Faecal Egg Output Research Articles

Epidemiology of gastrointestinal nematode parasitism in a commercial sheep flock and its implications for control programmes

The epidemiology of nematode infections in a uk commercial crossbred sheep flock was studied from January 2004 to January 2005. The ewes were treated orally with moxidectin when they were...

A survey of seasonal patterns in strongyle faecal worm egg counts of working equids of the central midlands and lowlands, Ethiopia

A study was conducted for two consecutive years (1998-1999) to determine the seasonal patterns of strongyle infection in working donkeys of Ethiopia. For the purpose 2385 donkeys from midland and lowland areas were examined for the presence of parasitic ova. A hundred percent prevalence of strongyle infection with similar seasonal pattern of strongyle faecal worm egg output was obtained in all study areas. However, seasonal variations in the number of strongyle faecal worm egg output were observed in all areas. The highest mean faecal worm egg outputs were recorded during the main rainy season (June to October) in both years in all areas. Although an increase in the mean strongyle faecal egg output was obtained in the short rainy season (March-April) followed by a drop in the short dry season (May), there was no statistically significant difference between the short rainy season and long dry season (Nov-Feb) (P > 0.05). A statistically significant difference however, was obtained between the main rainy season and short rainy season, and between the main rainy season and dry season (P < 0.05). Based on the results obtained it is suggested that the most economical and effective control of strongyles can be achieved by strategic deworming programme during the hot dry pre-main rainy season (May), when the herbage coverage is scarce and helminthologically 'sterile', and the arrested development of the parasites is suppose to be terminating. This could insure the greatest proportion of the existing worm population to be exposed to anthelmintic and also reduces pasture contamination and further infection in the subsequent wet season.

Equine parascarosis under the tropical weather conditions of Ethiopia: a coprological and postmortem study

A cross-sectional coprological survey in the regions of Ada, Akaki, Bereh and Boset, and a retrospective postmortem investigation were conducted to study the epidemiology of Parascaris equorum in donkeys and horses in Ethiopia. Faecal samples from 803 working donkeys and 402 horses were collected, and the numbers of worms recovered from 112 donkeys examined postmortem between 1995 and 2004 were analysed. There was a high prevalence of infection and faecal egg output of P equorum in both donkeys and horses, and the severity of the infection in donkeys was increased irrespective of their age. The prevalence of the infection in the donkeys was 51.1 per cent and in the horses 16.2 per cent, and the prevalence in the donkeys examined postmortem was 55 per cent. There was no significant difference between different age groups of donkeys in either the prevalence or the intensity of the infection. The prevalence of the infection was significantly higher in the Ada and Akaki regions than in the Bereh and Boset regions.

Effect of rainfall and temperature on liver and rumen fluke infestations of bovines in Sri Lanka

Fecal fluke egg output of bovines from three selected farms at Ma Eliya (site A), Ma Eliya (site B) and Delathure (site C) in Ja-Ela area of Gampaha district in Sri Lanka was examined for six months period from July to December 2006. The mean egg output of the animals of site A, B and C were 255, 84 and 95 eggs/g of feces respectively. Statistical analysis showed that mean fecal fluke egg output was significantly different between sites (df= 2, f= 126.05, p=0.000) and also between months (df= 5, f= 7.31, p=0.000). Regression analysis revealed that the fecal fluke egg output had a positive relation with rainfall (r2=0.6178) and a negative relation with temperature (r2= 0.6486). The female cattle had a higher fecal fluke egg output (x =202.76) than the male cattle (x =116.97) but egg output did not significantly differ. Also there was an increasing trend of mean fecal fluke egg count with the increment in the age of cattle (r2= 0.6057). Rumens and livers of slaughtered cattle and buffaloes from the study area were examined for fluke infections. Specimens were identified by making histological sections. One species of liver fluke, Explanatum explanatum and four rumen flukes, Paramphistomum spp., Gastrothylax crumenifer, Carmyerius spp., and Fischoederius elongates were identified. Two other flukes belonging to the family Gastrothylacidae were also found from the rumen of buffalo. Explanatum explanatum was found to be a great cause of condemnation of livers at slaughterhouses in Sri Lanka. Keywords: liver and rumen flukes, bovines, influence of climate, Sri Lanka. International Journal of Biological and Chemical Sciences Vol. 1 (3) 2007: pp. 229-236

