Factors influencing the fecundity of Moniliformis moniliformis (Acanthocephala): constant diet and varied dose

Aspects of the reproductive performance of Moniliformis moniliformis were investigated in rats allowed to feed ad libitum on a purified diet containing 1% (w/w) fructose as an energy source for the worms. The rats were infected with either 10, 20, 40 or 80 cystacanths each with the intention of investigating density-dependent effects on worm fecundity. The establishment of the worms in the gut was independent of dose, but survival, growth and reproductive performance generally were shown to be related to the infective dose given to the rats. The effects could not be related to the absolute numbers of worms present in the small intestine at post-mortem examination. In general, some unidentified regulatory process appeared to operate to create severe density-dependence in survival so that surviving parasites were not present in numbers expected to generate competition. Attainment of sexual maturity, growth and the production of mature eggs by worms from rats given doses of 80 cystacanths each were delayed compared with worms from rats given the other doses, but eventually the performance of the high-dose worms caught up. Worms attached more anteriorly in the small intestine grew bigger and produced more mature eggs. Possible mechanisms responsible for the observed effects are discussed.     

Hymenolepis diminuta: Worm loss and worm weight loss in long-term infections of the rat

Infections of one and two Hymenolepis diminuta established in newly weaned rats continued to grow for the duration of the experiment (238 days), whereas infections of 5 worms per rat became asymptotic around Day 55 postinfection and remained at or below this level thereafter as shown by biomass and mean weight per worm measurements. Infections of 50 worms established in newly weaned rats became asymptotic around Day 28 postinfection and thereafter worms were lost from the rats. Initially the biomass fell with the loss of worms, but by Day 56 a new lower biomass persisted for the remainder of the infection period. This level was maintained, despite diminishing numbers of worms, due to the growth of surviving individuals to a weight exceeding the original weight at maturity by a factor of more than 2. Experiments using rats that were mature at the time of infection demonstrated that the same response occurred, but approximately 3 weeks earlier.     

Density-dependent effects on the survival and growth of the rodent stomach worm Protospirura muricola in laboratory mice

The spirurid nematode, Protospirura muricola, is of intrinsic interest as a rodent model of gastric nematode infections. Since worm burdens can be very heavy in nature, density dependent processes may constrain parasite growth. Laboratory mice (BKW) were exposed to varying doses of infective larvae of P. muricola in the range 5 to 40 third-stage larvae (L3), in four separate experiments in which progressively higher doses were utilized. All mice were culled 60 days after infection and a total of 518 worms (226 male and 292 female worms) was recovered, measured and weighed. Overall survival was 58.9%, but survival declined significantly with increasing dose by approximately 21% (from 66% at 5 L3 per mouse to 52% at 40 L3 per mouse). The length and weight of worms correlated positively in both sexes. Total worm biomass increased linearly with increasing numbers of worms. However, whilst the length and weight of male worms declined with increasing worm burden (8.4 and 24.6% respectively), female worms were less affected, only length showing a significant reduction with increasing parasite burden (16.0%). Therefore, increasing worm burdens impeded growth of P. muricola, but reduction in length and weight were relatively small in relation to the overall size of this nematode. Increasing worm burdens were associated with loss of host weight and reduction in stomach weight and worm burdens in excess of 20 exerted a measurable cost to the host, which in the field, may be associated with loss of overall host fitness.     

Reproductive potential of Echinococcus multilocularis in experimentally infected foxes, dogs, raccoon dogs and cats

