The mortality and fecundity of Haemonchus contortus in parasite-naive and parasite-exposed sheep following single experimental infections.

Parasite-exposed lambs and their parasite-naive controls were experimentally infected once only with 30,000 H. contortus larvae at 3, 9, 12, and 20 weeks following termination of a moderate immunizing infection of 30,000 H. contortus larvae. Previously exposed lambs, challenged at 3 weeks, had a significant reduction in the total H. contortus worm burden as compared to parasite-naive controls. No difference in the total H. contortus worm burden was found between parasite-exposed or parasite-naive lambs challenged at 9 weeks or thereafter. Female worms were found to be significantly smaller in lambs previously exposed to the parasite as compared to those found in parasite-naive lambs. The average parasite fecundity was 4700 eggs per female worm per day. Previous exposure of the lambs to the parasite had no effect on parasite fecundity. Various mathematical models were used to examine parasite fecundity. Parasite fecundity was found to increase in the initial post-challenge period reaching a constant value approximately 58 days after challenge infection. No density-dependent constraints on fecundity were observed.     

Growth and development of Haemonchus contortus in jirds, Meriones unguiculatus.

Growth and development of Haemonchus contortus were examined in jirds and were compared to these processes in lambs. Number, sex, size, and stage of development were determined for worms recovered at necropsy at various times postinoculation (PI) from immunosuppressed jirds inoculated with approximately 1,000 exsheathed infective larvae (L3) of H. contortus. In addition, gastric tissue samples from jirds were examined histologically. Parallel studies were done in lambs inoculated with approximately 7,500 L3. Typically, 5-30% of the inoculum established and survived in jirds at reasonably stable numbers to day 14 PI. By day 21 PI, worm numbers in jirds decreased dramatically. Although the parasite was similar in size and development on day 4 PI in jirds and lambs, from day 7 PI on, worms were significantly smaller and less developed in jirds. On histological examination, the parasite was found only in the glandular portion of the stomach of jirds (anatomically similar to its predilection site in the abomasum of lambs), and histological changes were consistent for both host species. Although growth and development of H. contortus are slower and incomplete in jirds, the parasite establishes, grows, and develops (at anatomically comparable sites in both hosts) in this model. Thus, the model appears to provide a useful laboratory host to study H. contortus.     

Observations on egg production by Toxocara pteropodis

Studies in juvenile Pteropus poliocephalus showed an average daily egg production by Toxocara pteropodis of 25,000 per female, with concentrations of up to 16,000 epg. regardless of whether eggs were fertile or infertile. Production commenced as early as 35 and as late as 48 days post-partum and rose to plateau average levels over about 10 days. For 23 days one bat passed infertile eggs which, over 2 days, were then replaced completely by fertile eggs. The implicit delay in maturation of a male nematode suggests that transmammary passage of larvae to suckling bats may persist for at least 3 weeks. Patency was terminated by the spontaneous expulsion of worms. If male worms were lost first, the egg output converted from fertile to 100% infertile within 48 h and the females were devoid of spermatozoa, suggesting that T. pteropodis copulate at least once daily. In prolonged infections, worm fecundity and egg fertility diminished, so that females with stored spermatozoa were producing mixtures of fertile and infertile eggs.     

A study of the mortality and fecundity of Haemonchus contortus in sheep following experimental infections.

The regulation of the fecundity and mortality of H. contortus in sheep was examined using a series of mathematical models. Six-month-old Dorset crossbred lambs were infected once only with various doses of infective H. contortus larvae (500-20,000 larvae). Parasite mortality was found to be an increasing linear function of the magnitude of the initial infection over the range of doses examined. Parasite fecundity was found to remain constant over the intensity and duration of the infection. The average fecundity for H. contortus at the time of slaughter was found to be 7037 eggs per female worm per day. There was no evidence of time-dependent changes in fecundity or density-dependent regulation of fecundity.     

