Biomedical subjects
J Vercruysse
Publications and source records attributed to J Vercruysse.
The relationship between Schistosoma haematobium infection and school performance and attendance in Bamako, Mali.
Schistosomiasis due to Schistosoma haematobium was the most common helminth infection in school-age children from a poor area in Bamako, Mali. Almost half (47%) of the boys and 40% of the girls were infected, 18% of the children being heavily infected. There was a significant decline in academic performance and in school attendance with increasing intensity of infection. When all sources of variation were taken into consideration, absenteeism was the main factor explaining the variation in academic performance, although a significant effect of infection remained. School-based delivery of chemotherapeutic interventions is currently promoted by several international organizations. However, rates of school attendance are low in some areas and it is the absentees who appear to be at relatively high risk of ill health. Novel ways of reaching this elusive subset of the population are required.
Morbidity induced by Schistosoma haematobium infections, as assessed by ultrasound before and after treatment with praziquantel, in a recently expanded focus (Senegal River basin).
Seven years after the completion of two dams in the Senegal River basin, 203 individuals from four villages around Podor in the middle valley, where Schistosoma haematobium infections were present, were examined in June 1995. In December 1995 a single dose of praziquantel (40 mg/kg) was given to each of these subjects, who were re-examined in April 1996. Clinical and parasitological signs of infection were investigated at both examinations, and ultrasonography was performed to check for lesions of the urinary tract induced by S. haematobium. As uninfected controls, 200 people from four villages where S. haematobium was absent were similarly examined, in November 1995. Prior to treatment, bladder irregularities were observed in 43% of the subjects from Podor but only 6% of the uninfected controls. The severity of the bladder lesions visible by ultrasonography was significantly associated with intensity of infection, despite the generally low levels of infection in the subjects mean = 13.1 eggs/10 ml urine). Four months after treatment, however, the frequency of bladder irregularities among the subjects (11%) was similar to that in the uninfected controls and intensities of infection and other clinical signs of disease had also significantly declined. The prevalence of haematuria, for example, fell from 35% pre-treatment to 10% post-treatment. The results indicate that the onset of S. haematobium morbidity can be relatively rapid even in areas with seasonal and low levels of transmission, and demonstrate that treatment to reduce morbidity in such areas is important and could be relatively simple and very effective.
Relationship of impairment of schistosome 28-kilodalton glutathione S-transferase (GST) activity to expression of immunity to Schistosoma mattheei in calves vaccinated with recombinant Schistosoma bovis 28-kilodalton GST.
Sera from calves vaccinated with the recombinant Schistosoma bovis-derived 28-kDa glutathione S-transferase (28GST) and subsequently naturally or experimentally exposed to Schistosoma mattheei were studied for their content of specific immunoglobulin G (IgG) and IgA antibodies to recombinant S. bovis 28GST as well as for their capacity to inhibit the enzymatic activity of the antigen. The results were analyzed in regard to the presence (natural infection) or absence (experimental infection) of a protective effect(s) (reductions in worm burden, egg load, fecal egg counts, and excretion of viable eggs) toward S. mattheei challenge. Under such conditions, no differences in the IgG- and IgA-specific antibodies to recombinant S. bovis 28GST or in the ability to block the catalytic function of the antigen between the two groups were recorded. Nevertheless, correlation analysis between the specific antibody responses to recombinant S. bovis 28GST and the inhibition of GST activity suggested an association with IgG in experimentally infected vaccinated animals, while in naturally infected vaccinated calves, the inhibitory activity appeared to be linked to a greater degree with IgA. These results suggest that in contrast to schistosomiasis in humans, IgG antibodies in calves with schistosomiasis may exhibit inhibitory functions toward GST enzymatic activity or have a modulatory effect on IgA antibody properties. Furthermore, sera from animals immunized with recombinant S. bovis 28GST recognized the native S. mattheei 28GST and achieved comparable levels of inhibition of activity of recombinant S. bovis 28GST and S. matthei 28GST, indicating the presence of cross-reactive epitopes on these two molecules.
Development of immunity to Mecistocirrus digitatus (Nematoda: Trichostrongylidae) in calves.
