Protection of yearling ponies against Strongylus vulgaris by foalhood vaccination

The long-term efficacy of an irradiation attenuated larval (L3) vaccine against Strongylus vulgaris was tested in ponies which were reared on pasture. Prior to foaling, mares were divided into two groups. One group of mares and foals received regular (eight weekly) treatment with ivermectin and the second group remained untreated. Half the foals in each pasture group were vaccinated at eight to ten weeks of age. Foals were weaned at three to four months of age and maintained on separate pastures. At eight to ten months of age, ponies were placed in box stalls and half of each treatment group were challenged with S. vulgaris (5 x 1000 L3). Clinical signs and lesions typical of acute verminous arteritis were found at necropsy in the ivermectin treated non-vaccinated challenged yearlings. Ivermectin treated vaccinated challenged yearlings did not show these clinical signs, had markedly reduced to absent arterial lesions and showed an 89 per cent reduction in arterial larval burdens post mortem. Significant differences in clinical signs, arterial lesions or arterial larval burdens were not seen between vaccinated and non-vaccinated foals reared without benefit of ivermectin treatment.     

A method of automatic determination of "reference" spectra of CD elements of circular structure of proteins with the "aromatic contribution"

A field survey at 17 stables involving 221 horses was performed to evaluate the presence of anthelmintic resistance in the equine small strongyles (cyathostomes). The horses were allocated into treatment groups, and resistance to fenbendazole (FBZ), pyrantel pamoate (PYR) and ivermectin (IVM) was tested by the faecal egg count reduction test (FECR-test). Faecal samples were collected at the time of treatment, 14 days post treatment and 90 days post treatment. Resistance to FBZ, which was defined as a faecal egg count reduction < 95%, was found in 14 out of 17 stables. In 2 of the 14 stables the egg reductions were close to the limit of 95%, 91 and 93%, respectively. In 1 stable the egg reductions indicated resistance to PYR as well as detection of resistance to FBZ, 94% reduction for PYR and 85% for FBZ. No signs of resistance were detected to IVM. The investigation was performed in late autumn and winter, and due to the climatic conditions and cleaning procedures in the stables no reinfection took place during this period. The faecal egg count reduction from treatment till day 90 post treatment was used as an expression of the effect of PYR and IVM on the early stage (hypobiotic), late third stage and fourth stage larvae in the gut wall. This was justified because there was no reinfection and because the 14 day post treatment egg counts were zero or close to zero for the PYR and IVM treatment groups. The effects of PYR and IVM on the larval stages were compared and no statistically significant differences were found.     

Regional gastric pH measurement in horses and foals

The pH of the gastric mucosal surface and gastric content was measured in 18 foals (mean age: 20 days) and 27 horses (mean age: 2.9 years) with a pH electrode passed through an endoscope biopsy channel. A reference electrode was attached to a shaved area on the neck. pH Measurements of the gastric mucosal surface at the dorsal squamous fundus (SF), squamous mucosa adjacent to the margo plicatus (MP), glandular fundus (GF) and the fluid or feed contents of the stomach were recorded in duplicate for each animal. In adult horses, the SF pH was greatest (5.46 +/- 1.82), with a decreasing pH ventrally toward the MP (4.12 +/- 1.62), to the glandular fundic mucosa (3.09 +/- 1.90), and fluid contents (2.72 +/- 1.86). The differences in pH at each site within the stomach were significant (P < 0.05). In foals, mean pH measurement of the SF was 4.88 +/- 1.30, the MP was 4.92 +/- 1.29, the GF was 2.10 +/- 1.45, milk and fluid contents was 1.85 +/- 0.53 (six foals), and feed contents was 3.39 +/- 1.77 (12 foals). The pH of the SF and MP were significantly greater (P < 0.05) than that of feed contents, which was significantly greater (P < 0.05) than that of the glandular mucosal surface and fluid contents. The results indicate a dorsal to ventral pH gradient of the gastric mucosal surface in adult horses, and that gastric acid secretion is competent in young foals.     