Vaccine testing of a recombinant activation‐associated secreted protein (ASP1) from Ostertagia ostertagi

Previous vaccination trials against the economically important cattle parasite Ostertagia ostertagi have indicated the protective capacity of activation-associated secreted proteins (ASPs). The further development of these antigens into a commercial vaccine will require their recombinant expression. The aim of the current study was to clone and express Oo-asp1 in a baculovirus expression system and to evaluate the protective capacity of the recombinant protein against an O. ostertagi challenge infection in cattle. The full coding sequence of Oo-asp1 was cloned in a baculovirus expression vector in frame with a carboxy-terminal Histidine tag and recombinant virus was used to infect an insect cell culture. Western blot analysis with anti-His and anti-Oo-ASP1 antibodies showed the production of recombinant Oo-ASP1. The cell pellet containing the recombinant was subsequently used to immunize seven calves three times intramuscularly with QuilA as adjuvant. Control animals were solely injected with the QuilA adjuvant. The challenge infection with O. ostertagi consisted of 30,000 L3 larvae per animal given over 30 days (1000 larvae/day, 5 days/week) and started the same day as the final immunization. Immunization with the recombinant Oo-ASP1 did not result in any level of protection against the challenge infection. There was no reduction in faecal egg output or in worm burdens. Moreover, Western blot analyses and ELISA indicated that, although the animals raised an antibody response against the recombinant Oo-ASP1, there was hardly a response against the native Oo-ASP1, suggesting that the baculovirus expressed recombinant was wrongly folded or lacked essential secondary modifications. Further analysis of the structure of the native ASPs and their glycosylations is being done.

Experimental infection and adaptation ofRodentolepis nanato the Mongolian jirdMeriones unguiculatus

A mouse-derived strain of Rodentolepis ( = Hymenolepis) nana was transferred to the Mongolian jird Meriones unguiculatus. It was found that M. unguiculatus has low susceptibility to R. nana mouse isolates. Likewise, adaptation of the parasite to jird hosts, in the absence of dexamethasone treatment, was not demonstrable, at least during ten-passage trials. Nevertheless, the parasite was able to establish, grow and develop to gravid adults in M. unguiculatus treated daily with dexamethasone. Prepatent periods in dexamethasone-treated jirds in ten-passage series ranged from 10 to 17 days post-infection (DPI), the average being 12 days, and the patent periods lasted from 18 to 30 DPI, with an average of 25 days. The population pattern of faecal egg output in immunosuppressed jirds suggests that under a daily dexamethasone treatment protocol, the parasite is able to maintain egg production as long as treatment is sustained.

Real-time PCR for detection of low intensity Schistosoma japonicum infections in a pig model

Decades of successful Schistosoma japonicum control have increased the interest in how to diagnose low intensity infections. A real-time PCR assay targeting the mitochondrial NADH dehydrogenase I gene in S. japonicum was evaluated in infected pigs with very low egg output. Six out of 12 S. japonicum infected pigs were treated with praziquantel 8 weeks after infection and all pigs were followed for 16 weeks post-infection. One commercial and one non-commercial extraction method were evaluated in combination with PCR on faecal samples. PCR with either extraction method were equally sensitive as the DBL-filtration/sedimentation technique in the acute, productive stage. PCR recovered slightly more positive samples in the chronic stage, but most faecal samples were negative for both PCR and microscopy from week 9 post-infection irrespective of treatment. IgG antibody titers against soluble egg antigen IgG remained high throughout the study in both the treated and non-treated group. PCR was consistently negative in serum and urine samples and negative in most of the caecal biopsies. We conclude that the S. japonicum faecal PCR is a highly sensitive test. However, in clinical samples when faecal egg output almost reaches nil in the chronic stage despite persistent worm burdens, both the faecal PCR and microscopy results were negative. Real-time PCR is less labour intensive than most microscopy methods, but has a higher material cost per sample.

