Vaccination of young lambs against infection with Nematodirus battus using gamma irradiated larvae

Helminthologically naIve 6-week-old Suffolk lambs were given 1-3 doses of 20000 gamma-irradiated infective larvae (L3) of the nematode Nematodirus battus at weekly intervals. Following an anthelmintic drench they were challenged with 50000 viable L3 at 10 weeks of age. Nematode worm burdens 14 days post-challenge showed a significant (P<0.01) 66% reduction in the single vaccine dose group. The two and three dose groups had mean worm burdens which were 30 and 42% lower than controls, respectively, although these were not statistically significant. There was little measurable stimulation of the immune system in the vaccinated lambs, suggesting that the repeatedly dosed animals may have developed immunological unresponsiveness to the parasite.     

The length of Ostertagia ostertagi in populations of uniform age

Michel J. F., Lancaster M. B. and Hong C. 1978. The length of Ostertagia ostertagi in populations of uniform age. International Journal for Parasitology8: 437–441. The conclusion that, in calves exposed to daily infection with larvae of Ostertagia ostertagi, adult worms are constantly lost and replaced was based, in part, on the observation that the length of the worms present decreased with time. The underlying assumption that worms do not shrink was examined in an experiment in which groups of calves received 8300, 25,000 and 75,000 larvae respectively in a single occasion and were killed at various times between the 20th and 132nd day thereafter.The length of the worms was inversely related to the initial worm burden but as worm burdens declined the worms did not grow. Instead, in the groups that received 25,000 and 75,000 larvae, decreases in worm length of 7% and 8% respectively were seen when most of the worms had been lost. Although it appears very probable that this was due to the more rapid loss of large worms than of small, the point could not be conclusively demonstrated.     

Aspiculuris tetraptera in wild Mus musculus. Age resistance and acquired immunity.

Wild house mice, naturally infected with Aspiculuris tetraptera were segregated according to their weight into six age groups. The prevalence of infection and the mean worm burden of these mice were studied in the different age groups. The overall prevalence of infection was high (57% or more) in all the groups except the youngest. Mice acquired larvae soon after weaning; the highest larval burdens were reached in juvenile mice and the highest mature worm burdens, a group later, in mature mice. Older mice had fewer larvae and fewer mature worms. The mature worm burdens decreased but relatively slower than the larval burdens. It is suggested that eigher innate or acquired resistance could account for these observations.     

The responses of a tropical breed of domestic rabbit, Oryctolagus cuniculus, to experimental infection with Trichostrongylus colubriformis

Clinical, parasitological and pathological responses of a tropical out-bred domestic rabbit to experimental Trichostrongylus colubriformis infection were used to evaluate its suitability as a laboratory host and model for studying the host-parasite relationships of T. colubriformis. In the first experiment, three groups each of 16, predominantly juvenile male, 8- to 10-week-old rabbits were given a single pulse infection with 500, 5000 or 25000 infective larvae (L3) of T. colubriformis, to represent low, medium and high levels of infection, respectively. A fourth group of 16 rabbits of similar age formed the uninfected controls. In the second experiment, two groups of 10 juvenile (8- to 10-week-old) and 10 adult (8- to 10-month-old) rabbits were similarly infected with 20000 L3, with appropriate naive controls. Prepatency was 14 and 16 days and peak faecal egg counts occurred on days 24 and 20 after infection in young and adult rabbits respectively. Peak worm counts occurred on day 14 in both age groups and at all levels of infection. Subsequently, parasite burdens declined in a highly significantly dose- and age-dependent manner. At low and moderate levels of infection, approximately 83-98% of worms were recovered from the first 60 cm of the small intestine. Worm fecundity was also significantly influenced by host age and larval dose. Host age also had a significant effect on worm length. Infections with T. colubriformis were associated with a highly significant loss of body weight, accompanied by anorexia, diarrhoea and 25% mortality at high dose levels during the patent period of infection. There were no significant changes in packed cell volume and eosinophil counts at all ages and levels of infection but significant lymphocytosis occurred at the high dose level between days 7 and 21. Parasite-specific serum IgG responses were not related to worm burden. Overall, data showed that this miniature, docile and relatively inexpensive breed of rabbit is a potentially valuable laboratory host for studying T. colubriformis infections. The larval dose, duration of infection and host age were major determinants of host responsiveness to primary infections in this rabbit genotype.     

