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Results for “Virulence”

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205 records · Page 12Linked to original sources
USGS2001

Immunogenetics and resistance to avian malaria in Hawaiian honeycreepers (Drepanidinae)

Although a number of factors have contributed to the decline and extinction of Hawai‘i’s endemic terrestrial avifauna, introduced avian malaria ( Plasmodium relicturn ) is probably the single most important factor preventing recovery of these birds in low-elevation habitats. Continued decline in numbers, fragmentation of populations, and extinction of species that are still relatively common will likely continue without new, aggressive approaches to managing avian disease. Methods of intervention in the disease cycle such as chemotherapy and vaccine development are not feasible because of efficient immune-evasion strategies evolved by the parasite, technical difficulties associated with treating wild avian populations, and increased risk of selection for more virulent strains of the parasite. We are investigating the natural evolution of disease resistance in some low-elevation native bird populations, particularly Hawai‘i ‘Amakihi ( Hemignathus virens ), to perfect genetic methods for identifying individuals with a greater immunological capacity to survive malarial infection. We are focusing on genetic analyses of the major histocompatibility complex, due to its critical role in both humoral and cell-mediated immune responses. In the parasite, we are evaluating conserved ribosomal genes as well as variable genes encoding cell-surface molecules as a first step in developing a better understanding of the complex interactions between malarial parasites and the avian immune system. A goal is to provide population managers with new criteria for maintaining long-term population stability for threatened species through the development of methods for evaluating and maintaining genetic diversity in small populations at loci important in immunological responsiveness to pathogens.

Hawai'i↗
USGS1997

Immunization with viral antigens: Infectious haematopoietic necrosis

Infectious haematopoietic necrosis (IHN) is one of the most important viral diseases of salmonids, especially among juvenile fish where losses can be high. For over 20 years, researchers have tested a variety of preparations for control of IHN. Early vaccines consisted of killed virus and were effective when delivered by injection, but too costly to be practical on a large scale. Attenuated vaccines were developed by serial passage in cell culture and by monoclonal antibody selection. These offered excellent protection and were cost-effective, but residual virulence and uncertainty about their effects on other aquatic species made them poor candidates for licensing. Subunit vaccines using part of the IHNV glycoprotein gene cloned into E. coli or into an attenuated strain of A. salmonicida have been tested, appeared safe and were inexpensive. These vaccines were reported to provide some protection when delivered by immersion. Information on the location of antigenic sites on the glycoprotein led to trials using synthetic peptides, but these did not seem to be economically viable. Recently, plasmid vectors encoding the glycoprotein gene under control of a cytomegalovirus promoter were developed for genetic immunization. The constructs were highly protective when delivered by injection, but a more practical delivery system is needed. Thus, while several vaccine strategies have been tried in order to stimulate specific immunity against IHN, more research is needed to develop a commercially viable product for control of this important disease.

Developments in Biological Standardization↗
USGS2020

Herring Disease Program II 19120111-E - 2019 Annual Report

We will investigate fish health factors that may be contributing to the failed recovery of Pacific herring populations in Prince William Sound. Field samples will provide infection and disease prevalence data from Prince William Sound and Sitka Sound that will inform the ASA model, serological data that will indicate the prior exposure history and future susceptibility of herring to VHS, and diet information that will provide insights into the unusually high prevalence of Ichthyophonus that occurs in juvenile herring from Cordova Harbor. Laboratory studies will validate the newly-developed plaque neutralization assay as a quantifiable measure of herd immunity against VHS, provide further understanding of disease cofactors including temperature and salinity, investigate the possibility of an invertebrate host for Ichthyophonus, and assess the virulence of other endemic pathogens to Pacific herring. Information from the field and laboratory studies will be integrated into the current ASA model, a novel ASA-type model that is based on the immune status of herring age cohorts.

Alaska↗
USGS2018

Development and utility of a gene transcription panel for desert bighorn sheep (Ovis canadensis nelsoni)

Respiratory disease is a key factor impacting the success of the ongoing conservation and recovery of wild sheep populations (WAFWA 2017). Although the primary pathogens involved in the bighorn sheep pneumonia complex have been identified, the wide variability in herd response following infection is not well understood (Cassirer et al. 2018). The response of populations infected with Mycoplasma ovipneumoniae has been variable, from minimal to extensive herd mortality followed by years to decades of either poor lamb recruitment or little expression of disease and minimal impact on lamb survival (Coggins and Mathews 1992, Jorgenson et al. 1997, Cassirer et al. 2018). This variation is thought to be caused by differences in pathogen virulence, intrinsic or extrinsic factors that impact individual or herd immunity, including lungworm ( Protostrongylus spp.) or mite ( Psoroptes ovis ) infections, malnutrition, inbreeding, harsh weather conditions, or stress associated with overcrowding (Risenhoover et al. 1988, Bailey 1990, Jones and Worley 1994, Monello et al. 2001). Although substantial management strategies have been implemented, they have been ineffective in halting the spread of the epizootic (Cassirer et al. 2018).

