Specific serum antibody responses following a Toxoplasma gondii and Trichinella spiralis co-infection in swine

The aim of this study was to examine the dynamics of parasite specific antibody development in Trichinella spiralis and Toxoplasma gondii co-infections in pigs and to compare these with antibody dynamics in T. spiralis and T. gondii single infections. In this experiment, fifty-four pigs were divided into five inoculated groups of ten animals, and one control group of four animals. Two groups were inoculated with a single dose of either T. gondii tissue cysts or T. spiralis muscle larvae, one group was inoculated simultaneously with both parasites and two groups were successively inoculated at an interval of four weeks. Specific IgG responses to the parasites were measured by ELISA. T. gondii burden was determined by MC-PCR carried out on heart muscle and T. spiralis burden by artificial digestion of diaphragm samples. Specific IgG responses to T. gondii and T. spiralis in single and simultaneously inoculated animals showed a respective T. gondii and T. spiralis inoculation effect but no significant interaction of these parasites to the development of specific antibodies with the serum dilutions used. Moreover, our data showed that the specific IgG response levels in groups of animals successively or simultaneously co-infected were independent of a respective previous or simultaneous infection with the other parasite. Additionally, no differences in parasite burden were found within groups inoculated with T. gondii and within groups inoculated with T. spiralis. Conclusively, for the infection doses tested in this experiment, the dynamics of specific antibody development does not differ between single and simultaneous or successive infection with T. gondii and T. spiralis. However, lower parasitic doses and other ratios of doses, like low-low, low-high and high-low of T. gondii and T. spiralis in co-infection, in combination with other time intervals between successive infections may have different outcomes and should therefore be studied in further detail.     

Immunity of ivermectin treated cattle to challenge from helminth parasites in the following season

Two groups of yearling cattle which had been treated with ivermectin either three and eight, or three, eight and 13 weeks after turn out to trichostrongyle contaminated pasture in their first grazing season were exposed in the following season to natural challenge with helminth parasites. To assess their immunity to this challenge each group shared a pasture with parasite naive first season calves. No anthelmintic treatments were administered at any time during the year. Throughout the grazing period the yearlings showed normal respiratory rates, negative faecal lungworm larval counts, and, relative to the calves, low faecal trichostrongyle egg counts. All the first season calves developed patent lungworm infections and on one occasion the mean respiratory rates of each group of calves were significantly greater than those of the yearling cattle. At the end of the grazing period, from early May until late September or October 1986, the cattle were removed from pasture and together with parasite naive controls challenged with either 10 or 22 third stage larvae of Dictyocaulus viviparus/kg bodyweight and necropsied between 18 and 23 days later. Although the experimental challenge resulted in relatively heavy lungworm infection of the naive controls, none of the yearlings and only three of the 11 calves which had been at pasture were found to be infected. However, large numbers of arrested fourth stage larvae of Ostertagia ostertagi were present in all the naturally infected yearlings and calves.     

Serum and abomasal antibody response of sheep to infections with Haemonchus contortus

Serum and abomasal IgA, IgG and IgM antibody response against adult worm, L3 and egg antigens of Haemonchus contortus was monitored by the ELISA technique after one or two infections with this nematode. Following the first infection, antibody levels in serum did not change materially. After administration of a challenge dose of infective larvae, antibodies of the three immunoglobulin classes in infected animals rose slightly, but this rise appeared later than the fall in the faecal egg counts. In contrast, in abomasal mucosa, IgA anti-larval antibody levels, which did not increase materially after the primary infection, rose rapidly after a transient inhibition when sheep were challenged. A close temporal relationship was observed between the rise in local anti-worm IgA antibodies and the self-cure reaction, but antibody levels fell rapidly after worm diminution. The local antibody response was thus considered to be related to immunity of sheep to H. contortus.     

Epidemiological study of parasite infection in a cow-calf beef herd in Quebec.

The patterns of gastrointestinal and pulmonary nematode infections in a previously untreated Aberdeen Angus cow-calf herd were observed between May 1988 and December 1990. The cow-calf herd and replacement heifers were on separate pastures. The relatively high mean faecal egg counts of cows and heifers at the time of turnout were mainly owing to the maturation of hypobiotic worms. The strongyle egg counts of calves began to rise soon after turnout onto pasture and reached peak levels at the end of the grazing season. The number of infective larvae on pasture was highest during September/October. Ostertagia, Cooperia and Nematodirus were the most prevalent genera found at necropsy and on pasture. Larvae of these nematodes were able to overwinter on pasture and Ostertagia larvae, additionally, were able to overwinter in the host as arrested early fourth stage larvae. The high egg output of cows at the time of turnout may serve as a source of infection for their calves and be responsible for the late-season rise in pasture larval counts.     

