Modification of the pathogenicity of Schistosoma mattheei for sheep by passage of the parasite in hamsters

Border Leicester X Suffolk sheep infected with a strain of S. mattheei maintained in hamsters do not develop the same pathological changes as Romney Marsh sheep infected with the same strain of parasite before hamster passage. To determine the cause of this reduced pathogenicity, five Romney Marsh sheep were each infected with 10 000 cercariae of the hamster-passaged parasite and five with 10 000 cercariae of a S. mattheei strain from Onderstepoort, South Africa, passaged exclusively through sheep. Striking pathological and parasitological differences were found between the two strains. Infection with the "sheep" strain was lethal, whereas infection with the "hamster" strain produced little evidence of clinical disease. By 13 weeks post-infection the mean body weight of the sheep infected with the sheep strain had declined by 15% compared with both the uninfected controls and the sheep infected with the hamster strain, and the mean PCV was lowered to 20% in the sheep strain infected animals. Egg production began at seven weeks with the sheep strain, faecal counts rising to more than 300 e.p.g., whereas only two of the sheep infected with the hamster strain passed eggs in the faeces (at nine weeks) and the maximum egg count was 50 e.p.g. Twice as many adult worms of the sheep strain were recovered, and, although the number of eggs found in the tissues "per worm pair" was not significantly different, overall egg production was higher for the sheep strain; also more of the sheep strain eggs were deposited in the intestines. Similar parasite differences were seen in a supplementary study in mice and it seemed that "attenuation" of the parasite had occurred, presumably due to its maintenance in hamsters. Histopathological observations and faecal egg counts both indicated an inability of hamster strain eggs to penetrate the intestinal lumen; this was probably important in reducing the pathogenicity of the hamster strain.     

Schistosoma japonicum: the pathology of experimental infection

The pathology of experimental schistosomiasis japonica is reviewed and compared with the pathology of schistosomiasis japonica in man and to some aspects of schistosomiasis mansoni and schistosomiasis haematobia in experimental animals. The induction of granulomas around Schistosoma japonicum eggs depends upon cell mediated immunity, as do the reactions to Schistosoma mansoni and Schistosoma haematobium eggs. However, the modulation of the reaction to S. japonicum eggs can be greatly influenced by antibody, while antibody has no effect on the granulomas around S. mansoni eggs. Adult worm pairs of S. japonicum tend to cluster in the mesenteric venules, and most eggs are laid in a few sites. This leads to large, focal intestinal lesions similar to the discrete lesions produced by S. haematobium in the intestine and urinary tract but in contrast to the widespread, diffuse lesions produced by S. mansoni. Comparison with S. japonicum infection in humans is limited chiefly by our scant knowledge of the pathology produced by S. japonicum in infected persons. Most such comparisons are, in any case, limited by the marked differences in the reactions of various experimental host species to the infection and by differences in the reaction of a given host species to different strains of the parasite.     

Natural infection of wild rodents by Schistosoma mansoni

In Planalto, a small locality in the interior of the Bahia state, Brazil, 47% of sylvatic rodents were found to be naturally infected with Schistosoma mansoni, whereas the prevalence of the infection in the inhabitants of the area was 3.26%. The rodents (Nectomys) live near the houses, in contact with water, passing viable schistosome eggs in the stools. Worm burden is variable amongst such rodents. Periovular granulomas are small, especially in liver and intestines, and hepatic fibrosis is mild or absent, with no morphological evidence of portal hypertension being noted. Miracidia isolated from the eggs recovered from Nectomys readly infected laboratory-raised Bahia strain of Biomphalaria glabrata. Cercariae then obtained infected Swiss mice in a similar way as the human strains of S. mansoni kept in laboratory. Also, Swiss mice left in contact with water collections in Planalto were easily infected, which proved the transmissibility potential of the area. In conclusion: sylvatic rodents found in the area of Planalto tolerate well S. mansoni infection, eliminate viable eggs in the stools, are usually infected with a strain probably of human origin and therefore may play a role in maintaining parasite cycle in the area.     

A comparative study of the death of schistosomula of Schistosoma haematobium and Schistosoma mansoni in the skin of mice and hamsters.

This study shows that some cercariae of S. haematobium and S. mansoni die during penetration of mouse or hamster skin. Approximately 30-38% of cercariae of both species die in mouse skin and 14-16% die in hamster skin. The greater number of cercariae which die in the skin of mice seems to account for the higher yield of adult worms recovered in hamsters. Adult worm recoveries from animals infected with S. haematobium were, however, only about half the worm recoveries from hosts infected with S. mansoni.     

Schistosoma mansoni: mice infected with different worm strains.