Efficacy of an in-feed formulation of ivermectin against adult worms and somatic larvae of Strongyloides ransomi

The efficacy of an in-feed formulation (IVOMEC premix) containing 0.6% ivermectin was tested against Strongyloides ransomi in swine. The efficacy of ivermectin against patent infections of S. ransomi when given via the feed at 2 ppm for 7 days (Days 0-7) to provide 100 mcg ivermectin kg-1 body weight day-1 was evaluated in a study with 16 3-month-old male castrated piglets. Seven days prior to treatment each piglet was infected subcutaneously with 2500 infective larvae of S. ransomi. Fecal egg counts were carried out on Days -7, 0, 7 and 14, and worm counts on Day 14. Efficacy was 100% in all treated piglets. Two trials involving 40 pregnant gilts were carried out to evaluate the efficacy of ivermectin against the somatic larval stages of S. ransomi when given at a daily dose of 100 mcg kg-1 body weight for 7 days starting on Days 66, 78, 92 or 103 of pregnancy. The gilts were each experimentally infected with three subcutaneous injections of 250,000 infective larvae, with the last infection given between 12 and 30 days prior to commencement of treatment. Gilts were confirmed free of pre-existing intestinal stages of S. ransomi prior to ivermectin treatment. Fecal nematode egg counts were carried out in gilts/sows and piglets subsequently born. The Strongyloides larvae present in sow milk 1, 2 and 7 days post partum were counted. Fourteen days post natum, worm counts were performed in four randomly selected piglets for each litter. IVOMEC premix given to pregnant gilts prevented shedding of larvae in sow milk, egg output in feces and the establishment of S. ransomi in piglets.     

The effectiveness of a single treatment with doramectin or ivermectin in the control of gastrointestinal nematodes in grazing yearling stocker cattle

Four studies were conducted to a similar experimental design in the U.S. to evaluate the effectiveness of doramectin injectable administered to yearling stocker cattle in the control of gastrointestinal nematodiasis over the subsequent grazing period. Studies were conducted in Wisconsin (WI) and Arkansas (AR) during the summer season. The other two studies were conducted in Georgia (GA) and Mississippi (MS) during the winter/spring season. Doramectin was compared with both ivermectin injectable and ivermectin pour-on in the WI study, with ivermectin injectable alone in the GA study and with ivermectin pour-on alone in the other two studies. At each study site, an area of permanent pasture previously grazed by parasitized animals was subdivided by fencing into equal pasture units each with its own water supply. A treatment designation (non-medicated control, doramectin injectable, ivermectin injectable or ivermectin pour-on) was randomly assigned to each pasture unit. Weaned beef calves with confirmed gastrointestinal nematode infections were randomly allotted to a pasture unit and corresponding treatment group. Each treatment group consisted of three replicates of seven animals per pasture unit (total 21 animals) in the WI study, three replicates of four or six animals per pasture unit (total 16 animals) in the AR study, five replicates of six animals per pasture unit (total 30 animals) in the GA study and three replicates of 12 animals per pasture unit (total 36 animals) in the MS study. Treatments were 1% doramectin injectable solution, 1% ivermectin injectable solution, 0.5% ivermectin pour-on solution or non-medicated controls. The injectables were administered at a dose of 1 ml/50 kg body weight (200 micrograms doramectin or ivermectin/kg) by subcutaneous injection in the neck. Ivermectin pour-on solution was administered topically at a dose of 1 ml/10 kg body weight (500 micrograms ivermectin/kg). After receiving their prescribed treatment, animals were placed on their designated pasture unit where they remained for the entire grazing period (84-140 days). Fecal nematode egg counts and body weights were monitored at predetermined intervals throughout each study. Doramectin treatment reduced pretreatment egg counts by between 95 and 100% by 21 days post-treatment. Subsequent rises in egg output from exposure to infective pastures were delayed by two to four weeks resulting in substantial reductions in total egg deposition over the grazing period and, therefore, potential pasture recontamination. Doramectin treatment resulted in substantial average daily weight gain advantages (0.152-0.272 kg) over the grazing season compared to non-medicated controls. Advantages were statistically significant (P < 0.05) in three of the four studies. There were no significant differences (P > 0.05) in average daily gain between the doramectin and ivermectin injectable or ivermectin pour-on treated groups.     