Is there a relationship between haemoglobin genotype and the innate resistance to experimental Haemonchus contortus infection in Merino lambs?

Responses to a single or repeated infection with 7000 infective larvae of Haemonchus contortus were studied in an experiment using a total of 106 3-month-old lambs with AA, AB or BB haemoglobin (Hb) genotypes. Results were assessed by faecal egg counts, adult worm counts, haematocrit values, haemoglobin concentrations, total serum protein and serum antibody IgG1 and IgA ELISA titres. None of these parameters showed a strong relationship to the Hb type. The prevalence of low responder (greater than 500 worms) and of high responder (less than 50 worms) animals in groups AA, AB and BB Hb types was 3.8 and 34.6, 20.6 and 35.2, 28.1 and 43.7%, respectively, suggesting that the responsiveness to nematode infection is under the control of gene(s) not closely linked with those determining the Hb genotype. Worm counts of a primary infection are more subject to variation than those of a secondary infection. There is a strong relationship between adult worm counts and faecal egg counts taken close to the time of slaughter. In living animals low and high responder discrimination can be based on individual faecal egg counts around 50 days after a secondary infection. Haematocrit values proved to be of little value in the low and high responder selection. In this regard neither Hb concentration nor total serum protein values are of practical significance. In 3-month-old lambs primary infection induced partial immunity which could prevent the establishment of a part of the secondary infection, irrespective of the presence or absence of the primary worm population. The development of immunity was not associated with an increase of serum IgG1 and IgA antibody levels. Specific antibody production was not influenced by Hb types. Mean antibody levels of low responder lambs showed no difference from those of high responders. Thus, serum IgG1 and IgA levels are of no predictive value in identifying lambs which are genetically resistant to Haemonchus infection.     

Grazing study in Ireland using the morantel sustained release bolus for controlling nematodiasis in calves

The morantel sustained release bolus was administered at turnout to first-season grazing calves in order to assess its efficacy in the seasonal control of infection by nematode parasites in Ireland. The pastures grazed by control calves showed a marked increase in gastrointestinal trichostrongylid infective larvae by September, while numbers of infective larvae on pasture grazed by bolus-treated calves remained at a low level throughout the grazing season. In consequence, the controls showed significantly higher worm egg counts in late season and significantly higher worm burdens (mainly Ostertagia spp) at necropsy carried out in November on representative number of principal animals selected from each group. These reduced worm burdens were attributed to the suppression of egg output during the early part of the season as a result of treatment with the morantel sustained release bolus at turnout in the spring. Pasture contamination with Dictyocaulus viviparus larvae was present on all treatment pastures. The bolus-treated calves however were subjected to an increase in D. viviparus infection which occurred on their pasture in late season after the active life of the bolus had expired. It was concluded that bolus treatment delayed (rather than prevented) the buildup of D. viviparus infection on the pasture by 60-90 days.     

Effect of weaning on antibody responses and nematode parasitism in Merino lambs.

Lambs weaned at eight weeks old were compared with control lambs which remained with their dams; both groups grazed the same pasture. Weaning significantly reduced the growth rate, control lambs being, on average, 6 kg heavier than weaned lambs at 15 weeks old. When contamination of pasture with larval parasites was light, both groups of lambs suffered only modest parasitic infections. When lambs were experimentally infected with 5000 Haemonchus contortus and 10,000 Trichostrongylus colubriformis larvae at eight weeks old, the mean faecal egg count for weaned lambs was twice that for controls at 12 weeks old (P less than 0.001) and weaned lambs suffered a significantly greater decline in packed cell volume than controls over the next four weeks. Antibody responses following immunisation with either ovalbumin or Brucella abortus at four and at eight weeks old, did not differ significantly between control and weaned lambs. In contrast serum antibody responses to H contortus and T colubriformis differed significantly between the two groups, with controls responding earlier and more strongly than weaned lambs. The practical significance of these findings is that up to three months old, suckled lambs, when faced with a substantial parasite challenge, have much better prospects than weaned lambs.     

