Detection of antibodies to Francisella tularensis in cats

Blood samples were obtained from privately owned cats in Connecticut and New York State, USA in 1985-1990, and analyzed for evidence of Francisella tularensis, the etiologic agent of tularemia. Of the 91 sera tested by microagglutination (MA) methods, 11 (12%) contained antibodies to F. tularensis. Analyses of the same sera by indirect fluorescent antibody (IFA) staining methods revealed 22 (24%) positives. There was good agreement in results of both tests (73% concordance). However, we measured higher titers (1:80 to 1:640) with IFA analysis than by MA methods (1:80 to 1:160). Both tests were suitable for general screening purposes. The DNA of F.tularensis was not detected in the 24 antibody-positive sera tested. Cats living in Connecticut and New York State were naturally exposed to F.tularensis or a closely related organism. With exposure to ticks, other biting arthropods, mice, and rabbits, cats are at risk for acquiring F.tularensis infections and can be an important source of information on the presence of this agent in nature.     

Chromosome locations of leaf rust resistance genes in selected tetraploid wheats through substitution lines

Langdon durum D-genome disomic substitution lines were used to study the chromosome locations of adult-plant leaf rust resistance genes identified from tetraploid wheat accessions. The accessions are 104 (Triticum turgidum subsp. dicoccum var. arras) and 127 (T. turgidum subsp. durum var. aestivum). The complete sets of the substitution lines were crossed as female parents with the accessions and F₁ double monosomic individuals selected at metaphase I. Segregating F₂ individuals were inoculated during the flag leaf stage with pathotype UVPrt2 of Puccinia triticina. The substitution analysis involving accession 104 showed that the gene for leaf rust resistance is located on chromosome 6B. The analysis with accession 127 indicated that chromosome 4A carries a gene for leaf rust resistance. The two novel genes are temporarily designated as Lrac104 and Lrac127, respectively from accessions 104 and 127.     

Evolutionary strategies and adaptations for survival between mosquito-parasitic microsporidia and their intermediate copepod hosts: a comparative examination of Amblyospora connecticus and Hyalinocysta chapmani (Microsporidia: Amblyosporidae)

The epizootiology, transmission dynamics, and survival strategies employed by two mosquito-parasitic microsporidia that utilize copepods as intermediate hosts are examined in relation to the biological attributes of their hosts and the environments in which they inhabit. Amblyospora connecticus Andreadis, 1988, a parasite of Ochlerotatus cantator (Coquillett) and Acanthocyclops vernalis (Fischer) is found in an unstable salt marsh environment that is subject to periodic flooding and drying. Both hosts have distinct non-overlapping generations. A. connecticus exhibits a well-defined seasonal transmission cycle that relies heavily on maternal-mediated transovarial transmission by female O. cantator during the summer, and horizontal transmission via the copepod host during the spring (copepod to mosquito) and fall (mosquito to copepod). Its survival strategies include: delayed virulence, low pathogenicity and high tissue specificity that allow for transstadial transmission of horizontally acquired infections and maximum spore production, reliance on living hosts throughout most of its life cycle with overwintering in the copepod, polymorphic development that is well synchronized with host physiology, and production and dissemination of infectious spores that are coincident with the seasonal occurrence of susceptible stages in each host. Hyalinocysta chapmani Hazard et Oldacre, 1975, a parasite of Culiseta melanura (Coquillett) and Orthocyclops modestus (Herrick) is found in a comparatively stable, subterranean habitat that is inundated with water throughout the year. Copepods are omnipresent and C. melanura has overlapping broods. H. chapmani is maintained in a continuous cycle of horizontal transmission between each host throughout the summer and fall but lacks a developmental sequence leading to transovarial transmission in the mosquito host. It relies on living hosts for most of its life cycle and overwinters in diapausing mosquito larvae. Transstadial transmission does not occur and there is no dimorphic development in the mosquito host. The spatial and temporal overlap of both mosquito and copepod hosts during the summer and fall affords abundant opportunity for continuous horizontal transmission and increases the likelihood that H. chapmani will find a target host, thus negating the need for a transovarial route. It is hypothesized that natural selection has favoured the production of meiospores in larval female mosquitoes rather than congenital transfer of infection to progeny via ovarian infection as a strategy for achieving greater transmission success. Analysis of the molecular phylogeny data suggest that (1) transovarial transmission and the developmental sequence leading to ovarian infection have been secondarily lost in H. chapmani, as they occur in all other closely related genera, (2) the ancestral state included complex life cycles involving transovarial transmission and an intermediate host, and (3) mosquito-parasitic microsporidia are adjusting their life cycles to accommodate host ecological conditions.     