A total of 15 red foxes, 15 raccoon dogs, 15 domestic dogs and 15 domestic cats were each infected with 20,000 protoscolices of Echinococcus multilocularis. At 35, 63, and 90 days post inoculation (dpi), five animals from each group were necropsied and the worm burdens determined. The highest worm burdens in foxes (mean of 16,792) and raccoon dogs (mean of 7930) were found at 35 dpi. These declined to a mean of just 331 worms in foxes and 3213 worms in raccoon dogs by day 63 with a further decline to 134 worms in foxes and 67 worms in raccoon dogs by day 90. In dogs, there was no significant difference between worm burdens recovered at days 35 (mean of 2466) and day 90 (mean of 1563), although reduced numbers were recovered on day 63 (mean of 899). In cats, worms were found in four animals 35 dpi (mean of 642), in three at 63 dpi (mean of 28) and in two at 90 dpi (mean of 57). Faecal egg counts were determined at 3 day intervals from 25 dpi. A mathematical model of egg excretion dynamics suggested that the mean biotic potential per infected animal was high in foxes (346,473 eggs); raccoon dogs (335,361 eggs) and dogs (279,910 eggs) but very low for cats (573 eggs). It also indicated that approximately 114, 42 and 27 eggs per worm were excreted in the faeces of dogs, raccoon dogs and foxes, respectively. The fecundity of worms in cats was low with an average of less than one egg per worm. The peak levels of coproantigen were detected earlier in foxes and raccoon dogs than in dogs. Eggs recovered from foxes, raccoon dogs and dogs resulted in massive infections in experimental mice. However, metacestodes did not develop from eggs originating from infected cats. It is concluded that foxes, raccoon dogs and dogs are good hosts of E. multilocularis. In contrast, the low worm establishment, the very few excreted eggs and the lack of infectivity of eggs strongly indicate that cats play an insignificant role in parasite transmission.     

Factors influencing the fecundity of Moniliformis moniliformis (Acanthocephala): constant dose and varied diet

The reproductive performance, including survival, growth and mature egg production, of Moniliformis moniliformis was studied experimentally during primary infections in rats given 10 cystacanths each. Four isoenergetic purified diets containing either 1, 3, 6 or 12% fructose (w/w) were used and the amounts of fructose in the intestinal lumen of rats fed on these diets were measured. It was concluded that, while dietary composition had no effect on parasite establishment, there were associations between diet and the survival, growth and fecundity of the parasite. The host diet containing 3% fructose was considered to be more favourable for the worms than the others; 12% fructose was associated with a curtailment of survival time without any compensatory production of eggs. Female worms from rats fed on diets containing 3 or 6% fructose grew larger, and consistently carried more ovaries and produced more eggs than those from rats fed on the 1% fructose diet. It was concluded that these and other findings might be mediated not only through the amount of available fructose in the intestine for worm metabolism, but also by the responses of the host's intestinal physiology to the varying concentrations of fructose in the diet.     

Effects of a 100 metacercarial cyst inoculum on the host-parasite relationship of Echinostoma caproni and ICR mice

The host-parasite relationship of a 100 metacercarial cyst inoculum of Echinostoma caproni in the ICR mouse was examined. Three groups of mice, A, B and C, each with six mice per group were used and all mice were necropsied at 14 days postinfection (p.i.), at which time the worms were ovigerous. Group A consisted of uninfected controls, whereas group B received 25 cysts per mouse (low dose) and group C received 100 cysts per mouse (high dose). There was no significant difference in food consumption between any of the groups from 0 to 14 days p.i. Control mice increased their body weight by 12%, group B by 5%, and group C showed a less than 1% increase in body weight between 0 and 14 days p.i. Echinostome parasitism caused a significant increase in the diameter of the mouse gut, with the gut of group C being more significantly dilated than that of either group A or B. The average worm recovery from group B was 20 worms per host, compared to 72 worms per host from group C. The mean wet and dry weights per worm from group B were 2.4 and 0.4 mg, respectively as compared to 0.6 and 0.2 mg respectively for group C. The mean number of uterine eggs per worm from group B was 180 compared to 125 for worms from group C. Worms from group C were more widely distributed in the small intestine than those from group B. Crowding effects associated with the high dose infection were clearly demonstrated in E. caproni from ICR mice.     

Mannose and the ‘Crowding effect’ of Hymenolepis in rats

Hymenolepis diminuta from rats infected with 10 cysticercoids and fed on a diet containing 3% (w/w) mannose for 4 weeks were found to be, on average, much heavier in terms of dry weight (46 mg) than those from rats fed on diets containing an equivalent concentration of either galactose, glucose or fructose (18 mg). Subsequently, the numbers, egg production and dry weights of worms were determined from rats which had been infected with doses varying from 0 to 160 cysticercoids per rat and fed on diets containing either 0, 1, 4, or 8% mannose (w/w). Density-dependent decreases in both worm dry weight and egg production were detected at 5 weeks post-infection, but both the number of worms recovered and their prepatent period appeared to be independent of cysticercoid dose. Differences in the distribution pattern of individual worm dry weights were observed between rats harbouring low (1–15) and high (16–135) worm burdens. Worms recovered from rats infected with 10 cysticercoids and fed on a diet containing 4% mannose (w/w) for 3 weeks were found to be, on average, more than twice as heavy (37 mg) as those from rats fed on diets containing 1, 2, or 8% mannose (w/w) for equivalent periods of time (16 mg). The results indicate that the ‘crowding effect’ cannot be explained simply in terms of inter-worm competition for carbohydrate.     

