五种旋毛虫抗原对猪的免疫保护作用研究

本实验研究了旋毛虫肌幼虫可溶性粗抗原、排泄分泌抗原（ＥＳ）、表面抗原（ＳＡ）及成虫ＥＳ、ＳＡ５种抗原对猪的免疫保护作用。结果５种抗原对猪均具有一定程度的免疫原性，可诱导猪体产生对攻击感染的抵抗力（减虫率），其中肌幼虫粗抗原为５５．２０％；肌幼虫ＥＳ为４２．５６％，肌幼虫ＳＡ为７２．２１％；成虫ＥＳ为３２．９２％；成虫ＳＡ为４２．１７％。免疫５种抗原后用肌幼虫“Ｂ”抗原、新生幼虫可溶性抗原及成虫可溶性抗原进行ＥＬＩＳＡ检测，均可测出血清抗体应答反应，其中以相应抗原测出的抗体应答较强烈。免疫５种抗原后猪外周血液中Ｂ淋巴细胞减少，Ｔｈ及Ｔｓ增加，Ｔｈ／Ｔｓ比值降低，呈暂时的细胞免疫抑制现象。     

Immunity in swine inoculated with larvae or extracts of a pig isolate and a sylvatic isolate of Trichinella spiralis

Inoculation of swine with a sylvatic isolate of Trichinella spiralis, designated T s nativa, resulted in low numbers of muscle larvae, compared with muscle larvae accumulation in swine inoculated with a pig type of T s spiralis. Despite low infectivity of T s nativa for swine, primary inoculation resulted in high levels of immunity against challenge infection with T s spiralis. This immunity was expressed in accelerated expulsion of challenge adults from the intestine and reduced numbers of muscle larvae. Pigs inoculated with T s nativa developed cellular and humoral responses similar to those in pigs inoculated with T s spiralis. However, in immunoblots, sera from pigs inoculated with T s nativa recognized additional proteins in muscle larvae excretory-secretory (ES) products, compared with sera from pigs inoculated with T s spiralis. Active immunization of pigs with ES products from T s nativa resulted in numerically higher, but not significantly different levels of immunity, compared with pigs immunized with ES from T s spiralis. The highest levels of immunity were obtained in pigs immunized with a T s spiralis newborn larval extract. The combination of ES products and newborn larval extract did not result in additive levels of immunity. These results indicate that the major immune effector response to Trichinella sp in pigs is against the newborn larvae, regardless of the genetic type of Trichinella sp.     

Development of immune responsiveness to Ascarissuum antigens in pigs vaccinated with ultraviolet-attenuated eggs

Pigs fed $\text{Ascaris}$$\text{suum}$ eggs attenuated by short wave ultraviolet-radiation developed resistance to challenge infection. Per os inoculation of pigs on three successive weeks with 10,000 eggs irradiated to total exposures of 150,100 and 75 μW-min/cm², respectively, resulted in an 88% reduction in the number of larvae recovered from the lungs 7 days after challenge with 10,000 infective eggs. Peripheral blood lymphocytes (PBL) from vaccinated pigs were specifically stimulated in vitro to incorporate tritiated thymidine by egg hatching fluid (Ea) and by excretory-secretory products obtained from cultures in defined-media of second-stage larvae (L2) developing to third-stage (L2–3) and from cultures of third-stage larvae developing to fourth-stage (L3–4). PBL were also specifically stimulated by living L2. Ea and L2 stimulated pig PBL significantly at 7 days after the first inoculation; responses to L2–3 and L3–4 developed 7 days after a second inoculation. The antigen-responsive cells in the PBL population were non-immunoglobulin-bearing lymphocytes. Antibodies to Ea and L2–3 were not detected in the serum of vaccinated pigs, and only 3 of 7 pigs had low concentrations of serum antibodies to L3–4.     

Peripheral blood mononuclear cell subsets during Trichinella spiralis infection in pigs

The immune response of 'Yugoslav meat breed' pigs inoculated with low doses of Trichinella spiralis muscle larvae was followed over two to nine weeks of primary infection, by analysing changes in peripheral blood mononuclear cell subsets, the development of a humoral antibody response and muscle larvae burden. During the course of the infection, infected animals showed a persistent elevation of both CD4+ and CD8+ T cell subsets from days 15 to 60 after the parasite exposure. During this time, the number of peripheral blood mononuclear cells expressing major histocompatibility complex class II antigens was also increased, while no significant differences were found in the number of circulating monocytes/macrophages and B cells over time. Humoral antibody responses to muscle larvae excretory-secretory products were evident as early as 41 days after infection, while the muscle larvae were recovered as early as 27 days after infection. The increased levels of CD4+ and CD8+ T cell subsets, as well as cells expressing major histocompatibility complex class II antigens in pigs exposed to T spiralis, may be indicative of some considerable alterations in cell subsets that are involved in the regulation of the swine immune response to this parasite.     

