Different Levels Of Infection Research Articles

Does spatial heterogeneity and genetic variation in populations of the xanthid crab Rhithropanopeus harrisii (Gould) influence the prevalence of an introduced parasitic castrator?

Potential differences between two populations of the xanthid crab, Rhithropanopeus harrisii (Gould), in susceptibility to infection by an introduced (exotic) parasite, the sacculinid barnacle, Loxothylacus panopaei(Gissler) were investigated. The frequency of L. panopaei infection, which causes castration of the crab host, has risen to 80% during the last 4 yr in one population, while the second population has never been parasitized. Using eggs collected from females of both infected and uninfected populations, broods of larval crabs were reared through metamorphosis, and then placed in field enclosures at the site of the infected population where they were exposed to ambient levels of infective stages of the parasite. We used differences in infection levels among sibling hosts from each population to estimate the heritability (h 2) of susceptibility to parasite infection. Comparisons of infection levels between populations showed no significant differences, nor were there significant differences in parasitism levels among families within a population. The estimate of heritability for susceptibility to parasitic castration was low (h 2 = 0.10), and not significantly different from zero, suggesting little additive genetic variance. In a second experiment, we examined how levels of parasite infection within a single population were affected by the spatial distribution of the crab population. We placed susceptible juvenile R. harrisii in enclosures either 0.1, 1.0, or 10.0 m from experimental aggregations of infected crabs, which acted as a potential source of infective parasite larvae. The spatial distribution significantly influenced levels of parasitic castration with significantly more infected juvenile crabs in enclosures nearest to experimental aggregations (0.1 m) than in enclosures 1.0 m and 10.0 m away. The lack of differences in susceptibility among populations, as well as families within populations, may be explained by several mechanisms including significant gene flow between populations and insufficient time for a measurable response to selection. The data are also consistent with the idea that equivalent generation times of host and parasite may allow the parasite to evolve infectivity as fast as the host can evolve resistance. The significant influence of the spatial distribution of the host population on the prevalence of the parasite suggests that both the rate of spatial spread and prevalence of this parasite in Chesapeake Bay may be influenced by the distance between aggregations of the host population.

Weight gain and the course of some estimators of gastrointestinal nematode infection in calves during winter housing in relation to the level of exposure during the previous grazing season

In two experiments groups of calves were exposed to different levels and patterns of infection with Ostertagia spp. and Cooperia spp. The experimental design simulated the stereotypic pattern of herbage infestation, including a normal or a delayed midsummer increase, under conditions of set-stocking. After this simulated ‘first grazing season’, calves were monitored throughout the subsequent winter housing period. No continuing negative effects of previous infection on growth performance were observed. Calves in all groups gained on average over 0.7 kg day −1, irrespective of previous level of exposure. Differences between the experiments with respect to either level or pattern of infection during the preceding ‘first grazing season’ were all, to a greater or lesser extent, reflected in faecal egg counts, pepsinogen values, gastrin values and antibody titres against Cooperia spp. or Ostertagia spp. Depending on the time of sampling, pepsinogen values and antibody titres against Ostertagia spp. particularly were useful variables for assessing differences in levels of infection to which groups of calves had been exposed.

The occurrence of metacercariae of Bucephaloides gracilescens (Digenea: Gasterostomata) in an intermediate host, the four‐bearded rockling, Enchelyopus cimbrius (Gadidae)

Infections with metacercariae of Bucephaloides gracilescens in the four‐bearded rockling Enchelyopus cimbrius were studied for a year in a Norwegian fjord. The prevalence was at all times high, but abundance showed a marked decline in spring to a low level during summer. A rise in abundance, variance‐to‐mean ratio and frequency of smaller metacercariae in early autumn (August‐September) shows infection to have occurred mainly in autumn. There were no differences in level of infection between host sexes, but a highly significant positive correlation of parasite burden with host length. No influence on the condition factor of the host was revealed, the parasite cysts in the central nervous system are believed to have low pathogenicity. A detailed account of the distribution of metacercarial cysts is given. No support for infection being via the lateral line canals is revealed, cercarial penetration is believed to be through the general surface of the head and through the unpaired fins of the trunk and tail.