Relative importance of winter survival of larval nematodes in pasture and infected carrier calves in a study of parasitic gastroenteritis in calves.

A study was done in Maine to determine the relative importance of winter survival of nematode larvae in pasture and infected carrier animals as sources of infection for susceptible calves. Under the conditions of the experiment, it appeared that winter survivals in pasture of the infective stages of the genera Ostertagia, Cooperia, Nematodirus, and Trichostrongylus were of greater importance than carrier animals as sources of infection for susceptible calves. While animals in plots infected the previous summer and simultaneously allowed to graze alongside infected carrier animals did show more worms than those grazed only in infected plots, these differences were not statistically significant. Both groups had significantly (P greater than 0.01) more worms than did calves grazed only with carrier animals for the period of the experiment (8 weeks). It was also observed that carrier calves with low fecal egg counts (less than 200 eggs/g of feces) introduced in early spring to uncontaminated pasture could produce enough parasitic contamination by early fall to cause fulminating infections in susceptible calves grazing the pasture at the same time. Infected animals that survived clinical disease during their 1st summer developed a strong immunity which limited their acquisition of further infections when they were exposed to severe pasture contamination the following year.     

Immune modulation by Ostertagia ostertagi and the effects of diet

IgG1 antibody responses to Ostertagia ostertagi third stage larvae (L3) and the third party antigen, keyhole limpet haemocyanin (KLH), and faecal egg counts were determined in calves infected with a single dose of O. ostertagi and in uninfected, pair-fed calves. The infected and uninfected calves were given diets either high (H) or low (L) in protein and energy. The diets were within the normal range of husbandry practice in the UK. IgG1 antibody responses to L3 antigen were significantly greater from 6 weeks post-infection in infected calves given the L diet than in infected calves given the H diet (P less than 0.05). The effects of diet and infection on anti-KLH IgG1 responses were independent of each other. IgG1 responses to KLH were decreased by infection and by the L diet compared with the H diet.     

Effects of Mixed Grazing of First- and Second-year Calves on Trichostrongylid Infections in Lithuania

The objective of this study was to examine whether susceptible calves grazing together with second-year resistant heifers are less exposed to trichostrongylid infection than are calves grazing on their own. Two groups of animals representing each age category were turned out onto pasture on 24 May 1997 and grazed at comparable stocking rates. The grazing of calves and heifers together was compared to groups of each age category grazing separately. The results indicated that herbage larval counts were significantly reduced in the second part of the grazing season on the plot grazed by the mixed group compared to the plot grazed by the first-season calves only. The mixed grazing strategy protected the young calves and no clinical signs were observed in this group, while most of the calves that grazed alone exhibited clinical signs. The availability of herbage was reduced towards the end of the season, with subsequent competition for the grass forcing all the animals to graze the tufts around the faecal pats, where the quality of the grass is poor and the numbers of infective larvae are high. The effect of this was visible in the form of increased parasite burdens in the calves that were grazed together with the heifers, confirmed by increased blood serum pepsinogen concentrations and reduced daily weight gains in the second part of the grazing season. The lower numbers of infective larvae on the pasture were probably achieved through the heifers ingesting many of the larvae but subsequently depositing relatively few eggs, since they had acquired some degree of resistance against trichostrongylid infections during their first grazing season. Thus they did not suffer any parasitological ill-effects during mixed grazing with first-season calves.     

Serum protein changes in ponies on different parasite control programmes

Serum protein responses were examined in 52 ponies divided into five groups and subjected to various control strategies that resulted in pasture infectivity ranging from 706 to 18,486 infective third stage, cyathostome and Trichostrongylus axei larvae per kilogram of herbage (L3/kg) by 17 September 1984. Major protein changes occurred only in young ponies (Groups 4 and 5) and were observed before exposure to maximum numbers of pasture larvae (Group 4; 10,210 L3/kg, Group 5: 10,042 L3/kg) on 17 September. It appeared that a primary infection of T axei was a greater stimulus to serum beta-globulin and immunoglobulin (Ig)G(T) responses that provided by continued infection with cyathostome (small strongyle) worms. The large strongyles (Strongylus vulgaris, S edentatus and S equinus) were not detected in any larval cultures or on pastures grazed by the young ponies. A fall in beta-globulin and IgG(T) concentrations of Group 5 ponies one month after treatment with ivermectin indicated a larvicidal action against T axei and/or the cyathostomes. A subsequent rise in serum albumin concentrations of Group 5 ponies suggested that a protein-losing gastroenteropathy had been alleviated by the larvicidal action of ivermectin. Mature control ponies (Group 1) showed little beta-globulin response and only a modest IgG(T) response in six of the 10 ponies after exposure to heavily infected lawns (18,486 L3/kg) in September 1984. It was concluded that serum protein and IgG(T) responses were of limited value as an aid to diagnosis of parasitism because of numerous difficulties of interpretation.     