The importance of the third (L3), fourth (L4) and adult stages of Mecistocirrus digitatus in inducing resistance to reinfection was examined. Three groups of 5 calves (A, B, C) were immunized for 2 consecutive days with a daily dose of 20,000 M. digitatus infectious larvae. Group A was treated with ivermectin 7 days post-infection (exposed to L3), group B was treated after 26 days (exposed to L3 and L4) and group C after 60 days (exposed to L3, L4 and adults). Thirty days posttreatment, animals were challenged with 30,000 M. digitatus L3. Five previously uninfected control animals (group D) also received 30,000 L3. All animals were necropsied 75 days post-challenge. Increases in exposure to the immunizing infection resulted in significant increases in the pre-patent period post-challenge; 54 days in the controls, compared with 63, 70 and 72 days for groups A, B and C, respectively. Only adult worms were recovered at necropsy, and the mean number of worms significantly increased with increasing exposure to the immunizing infection: 355 in the controls, compared to 481, 937 and 1174 in groups A, B and C, respectively. No significant changes in worm length were observed. Infection with M. digitatus significantly affects a subsequent challenge infection--stimulation of the immune system by exposure to L3 extends the pre-patent period, and suppression by later stages (L4, adult) leads to higher worm burdens.
Effect of chemoprophylaxis with an ivermectin sustained-release bolus on acquired resistance to gastrointestinal parasites in cattle.
The influence of chemoprophylaxis with an ivermectin sustained-release bolus in the first grazing season on the resistance of cattle to gastrointestinal nematodes during the following grazing season was investigated. In 1993 and 1994 dairy replacement calves were either given one bolus at the start of their first grazing season or left untreated. The two groups were grazed separately on a pasture that was divided into two similar sized paddocks. Faecal egg counts, serum pepsinogen and antibody levels were measured to evaluate host-parasite contact. Pasture infection levels were estimated by pasture larval counts and worm counts in tracer calves. After winter housing the animals were monitored during their second grazing season on a pasture that was also divided into two similar sized paddocks. Acquired resistance to gastrointestinal nematodes was evaluated by faecal egg counts and weight gains. Again, pasture infection levels were determined and pepsinogen and antibody levels were measured. During the first grazing seasons gastrointestinal nematode infections were controlled very effectively by the bolus, as shown by the greater weight gains, the negligible faecal egg counts and the low serum pepsinogen and antibody levels in the treated calves. In contrast, all parameters showed extensive parasite-host contact in the untreated animals. The efficient prophylaxis in the treated groups resulted in low levels of larval contamination on the paddocks grazed by the treated animals, compared to moderate infection levels at the end of both first grazing seasons on the paddocks grazed by the untreated animals. During the second grazing seasons (1994 and 1995) the faecal egg output was low in all groups. Although in the previously treated animals faecal egg counts were consistently higher, the differences were minimal, resulting in comparable levels of larval contamination on both paddocks. Serum pepsinogen and antibody levels were not significantly different between the groups and indicated a similar level of larval uptake on both paddocks. No negative effect of the previous chemoprophylaxis on the clinical condition and the weight gain of the second season grazing animals was observed.
Comparative studies of ivermectin and moxidectin in the control of naturally acquired cyathostome infections in horses.
The control of naturally acquired cyathostome infections in horses by treatments with ivermectin and moxidectin was evaluated in three field studies. In a first study the efficacy of both drugs was assessed in a faecal egg count reduction test. Both ivermectin and moxidectin demonstrated efficacies greater than 99 per cent for up to 60 days after treatment. In a second study, the period required for strongyle eggs to reappear was estimated in horses treated either with ivermectin or moxidectin. For the horses treated with ivermectin the period varied between 10 and approximately 13 weeks, and for moxidectin between 22 and approximately 24 weeks. With both drugs strongyle eggs started to reappear in the faeces significantly earlier in foals and young horses than in adults. In a third study, two prophylactic dosing schemes involving three ivermectin treatments at intervals of eight weeks, and two moxidectin treatments 12 weeks apart, were found to be highly effective in controlling strongyle infections of horses on pasture.
Comparison of the persistent activity of ivermectin, abamectin, doramectin and moxidectin in cattle in Zambia.