Concomitant immunity in a rodent model of filariasis: the infection of Meriones unguiculatus with Acanthocheilonema viteae

In an attempt to study the occurrence of concomitant immunity in filarial infections, jirds (Meriones unguiculatus) were experimentally infected with Acanthocheilonema viteae, and patent animals were superinfected with a defined dose of A. viteae stage 3 larvae (L3). Infected animals harbored significantly less worms deriving from the superinfection than the control group (P < 0.05, 56.2%, and 63.4% protection), as shown by analysis of female worms 6 wk after superinfection on the basis of their developmental status and their length. This protection was not due to contact with L3 antigens because a significant reduction of worm burdens deriving of a superinfection was also observed after subcutaneous implantation of a single female worm (P < 0.05, 40.2% and 64.9% protection). The induced protective responses target L3 and restrict their migration because an established infection resulted in a reduction of L3 recovery (95.6% and 94.3%, P < 0.001) from tissues of jirds at day 5 after superinfection. Other data show that L3 from a superinfection are trapped within eosinophil-rich granulomas, which is likely to create unfavorable conditions for the worms and to lead to later death. Taken together, established A. viteae-infections partially protect hosts against homologous superinfection by an immune-mediated mechanism and, thus, regulate the population density of the parasites within the host by concomitant immunity.     

The growth and development of Schistosoma mansoni in mice exposed to sublethal doses of radiation

The maturation of Schistosoma mansoni was studied in mice exposed to various sublethal doses of radiation. Although the treatment of mice with 500 rads of radiation prior to infection did not alter parasite maturation, doses in excess of 500 rads led to a reduction in worm burden. This could not be attributed to a delay in the arrival of parasites in the hepatic portal system. Worms developing in mice treated with 800 rads commenced egg-laying about 1 wk later than worms in intact mice, and the rate of egg deposition appeared to be lower in irradiated hosts. The data demonstrate that exposure of C57BL/6 mice to doses of radiation in excess of 500 rads impairs their ability to carry infections of S. mansoni. The findings do not support the hypothesis that primary worm burdens in the mouse are controlled by a host immune response.     

The effects of single and repeated inoculations of various larval doses on Strongyloides ratti burden and distribution in rats

The changes in worm burden, distribution, length, and fecundity after and during single and repeated inoculations of 10, 50, or 500 larvae of Strongyloides ratti were examined in rats. Worm burden after a single inoculation of a higher larval dose reduced rapidly. Repeated inoculations of lower larval doses at weekly intervals led to a delayed peak and slower reduction of worm burden; the repeated inoculations of 10 larvae did not induce worm expulsion for at least 7 wk. In repeated inoculations at 3-wk intervals, a primary inoculation of 500 larvae induced strong resistance to reinfection at week 3, whereas no resistance was induced until week 6 in rats receiving repeated inoculations of 10 or 50 larvae. Similar dose-dependent reductions in worm length and fecundity were observed in single and repeated inoculations, and the reductions began earlier than worm expulsion. Intestinal migration of worms from the upper small intestine to the large intestine was observed during the course of single and repeated inoculations. Earlier and clearer migration was observed in rats receiving higher doses. These findings indicate that in S. ratti infection, the changes of worm burden, distribution, length, and fecundity are dependent on the inoculated larval dose.     

Intestinal helminths of spiny mice (Acomys cahirinus dimidiatus) from St Katherine's Protectorate in the Sinai, Egypt

Spiny mice, Acomys cahirinus dimidiatus, inhabiting the wadis close to St Katherine in the mountains of the Sinai peninsula, were trapped and their helminth parasites were studied. Sixty one mice provided faeces for analysis and 27 were killed and autopsied. Six species of helminths were recorded (the spirurid nematodes, Protospirura muricola (74.1%) and Mastophorus muris (11.1%), the oxyuroid nematodes, Dentostomella kuntzi (59.3%), Aspiculuris africana (3.7%), and Syphacia minuta (3.7%) and the hymenolepidid cestode Rodentolepis negevi (18.5%)). The spirurids were the dominant species present, accounting for up to 0.87% of total host body weight. Analysis of worm weights and lengths suggested that transmission had been taking place in the months preceding our study. No sex difference in the prevalence or abundance of spirurids was detected. Significant differences were identified in the abundance of total nematode burdens and the mean helminth species richness between the three wadis which provided multiple captures of mice. There was also a marked effect of host age on both parameters. A highly significant positive correlation between spirurid egg counts and total worm biomass indicated that non-invasive techniques based on egg counts could be used to quantify worm burdens and when this technique was applied to a larger sample size (n = 61), a significant difference between sites but no host sex or age effects were detected for spirurid faecal egg counts. The data suggest that there are differences between helminth component communities infecting spiny mice in different neighbouring wadis, a hypothesis which will be explored further through our continuing studies in the Sinai.     

