Epizootics In Populations Research Articles

Epidemiological Manifestation of Combined Natural Foci of Tularemia, Leptospirosis and Hemorrhagic Fever with Renal Syndrome: Mixed Infections

Epidemiological Manifestation of Combined Natural Foci of Tularemia, Leptospirosis and Hemorrhagic Fever with Renal Syndrome: Mixed Infections

Effectiveness of antifungal treatments during chytridiomycosis epizootics in populations of an endangered frog.

The recently-emerged amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has had an unprecedented impact on global amphibian populations, and highlights the urgent need to develop effective mitigation strategies. We conducted in-situ antifungal treatment experiments in wild populations of the endangered mountain yellow-legged frog during or immediately after Bd-caused mass die-off events. The objective of treatments was to reduce Bd infection intensity (“load”) and in doing so alter frog-Bd dynamics and increase the probability of frog population persistence despite ongoing Bd infection. Experiments included treatment of early life stages (tadpoles and subadults) with the antifungal drug itraconazole, treatment of adults with itraconazole, and augmentation of the skin microbiome of subadults with Janthinobacterium lividum, a commensal bacterium with antifungal properties. All itraconazole treatments caused immediate reductions in Bd load, and produced longer-term effects that differed between life stages. In experiments focused on early life stages, Bd load was reduced in the 2 months immediately following treatment and was associated with increased survival of subadults. However, Bd load and frog survival returned to pre-treatment levels in less than 1 year, and treatment had no effect on population persistence. In adults, treatment reduced Bd load and increased frog survival over the entire 3-year post-treatment period, consistent with frogs having developed an effective adaptive immune response against Bd. Despite this protracted period of reduced impacts of Bd on adults, recruitment into the adult population was limited and the population eventually declined to near-extirpation. In the microbiome augmentation experiment, exposure of subadults to a solution of J. lividum increased concentrations of this potentially protective bacterium on frogs. However, concentrations declined to baseline levels within 1 month and did not have a protective effect against Bd infection. Collectively, these results indicate that our mitigation efforts were ineffective in causing long-term changes in frog-Bd dynamics and increasing population persistence, due largely to the inability of early life stages to mount an effective immune response against Bd. This results in repeated recruitment failure and a low probability of population persistence in the face of ongoing Bd infection.

Neozygites osornensis sp. nov., a fungal species causing mortality to the cypress aphid Cinara cupressi in Chile

An entomophthoralean fungus causing epizootics in populations of the cypress aphid, Cinara cupressi Buckton, in Chile is described as a new species, Neozygites osornensis Montalva et Barta. The aphid pathogen is described based on morphological characters. An exhaustive description, illustrations and a comparison with closely related species are provided. The fungus differs from similar Neozygites species by smaller hyphal bodies, nuclei, primary conidia, capilliconidia and capilliphores and by noticeably different shape of capilliconidia. A key to aphid-pathogenic species of Neozygites is also included.

Passive Immunization of Pacific Herring against Viral Hemorrhagic Septicemia

The plasma of Pacific herring Clupea pallasii that survived laboratory-induced viral hemorrhagic septicemia (VHS) epizootics contained humoral substances that, when injected into naive animals, conferred passive immunity against the disease. Among groups exposed to viral hemorrhagic septicemia virus (VHSV), injection of donor plasma from VHS survivors resulted in significantly greater survival (50%) and significantly lower tissue titers (1.5 x 10(5) plaque-forming units [PFU]/g) than the injection of plasma from VHSV-naive donors (6% survival; 3.7 x 10(6) PFU/g). Additionally, the magnitude of the protective immune response increased during the postexposure period; plasma that was collected from survivors at 123 d postexposure (931 degree-days) provided greater protection than plasma collected from survivors at 60 d postexposure (409 degree-days). These results provide proof of concept that the VHSV exposure history of Pacific herring populations can be determined post hoc; furthermore, the results can be used as the foundation for developing additional high-throughput diagnostic techniques that may be effective at quantifying herd immunity and forecasting the potential for future VHS epizootics in populations of wild Pacific herring.

Observation on the initial inoculum source and dissemination of Entomophthorales-caused epizootics in populations of cereal aphids.

