Protection of lambs with a purified metabolite of exsheathed third-stage Haemonchus contortus larvae

Helminth-free lambs (approx 4 months old) were inoculated SC with a purified metabolite of exsheathed third-stage Haemonchus contortus larvae. The metabolite was obtained from in vitro cultivation and was identified as XL3FA1. After 3 periodic XL3FA1 inoculations, lambs were challenge exposed with H contortus. Multiple vaccinations with XL3FA1 did not inhibit the development of worm populations in the lambs; however, worm egg production seemed to be inhibited.     

The effect of age on the response of sheep to vaccination with irradiated trichostrongylus colubriformis larvae

Vaccination with irradiated Trichostrongylus colubriformis larvae produced a high level of immunity, as judged by faecal egg counts and worm burdens following challenge with normal larvae, in nine of ten sheep aged 10 months. In lambs aged 3 months, vaccination was less effective. Some lambs developed partial immunity, but others did not respond.Serum levels of antibodies to T. colubriformis acetylcholinesterase reflected the extent of antigenic exposure rather than the degree of immunity acquired, and there was no evidence that the unresponsiveness of the lambs was due to a deficiency in antibody production.Unresponsiveness was not associated with the numbers of circulating lymphocytes, monocytes or granulocytes, or with the numbers of mast cells, eosinophils and neutrophils at the site of infection. However, there were many globule leucocytes in the intestinal mucosa of adult sheep which were resistant to challenge infection. On the other hand, few of these cells were found in vaccinated lambs which generally gave a poor response to challenge.     

Trichostrongylus colubriformis and Haemonchus contortus infections in light bodyweight Merino lambs

OBJECTIVE; To show that low bodyweight is a predisposing cause of high Trichostrongylus colubriformis and Haemonchus contortus burdens and egg counts in Merino lambs. DESIGN: A comparison was made, among lambs of different bodyweights, on the effect on immunity of a primary or secondary viable infection with T colubriformis or H contortus larvae. PROCEDURE: Sixty-one Merino lambs, 1 or 6 months of age, were penned indoors and given primary, or both primary and secondary, infection of T colubriformis or H contortus. Faecal egg counts, worm counts and parasite-specific immunoglobulin concentrations were examined for their relationships with bodyweight. RESULTS: Bodyweight at the start of a primary infection was correlated with worm burden, worm fecundity and jejunal IgA antibody concentration. Merino lambs weighing less than 23 kg at the time of first exposure to T colubriformis or H contortus had impaired ability to develop protective mucosal immunity and to resist homologous challenge. CONCLUSION: If the goal is to ensure that lambs develop immunity before weaning, then every endeavour should be made to achieve the combination of critical bodyweight and exposure to moderate levels of nematode infection as soon as possible.     

Onset and duration of fecal shedding,cell-mediated and humoral immune responses in pigs after challenge with a pathogenic isolate or attenuated vaccine strain of Lawsonia intracellularis

Little is known about the humoral and, especially, cell-mediated immune response in pigs exposed to Lawsonia intracellularis. The objectives of this study were to investigate the onset and duration of fecal shedding, cell-mediated and humoral immune responses in pigs after challenge with a pathogenic isolate or a commercial live vaccine strain of L. intracellularis. Twenty-four 5-week-old pigs were exposed to 4.4x10(9) organisms of a pathogenic L. intracellularis isolate PHE/MN1-00 (10 pigs), a L. intracellularis live attenuated vaccine strain (10 pigs) or sham inoculum (4 pigs). Fecal, serum and whole blood samples were collected from all animals before exposure and weekly up to 13 weeks post inoculation and tested by PCR, immunoperoxidase monolayer assay serology and an interferon-gamma assay, respectively. One animal from each group was euthanized on day 22 post exposure to confirm infection. Humoral and cell-mediated immune responses were initially detected 2 weeks after exposure in pigs challenged with the pathogenic isolate, and 5 and 4 weeks, respectively, in pigs exposed to the modified-live vaccine group. Humoral and cell-mediated immune responses were still detected in some pigs from both L. intracellularis exposed groups 13 weeks after exposure. Fecal shedding was initially detected 1 week and lasted, intermittently, 12 weeks post exposure in pigs challenged with the pathogenic isolate, while fecal shedding was first detected 2 weeks and lasted, also intermittently, 9 weeks after exposure to the vaccine. In summary, both pathogenic isolate challenged and vaccine exposed pigs demonstrated long-term shedding of and immune responses to L. intracellularis.     