The persistent efficacy of four commercially available macrocyclic lactones (ML) in maintaining reduced faecal egg counts in cattle grazing naturally infested pastures was evaluated in 44 zebu animals aged 1-2 years in Zambia. The study started in February (rainy season) when the strongyle egg output was increasing. Four days before the start of the trial, all animals were treated with a double dose of oxfendazole. They were then divided into five groups which were again treated on day 0. Groups A, D, I and M received 0.2 mg kg-1 of abamectin, doramectin, ivermectin and moxidectin, respectively. Animals of group C received albendazole (7.5 mg kg-1). Faecal samples were collected twice a week for egg counts and larval differentiation. Faecal egg counts in the C group increased from day 21 onwards and plateaued from day 42 between 180 and 380 eggs per gram. The main genera found in cultures were Cooperia (90%) and Haemonchus (7%). Faecal egg excretion in groups M, A, D and I started on day 35, 42, 42 and 45, respectively. Subsequently and until day 84, average counts in these four groups were always significantly lower than in group C. Compared with albendazole, all four ML gave over 95% reduction in cumulative faecal egg counts for 42 days after treatment. The percentage efficacy was still over 84% by day 84 when an average cumulative egg count of 11320 eggs per gram faeces was calculated in group C. In addition, there was no significant difference in efficacy between the four ML groups at any of the sampling dates. During the trial no significant difference in weight gain between any of the groups was observed.
Persistence of the efficacy of pour-on and injectable moxidectin against Ostertagia ostertagi and Dictyocaulus viviparus in experimentally infected cattle.
The persistence of the efficacy of moxidectin 0.5 per cent pour-on and moxidectin 1 per cent injectable against Ostertagia ostertagi and Dictyocaulus viviparus in calves was studied in two experimental trials. In the first trial two groups of seven calves were treated with either the pour-on or the injectable formulation, while a third group remained untreated. All the animals were infected daily from Monday to Friday with infective stages of O ostertagi and D viviparus between the day of treatment (day 0) and day 33, and were necropsied for worm counts three days later. The experimental design of the second trial was similar to that of the first but the period of infection was from 28 to 45 days after the treatment, and the necropsy was five days after the last infection. In both trials both moxidectin formulations had very high efficacies (99.6 per cent) against adult and developing stages of O ostertagi and D viviparus. The higher efficacy of the moxidectin pour-on preparation against early fourth stage larvae in both trials suggested that its effect was more persistent. It was calculated that the efficacy of moxidectin against O ostertagi persisted for at least five weeks for the injectable formulation and six weeks for the pour-on. The efficacy of moxidectin against D viviparus lasted for at least six weeks for both formulations.
Assessment of cure by detection of circulating antigens in serum and urine, following schistosomiasis mass treatment in two villages of the Office du Niger, Mali.
Eight weeks after mass chemotherapy with 40 mg/kg praziquantel in two villages in Office du Niger (an irrigation area in Mali, endemic for both Schistosoma haematobium and Schistosoma mansoni) the circulating anodic (CAA) and cathodic (CCA) antigen detection assays were carried out on serum and urine samples. Both prior and post treatment highest prevalence was measured with the urine-CCA assay. Cure rates determined by antigen detection were almost half that of the egg counting methods. It was shown that the reduction in intensity should be preferentially assessed by the serum-CAA assay. Compared with egg detection, a single antigen detection assay gave a much better assessment of the impact of chemotherapy.
Induction and suppression of lymphocyte proliferation by antigen extracts of Ostertagia ostertagi.
To obtain an insight into the responses of T-cells of cattle to Ostertagia ostertagi, the responses of peripheral blood and lymph node lymphocytes to O. ostertagi antigen extracts were determined in both exposed and naive calves. The lymphocyte responses induced by O. ostertagi antigen extracts of the third (L3) and fourth (L4) larval stages, as well as adult worms, were analysed. Although peripheral blood lymphocyte responses were very low or absent, abomasal lymph node lymphocytes of exposed animals showed a strong response to the L3 antigen extract. No such response was observed in naive calves or in mesenteric lymph node cells of exposed calves. L4 and adult worm antigen extracts suppressed the proliferative responses induced by the L3 antigen extract. Whether or not this suppressive effect plays a role in the slow rate at which protective immunity develops against O. ostertagi is under further investigation.
The epidemiology and control of cattle schistosomiasis.