Detection of antibodies to Borrelia burgdorferi in naturally infected horses in the USA by enzyme-linked immunosorbent assay using whole-cell and recombinant antigens

Blood samples were collected from 98 horses suspected of having borreliosis or granulocytic ehrlichiosis in Connecticut and New York State, USA during 1985, 1995, and 1996. Serum antibodies to Borrelia burgdorferi were detected by an enzyme-linked immunosorbent assay (ELISA), based on whole-cell and recombinant antigens, in 82 (84%) horses. Of the 181 sera tested, 59% were positive, using whole-cell antigens, compared to 48% with protein (p)37 and 35% with VlsE antigens. An ELISA containing either of these fusion proteins can be used as an adjunct to general screening by an ELISA or immunoblotting in animals not vaccinated for this disease.     

Effect of crop growth and canopy filtration on the dynamics of plant disease epidemics spread by aerially dispersed spores

Most mathematical models of plant disease epidemics ignore the growth and phenology of the host crop. Unfortunately, reports of disease development are often not accompanied by a simultaneous and commensurate evaluation of crop development. However, the time scale for increases in the leaf area of field crops is comparable to the time scale of epidemics. This simultaneous development of host and pathogen has many ramifications on the resulting plant disease epidemic. First, there is a simple dilution effect resulting from the introduction of new healthy leaf area with time. Often, measurements of disease levels are made pro rata (per unit of host leaf area or total root length or mass). Thus, host growth will reduce the apparent infection rate. A second, related effect, has to do with the so-called "correction factor," which accounts for inoculum falling on already infected tissue. This factor accounts for multiple infection and is given by the fraction of the host tissue that is susceptible to disease. As an epidemic develops, less and less tissue is open to infection and the initial exponential growth slows. Crop growth delays the impact of this limiting effect and, therefore, tends to increase the rate of disease progress. A third and often neglected effect arises when an increase in the density of susceptible host tissue results in a corresponding increase in the basic reproduction ratio, R(0), defined as the ratio of the total number of daughter lesions produced to the number of original mother lesions. This occurs when the transport efficiency of inoculum from infected to susceptible host is strongly dependent on the spatial density of plant tissue. Thus, crop growth may have a major impact on the development of plant disease epidemics occurring during the vegetative phase of crop growth. The effects that these crop growth-related factors have on plant disease epidemics spread by airborne spores are evaluated using mathematical models and their importance is discussed. In particular, plant disease epidemics initiated by the introduction of inoculum during this stage of development are shown to be relatively insensitive to the time at which inoculum is introduced.     

Tracking the potato late blight pathogen in the atmosphere using unmanned aerial vehicles and Lagrangian modeling

A means for determining the aerial concentration, C (sporangia m⁻³), of plant pathogenic spores at various distances from a source of inoculum is needed to quantify the potential spread of a plant disease. Values of C for Phytophthora infestans sporangia released from an area source of diseased plants in a potato canopy was quantified in three ways: (1) by using Rotorods to sample the air just above the source, (2) by using unmanned aerial vehicles to sample the air at altitudes up to 90 m above the source and at downwind distances up to 500 m from the source, and (3) by using a Lagrangian stochastic simulation of sporangia flight trajectories to tie these two measurements together. Experiments were conducted using three potato crops over two years. Model predictions of time-average, crosswind-integrated concentrations were highly correlated (r = 0.9) with values of C measured using the unmanned aerial vehicles. The model describes the release and dispersal of sporangia from a potato canopy to a downwind distance of 500 m. Thus, it may have utility as a part of an area-wide decision support system by helping to predict risk of disease spread between neighboring or distant potato fields.     

Management of bacterial spot of tomato with phosphorous acid salts

Phosphorous acid salts (PASs) were evaluated alone or in combination with other products for managing bacterial spot of tomato in greenhouse and field experiments in Florida during a 3-year period. Field treatments included a weekly schedule of PAS alone, PAS combined with standard copper-bactericide at full rate or half rate, PAS alternated with a standard copper-bactericide, and PAS every week plus biweekly applications of acibenzolar-S-methyl (ASM). Field data showed that disease control with PAS combined with standard copper-bactericide full rate, PAS alternated with a standard copper-bactericide, and PAS every week plus biweekly applications of ASM was similar to that obtained using the standard copper-bactericide program. In greenhouse experiments PAS alone had a similar level of disease compared to the standard program, whereas PAS combined with standard copper-bactericide full rate was significantly better than the standard program. Yields in the field experiments were not affected by any of these treatments. Phytotoxicity was observed when PAS was applied to the foliage of tomato seedlings under greenhouse conditions. These data suggest that PAS combined with standard copper-bactericide full rate and PAS plus ASM could be used for managing bacterial spot of tomato in the field in Florida. The mode of action of PAS is still unclear, as it only slightly affected multiplication of Xanthomonas perforans in vitro, and was also ineffective as a plant activator.     