A total number of 1092 migratory alates were trapped from air in wheat grown area of Yuanyang County, Henan Province from early April through May 2002 in order to confirm the source and dissemination of entomophthoralean inocula to cause epizootics of cereal aphids. Those included 415 Sitobion avenae, 642 Rhopalosiphum padi, 22 Metopolophium dirhodum, and 13 Schizaphis graminum. The trapped alates were daily collected and individually reared for 7 days on wheat plants in laboratory. Of those 341 alates died of fungal infection, taking 31.2% in the trapped alates. These included 224 S. avenae, 106 R. padi, 8 M. dirhodum, and 3 S. graminum. Deaths of all infected alates occurred during the first 5 days and 78.9% of the deaths occurred within the first 3 days. Individual examination under microscope proved that all deaths were attributed to entomophthoralean fungi. Of those Pandora neoaphidis accounted for 84.6%, Conidiobolus obscurus for 9.9%, and Entomophthora planchoniana for 5.5%. Four alate deaths died of cross infection of P. neoaphidis and C. conidiobolus. Based on the high infection rate of the migratory alates trapped from air and the field occurrence of epizootics in populations of cereal aphids during the trapping period, Entomophthorales-caused epizootics were likely disseminated by infected alates through their flight and colonization. This makes it reasonable to interpret worldwide distribution of aphid epizootics, particularly caused by P. neoaphidis that has no resting spores discovered.

Storage of Resting Spores of the Gypsy Moth Fungal Pathogen, Entomophaga maimaiga

The fungal pathogen, Entomophaga maimaiga causes epizootics in populations of the important North American forest defoliator gypsy moth ( Lymantria dispar ). Increasing use of this fungus for biological control is dependent on our ability to produce and manipulate the long-lived overwintering resting spores (azygospores). E. maimaiga resting spores undergo obligate dormancy before germination so we investigated conditions required for survival during dormancy as well as the dynamics of subsequent germination. After formation in the field during summer, resting spores were stored under various moisture levels, temperatures, and with and without soil in the laboratory and field. The following spring, for samples maintained in the field, germination was greatest among resting spores stored in plastic bags containing either moistened paper towels or sterile soil. Resting spores did not require light during storage to subsequently germinate. In the laboratory, only resting spores maintained with either sterile or unsterilized soil at 4°C (but not at 20 or -20°C) germinated the following spring, but at a much lower percentage than most field treatments. To further investigate the effects of relative humidity (RH) during storage, field-collected resting spores were placed at a range of humidities at 4°C. After 9.5 months, resting spore germination was highest at 58% RH and no resting spores stored at 88 or 100% RH germinated. To evaluate the dynamics of infections initiated by resting spores after storage, gypsy moth larvae were exposed to soil containing resting spores that had been collected in the field and stored at 4°C for varying lengths of time. No differences in infection occurred among larvae exposed to fall-collected soil samples stored at 4oC over the winter, versus soil samples collected from the same location the following spring. Springcollected resting spores stored at 4°C did not go into secondary dormancy. At the time that cold storage of soil containing resting spores began in spring, infection among exposed larvae was initiated within a few days after bringing the soil to 15°C. This same pattern was also found for spring-collected resting spore-bearing soil that was assayed after cold storage for 2-7 months. However, after 31-32 months in cold storage, infections started 14-18 days after soil was brought to 15°C, indicating a delay in resting spore activity after prolonged cold storage.

Prevalences of fungal pathogens and othernatural enemies of cereal aphids (Homoptera:Aphididae) in wheat under dryland and irrigatedconditions in South Africa

Surveys were conducted in the summer andwinter rainfall wheat producing regions of SouthAfrica in a first attempt to investigate theidentity and impact of entomopathogenic fungi withinthe cereal aphid complex. Wheat produced underdryland and irrigated conditions was surveyed duringthe 1996 and 1997 seasons. Six cereal aphid specieswere recorded of which the Russian wheat aphid, Diuraphis noxia, was the most abundantunder dryland conditions in the summer rainfallregion as opposed to the oat aphid, Rhopalosiphum padi, in the winter rainfallregion. Rose grain aphid, Metopolophiumdirhodum, was most prevalent underirrigated conditions in the summer rainfall region.Five species of entomopathogenic fungi were recordedincluding four entomophthorales and the hyphomycete,Beauveria bassiana. TheEntomophthorales included Pandora neoaphidis, Conidiobolus obscurus, C.thromboides, and Entomophthoraplanchoniana. Pandora neoaphidis wasthe most important etiological agent recorded fromD. noxia, with up to 50% mycosis recordedunder dryland conditions in the Bethlehem summerrainfall region. Similarly, P. neoaphidis wasthe most prevalent species within populations ofM. dirhodum. under irrigated conditions in theBergville/Winterton summer rainfall region (up to77% mycosis). However, mycoses of R. padi didnot exceed 1.7% in samples from these areas,suggesting that R. padi may be lesssusceptible to P. neoaphidis than M.dirhodum. Epizootics in populations of D.noxia under dryland conditions in both the winterand summer rainfall regions indicated a high levelof susceptibility to P. neoaphidis.Occurrences of hymenopterous parasitoids andpredators in populations of D. noxia were low,although a parasitism level of 25% was recorded inone small sample of R. padi collected from anirrigated field in the summer rainfall region.