Loss of Hymenolepis diminuta from the rat

One, 5, 15 and 30 worm infections of Hymenolepis diminuta were established in juvenile or adult male (Hooded Rowett or Sprague-Dawley) rats. Worm numbers and weight, and egg output were determined from day 15 to day 85 post infection. Gradual worm loss occurred only from 15 and 30 worm infections. In 5, 15 and 30 worm infections worm weight decreased from day 19 to day 50 but no weight loss occurred in single worm infections. The size range of individual worms from a multiple infection of a single rat increased markedly following infection. Adult rats showed a greater worm loss and harboured smaller worms than juvenile rats. The data will fit either a competitive or an immunological model.     

Inequalities in size and intensity-dependent growth in a mermithid nematode parasitic in beach hoppers

Inequality in body sizes is a common feature in populations of helminth parasites, with potential consequences for egg production and population genetics. Inequalities in body lengths and the effects of intraspecific competition on worm length were studied in a species of mermithid nematode parasitic in the crustacean Talorchestia quoyana (Amphipoda: Talitridae). The majority of the 753 worms recovered were relatively small, and an analysis using a Lorenz curve and Gini coefficient suggested that there were no marked inequalities in body lengths among the worms. Total worm length in the 356 infected amphipods (i.e. the sum of the lengths of all the worms in a host) increased steadily as a function of the number of worms per amphipod, whereas the length of the longest worm per amphipod peaked in amphipods harbouring intermediate numbers of worms. This last result was not significantly accounted for by the observed increase in host size with increasing intensity of infection, but resulted from a correlation between worm length and host size. As the number of worms per amphipod increased, the relative sizes of the second-, third-, and fourth-longest worms per host increased markedly. This means that relative inequalities in sizes become less pronounced, i.e. subordinate worms get closer in size to the longest worm, as the number of worms per host increases. The main consequence of this phenomenon is that worm sizes in the mermithid population are more homogeneous than they would be if intraspecific competition had stronger effects on worm growth.     

Some influences of population density on Hymenolepis diminuta in rats.

When measured 56 days postinfection the length, wet weight and dry weight of Hymenolepis diminuta were all found to decrease with increasing number of cysticercoids given up to 20. The mean position of the worms in 10, 12 and 20 worm infections is significantly posterior to that of 1, 2 and 5 worm infections and the worms are attached over a wider area of the intestine. Egg production by the worms was followed up to day 56 postinfection; the number of eggs produced per worm and even per rat decreased with increasing population density. Thus the best way to get most eggs and to maintain the parasite in the laboratory is to have rats infected with only one tapeworm. Rats given 1-20 cysticercoids showed a mean recovery of 100-65%, while rats given 40-200 cysticercoids showed a mean recovery ranging from 13 to 2%. In addition to 'normal' worms, defined as worms greater than 10 mm, small, most probably destrobilated, worms were found. In the 50 and 100 cysticercoid infections, worm recoveries were, respectively, 8% 'normal', 16% small, and 2% 'normal', 5% small. From the significantly lower recovery from heavy infections it is concluded that a deleterious factor is operating during the 8 weeks after the infection.     

Effect of cystacanth body size on adult success

Laboratory-reared cystacanths of Leptorhynchoides thecatus (Acanthocephala: Rhadinorhynchidae) were used to study the effect of cystacanth size on adult success and the factors that influence cystacanth size within the intermediate host. To assess how host size and intensity of infection influence cystacanth size, infected amphipods (Hyalella azteca) were measured, and sex, length, and width of cystacanths were determined. After a subset of cystacanths was measured, small- and large-size classes of cystacanths were designated. To determine how cystacanth size relates to adult size, green sunfish (Lepomis cyanellus) were fed 10 large or small cystacanths. Fish were dissected 6 wk after infection, and worms were removed. After adult worms were permanently mounted on slides, their length and width were measured. Intensity of infection and amphipod size significantly influenced cystacanth size in that large amphipods harbored larger cystacanths than did small amphipods and heavy infections produced smaller cystacanths than did light infections. Adult worms from the small and large cystacanth-size classes showed no significant difference in size; however, large cystacanths had a significantly higher establishment and survival than did small cystacanths: 40% of large worms and 14% of small worms were recovered. The results of this study indicate that host size and host sharing influence cystacanth size and that cystacanth size is an important factor in determining adult success.     