Some observations on the use of the morantel sustained-release bolus in first season-grazing calves on a Belgian dairy cattle farm

The efficacy of the morantel sustained-release bolus (MSRB) in controlling gastrointestinal parasites in first-season grazing calves was evaluated on a dairy cattle farm in Belgium. The calves grazed a pasture which had been used by bolus-treated animals in the three previous years. The effect of bolus administration was determined with respect to live weight gain, faecal egg shedding, herbage larval counts, serum pepsinogen levels and ELISA antibody titres. In spite of an incomplete reduction of faecal egg shedding during the first months of the grazing season, bolus administration resulted in the prevention of parasitic gastro-enteritis in the calves. A weight gain advantage of 35,2 kg of the bolus-treated animals over the controls was noted already at two months after turnout. This weight gain advantage was maintained until housing. The usefulness of serum pepsinogen values and ELISA antibody titres as parameters in prevention experiments is stressed. Both serological parameters gave more information concerning infection level than did the faecal egg output and the herbage larval counts.     

Development of immunity to Ostertagia ostertagi (Trichostrongylidae: Nematoda) in pastured young cattle.

This experiment comprised 3 groups of calves, (+P2), (-P2) and (-P1), which all started their first grazing season as parasite-free calves. The (+P2)- and (-P2)-group grazed 2 seasons. In the first season the (-P2)-group of calves was grazing a pasture with no detectable trichostrongyles and treated with anthelmintics every second week. The untreated (+P2)-group grazed an Ostertagia ostertagi contaminated pasture. During the second grazing season these 2 original groups grazed together with a new group of first-year grazing calves (-P1) on paddocks infected with O. ostertagi. Parasitological analyses showed that (+P2)-group had negligible egg excretions in the second year in comparison with (-P2) and (-P1). This indicated, that the egg output may be regulated through acquired immunity. The difference in egg excretions was not reflected in the serum pepsinogen levels, which were only slightly elevated for all groups in the second year. Post mortem examination at the end of the experiment showed that only the (-P1)-group harboured relatively high numbers of worms in the abomasa at that time. Antibodies of 3 immunoglobulin classes were investigated: IgA, IgG1 and IgG2. The IgA and IgG1 responses correlated with the presence of developing and adult worms in the abomasa and they remained elevated in the (+P2)-group throughout the experiment, perhaps indicating an involvement of these antibodies in a protective immune response. In the (-P2)-group the IgA and IgG1 showed fast and sharp rises during the second season that most likely were age-related and as such a result of maturation of the immune system. The role of IgG2 is unclear as the IgG2 response was weak in all groups of calves and difficult to relate to the parasitological data.     

The influence of relative resistance and urea-supplementation on deliberate infection with Teladorsagia circumcincta during winter

The consequences for lambs of infection over the winter with Teladorsagia circumcincta were quantified by deliberate, trickle infection of selected animals at 7 months of age. Infected and control uninfected animals were each allocated into four groups, relatively resistant animals on a normal diet, relatively resistant animals on an isocaloric diet supplemented with urea, and relatively susceptible animals on the same two diets. Resistance and susceptibility was assessed by faecal egg counts following natural infection during the summer preceding the deliberate infection. During the deliberate infection egg counts remained low and most parasites recovered at necropsy were inhibited larvae. Nonetheless, infection reduced weight gain, decreased albumin and fructosamine concentrations and provoked a noticeable pepsinogen and eosinophil response. As most larvae were inhibited these responses may have been largely a consequence of immuno-inflammatory responses in the host rather than the direct action of parasites themselves. Relatively resistant animals on the supplemented diet allowed fewer larvae to establish and had higher fructosamine concentrations, higher albumin concentrations and decreased pepsinogen responses. Therefore, a combination of relatively resistant sheep and nutritional supplementation appears most efficient at controlling infection.     

