Natural history of Schistosoma mansoni infection in mice: egg production, egg passage in the feces, and contribution of host and parasite death to changes in worm numbers.

Mice, C57Bl/6N (B6) and BALB/cAnN (BALB), infected with Schistosoma mansoni were examined 8-26 weeks postinfection (PI) to estimate the fecundity of the worms and the contribution of death of worms and the death of heavily infected mice to the decrease in worm numbers in chronic infections. Portal worms were recovered by perfusion and the lungs were examined for parasites shunted from the portal circulation. Animals that died were more heavily infected than those that survived. Between eight and 12 weeks PI, this loss of worms resulted in a net decrease of approximately 19% of worm pairs in surviving BALB mice, but of only 4% in B6 mice. Loss of portal worms to the lungs after the eighth week of infection was 9-13% of portal worms in BALB mice and 3-4% in B6 mice. The estimated rates of egg production by S. mansoni decreased slightly with time in both strains of mice. At 12 and 20 weeks PI, tissue eggs per worm pair and eggs passed in the feces per worm pair often decreased as the intensity of infection increased. We do not consider the loss of worms in the murine host relevant to most infections in humans because of the high intensity of infection relative to body size in mice and the high frequency of severe portal obstruction in murine infections.

Kinetics of egg production and egg excretion by Schistosoma mansoni and S. japonicum in mice infected with a single pair of worms.

Individual male and female schistosomes approximately three weeks of age were implanted into the portal venous system of C57Bl/6 mice to produce infections with a single pair of Schistosoma mansoni or S. japonicum. Mice were killed between seven and 54 weeks after infection. Worm fecundity was measured by counting eggs accumulating in the tissues and eggs passed in the feces. Schistosoma mansoni worm pairs laid approximately 350 eggs per day with no change in the apparent rate of egg laying between eight and 52 weeks after infection and approximately one-third of the eggs were passed in the feces. Schistosoma japonicum worm pairs laid approximately 2,200 eggs per day initially and this decreased to 1,000 eggs per day by the end of the experiment, with one-third to one-half of the eggs being passed in the feces. There was marked variability in the fecundity of individual worm pairs, but the number of eggs passed in the feces of individual mice correlated well with the number of eggs in the intestines at all time points in S. mansoni-infected mice and at the seventh and tenth week of S. japonicum infection.

Persistence of eggs and hepatic fibrosis after treatment of Schistosoma mansoni-infected mice.

In 1971 we estimated that Schistosoma mansoni eggs in the tissues of mice were destroyed with an approximate half-life of four weeks. Our present results of five experiments suggest that egg destruction is not as rapid, and no significant destruction of eggs was detected for up to 26 weeks after treatment. However, in these experiments, a mean of 60% of the eggs in intestinal tissues were found in the feces at the time of treatment. In previously reported experiments, only 15% of gut eggs were passed in the feces. We now believe that underestimation of the number of eggs passed in the feces led to an overestimation of the number of eggs destroyed in the tissues. We analyzed liver eggs separately because eggs lost from this site are unaffected by eggs passed in the feces. No significant decrease in liver eggs occurred in the present experiments, but reanalysis of previously published data showed significant egg destruction in the liver in several experiments, although at a much slower rate than previously estimated. However, inspection of the data in the previously published and present experiments does not show a convincing difference in the number of eggs in the liver after treatment. The persistence of egg shells is probably not important in the pathogenesis of disease, but is of concern in calculating worm fecundity. Hepatic collagen levels increased markedly two weeks after treatment and subsequently decreased significantly in some, but not all, experiments.

Comparative safety and efficacy of short ragweed extracts differing in potency and composition in the treatment of fall hay fever. Use of allergenically bioequivalent doses by parallel line bioassay to evaluate comparative safety and efficacy.

One high potency (HP) and two low potency (LP) commercial whole short ragweed (WSR) extracts were assayed for relative potency (RP) by antigen E (AgE-Amb a 1), RAST inhibition, and parallel line bioassay (PLBA). The RP of the HP extract (300 micrograms AgE) was equal to the reference WSR, but the LP extracts were only approximately 0.01 of the RP of the reference. Each extract was administered to fall hay fever patients with skin sensitivity to WSR (less than or equal to 10(-3) micrograms/ml AgE for sum of erythema = 50 mm) to the maximum tolerated dose, or 0.5 cc of the concentrate, by either a 9- or 40-dose regimen. HP-treated patients had significantly lower symptom scores than untreated controls. No significant difference was noted in the total symptom scores between HP and LP extract-treated patients. Despite approximately 100-fold differences in the RP of HP versus LP extracts, both produced similar frequencies of severe systemic and severe late phase local reactions. Furthermore, when RP of HP and LP extracts were estimated by PLBA, both reached similar peak dosages, similar dosage for IgG WSR antibody response, and comparable IgG WSR antibody levels, indicating that the WSR dose estimates based on RP were bioequivalent. The 9-dose HP regimen produced fewer late phase local and systemic reactions per patient than the 40-dose HP regimen. Most patients experiencing severe systemic reactions were among those most skin sensitive to WSR. The number of systemic reactions per injection was significantly higher at higher WSR doses. One LP extract produced a high incidence of systemic reactions in the initial three injections. With respect to HP, its RP varied approximately 10-fold depending on the skin sensitivity of the patient to heat-stable ragweed allergens, demonstrating that it was compositionally different. However, when the dose of this extract was estimated by RP based on the skin sensitivity of each patient, the peak dose of the extract as well as the doses associated with late phase and systemic reactions were found to be similar to the HP doses. This indicated that immunizing dose estimates of compositionally different WSR extracts based on RP by PLBA were also bioequivalent.