A comparison of three geographical isolates of Trichinella spiralis from the mid-Atlantic United States

Three isolates of Trichinella spiralis (black bear: 41o50'N, 79o00'W, 1982; grey fox: 41o00'N, 76o00'W, 1982; domestic pig: 39o80'N, 75o30'W, 1983) from the mid-Atlantic United States were characterized in Crl: COBS CFW (SW) mice during 10 successive 40-day generations. Over 10 generations, the isolates differed as follows: worm position of the ursine isolate was significantly more posteriad compared to the porcine isolate; sex ratio of the vulpine isolate was significantly lower compared to the ursine and porcine isolates; females of the porcine isolate produced significantly more newborn larvae in vitro than the sylvatic isolates; both the larvae per gram (LPG) and reproductive capacity index (RCI) were significantly higher for the porcine isolate; and male worms of the vulpine isolate were significantly smaller than those of the porcine or ursine isolates. No differences were observed among isolates for percentage of inoculum recovered, length of female worms, or uterine length. The fecundity of the isolates in hamsters, gerbils, multimammate rats, Sprague-Dawley rats, and Peromyscus sp. was examined also. Based upon RCI and LPG, the porcine isolate was the most fecund in all hosts except gerbils. This higher fecundity was often manifest as increased morbidity and mortality in hosts infected with this isolate. The relationship between the virulent nature of the porcine isolate and the enhanced transmission of T. spiralis are discussed.     

In vitro and in vivo studies on the bioactivity of a ginger (Zingiber officinale) extract towards adult schistosomes and their egg production

The bioactivity of an ethyl acetate extract of ginger (Zingiber officinale) towards Schistosoma mansoni adult pairs, both cultured in vitro and in vivo in laboratory mice, was investigated by monitoring worm mortality and fecundity. In vitro, a concentration of 200 mg l(-1) of extract killed almost all worms within 24 h. Male worms seemed more susceptible than female under these conditions. Cumulative egg output of surviving worm pairs in vitro was considerably reduced when exposed to the extract. For example, after 4 days of exposure to 50 mg l(-1), cumulative egg output was only 0.38 eggs per worm pair compared with 36.35 for untreated worms. In vivo efficacy of the extract was tested by oral and subcutaneous delivery of 150 mg kg(-1) followed by assessment of worm survival and fecundity. Neither delivery route produced any significant reduction in worm numbers compared with untreated controls. Worm fecundity was assessed in vivo by cumulative egg counts per liver at 55 days post infection with mice treated subcutaneously. Such infections showed egg levels in the liver of about 2000 eggs per worm pair in 55 days, in both treated and control mice, with no significant difference between the two groups. To ensure that density-dependent effects did not confound this analysis, a separate experiment demonstrated no such influence on egg output per worm pair, at intensities between 1 and 23 worms per mouse.     

Infections of forest rat filaria, Breinlia booliati, in neonate and juvenile laboratory white rats

