Schistosoma japonicum infection in pregnant mice.

Ten 1-week and ten 2-weeks pregnant female NMRI mice were experimentally exposed to 70 Schistosoma japonicum cercariae. Ten littermice from each group were examined for worms by perfusion 4, 6 and 8 weeks post infection. Although the mothers (n = 15) were found infected with 15.5 +/- 13.4 worms at perfusion 6 and 7 weeks post infection, no worms were found in any of the examined littermice, as well as no detection of faecal or tissue eggs. Litter sizes did not differ from control groups and all littermice were healthy. The present study therefore suggests that congenital infection with S. japonicum does not occur in percutaneously infected mice and that infection of the mother during pregnancy does not seem to affect the offspring.     

Parasitological and histopathological effects of immunosuppression in guinea-pigs (Cavia porcellus) experimentally infected with Schistosoma haematobium

The parasitological and histopathological effects of immunosuppression in guinea-pigs (Cavia porcellus) experimentally infected with Schistosoma haematobium were studied. A total of 16 guinea-pigs were divided into four groups (four per group): non-immunosuppressed, non-infected group (NN); immunosuppressed, non-infected group (IN); immunosuppressed, infected group (II); non-immunosuppressed, infected group (NI). The IN and II groups were immunosuppressed with 5?mg/kg prednisolone while the II and NI animals were infected with 200-300 S. haematobium cercariae. Excretion of eggs in urine/faeces, worm burden and histopathology of some vital organs of the guinea-pigs were studied. Eggs of S. haematobium were observed in the urine of the NI and II groups from 9 weeks post-infection and in faeces from 10 and 13 weeks post-infection for the NI and II groups, respectively. However, II animals excreted more viable eggs in urine and faeces than those of the NI group. Worm recovery at 14 weeks post-infection showed that NI and II guinea-pigs had more female worms than male worms and a greater proportion of worm recovery for NI animals was of immature worms. Significant differences (P?0.05). Histological changes, which were notably reactions to adult S. haematobium worms, were observed in the organs of the NI and II groups but these changes were seen more in the organs of the immunosuppressed, infected (II) than in the non-immunosuppressed, infected (NI) guinea-pigs. The results suggest that immunosuppression before infection increased worm survival and had a moderate effect on liver and bladder histology of S. haematobium infected guinea-pigs.     

Studies on experimental mixed infections of Schistosoma mansoni and S. haematobium in hamsters

Golden hamsters were superinfected simultaneously with 100 Schistosoma haematobium cercariae, 1 and 3 weeks after initial infection with 100 S. mansoni cercariae. Results indicate that there was a higher degree of resistance to superinfection with S. haematobium at 1 week following initial infection with S. mansoni than that produced in the other two superinfections. This resistance was evidenced by a reduction in the number and size of worms of both species, decrease in S. haematobium egg extrusion per female and by a striking deviation in the egg distribution pattern of both species. Such an early host resistance was not recorded in previous works. Cross-mating was observed but no hybridization took place and the eggs produced were hatchable and typical of their species.     

Effect of praziquantel on the immature stages of Schistosoma haematobium

Schistosoma mansoni is known to be refractory to praziquantel treatment in the pre-patent period of infection. Since Schistosoma haematobium has a much longer pre-patent period (10-12 weeks vs. 5-6 for the former species), we asked the question whether a correspondingly longer period of insusceptibility exists in urinary schistosomiasis. In hamsters treated at different times after infection, S. haematobium was partially refractory to praziquantel when treatment was given at week 5, but showed practically full sensitivity at 7-8 weeks and later times. Schistosoma haematobium worms obtained at different times after infection and exposed in vitro to praziquantel were refractory to low drug concentrations between 4 and 6 weeks, but were clearly affected at higher concentrations and at later time points. We conclude that S. haematobium does not have a praziquantel-insensitive window longer than in S. manson, in spite of its much longer maturation period. In addition, refractoriness of immature stages can be overcome at higher drug concentrations.     

