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PubMed1982

Genetic control of resistance to infection with Nematospiroides dubius in mice: selection of high and low immune responder populations of mice.

F1, Quackenbush (Q) x Wild (W) Mus musculus were assayed and selected for their level of immunity to secondary infections with 100 Nematospiroides dubius using faecal parasite egg counts. A significant positive linear correlation was found between the number of parasite eggs voided in the faeces and the number of N. dubius recovered after secondary infections in mice. Selection for immunity was not influenced by the conformation of the mice. High (H) and low (L) responder colonies together with a randomly (Rd) bred colony of mice were established over 5 generations. Adaptive immunity was more efficacious in protecting female than male mice and appeared to be controlled by a few dominant genes; the heritability (h2) of the trait was estimated at 0.56 for the parental stock and 0.55 for the F5 Rd colony and the realized heritability was 0.49. Higher anti-N. dubius antibody titres were detected in H than L mice. H mice harboured fewer and less fecund parasites than Rd colony mice; L mice had more worms with greater fecundities than Rd mice. The levels of primary infections in H and L mice related to the levels developed after secondary infection from F4. This suggested at least partial linkage of genes controlling innate with genes controlling adaptive immunity against N. dubius.

Animals↗
PubMed1982

Population dynamics of Angiostrongylus cantonensis during primary infections in rats.

About 35% of Angiostrongylus cantonensis larvae became patent adults irrespective of the dose used to establish primary infections in laboratory rats. Worm growth and fecundity was depressed in infections from high compared with low doses of infective larvae. Rats infected with up to 50 A. cantonensis larvae survived infection better than rats given greater numbers of larvae. The biology of A. cantonensis surviving in laboratory rats from single infections with 50 larvae for over a year was studied. Stable worm numbers and fecundity were established 90 days after infection but the worms continued to grow until the experiment was terminated.

Angiostrongylus↗
PubMed1983

The effect of temperature on the survival and infectivity of the free-living larvae of Nippostrongylus brasiliensis.

The development, survival and infectivity of larvae of Nippostrongylus brasiliensis at 10 and 21 degrees C have been studied. In cultures developed for 1 week at 21 degrees C but stored at either 10 or 21 degrees C the mean recovery of larvae in 1.5 h Baermann sediment (46% and 42% of total eggs, respectively) and their infectivity (66% and 70% day 8 p.i. recovery, respectively) at 4 weeks of cultivation were similar. However, at 20 weeks of cultivation only a few larvae survived storage at 21 degrees C (1.4%) and the survivors showed very low infectivity (4.1%), whereas larvae stored at 10 degrees C retained most of their survival and infectivity rates (41% and 44%, respectively). In cultures developed and stored at 10 degrees C a lower mean proportion (17%) of the eggs was recovered as larvae at 4 weeks of cultivation. The mean infectivity rate of these larvae increased from 4 to 12 weeks of cultivation (18% and 42%, respectively) but was reduced at 20 weeks of cultivation (27%). An increased proportion of adult female worms was recovered from rats infected with larvae from cultures showing poor development or survival and the fecundity of the adult females decreased in all groups as the storage time of the cultures was increased. Eggs from low fecundity adult worms showed normal development of larvae. The relation between survival, temperature in the habitat and the geographical distribution of the larvae of N. brasiliensis is discussed.

Animals↗
PubMed1987

Differences in biological characteristics of two strains of the cestode Hymenolepis diminuta.

Biological characteristics of infectivity, growth rate and fecundity of Hymenolepis diminuta isolated from wild Rattus rattus in Japan were compared with parasites of Texas origin maintained for several generations in this and many other laboratories in laboratory bred Rattus norvegicus. The timing of development and maturation was similar in parasites from both sources, but the mean parasite dry weight was less and the mean egg production lower in Japanese parasites in both single and multiple infections. The differences persisted over 10 weeks in single infections, and were unaffected by rat strain. In all experiments there was much greater variation and heterogeneity in the biological characteristics of the Japanese parasites. It was concluded that the Texas parasites were better adapted to R. norvegicus and in the course of adaptation had become more homogeneous, and that the difference between the parasite strains had a complex genetic basis. Some Japanese parasites of the early isolated generations failed to produce normal eggs, but the proportion of these decreased in later generations. However, selected individual Japanese parasites whose egg production was equal to that of parasites of Texas origin did not produce offspring of larger mean size or higher mean fecundity, and heterogeneity of these characteristics was maintained. In the intermediate host, the mean number of cysticercoids of the Japanese isolate per beetle was higher than that of the Texas strain in Tribolium confusum but lower in Tenebrio molitor. The greater heterogeneity exhibited by Japanese parasites and the genetic basis of the strain difference are discussed with particular reference to geographical isolation, differences in definitive hosts and co-evolution of wild and laboratory host and parasite populations.