Recovery,growth, and development of Acanthoparyphium tyosenense (Digenea: Echinostomatidae) in experimental chicks

Chicks were experimentally infected with Acanthoparyphium tyosenense (Digenea: Echinostomatidae) metacercariae per os, and the growth and development of worms in this host were observed from days I to 38 postinfection (PI). The worms grew rapidly and matured sexually in the small intestine (chiefly in the jejunum) of chicks by day 5 PI. and survived at least up to day 38 Pi, although worm recovery decreased after day 5 PI. Both parenchymal and reproductive organs increased greatly in size from day 2 to day 10 PI and then continued to increase gradually in size up to day 38 PI. The number of uterine eggs reached a peak on days 10 and 15 PI and then decreased gradually. The results suggest that chicks are a fairly suitable definitive host for experimental infection with A. tyosenense.     

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.     

Fecundity and egg output by Toxocara canis in the red fox, Vulpes vulpes

The role of the red fox Vulpes vulpes in the dissemination of eggs of Toxocara canis into the environment is considered with reference to female worm fecundity and egg output in the faeces of infected foxes collected from four localities in southern England. A significant positive correlation was found between female worm size and the number of eggs in the uterus but there was no significant relationship between T. canis worm numbers and egg output in fox faeces. Reliable estimates of worm burdens in foxes could not, therefore, be determined from faecal egg counts alone. The highest mean egg output of 2145.0 epg recorded from adult foxes indicated that fox cubs are not necessarily the main sources of environmental contamination with T. canis eggs. Saturated magnesium sulphate was found to be a more effective flotation solution than zinc sulphate and sodium chloride for recovering eggs from fox faecal samples.     

Growth and development of Gymnophalloides seoi in immunocompetent and immunosuppressed C3H/HeN mice

The growth and development of Gymnophalloides seoi were studied in C3H/HeN mice and effects of immunosuppression of the host on the worm development were observed. Two hundred metacercariae of G. seoi were orally administered to each mouse, and worms were recovered on days 1, 3, 5, 7, 14 and 21 post-infection (PI). The worm recovery rate was significantly higher in immunosuppressed (ImSP) mice than in immunocompetent (ImCT) mice except on days 1 and 3 PI. The worms attained sexual maturity by day 3 PI with eggs in the uterus, and worm dimensions and the number of uterine eggs continuously increased until day 14 PI in ImSP mice. Worms recovered from ImSP mice were significantly larger in size than those from ImCT mice on days 1 and 3 PI, and the number of uterine eggs was significantly larger in ImSP mice on days 5 and 7 PI. Genital organs such as the ovary, testes, and vitellaria, that were already developed in the metacercarial stage, grew a little in size until day 14 PI. The results show that the C3H/HeN mouse is, though not excellent, a suitable laboratory host for G. seoi.     

In vivo and in vitro egg production by Nematospiroides dubius during primary and challenge infections in resistant and susceptible strains of mice

Experiments were conducted to examine adult worm burdens, fecal egg output, and in vitro fecundity of Nematospiroides dubius in resistant LAF1 and susceptible CBA mice 12, 15, 18, and 21 days following primary and challenge infections. A strong correlation was obtained on the number of eggs produced by worms cultured in vitro and the egg production as assessed by fecal egg count. Worm counts, fecal egg counts, and in vitro fecundity were similar on all days studied following a primary infection in both mouse strains. However, after challenge infection, LAF1 mice showed lower worm burdens, fecal egg output, and in vitro egg production when compared to CBA mice. Although the egg production of surviving female worms from immune LAF1 mice was decreased, it never fell below a threshold of 100 eggs/day. The reduced fecundity may be a manifestation of a general anti-worm response rather than responses directed specifically at worm reproduction.     

Fecundity of Litomosoides carinii (Nematoda, Filarioidea) in vivo and in vitro

Several parameters concerning the reproduction of Litomosoides carinii were assessed using quantitatively infected cotton rats (Sigmodon hispidus). The course of embryogenesis from the fertilization of eggs to the delivery of the first microfilariae was observed by daily autopsies during prepatency. The duration of embryogenesis in vivo could thus be determined as 18 +/- 2 days. The contents of embryos in the uteri of female worms had been examined at various intervals. At the onset of patency 7-8 weeks p.i. the females were 71 +/- 6 mm long and on average contained 308 X 10(3) embryos/female, of which 19% were pathologically altered. In the middle of patency 16-20 weeks p.i. the females had grown up to 100 +/- 11 mm in length and now contained 509 X 10(3) embryos/female, 25% of them were pathologically altered, the others were normally developed. A positive correlation between the body length of a female worm and its number of embryos in utero was evident. Additionally the percentage of pathologically altered embryos was increased with respect to the age of the worms. The calculated fecundity of a female L. carinii in vivo of around 20 X 10(3) microfilariae/female per day had been confirmed with worms maintained in vitro. Three combinations of media and serum supplements were used and their influence on embryogenesis evaluated.     