Schistosoma mekongi and Schistosoma japonicum: Differences in the distribution of eggs in the viscera of mice

The difference in the distribution of Schistosoma eggs in the viscera has not been clearly elucidated in the two closely related species Schistosoma japonicum and Schistosoma mekongi. In this study, we quantitatively compared the distribution of eggs in mice infected with the two species. In S. mekongi-infected mice, 56.6% to 69.4% of total eggs were found in the distal small intestine 9 to 15 weeks after infection, while in S. japonicum-infected mice, 48.8% to 71.8% of eggs were found in the proximal small intestine during the same period. There were significantly more eggs in the liver in mice infected with S. japonicum than in those infected with S. mekongi. The number of adult worms recovered did not differ between the two species during the study period. The total number of eggs laid in the tissues also did not differ between the two species at 12 to 15 weeks postinfection, but in the earlier period the total number of eggs was significantly fewer in S. mekongi-infected than in S. japonicum-infected mice, suggesting the delayed maturation of the former compared with the latter. These results clearly show that S. japonicum and S. mekongi exhibit different oviposition behavior in their hosts.     

Elucidation of Schistosoma japonicum population dynamics in pigs using PCR-based identification of individuals representing distinct cohorts

The study reported here investigated the interactions of successive infections and acquired resistance of pigs to challenge infections of Schistosoma japonicum. Two morphologically indistinguishable geographical isolates from China (from Anhui and Zhejiang provinces) were used for the infections. The worms of the two isolates were distinguishable by PCR-linked restriction fragment length polymorphism analysis of the nicotinamide adenine dinucleotide phosphate dehydrogenase I gene of the mitochondrial genome. Thirty-two pigs divided into seven groups were used in the experiment. Two groups received a single infection by either the Anhui or the Zhejiang isolate. In Challenge Groups 1, 4, 6, 8 and 12, a primary infection of the Zhejiang isolate was followed by a challenge infection with the Anhui isolate at week 1, 4, 6, 8 or 12 after the primary infection. In this way it was possible to determine whether worms recovered by perfusion originated from the primary or the challenge infection. Only the challenge infection at week 1 resulted in a higher worm burden when compared with a single primary infection with the Zhejiang isolate. The results showed that challenge worms were able to establish, and that the proportion of worms originating from challenge infection increased at the later challenge infections, however without an increase in the total number of worms. In addition, mixed pairs of the two isolates were found in all challenge-infected groups. The results indicate that pigs are able to mount a partial resistance against re-infection with S. japonicum by 4 weeks after a primary infection, but that worms of the challenge infections eventually replace the primary infection. The finding of mixed pairs of the two isolates indicates that worms of S. japonicum are either polygamous or able to wait in solitude for up to 12 weeks for a partner.     

Longevity of Zygocotyle lunata in Balb/c mice and long-term survival of digeneans in vertebrate hosts

This study used Balb/c mice to examine the longevity of Zygocotyle lunata in a murine host. Of 11 mice, each exposed to 20 Z. lunata cysts, six were infected with a total of 12 worms from 11 to 24 weeks postinfection (PI). Live worms recovered at 24 weeks PI had a mean body area of about 25?mm2. These worms produced viable eggs with well-developed miracidia following embryonation in artificial spring water for 2 weeks at 28°C. The Balb/c mouse is a useful model to study longevity of this paramphistomid trematode for at least 6 months PI. An additional aspect of this article is a review of the pertinent literature published from 1937 to 2007 on ageing and longevity of digeneans.     

Hybridisation between the digeneans Schistosoma haematobium and S. mattheei : viability of hybrids and their development in sheep

The F1 and F2 hybrids of Schistosoma haematobium male × S. mattheei female were studied with regard to infectivity to intermediate and definitive hosts, isoenzymes (phosphoglucomutase) of individual male worms, randomly amplified polymorphic DNAs of individual adult worms and scanning electron micrographs of the tubercles of male worms. The infection rate of the F1 hybrid miracidia in Bulinus globosus (41.7%) was greater than that achieved in B. wrighti (16.3%); the infection rate of the F2 in B. wrighti was 15.4%. In the definitive hosts: in sheep only male F1 hybrids (i.e. no females and no F2 worms)were recovered; but in hamsters both paired F1 worms and unpaired F1 males were recovered, as were one pair of worms and unpaired males of the F2 generation. The S. mattheei and S. haematobium male worms showed very distinctive PGM patterns, and the F1 hybrids showed additive patterns and a polymorphism with two distinct types of band patterns which are the result of polymorphism in the S. haematobium. The RAPD profiles of the F1 hybrids were also composite of the two parental species. Scanning electron micrographs of the tubercles of male S. haematobium showed them to be heavily spined, whereas those of S. mattheei males were devoid of spines. The F1 hybrids did show variation ranging from non-spined, some with partial spination, to those with heavily spined tubercles. Male worms of the F2 generation possessed tubercles either with or without spines. The potential significance of hybridisation in areas of sympatry between S. haematobium and S. mattheei is discussed.     