Toxicity and anthelmintic efficacy of crude aqueous of extract of the bark of Sacoglottis gabonensis

The water extract of the stem bark of Sacoglottis gabonensis was evaluated for its preliminary acute toxicity and anthelmintic efficacy against gastro-intestinal nematodes of small ruminants and mice in both in vitro and in vivo studies. Intra-peritoneal administration of doses ranging from 400 to 3200 mg/kg of the aqueous stem bark extract produced varying degrees of toxicity manifested as depression, drowsiness and unsteady gait, paralysis of the hind limbs, dyspnoea, coma and death. The pathological lesions noted at necropsy were mainly congestion and edema of the lungs, bronchi and bronchioles and hepatomegally with focal necrosis of liver cells. The severity of the clinical symptoms and pathological lesions were dose-related. In the in vitro study, the extract significantly ( P < 0.05) reduced the hatching of strongyline nematode eggs from naturally infected small ruminants. The 100 mg/ml concentration of the extract produced the highest (94.4%) inhibition on nematode egg hatch and the result was comparable to similar effect produced by either levamisole (100% at 15 mg/ml) or albendazole (99.7% at 6.25 mg/ml). In rats experimentally infected with Heligmosomoides polygyrus, treatment with the S. gabonensis stem bark aqueous extract significantly ( P < 0.05) reduced adult worm burden and completely inhibited faecal egg output 5 days post treatment.

Vaccination of goats with recombinant galectin antigen induces partial protection against Haemonchus contortus infection

The efficacy of vaccination against Haemonchus contortus infection with two recombinant proteins, rHco-gal-m and rHco-gal-f, was studied in 9-10-month-old goats. Vaccination with 100 microg protein reduced faecal egg output and worm burdens by 37.25% and 41.1%, respectively. Corresponding reductions with 200 microg protein were 48.03% and 46.19%. Vaccinated groups had significantly higher IgG levels than the negative and positive controls. Significant negative correlations were detected between IgG level, mucosal homogenate IgA concentration, haemoglobin and abomasal worm burden at necropsy. By contrast a positive correlation was found between the percentage of B cells, monocytes and abomasal worm burden. These findings suggested that vaccination with a combination of recombinant rHco-gal-m/f proteins had a role in protecting goats against H. contortus infection.

Epidemiology of subclinical dairy cow nematode infections on five farms in England in 2002 and a comparison with results from 1978 to 1979

A detailed study of the epidemiology of subclinical nematode infections in adult dairy cows was conducted on five well-managed English dairy farms during the 2002 grazing season. These same farms had also participated in a similar study in 1978–1979 and thus provided a unique opportunity to compare the epidemiological findings after an interval of over two decades. Common factors, including the prevalence of infection, faecal worm egg output, pasture larval count and nematode genera present, and estimated daily larval intake at pasture, were compared between the two studies. Subclinical roundworm burdens, as judged by faecal egg counts, were widespread in dairy cows in 2002, but the prevalence of animals with patent infections and the magnitude of the worm egg output were significantly lower than in 1978–1979. Both the prevalence of infection and mean faecal worm egg output exhibited a marked seasonal peak during the summer months in 2002. Pasture larval numbers were, however, nearly three times higher in 2002 with Ostertagia dominating the nematode genera to which cows were exposed at pasture in both surveys. Factors considered likely to account for differences in parasite epidemiology include the marked increase in herd productivity over the intervening period, the increased proportion of Holstein genetics with the consequent increase in milk yield and feed intake, changes in grassland management and increased stocking rate seen on the majority of farms.