Animals↗
PubMed1992

A further model for temporal patterns in the epidemiology of schistosome infections of snails.

The prevalence of Schistosoma mansoni infections of Biomphalaria pfeifferi shows seasonal variation. Field data from Zimbabwe show annual ranges from 0 to 7%. In this paper a mathematical model of B. pfeifferi population dynamics and S. mansoni epidemiology is used as a framework for analysis of these patterns. Snail fecundity is a function of snail age and of temperature, and is apparently affected by other seasonal factors. The pre-patent period is dependent on temperature. Infection affects snail fecundity and mortality. Parameter values are derived from previous field and laboratory studies. The force-of-infection is estimated from the analysis of size-prevalence data. Using observed temperatures, model output agrees well with field data on snail abundance and prevalence of infection over a 14-month period. Seasonal variation in prevalence largely reflects variation in the pre-patent period and in snail population age structure. The possible role of seasonality in the force-of-infection is discussed. Prevalence patterns are not greatly affected by year-to-year differences in temperature. Significant seasonal variation in snail-man transmission rates is expected.

Animals↗
PubMed1994

The population dynamics of parasitic helminth communities.

This paper describes a mathematical model which allows us to compare the data collected from short-term cross-sectional surveys with the population dynamics of host and parasite populations over longer periods of time. The model extends an earlier framework for two parasite species in one host, to one for an arbitrary number of parasite species. We show that the conditions necessary for the coexistence of two parasite species extend to expressions for the coexistence of three or more parasite species. Furthermore, the model suggests that those species which form the 'core' of the parasite community are those whose high fecundity and transmission efficiency permit them to colonize hosts readily. In contrast, those species which are classified as 'satellite' species of the community are either species with low fecundity, or low transmission efficiencies. This work confirms earlier studies that suggest that increasing degrees of aggregation are crucial in allowing several species of parasites to coexist in the same species of hosts. The properties of the model are compared with patterns observed in data collected for helminth parasites of Anolis lizards, wood mice and eels. This combined theoretical and empirical approach confirms the importance of the life history strategies of the parasite in determining the abundance of each species in the community. It suggests that studies of parasite community structure have to pay more attention to the strategies pursued by each individual species before interactions between species are considered.

Animals↗
PubMed2002

Experimental evidence of hybrid breakdown between the two geographical strains of Schistosoma intercalatum.

Reciprocal crosses (Schistosoma intercalatum male Zaire x S. intercalatum female Cameroon: S. intercalatum female Zaire x S. intercalatum male Cameroon) were produced in 10 mice by exposing each mouse to 60 male cercariae of one isolate and 60 female cercariae of the other isolate, and vice versa. Hybrid generations originating from the two crosses were established. The infectivity of the F1, F2, F3 and F4 hybrid generations were evaluated after exposing snails individually to 5 miracidia. A comparative histological study of snails infected with F2 and F4 hybrid sporocysts from both crosses was made to assess abnormalities in the intramolluscan development of the hybrids. The worm recovery rate and fecundity were measured by comparing the fitness of the mid-parents with that of the hybrids. S. intercalatum Cameroon was compatible with Bulinus forskalii and incompatible with B. globosus whereas S. intercalatum Zaire was compatible with B. globosus and incompatible with B. forskalii. In the case of S. intercalatum male Cameroon x S. intercalatum female Zaire, hybrid miracidia develops in both B: forskalii and B. globosus in F1, F2 and F3 generations. The infection rate was much lower for B. globosus and F2 and F3 generations produced few cercariae (less than 30 cercariae in overall per snail) and F4 miracidia were only infective to B. forskalii again producing few cercariae. At 40 days post-infection the sporocyst contains masses of acidophilic granules originating from the breakup of pycnotic nuclei. Similarly the F1, F2 and F3 miracidia of the reciprocal cross (S. intercalatum male Zaire x S. intercalatum female Cameroon) exhibited a dual infectivity for B. forskalii and B. globosus, but cercarial productivity was low (less than 30 cercariae overall per snail for F2 and F3 generations). Histological studies demonstrated sporocyst degeneration in snails infected with F4 generation. In the definitive host, the F, generation (both crosses) exhibited hybrid vigour in that the worm return was greater than that of the mid-parent, F2 and F3 generations. No significant difference in fecundity was demonstrated between the parental strains and the F1 and F2 generations, yet egg production of the F3 generation was significantly lower. It is apparent that there is a post-zygotic barrier in the crosses of S. intercalatum Zaire and S. intercalatum Cameroon from the F2 generations onwards, and sterility of the F4 hybrid sporocyst supports the concept of the existence of 2 distinct taxa.