Prevention of Schistosoma japonicum infection in mice with long-acting praziquantel implants

This work reports the prevention outcomes of a praziquantel (PZQ) implant against the infection of Schistosoma japonicum in mice. The PZQ implant produced stable plasma PZQ concentrations in a range of 100-1300 ng/mL for a period of 70 days, by releasing PZQ in subcutaneous tissues in a sustained manner. To assess the prevention effects, the mice were infected at varying times after implantation. All the mice were sacrificed at 6 weeks after infection for worm and egg recovery and counting, worm morphological examination, determination of egg-hatching rates, and analysis of hepatic histology. The infection was successfully prevented for mice with early infection times (within 2-3 weeks), as nearly no worms, paired worms, eggs, or miracidia were recovered. However, in mice with late infection times (after 3 weeks), the prevention effects were diminished due to the decreased plasma PZQ concentrations at late times. Interestingly, the implants showed robust prevention effects on repeated infection at 1 and 3 weeks. In the infection-prevented mouse livers, no granuloma formation or granulomatous inflammation was observed. The results demonstrated that by blocking the development of infecting miracidia and by deactivating the eggs, the PZQ implants encouragingly prevented the S. japonicum infection and avoided liver damage.     

Schistosoma japonicum: interactions of successive infections in pigs and mice using polymerase chain reaction-based identification of individual worms

The study reported here investigated acquired resistance of mice and pigs to challenge-infections with Schistosoma japonicum. Two morphologically indistinguishable isolates of the parasite (from the Anhui and Zhejiang provinces of China), which could be typed by polymerase chain reaction-linked restriction fragment length polymorphism analysis (PCR-RFLP), were used for the infections. In two parallel infection studies, 60 female outbred NMRI mice and 29 Danish Landrace/Yorkshire/Duroc crossbred pigs were used. Two of the groups received a primary infection with either the Anhui or the Zhejiang isolate, respectively. The remaining groups received a primary infection with the Zhejiang isolate and challenge-infections with the Anhui isolate at either week 2, 3, 4 or 6 post primary infection. The results of the study indicated that both mice and pigs are partially resistant to challenge-infection from week 4 post primary infection. Resistance appeared to decrease in pigs 6 weeks after primary infection, while it remained effective in mice. These results suggest that the mechanism responsible for acquired resistance in mice and pigs may not be the same and support the theory that worm burdens in pigs receiving repeated infection are in a balance between acquisition and loss of worms.     

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.     

Elucidation of Schistosoma japonicum population dynamics in pigs using PCR-based identification of individuals representing distinct cohorts

The study reported here investigated the interactions of successive infections and acquired resistance of pigs to challenge infections of Schistosoma japonicum. Two morphologically indistinguishable geographical isolates from China (from Anhui and Zhejiang provinces) were used for the infections. The worms of the two isolates were distinguishable by PCR-linked restriction fragment length polymorphism analysis of the nicotinamide adenine dinucleotide phosphate dehydrogenase I gene of the mitochondrial genome. Thirty-two pigs divided into seven groups were used in the experiment. Two groups received a single infection by either the Anhui or the Zhejiang isolate. In Challenge Groups 1, 4, 6, 8 and 12, a primary infection of the Zhejiang isolate was followed by a challenge infection with the Anhui isolate at week 1, 4, 6, 8 or 12 after the primary infection. In this way it was possible to determine whether worms recovered by perfusion originated from the primary or the challenge infection. Only the challenge infection at week 1 resulted in a higher worm burden when compared with a single primary infection with the Zhejiang isolate. The results showed that challenge worms were able to establish, and that the proportion of worms originating from challenge infection increased at the later challenge infections, however without an increase in the total number of worms. In addition, mixed pairs of the two isolates were found in all challenge-infected groups. The results indicate that pigs are able to mount a partial resistance against re-infection with S. japonicum by 4 weeks after a primary infection, but that worms of the challenge infections eventually replace the primary infection. The finding of mixed pairs of the two isolates indicates that worms of S. japonicum are either polygamous or able to wait in solitude for up to 12 weeks for a partner.     