Infections with five geographical strains and substrains of Schistosoma mansoni were compared in mice. Two substrains (Lc-1 and Lt-1) were derived from the parent (L-1) St. Lucian strain on the basis of differing infectivity for various snail strains. The Puerto Rican strains (PR-1 and PR-2) were obtained with an interval of 25 years. Consistent differences among the lines were found in egg distribution and numbers of eggs in tissues and feces. One Puerto Rican strain (PR-2) and one St. Lucian substrain (Lc-1) had longer prepatent periods than the other strains. Mice infected with the PR-1 strain consistently had the highest egg accumulation in the tissues per worm pair. Relatively few eggs were passed in the feces of the Lt-1 strain. By Week 9 of infection, eggs were noted in the spleens of mice carrying each of the strains and substrains.     

Host parasite relationship among 3 Schistosoma mansoni and 6 Biomphalaria glabrata strains from epidemic and no epidemic Venezuelan areas is studied

Six lots of 18 B. glabrata from: La Victoria, Turmero, Cagua in Aragua state; Caserío El 25 in Carabobo state, Chabasquén in Portuguesa state and Humocaro Bajo in Lara state, were experimentally infected with miracidia of SM, C5 and C6 strains of Schistosoma mansoni (18 snails/Schistosoma mansoni strain). The averages of the intramolluscal period (IMP) obtained for the S. mansoni strains were very similar and comprised between 35.4 and 36.1 days. No significative statistical differences in the IMP were found according to the S. mansoni strain and the size of snails: < 7 mm and > 7 mm. However, significative statistical differences in the IMP were found, in relation to the B. glabrata strain and between the snails classified in two groups according to the S. mansoni dose (5 miracidia/snail and 10 miracidia/snail). The higher percentages of infection (PI) were found for the following parasite-snail combinations: C6-Cas. El 25 (80.7%), SM-La Victoria (73.1%) and C5-Cagua (62%). No significative statistical differences were found for the PI a) between the snail classified in two groups according to the size (< 7 mm and > 7 mm), b) in relation to the miracidium dosification (5 and 10 miracidia/snail and c) in accord to the S. mansoni strain. However, significative statistical differences were found for the PI obtained with different strains of the snail.     

Effect of carnosine administration on metabolic parameters in bilharzia-infected hamsters

Carnosine is a naturally occurring dipeptide (beta-alanyl-L-histidine) found in muscles, brain and other tissues. This study was designed to test the ability of carnosine to offset metabolic disturbances induced by Schistosoma mansoni parasitism. Results indicate that parasitic infection caused elevation of liver weight/body weight in S. mansoni-infected hamsters, induced lipid peroxidation and reduced glycogen levels. Moreover, adenylate energy charge (AEC) and ATP/ADP and ATP/AMP concentration ratios were markedly lower in infected hamsters. Administration of carnosine (10 mg/day) for 15 days concurrent with infection effectively reduced worm burden and egg count. Administration of carnosine 2 and 4 weeks post-exposure only partially ameliorated the S. mansoni effects on metabolism. Carnosine treatment also normalized most of the parameters measured, including glycogen repletion, the antioxidant status and AEC. These finding support the use of carnosine for possible intervention in schistosomiasis.     

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.     

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.     

Lack of effect of unmated schistosomes on the fecundity of mated worm pairs

An imbalance between the numbers of male and female worms had no significant effect upon the fecundity of Schistosoma mansoni in rhesus monkeys or upon the number of S. mansoni eggs in the tissues of infected persons or mice. The number of S. japonicum eggs in the tissues of infected rabbits was similarly unaffected by disproportion between worm genders.     

Host mouse strain is not selective for a laboratory adapted strain of Schistosoma mansoni

We genotyped pooled adult worms of Schistosoma mansoni from infected CF1, C57BL/6, BALB/c, and BALB/c interferon gamma knockout mice in order to establish if mouse strain differences selected for parasite genotypes. We also compared differentiation in eggs collected from liver and intestines to determine if there was differential distribution of parasite strains in the vertebrate host that might account for any genotype selection. We found that mouse strains with differing immune responses did not differ in resistance to infection and did not select for parasite genotypes. Schistosoma mansoni egg allele frequencies were also equally distributed in tissues and the difference between adult and egg allele frequencies was negligible.     