Periparturient rise in faecal nematode egg counts in west African dwarf sheep in southern Ghana in the absence of arrested strongyle larvae

The nematode egg output of two groups of ewes, a pregnant test group (2-3 years of age) mated between March and April and a non-pregnant control group (5-6 years of age) was followed. The worm burdens acquired by worm-free 'tracer' lambs were also followed on the same pasture from March 1988 to February 1989. There was a significant difference (P less than 0.05) in the magnitude of the egg output in the test group compared with the control group. In the test ewes, an initial rise in egg production occurred 2 weeks after lambing and was maintained for five consecutive months. Necropsy worm counts from the 'tracer' lambs revealed that pasture larval levels were directly related to the levels of rainfall. Adult nematodes (Trichostrongylus colubriformis, Trichostrongylus axei, Haemonchus contortus, Oesophagostomum venulosum and Trichuris ovis), and some Moniezia expansa were present in almost all the lambs throughout the year, with the exception of January and February 1989. The absence of immature larvae in these lambs indicates that arrested development is not a feature of the life cycle of these species in Southern Ghana. The occurrence of a periparturient rise of nematode eggs in West African Dwarf ewes, a year-round breeder, means that susceptible lambs could be open to infection throughout the year. Control should, therefore, be conducted by treating ewes after lambing and restricting the breeding season to particular periods of the year.     

Partial protection of lambs against Haemonchus contortus by vaccination with a fractionated preparation of the parasite

Florida Native lambs, less than 6 months of age, were successfully vaccinated against Haemonchus contortus with a high mol. wt fraction (greater than 30,000 daltons) derived from a somatic extract of H. contortus larvae (SEL) and excretions and secretions (ES) of larvae isolated during in vitro development from the infective 3rd to 4th stage. A 59% reduction in adult worm numbers was obtained in vaccinates compared to naive lambs following challenge. The protection in vaccinated lambs was similar to that seen in lambs exposed to a primary infection of H. contortus larvae which had been cleared with anthelmintic prior to the challenge infection. The unfractionated SEL/ES preparation and a low mol. wt fraction gave no significant protection against challenge infection.     

Influence of dietary protein on the immune responsiveness of sheep to Haemonchus contortus

Twenty helminth-free lambs were fed diets containing either 169 g crude protein (CP) kg-1 dry matter (DM) or 88 g CP kg-1 DM from the age of seven months. One month later five lambs from each dietary group were vaccinated against Haemonchus contortus by the oral administration of 10,000 irradiated larvae on two occasions, four weeks apart. Four weeks following the administration of the second dose of irradiated larvae both the vaccinated and unvaccinated lambs were exposed to an experimental infection of 10,000 non-irradiated H contortus larvae Faecal egg output and haematological changes were monitored throughout the study. The lambs were slaughtered 28 days after challenge when worm burdens were assessed. Vaccination was equally successful in inducing a strong resistance to the challenge infection regardless of dietary status. It was concluded that dietary protein does not influence the response to vaccination with irradiated H contortus larvae of lambs more than seven months old.     