Cross-resistance between Schistosoma mansoni and Fasciola hepatica in sheep

Five sheep were exposed to 5,000 S. mansoni cercariae percutaneously and the stools examined for 20 wk to determine patency. The sheep were found to be partially susceptible to a primary infection and showed great individual variations in their pathophysiological responses. All of the sheep acquired a patent infection with S. mansoni and eggs were first seen in feces 9 wk postexposure with no eggs detected after 14 wk. At necropsy 20 wk postexposure only dead S. mansoni worms were found. KOH digests revealed that tissue egg counts were low, ranging from 0 to 133 in the liver, and 0 to 257 in the intestine. Primary infection of sheep with S. mansoni followed by oral infection with F. hepatica metacercariae 10 wk later resulted in a reduction of 51% in F. hepatica worms recovered over controls infected with F. hepatica for 10 wk. All 5 of the S. mansoni-infected/F. hepatica-challenged sheep developed 71 or less F. hepatica worms. In contrast, 3 of the 5 F. hepatica-infected sheep developed 113-197 worms. However, although the experimental mean worm burden was lower than the control group, the variability in the control group was too great to obtain significance between the groups. There was a clear tendency toward normocytic normochromic anemia following a primary infection with S. mansoni; however, blood values were more reduced in the F. hepatica challenge controls than in the animals that received primary infection with S. mansoni.     

Nematospiroides dubius in mice selected for liability to infection: Modification of parasite biology through host selection

Brindley P. J. and Dobson C. 1982. Nematospiroides dubius in mice selected for liability to infection: modification of parasite biology through host selection. International Journal for Parasitology12: 573–578. Mice selected as liable (L) and refractory (R) over ten generations voided significantly more and less Nematospiroides dubius eggs compared with randomly mated (Rd) mice after primary infections with 100 larvae. There was little difference between the number of parasite eggs voided g^?1 faeces (epg) by individual mice on day 14 compared with day 15 after infection.However there was a significant diurnal variation in the egg values for individual mice but the mean differences observed between the R, Rd and L mice were maintained over a 24 h period. There was a strong correlation between both the total number and the number of female worms, surviving 21 days after infection, and the mean epg 14 and 15 days after infection. Female N. dubius produced more eggs in L mice and fewer eggs in R mice compared with worms in Rd mice. Similarly, worms grew longer in L mice and were shorter in R mice compared with parasites in Rd mice.     

Serodiagnosis of experimental fascioliasis by immunoprecipitation tests

Hillyer G. V. and Santiago de Weil N. 1981. Serodiagnosis of experimental fascioliasis by immunoprecipitation tests. International Journal for Parasitology11: 71–78. Counterelectrophoresis (CEP) was useful in detecting 100% of infections with fascioliasis in mice, rats, and rabbits by 4–5 weeks post infection, and in most rats as early as 2 weeks post infection. A rapid decrease of precipitins was observed when the animals were cured with a fasciolicidal drug at 4 or more weeks post infection. When rats were treated at 2 weeks, however, antibody reactivity remained high for at least 3 weeks post treatment suggesting that worm antigens are released in the liver parenchyma stimulating additional antibody production. Partial purification of F. hepatica adult worm extracts using Sephacryl S-200 was necessary for testing the serum of rats by CEP. In addition, the Sephacryl S-200 elution profile of F. hepatica antigens reactive with antisera to S. mansoni adult worms or eggs was shown. These studies demonstrate that CEP is useful for the early detection of antibodies in experimental fascioliasis and for the clear prediction of chemotherapeutic success when treatment is carried out at 4 or more weeks after infection.     

PCR-based identification of individuals of Schistosoma japonicum representing different subpopulations using a genetic marker in mitochondrial DNA.

A mitochondrial NADH dehydrogenase I gene fragment (NDI) was sequenced for three laboratory maintained isolates of Schistosoma japonicum. Comparison of sequences representing the isolates (originally obtained from the Anhui and Zhejiang provinces of the People's Republic of China, and from the Philippines) revealed inter-isolate sequence variations of 0.2-0.6% and no intra-isolate variation was found. The sequences also indicated that while the amplification products of the Zhejiang and Philippine isolates contained a recognition site for the endonuclease RsaI, there was no such site in the Anhui isolate. This was tested by digesting amplification products from a number of individual worms with RsaI. Then an infection experiment was designed to test the value of this genetic marker for studies of the population biology of S. japonicum in the final host. For this, the two Chinese isolates were used. Three groups of mice (A-C) were exposed firstly to a primary infection and then challenge-infected at weeks 4 and 7 of the experiment. In group A the first infection was done with the Anhui isolate, and the two others with the Zhejiang isolate, thereby providing a specific, detectable cohort. In groups B and C the Anhui isolate was used for the second and third infection. All mice were perfused 5 weeks after the last challenge infection, and the NDI was subsequently amplified from DNA of the perfused worms and digested with RsaI. The digestion revealed that while infection groups A and B contained mixed populations of the Anhui and Zhejiang isolates, only Zhejiang worms were present in group C. We concluded that the absence/presence of the RsaI site in the NDI provides a useful marker for the delineation of cohorts of S. japonicum.     