Modeling and Biological Implication of Time–Dose–Mortality Data for the Entomophthoralean Fungus,Zoophthora anhuiensis,on the Green Peach AphidMyzus persicae

The entomophthoralean fungusZoophthora anhuiensisfrequently causes epizootics in populations of the green peach aphid,Myzus persicae,infesting cruciferous crops in the middle and lower regions of the Changjiang River, China, during late autumn and early winter. In this study, a bioassay was conducted by exposing aphids on detached leaves to varying doses ofZ. anhuiensisconidia discharged fromin vitrocultures. Ten doses (1.5–198 conidia/mm2) were used, with each dose including 64–120 aphids. The aphids were maintained at 18°C under a photophase of 12:12 (L:D) and observed daily for mortality. The resulting time–dose–mortality data fitted well to a conditional mortality probability model based on the Hosmer–Lemeshow test (Ĉ=9.52,df=8,P=0.70), resulting in a cumulative mortality probability model. The parameters from the latter model were used to estimate the lethal dose (LD50) and time (LT50) for the fungal species against the pest. The LD50values were 87, 44, and 34 conidia/mm2on days 5, 6, and 7 after exposure, respectively. The estimates of the LT50values decreased from 6.7 days at 37 conidia/mm2to 4.5 days at 198 conidia/mm2. The results indicate thatZ. anhuiensiscould be a promising aphid pathogen for microbial control competitive with otherZoophthoraspecies. The model is recommended for use in the analysis of time–dose–mortality data for fungus–insect associations. The biological implications of the parameters and the advantages of the modeling technique over the conventional method of probit analysis are discussed.

Immune functions in beluga whales ( Delphinapterus leucas): evaluation of natural killer cell activity

Natural killer (NK) activity, an important non-specific defense mechanism against viral infections and tumors, was demonstrated in beluga whales using two different methods: 51Cr release and flow cytometry. Using the 51Cr release assay, NK activity in belugas was shown to be higher against K-562 than against YAC-1 cell lines. Moreover, it was enhanced by the addition of human recombinant interleukin-2 with both cell lines. NK activity evaluated by flow cytometry in the peripheral blood of eight belugas increased when the effector:target cell (E:T) ratio increased, and averaged 13.9% ± 3.8% (range 9.9% to 17.8%) at an E:T ratio of 100:1. While NK activity could be readily detected using both methods, the lack of radio-isotopes and related laboratory room make the flow cytometric method a viable and safe alternative. The evaluation of this function in cetaceans could lead to better understanding of the early events that lead to viral epizootics in populations of marine mammals in different parts of the world, as well as to the high prevalence of neoplasms in St. Lawrence beluga whales.

MECHANISMS OF DEUTEROMYCETE FUNGAL INFECTIONS IN GRASSHOPPERS AND LOCUSTS: AN OVERVIEW

AbstractSeveral species of entomopathogenic deuteromycetous fungi can produce epizootics in populations of grasshoppers and locusts. Consequently there is considerable interest in development of these fungi as biocontrol agents. To this end we need information about the genetic and molecular basis of deuteromycete pathogenesis in acridids to develop a rational plan for strain improvement. Herein we present an overview of the infection processes of deuteromycetous fungi in acridids. These fungi penetrate through the cuticle which is composed primarily of proteins. Hydrophobic interactions, appressoria formation, and mucus production by the fungus are involved in fungal adhesion to the acridid cuticle. Extracellular proteases produced by Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metchnikoff) Sorokin solubilize cuticle proteins, which assists penetration and provides nutrients for further growth. Fungal infection through the locust gut is rare because indigenous gut microflora produce antifungal metabolites. Little is known of the events providing host specificity or those that lead to insect death once the cuticle is breached by the fungus; however, mechanical damage, nutrient deprivation, and toxic metabolites may be involved.