Animals↗
PubMed2001

Effect of iron deficiency on Trichuris suis and Ascaris suum infections in pigs.

The objective of this experiment was to detect a possible interaction between iron deficiency and intestinal nematode infections. We report on a 2 x 2 study where thirty-one 10-week-old pigs fed a low or a normal iron diet were infected with both Trichuris suis (4500 eggs) and Ascaris suum (1200 eggs). No significant difference was detected between diet groups with respect to parasitological parameters for A. suum or the total number of adult T. suis recovered at necropsy 10 weeks p.i. However, in the low iron group T. suis were located more proximally and the worms were increased in length. A higher proportion of pigs with initial faecal egg excretion at 6 weeks p.i. was observed in the low iron group, indicating a shortened pre-patency period. Worm fecundity and total faecal egg excretion were also highest in the low iron group. A significant correlation was found between female worm length and fecundity. The peripheral eosinophil counts were diminished in the low iron host groups. The infected low iron group experienced more severe pathophysiological changes in terms of hypoalbuminaemia and decreases in erythrocyte volumes. A significant inverse correlation existed between iron content in the bone-marrow and liver (body) store. In conclusion, iron deficiency increased the severity of T. suis infection in pigs.

Anemia, Iron-Deficiency↗
PubMed2001

Snail-trematode life history interactions: past trends and future directions.

Life history traits expressed by organisms vary due to ecological and evolutionary constraints imposed by their current environmental conditions and genetic heritage. Trematodes often alter the life history of their host snails by inducing parasitic castration. Our understanding of the variables that influence the resulting changes in host growth, fecundity and survivorship is insufficient to confidently predict specific outcomes of novel snail-trematode combinations. In a literature review of the last 30 years, we found 41 publications examining various life history characteristics of trematode-infected snails. These publications reported 113 different field and laboratory experiments involving 30 snail species and 39 trematode species and provided a data set for assessing factors that potentially affect life history outcomes. Analysis of the diverse responses across various snail-trematode systems and experimental conditions teased out general patterns for the expression of host growth, fecundity and survival. These were used to address existing hypotheses and develop several new ones relating the response of snail-trematode interactions to environmental and genetic factors. Finally, we propose directions for future experiments that will better assess the ecological and evolutionary factors influencing snail life history responses to trematode parasitism.

Animals↗
PubMed2001

Immunity in calves against Dictyocaulus viviparus following a low primary infection.

Thirty Holstein Friesian heifer calves, 3 months of age, were used to evaluate whether a low primary infection with Dictyocaulus viviparus would result in immunity against challenge infection 5 or 12 weeks later. Fifteen calves were experimentally infected with 30 larvae at day 0, while the other calves remained as uninfected controls. On day thirty-five 6 primary infected (G1) and 6 non-infected calves (G2) were challenged with 2000 larvae. These groups were necropsied on day 70. On day 84 the remaining 9 primary infected (G3) and 9 non-infected (G4) calves were similarly challenged and necropsied on day 119. Respiratory signs developed in most calves from approximately 2 weeks after challenge, but signs were more severe in G2 and G4 than in G1 and G3. The low primary infection resulted in significantly reduced faecal larval excretion (> 80%) and worm burdens (> 70%). In the primary infected groups the proportion of female worms in the worm burden was increased, suggesting that part of the developed immunity affected survival of the worms after their establishment in the host. Worm lengths and worm fecundity were also significantly reduced. All observed effects were stronger following challenge on day 84 than on day 35, but the effect of the duration of a primary infection (contrast between G1 and G3) was only statistically significant in the case of mean faecal larval excretion on the day of necropsy (P < 0.05) and fecundity (P < 0.05).

Animals↗
PubMed2002

Costs of resistance in insect-parasite and insect-parasitoid interactions.