Experimental infections with Cooperia oncophora (Railliet, 1918) in calves. Results of single infections with two graded dose levels of larvae.

Two experiments were carried out in which calves reared parasite-free were infected with a single dose of 3rd-stage larvae of Cooperia oncophora. In the first experiment the calves received 20 000 or 200 000 infective larvae and they were autopsied 28 or 56 days after the infection. In the second experiment the doses were the same but the animals were killed 14, 84 or 140 days after infection. If a dose of 20 000 was given, clinical signs were never observed, while at a dose level of 200 000 the weight gain was less on 56 and 84 days after the infection compared with the low-infected groups or the control animals. After 170 days the differences in weight gain were compensated. Faecal egg output was higher in the 200 000 groups only in the first period of patency, thereafter the calves in the 20 000 groups produced more. No obvious differences between the two infection levels were observed with regard to the haematological data. In the low-infected groups worm counts were only slightly lower when the results after 28 days were compared with those after 56 days. Also, the worm numbers after 14 days were almost equal to those after 84 days, while at 140 days 1 animal still had the same number, the other one had lost its worm burden. In the high-infected groups the worm loss was much quicker. After 28 days a great part of the population had already been lost. Obviously, at the 200 000 level the reaction of the host against the parasite was much stronger. Adult worms were expelled at a higher rate than early 4th-larval stages. In the first experiment worm measurements revealed differences between the length of females, males and spicules of males, these being significantly longer in the low-infected groups. Analysis of the distribution of worms over the small intestine showed that in the low-infected groups worms were mainly restricted to the first 6 metres. In the high-infected groups the worm population was distributed more evenly over the whole small intestine.     

Experimental infection of Dirofilaria immitis in raccoon dogs

Canine heartworm (Dirofilaria immitis) is a nematode that naturally parasitizes in the pulmonary arteries and the right ventricle of domestic dogs (Canis familiaris) as final hosts. Japanese raccoon dogs (Nyctereutes procyonoides viverrinus) also are known to be susceptible to infection by the parasite. However, prevalence of this infection among free-ranging raccoon dogs is low and so is the worm burden. To examine the susceptibility of the raccoon dog to D. immitis infection, 3 raccoon dogs and 2 beagles were inoculated 4 times with 25 third-stage larvae (L3s) of D. immitis at 3-wk intervals. Worms were recovered from 2 raccoon dogs and both domestic dogs. The average percentage of recovery (2.3%) of the raccoon dogs was almost 10 times lower (24.5%) than that of the domestic dogs, but there was no significant difference in the body length of worms recovered from 2 types of hosts. To examine microfilaremia, 2 raccoon dogs were infected with 100 L3s. Microfilaremia was observed for 180 days postinoculation (PI) but disappeared at about 300 days PI. The raccoon dog was mildly susceptible to infection with D. immitis, but surviving worms developed and matured normally.     

Nippostrongylus brasiliensis: Effect of cyclophosphamide treatment on worm expulsion in rats

The precise immunological mechanisms associated with expulsion of the gastrointestinal nematode Nippostrongylus brasiliensis remain controversial. In order to investigate the effects of drug-induced immunosuppression on parasite burdens and expulsion, various regimens of cyclophosphamide were administered to parasitized Wistar rats. It was observed that both the number of worms established from an infective dose of 3000 larvae and the time of expulsion were markedly increased with higher doses of cyclophosphamide. Thus, at the highest sublethal level of treatment (100 mg/kg), 82% of the infective dose was recovered at Day 9 postinfection compared with 51% in nontreated controls. Furthermore, in such treated rats expulsion was delayed in 6 days beyond that of nontreated animals. As cyclophosphamide, at the levels used in the present study, is known to primarily effect B-cell function, the results support the view that antibody-mediated responses play an essential role in worm expulsion.     