Some observations on the use of the morantel sustained‐release bolus in first season‐grazing calves on a Belgian dairy cattle farm

Summary

The efficacy of the morantel sustained‐release bolus (MSRB) in controlling gastrointestinal parasites in first‐season grazing calves was evaluated on a dairy cattle farm in Belgium. The calves grazed a pasture which had been used by bolus‐treated animals in the three previous years. The effect of bolus administration was determined with respect to live weight gain, faecal egg shedding, herbage larval counts, serum pepsinogen levels and ELISA antibody titres.

In spite of an incomplete reduction of faecal egg shedding during the first months of the grazing season, bolus administration resulted in the prevention of parasitic gastro‐enteritis in the calves. A weight gain advantage of 35,2 kg of the bolus‐treated animals over the controls was noted already at two months after turnout. This weight gain advantage was maintained until housing.

The usefulness of serum pepsinogen values and ELISA antibody titres as parameters in prevention experiments is stressed. Both serological parameters gave more information concerning infection level than did the faecal egg output and the herbage larval counts.     

Local antibody responses in the bile and faeces of sheep infected with Fasciola hepatica

The effect of infection with the liver fluke Fasciola hepatica on serum, bile and faecal immunoglobulin and antibody levels was studied in Scottish Blackface sheep. In the serum the immunoglobulins showing the most marked increase were IgG1 and IgG2 and their maximal values were reached at 16 weeks after infection. In the bile IgG2 rose to peak values at two weeks and IgG1, IgA and IgM were maximal at four weeks after infection. The levels of faecal IgG and IgA were low after primary infection but after reinfection a rapid increase in IgA concentration was observed within one to two weeks. Haemagglutinating antibody levels against egg antigens, juvenile and adult excretory-secretory antigens and adult fluke somatic antigens were evaluated. In the sera high titres were observed starting from two to four weeks after infection and persisting until 14 to 16 weeks. Bile haemagglutinating antibodies against excretory-secretory antigens showed the highest level at two and four weeks after infection while antibodies against adult somatic antigens reached maximal titres between four and eight weeks. Faecal antibody levels after primary infection were low but increased rapidly within two weeks after reinfection, coinciding with the elevation in faecal IgA concentration. However, there was no reduction in the number of flukes established in reinfected animals.     

Vaccination against Haemonchus contortus: performance of native parasite gut membrane glycoproteins in Merino lambs grazing contaminated pasture

In a replicated trial, parasitological and antibody responses of grazing weaner Merino sheep were assessed following vaccination with gut membrane proteins prepared from adult worms of the gastrointestinal nematode, Haemonchus contortus. Each vaccinated animal received 100 microg native H11 and 100 microg native H-gal-GP combined together in 5mg Quil A administered intramuscularly on days 0, 34, 80 and 127. Control animals received 5mg Quil A alone on the same days. Vaccinated and unvaccinated control animals grazed pastures contaminated with the parasite from day 34 of the trial, and levels of parasitism were monitored by worm-egg counts (WECs) in faeces and packed cell volumes (PCVs) in blood. The level of larval contamination on pasture was estimated from the worm counts of tracer sheep introduced monthly to the paddocks. WECs and anaemia were significantly reduced in vaccinated animals, and, in contrast to vaccinates, all control sheep required salvage treatment with anthelmintic. By the last 2 months of the trial, pastures grazed by vaccinated animals had significantly lower contamination with H. contortus larvae. Vaccinated animals had high levels of vaccine antigen-specific IgG1 and IgG2 antibodies in plasma, whereas those responses in the control sheep were very low. IgG1 titres in the vaccinated group, but not IgG2 titres, were inversely correlated with worm-egg counts. The levels of systemic IgA and IgE remained low but increased in both groups towards the end of the experiment most probably from exposure to the natural infection from pasture. The results showed that H11 and H-gal-GP behaved like "hidden" antigens producing high levels of protection that were probably mediated through mechanisms involving antibodies, and in particular, IgG1. It was concluded that if similar protective effects could be obtained with recombinant versions of the proteins present in either H11 or H-gal-GP, then the prospects for a commercial Haemonchus vaccine were real.     