Benzimidazole resistance in cyathostomes in horses in the Ukraine

The efficacy of treatment with cambendazole was tested in 1-year-old horses on a farm in Dubrovka, Ukraine. Thirty-five horses were treated. Their egg output was compared on the day of treatment and 14 days later with that of 33 untreated horses. Before treatment the mean number of eggs g-1 faeces was 614 in the controls and 766 in horses that had been treated. After 14 days the mean egg output in the controls was 580 and in the treated horses 369. This means a reduction of 54.5%. Only cyathostome larvae could be cultured from faeces collected after treatment. It can be concluded that benzimidazole resistance in cyathostomes is present in the Ukraine.     

Opsonic effect of equine plasma from different donors

The ability of equine plasma from different donors to enhance phagocytic capacity was assessed in neutrophils obtained from seven foals, aged 7-8 days (Study A), and from seven adult horses (Study B). Neutrophils were allowed to phagocytize fluorescent yeast cells opsonized with plasma from one of three donors or with pooled serum, all previously frozen (-18 degrees C) and thawed. The results were analysed by flow cytometry. In study A, fresh autologous foal serum was also used for opsonization, and in study B, heat-inactivated plasma and pooled serum were used in addition to untreated samples. The plasma from donor GN induced a higher number of truly phagocytic neutrophils (mean 78%) than did plasma from donors GD (68%), OD (66%) and pooled serum (59%) when neutrophils from foals were used (p < 0.05). Similar results were obtained when adult neutrophils were used. Phagocytosis was markedly reduced with beat-inactivated plasma as a result of there being fewer phagocytic neutrophils and less phagocytized material per cell. The opsonic capacities of the autologous foal sera were lower than that of adult donor plasma in six out of seven foals. It is concluded that there is significant individual variation in the opsonic activity amongst plasma donors with similar serum IgG concentrations. The results were consistent irrespective of whether neutrophils from adults or foals were used.     

Digital perfusion, evaluated scintigraphically, and hoof wall growth in horses with chronic laminitis treated with egg bar-heart bar shoeing and coronary grooving

Nuclear scintigraphy was used to assess digital perfusion before and after treatment in 10 horses with clinical and radiographic evidence of chronic laminitis. Horses were evaluated for lameness, degree of distal phalanx rotation, and heel-toe hoof wall growth ratio, and randomly divided into two treatment groups. Group 1 horses received only egg bar-heart bar shoeing; Group 2 underwent egg bar-heart bar shoeing and coronary grooving. Horses were re-evaluated for digital perfusion, lameness, degree of distal phalanx rotation, and hoof wall growth at 6 week intervals over the 18 week follow-up period. Prior to treatment, relative scintigraphic activity at the dorsal laminar area was decreased and relative scintigraphic activity at the toe and adjacent solar area was increased. Egg bar-heart bar shoeing was associated with significantly increased dorsal laminar scintigraphic activity and significantly decreased solar scintigraphic activity over the 18 week period. Coronary grooving, in combination with egg bar-heart bar shoeing, resulted in a significantly lower heel-toe hoof wall growth ratio but did not enhance digital perfusion. Seven of 10 (70%) horses were responsive to treatment, defined as an improvement in lameness by at least one grade. Horses that were refractory to treatment had significantly lower dorsal laminar scintigraphic activity and higher palmar coronary scintigraphic activity prior to treatment than horses that responded to treatment. Our results are the first to demonstrate that egg bar-heart bar shoeing is associated with improved dorsal laminar perfusion, and support the use of this technique. In addition, we found that pre-treatment nuclear scintigraphy was predictive of clinical outcome in horses with chronic laminitis treated with corrective shoeing.     