Faecal egg output and herbage contamination with infective larvae of species ofOstertagiaandOesophagostomumfrom naturally infected farmed sika deerCervus nipponin Lithuania

Faecal egg outputs and subsequent herbage larval contamination with third stage larvae (L3) of Ostertagia spp. and Oesophagostomum spp. from a herd of naturally infected sika deer Cervus nippon were examined in the same pasture in 2001/2002 in Lithuania. Sika deer were infected with Ostertagia circumcincta, O. kolchida, O. spiculoptera, Oesophagostomum radiatum, O. columbianum and O. venulosum. Faecal egg output in adult deer peaked in the spring during the periparturient period and also in late August, compared with a peak in egg output in calves during September to November. Herbage contamination with L3 of Ostertagia spp. peaked in June but larvae were not present on pastures from the end of September. Hence the highest risk of infection was in early born calves grazed on pastures in July. Infective larvae of Oesophagostomum spp. did not survive during the winter, but the nematodes were reintroduced onto the pastures by adult deer in the spring.

Individual administration of three tanniferous forage plants to lambs artificially infected with Haemonchus contortus and Cooperia curticei

We investigated direct anthelmintic effects associated with the feeding of fresh tanniferous forages against established populations of Haemonchus contortus and Cooperia curticei in lambs. Twenty-four parasite naive lambs were inoculated with a single dose of infective larvae of these two parasites 27 days prior to the start of the feeding experiment. Lambs were individually fed with either chicory ( Cichorium intybus), birdsfoot trefoil ( Lotus corniculatus), sainfoin ( Onobrychis viciifolia) or a ryegrass/lucerne mixture (control) for 17 days. Animals where then united to one flock and subjected to control feeding for another 11 days to test the sustainability of potentially lowered egg excretion generated by tanniferous forage feeding. When compared to the control, administration of all tanniferous forages was associated with significant reductions of total daily faecal egg output specific to H. contortus (chicory: 89%; birdsfoot trefoil: 63%; sainfoin: 63%; all tests P < 0.05) and a tendency of reduced H. contortus worm burden (chicory: 15%; birdsfoot trefoil: 49% and sainfoin: 35% reduction). Irrespective of the condensed tannin (CT) containing fodder, no anthelmintic effects were found against C. curticei. Cessation of CT-feeding followed by non-CT control feeding did not result in a re-emergence of faecal egg counts based on faecal dry matter (FECDM) in any group, suggesting that egg output reductions are sustainable. The moderate to high concentrations of CTs in birdsfoot trefoil (15.2 g CTs kg −1 dry matter (DM)) and sainfoin (26.1 g CTs kg −1 DM) were compatible with the hypothesis that the antiparasitic effect of these forages is caused by their content of CTs. For chicory (3 g CTs kg −1 DM), however, other secondary metabolites need to be considered. Overall, birdsfoot trefoil and in particular sainfoin seem promising candidates in contributing to an integrated control strategy against H. contortus not only by mitigating parasite related health disturbances of the host but also by a sustained reduction of pasture contamination.

Observations on the emergence of multiple anthelmintic resistance in sheep flocks in the south-east of Scotland

Multiple resistance to benzimidazole, imidazothiazole and macrocyclic lactone anthelmintics is an emerging problem in the south-east of Scotland. The general management and nematode control strategies employed in four affected flocks (flocks 1–4) were investigated in an attempt to identify the risk factors which might have led to the appearance of production limiting disease associated with anthelmintic resistance. The important risk factors for multiple anthelmintic resistance could not be confirmed and it proved easier to criticise nematode control practices on theoretical grounds, than to propose practical solutions. It seems likely that different risk factors were involved in the four flocks. Lambs in flocks 1 and 2 had been treated with an anthelmintic at 3–4 weekly intervals with the aim of achieving suppressive nematode control, while sheep in flock 1 had been treated with an anthelmintic after they were moved onto clean grazing. Recently lambed ewes had been treated with moxidectin in three of the four flocks, with the aim of controlling their periparturient rise in faecal nematode egg output. All of these factors might have contributed to the emergence of multiple anthelmintic resistance, because they could have led to anthelmintic treatments at times when the nematode population in refugia was small, compared to that in the sheep. Annual rotation of the anthelmintic group was compromised by the emergence of benzimidazole resistance and did not prevent the emergence of multiple resistance in any of the flocks described, although the practice may have slowed the development of resistance. Underdosing may have selected for benzimidazole and imidazothiazole resistance in flock 2, associated with inaccurate estimation of the weights of terminal sire lambs. These investigations also highlighted problems associated with the diagnosis of anthelmintic resistance, in particular the confounding effects of the onset of host immunity to nematode parasites, the possible influence of the age of the adult nematode population, and the insensitivity of the undifferentiated faecal egg count reduction test in situations where resistance is emerging.