Dipetalonema viteae: in vitro blastogenesis of hamster spleen and lymph node cells to phytohemagglutinin and filarial antigens

Hamsters of the randomly bred LAKZ and inbred LSH strains were infected with Dipetalonema viteae, and the in vitro responses of lymph node and spleen lymphocytes to male and female worm antigens and phytohemagglutinin (PHA) were measured by a [³H]-thymidine-uptake assay at various times after infection. The PHA response remained unchanged at the level of controls in infected LAKZ hamsters while LSH hamsters showed a depressed response to the mitogen during late infection. Stimulation of lymph node cells by filarial antigens was maximal in both strains of hamsters at Week 4 postinfection, almost reaching values obtained in PHA stimulated cultures. A similar high lymphocyte transformation reaction was measured after the injection of dead third stage larvae. During transient microfilaremia, when antibody titers reached a maximal level, the lymphocyte reactivity to filarial antigens decreased drastically and only occasionally was demonstrated in hamsters 20 and 30 weeks after infection. No correlation between lymphocyte reactivity and parasitological findings (worm load or intensity and duration of microfilaremia) could be demonstrated. The cellular unresponsiveness to filarial antigens was further analyzed in chronically infected LAKZ hamsters. No suppressor cells could be found in lymphocyte suspensions of nonresponding hamsters. A challenge infection did not restore lymphocyte reactivity. Serum of chronically infected hamsters caused marked inhibition when added to filarial antigen-sensitive lymphocytes. Lymphocytes from hamsters with a mixed D. viteae and Schistosoma mansoni infection responded as well to soluble schistosomal egg antigens at Week 30 of a D. viteae infection as lymphocytes from hamsters infected with S. mansoni alone. The humoral immune response to schistosomal antigens, however, was significantly lower in animals with a mixed infection.     

Rodents as reservoir hosts in the transmission of Schistosoma mansoni in Richard-Toll, Senegal, West Africa

More than 2000 animals belonging to six different rodent species and one insectivore species were examined for infection with schistosomes in the region of Richard-Toll, Senegal. Two murid rodents, Arvicanthis niloticus and Mastomys huberti, were found infected with Schistosoma mansoni. Prevalences were about 5% for both rodent species with a mean worm burden of about 20 worms per host. The sex-ratios of S. mansoni worms were always biased towards males. Prevalences and worm burdens, although similar in both male and female rodents, increased significantly with age. The highest prevalences and worm burdens were found near habitations and decreased significantly with the distance from the town of Richard-Toll. Eggs were also observed in the liver and faeces of the two naturally infected rodent species. The results suggest that rodents participate in the transmission of intestinal schistosomiasis in Richard-Toll but the human population is the main source of infection. The genetic resemblance between human and murine isolates of S. mansoni suggests that further epidemiological studies are needed in this region of Senegal.     

Schistosoma mansoni: chemotherapy of infections of different ages

Mice were treated with potassium antimony tartrate, hycanthone, oxamniquine, niridazole, or praziquantel at different times after infection with Schistosoma mansoni. The rate of cure was assessed by perfusion of surviving worms approximately 4 weeks after treatment, and the percentage reduction in worm burden was estimated relative to the number of adult worms perfused from control mice, comparably infected but untreated. All six drugs were relatively inactive against S. mansoni between 3 and 4 weeks after infection when compared with treatment at 5 to 6 weeks. However, the drugs differed in the patterns of cure they achieved in the 2-week period after administration of cercariae and in the period around the onset of patency. Worms that had been subjected to amoscanate or hycanthone in the third week after infection showed evidence of this as adults in having a reduced fecundity. Factors such as worm or host physiology, or host immune status may have had roles in the outcome of chemotherapy at different stages of maturation of S. mansoni.     

Evaluation of the anthelmintic effects of artesunate against experimental Schistosoma mansoni infection in mice using different treatment protocols

The therapeutic effects of artesunate against experimental Schistosoma mansoni infection in mice were analyzed. Previous studies showed that artesunate is highly effective against S. japonicum infection, but the action of this drug against S. mansoni remained uncovered. The present study examines the optical conditions for artesunate against S. mansoni and evaluates the effects of inhibiting the sexual maturation of adult worms. Mice infected with S. mansoni were orally administered with artesunate according to different schedules. Four consecutive administrations of 300 mg/kg of artesunate at 2-week intervals conferred almost total protection without the development of pathological lesions in the liver. The significant reduction in the number of eggs produced by surviving worms and the status of egg maturation suggested that artesunate inhibits sexual maturation. Electron microscopy revealed that artesunate caused morphological damage, especially on the worm tegument. Artesunate was also very effective in iron-deficient mice. Furthermore, the efficacy of artesunate was equal to or better than that of artemether against S. japonicum infection. Considering that artemether is more toxic, artesunate is currently one of the most efficient drugs against immature S. mansoni.     