Identification and characterization of a pyrantel pamoate resistant cyathostome population

Three fecal egg count reduction assays (FECR) and one critical trial were performed to determine the efficacy of pyrantel pamoate (PP) at 6.6 mg base kg-1 on a well managed stud farm in Louisiana where a loss of efficacy was suspected. Efficacy of PP based on FECR varied from 25% in mares to 83% in yearlings. Second treatments with PP 2 weeks following an initial treatment failed to reduce eggs per gram (EPG). A critical trial was performed to determine the cyathostome species resistant to PP. Three strongyle-naive ponies which acquired infections on the farm were used for this purpose. Following treatment with PP at the recommended dose, 11 species of cyathostomes remained in the intestine of the tracer ponies. Reduced efficacies (62%-88%) were noted for seven species. Resistance to oxibendazole (OBZ), which was > 90% effective on this farm in 1982, was also evaluated by FECR and found to exist. The results of one experiment indicate that dual resistance of parasites to PP and OBZ also exists.     

The kinetic disposition of pyrantel citrate and pamoate and their efficacy against pyrantel-resistant Oesophagostomum dentatum in pigs

The pharmacokinetic disposition of pyrantel after intravenous (i.v.) and oral (p.o.) administration as the citrate and p.o. administration as the pamoate salt was determined in pigs. Following i.v. administration pyrantel was quickly cleared from the bloodstream, exhibiting a terminal half-life of 1.75 +/- 0.19 h and a residence time (MRT) of 2.54 +/- 0.27 h. After p.o. administration as the citrate salt, the absorption time (MAT) of pyrantel was 2.38 +/- 0.25 h and although significant quantities of pyrantel were absorbed (mean bioavailability of 41%) the rapid clearance resulted in a MRT of only 4.92 +/- 0.36 h. By comparison, the significantly extended MAT of the less soluble pamoate salt resulted in reduced circulating concentrations and a significantly lower mean bioavailability of 16%. The poor efficacy of pyrantel citrate against nematodes inhabiting the large intestine of pigs is therefore suggested to result from insufficient quantities of drug passaging to the site of infection. When tested against pyrantel-resistant adult Oesophagostomum dentatum the mean efficacy of pyrantel citrate was only 23%, whereas the efficacy of the lesser absorbed pyrantel pamoate was 75%. These results indicate that for maximum activity pyrantel should be administered to pigs as the pamoate salt.     

Bronchoalveolar lavage in horses: effect of exercise and repeated sampling on cytology

Bronchoalveolar lavage (BAL) was performed at weekly intervals in 10 Thoroughbred horses in race training (group 1) and in 4 rested horses (group 2) for 10 weeks. Lavages were continued on a weekly basis in 4 group 1 horses for an additional 9 weeks (group 3). Cytological analysis of samples included leukocyte counts, erythrocyte counts, differential leukocyte counts, and haemosiderophage score. The mean leukocyte concentration was significantly lower in group 1 (92.1 +/- 4.6 cells/microL) when compared with group 2 (133.5 +/- 8.2 cells/microL), P = 0.037. The differential leukocyte data were not significantly different between groups. There was a large amount of variability in the percentage of macrophages and lymphocytes in the differential counts over time with no obvious trends. The proportion of neutrophils demonstrated a tendency to decrease over time for both groups 1 and 2. Erythrocyte counts and haemosiderin scores were significantly higher in the exercising group than the rested horses. Neither exercise nor the technique itself evoked an inflammatory response in the BAL fluid.     