Dynamics of Infestation of Cattle and Pasture by Gastrointestinal Nematodes in an Atlantic Temperate Environment

The objective of the present study was to determine the dynamics of infestation of cattle and pasture by gastrointestinal nematodes in a mild humid environment in northwestern Spain. For this, infestation of pasture by free-living stages (L3), dynamics of faecal egg output, blood pepsinogen levels and worm burden in slaughtered animals were quantified. The results showed a high degree of annual variability, which was dependent on weather conditions. The seasons were clearly defined in the study area, with mild humid winters and relatively dry summers registered throughout the years of the study. Infestation of pasture by larvae varied from year to year, peaking during August in the first year, between August and December in the second year, and during October in the third year. The annual variation was mainly due to weather conditions, particularly the amount of rain in summer. The patterns of faecal egg output were similar in the first and third grazing seasons, with maximum levels observed in May/June; however, in the second year, the peak was reached in October. Blood pepsinogen levels increased from pasture turnout (March/April) until the end of the grazing season (November/December), reaching maximum values from August/September onwards. The nematode parasite species identified at necropsy were Ostertagia osteragi, O. lyrata, Cooperia oncophora, C. macmasteri, C. punctata and Trichuris ovis, with O. ostertagi and C. oncophora predominating. In faecal cultures, the following genera were also identified: Haemonchus, Trichostrongylus, Nematodirus, Bunostomum, Oesophagostomum and Strongyloides. There was a significant correlation (r=0.97, P<0.01) between worm burden (Ostertagia spp.) and pasture infestation (Ostertagia L3) 3 weeks prior to slaughter of the calves, and also between blood pepsinogen levels and pasture infestation by Ostertagia L3 (r=0.33, P<0.02). Correlations between worm burden and faecal egg output and between blood pepsinogen level and faecal egg output were not significant. The results obtained in the present study confirm that there is annual variability in the time-course of nematodosis in cattle, and demonstrate the importance of weather, particularly summer rainfall, in an Atlantic temperate environment.

Epidemiological studies of &lt;i&gt;Fasciola gigantica&lt;/i&gt; infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

During the period between January 1999 and December 2000, the distribution and seasonal patterns of Fasciola gigantica infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Cattle faecal samples were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas respectively. Patterns of distribution and seasonal fluctuations of the intermediate host-snail populations and the climatic factors influencing the distribution were also determined by sampling at monthly intervals for a period of 24 months (November 1998 to October 2000) in six dams and six streams in the highveld and in nine dams in the lowveld communal grazing areas. Each site was sampled for relative snail density and the vegetation cover and type, physical and chemical properties of water, and mean monthly rainfall and temperature were recorded. Aquatic vegetation and grass samples 0-1 m from the edges of the snail habitats were collected monthly to determine the presence or absence of F. gigantica metacercariae. Snails collected at the same time were individually checked for the emergence of larval stages of F. gigantica. A total of 16264 (calves 5418; weaners 5461 and adults 5385) faecal samples were collected during the entire period of the study and 2500 (15.4%) of the samples were positive for F. gigantica eggs. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), for adult cattle than calves (P < 0.01) and in the wet season over the dry season (P < 0.01). Faecal egg output peaked from August/September to March/April for both years of the study. Lymnaea natalensis, the snail intermediate host of F. gigantica was recorded from the study sites with the highveld having a significantly higher abundance of the snail species than the lowveld (P < 0.01). The snail population was low between December and March and started to increase in April reaching a peak in September/October. The number of juvenile snails peaked between April and August. The mean number of snails collected was negatively correlated with rainfall and positively correlated with temperature. Mean number of snails collected was also positively correlated with Potamogeton plant species and negatively correlated with Cyperus plant species. However, none of the L. natalensis collected from the habitats were found shedding Fasciola cercariae. Metacercariae were found on herbage from the fringes of the snail habitats between February and August for both years, with most of the metacercariae concentrated on herbage 0-1 m from the banks of the habitats. Based on the findings of this study, anthelmintic treatment should be administered in December/January to control chronic and mature fasciolosis. A second treatment should be given in April/May to reduce pasture contamination and subsequently snail infection, as this is the time the snail population starts to build up. To control acute fasciolosis due to the immature liver flukes a third treatment should be given in August. The first application of molluscicides to control the snail intermediate hosts can be done in June the time when the snail is harbouring the parasite and a second application in September in order to kill new generations of infected snails