Impeded establishment of the infective stage of Trichinella in the intestinal mucosa of mice by passive transfer of an IgA monoclonal antibody

Our previous study showed that the IgA monoclonal antibody (mAb) HUSM-Tb1 forms immunoprecipitates on the cuticular surface of infective larvae of Trichinella britovi, and that intraperitoneal injection of this mAb to mice 5 hr before challenge infection confers a high level of protection against intestinal T. britovi. The same treatment produced a similar effect in BALB/c mice inoculated orally with Trichinella pseudospiralis larvae, indicating that the effects may be seen upon most members of the genus Trichinella. Worms recovered from the intestinal mucosa at 1 hr after challenge infection with T. pseudospiralis was few in mice passively immunized with the mAb, whereas a substantial number of worms were recovered from the mucosa of control groups. These results suggest that the IgA mAb impedes establishment of infective Trichinella worms in the intestinal mucosa. Trichinella worms inoculated orally into BALB/c mice vaccinated with ultraviolet-irradiated muscle larvae 3 weeks earlier were expelled between days 4 and 7 after challenge infection. Although the mAb HUSM-Tb1 originated from the mesenteric lymph node cells of mice vaccinated repeatedly with such irradiated larvae, IgA-mediated expulsion does not seem to play an important role in this vaccination model.     

Immune responses in swine given lipid-conjugated pseudorabies viral antigens.

The immune response was compared in pigs given inactivated pseudorabies virus (PRV) antigens (with or without adjuvant) or PRV antigens covalently conjugated with a fatty acid (lauric acid) to enhance delayed-type hypersensitivity. The pigs were given 2 inoculations, 14 days apart, and were challenge exposed 28 days after the 1st inoculation. Pibs inoculated with PRV antigens, with or without adjuvant, had significant virus-neutralizing (VN) antibodies before challenge exposure, but the pigs inoculated with lipid-conjugated PRV antigens had no detectable VN antibodies, with the exception of 1 pig. All inoculated pigs were positive by the microimmunodiffusion test at postinoculation day 14 and remained positive throughout the experiment. The inoculated pigs had delayed-type hypersensitivity reactions when skin tested a postinoculation day 25; the pigs inoculated with lipid-conjugated PRV antigens had a more pronounced reaction. Inoculated pigs had mild respiratory signs on the 3rd through the 6th days after challange exposure, with no observable difference in severity between the inoculated groups. The control pigs had acute signs of PRV, and 3 or 4 pigs died 5 to 8 days after challenge exposure. The average VN titers of the different inoculated groups of pigs were nearly equal 2 weeks after challenge exposure. Results indicated that both humoral antibodies and cell-mediated immunity have a role in PRV infections in swine.     

Immunodiagnosis of experimental Parelaphostrongylus tenuis infection in elk

Elk infected with the meningeal worm, Parelaphostrongylus tenuis (Protostrongylidae), do not consistently excrete larvae in feces, making the current method of diagnosing live animals using the Baermann fecal technique unreliable. Serological diagnosis could prove more useful in diagnosing field-infected animals but depends on the identification and availability of good quality antigen. To mimic field infections, 2 elk were inoculated with 6 infective L3 larvae of P. tenuis, and another 2 with 20 L3 larvae. Fecal samples were examined for nematode larvae using the Baermann technique and serum samples taken were tested for anti-P. tenuis antibody with ELISAs by using the excretory-secretory (ES) products of L3, and sonicated adult worms as antigens. One animal passed first-stage larvae in its feces 202 days postinoculation, but passed none thereafter. The remaining 3 inoculated animals did not pass larvae. In contrast to parasite detection, antibodies against larval ES products were detected in all animals starting from 14 to 28 days postinoculation and persisted until the termination of the experiment on day 243 in 2 animals that harbored adult worms. Antibodies against somatic antigens of the adult worm were not detected until day 56 but also persisted until the end of the experiment in the animals with adult worms. In 2 elk that had no adult worms at necropsy, anti-ES antibodies were detected transiently in both, while anti-adult worm antibodies were present transiently in one. These findings confirm the superiority of P. tenuis larval ES products over somatic adult worm antigens as serodiagnostic antigens, as previously observed in studies of infected white-tailed deer, and extend the application of the newly developed ELISA test in diagnosing and monitoring cervids experimentally infected with P. tenuis.     