Viral pathogens and the advantage of sex in the perennial grass Anthoxanthum odoratum

The ubiquity of sexual reproduction among plants and animals remains one of the major unresolved paradoxes of modern evolutionary biology. In order for sex to be maintained in populations, sex must confer immediate and substantial fitness benefits. Theoreticians have proposed numerous mechanisms to explain how such advantages arise, but experimental data are few. In one well-studied population of the perennial grass Anthoxanthum odoratum in a mown North Carolina field, sexual offspring have been found to have significantly higher fitness than asexual offspring. More recent field experiments show that an aphid-transmitted virus, barley yellow dwarf (BYDV)-strain SGV, specifically transmitted by Schizaphus graminum , frequently infects Anthoxanthum progeny soon after transplantation into the field, BYDV infection is asymptomatic in Anthoxanthum , but BYDV-inoculated clones planted directly in the field had significantly lower fitness than healthy controls. Sexual females have been hypothesized to gain a fitness advantage for their offspring in the presence of pathogens either by providing ‘an escape in time’ from pathogens preadapted to the parental genotype or through the production of rare genotypes, which escape frequency-dependent infection. When parental clones and seed-derived sexual offspring were planted in identical but separate arrays in sites near where the parent was collected, parental clones were twice as frequently infected as sexual offspring. Factors other than genetic variation may have contributed to differences in levels of infection between sexual and asexual progeny: in this experiment, clonally derived asexual offspring tillers were slightly larger than seed-derived sexual tillers; in field experiments, larger plants were more frequently infected than smaller plants. When different families were planted into a common site, there was evidence that genotypes were less frequently infected when locally rare than when common. Taken together, the data suggest that BYDV infection generates advantages for rare or sexually produced genotypes in Anthoxanthum . The pattern of infection is likely to result from a complex interaction between vector, host, and viral genetics and population structure, vector behaviour, and host and vector dispersal patterns. Sexually produced genotypes appear to benefit because they are both novel and rare, but the observed minority advantage was weak. Other viral, bacterial, and fungal pathogens in this Anthoxanthum population may act as frequency-dependent selective forces in different places in the field, collectively generating the substantial and observed overall fitness advantage of rare genotypes. Further study is needed to elucidate their role. Nevertheless, the data do show that viral pathogens, which are often asymptomatic, play a significant evolutionary role in plant populations.

Assessing cercarial transmission of Cyathocotyle bushiensis and Sphaeridiotrema pseudoglobulus by use of sentinel snails

Sentinel snails (Bithynia tentaculata) were used to assess spatial and temporal variation in cercarial transmission of Cyathocotyle bushiensis and Sphaeridiotrema pseudoglobulus at two field locations in southern Quebec and southeastern Ontario from mid-August to the end of October, 1989. Sentinels acquired infections with both digeneans; however, low levels of metacercariae of C. bushiensis precluded any conclusions regarding transmission of this parasite from being reached. In contrast, extensive spatial heterogeneity existed in the S. pseudoglobulus – snail system. Sentinel snails within 10 m of each other were apparently exposed to vastly different levels of naturally occurring cercariae. All size classes of sentinels were apparently equally susceptible to cercarial infections but no consistent temporal differences in infection levels were found.

Effects of sowing seed with different levels of infection, plant density and the growth stage at which plants first develop symptoms on cucumber mosaic-virus infection of narrow-leafed lupins (Lupinus angustifolius)