Schistosomiasis remains a major health problem in much of the developing world. Despite decades of research, many fundamental questions on the dynamics of infection and immunity development remain unanswered. Schistosomiasis is also a common parasitic infection in cattle, and studies on livestock exposed to their own species of schistosome may help in understanding some aspects of the host-parasite relationship. Here, Jan De Bont and Jozef Vercruysse review the current knowledge on the epidemiology and control of cattle schistosomiasis.
The presence of an early L4 population in relation to the acquired resistance of calves naturally infected with Ostertagia ostertagi.
The aim of the present study was to determine if the presence of inhibited L4 Ostertagia ostertagi populations during the housing period influenced the level of acquired immunity in calves at the start of the second grazing season. Four groups (A-D) of first season grazing calves were turned out onto a heavily infected pasture for five months, while the fifth group (E) was kept as uninfected controls. At housing all group A calves were necropsied for worm counts. A mean total of 78915 Ostertagia worms were found, of which 85% were in the early L4 stage. The calves of group C were dewormed with ivermectin at housing, while groups B and D remained untreated. After the calves were housed, egg counts, pepsinogen and antibody levels all declined in groups B, C and D, but during the second half of the housing period pepsinogen and antibody levels increased again in groups B and D. The effect of housing on the resident worm population was evaluated by slaughtering all group B calves for worm counts at the end of the housing period. A mean burden of 57,950 Ostertagia was present, with 78% as early L4 larvae. The remaining three groups (C, D and E) were treated with oxfendazole and turned out on the same pasture as the previous year for a challenge period of four weeks. In the control calves (group E) the egg output rose steeply, while egg counts remained low in groups C and D. In addition the worm burdens of the previously infected groups C and D were significantly reduced (75-90%), and the percentage of inhibited L4 larvae was significantly increased compared to the control group E. No significant difference was observed between the calves that were treated at housing (group C) and the untreated animals of group D. It was concluded that the continued presence of an inhibited L4 population during housing was not essential for maintenance of immunity.
Gastrointestinal nematode infections of first-season grazing calves in Belgium: general patterns and the effect of chemoprophylaxis.
Comparative analyses of the patterns of gastrointestinal nematode infections of first-grazing season cattle in Belgium are presented. The analysis involves 17 studies covering a 10 year period on 13 different farms in Flanders, Belgium. In all studies the calves were divided into an untreated control group, and one or two groups treated with chemoprophylactic systems. Two general infection levels emerged-'sub-clinical' (14 studies) and 'clinical' (three studies). The 'sub-clinical' infections were characterised by no clinical signs of parasitic gastroenteritis in the untreated control groups. Mean faecal egg counts remained low (less than 200), maximum pepsinogen levels only reached about 3500 mU tyrosine, and very small reductions in overall daily weight gain were observed compared with calves given chemoprophylaxis (less than 40 g day-1). Based on these results, on these 'sub-clinical' farms, chemoprophylaxis may not have been needed. In contrast, multiple salvage treatments of the control calf groups were required in the 'clinical' infections. Even with these salvage treatments mean faecal egg counts were high (more than 300), maximum pepsinogen levels were over 5500 mU tyrosine and there was a very large reduction in overall daily weight gain (more than 300 g day-1). However, it was not possible to predict either at turnout, or during the first month afterwards whether an infection on a particular farm would develop into a 'clinical' infestation. With the present data this prediction was possible from 8 weeks (Day 56) onwards, based on faecal egg counts and pasture larval contamination. It was also possible to predict using serum pepsinogen levels on Day 84. Therefore, one possible strategy for the effective control of gastrointestinal nematode infections of calves in temperate regions would be to evaluate faecal egg counts 2 months after turnout, and then only start treatment (i.e. metaphylaxis) if required.
Epidemiological observations on gastrointestinal nematode infections in grazing cow-calf pairs in Belgium.