Concurrent Ascaris suum and Oesophagostomum dentatum infections in pigs.

The aim of this study was to examine interactions between Ascaris suum and Oesophagostomum dentatum infections in pigs with regard to population dynamics of the worms such as recovery, location and length; and host reactions such as weight gain, pathological changes in the liver and immune response. Seventy-two helminth-na?ve pigs were allocated into four groups. Group A was inoculated twice weekly with 10000 O. dentatum larvae for 8 weeks and subsequently challenge-infected with 1000 A. suum eggs, while Group B was infected with only 1000 A. suum eggs; Group C was inoculated twice weekly with 500 A. suum eggs for 8 weeks and subsequently challenge-infected with 5000 O. dentatum larvae, whereas Group D was given only 5000 O. dentatum larvae. All trickle infections continued until slaughter. Twelve pigs from Group A and B were slaughtered 10 days post challenge infection (p.c.i.) and the remaining 12 pigs from the each of the four groups were slaughtered 28 days p.c.i.. No clinical signs of parasitism were observed. The total worm burdens and the distributions of the challenge infection species were not influenced by previous primary trickle-infections with the heterologous species. Until day 10 p.c.i. the ELISA response between A. suum antigen and sera from the O. dentatum trickle infected pigs (Group A) pigs were significantly higher compared to the uninfected Group B. This was correlated with a significantly higher number of white spots on the liver surface both on Day 10 and 28 p.c.i. in Group A compared to Group B. The mean length of the adult O. dentatum worms was significantly reduced in the A. suum trickle infected group compared to the control group. These results indicate low level of interaction between the two parasite species investigated.     

Improved protection from velogenic Newcastle disease virus challenge following multiple immunizations with plasmid DNA encoding for F and HN genes

Specific-pathogen free (SPF) chickens were inoculated with the plasmid constructs encoding the fusion (F) and haemagglutinin-neuraminidase (HN) glycoproteins of Newcastle disease virus (NDV), either individually or in combination and challenged with velogenic NDV. The antibody level against NDV was measured using commercial enzyme linked immunosorbent assay (ELISA). In the first immunization regimen, SPF chickens inoculated twice with NDV-F or NDV-HN constructs elicited antibody responses 1 week after the second injection. However, the levels of the antibody were low and did not confer significant protection from the lethal challenge. In addition, administration of the plasmid constructs with Freund's adjuvant did not improve the level of protection. In the second immunization regimen, chickens inoculated twice with the plasmid constructs emulsified with Freund's adjuvant induced significant antibody titers after the third injection. Three out of nine (33.3%) chickens vaccinated with pEGFP-HN, five of ten (50.0%) chickens vaccinated with pEGFP-F and nine of ten (90.0%) chickens vaccinated with combined pEGFP-F and pEGFP-HN were protected from the challenge. No significant differences in the levels of protection were observed when the chickens were vaccinated with linearized pEGFP-F. The results suggested that more than two injections with both F and HN encoding plasmid DNA were required to induce higher level of antibodies for protection against velogenic NDV in chickens.     

CpG-oligodeoxynucleotides enhance porcine immunity to Toxoplasma gondii

Protection against a challenge infection with Toxoplasma gondii VEG strain oocysts was examined in pigs after vaccination with T. gondii RH strain tachyzoites with or without a porcine specific synthetic oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs. Six groups of pigs were immunized with incomplete Freund's adjuvant (IFA) and either vehicle, tachyzoites alone or in combination with three different doses of CpG ODN or with CpG ODN alone. Protection from challenge was significantly (P < 0.05) improved in pigs vaccinated using CpG ODN as an adjuvant with tachyzoites compared to all other groups. The CpG ODN tachyzoite-immunized pigs also had higher serum parasite specific IgG antibody, no clinical signs of disease, and 52% had no demonstrable tissue cysts after the challenge infection. These data indicate that CpG ODN is a potential safe and effective adjuvant for the T. gondii RH strain vaccine in pigs.     