The kinetics of Breinlia booliati infection in 3 inbred rat strains (Lewis, Wistar and Sprague Dawley) were investigated. One group of rats was infected as neonates (less than 24 hours of age) with third-stage larvae of B. booliati and the other group was infected as juveniles (4 weeks of age). The results showed that infection in the neonates were significantly different from the infection in the juveniles. The 60 rats infected as neonates, when necropsied between 8 to 10 months postinfection, yielded adult worms. The 2 neonatal infection groups of Lewis and Wistar strains showed highest susceptibility to the infections. The mean prepatent period was 85 days. Ninety to 95% of the infected rats were patent with microfilaraemia and a large percentage (33 to 47%) of them had high microfilaraemia counts exceeding 3000 mff/20 mm3 of blood and larger sizes (mean 157.11 mm for female adult worms and 61.88 mm for male adult worms. The adult worms were distributed equally in both the pleural (57%) and peritoneal cavity (43%). In most aspects, the neonatal infection group of the Sprague-Dawley strain was intermediate in susceptibility between the 2 neonatal infection groups of the Lewis and Wistar strains and the 3 juvenile infection groups. In contrast to neonatal infection groups, the 3 juvenile infection groups exhibited low infection rates (37%, 58% and 47% for the Lewis, Wistar and Sprague Dawley strains respectively), longer prepatent periods (mean 101 days), lower recovery rates (2 to 4%), lower adult worm loads (mean 0.4 to 0.8 female worms, and 0.2 to 0.8 male worms per rat), and smaller sizes (mean 141.24 mm for female adult worms and 53.75 mm for male adult worms). Forty-four to 57% of these infected rats harboured either single male or single female adult worms in the body cavity. Most (92%) of the adult worms recovered from the juvenile infection groups resided in the pleural cavity and the remaining 8% were recovered from the peritoneal cavity. Microfilaraemia could be detected in only 3/20 Lewis rats, 5/20 Wistar rats and 5/20 Sprague Dawley rats. The mean peak microfilaraemia of the 3 pooled juvenile infection groups was 632 mff/20 mm3 of blood, ranging from 7 mff/20 mm3 to 1856 mmf/20 mm3. Our results indicate that the susceptibility to B. booliati infection in white rats is both genetic and age-associated. The responses of the 2 distinct infection groups to B. booliati infections are discussed.     

Action of diethylcarbamazine citrate on protective immunity in rats infected with Nippostrongylus brasiliensis

Rats made immune to Nippostrongylus brasiliensis and treated with diethylcarbamazine citrate (DEC) orally (250 mg/kg X 6) exhibited significant suppression of functional immunity. Similarly, administration of compound 48/80 (100 micrograms/rat i.p.) made the immune rats susceptible to challenge infection. Treatment of rats, with 22-day infection with compound 48/80, histamine (20 mg/rat, per os), or L-histidine (20 mg/rat, orally s.c.) did not accelerate worm expulsion. A massive complement-dependent adherence of peritoneal cells (1 X 10(8], isolated from immune DEC-treated and untreated rats, to infective larvae (L3) was observed. Likewise, heavy congregation of normal peritoneal cells to larvae was noticed when the cells were incubated with sera obtained from immune, DEC-treated or untreated rats. The rats receiving mesenteric lymph node cells (125 X 10(6) i.v.) or sera (0.5 ml or 1 ml X 3 i.p.), obtained from immune DEC-treated rats and challenged with infective larvae developed 50% more worms than those which received cells or serum from untreated immune donors. DEC appears to cause suppression of functional immunity and worm expulsion is not histamine mediated.     

Host-parasite relationship of Angiostrongylus cantonensis. 1. Intracranial transplantation into various hosts.

Various stages of Angiostrongylus cantonensis recovered from the brain of experimentally infected mice were transplanted intracranially into rats. Third and fourth-stage worms recovered 2--7 days postinfection were able to develop normally after transplantation into recipient rats. The fifth-stage worm obtained 14--15 days postinfection would enter the brain tissue of rats but died shortly afterwards. However, the same stage of worms recovered from rats, after a similar transplantation, were found to develop normally in the recipient animal. Young fifth-stage worms, from the subarachnoid space of rats, which were ready for the pulmonary migration were also transplanted into rabbits but the worms failed to reach the lungs. In the control rat-to-rat transplantation, the worms successfully completed the pulmonary migration. The morphogenesis and initial growth rate of A. cantonensis were similar in both mice and rats but in the former host the worms started to grow at a markedly slower rate after the last moult and gradually degenerated.     

