Habitat and Vegetation Variables Are Not Enough When Predicting Tick Populations in the Southeastern United States

Two tick-borne diseases with expanding case and vector distributions are ehrlichiosis (transmitted by Amblyomma americanum) and rickettiosis (transmitted by A. maculatum and Dermacentor variabilis). There is a critical need to identify the specific habitats where each of these species is likely to be encountered to classify and pinpoint risk areas. Consequently, an in-depth tick prevalence study was conducted on the dominant ticks in the southeast. Vegetation, soil, and remote sensing data were used to test the hypothesis that habitat and vegetation variables can predict tick abundances. No variables were significant predictors of A. americanum adult and nymph tick abundance, and no clustering was evident because this species was found throughout the study area. For A. maculatum adult tick abundance was predicted by NDVI and by the interaction between habitat type and plant diversity; two significant population clusters were identified in a heterogeneous area suitable for quail habitat. For D. variabilis no environmental variables were significant predictors of adult abundance; however, D. variabilis collections clustered in three significant areas best described as agriculture areas with defined edges. This study identified few landscape and vegetation variables associated with tick presence. While some variables were significantly associated with tick populations, the amount of explained variation was not useful for predicting reliably where ticks occur; consequently, additional research that includes multiple sampling seasons and locations throughout the southeast are warranted. This low amount of explained variation may also be due to the use of hosts for dispersal, and potentially to other abiotic and biotic variables. Host species play a large role in the establishment, maintenance, and dispersal of a tick species, as well as the maintenance of disease cycles, dispersal to new areas, and identification of risk areas.     

Role of cyclic adenosine 3',5'-monophosphate in mediating the effect of prostaglandin E2 on decidualization in vitro.

When rat endometrial stromal cells from uteri sensitized for decidualization are cultured in vitro, there is an increase in alkaline phosphatase (ALP) activity paralleling that seen in vivo during decidualization. The addition of indomethacin to the culture medium decreases the endogenous production of prostaglandin E2 (PGE2) to below detectable levels and substantially reduces the increase in ALP activity. The addition of either PGE2 or its analog 16,16-dimethyl-PGE2, but not PGF2 alpha or its analog 15(S),15-methyl-PGF2 alpha, overrides this inhibitory effect, suggesting that PGE2 has a specific stimulatory effect upon ALP activity. This in vitro system was used to investigate the role of the cAMP pathway in mediating the stimulatory effect of PGE2 on ALP activity. The data indicate that PGE2 causes an increase in cAMP accumulation by the cells and that the addition of an analog of cAMP or substances which increase the level of cAMP in the cells (1-methyl-3-isobutyl xanthine, cholera toxin, forskolin) causes an increase in ALP activity. Collectively, the results suggest that the stimulatory effect of PGE2 is at least partially mediated by the cAMP pathway.     

The importance of fish stocking in the dissemination of parasites throughout a group of reservoirs

In view of the known importance of anthropochore movements of fish in disseminating their parasites, it was hypothesized that local movements of fish between neighbouring water bodies for stocking and management purposes would similarly disseminate their parasites, resulting in a high degree of similarity in the parasite communities of fish in water bodies that have been linked by fish transfers. This hypothesis was tested by comparing the helminth parasite communities in brown trout, Salmo trutta Linnaeus and rainbow trout, Oncorhynchus mykiss (Walbaum), in reservoirs in south west England. In one group of six reservoirs there is a recent history of transfers of rainbow trout, and in the second group of four there have been no transfers over the last decade. There was no difference in mean similarity, using Jaccard's Coefficient and a Percentage Similarity Index, between the helminth faunas of trout in the reservoirs linked by transfers and those not so linked, and the distribution of several individual species of helminths was not consistent with their having been disseminated in the course of fish stockings. The hypothesis is thus rejected and it is concluded that anthropochore transfers of trout between reservoirs have been of little or no significance in the dispersal of parasites throughout the reservoirs or in the transfer of helminths from one reservoir to another. The reasons for this unexpected conclusion are discussed in the light of indications that factors unrelated to fish transfers were important determinants of helminth community composition in individual reservoirs.     

Evaluation and Estimation of Various Markov Models with Applications to Membrane Channel Kinetics

Hidden Markov modelling is a powerful and efficient digital signal processing strategy for extracting the maximum likelihood model from a finite length sample of noisy data. Assuming the number of states in the model is known, then the state levels, transition probabilities, initial state distribution and the noise variance can be estimated. We investigate the applicability of this technique in membrane channel kinetics not only as a parameter estimator, but also as an aid to discriminating between various model types according to their statistical likelihood. We survey three representative classes of channel dynamics, namely: aggregated Markov models, semi-Markov models (with asymptotically convergent transition probabilities), and coupled Markov models; reformulating each within a discrete-time hidden Markov model framework. We then provide numerical evidence of the effectiveness of the procedure using simulated channel data and hence show that the correct model, as well as the model parameters, can be discerned. We also demonstrate that the model likelihood can be used to indicate the approximate number of states in the model.     