Effects of the chitin synthesis inhibitor diflubenzuron on development of Ascaris suum and Haemonchus contortus

The potential of the chitin synthesis inhibitor diflubenzuron (DFB) to alter the development of the parasitic nematodes (Ascaris suum and Haemonchus contortus was investigated. DFB given orally (10 mg kg-1 per day for 30 days) to sheep inoculated with H. contortus infective larvae did not prevent the establishment of adults or affect fecal egg output. However, there was a significant (greater than 90%) decrease in the number of infective larvae recovered from fecal cultures derived from lambs harboring H. contortus adults that were treated with DFB. DFB did not affect egg hatching. Oral administration (10 mg kg-1 per day for 20 days) of DFB to swine harboring adult A. suum adults had no effect on the adult worm burden or on egg morphology, but eggs removed from worms obtained from DFB-treated swine contained less chitin than eggs removed from untreated control swine. DFB also inhibited chitin synthesis in vitro in the isolated reproductive tract of A. suum adults. These results indicate that DFB at high doses can inhibit the subsequent development of H. contortus larvae in the feces. Since H. contortus larvae lack chitin, DFB may act on these larvae by a mechanism independent of a direct effect on chitin synthesis.     

Specificity of the indirect enzyme-linked immunosorbent assay for detection of pseudorabies virus antibodies in pigs exposed to bovine herpesvirus-1

Six 5-week-old pigs were inoculated intranasally (IN) with 10(7.6) TCID50 of bovine herpesvirus-1 (BHV-1). Three of the pigs also were inoculated IV with a similar dose of BHV-1. Clinical responses were not observed in these 6 pigs before oronasal challenge exposure with 10(7.8) TCID50 of virulent pseudorabies virus (PRV) at postinoculation day 42. Two pigs inoculated IN with BHV-1 and challenge exposed with PRV remained healthy, whereas the remaining 4 pigs developed severe clinical signs of pseudorabies and were moribund at postinoculation day 50 (8 days after challenge exposure). Anti-BHV-1 antibodies were demonstrable by ELISA in all 6 pigs and by serum neutralization (SN) in 5 pigs before challenge exposure with PRV. Anti-PRV antibody was not detected by ELISA or SN before challenge exposure to PRV. After challenge exposure to PRV, pigs with humoral antibody to BHV-1 responded anamnestically, and anti-PRV antibody activity was demonstrable by ELISA and SN in the 2 surviving pigs.     

The response of pigs inoculated with a thymidine kinase-negative (TK-) pseudorabies virus to challenge infection with virulent virus

12 Large-White-Landrace piglets were subdivided in four groups of 3 and housed in separate units. The piglets of three groups were inoculated with the 86/27V 6C2 thymidine kinase negative (TK-) mutant of pseudorabies virus (PRV), by different routes. A second inoculation with the same mutant was given to the pigs 21 days later. The animals of a fourth group were left as uninoculated controls. 21 days following the second inoculation with the TK- mutant all pigs were challenge infected with the virulent PRV. On post challenge day (PCD) 30 all pigs were killed and samples for virus detection and histology were taken from several organs. The inoculated TK- mutant of PRV did not induce any ill effects in the pigs except a transient febrile reaction in some animals. Virus was recovered from nasal swabbings from one pig 2 days after the first inoculation of the mutant. After challenge exposure with virulent PRV, the TK- mutant-inoculated pigs were apparently protected, whereas the control pigs all were severely affected and recovered very slowly over 3 weeks. Virus was isolated from the nasal swabbings from the TK- mutant-inoculated pigs on PCDs 2 and 4, whereas the nasal swabbings from the control piglets were all positive for virus from PCD 2 through PCD 10. DNA analysis of the virus recovered showed a pattern identical to that of the virulent PRV. Histologic lesions were found in the respiratory and the central nervous systems, however, the lesions in the TK- mutant-inoculated pigs were much milder compared to those registered for the control pigs. Virus was not isolated from any of the tissue samples that were tested, but viral DNA with sequences typical of PRV genome was detected by PCR in all samples of trigeminal ganglia from either the TK- mutant-inoculated pigs or from the controls.     

Immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine in pigs

The immunogenicity and safety of an attenuated Bordetella bronchiseptica vaccine for swine atrophic rhinitis (AR) was evaluated in 22 hysterectomy-produced, colostrum-deprived pigs and 18 conventional pigs. None of 8 pigs inoculated at 7 days of age intranasally with greater than or equal to 3 X 10(5) colony-forming units (CFU) of vaccinal strain/pig and 2 of 5 pigs inoculated at 7 days of age intranasally with 3 X 10(4) CFU of the vaccinal strain/pig developed AR after intranasal challenge exposure with a virulent strain at postinoculation week (PIW) 3. The remaining 3 vaccinated pigs and 4 nonvaccinated pigs developed AR. Thirteen pigs were inoculated intranasally with 3 X 10(6) to 3 X 10(9) CFU of the vaccinal strain at 7 days of age. At PIW 12, the pigs were killed and necropsied. None of the pigs had clinical signs of AR and/or pneumonia. Virulence was studied by transmission of vaccinal strain through 3 serial growing passages on the nasal mucosa of a litter of hysterectomy-produced colostrum-deprived pigs. Inoculum (nasal swab samples from 2 pigs 4 days after inoculation with 10(8) CFU of vaccinal strain at 5 days of age) was inoculated into the nasal cavity of 2 nonvaccinated pigs. This procedure was repeated 3 times. After the 1st passage, the vaccinal strain was recovered on postinoculation day 4, but after postinoculation day 4, the vaccinal strain was not recovered until the end of the 3rd passage. Turbinate atrophy or pneumonia was not recognized in these inoculated pigs. The vaccinal strain provided immunogenicity without ill effects.     

Susceptibility of fourth-stage Ascaris suum larvae to fenbendazole and to host response in the pig

Fenbendazole given at the rate of 2.5 g/kg of feed for 3 days had 100% efficacy against 4th-stage Ascaris suum larvae in 8 pigs. Eight control pigs had a total of 108 A suum. In 6 pigs infected 3 times with 3rd-stage A suum larvae and treated with fenbendazole after the larvae molted to the 4th stage, the challenge exposure-derived population was decreased by 64%. Similar sequential infections in 6 pigs similarly infected, but not treated with fenbendazole, decreased the challenge exposure-derived population by 98%; however, developing and/or adult worms from the vaccinating infections were present.     

Evaluation of an enzyme-linked immunosorbent assay for diagnosis of trichinellosis in swine.

Experimental and field trials were conducted to evaluate an ELISA for its ability to detect Trichinella-infected domestic swine and to compare ELISA results with muscle-digestion test results. The ELISA used was a commercial double-antibody kit, containing an excretory-secretory antigen, and was evaluated principally for epidemiologic use. Experimentally induced infection in swine (4 groups of 3 pigs each; inoculated with 0, 50, 500 or 5,000 larvae) was detected as early as postinoculation week 4, with seroconversion of all inoculated swine by postinoculation week 8. The rate of seroconversion appeared to be affected by initial larval dose, time after inoculation, and immunocompetence of the individual host. Determination of antibody kinetics generally revealed rapidly increasing antibody titer, followed by its steady decrease in most pigs. Once seropositive, however, all pigs remained seropositive for the duration of the 10-week study. Presence of muscle larvae was confirmed in all infected pigs at termination of the study. We recognize that the experimental conditions may not be truly representative of those under which natural infection develops in pigs; however, the ELISA detected an infected pig with muscle larval density of 0.87 larvae/g of tissue. Results of a field trial (n = 310) indicated no muscle digestion test-positive pigs (35 g of diaphragm muscle digested/pig), but 3 samples tested positive by ELISA for specificity of 99.0%.     

A novel technique for identification of Ascaris suum cohorts in pigs

The objective of the present study was to develop a fast, cheap and reliable technique for identifying different cohorts of the swine parasite, Ascaris suum. A polymerase chain reaction linked restriction fragment length polymorphism (PCR-RFLP) technique on mt-DNA was used to identify unique haplotypes of four gravid A. suum females on agarose gels after eggs were recovered from each of the worms. Each of four pigs was inoculated with 2000 embryonated eggs originating from one of the four identified Ascaris haplotypes, respectively. Ascaris larvae were isolated from the small intestine at day 14 post-infection using an agar technique. Single larvae from each pig were transferred to 96-well PCR plates and a simple DNA extraction using a worm lysis buffer was carried out and followed by the PCR-RFLP analysis. More than 100 larvae from each of the four pigs were analysed and all were found to have the same haplotype as the parental female. We conclude that unique haplotypes of female A. suum and offspring can be identified by means of PCR-RFLP on mt-DNA and suggest that this method can be used in future research on Ascaris population biology using cohorts with distinct mt-DNA profile.     

Immunosuppression of in vivo and in vitro lymphocyte responses in swine induced by Trichinella spiralis or excretory-secretory antigens of the parasite.