Characterization of the protective response against a homologous challenge infection with Strongyloides venezuelensis in rats

The protective response in rats against a homologous challenge infection with Strongyloides venezuelensis was characterized. In an initial infection with 1000 filariform larvae and migrating larvae (L(3)) of S. venezuelensis, the population of L(3) in the lungs on day 3 postinfection (PI), and that of adult worms in the small intestine on day 7 PI, were 180.8+/-14.5 and 336.8+/-70.7, respectively. The latter were gradually expelled towards day 42 PI. After the initial infection, the rats developed strong immunity against a homologous challenge infection as manifested by a marked reduction in worm populations, stunted body length and width, damage to reproductive organs, impaired egg production and rapid expulsion of the worms by day 14 after challenge. Expulsion of the worms was preceded by a significantly elevated (P<0.05) peripheral blood eosinophil (PBE) count, both in the initial (200.0+/-26.5 x 10(3)ml) and the challenge infection (400.9+/-165.4 x 10(3)ml). These findings suggest that rats acquire strong homologous immunity following initial exposure to S. venezuelensis. It is suggested that PBEs are involved in worm expulsion. A major target of these effector mechanisms is the reproductive system of S. venezuelensis.     

Enhancement of resistance of lambs to Haemonchus contortus by previous infection with Ostertagia circumcincta

Two experiments were performed to determine whether previous infection of young lambs with Ostertagia circumcincta increased their resistance to the development of Haemonchus contortus and to explore alterations in the microenvironment of the abomasum related to the interaction. The parasitic infections were monitored with periodic fecal egg counts and by recovery and enumeration of parasites at necropsy of the lambs. Alteration of the microenvironment was examined by measurement of serum gastrin concentrations at critical times during both experiments. The results indicated that the numbers of H contortus were significantly (P less than 0.05) less in lambs which had O circumcincta infections before their exposure to H contortus. There was less reduction in lambs from which O circumcincta was removed (anthelmintic therapy) before their exposure to H contortus. Fecal egg counts also were significantly (P less than 0.05) less in the former group of lambs (exposed to both parasites) than those in lambs exposed only to H contortus. Serum gastrin values were significantly (P less than 0.05) increased in lambs infected with O circumcincta and indicated that the interaction observed could be due, in part, to alteration of abomasal pH.     

Effects of molybdenum intake on primary infection and subsequent challenge by the nematode parasite Trichostrongylus colubriformis in weaned Merino lambs.

In a study designed to test the effect of molybdenum (Mo) on resistance to trichostrongylosis, the Mo content of the diet during primary infection of 8-month-old Merino lambs with Trichostrongylus colubriformis was found to affect the number of worm eggs found in the faeces during challenge and the total number of worms in the jejunum after six weeks of challenge infection. The optimal intake of Mo in this experiment was in the range of 4-8 mg sheep(-1)day(-1), approximately equivalent to feeding a diet containing 6-10 mg Mo kg(-1)dry matter (DM) and to 0.15-0.30 mg Mo kg(-1)liveweight. Lambs fed Mo at this rate showed a 90 per cent reduction in faecal egg count and total worm count six weeks after challenge compared with lambs fed quantities of Mo outside this range. The mechanism by which Mo exerted these effects was not defined, although the interactions of molybdenum, worm establishment and faecal egg count suggested that this trace element may be acting via an effect on the host's acquired immune response. This hypothesis is supported by the observed enhancement of immune responses (intestinal antibody and granulocyte numbers and in vitro worm-specific proliferation of lymphocytes) associated with Mo intake of 0.15-0.3 mg kg(-1)Lwt.     

Development of a protective immunity against Ostertagia leptospicularis in trickle-infected sheep and parallel changes of serum gastrin, pepsinogen and antibody levels

Nine lambs, approximately 9 months of age were allocated to three groups (A, B, C), with three animals in each. Sheep in Groups A and B were trickle-infected with doses of 1000 third-stage larvae (L3) of Ostertagia leptospicularis (five times per week) over periods of 7.5 and 10.5 weeks, respectively, and were subsequently treated with fenbendazole (7.5 mg/kg). Approximately 3 weeks after anthelmintic treatment, all sheep were challenged with a single dose of 100,000 L3, whereas sheep of Group C received the same dose as a primary infection. Sheep of Groups A and B were almost completely refractory against the challenge infection, as indicated by negative faecal egg counts and adult worm burdens. A relatively high infection level was present in the sheep of Group C. The results indicate that a comparatively short immunization period of 7.5 weeks is sufficient to protect lambs against subsequent larval challenge. During immunization, the pepsinogen-, gastrin- and IgA-responses were similar in the individual sheep. In contrast to parasite-specific IgG1 and IgG2 levels, IgA decreased rapidly after cessation of trickle infection and parallel anthelmintic treatment, and may therefore indicate current exposure to parasite antigen. After challenge, the majority of the immunized sheep exhibited immediate and short-term responses of pepsinogen, gastrin and IgA in the serum. The time course and the level of each of these responses were very similar in the individual sheep, suggesting that the release of pepsinogen, gastrin and IgA into the circulation was influenced by related mechanisms.     