Persistence of the activity of topical ivermectin against biting lice (Bovicola bovis)

To assess the persistence of the activity of topical ivermectin against a natural challenge with biting lice (Bovicola bovis), 90 mixed-breed cattle that had been treated to remove lice, were blocked by bodyweight within sex and randomly allocated to three treatments: untreated control, doramectin at 200 micrograms/kg by subcutaneous injection, and ivermectin at 500 micrograms/kg by topical application. Forty-five pens were blocked into three groups of 15, and the blocks of pens were randomly allocated to three 14-day challenge periods starting 21, 28 and 35 days after treatment. There were five pens per treatment for each challenge period, and one B bovis-infested donor calf was introduced into each pen containing two principal calves at the start of the challenge period for that block of pens. The calves were examined thoroughly for B bovis seven, 14 and 21 days after the introduction of the donors. There were no significant differences between the control and doramectin groups for the numbers of animals infested, or the geometric mean louse counts at the final examination for any of the challenge periods. At the final examination for each challenge period, the louse counts of the cattle treated with topical ivermectin were all zero, and significantly (P < 0.05) fewer cattle treated with topical ivermectin were infested than either the controls or cattle treated with doramectin.     

Enhanced expression of inducible nitric oxide synthase in chronic gastritis with intestinal metaplasia

Twelve Standardbred foals (age 3-6 months), with little previous exposure to parasites, were allocated to 2 groups and put onto pasture with low (Group L) or high (Group H) levels of larval contamination of large strongyles and cyathostomes. After 4 weeks grazing in September, the foals were housed indoors until necropsy 15 weeks later. Foals in Group H became clinically more affected than those of Group L in that they showed loss of vigour, weight gain depression, intermittent soft faeces and inappetence. One foal of Group H had persistent diarrhoea and was subjected to euthanasia 12 weeks after housing. Signs of colic were not observed. Faecal egg counts were significantly higher in Group H than in Group L (P<0.05). At necropsy, the mean number of S. vulgaris and cyathostomes was 20 and 18,000, respectively, in Group L, and 167 and 25,000 in Group H. Routine blood chemistry did not specifically reveal presence of S.vulgaris in pre-patency. A transient neutrophilia and eosinophilia, most prominent in Group H, was seen 2-8 weeks after start of exposure and anaemia was observed later in Group H. Serum albumin and albumin/globulin ratio were reduced, particularly in Group H, and a marked hyperbetaglobulinaemia was observed at 16-20 weeks in Group H. In conclusion, heavy infections with strongyles including S. vulgaris may become established in weaned foals after a brief period on pasture. Infections may be expressed clinically as debilitation, inappetence and intermittent diarrhoea without colic, and the need for control is imperative.     

Innervation of the equine mature and immature proximal sesamoid bone by calcitonin gene-related peptide and substance P-containing nerves

OBJECTIVE: To localize and determine relative frequency of occurrence of calcitonin gene-related peptide (CGRP) and substance P (SP) fibers in the proximal sesamoid bones (PSB) and adjacent structures in sound horses. SAMPLE POPULATION: 4 foals and 3 adult horses. PROCEDURE: Medial PSB and adjacent ligaments of both forelimbs were collected, flushed, and fixed in buffered 4% formalin. The left PSB were cut into 5 longitudinal, sagittally oriented slabs, and the right PSB were cut into 5 transverse slabs. After decalcification in EDTA, slices were transferred to a 30% sucrose solution, deep frozen, sectioned (80 microm), and stored in Tris-buffered saline solution for free-floating immunocytochemical processing, staining of which was performed by use of the peroxidase-antiperoxidase method with polyclonal rabbit antibodies against CGRP and SP. Sections were examined by light microscopy. RESULTS: Calcitonin gene-related peptide and SP fibers were present throughout the PSB; in ligaments, they were concentrated at the attachment sites. Presentation of the fibers, the innervation pattern, and intensity in the bones of horses differed from that in foals, in which the fibers were more delicate and frequency of occurrence was lower. In horses, innervation with CGRP and SP fibers was more dense in the periphery of the bone, whereas in foals, local difference in innervation of the bone was not evident. With the exception of the intersesamoidean ligament, ligaments were more richly innervated than was bone. CONCLUSION: Presence of the nociceptive peptides CGRP and SP indicated that the PSB and, more practically, the adjacent ligaments are sensitive structures.     

