Darren Shaw

Efficacy of praziquantel against Schistosoma mansoni in northern Senegal

Two treatments with praziquantel (PZQ) 40 mg/kg, 40 d apart, were given to individuals in a recently established (< 6 years) Schistosoma mansoni focus in the Senegal River Basin (SRB). Efficacy of treatment was evaluated 4 weeks after each treatment. Among 130 individuals who provided stool samples on days 0, 118 and 153 and were treated on days 85 and 125, 113 (87%) were infected with S. mansoni before treatment. The overall geometric mean faecal egg count of the infected individuals was 478 eggs/g. Four weeks after the first treatment (day 118), the overall cure rate was only 42.5% and the overall reduction in intensity of infection was 70.7%. However, 4 weeks after the second treatment (day 153), the overall cure rate rose to 76.1% and the overall reduction in intensity was 88.1%. The greatest increase in cure rate between the 2 treatments was in those individuals who were initially the most heavily infected (> 1000 eggs/g). There was no apparent difference in cure rate between younger (< 20 years) and older individuals (> 20 years). No evidence for the existence of a PZQ tolerant strain of S. mansoni was found. Two treatments of PZQ 40 mg/kg, 40 d apart, were sufficient to give an adequate cure rate and high reductions in the intensity of infection. As there was insufficient time for reinfection between treatment and follow-up to result in egg production, the low cure rate observed after one treatment was probably the result of a combination of high infection intensity and the maturation of pre-existing prepatents S. mansoni infections.

Gastrointestinal nematode infections of first-grazing season calves in Western Europe: general patterns and the effect of chemoprophylaxis

Research on the prevention of gastrointestinal nematode infections of cattle has mainly concentrated on comparing a specific chemoprophylactic treatment system to an untreated control group on a particular farm. Here, the results from analysis of 85 studies involving over 2000 first grazing season (FGS) calves put onto pasture for at least 4 months from late spring/early summer over a 26-year period in 13 countries in Western Europe are presented. Both control and chemoprophylactic treated FGS calf groups were considered. All chemoprophylactic systems (slow- and pulse-release boli, strategic treatments) were given early in the grazing season. Two general infection levels emerged--sub-clinical (32 studies) and clinical (53 studies). The sub-clinical infections were characterised by no clinical symptoms of parasitic gastroenteritis (PGE) being observed in the control groups. Mean faecal egg counts in the clinical control groups were significantly higher than those for sub-clinical control groups for almost the entire season with overall peaks of 275 and 100 EPG respectively. Maximum pasture larval counts were also significantly higher in the clinical control groups with 44% of clinical pastures > 10,000 L3 kg(-1) dry herbage by the end of the FGS, compared to only 15% of sub-clinical pastures. There was a significant positive relationship between log transformed worm burdens from tracers put onto pastures for 2 weeks and the corresponding pasture larval count. No evidence of density dependence in tracer worm burden was observed. Weight gains in the clinical control groups (375 g/day) were significantly lower than those of the sub-clinical control groups (530 g/day). No symptoms of PGE were observed in any of the chemoprophylactic treated groups, but in those studies with an outbreak of PGE in the control group, the treated groups had significantly higher faecal egg and pasture larval counts than treated groups in sub-clinical studies. The overall weight gain in chemoprophylactic treated calves in clinical studies (600 g/day) was significantly lower than the chemoprophylactic treated calves in sub-clinical studies (690 g/day), and was not significantly different from the weight gain of control calves in sub-clinical studies. These results indicate that on heavily infected pastures, chemoprophylaxis will prevent PGE, but calves will still suffer production losses.

Gastrointestinal nematode infections of first-grazing season calves in Western Europe: Associations between parasitological, physiological and physical factors

Analysis of 85 studies on gastrointestinal nematode infections in first-grazing season (FGS) calves is presented. The studies cover a 26-year period and were carried out in 13 countries in Western Europe. Both control and chemoprophylactic-treated (early in the season) FGS calf groups were included. In 53 of the 85 studies, clinical outbreaks of parasitic gastroenteritis (PGE) were observed during the FGS in the control groups. The mean initial age (and weight) of the control calf group was significantly associated with PGE outbreaks: 82% of control calf groups < or = 6 months of age had outbreaks of PGE, compared to only 33% of control calf groups > 6 months of age. In 92% of trials where the geometric mean faecal egg count (MFEC) was > or = 200 EPG on Day 56, PGE outbreaks were observed, but where it was < 200 EPG, only 29% had PGE. The use of these two factors in assessing the likelihood of PGE outbreaks in untreated calf groups in the future FGS is therefore, proposed. No chemoprophylactic-treated groups had PGE, but there was a highly significant negative relationship between maximum faecal egg counts in the chemoprophylactic-treated calves and the proportion of the trial covered by the different chemoprophylactic systems. Higher stocking densities were significantly associated with higher pasture contamination in both control and chemoprophylactic-treated calves. A highly significant positive relationship between the weight gained in the chemoprophylactic-treated groups and the estimated duration of the various chemoprophylactic systems was found, but there were large variations in weight gains (60-160 kg) between groups even with the same chemoprophylactic. Despite this and other highly significant associations, it was not possible to indicate what weight gains were obtained by the end of the FGS, from factors measured early in the FGS.

The epidemiology of a recent focus of mixed Schistosoma haematobium and Schistosoma mansoni infections around the "Lac de Guiers" in the Senegal River Basin Senegal.