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.     

The fecundity of Schistosoma mansoni in chronic nonhuman primate infections and after transplantation into naive hosts

Adult Schistosoma mansoni worms were transplanted from 8 nonhuman primates with chronic infections into 8 naive recipients, in an effort to test the hypothesis that worm fecundity reduction in chronic infections is the result of host immunity or some other host effect. Techniques for perfusing living donors without the added use of anti-schistosomal drugs and for reducing the likelihood of post-operative bacterial endotoxemia and septic shock are described. Fecundity values in terms of eggs per day per female worm were obtained for the worms in their original and in their new hosts and compared. In 3 experiments, perfusions were incomplete and the donors were saved, enabling direct comparisons of fecundity to be made in subpopulations of worms in both their original and new hosts, after equal life spans. In only 1 of the 8 transplantations was there a clear increase in fecundity after surgical introduction into a naive host. Therefore, these experiments fail to support the hypothesis that reduced fecundity of S. mansoni worms in permissive nonhuman primate hosts is a reversible result of host immunity or some other host-derived factor. Despite this negation, further evidence for reduced worm fecundity in older infections was obtained. In the absence of in vivo evidence for immune-mediated antifecundity, worm senescence is the most likely explanation for this finding, with irreversible immune damage to the worms being a less attractive alternative hypothesis.     

Effect of diet upon singly established Hymenolepis diminuta in rats

The onset and course of the elimination of eggs in the feces of rats of singly-established Hymenolepis diminuta has been studied. In both male and female hosts, eggs of this tapeworm first appeared about 18 to 20 days after inoculation, and the daily output gradually increased to a fairly stable level which was higher in males (average about 205,000) than in females (average about 167,000). Egg outputs were maintained at these levels for at least 150 days.In male rats on a complete diet the average number of eggs per proglottid was about 2100. Approximately 7.6 cm of strobila was shed daily which is equivalent to about 8% of the worm's length.In female rats on deficient diet there was a drop in egg output to about 50,000 eggs/24 hours in about 30 days whereas in male hosts on deficient diet a comparable drop occurred only after a period of approximately 3 months.In normal male rats on deficient diet there was very little stunting of worm growth. In females on complete diet worm-size approximately equaled that in male rats, but on deficient diet the worms were significantly smaller.Vitamin B₁₂ failed to raise the egg output in two normal female rats on deficient diet.An increase in egg output was associated with administration of male dog bile in both male and female hosts which continued in males until termination of the experiment, but which failed in females and resulted in a subsequent decrease in elimination of eggs. In both sexes there were unusually large fluctuations in egg output from day to day.     

Genetic difference in susceptibility and fatality of three strains of mice experimentally infected with Neodiplostomum seoulense

The genetic influence on host susceptibility to Neodiplostomum seoulense infection and fatality of the host was studied in 3 inbred strains of mice (BALB/c [H-2d], C3H/He [H-2k], and C57BL/6 [H-2b]). The survival of the mice, worm expulsion kinetics, worm size, number of eggs produced per day (EPD), and number of uterine eggs were observed from day 1 to day 40 postinfection (PI) with 100 or 200 metacercariae per mouse. Infection with N. seoulense was highly lethal to all 3 strains of mice, but the lethality was dose-dependent and varied according to the genetic backgrounds of the mice. The C3H/He mice exhibited the highest mortality, the lowest worm burdens and EPD, and the quickest expulsion of worms. It is suggested that different genetic backgrounds of mice appear to affect the host's capacity to expel N. seoulense and the fatality of the hosts themselves.     