Immunity to Heligmosomoides polygyrus induced by subcutaneous vaccination with post-infection larvae

The objective of this study was to investigate, using the Heligmosomoides polygyrus (= Nematospiroides dubius)-mouse model, whether live post-infection trichostrongylid larvae recovered from the intestinal wall of donor animals and placed subcutaneously would serve as vaccine protecting against oral challenge by third-stage (infective) larvae (L3). Experiments were conducted to determine the effect of number and age of post-infective larvae as well as age and sex of host on vaccination. Vaccinated BALB/cByJ mice were challenged with 30 L3 and total adult worm burdens compared between vaccinated groups and sham-treated controls (greater than 90% infection rates). All mice subcutaneously vaccinated with either five or 10 larvae harbored significantly fewer challenge parasites in their intestines than did sham-treated controls (P less than 0.001). Both young and mature mice were significantly protected against challenge by the subcutaneous larval vaccine. Adult female mice had significantly (P less than 0.05) fewer parasites than adult male mice. The age of the larvae (indicated as the days between infection and harvesting of the larvae) was important in that day-4 or day-6 larvae (L4) were significantly more protective (P less than 0.001) than day-2 (L3) or day-8 larvae (L5-preadult). Reduction in worm burden for young vaccinated animals ranged from 31 to 39% (P less than 0.001) and for mature animals from 88 to 100% (P less than 0.001). Passive transfer to serum resulted in the reduction of worm burdens by 26-40% (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunological aspects of murine infection with the rat nematode Strongyloides ratti Sandground, 1925

In a study of the immune response of the rat to infection with the nematode Strongyloidis ratti, the antigens of the infective larval stage (L3) and of the parasitic, parthenogenetic female (Fp) were investigated. From both the larvae and the adult females, one metabolic (exoantigen) and two somatic antigens were extracted. Of the two somatic antigens, one was soluble and obtainable by physical means while the other was separated by chemical means from the tegument of the parasite. Humoral responses to the various antigens were evaluated by immunodiffusion and ELISA techniques, while the overall immune response was assayed by the worm burden in the immunized and subsequently infected rats. Agar-gel double diffusion yielded precipitin bands only with larval somatic antigens. ELISA proved positive at a titer of 20,000 with larval metabolic antigen and sera of rats immunized against either larval metabolic or somatic antigens. By 20 days post challenge infection, however, this titer diminished to 4000. In vivo studies of worm burden in rats immunized with the various antigens and then exposed to the live L3 of the nematode showed that there were significantly fewer adult worms in the rats immunized with larval somatic antigen and adult metabolic antigen than in those immunized with adult somatic antigen or larval metabolic antigen.     

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

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

The phospholipase B content of the intestines of rats infected with varied larvae doses of Nippostrongylus brasiliensis.

Phospholipase B activity, bone marrow eosinophilia and worm burden were measured in separate groups of rats that received initial infections of 100, 400, 800, 1200, 2400, and 4800 Nippostrongylus brasiliensis larvae. The results indicated that as the numbers of larvae in the inocula were increased, the resulting higher worm burdens caused the development of earlier and more intense bone marrow eosinophilias and earlier and greater phospholipase B activities. The expulsion of the adult worms from the host was followed by equally rapid decreases in bone marrow eosinophilia and enzyme activity. It was found that as the number of intestinal adult worms was increased from low to large numbers, the degree of the inflammatory response changed from mild to severe. This suggests that the inflammatory response was responsible for the elevated phospholipase B levels.     

Population biology of Camallanus oxycephalus Ward and Magath, 1916 (Nematoda: Camallanidae) in white bass in western Lake Erie.

The distribution and abundance of the nematode Camallanus oxycephalus infecting white bass, Morone chrysops, in western Lake Erie was studied for over 2 years. Infection was generally more frequent and of higher intensity in large fish. The frequency distributions of nematode abundance in all segments of the fish population followed the negative binomial distribution. The data show seasonal cycles in population structure, site selection, intensity of infection, maturation, and reproduction. Infection occurs during July and August with a resulting peak in population density; during late summer and autumn, mortality, probably density-dependent, reduces the population by 30 to 60%; surviving worms are eliminated at 1 year of age. Growth and development of female worms is arrested from November to April, then proceeds at a rapid rate until the worms release their larvae and die. This growth pattern is probably related to temperature but may also involve host hormone cycles. The dispersal period of the nematode coincides with the annual maximum density of the intermediate host, a cyclopoid copepod,and is interpreted as an adaptation which increases the probability of successful transmission. Because the number of larvae produced by each female worm is a function of body volume, natural selection has favored rapid spring growth and attainment of large body size relative to the male worm. Both seasonal timing in the life cycle and the number of larvae produced are important factors in determining the abundance of this and perhaps other parasites. Evidence is presented suggesting that fluctuations of environmental parameters may disrupt the timing of transmission and alter the distribution and abundance of the parasite. It is hypothesized that the magnitude of such changes in parasite abundance may be related to the complexity of the host-parasite system.     