X-ray induction of O6-alkylguanine-DNA alkyltransferase protects against some of the biological effects of N-methyl-N'-nitro-N-nitrosoguanidine in C3H 10T1/2 cells

We have shown previously that the repair of O6-methylguanine can be induced in murine fibroblasts (C3H 10T1/2 cells) by exposure to X rays. The magnitude of the response is less, however, than is observed in the well-characterized adaptive response of various prokaryotes to methylating agents. To determine whether the induction of O6-alkylguanine-DNA alkyltransferase in C3H 10T1/2 cells is sufficient for protection against the genotoxic effects of the methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), cells were challenged with MNNG after alkyltransferase induction by 1.5 Gy X rays and assayed for cytotoxicity, mutagenicity, and neoplastic transformation. Preirradiated cells were significantly more resistant to the mutagenic effects of MNNG as scored by formation of ouabain-resistant colonies. The protective effect was greatest in cells challenged with a low dose (0.2 or 0.4 micrograms/ml) of MNNG. Protection against neoplastic transformation by MNNG was also observed, although the protective effect in this case was significant only in cells treated with a high dose (1.0 micrograms/ml) of MNNG. In cells that were preirradiated, there was no reduction in the cytotoxicity caused by MNNG or the chloroethylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). These data indicate that alkyltransferase induction in C3H 10T1/2 cells is sufficient to protect cells against some of the genotoxic effects of the alkylating agent MNNG. The data also suggest that formation of O6-alkylguanine may not be the only means by which alkylating agents can transform C3H 10T1/2 cells.     

Regional distribution and pH sensitivity ofAzospirillum associated with wheat roots in Eastern Australia

In a survey ofAzospirillum spp. on the roots and associated soil of wheat grown in eastern Australia, azospirilla were isolated from approximately 40% of samples from areas of soil pH between 5.0 and 6.6. However, azospirilla isolates were rare in soil between pH 4.5 and 5.0 and absent below pH 4.5. Of 25 independent isolates, 17 wereA. brasiliense and eight wereA. lipoferum. No selection forA. brasiliense Nir^– strains by wheat roots was observed. Only one of six endorhizosphere isolates wereA. brasiliense Nir^–, compared with three of nine from unsterilized roots plus associated soil, and three of eight from soil. With a medium buffered with 0.05 M malate and 0.05 M phosphate, it was found that allAzospirillum isolates had a lower minimum pH for growth when supplied with fixed nitrogen than when grown under nitrogen-fixing conditions. Strains isolated from soils had a minimum pH for growth that was less than the pH of the soil from which they were isolated. However, a significant proportion of strains isolated from roots had a minimum pH for growth that was higher than the pH of the associated soil suggesting that the wheat roots provided an ecological niche protecting against soil acidity.     

A face mask for estimation of whole body leucine turnover in unanesthetized beagle dogs

As part of a long-term study of protein and energy metabolism in Beagle dogs, a latex face mask was developed to facilitate respiratory gas collection. The mask described here is easily assembled using readily available materials and meets the following criteria: small dead air space, lightweight, readily acceptable by conscious dogs over a prolonged period of time, leakproof , and inexpensive. The mask has been successfully used with L-[1-13C] leucine to measure 13CO2 excretion rates in studies of leucine metabolism.     

The sites occupied by the acanthocephalan Pomphorhynchus laevis in the alimentary canal of fish.

The distribution of the acanthocephalan Pomphorhynchus laevis along the alimentary tract of several species of freshwaster fish was studied in both natural and experimental infections. The parasite exhibits a clear preference for a particular region of the alimentary canal, which differs from host species to host species, but it is capable of surviving in all regions of the intestine. In some species, but not in all, its growth rate may be reduced in regions outside of the preferred site. The parsite remains in the same site throughout the period of infection, emigrations occurring only preparatory to complete loss of the parasite from the host. The presence of cestodes in the region of the preferred site has no effect upon the distribution of the parasite. At high levels of infection the range of the parsite's distribution is extended. The feeding of larval parasites to fish by stomach tube also leads to an extension of range, whereas when fish are allowed to feed on cystacanths removed from their intermediate host the parasite establishes in a more anterior position than usual and in a site that it does not occupy to any extent in natural infections. It is concluded that the distribution of P. laevis in the alimentary canal of fish is determined primarily by the process of liberation, activation and establishment of the parasite, and that it normally attaches in the first available space and remains there. Unsuitable physico-chemical or feeding conditions affect only its growth, not the site that it occupies. It is suggested that P. laevis may be atypical in this respect.