Corticosterone promotes increased heme oxygenase-2 protein and transcript expression in the newborn rat brain

Ultrastructural changes induced in vitro by thiabendazole, levamisole, pyrantel and ivermectin in the free living larval stages of two trichostrongyles (Heligmosomoides polygyrus and Haemonchus contortus) were analysed. The observed damage for each anthelmintic is related to the known mode of action and compared to the damage commonly described in adults. The advantage of using larvae to study the effects of anthelmintics on the fine structure of nematodes rather than adults is described. Thiabendazole induced alteration of the cellular organization especially epithelial cells of the digestive tract. Changes in mitochondria were also seen. Levamisole caused contraction of muscle fibres whereas no specific lesions were observed with pyrantel. Ivermectin caused an hypertrophy of muscular groups. The interest of such a technique in research on the modes of action of anthelmintics is emphasized.     

Matrix metalloproteinase activity in equine synovial fluid: influence of age, osteoarthritis, and osteochondrosis

OBJECTIVE: To investigate the influence of age, osteoarthritis (OA), and osteochondrosis (OC) on the matrix metalloproteinase (MMP) activity in the synovial fluid (SF) of equine joints. METHODS: SF was collected from normal and osteoarthritic metacarpophalangeal joints (normal: 14 adult, 28 juvenile; OA: 22 adult). And from normal and osteochondrotic tarsocrural joints (5 months: 11 normal, 8 OC; 11 months: 7 normal, 6 OC). Subsequently, overall MMP activity was measured. RESULTS: The level of active MMPs was almost twofold higher in SF from juvenile horses (age up to 11 months) than in SF from mature animals (4-30 years; p < 0.001). In juvenile horses MMP activity was higher in 5 month old foals than in 11 month old foals (p < 0.01). In adult horses MMP activity was independent of age. In OA joints the activity was nearly twice as high as in normal joints (p < 0.001). In OC joints MMP activity was not significantly different from normal, age matched, control joints. CONCLUSIONS: MMP activity in SF from normal adult joints is not related to age. In juvenile joints MMP activity is significantly higher than activity in joints from adult animals. It is hypothesised that the gradual decrease in MMP activity with increasing age reflects the declining metabolic activity resulting from ceasing growth and the accompanying decrease in cartilage remodelling. The increased MMP activity in osteoarthritis joints most likely reflects matrix destruction. In osteochondrosis MMP mediated matrix degradation appears not to be different from normal joints.     

Efficacy of the oral antiparasitic mebendazole plus trichlorfon (telmin plus trichlorfon) against Gasterophilus in the horse

The combined drug Mebendazole plus Trichlorfon (Telmin plus Trichlorfon, Janssen Pharmaceutica, Beerse/Belgium) has been tested in a field trial against naturally acquired Gasterophilus spp. infestations in horses. 44 foals (1 to 1.5 years old, 350-450 kg body-weight) originating from different endemic areas of Switzerland, have been randomly allocated to two groups as follows: 28 foals were treated with Mebendazole plus Trichlorfon, 16 animals served as untreated controls. The drug (paste) was administered and dosed according to the user's instruction. Macroscopic examinations of the digestive tractus and the larval counting has been performed immediately after slaughtering, i.e. 30 and 33 days after treatment, resp.. The efficacy of the product against Gasterophilus spp. amounts to 97.04% which is considered as highly effective. A further proof for the high efficacy is the observation of a lot of larvae-carrying foals in the control group. Since the larvae of Gasterophilus spp.--according to their life cycle--are essentially found in their hosts between November and February, an appropriate treatment should be performed during that period of time.     