Most, if not all, organisms face attack by natural enemies and will be selected to evolve some form of defence. Resistance may have costs as well as its obvious benefits. These costs may be associated with actual defence or with the maintenance of the defensive machinery irrespective of whether a challenge occurs. In this paper, the evidence for costs of resistance in insect-parasite and insect-parasitoid systems is reviewed, with emphasis on two host-parasitoid systems, based on Drosophila melanogaster and pea aphids as hosts. Data from true insect-parasite systems mainly concern the costs of actual defence; evidence for the costs of standing defences is mostly circumstantial. In pea aphids, the costs of standing defences have so far proved elusive. Resistance amongst clones is not correlated with life-time fecundity, whether measured on good or poor quality plants. Successful defence by a D. melanogaster larva results in a reduction in adult size and fecundity and an increased susceptibility to pupal parasitoids. Costs of standing defences are a reduction in larval competitive ability though these costs only become important when food is limited. It is concluded that costs of resistance can play a pivotal role in the evolutionary and population dynamic interactions between hosts and their parasites.

Animals↗
PubMed2002

Host immune responses are necessary for density dependence in nematode infections.

Nematode infections are subject to density-dependent effects on their establishment, survivorship and fecundity within a host. These effects act to regulate and stabilize the size of nematode populations. Understanding how these density-dependent effects occur is important to guide the development of control strategies against parasitic nematodes and the diseases that they cause. These density-dependent effects have been hypothesized to result from intraspecific competition between parasites for limited resources or from the action of host immune responses. However, no specific evidence exists to distinguish between these two hypotheses. We find that in nematode (Strongyloides ratti) infections, density-dependent effects on parasite establishment, survivorship and fecundity are mediated by the host immune response. These density-dependent effects are only observed late in primary infections and no density-dependent effects are observed in infections in immuno-compromised animals. We find no evidence for intraspecific competition between parasites in experimental infections over a range of doses that encompasses all that is observed in natural infections. We conclude that density-dependent effects due to the immune response will act to regulate S. ratti infections before competition for space or nutrients within the host gut ever occurs.

Animals↗
PubMed2004

The dynamics of Wuchereria bancrofti infection: a model-based analysis of longitudinal data from Pondicherry, India.

This paper presents a model-based analysis of longitudinal data describing the impact of integrated vector management on the intensity of Wuchereria bancrofti infection in Pondicherry, India. The aims of this analysis were (1) to gain insight into the dynamics of infection, with emphasis on the possible role of immunity, and (2) to develop a model that can be used to predict the effects of control. Using the LYMFASIM computer simulation program, two models with different types of immunity (anti-L3 larvae or anti-adult worm fecundity) were compared with a model without immunity. Parameters were estimated by fitting the models to data from 5071 individuals with microfilaria-density measurement before and after cessation of a 5-year vector management programme. A good fit, in particular of the convex shape of the age-prevalence curve, required inclusion of anti-L3 or anti-fecundity immunity in the model. An individual's immune-responsiveness was found to halve in approximately 10 years after cessation of boosting. Explanation of the large variation in Mf-density required considerable variation between individuals in exposure and immune responsiveness. The mean life-span of the parasite was estimated at about 10 years. For the post-control period, the models predict a further decline in Mf prevalence, which agrees well with observations made 3 and 6 years after cessation of the integrated vector management programme.

Adolescent↗
PubMed2006

The effect of inulin on new and on patent infections of Trichuris suis in growing pigs.

The objective of this experiment was to investigate the potential influence of inulin on the establishment of new and patent infections of Trichuris suis in growing pigs. Two experimental diets were formulated based on barley flour with either added insoluble fibre from oat husk (Diet 1) or a pure inulin (16%) supplementation (Diet 2). Twenty-eight 10-week-old pigs were divided randomly into 4 groups (Groups 1-4) each of 7 pigs. After 3 weeks adaptation to the experimental diets all pigs were infected with a single dose of 2000 infective T. suis eggs. Group 1 was fed Diet 1 until 7 weeks post-infection (p.i.) and Group 3 until 9 weeks p.i., Group 2 was fed Diet 2 until 7 weeks p.i., Group 4 was fed Diet 1 until week 7 p.i. and was switched-over from Diet 1 to Diet 2 until week 9 p.i. Seven weeks p.i. pigs in Groups 1 and 2 were slaughtered, and pigs in Groups 3 and 4 were slaughtered at 9 weeks p.i. Trichuris suis worm burdens were determined for all pigs. Inulin-fed pigs (Group 2) exhibited an 87% reduction in EPG, compared to the pigs on standard diet (Group 1) (P < 0.0001). The number of worms recovered at week 7 p.i. from pigs on the inulin diet (Group 2) was significantly reduced by 71%, compared to the pigs on standard diet (Group 1) (P < 0.01). At week 9, worm recovery in pigs on the inulin diet switch protocol (Group 4) was reduced by 47% compared to the control pigs in Group 3 (P < 0.01). Further, the inulin-fed pigs exhibited a significant reduction in female worm fecundity and worm large intestine location was more distal compared to those from pigs on standard diet. These results demonstrate that inclusion of the highly degradable fructose polymer inulin in the diet leads to significant reductions in T. suis establishment, egg excretion, and female worm fecundity and can be used as a treatment for patent infections.