Tests for character displacement.

Character displacement is an important concept in ecology which has been surrounded by controversy due largely to a lack of clearly stated hypotheses and statistical tests. Existing tests implicity assume random species sizes estimated without error--a random-effects model. We introduce the log-uniform distribution for species sizes and show that it has properties of direct relevance to character displacement. We present tests which assume uniform and log-normal species sizes and have the log-uniform distribution as an alternative. The tests have low power for sample sizes typically encountered in ecology. The effect of estimating species sizes is small. The results exemplify the shortcomings of the traditional random-effects model for species sizes.

Tests for deletion.

It has been suggested in the ecological literature that species may be excluded (or "deleted") from an environment because they do not differ sufficiently from other species in the environment. We develop tests of various deletion hypotheses based on the assumption of a random distribution of species sizes. The results provide information on the behavior of quantities of interest to ecologists studying this phenomenon, namely contiguous ratios, and allow us to gauge the extent of deletion required before we can be confident of detecting it. The results indicate that this random-effects approach leads to tests which have low power for ecological applications but may be more useful in fields which permit larger sample sizes.

Estimation of the number of monoclonal hybridomas in a cell fusion experiment. Effect of post-fusion cell dilution on hybridoma survival.

A practical method is described for the estimation of the number of monoclonal hybridomas in a cell fusion experiment as a function of the percent of culture dishes showing hybridoma growth. Our method is based on the Poisson probability model. A justification for the method is included. The application of this model to our experimental results indicates that the probability of hybridoma survival decreases with post-fusion cell dilution even in the presence of a constant number of feeder cells.

Size and shape analysis of schistomsome egg-counts in Egyptian autopsy data.

We study egg-counts from a series of Egyptian autopsy cases with active schistosomiasis at death (Kamel, Cheever, Elwi, Mosimann and Danner 1977). The data are unique, and enable us to study the proportional distribution of eggs among various organs in relation to infection intensity for two species of schistosome worms. We develop a model for the distribution of eggs in three organs of the mesenteric circulation. Under a lognormal distribution assumption, several exact statistical procedures are presented and used to examine model consistency as well as isometry with respect to geometric means. Mesenteric egg counts for both Schistosoma mansoni and S. haematobium behave consistently with the model, and show little or no departure from isometry in cases without Symmers' fibrosis of the liver. We show that cases with Symmers' fibrosis have relatively more S. mansoni eggs in the small, as opposed to large, intestine. In the genito-urinary organs we show that the proportion of S. haematobium eggs in the bladder is high for low-intensity infections. This is consistent with the conclusion of Smith, Elwi, Kamel and Lichtenberg (1975), based on egg/gram data, that such infections may be initiated in the bladder. The correspondingly high proportion of eggs in the ureters with high-intensity infections indicates that increased intensity may have a disproportionately large pathologic effect on the infected individual.

Schistosoma mansoni and S. haematobium infections in Egypt. IV. Hepatic lesions.

We performed 400 consecutive autopsies in Cairo, Egypt. The intensity of schistosome infection in these cases was measured by counting adult worms recovered by perfusion and dissection and by counting eggs in the tissues of infected cases. Symmers' clay pipestem fibrosis of the liver was clearly related to the presence and intensity of Schistosoma mansoni, but not S. haematobium, infection. Morphologic findings in cases with Symmers' fibrosis were comparable to those in Brazilian cases, and the intensity of S. mansoni infection associated with Symmers' fibrosis was similar in Brazil and Egypt. The fine bilharzial periportal fibrosis described by Hashem was not identified in our material, and Symmers' fibrosis was present in all cases of portal hypertension caused by schistosomiasis. Schistosome eggs were found concentrated in areas of portal fibrosis of cases with Symmers' fibrosis. In the absence of Symmers' fibrosis, eggs did not concentrate in large portal areas regardless of the intensity of infection or the presence of lesser degrees of portal fibrosis. We thus feel it unlikely that Symmers' fibrosis is formed by the fusion of fibrotic granulomas around the schistosome eggs.

Schistosoma mansoni and S. haematobium infections in Egypt. I. Evaluation of techniques for recovery of worms and eggs at necropsy.

Four hundred consecutive autopsy cases were examined in Cairo, Egypt. Sixty percent of cases had Schistosoma haematobium eggs in the tissues and 25% also were infected with S. mansoni. Only a quarter of S. haematobium infections were active, while nearly two-thirds of S. mansoni cases remained active. Adult S. haematobium and S. mansoni were effectively recovered from the mesenteric circulation by a combination of perfusion and dissection. Quantitative recovery from the genitourinary system was reasonably complete, although small numbers of worms were missed in the dissection of these organs.