Resistance exercise prevents glucocorticoid-induced myopathy in heart transplant recipients

During the winter 1991-92, 42 reindeer hinds of the Kaamanen Experimental Reindeer Herd in Finnish Lapland, naturally infected with various parasites, were allocated to 3 groups. One group was an untreated control group and the other 2 groups received either moxidectin or ivermectin at a dose of 200 micrograms kg-1 subcutaneously. The efficacy of treatment was followed with monthly faecal examinations for nematode eggs and counting of warbles, Hypoderma tarandi larvae, and throat bots, Cephenemyia trompe larvae, from live animals in spring. The efficacy of moxidectin against warbles (92.8%) and throat bots (70.8%) did not match that of ivermectin, which was 100% against both species. Both moxidectin and ivermectin were effective against gastrointestinal trichostrongylid egg production over the December to May trial period indicating good efficacy against adult and inhibited trichostrongylids. Only non-significant differences were seen in weight development and calf birth weights between the groups. Because of its only moderate insecticidal efficacy, moxidectin cannot be recommended as an endectocide in reindeer.     

Efficacy of ivermectin in a beef-based chewable formulation against Ancylostoma caninum and Uncinaria stenocephala in dogs

The effective dosage of a chewable formulation of ivermectin was determined in 35 young dogs with induced infections of Ancylostoma caninum and Uncinaria stenocephala. Dogs were inoculated with these parasites and held until the infections were patent. Within each of 7 replicates, dogs were allocated randomly to 1 of 5 treatment groups: vehicle control, or ivermectin at 6, 12, 18, or 24 micrograms/kg. Chewable treatments were tailored to body weight. Seven or 8 days after treatment, parasites were recovered using standard techniques. All 7 controls had adult A. caninum (geometric mean = 35.5) and U. stenocephala (geometric mean = 82.6). Against A. caninum, the efficacy of ivermectin was 52%, 98%, 95%, and 97% at 6, 12, 18, and 24 micrograms/kg, respectively. The statistical model that best described the dose response was linear to 12 micrograms/kg with a plateau thereafter. Using this model, the estimated reduction from the predicted control mean was 97.2%; the estimated dose to eliminate 90% of the worms (ED90) was 8.4 micrograms/kg, and the ED95 was 10.5 micrograms/kg. Against U. stenocephala, the dose response was linear in the range studied, with an ED90 of 20.8 micrograms/kg; it was estimated that 93.2% of the worms would be eliminated.     

Specific immune responses are required to control parasitemia in Babesia equi infection

Horses possessing a normal immune system and spleen often control infection caused by Babesia equi. However, splenectomized horses are unable to control B. equi infection and usually succumb to the infection. To investigate the role of the spleen in the control of B. equi infection in the absence of specific immune responses, two 1-month-old foals with severe combined immunodeficiency (SCID) and two age-matched normal foals were inoculated with B. equi. The SCID foals became febrile seven days postinoculation and developed terminal parasitemias of 41 and 29%. The SCID foals had greater than 50% decreases in indices of total erythrocytes, packed-cell volumes, and hemoglobin concentrations. Both SCID foals were euthanized in extremis at 10 days postinoculation. As expected, the serum of the SCID foals lacked detectable antibodies to B. equi antigens. In contrast, the normal foals inoculated with B. equi produced detectable anti-erythrocyte-stage parasite antibodies by 7 days and controlled clinical disease by 12 days postinoculation. Although SCID foals lack functional T and B lymphocytes, they do possess complement, macrophages, granulocytes, and natural killer cells, as well as a spleen. Therefore, the data indicate that specific immune responses are required to control B. equi parasitemia but are not required for erythrocyte lysis in infected horses. Furthermore, the spleen is not able to control B. equi parasitemia in the absence of specific immune responses to parasite antigens.