The effects of immunization of sheep with Trichostrongylus colubriformis larvae on worm burdens acquired during grazing

The effects of immunization of sheep with Trichostrongylus colubriformis larvae on worm burdens acquired during grazing. International Journal for Parasitology 19: 177-181. Romney sheep, reared helminth-free in pens to 5 months of age, were immunized against Trichostrongylus colubriformis by giving two doses of 200,000 T. colubriformis infective larvae at 15 day intervals to assess protection from natural challenge during grazing. Five immunized sheep and five unimmunized sheep were grazed on infested pasture for 4 weeks, and were then returned to the pens for 4 weeks before slaughter. Worm burdens, gastrointestinal histology and mucus antiparasite activity were examined at slaughter. Faecal egg counts and haematological examinations were carried out at regular intervals throughout the trial. Significant protection (P less than 0.05) was afforded immunized sheep against adult T. colubriformis (87%), T. axei (67%), Nematodirus spathiger (91%) and Ostertagia spp. (42%). Greater numbers of immature Nematodirus spp. and Ostertagia spp. were present in immunized sheep Overall, a significant (P less than 0.05) 42% reduction in total nematode burdens was afforded by immunization of the sheep with T. colubriformis larvae. Immunized sheep had significantly (P less than 0.05) more globule leukocytes, mast cells and eosinophils in gastrointestinal tissue and significantly (P less than 0.05) higher levels of mucous antiparasite activity than unimmunized sheep. Haematological observations showed some sheep had transient eosinophilia during immunization or grazing. Both immunized and unimmunized sheep showed depressed (P less than 0.05) total leukocyte counts during grazing which returned to pre-grazing levels within 1 week of return of the sheep to the pens. Overall, haematological parameters reflected parasite challenge and were unrelated to worm burdens acquired.     

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.     

Immunization of mice with cells from juvenile worms of Schistosoma japonicum provides immunoprotection against schistosomiasis

To validate the protective efficacy against schistosomiasis by immunization with cells from juvenile Schistosoma japonicum in a murine model and to analyze possible factors related to protection, in this study, two independent repeated vaccination trials were performed. After three subcutaneous vaccina- tions, in trial one, in the absence of adjuvant, primary juvenile worm cells (pJCs) from S. japonicum induced remarkable average reductions in worm burden (54.3%), liver eggs per gram (LEPG) load (59.8%) as well as egg granulomas size (66.5%) compared to PBS control group (P<0.01), which were significantly higher than those elicited by fractions of juvenile worm cells (JCFs) or fractions of juvenile worms (JWFs) (P<0.05). Non-cell components of worms (WNCs) showed no significant protection. In trial two, compared to PBS control group, significant protective effect was also observed for cultured juvenile worm cells (cJCs) from S. japonicum with 58.4% worm reduction and 68.1% LEPG reduction (P<0.01). However, cultured adult worms cells (cACs) showed significantly higher worm burden (P<0.05) and egg burden (P<0.01) when compared to cJCs. Immunological analysis of trial two revealed that cJCs engendered a Th1-biased mixed Th1/Th2 type of immune response while cACs elicited a Th2-type response. Our data indicated that immunization with both primary and cultured cells from S. japonicum juvenile worms provided high immunoprotection, for which the physical character of immunogens, stage-specific parasite and the type of immune response induced might be responsible, suggesting that vaccination with whole cells from S. japonicum larvae is a promising approach to produce protec- tive immunity against schistosomiasis.     

Adult worms as a factor in the inhibition of development of Ostertagia ostertagi in the host

The removal, by anthelmintic treatment, of adult worms from calves that had been infected daily for 204 days with larvae of Ostertagia ostertagi, stimulated the resumed development of inhibited early fourth stage larvae. The calves remained susceptible to the establishment of worms and the continued administration of infective larvae after the 204th day reduced the rate at chich the burden of inhibited forms decreased. The relevance of these findings to the regulation of worm burdens is discussed.