Summary A village with mixed Schistosoma mansoni and S. haematobium infections (probably in a early endemic phase) was identified around the Lac de Guiers in the Senegal River Basin. In documenting the epidemiology of both schistosomes, we focused on prevalence and intensity of infection, transmission patterns and the impact of treatment. S. mansoni prevalences (near 100%) and egg counts (overall geometric mean eggs per gram of faeces (epg) of 589 were high in all age groups, with 35% of individuals excreting > 1000 epg, and showing a slow decline in egg output only after the age of 30 years. The overall prevalence (28%) and egg counts (2% > 50 eggs/10 ml) of S. haematobium were low, with mean counts of 6.3 eggs/10 ml. Maximal mean S. mansoni egg counts were found in 5–9 year‐old boys and in 15–19 year‐old girls; S. haematobium maximal counts in 1–4 year‐old boys and in girls aged 5–9. Extremely high Biomphalaria pfeifferi infection ratios were recorded over the whole year. Following a single treatment, re‐infection was rapid with prevalences and mean egg counts of both Schistosoma species reaching pretreatment levels within 7 months.

The determination at housing of exposure to gastrointestinal nematode infections in first-grazing season calves.

Various parameter estimates were assessed at housing in calves that had been exposed to gastrointestinal nematodes during a first grazing season. The analysis involved 41 groups of first grazing season (FGS) calves on 15 different farms in Belgium and comprised groups that had received chemoprophylactic treatment and untreated controls. Serum pepsinogen levels gave the clearest division between chemoprophylactic-treated calf groups (all were <2.6 U tyr), and untreated calf groups in which sub-clinical (range: 2.0-4.1 U tyr) and clinical infections (range 3.7-6.3 U tyr) occurred. There was also a tight relationship between individual pepsinogen values and adult Ostertagia burdens obtained at slaughter. In chemoprophylactic-treated groups there was a significant negative relationship between mean serum pepsinogen levels at housing and the proportion of the grazing season covered by different chemoprophylactic systems. Although only limited data on crude adult Ostertagia antigen ELISA were available, a good relationship between optical densities and estimated exposure was also found. The parasitological parameters, faecal egg counts and pasture Ostertagia larval counts at housing, and weight gain per day, gave less clear divisions among the three categories (chemoprophylaxis, sub-clinical and clinical). Distinguishing how much exposure a calf group has experienced during a first grazing season could help in designing more appropriate control measures for the FGS calves in the next year, assuring good protection and at the same time allowing sufficient exposure for the development of acquired immunity to Ostertagia, and for this serum pepsinogen is recommended.

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.

Diagnosis of larval cyathostominosis in horses in Belgium.

Between October 1996 and May 1997,94 horses which were suspected of being infected with strongyles were examined clinically, and samples of faeces were examined for strongyle eggs and cyathostome larvae (L4) and adults. Blood samples were monitored for total protein, albumin and β-globulins. In 28 of the horses (30 per cent) cyathostome L4 and adults were detected in the faeces, and were significantly associated with the horses condition, the occurrence of diarrhoea, with lower concentrations of total protein and albumin, and with higher percentages of β-globulin. Thirty-four of the horses (36 per cent) were excreting strongyle eggs, but in these animals the associations were with high concentrations of total protein and albumin, and lower percentages of β-globulin. The results showed that during the winter, a horse in poor condition which has diarrhoea, an albumin concentration less than 20 g/litre, and a ratio of albumin:globulin less than 0.7 is very likely to be infected with L4 and adult stages of cyathostomes.

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.

Index of potential contamination for schistosomiasis

Schistosomiasis occurs under a wide variety of climatic, geographical and other conditions. The basic reason for the transmission of schistosomes is, however, the low level of sanitation in endemic areas with the result that faeces or urine, or both, containing schistosome eggs get into water that contains freshwater snails susceptible to infection. Unfortunately, the degree of contamination of natural habitats with schistosome ova is difficult to estimate; consequently, there are few data on how much contamination, relative to a defined snail population density, is necessary to initiate or maintain transmission of schistosomiasis. This article discusses a little-used method to estimate the degree of contamination or transmission - the index of potential contamination (IPC). The expected changes in IPC after praziquantel treatment will be considered, as well as the level of reduction in IPC that might be needed to affect transmission or reduce morbidity.

The effect of different treatment regimens on the epidemiology of seasonally transmitted Schistosoma haematobium infections in four villages in the Senegal River Basin, Senegal

This paper describes the present epidemiological situation of Schistosoma haematobium in 4 villages in the middle valley of the Senegal River Basin, in terms of level and intensity of infection, seasonality of transmission, and intermediate hosts, and the effect of different treatment schedules with praziquantel on the overall infection levels and re-infection rates. The longitudinal study involving 7 surveys was carried out between June 1995 and March 1997 in Diatar, Guia, Donaye and Niandane. The prevalence and intensity of infection remained low throughout the survey (< 55% and < 12 eggs/10 mL urine), and there were no systematic differences in the prevalence or intensity of infection between men and women. Before treatment, infections were highly aggregated in individuals and were concentrated in children (aged < 15 years) with 85% of the potential contamination; no individual aged > 24 years produced > 50 eggs/10 mL urine. Using WHO guidelines mass treatment was given to all Diatar and Guia villagers in December 1995, whereas in Donaye and Niandane only individuals positive for eggs were treated. Six weeks post-treatment cure rates in all villages were > 80%, with marked declines in levels of infection (< 20% and < 4.5 eggs/10 mL). By March 1997 infection levels in Donaye and Niandane had returned to pre-treatment levels, whereas in the 2 mass-treated villages (Diatar and Guia) infection levels were still markedly reduced compared to pre-treatment levels. Rates of conversion were very low between all surveys; however, there was an apparent high level of reversion (> 20%), due to the alternation of individuals apparently positive and negative between surveys. Water and infected snails were present from June to March. Therefore, owing to the high aggregation of infections in children, the low overall infection levels and the transmission period, it is suggested that in this area the best treatment schedule would be selective treatment of school-aged children in March/April, probably on an annual basis.