Developmental and age-related changes in proteins in the female reproductive tract of Heligmosomoides polygyrus (Nematoda)

Proteins in the female reproductive tract of Heligmosomoides polygyrus at days 8, 16, 35, 90, and 140 postinfection (PI) were examined using polyacrylamide gel electrophoresis. Sixteen-day-old and 140-day-old worms also were examined histochemically. Egg production of these worms was assessed for each age group. In analyzing proteins using electrophoresis, the reproductive tracts were separated into 3 sections: the tip, or anteriormost part of tract, containing oogonia; the middle region, containing developing oocytes; and the posterior region, containing the uterus with fertilized eggs. Three major reproductive tract proteins were identified as having molecular weights of greater than 140 kDa, 115 kDa, and 82 kDa. These were found in all parts of the reproductive tract from worms of all ages except those at 8 days PI (which are too young to produce eggs) and are believed to be yolk proteins. Four low molecular weight proteins (L1-4) are believed to be nucleoproteins. L4 was absent from the posterior section of the reproductive tracts and L3 was limited to the posterior sections and may be associated with sperm stored in the uterus. Of 5 high molecular weight proteins the second heaviest, designated H2, appeared to be relatively more concentrated in the posterior sections of the reproductive tract. An 85-kDa protein was limited to the tip and middle sections of reproductive tracts. Histochemical tests on sectioned H. polygyrus showed strong positive reactions for protein in cytoplasmic granules in developing oocytes and in eggs of younger worms (16 days) but a reduced reaction in older worms (140 days). Strains for collagen showed a slight positive reaction in and between developing oocytes and a strong reaction in the egg shells. Stains for nucleoproteins particularly reacted with sperm stored in the uterus, and slightly reacted with fertilized eggs and the nucleoli of the intestinal and ovarian epithelium. Egg production by H. polygyrus increased to 123 eggs/female/day by 16 days PI but declined from 121 eggs/female/day at 35 days PI to 64 eggs/female/day in worms 140 days old. Electrophoresis indicated no loss in the different types of proteins in the reproductive tract of older worms, but histochemistry and protein content assays suggest that older worms that produce fewer eggs contain a relatively smaller amount of protein in the female reproductive tract.     

Experimental infection of pigs with three dose levels of Trichuris suis

The objective of the study was to follow the course of Trichuris suis infection in pigs given infective eggs at low (400 eggs), medium (4,000 eggs) and high inoculation dose (40,000 eggs), respectively. Interestingly, despite a 100-fold difference in dose level no significant difference was found in either blood parameters, total faecal egg excretion, fecundity or worm burdens at necropsy 12 weeks post inoculation. The highest and lowest median faecal egg output was found in the medium and high dose group, respectively. With increasing dose level, worm size, establishment and prevalence of T. suis positive pigs decreased while worms were dislocated aborally. In addition there was a highly significant correlation between female worm burden and faecal egg excretion.     

Infectivity of plerocercoids of Schistocephalus solidus (Cestoda: Ligulidae) and fecundity of the adults in an experimental definitive host, Gallus gallus.

Aspects of the infectivity of the plerocercoid stage and the fecundity of the adult stage of Schistocephalus solidus were examined using the chicken, Gallus gallus, as an experimental host. To investigate size-related infectivity of the plerocercoid stage to a definitive host, a range of plerocercoids (166) were weighed, and each was fed to an individual male chicken. Only a very small percentage of plerocercoids weighing less than 50 mg established compared with in excess of 50% in all other weight classes. To examine the factors affecting the quantity of eggs produced by the adult stage, 15 similar-sized plerocercoids (160-218 mg) were fed to chickens. The majority of plerocercoids administered established as adults and survived until the experiment was terminated on day 7 postinfection (PI). Fecal egg counts indicated that all established worms commenced egg production on day 2 PI with peak output on day 2 or 3 PI. By day 7 PI, egg production in the surviving worms had declined, but it was still evident. The final weight of the adult and the average egg output per worm were unrelated to the initial weight of the infecting plerocercoid. However, the average egg output was predicted by the final adult dry weight and to a lesser extent by the proportion of weight lost in the transition from plerocercoid to adult, but not by the absolute weight loss.     