During 1990-92, narrow-leafed lupins (Lupinus angustifolius) cv. Gungurru, were grown in six field experiments in which plots were sown with healthy seed or seed that carried 0.5-5% infection with cucumber mosaic virus (CMV). Seed-infected plants were the primary source for subsequent virus spread by aphids. The rate of CMV spread and the extent of infection in plots depended on the level of infection in the seed sown, the proportion of infected seeds that successfully developed into established plants and the time of arrival and number of aphid vectors. In general, higher seed infection levels, better establishment of seed-infected plants and early aphid arrival favoured greater virus spread, yield loss and infection in the harvested seed. In 1991, in two experiments, late arrival of aphids resulted in minimal CMV spread, no effect on yield and much less infection in the harvested seed than in the seed sown. In the other four experiments, significant yield losses (25-42%) always resulted when seed with 5% or 3% infection was sown. Sowing 1% infected seed resulted in significantly decreased yields in two experiments, while 0.75% and 0.5% infected seed caused significant losses in one experiment (16-19% losses). Yield decreases were due to both fewer seeds being formed and decreased seed size. Levels of infection in harvested seed did not exceed 15%. In a further field experiment in 1991, individual plants that developed CMV symptoms before initiation of flowering or during flowering had significantly smaller yields than those that developed symptoms after flowering had finished. In four field experiments during 1990-91, 10-15% CMV-infected lupin seed was sown at rates of 20-150 kg ha-1 to generate a range of plant densities. The numbers of seed-infected plants were recorded at different times. The extent of loss of seed-infected plants due to shading by neighbouring healthy plants depended on plant density and the time when canopy closure developed. Where no canopy formed there was little or no loss of seed-infected plants, while early canopy formation at high plant density was most effective in removing them. Current-season spread was also decreased by early canopy formation and high plant density, but this effect was smaller when aphids arrived early. This work supports recommendations for management of CMV infection in lupins by sowing seed with low infection (<0.5%) to minimize infection sources, and sowing early at high seeding rates to remove seed-infected plants through improved canopy formation.

The presence of an early L 4 larvae population in relation to the immune response of calves against Ostertagia ostertagi

The influence of different levels of infection with Ostertagia ostertagi on the development of a protective immune response in calves was investigated. Four groups of calves were infected with either 5000 (Group A), 10 000 (Group B), 20 000 (Group C) or 40 000 (Group D) infective larvae ( O. ostertagi L 3) weekly until treatment began. Group E functioned as controls. All animals were treated with oxfendazole (9 mg ml −1) at Week 17 (Groups A, B and E) or Week 18 (Groups C and D). Sixteen days post-treatment all calves received a challenge infection of 150 000 O. ostertagi L 3 spread over 10 consecutive days. Faeces and blood were collected weekly for egg counts and to assess levels of pepsinogen, gastrin and IgG1 and IgG2 Ostertagia antibodies. All calves were necropsied 31 days post-challenge for worm counts. Egg counts and pepsinogen levels were proportional to the infection level during the first few weeks of the experiment. Only in the high-dosed Group D was a gastrin response evoked. Ostertagia IgG1 antibodies increased between Day 25 and Day 95, and in the non-infected control group an antibody rise was observed from Day 67 onwards. All measured parameters except Ostertagia antibodies showed a gradual decrease from Day 70 until the day of treatment. At necropsy there was no significant difference between the groups in the total worm populations. Only the composition of the worm populations differed, with 35% early L 4 (EL 4) larvae in the previously infected Groups A, B, C and D and only 5% in the control Group E. The results indicate a slow immune response against O. ostertagi in cattle and question the possible role of the EL 4 stage in developing immunity.

Pathogenicity of Some European Collections of Crown Rust (Puccinia coronata Corda) on Cultivars of Perennial Ryegrass

AbstractThree collections of crown rust (Puccinia coronata), from Czechoslovakia, West Germany and the U.K., were tested for their pathogenicity on sixteen cultivars of perennial ryegrass. The Czechoslovakian collection had the highest level of infection on twelve of the cultivars, although with most cultivars there were no significant differences in infection levels. Three cultivars, although with most cultivars there were no significant differences in infection levels. Three cultivars, Kerem, Loret, ta and Tando, contained qualitative resistance to crown rust which was overcome by the Czechoslovakian collection, although they retained a moderately high level of background resistance to this collection.

Modelling regional differences in ‘sealworm’, Pseudoterranova decipiens (Nematoda, Ascaridoidea), infections in some North Atlantic cod, Gadus morhua, stocks

The ascaridoid nematode Pseudoterranova decipiens has a complex life‐cycle. Adult worms reproduce in the stomach of grey seals, Halichoerus grypus, and other pinnipeds, and the larvae are found encysted in the musculature of Atlantic cod, a common host. An increase in infection levels in Canadian, Icelandic and Norwegian cod stocks over the last decade has been attributed to recent increases in seal population numbers. A simple model is proposed for the accumulation of larval parasites in the fish through its food. The model describes how regional differences in fish growth can also explain some differences in infection levels.