AERIAL APPLICATION OF TWO BACULOVIRUSES AGAINST THE WESTERN SPRUCE BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN (LEPIDOPTERA: TORTRICIDAE), IN BRITISH COLUMBIA

AbstractTwo viruses, one a nuclear polyhedrosis virus and the other a granulosis virus, were applied in an attempt to initiate epizootics in populations of western spruce budworm, Choristoneura occidentalis Freeman, on Douglas-fir trees, Pseudotsuga menziesii (Mirb.) Franco, in southeastern British Columbia. Two 172-ha plots were aerially treated in 1982 with 9.0 kg of lyophilized, virus-infected larval powder that was formulated in an emulsifiable oil tank mix and applied at 9.4 L per hectare. Each plot was treated when larval populations were at the peak of the fourth instar. The nuclear polyhedrosis virus was applied at 5.4 × 1011 polyhedral inclusion bodies per hectare and the granulosis virus at 1.7 × 1014 capsules per hectare. Results showed that the granulosis virus treatment caused 34.6% population reduction (Abbott’s formula) and the nuclear polyhedrosis virus 51.8%. Larvae from treated and check plots were reared individually in the laboratory and the incidence of viruses, parasitoids, and successful adult emergence was recorded. Studies m these plots continued in 1983 and 1984. Although vertical transmission of both viruses was evident, their impact on budworm mortality was less than in 1982. Consequently, the epizootics were not sufficiently intense to control the target insect population.

Metarhizium album, a fungal pathogen of leaf- and planthoppers of rice

Metarhizium album, a name widely regarded as a synonym of M. anisopliae, is restored for a fungus collected on plant- and leafhoppers (Homoptera : Auchenorrhyncha) from rice. In the Philippines and Indonesia it caused epizootics in populations of Nephotettix virescens and/or Cofana spectra, respectively. A single collection on an unidentified leaf hopper from mango is reported. Comparison of types revealed that M. brunneum is a synonym of M. album; the species is characterized by the pale brown colour of its conidial masses, clavate phialides (10–12.5 × 2–3.5μm), ovoid to ellipsoidal conidia ((3–4)4–6 × 1.5–2.5 μm) and growth of bulging masses of hyphal bodies rather than mycelium prior to sporulation. The primary taxonomic criteria for delimiting species of Metarhizium are the shapes of conidia and conidiogenous cells, presence or absence of a subhymenial zone of swollen hyphal bodies, and whether conidial chains adhere laterally to form prismatic columns. The occurrence of many natural and artificial colour variants of Metarhizium species suggests that colours of conidial masses and mycelium have only secondary taxonomic value. Conidial size is useful in delimiting varieties. A synoptic key to the taxa of Metarhizium is provided.

A new fungal pathogen of the scavenger mite, Tydeus gloveri

A new fungal pathogen, Hirsutella tydeicola, was found causing epizootics in populations of the scavenger mite, Tydeus gloveri, during the summer of 1979 and 1980 on citrus in Florida. The fungus is described in association with its host using light and scanning electron microscopy. H. tydeicola is compared with a closely related species, H. thompsonii, a coexisting pathogen of the citrus rust mite. All attempts to isolate the fungus on various agar media failed.

Entomophthora thripidum, a new fungal pathogen of Thrips tabaci

Entomophthora thripidum sp. nov. is described and illustrated. The species is pathogenic for Thrips tabaci Lind. (Thysanoptera: Thripidae) and caused epizootics in populations of this species in glasshouses in the Netherlands. Entomophthora thripidum is characterized by spores which are broadly ellipsoidal with a pointed apex and truncate base. Infection is restricted to the abdominal parts of the body and primary spores can be discharged from the living hosts. The secondary spores are similar but smaller than the primary ones. Details about the seasonal history and symptoms of the disease are described. The invalidly published name Empusa weberi Lakon (= Entomophthora weberi (Lakon) Batko) is validated by a Latin diagnosis.

Promoting Virus Epizootics in Populations of the Swaine Jack Pine Sawfly by Infected Adults

Promoting Virus Epizootics in Populations of the Swaine Jack Pine Sawfly by Infected Adults