Conference Paper↗
USGS2026

An evaluation of next-generation biological control methods for the invasive brown treesnake in the Mariana Islands

The brown treesnake (BTS) invasion in Guam continues to cause extensive ecological and economic damage, yet existing control tools cannot achieve islandwide suppression or eradication, highlighting the need for new strategies. This review evaluates the feasibility of classical and genetic biocontrol approaches for BTS and identifies priority knowledge gaps. Classical biocontrol, which relies on pathogens or parasites from a pest’s native range, has had limited success in vertebrates, though certain viruses may hold potential. For BTS, prior work has identified candidate agents, including hemogregarines and paramyxoviruses, but major uncertainties remain in transmission, specificity, long term efficacy, and ecological risk. Theoretical models suggest that moderately virulent pathogens may offer the strongest potential for sustained suppression, with Ophidian paramyxoviruses emerging as a leading prospect, though substantial empirical research is still required. Genetic biocontrol offers additional possibilities, including gene drives that could bias inheritance, reduce fertility, or skew sex ratios. Self sustaining homing and shredding drives could theoretically produce long term reductions, while “enhanced” self limiting systems may provide geographically restricted alternatives. Approaches involving genetically modified prey and toxic males that shorten female lifespan through mating may have future relevance but require major development and validation. Risks across genetic strategies include unintended spread, ecological side effects, technical constraints such as producing engineered snakes, potential resistance, and regulatory complexity. Because feasibility depends on societal acceptance, the review emphasizes the need for early engagement with Guam’s local and Indigenous communities, whose perspectives will shape future development and implementation. Key research priorities include improved modeling, native range genomic characterization of BTS, expanded pathogen surveys, advances in BTS genetic tools and captive rearing methods, and further exploration of both classical pathogen candidates and genetically engineered prey systems. Collectively, the review concludes that classical and genetic biocontrol hold promise for long term, cost effective BTS suppression, but substantial scientific, ethical, ecological, and social groundwork remains before deployment.

Hawai’i Cooperative Fishery Research Unit Technica↗
USGS2022

Plant pathogens provide clues to the potential origin of bat white-nose syndrome Pseudogymnoascus destructans

White-nose syndrome has killed millions of bats, yet both the origins and infection strategy of the causative fungus, Pseudogymnoascus destructans , remain elusive. We provide evidence for a novel hypothesis that P. destructans emerged from plant-associated fungi and retained invasion strategies affiliated with fungal pathogens of plants. We demonstrate that P. destructans invades bat skin in successive biotrophic and necrotrophic stages (hemibiotrophic infection), a mechanism previously only described in plant fungal pathogens. Further, the convergence of hyphae at hair follicles suggests nutrient tropism. Tropism, biotrophy, and necrotrophy are often associated with structures termed appressoria in plant fungal pathogens; the penetrating hyphae produced by P. destructans resemble appressoria. Finally, we conducted a phylogenomic analysis of a taxonomically diverse collection of fungi. Despite gaps in genetic sampling of prehistoric and contemporary fungal species, we estimate an 88% probability the ancestral state of the clade containing P. destructans was a plant-associated fungus.

Virulence↗
USGS2014

Pathology in euthermic bats with white nose syndrome suggests a natural manifestation of immune reconstitution inflammatory syndrome

White nose syndrome, caused by Geomyces destructans, has killed more than 5 million cave hibernating bats in eastern North America. During hibernation, the lack of inflammatory cell recruitment at the site of fungal infection and erosion is consistent with a temperature-induced inhibition of immune cell trafficking. This immune suppression allows G. destructans to colonize and erode the skin of wings, ears and muzzle of bat hosts unchecked. Yet, paradoxically, within weeks of emergence from hibernation an intense neutrophilic inflammatory response to G. destructans is generated, causing severe pathology that can contribute to death. We hypothesize that the sudden reversal of immune suppression in bats upon the return to euthermia leads to a form of immune reconstitution inflammatory syndrome (IRIS), which was first described in HIV-infected humans with low helper T lymphocyte counts and bacterial or fungal opportunistic infections. IRIS is a paradoxical and rapid worsening of symptoms in immune compromised humans upon restoration of immunity in the face of an ongoing infectious process. In humans with HIV, the restoration of adaptive immunity following suppression of HIV replication with anti-retroviral therapy (ART) can trigger severe immune-mediated tissue damage that can result in death. We propose that the sudden restoration of immune responses in bats infected with G. destructans results in an IRIS-like dysregulated immune response that causes the post-emergent pathology.

Virulence↗