic avian species, European Starlings ( Sturnus vulgaris ), with novel Influenza A H7N9 virus from China

In 2013 a novel avian influenza H7N9 virus was isolated from several critically ill patients in China, and infection with this virus has since caused more than 200 human deaths. Live poultry markets are the likely locations of virus exposure to humans. Peridomestic avian species also may play important roles in the transmission and maintenance of H7N9 at live poultry markets. We experimentally challenged wild European Starlings ( Sturnus vulgaris ) with the novel H7N9 virus and measured virus excretion, clinical signs, and infectious dose. We found that European Starlings can be infected with this virus when inoculated with relatively high doses, and we predict that infected birds excrete sufficient amounts of virus to transmit to other birds, including domestic chickens. Infected European Starlings showed no clinical signs or mortality after infection with H7N9. This abundant peridomestic bird may be a source of the novel H7N9 virus in live poultry markets and may have roles in virus transmission to poultry and humans.

Journal of Wildlife Diseases