Distribution of Trichinella spiralis in the Diaphragm of Experimentally Infected Swine

The objectives of this study were to determine whether the distribution of Trichinella spiralis larvae within the diaphragm of infected swine was the same throughout five anatomically identifiable portions, and to assess the tenability of the Poisson model to describe the probability of detecting larvae in samples of digested tissue.To examine differences in levels of infection among the regions of the diaphragm, sixteen 2-month-old and fourteen 6-month-old swine were infected with approximately 300 T. spiralis larvae per animal. Since the infective dose was not adjusted for age (weight), higher infection rates resulted in the younger hogs. Because of this higher infection rate, the occurrence of positive samples judged to be free of larvae (false negatives), was lower for the younger hogs (0.9% vs 14.6%). Pooling over both age groups and across all five anatomical regions yielded the directional difference in false negative rates one would expect between 1 g and 5 g samples (viz., 12.3% for 1 g vs 2.6% for 5 g).In both age groups, levels of infection were significantly different among the five anatomical regions of the diaphragm (p=.06 at 2 mo; p=.0002 at 6 mo). The Crus muscle consistently yielded more larvae/g than the lumbocostal arch, the dorsal and ventral Pars costalis, and the Pars sternalis. Accordingly, the false negative rates were found to be lowest in the Crus muscle (5 of 59 or 8.5% in 1 g samples and 0 of 58 in the 5 g samples). We conclude that sampling from Crus muscle increases the ability to detect T. spiralis larvae in the diaphragm of infected pork carcasses. Moreover, we demonstrate that the Poisson model (random or “homogenous distribution” of larvae) grossly underestimates the observed false negative rates while predictions based on the negative binomial model provide close agreement.

Junghuhnia vincta(Berkeley) comb. nov., root pathogen ofPinus radiata

Abstract Junghuhnia vincta (Berkeley) comb. nov. is proposed for Poria vincta (Berkeley) Cooke, causal agent of a root disease of Pinus radiata D. Don. The disease occurs in young plantations in the Bay of Plenty, predominantly on sites previously stocked in native forest. The fungus also attacks dicotyledonous and coniferous trees in orchard shelterbelts in the same region. An isolate from a diseased Salix matsudana Koidzumi tree was used to inoculate one-year-old seedlings of ten introduced host species from seven genera. After 18 months, 51 outof 110 inoculated plants had become infected, 30 of which had died. There were significant differences in levels of infection between species. Of 13 inoculated seedlings of P. radiata, three became diseased, confirming the pathogenic behaviour of J. vincta to this host species in the field.

Interaction of Chlamydia trachomatis with human genital epithelium in culture.

Primary cultures of human endometrial and ectocervical epithelial cells were examined as a new model system to study genital infection by Chlamydia trachomatis. Initial studies demonstrated that these cells were indeed susceptible to chlamydial infection. Inocula, adjusted to produce inclusions in 50 to 80% of equivalent numbers of standard McCoy cells, resulted in infection rates of approximately 15 to 30% for the columnar cells of the endometrium and 5 to 10% for the squamous cells of the ectocervix. Exposure of cultures to DEAE-dextran and centrifugation-assisted inoculation, manipulations reported to enhance infection of HeLa and McCoy cells, did not alter the number of inclusion-positive genital cells. Addition of cycloheximide to the post-inoculation culture medium slightly increased numbers of inclusion-bearing cells while growth of genital cells in hormone-supplemented medium resulted in a variable effect on inclusion development and a significant reduction in the association of radiolabelled organisms with these cells. The basis for the different levels of infection in McCoy versus genital cell cultures was revealed by immunofluorescence analysis of chlamydial association with host cells immediately after inoculation. Chlamydiae failed to adhere to many cells in the genital cell cultures while adherence to McCoy cells was uniform. In addition, the association of radiolabelled C. trachomatis was significantly lower with genital cells than with McCoy cells. Finally, culture conditions were defined which markedly inhibited inclusion development without an immediate loss of chlamydial growth potential. This investigation indicates that primary genital cell cultures are susceptible to chlamydial infection and will be valuable for studies on the nature of C. trachomatis interactions with natural human target cells.