Biochemical effects of thiabendazole and cambendazole on Hymenolepis diminuta (Cestoda) in vivo

An investigation of the chemotherapeutic and biochemical effects of two benzimidazole anthelmintics, thiabendazole (TBZ) and cambendazole (CBZ), on Hymenolepis diminuta in experimentally infected rats is reported. Thiabendazole was active against H. diminuta at a relatively high dosage. A single oral dose of TBZ at 250 mg/kg body weight on day 15 of infection eliminated 100% of the tapeworms as determined at necropsy 5 days after treatment. The chemotherapeutic actions of TBZ on H. diminuta were accompanied by marked changes in worm weight and chemical composition. Tapeworms recovered from rats that had received a therapeutically effective dose of TBZ 24 hr earlier were significantly smaller and contained much less glycogen (as a percent of the wet weight) than worms from unmedicated controls. Protein concentrations increased in TBZ-treated worms and at a rate sufficient to offset the decline in glycogen concentration. Glycogen/protein ratios in TBZ-treated worms were significantly lower than the corresponding control values. Cambendazole proved to be five times more potent than TBZ against H. diminuta and produced the same basic changes in worm weight and chemical composition within 18 hr of treatment of the host. Administration of a single oral dose of TBZ or CBZ to the host produced in H. diminuta another change, the onset of which coincided with, or preceded, the gross alterations in worm weight and chemical composition. That change, observed in in vitro studies carried out 14 hr after treatment, revealed that tapeworms from drug-treated rats absorbed and metabolized much smaller quantities of exogenous glucose than did the controls, and the ability of the worm to accumulate glucose against a concentration difference was significantly depressed.     

Further studies on the effect of cyclosporin A on the course of Paragonimus infection in rats

Paragonimus ohirai-infected rats were treated with cyclosporin A (CyA) at different times during the course of infection. CyA (5 x 80 mg/kg) affected the worm recovery, growth and maturation rates of P. ohirai with respect to control values. This tendency was most remarkable in animals treated 15 days and more after infection with CyA (groups B, +15 to +19 days; C, +25 to +29; D, +35 to +39 and E, +45 to +49). In group A (0 to +4), however, the drug did not affect markedly the growth and maturation of worms, although it significantly lowered worm recovery rates. CyA administration also affected normal migration of P. ohirai in the highly susceptible host (rat), when the drug was administered during the peritoneal and/or liver phase of infection. Thus, in this P. ohirai/rat model, CyA significantly reduced worm recovery rates, and affected the growth, maturation and migration of the worms depending on the time of administration.     

The miniature pig: a unique experimental model for Schistosoma japonicum infection

As part of a search for good animal models for human schistosomiasis, two miniature pigs of the CLAWN strain (C-1, C-2) were inoculated percutaneously with 200 Schistosoma japonicum cercariae of the Chinese strain, and the subsequent infection was monitored parasitologically, pathologically and serologically. Egg excretion into feces began at 5 weeks post-infection (p.i.) and became pronounced from 8 weeks to 17–20 weeks p.i. The average number of eggs in 1 g feces of each pig at the peak period between 8 and 20 weeks were 288 and 277, respectively. C-1 and C-2 were killed and perfused at 27 and 47 weeks p.i. and adult worm numbers recovered were 35 and 15, respectively. C-2 had at least four pairs of viable mature worms but no detectable fecal eggs for a month before perfusion, suggesting that any produced eggs were not excreted into the feces during this period. Egg deposits associated with inflammatory reactions were observed by histological examination of the liver, spleen, pancreas, mesenteric lymph nodes, lung, and small intestine. This suggests that reduced fecal excretion of eggs into the feces did not correlate to reduced parasite numbers in the chronic phase of schistosomiasis. This is the first report showing the miniature pig to be a potential model for human S. japonicum infection.     

Population dynamics and epidemiology of Toxocara canis in Danish red foxes

Toxocara canis, an intestinal helminth of canids with zoonotic potential, was found in 618 (59%) of 1,040 red foxes (Vulpes vulpes) collected from all Danish provinces (1997-2002). The prevalence and average worm burden were significantly higher for cubs than older foxes and in males than in females. A multiple logistic regression demonstrated that the prevalence was influenced significantly by sex and age of foxes in addition to location, season, and year of collection. The highest prevalence and worm burden were found in rural areas. The size and number of female worms was positively correlated to the fecal egg excretion. The length and fecundity of the worms was significantly higher in male foxes, and a general intensity dependence was suggested from a negative correlation between worm numbers and worm lengths. As compared to intestinal recovery of worms, somatic larvae were recovered from 20% of muscle samples and fecal eggs in 41% of fecal samples. The consistent finding of T. canis larvae in somatic tissues of naturally infected foxes is new.