Effectiveness of copper oxide wire particles for Haemonchus contortus control in sheep

OBJECTIVE: To assess the efficacy of copper oxide wire particles (COWP) for the control of H contortus infections in grazing sheep. PROCEDURE: In experiment 1, 40 worm-free Merino hoggets (11 to 12 months of age) were divided into four equal groups and allocated to separate 0.8 ha pasture plots. Two groups then received 2.5 g COWP whereas the other two groups were untreated. From 1 week after COWP treatment all lambs received a weekly infection of 2000 H contortus larvae. At week 8, six sheep from the untreated group were then allocated to two groups and treated with either 2.5 or 5.0 g of COWP to establish therapeutic efficacy of treatment. Experiment 2 followed a similar protocol but was conducted with 40 worm-free Merino lambs (3 to 4 months of age) and no assessment of therapeutic efficacy was made. Results: In experiment 1 no significant difference in faecal worm egg counts was observed between treatments and faecal worm egg counts remained less than 3000 epg in all animals. Total worm counts were reduced by 37% by COWP treatment (P = 0.055). Both 2.5 g and 5.0 g doses of COWP at 8 weeks of infection reduced faecal worm egg counts by > 85% with the higher dose giving an earlier response to treatment. In experiment 2, faecal worm egg counts at 4 and 6 weeks were reduced by more than 90% in the COWP treated lambs and worm numbers were 54% lower after 6 weeks when all remaining untreated lambs had to be treated for haemonchosis. Mean faecal worm egg counts in the COWP lambs remained below 3500 epg and clinical disease did not develop in the majority of lambs before the end of the experiment at 10 weeks. CONCLUSION: Treatment with COWPs appears to have the potential to reduce establishment and worm fecundity of Haemonchus spp for an extended period and may offer livestock producers a supplementary means of reducing larval contamination of pasture particularly in areas where anthelmintic resistance is a problem and copper supplementation is likely to be beneficial.     

Haemonchus contortus (Nematoda: Trichostrongylidae) infection in lambs elicits an unequivocal Th2 immune response

Selection of resistant animals and host immunization have been proposed as alternative methods for the control of gastrointestinal nematode parasites. However, a better knowledge of the mechanisms involved in protective immunity against these parasites is required for the development of optimal strategies. In this study, 3 month old INRA 401 lambs (n = 81) were allocated into three groups: uninfected control, challenged either once (primary-infected animals) or twice (previously-infected animals) with 10,000 Haemonchus contortus L3. Uninfected control and challenged animals were sequentially sacrificed at 3, 7, 15 and 28 days post challenge. In both challenged groups, a clear Th2-oriented immune response was observed in the abomasal lymph node and mucosa. IL-4 and IL-13 mRNA over-expression, recruitment of eosinophils, mast cells and globule leukocytes and production of specific systemic IgG and mucosal IgA were observed earlier in previously-infected animals than in primary-infected ones. At 28 days post infection, no differences between intensities of these responses were observed between the challenged groups. Worm establishment rates were similar in previously-infected and primary-infected lambs. However, reductions of worm development, female fecundity and fecal egg output were observed in previously-infected sheep. We conclude that H. contortus infection in young INRA 401 lambs induced an unequivocal Th2 immune response resulting in the regulation of worm egg production without affecting their establishment.     