Localization and associated histopathology of asexually proliferative Mesocestoides corti tetrathyridia (cestoda) infecting mouse mammary glands

Female mice of pregnant random-bred, or unmated BALB/c groups were exposed per os to Mesocestoides corti tetrathyridia and necropsied at various intervals postexposure. The right posterior subcutaneous fat pad with two mammary glands was removed from each mouse, stained, mounted whole and examined microscopically for localization of worms. The left fat pad/gland set was processed, sectioned and stained using standard histological techniques. In pregnant mice, tetrathyridia were localized primarily in the fat pad's posteroventral lobe. Unmated mice had few worms in the mammary glands or associated fat pads. The difference in infection levels between the two host groups may result from mouse strain difference or the pregnant condition of one group.

LOLIUM ENDOPHYTE LEVELS IN COMMERCIAL PERENNIAL RYEGRASS SEED LINES

A survey of perennial ryegrass seed lines received for testing in 1982 revealed different Lolium endophyte infection level characteristics for different cultivars. Grasslands Ruanui had low infection levels, Ellett had high and Grasslands Nui and other perennial ryegrass samples had variable infection levels. Differences in infection levels are ascribed to the infection status of the original cultivar material and the storage period between harvest and sowing during the seed multiplication process. The problems associated with providing a seed testing service for Lolium endophyte are also discussed.

The population dynamics of eyeflukes Diplostomum spathaceum and Tylodelphys clavata (Digenea: Diplostomatidae) in rainbow and brown trout in Rutland Water: 1974?1978

The development of populations of eyeflukes Diplostomum spathaceum and Tylodelphys clavata in trout introduced into Rutland Water is related to the availability of infected Limnaea pereger, the first intermediate host, and the differential resistance to eyeflukes in Salmo gairdneri and S. trutta. The numbers of snail and fish intermediate hosts were monitored from impoundment of the Gwash in 1974 to completion of the reservoir in 1978. High infection rates in coarse fish in the feeder streams in 1974 are related to high infection rates in Limnaea pereger. Large eyefluke populations in introduced rainbow trout but not in brown trout confirm their differential resistance. Differences in levels of infection in seine-netted and rod-caught rainbow trout suggest that heavily infected fish could not respond to the fishermens' lures. Reduced numbers of eyeflukes in rainbow trout from 1979 onwards are related to the vast increase in volume of the reservoir in 1977 and decrease in abundance of Limnaea pereger.

Schistosoma mansoni: Electrophoretic characterization of strains selected for different levels of infectivity to snails

Individual adult Schistosoma mansoni from strains selected for high or low infectivity to specific strains of the snail intermediate host, Biomphalaria glabrata, were subjected to enzyme electrophoresis on starch gels. Fourteen enzyme systems were analyzed in an attempt to find electrophoretic markers associated with genes for infectivity to snails. The S. mansoni strains were selected from different isolates from Puerto Rico in several strains of B. glabrata. Of an estimated 18 loci, 3 were polymorphic and the remainder monomorphic. For 1 of the 3 polymorphic enzyme loci, lactate dehydrogenase ( Ldh, EC 1.1.1.27), phenotype frequencies were correlated with infectivity to snails. In schistosome strains of low infectivity, frequencies of the Ldh-N phenotype ranged between 0.56 and 0.69, while in strains of high infectivity, Ldh-N frequencies were typically 0.91 to 1.00. Whether the correlation is accidental or due to some form of association, such as chromosomal linkage, between the locus responsible for variation in lactate dehydrogenase and a gene for infectivity to snails remains to be determined.

Studies on Onchocerca tarsicola Bain and Schulz-Key, 1974 in reindeer (Rangifer tarandus) in northern Finland

A survey revealed that Onchocerca tarsicola Bain & Schulz-Key, 1974 is a widespread parasite among reindeer in northern Finland. Of 407 animals studied from 12 reindeer herds, 124 (30.5%) were infected. There was a marked difference in infection levels between different reindeer herds and the frequency as well as the intensity of infection was highest in old animals whereas the parasites were rare in yearlings.