Rapid improvement of immunity to Teladorsagia circumcincta is achieved through a reduction in the demand for protein in lactating ewes

Protein supplementation can improve the resistance to parasites of periparturient ewes, as indicated by reduced nematode egg excretion and worm burdens. However, the rate at which this improvement can occur is largely unknown. We investigated the rate of improvement by assessing temporal changes in faecal egg counts after we experimentally reduced nutrient demand. Three groups of nine pregnant ewes each were trickle infected with Teladorsagia circumcincta from day(-70) to day(16) (parturition is day0). Two groups of twin-rearing ewes were fed at 0.8 (L22) or 1.2 (H22) times their assumed metabolizable protein requirements, and a third group was fed the same daily food allowances as L22 ewes, but one of their lambs was removed on day10 (L21). Ewes were slaughtered on day21 to assess worm burdens, in vitro larval establishment on abomasal explants, and mucosal inflammatory cells. Faecal egg counts of L22 ewes were higher than H22 ewes throughout lactation. After the removal of one lamb, faecal egg counts of L21 ewes decreased within 5 days to levels similar to H22 ewes. Relative to L22 ewes, L21 and H22 ewes had lower worm burdens, parasite per capita fecundity and in vitro establishment rates of both T. circumcincta and Haemonchus contortus. Mucosal mast cell and eosinophil counts were similar for all ewes, but H22 ewes had higher globule leukocyte counts than L22 and L21 ewes. The data suggest that a reduction in protein demand can rapidly improve periparturient immunity to T. circumcincta. This may be associated with increased parasite expulsion, reduced fecundity and non-parasite specific reduction of in vitro larval establishment.     

Resistance to ivermectin by Haemonchus contortus in goats and calves.

Efficacy of ivermectin on susceptible or resistant populations of the parasitic nematode Haemonchus contortus was determined in cattle and goats held in a barn. Goats were each infected with 3000 infective, ivermectin-susceptible or -resistant H. contortus larvae on day 0 and reinfected with 2000 infective larvae on day 24. Goats were treated orally with 600 micrograms kg-1 ivermectin on day 31. No significant differences were detected in blood packed cell volume (PCV) or total protein (TP), prepatent period, or epg among the four groups of goats that were each infected with one of four parasite strains (one susceptible, three resistant). There were no differences among the four parasite strains in the numbers of infective larvae that developed to the third larval stage from fecal cultures or in the viability of cultured infective larvae when held in the laboratory at 27 +/- 1 degrees C for 14 weeks. After treatment with ivermectin, there were significant differences among the parasite strains in PCV, TP, and epg. Total worm counts were reduced by 94 to 97% with three times the recommended dose. Immature and adult Skrjabinema ovis were also present in two treated goats. In a second test, one goat infected once with 10,000 infective larvae of a resistant strain of H. contortus and then treated with nine doses of ivermectin, increasing from 500 to 2000 micrograms kg-1 over a period of 133 days, had 35 adult worms at necropsy. In a third test, three calves were readily infected with an ivermectin-resistant strain of H. contortus from goats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental Oesophagostomum dentatum infection in the pig: Worm populations resulting from single infections with three doses of larvae

This report describes the effect of different dose levels of infection upon worm burdens and development and fecundity of the parasites. Three groups each of 40, 9-week-old, helminth naïve pigs were inoculated once with either 2000 (group A), 20,000 (group B), or 200,000 (group C) infective third stage larvae of Oesophagostomum dentatum. Subgroups of 5 pigs from each major group were killed 3, 6, 11, 14, 18, 25, 34 and 47 days post inoculation (p.i.) and the large intestinal worm burdens were determined. Faecal egg counts were determined at frequent intervals after day 13 p.i. There were no overt clinical signs of gastrointestinal helminthosis during the experiment. Faecal egg counts became positive in groups A and B at around day 19 p.i., whereas most pigs in the high dose group C did not have positive egg counts until day 27–33 p.i. and some pigs remained with zero egg counts until the end of the study. Throughout the experiment the worm populations in group C consisted mainly of immature larval stages, while those in groups A and B were predominantly adult stages after days 14–18. Adult worms from the low dose group A were significantly longer than those from group C. At high population densities, stunted development of worms and reduced fecundity among female worms were found. Furthermore, there was a tendency for the distribution of the worms within the intestine to be altered with increasing population size.