Immunostimulatory property of a synthetic peptide belonging to the soluble ATP diphosphohydrolase isoform (SmATPDase 2) and immunolocalisation of this protein in the Schistosoma mansoni egg

A peptide (SmB2LJ; r175-194) that belongs to a conserved domain from Schistosoma mansoni SmATPDase 2 and is shared with potato apyrase, as predicted by in silico analysis as antigenic, was synthesised and its immunostimulatory property was analysed. When inoculated in BALB/c mice, this peptide induced high levels of SmB2LJ-specific IgG1 and IgG2a subtypes, as detected by enzyme linked immunosorbent assay. In addition, dot blots were found to be positive for immune sera against potato apyrase and SmB2LJ. These results suggest that the conserved domain r175-194 from the S. mansoni SmATPDase 2 is antigenic. Western blots were performed and the anti-SmB2LJ antibody recognised in adult worm (soluble worm antigen preparation) or soluble egg antigen antigenic preparations two bands of approximately 63 and 55 kDa, molecular masses similar to those predicted for adult worm SmATPDase 2. This finding strongly suggests the expression of this same isoform in S. mansoni eggs. To assess localisation of SmATPDase 2, confocal fluorescence microscopy was performed using cryostat sections of infected mouse liver and polyclonal antiserum against SmB2LJ. Positive reactions were identified on the external surface from the miracidium in von Lichtenberg's envelope and, in the outer side of the egg-shell, showing that this soluble isoform is secreted from the S. mansoni eggs.     

Influence of intramolluscan larval stages of Echinostoma liei on the infectivity of Schistosoma mansoni cercariae

During co-infection of Biomphalaria glabrata with Schistosoma mansoni and Echinostoma liei, S. mansoni cercariae released before the complete resorption of S. mansoni sporocysts show a very strong decrease of their infectivity in mice. Under conditions of high interspecific competition (i.e. when the snails are infected by E. liei 8 days after infection by S. mansoni), the mean overall worm return is five times lower than that of the control experiment. A marked decrease of the infectivity of cercariae is also noted when snails, infected exclusively with either sporocysts of S. mansoni or rediae of E. liei, are associated in the same tank.     

Opisthorchis viverrini: influence of maternal infection in hamsters on offspring infected with homologous parasite and their IgG antibody response

We investigated the influence in hamsters of a maternal Opisthorchis viverrini infection on their offspring infected with homologous parasites and the kinetics of the O. viverrini-specific IgG antibody responses. No significant difference (P > 0.05) was found in the specific IgG antibody response and the number of O. viverrini eggs per gram feces (EPG) between infected offspring from infected mothers and infected offspring from uninfected mothers. A significant difference (P < 0.05) of EPG per worm was found between infected offspring from infected mothers and infected offspring from uninfected mothers only when the offspring were infected with O. viverrini after weaning at 5 weeks of age. The worm loads in infected offspring from infected mothers were significantly less than that in infected offspring from uninfected mothers. This study demonstrated that maternal infection effects worm fecundity and the worm load in an infected offspring.     

A comparative study of the Feira de Santana (Bahia) and Porto Rico strains of Schistosoma mansoni in experimental infection of mice

A comparative study of mice infected either with the Porto Rican or a Brazilian (Feira de Santana) strain of Schistosoma mansoni failed to show any difference regarding recovery of five day lung worms, recovery of adult worms from the portal system, number of eggs per gram of tissue in liver and intestines, histopathology or mortality rate. In fact, the differences, although small, were greater among animals infected with the same strain, that when the total results from both strains were compared.     

Schistosomiasis mansoni in Bananal (State of São Paulo,Brazil): I. Efficiency of diagnostic and treatment procedures

Bananal is an important focus of Schistosoma mansoni in the State of S?o Paulo. Accordingly, programmed active search for human cases, annual coproscopic surveys and treatment of infected cases were started in 1998, aiming at producing a sharp prevalence rate drop by the year 2000. S. mansoni eggs were searched for in two Kato-Katz slides per patient. Cases were followed up according to the routine of the local Family Health Program. In 1998, 130 samples out of 3,860 showed S. mansoni eggs; in 1999, 105 out of 3,550, and in 2000, 64 out of 3,528. Prevalence rates were 3.4%, 2.9%, and 1.8%, and average egg-counts 59, 64, and 79 eggs per gram of feces respectively. Prevalence rates decreased steadily after treatment, but persistently positive cases showed no significant decrease in parasite burdens. Egg count variation depended on sex and age bracket. Persistent residual cases admittedly preclude the eradication of this infection by only searching for and treating carriers. In addition, resistance to therapy and low sensitivity of fecal examinations, can not be ignored. Moderate to heavy worm burdens, frequently associated with hepatomegaly elsewhere, produced no serious cases in Bananal.