Observations on the egg output resulting from continuous low level infections with Ostertagia circumcincta in lambs

Faecal egg counts were determined twice weekly for two groups of four-month-old worm free cross Suffolk lambs experimentally infected with 100 and 320 Ostertagia circumcincta larvae, five times per week for 20 weeks. The group mean egg count in both groups rose to a maximum of approximately 500 eggs per gram during weeks 12 to 14 and had fallen to less than half of that value at slaughter. There was no statistical difference in egg output between these two groups or between them and a comparable group of lambs receiving 4000 Ostertagia circumcincta larvae per day. No significant changes in live weight gain or serum pepsinogen levels were observed in the lambs given 100 and 320 larvae per day.     

Moxidectin: persistence and efficacy against drug-resistant Ostertagia circumcincta

In order to determine whether the efficacy of moxidectin against Ostertagia circumcincta is enhanced by its persistency, therapeutic efficacy was compared at intervals after treatment and with that of ivermectin, a closely related but more transient endectocide. Groups of 7-month-old New Zealand Romney lambs were infected with a strain of O. circumcincta known to be resistant to moxidectin. At patency of the infections, groups of lambs were treated with either moxidectin or ivermectin at the manufacturer's recommended dosages, or left untreated. At 3, 6 and 10 days post-treatment, faecal egg count was measured and groups of lambs were slaughtered for estimation of adult worm burden. Drug-resistant worm burdens were significantly reduced in those animals treated with moxidectin but not in those treated with ivermectin. No effect of time of slaughter on worm burden was observed with either drug, demonstrating that the higher therapeutic efficacy of moxidectin against this parasite was not due to an increased period of drug exposure. Faecal egg counts in the moxidectin treated animals increased with time after treatment indicating a temporary suppression of egg output by surviving worms. The implications of these findings on selection for anthelmintic resistance are discussed.     

Anthelmintic effects of Salix babylonica L. and Leucaena leucocephala Lam. extracts in growing lambs

Twenty Katahdin?×?Pelibuey crossbreed male lambs, 3 to 4 months of age and 24?±?0.3 kg of body weight, were used to study the anthelmintic effects of administering extracts of Salix babylonica L. (SB) and Leucaena leucocephala Lam. (LL). Lambs had not been treated with anthelmintics previously and were randomly allocated into four groups of five lambs each in a completely randomized design. Treatments were as follows: control (lambs fed on total mixed ration without extracts), SB (as control plus S. babylonica L. extract at 30 ml/day), LL (as control plus L. leucocephala Lam. extract at 30 ml/day), and SBLL (as control plus 30 ml/day of S. babylonica L. and L. leucocephala Lam. extracts in a 1:1 (v/v) mixture) for 63 days. Extracts were orally administered before the 8:00 a.m. feeding to each lamb. Rectal fecal samples were collected from each lamb at day 22 (P1), day 43 (P2), and day 63 (P3) of the experiment. Adult worm and egg counts were determined in each fecal sample immediately after collection. Plant secondary metabolites of total phenolics, saponins, and the aqueous fraction were 50 % lower in the SB versus LL extracts. Overall, the oral administration of extracts has improved the egg and worm count reductions in lamb feces by 54, 47, and 40 % for LL, SB, and SBLL, respectively, versus the control lambs. Reductions of worm egg counts in lamb feces were higher (P?<?0.05) in P2 and P3 versus P1. Extracts of SB and LL or possibly isolated bioactive compounds could be a promising alternative to conventional anthelmintics to treat gastrointestinal parasites of small ruminants. Such treatments could be used in control strategies against gastrointestinal nematodes in organic and conventional production systems.     

Population dynamics of Trichostrongylus colubriformis in sheep following anthelmintic treatment

Three groups of five, three-and-a-half to four-month-old lambs were put to graze on three plots contaminated by Trichostrongylus colubriformis. One group (control) was free of parasites, while the other two were infected just before turning out with 3 X 700 third stage larvae. Depending on whether or not the lambs were treated with 50 mg kg-1 thiabendazole nine days after the first infection, the worm burden and the egg output increased or decreased during the grazing period when compared with the control group. In tracer animals put to graze on the same plots afterwards, it was found that the smaller the number of eggs excreted by the first lambs, the higher were the worm burdens of the tracer lambs.     