The in vivo and in vitro effects of Trichinella spiralis excretory-secretory (ES) antigens on porcine peripheral blood lymphocyte (PBL) responses induced with mitogens (phytohemagglutinin, PHA; concanavalin A, Con A; pokeweed mitogen, PWM) or unrelated antigen (Protein A) were studied to determine whether ES antigens depress lymphocyte responses in experimental swine trichinosis, and/or if this response was manifested after lymphocytes from infected pigs had been pretreated with ES antigens. Additionally, the range of inhibition of lymphocyte responses was tested in parasite-free pigs using different doses of ES antigens and compared with the responsiveness of control cultures from the same animals. The responses of lymphocytes from pigs inoculated with 4 x 10(3) muscle larvae (ML) were strongly depressed (P < 0.05) at post-inoculation days (PID) 7 (after stimulation with PHA), 14, 35 (Con A or PWM), and 49 (PWM). At PID 56 and 63 the lymphocytes from T. spiralis-infected pigs responded better (P < 0.05) to all three mitogens than those from non-infected controls. After 7 weeks post-inoculation, PBL which were pretreated with 10 or 250 micrograms ml-1 of ES antigens showed significantly weaker (P < 0.05, P < 0.001) responses to PWM or PHA, respectively, than those from non-infected animals. The responsiveness of lymphocytes from both groups of pigs to Protein A was not affected by the pretreatment with ES antigens in vitro. The responses of lymphocytes from the parasite-free pigs induced by PHA, PWM or Protein A were strongly depressed (P < 0.01) after in vitro pretreatment regardless of the dose of ES antigens (5, 10, 15, or 20 micrograms ml-1) applied.     

Immunisation of lambs with excretory secretory products of Oestrus ovis third instar larvae and subsequent experimental challenge

Excretory-secretory products (ESP) of myiasis producing agents are involved in nutrition and development of larvae and are often immunogens. This study was carried out in order to define the antigenicity, the immunogenicity of Oestrus ovis ESP and the role of sheep immune response to ESP. Twenty-four six to eight month old female lambs were randomly allocated into two groups. The first one was immunised twice, four weeks apart, with excretory-secretory products of Oestrus ovis third instar larvae (L3ESP) in complete then incomplete Freund adjuvant. The second one served as a control, and received two injections of PBS plus complete and incomplete Freund adjuvant. Fifteen and twenty-eight days after the second immunisation, animals of both groups were experimentally challenged with O. ovis first instar larvae. Twelve days after the second experimental challenge, the twenty-four lambs were necropsied. The total number of O. ovis larvae, their stages of development, weights and sizes were recorded per animal and compared between the two groups. Establishment rates were very similar in both groups: 39% and 35% in control and vaccinated groups respectively but the percentage of developing stages was higher in the control group (13%) than in the vaccinated group (6%). It was concluded that the L3ESP immunisation of sheep did not protect against larval establishment but provided an inhibitory effect on larval growth.     

Haemonchus contortus infection in sheep: parasite fecundity correlates with worm size and host lymphocyte counts

Two experiments were conducted to elucidate the timing and nature of the sheep immune response to Haemonchus contortus (Barber's pole worm). The first experiment examined the establishment of H. contortus populations and the immune response by comparing a bolus infection of third-stage larvae in na?ve sheep with a group previously primed by a trickle infection. The second experiment used staggered doses of ivermectin-resistant larvae to compare the development of adult worms during different durations of trickle infection with ivermectin-sensitive larvae. Infections successfully generated pathological signs of haemonchosis such as anaemia. Image analysis software was used to measure the area and perimeter of worms collected at post-mortem, and the number of eggs present in individual adult females (fecundity) was significantly correlated with worm size. A significant inverse correlation was found between blood lymphocyte counts and worm fecundity. The absence of correlation between worm fecundity and other leukocyte and erythrocyte counts highlighted the specificity of the lymphocyte response. This is the first report of a link between haematology profiles and worm fecundity in haemonchosis. The correlation observed between adult worm size and egg content leads to the hypothesis that egg production in H. contortus is limited by immune regulation of worm size and presumably growth. Mean worm size and fecundity declined as sheep received more prolonged trickle infections before necropsy, confirming previous reports that immune responses to adult worms are enhanced by ongoing larval challenge. Immunohistochemical results showed trends consistent with a Th2 (humoral) immune response which has been implicated in reducing nematode burdens in several species.