The epidemiology of gastrointestinal helminth infections in beef cows and calves on pasture was studied in Belgium during the 1990 and 1992 grazing seasons. Weight gain, faecal egg counts, generic differentiation of infective larvae, serum pepsinogen levels, herbage larval counts and worm burdens of tracer calves were used as parameters. In Study 1 two groups of ten cows with their spring-born calves grazing on separate pastures (A and B) were monitored during the 1990 grazing season. Ostertagia ostertagi was the predominant species shed by cows and calves. Cows on Pasture A had significantly higher egg counts at turn-out than the B cows, creating a high pasture contamination in the autumn, evidenced by high Ostertagia worm burdens in the Pasture A tracer calves. Calves of both groups showed low egg counts (mean < 60 eggs g-1 faeces, EPG) throughout the grazing season. In Study 2 nine cow-calf pairs were monitored during the 1992 grazing season. The calves were born in winter or spring. Faecal egg counts of the cows remained low throughout the trial period. During the grazing season high egg counts were observed in the calves (mean up to 778 EPG). Cooperia oncophora was the predominant species in the calves. In the cows O. ostertagi, Oesophagostomum, C. oncophora and Trichostrongylus axei were present. It is suggested that, in the first study, the cows were the major source of pasture contamination, while in the second study the winter-born calves, being older and having a higher herbage intake resulting in a higher infection level, were largely responsible for the high Cooperia pasture infection level at housing.
Evaluation of an enzyme-linked immunosorbent assay (ELISA) for the serological diagnosis of sarcoptic mange in swine.
An enzyme-linked immunosorbent assay (ELISA) using an extract from Sarcoptes scabiei var. culpes as antigen was evaluated for its usefulness in monitoring antibodies to S. scabiei var. suis in naturally infected pigs. Five hundred and fifty-eight serum samples from certified Sarcoptes-free pigs (120 from weaned piglets, 218 from fatteners and 220 from adult sows) and 94 samples from certified Sarcoptes-infected pigs (35 from weaned piglets, 45 from fatteners and 14 from adult sows) were examined. The cut-off optical density (OD) values, considered to reflect the presence of antibodies to S. scabiei var. suis, were determined to be 0.059, 0.213 and 0.374 for weaners, fatteners and sows, respectively. The specificity of the ELISA was high (> or = 98%) for all age groups. Sensitivity was highest in the piglets (80%), followed by fatteners (78%) and sows (50%). These results indicate that an ELISA may be a simple and valuable alternative to monitor S. seabiei var. suis infections in naturally infected weaners and fatteners.
Pathophysiological aspects of Mecistocirrus digitatus (Nematoda: Trichostrongylidae) infection in calves.
Three groups of four calves were experimentally infected with infectious larvae of Mecistocirrus digitatus. One group received a trickle infection of 5000 L3 per day for 8 days, the other two groups received a single infection of 5000 and 40,000 L3, respectively. All animals were necropsied 120 days after infection. Prepatent periods varied between 61 and 79 days, and maximal faecal egg output was reached between 80 and 100 days after infection. Repeated infections were not additive and worm counts at 120 days after infection varied between 100 and 440 in the first two groups and between 120 and 1700 in the last group. There was no significant difference in worm counts between the different infection regimes. However, there was a significant positive relationship between worm burden and faecal egg counts. In addition, there were significant negative relationships between worm burden and packed cell volume, and weight gain. The relative decreases in packed cell volume and weight gain emerged 70-80 days after infection. Serum pepsinogen levels were significantly elevated by the end of the trial, but the observed positive relationship between worm burden and pepsinogen was not significant. An enzyme immunoassay based on crude adult antigen was able to detect M. digitatus infection at 90 and 100 days after infection, but again there was no significant association between worm burden and antibody levels. Therefore, anaemia and a reduction in weight gain caused by the haematophagous activity of adult stages seem to be the most important pathogenic effects of M. digitatus infection in calves.
The influence of a Cooperia oncophora priming on a concurrent challenge with Ostertagia ostertagi and C. oncophora in calves.
The development of immunity to Ostertagia ostertagi and Cooperia oncophora and interactions between these species were investigated in experimentally infected calves. Parasitological, serological and histological parameters were used for assessing immune responses. No conclusive evidence of an effect of C. oncophora on the course of an O. ostertagi infection in calves could be shown. Following a challenge with C. oncophora and O. ostertagi of C. oncophora primed calves, no significant reductions in establishment rate, faecal egg counts, worm length or the percentage of early fourth stage larvae could be demonstrated. Results also confirmed earlier work showing the very different degrees of immunity conferred following immunisation with either C. oncophora or O. ostertagi. While a protective immunity was generated in the case of C. oncophora, continuous infection of calves with 420000 L3 of O. ostertagi during almost 5 months induced immune reactions which affected growth and fecundity of the worms but not the establishment rate.