Protection studies with a globin-enriched protein fraction of Ostertagia ostertagi

The protective capacity of an adult stage Ostertagia ostertagi globin antigen was tested in four vaccination experiments in cattle. In a preliminary experiment, calves were vaccinated three times intraperitoneally with 250 microg globin in Freund's adjuvant and challenged with a trickled infection of 25,000 infective larvae. In three subsequent field studies, calves were vaccinated twice or three times intramuscularly with 80-100 microg globin in Quil A and challenged with a natural gastrointestinal nematode infection on pasture. Higher globin-specific antibody levels were detected in the vaccinated calves than in the control animals in all vaccine trials. In the preliminary experiment, geometric mean cumulative egg counts in the globin group were reduced by 52% and total worm burdens were reduced by 28%, compared to the controls. In the first field trial cumulative faecal egg counts were reduced by 63% in the vaccinated calves. However, the reduction in faecal egg output in these two experiments was not statistically significant and no reduction in faecal egg counts was observed in the vaccinated animals in the two last field trials. In conclusion, vaccination of calves with O. ostertagi globin resulted in highly variable protection levels after challenge infection.     

Pre-exposure of cattle to drug-abbreviated Fasciola hepatica infections: the effect upon subsequent challenge infection and the early immune response

In this study we examined whether juvenile liver flukes are capable of stimulating protective immune responses in cattle. Four experimental groups of cattle were studied as follows: group A, a positive control, received a primary infection on day 0 and a secondary infection 28 days later; group B also received two infections but the primary infection was terminated by drug treatment on day 5; group C, received infections on days 0, 5 and 10 which were terminated by drug treatments on days 1, 6 and 11 and then a secondary infection on day 28; group D received an infection only on day 28. Juvenile flukes appear to induce protective responses because: (a) group B animals had significantly lower levels of gamma-GT (P<0.05) than group D; (b) both groups B and C exhibited lower parenchymal phase GLDH levels (P=0.006 and 0.041, respectively); and (c) both groups B and C had lower secondary phase eosinophilia (P=0.002 and 0.02, respectively) than those in group D. Sera taken from groups A-C contained antibodies reacting to a variety of proteins in adult fluke somatic antigen and excretory-secretory preparations, particularly to proteins of 52-60, 68-72 and 82-96 kDa. After secondary challenge the antibody responses of group A to these proteins declined while reactivity to proteins of 28-30 kDa increased. Antibody responses to the 28-30 kDa proteins were not detected in groups B-D until 3 weeks later than those observed in group A. Antibody responses to Fasciola hepatica cathepsin L proteases, which are known to induce protection, were monophasic, of the IgG1 isotype only and were not observed prior to secondary challenge in any of the four groups. In contrast, the response to another protective antigen fraction, a high molecular sized haem protein, was of a mixed IgG1/IgG2 nature and was detected within 14 days of primary infection. However, no significant difference in antibody titres to either protein preparation was observed after the secondary infection when groups B and C were compared to group D.     

Experimental infections with Cooperia oncophora in calves. A study with two different larval dose levels and dosing regimens.

The effect of different larval dose level and dosing regimens on the course of Cooperia oncophora infection in calves was studied. Four groups each of 4 calves were experimentally infected either with 50,000 or 200,000 C. oncophora larvae (L3) given either as single infections or as daily trickle infections. An additional group of calves remained as uninfected controls. The animals were necropsied on week 4 after infection. Mild to moderate clinical signs of parasitic gastroenteritis developed among calves given high doses of larvae, but liveweight gains were not significantly different from those of the uninfected controls. Serum pepsinogen levels of dosed animals were within normal ranges but rose slightly, and on day 14 p.i. they differed significantly from those of the controls. On that occasion, the levels of serum pepsinogen in the trickle infected groups significantly exhibited the levels of the single infected groups. Hypoalbuminaemia was not a feature on any occasion. The various groups did not differ significantly with regard to total worm counts and adult worm counts, but the groups receiving high larval dose harboured significantly more fourth stage larvae than the group receiving low doses of larvae, both in terms of absolute counts and in terms of percentages of total worm burdens. Within the same dose level, there was a tendency of a more even distribution of worms along the small intestine when the infections was given as a single infection compared with a trickle infection. The results indicate that C. oncophora larval dose and dosing regimens may influence the pathogenic effects and to some extent the distribution of the parasite in the small intestine.