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.     

Schistosoma haematobium (Egyptian strain): rate of development and effect of praziquantel treatment

This study investigates the development of the Egyptian strain of Schistosoma haematobium and the resultant immunohistopathology and biochemical changes in organs affected. In addition, the response of different developmental stages of S. haematobium worms to praziquantel (PZQ) was examined. Schistosoma haematobium-infected hamsters were classified into 4 groups and were treated at day 35, 55, 75, and 95 postinfection (PI), respectively. Each group was subdivided into 3 subgroups. Two of them were treated orally with PZQ (300 mg/kg or 500 mg/kg divided equally on 2 consecutive days), and the third group was left without treatment. Treated groups were killed 20 days posttreatment. Infection with S. haematobium became patent 73 days PI; tissue egg load and worm fecundity were higher at 95 days and maximal 115 days PI, with an oogram pattern comparable to that in Schistosoma mansoni infection. In the liver, small cellular granulomas were observed 75 days PI, with preponderance of CD4+ T-cell phenotypes. In the urinary bladder, only submucosal focal Brunn's-nest formation and angiogenesis without typical granulomas were observed. Ninety-five and 115 days PI, confluent granulomata with multiple eggs in the center were observed in the liver and urinary bladder, with a preponderance of CD8+ positive T cells in the liver and hyperplasia of the urinary bladder epithelium with cystitis cystica and papillae formation. One hundred percent worm eradication was recorded with the higher dose of PZQ in animals treated 75 and 95 days PI. In conclusion, in spite of the long prepatent period of the Egyptian strain of S. haematobium, sensitivity to PZQ was recorded soon after infection. Granulomata were similar to those of S. mansoni in the livers and urinary bladders, but they were confluent with multiple eggs in the centers, hyperplasia of the urinary bladder urothelium with cystitis cystica, papillae, and Brunn's-nest formation predictive of malignant changes with no hepatocyte dysplasia.     

Echinostoma friedi: the effect of age of adult worms on the infectivity of miracidia

The effect of ageing of adults of Echinostoma friedi (Trematoda: Echinostomatidae) on the infectivity of miracidia yielded was analysed. Miracidia were obtained after hatching of eggs obtained from adult worms of E. friedi collected weekly during the course of experimental infections in golden hamsters. Miracidial infectivity, measured in terms of percentage of infection in Lymnaea peregra, was significantly influenced by the age of the adult worms from which the miracidia were derived. Infective miracidia only were obtained from adult worms in the age range from 4 to 9 weeks post-infection. Infectivity was maximal in those miracidia derived from adults collected 8 and 9 weeks post-infection. The results suggest that adult worms producing viable eggs require additional maturation to be able to yield eggs containing infective miracidia.     

Immune changes of Schistosoma japonicum infections in various rodent disease models

Rodent models for Schistosoma japonicum infections have demonstrated that these animals possess a degree of resistance to schistosome infections that may be both T and B lymphocyte-mediated. However, their exact role is not well-defined and other immune mechanisms are likely to also play a role in protecting against infection. Immunosuppressed and immunocompetent reed voles (Microtus fortis, Mf), rats and mice (n=24/group) were infected with S. japonicum, and animals were sacrificed 42 days later under anesthesia. Neither worms nor eggs were observed in infected immunosuppressed Mf or rats, with the exception of one rat that presented with few eggs. In immunosuppressed mice, changes in the number and size of the worms were not significantly different compared to immunocompetent mice, but worm fecundity was affected. The size and number of granulomas in immunosuppressed animals was also reduced. Analysis of serum antibodies specific to schistosome adult worm antigen at 3 weeks post-infection demonstrated that the levels of antibodies in the sera of rats were significantly higher than in Mf and mice. In addition, Mf serum levels of IL-4 and IL-12 were significantly higher than levels observed in rats and mice. Antibodies and cytokines in the sera of Mf peaked 3 weeks post-infection and then began to decrease, while antibody responses in rats and mice increased gradually between weeks 3-7 post-infection. It is possible that T and B cells have a dual role in both mediating protection and exacerbating disease outcomes.