The distribution and biology of the cestode Eubothrium parvum in capelin, Mallotus villosus, (Pallas) in the Barents Sea, and its use as a biological tag

Samples of Eubothrium parvum were obtained from capelin Mallotus villosus at 55 stations throughout the Barents Sea and from Balsfjord, North Norway. The parasite is distributed widely throughout the Barents Sea, but both incidence and intensity of infection are higher in the regions off Murmansk and the Kola peninsula, and Spitsbergen. E. parvum exhibits a seasonal peak in maturation and probably also in acquisition of new infections. The incidence of infection is greatest in 1 + fish, whereas the intensity is more independent of host age. It is suggested that the parasite requires only a single intermediate host, a plank‐tonic copepod, and its distribution in relation to age of host is a reflection of the dietary preference shown by young capelin for copepods. The frequency distribution of E. parvum in capelin was over‐dispersed in Balsfjord, where infection levels of between 1 and 28 parasites per fish were encountered in all samples, but under‐dispersed in the Barents Sea, where infections of more than four parasites per fish were never found and even infections with three and four parasites were very local. It is suggested that the underdispersion is due to a very low probability of infection in the open waters of the sea. Although the presence of E. parvum cannot be used as a biological tag for capelin, its abundance and frequency distribution can. The difference in frequency distribution and the failure to find any heavily infected fish in the Barents Sea confirm the suggestion that the capelin of Balsfjord form a local isolated population, which does not migrate into the Barents Sea. The differences in infection levels within the Barents Sea suggest the further possibility that there are at least two stocks of capelin there, but this requires further investigation and confirmation.

Ostertagiasis in calves. II. infection parameters and body weight gains following housing

The performance of six groups of six calves each from a previous field experiment was followed from the beginning of housing until turning out seven months later. When housed the groups harboured different levels of infection with Ostertagia ostertagi and had corresponding weight and gain reductions. The most heavily infected groups improved rapidly following housing. Elevated serum pepsinogen levels decreased markedly, and approached normal values at eight weeks. Differences in serum pepsinogen levels between groups diminished considerably, but remained significant over the entire stabling period. The serum albumin level was low in the most seriously affected animals at the time of housing, but normal levels were restored within the first twelve weeks. In general, the number of parasite eggs in the faeces of the animals decreased, but there was considerable fluctuation. Apart from a single sampling date, no significant difference in egg per gram (EPG) could be demonstrated between the experimental groups during the stabling period. The calves were fed according to their age. The live weight differences between most and least affected groups diminished from 64 kg at the time of housing to 37 kg at the end of the stabling period. The reduction took place particularly during the first four weeks of housing. Considering both the grazing and stabling periods, it appeared that anthelmintic treatment twice during the period had no effect on the final live weight, whereas remeated treatments at three-week intervals resulted in an increase of 24 kg. Similarly, moving the animals to a clean pasture in mid-July resulted in an increase of 39 kg at the end of the stabling period when compared to calves which were not moved. Treatment of moved animals did not result in further body weight gain after seven months of housing. No significant correlation was found between parasite EPG of faeces and growth rate during the stabling period. However, a positive correlation was found between serum pepsinogen during the first eight weeks of housing and the weight gain over the entire stabling period. This was in contrast to the correlation experienced during the grazing period.

The immune response of pigs to infection with the stomach worm Hyostrongylus rubidus (Hassall and Stiles, 1892) : I. Antibody production in response to primary infection

Pigs infected with single doses of third stage Hyostrongylus rubidus larvae showed a detectable circulating agglutinin response as early as 2 days post infection. Although titres fluctuated considerably before patency, a trend in antibody production could be detected which followed the active development and growth of larvae in the gastric mucosa. At patency, titres showed a large, rapid increase followed by an equally dramatic decrease, after which titres remained stable or increased gradually. Pigs infected with adult worms did not show a detectable agglutinin response until 7 days post infection or later. Little fluctuation in titre was observed. Response variation between different levels of infection was great as was the variation between different litters subjected to the same infection regime. No statistical difference could be found in total antibody production between pigs infected with different larval numbers at any time during the duration of the trial.