Animal Feed↗
PubMed1997

Experimental Oesophagostomum dentatum infections in the pig: worm populations at regular intervals during trickle infections with three dose levels of larvae.

A trickle infection experiment was undertaken to study in detail the population dynamics of Oesophagostomum dentatum in pigs. Three groups of 32 pigs were inoculated via the feed twice weekly with 100 (Group A), 1000 (Group B) or 10,000 (Group C) O. dentatum infective larvae (L3). Five pigs from each group were killed 2, 4, 8, 12, 16, and 20 weeks after the first inoculation (p.i.) to determine their worm burdens. Weekly faecal egg counts were determined. At slaughter, worms were counted, differentiated according to sex and developmental stage, and their length measured. Faecal egg counts ranked with dose rate until week 15, but later were more variable. The proportion of the total number of L3 administered which were recovered at slaughter inversely ranked with dose rate. In group C it decreased over time, whereas in groups A and B there was no consistent pattern. Worm fecundities (epg/female) in groups A and B were higher than in group C. The lengths of the female worms increased over time, whereas the lengths of the male worms remained approximately constant from week 8. The study suggests reduced establishment of incoming larvae and lower fecundity of the female worms at high dose levels.

Animals↗
PubMed1998

Experimental evidence of hybrid breakdown between genetically distinct populations of Echinostoma caproni.

In this paper we investigate whether the assortative mating between individuals of the same genetic entity (i.e. coming from the same geographical area) of Echinostoma caproni, reported in a previous paper, may be explained by a post-zygotic isolating mechanism. The fecundity of the adults of 2 parental genetic entities and of their hybrids (i.e. F1, F2, F3) was quantified through 3 successive generations. Whereas the number of eggs released by F1 hybrids is similar to that of the mid-parent, that of recombinant hybrids (F2-3 hybrids) is significantly lower than that of F1 and that of the mid-parent. Since these results seem to demonstrate hybrid breakdown, 2 important factors maintaining reproductive isolation, i.e. pre-mating reproductive isolation and low hybrid fecundity, may influence the evolution of E. caproni.

Analysis of Variance↗
PubMed1999

Fitness of wild-caught Drosophila melanogaster females: allozyme variants of GPDH, ADH, PGM, and EST.

We have collected several hundred Drosophila melanogaster flies (near Davis, California), isolated them individually, without anesthesia, at the collecting site, and estimated the fitness components of the wild-caught females under different environmental conditions. The fitness parameters measured are fecundity, oviposition rate, and productivity (egg-to-adult viability, development rate, and number of progeny). The environmental variables are two temperatures (22 degrees C and 28 degrees C) and two densities ('scant' and 'crowded'). After the fitness measurements are completed for each individual female, its genotype is determined at four loci encoding enzymes: GPDH and ADH, located on chromosome II; and PGM and EST-C, located on chromosome III. Density has a large significant effect on productivity; temperature has significant effects on fecundity, oviposition rate, and development rate. The experiments show that allozyme polymorphisms are associated with selection effects. Fitness differences between allozyme genotypes occur for all fitness components, except oviposition rate. But which genotype is superior depends on the environmental conditions; heterozygotes exhibit higher fitness than homozygotes in a number of cases, but inferior in others. A unique feature of the present experiments is that the experimental flies are wild-caught females rather than laboratory-bred individuals.

Alcohol Dehydrogenase↗
PubMed2001

Feeding by the aphid Sipha flava produces a reddish spot on leaves of Sorghum halepense: an induced defense?

Feeding by the aphid Sipha flava produces a reddish spot on mature leaves of Sorghum halepense. The present work is aimed at determining whether this plant response entails induced resistance against the aphid. Old and young leaves showed the same response to aphid feeding (reddish coloration). Water-stressed plants displayed a similar reddish coloration to aphid-infested plants. This was verified by evaluation of absorbance peaks of the respective leaf extracts. Aphid fecundity was reduced on previously infested (and hence reddish colored) leaves. However, aphid fecundity was not affected on water stressed plants. Furthermore, aphid survival was not different on artificial diets containing increasing concentrations of the reddish pigment. It is concluded that the reddish spot is correlated with, but is not itself responsible for, the observed induced resistance of S. halepense against S. flava.

Animals↗