Comparison of the resistance to sympatric and allopatric isolates of Haemonchus contortus of Black Belly sheep in Guadeloupe (FWI) and of INRA 401 sheep in France

The resistance of a tropical breed of sheep towards the nematode parasite Haemonchus contortus (Hc) was compared to that of a European breed after artificial infection with the parasite following a 2 x 2 x 2 experimental design: two isolates (Hc Gua from Guadeloupe versus Hc Fra from France), two breeds each reared in their native habitats (Black Belly (BB) in Guadeloupe, FWI, INRA 401 reared in France), and two groups of lambs with differing infection status (one naive, i.e. infected for the first time during the experiment, and one primed, i.e. which had previously received doses of 5000 L3 on Days -35 and -32 before the infection during this experiment). Both groups were composed of 10 male lambs, which were 20 weeks of age when they were given a dose of 10,000 L3 of the relevant isolate on Day 0. Resistance was assessed by regular fecal egg counts (FECs) and blood samples, and worm counts were processed on Day 35 p.i. The FEC was lower in the BB than in INRA 401 lambs, lower in the primed than naive groups, and lower in Hc Fra than in Hc Gua. The eosinophil count remained unchanged in the naive INRA 401 groups, but increased in all the other groups. The hematocrit fell after infection, but the live weight was not affected by the infection. Worm burdens were 1868 and 5237 in the naive BB and INRA 401 groups, respectively, and 596 and 4835 in the primed BB and INRA 401 groups. The daily production of eggs per Hc Gua female worm was 1.5-fold that of Hc Fra. The number of worms had no effect on worm length or Hc in utero egg count in the BB sheep, but a positive and significant correlation between these two traits was seen in the INRA 401 lambs. These findings are indicative of innate resistance, and confirmed the high acquired resistance of the BB sheep to both sympatric and allopatric isolates of Hc. The regulation of worm population and fecundity differed in the BB and INRA 401 sheep.     

The impact of daily Duddingtonia flagrans application to lactating ewes on gastrointestinal nematodes infections in their lambs in the Netherlands

Two experiments were performed in 2002 and 2003 to evaluate the effect of biological control of gastrointestinal nematodes in sheep through the daily feeding of 500,000 chlamydospores of Duddingtonia flagrans/kg bodyweight to lactating ewes during the first 9 weeks with their young lambs on pasture. In both experiments four groups of eight ewes and their April-borne lambs were used. They were turned out on four separate plots (plots A) at the beginning of May, moved to similar separate plots after 3 (plots B) and 6 weeks (plots C), respectively, and weaning occurred after 9 weeks. In both experiments, two groups were fed spores daily while the two other groups served as controls. The effect of D. flagrans application was evaluated through faecal egg counts of ewes and lambs, the yield of faecal cultures in ewes, pasture larval counts and worm counts of lambs and tracer lambs. The results demonstrated no effect of D. flagrans application during the first 5 (2002) or 4 (2003) weeks. Subsequently, fungus application strongly reduced the yield in faecal cultures of the ewes. This was, however, not reflected in the pasture larval counts, but lower worm burdens were observed in tracer lambs of 'treated' plots C in 2002 than on those of 'control' plots. In 2003 worm burdens in 'treated' lambs returned to plots B were lower than those of 'control' lambs and a tendency for the same was observed for plots C. However, in all groups, lambs and tracer lambs developed severe haemonchosis.     

Further attempts to immunise lambs using metabolites and in vitro grown larvae of Ostertagia circumcincta

Attempts were made to immunise lambs by the intramuscular injection of either lyophilised or concentrated metabolites produced by Ostertagia circumcincta when grown in vitro, or macerated fourth and fifth stage worms. The lyophilised metabolites did not stimulate protection against the establishment of worms in nine-months-old lambs but the macerated worms and concentrated metabolites elicited protection in six-months-old and three-months-old lambs respectively. The worm burdens and worm egg counts of the immunised lambs were less than those of control lambs.