Preventing spread of Fusarium wilt of Hiemalis begonias in the greenhouse

To develop strategies to manage Fusarium wilt of Hiemalis begonias (Begonia×Hiemalis), caused by Fusarium foetens, studies were conducted to understand how the disease might be spread in the greenhouse. Inoculum density studies showed that as few as 100 conidial ml⁻¹ were sufficient to cause significant disease indicating that shared irrigation systems need strict sanitation along with bench tops, pots, and trays. The role of fungus gnats (Bradysia spp.) in vectoring F. foetens within a greenhouse was studied using nylon tent cages with diseased and healthy Hiemalis begonias. Fungus gnats were released into half of the cages. In cages where fungus gnats were present only healthy plants became diseased, indicating the effectiveness of fungus gnats in spreading Fusarium wilt. The pathogen was also isolated from adult fungus gnats. In vitro studies showed that two commercially available H₂O₂-based compounds, ZeroTol^® (2.0% peroxyacetic acid and 27.0% hydrogen peroxide), and SaniDate^® (12.0% peroxyacetic acid and 18.5% hydrogen peroxide), were effective in causing 100% spore mortality at rates that would allow their use in irrigation water. Seven cultivars of Hiemalis begonias (Begonia×Hiemalis) grown in soil infested with F. foetens were highly susceptible. No other Begonia species showed typical symptoms of chlorosis and wilt, but two cultivars of Rex begonia (Begonia rex) exhibited significant stunting in repeated trials.     

Spatial dispersion of trees in an old-growth temperate hardwood forest over 60 years of succession

An analysis of spatial dispersion was conducted for individual tree species in the old-growth forest at the Davis-Purdue Research Forest in Indiana. This 20.6 ha stand has been left largely undisturbed by exogenous factors since its acquisition by Purdue in 1917. It is the only long-term study plot of its size for a temperate hardwood forest with x–y coordinates (rectangular plot) for all species above 10 cm diameter. Full censuses have been conducted spanning 60 years (1926, 1976 and 1986).

Ripley’s L(t) function revealed that most species are characterized by some form of aggregation, agreeing with a prior evaluation from 1981. Heterogeneity of spatial structure was evident between two large plots, indicating that differences in site quality and history had influenced spatial structure. Shade-intolerant species were numerically dominant and spatially aggregated in 1926 but have declined over the 60-year interval and become more random in spatial dispersion. Shade-tolerant species have increased in number and become more aggregated over time, or they exhibit little change in spatial structure. Examples of the latter include Acer saccharum and Ulmus americana, species that experienced explosive population growth. These contrasting patterns are masked by stand-level patterns that show a trend toward uniformity over the same time frame.

These data reveal that changes in dispersion accompany the demographic failure experienced by numerous tree species in Central Hardwood old-growth stands, and these changes may feed back into a negative population cycle and further impede regeneration. The simultaneous manipulation of dispersion and density should be considered as a tool for influencing forest succession and promoting regeneration of desired tree species.     

A comparison of serologic tests for the detection of serum antibodies to whole-cell and recombinant Borrelia burgdorferi antigens in cattle

Serum samples from healthy dairy and beef cattle, living in tick-infested areas of Connecticut, USA, were analyzed by polyvalent enzyme-linked immunosorbent assays (ELISA), indirect fluorescent antibody (IFA) staining methods, or Western blot procedures to detect antibodies to tick-borne agents. Of the 80 sera tested by ELISA with whole-cell or 10 separate recombinant antigens (fusion proteins) of Borrelia burgdorferi sensu stricto, 57 (71%) were positive to 1 or more antigens, while 36 (45%) reacted to whole-cell antigens by IFA staining methods. Three (4%) of 80 samples had antibodies to Anaplasma phagocytophilum. There were antibodies to outer surface protein (Osp) A, OspB, OspC, OspE, OspF, protein (p) 41-G, p35, p37, and VlsE antigens of B. burgdorferi, but there was no reactivity to the p39 antigen by ELISA. Western immunoblots of a subset of 9 sera verified antibody presence in all samples and showed distinct reactivities to multiple proteins having molecular masses of about 31 kilodaltons (kDa), 34 kDa, 35 kDa, 41 kDa, and 83/93 kDa. High specificity (97%) was noted when 16 cattle sera containing antibodies to Leptospira interrogans serovars, Brucella sp., Anaplasma marginale, or A. phagocytophilum were tested by ELISA with separate whole-cell or recombinant B. burgdorferi antigens. An ELISA and Western blot analyses can be used to confirm the exposure of cattle to B. burgdorferi.