Epidemiological studies of &lt;i&gt;Schistosoma mattheei&lt;/i&gt; infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

During the period between January 1999 and December 2000, the distribution and seasonal patterns of Schistosoma mattheei infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Faecal samples of cattle were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas, respectively. Patterns of distribution and seasonal fluctuations of the intermediate host-snail populations and the climatic factors influencing the distribution were also determined at monthly intervals from November 1998 to October 2000, a period of 24 months, in six dams and six streams in the highveld and nine dams in the lowveld communal grazing areas. Monthly, each site was sampled for relative snail density, the vegetation cover and type, and physical and chemical properties of the water. Mean monthly rainfall and temperature were recorded. Snails collected at the same time were individually examined for shedding of cercariae of S. mattheei and Schistosoma haematobium. A total of 16264 (5418 calves, 5461 weaners and 5385 adults) faecal samples were collected during the entire period of study and 734 (4.5%) were positive for S. mattheei eggs. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), calves compared to adult cattle (P < 0.01) and the wet season compared to the dry season (P < 0.01). Faecal egg output peaked from October/ November to March/April for both years of the study. Bulinus globosus, the snail intermediate host of S. mattheei was recorded from the study sites with the highveld having a significantly higher abundance of the snails than the lowveld (P < 0.01). Monthly densities of B. globosus did not show a clear-cut pattern although there were peaks between March/May and September/November. The mean number of snails collected was positively correlated with the water plants Nymphaea caerulea and Typha species. Overall, 2.5% of B. globosus were shedding Schistosoma cercariae. In the highveld, 2.8% of B. globosus were infected with schistosome cercariae and 1.5% in the lowveld, with the figures at individual sites ranging from 0-18.8% in the highveld and from 0-4.5% in the lowveld. The cercariae recorded here were a mixture of S. mattheei and S. haematobium since they share the same intermediate host. The transmission of Schistosoma cercariae exhibited a marked seasonal pattern, being more intensive during the hot, dry season (September/November).

The detection limits for estimates of infection intensity in schistosomiasis mansoni established by a study in non-human primates

In human schistosomiasis mansoni, it is impossible to directly determine worm burden and hence infection intensity, so surrogates must be used. Studies on non-human primates revealed a linear relationship between worm burden and three surrogates, faecal egg output, circulating anodic and circulating cathodic antigens. By regression, the thresholds of detection were determined as 40, 24 and 47 worms, respectively. These observations provide a quantitative basis for the contention that low intensity infections in humans are being missed. The significance for estimates of disease prevalence, evaluation of the effects of chemotherapy and the implementation of vaccine trials is emphasised.

Seasonal patterns of gastrointestinal nematode infections in sheep in a semi-arid Kajiado District of Kenya

The seasonal patterns of trichostrongylid nematode infections in Dorper yearlings in a semi-arid area of Kajiado District, Kenya were investigated by analysis faecal egg output, herbage infectivity and post-mortem worm recovery. Rectal faecal samples from 60 animals as well as herbage samples from their grazing fields were collected at three weeks intervals between May 1999 and December 2001. Fecal egg counts and herbage larval counts closely followed the rainfall distribution pattern. Major peaks in egg output occurred between December and August as a result of increased pasture infectivity and minor peaks between September and November following maturation of hypobiotic larvae of Haemonchus . Self-cure occurred in August/ September and November/ December. From September 2000 to July 2001, post-mortem worm counts conducted on 24 yearlings permanently on pastures during the dry and wet seasons showed mixed infections where Trichostrongylus, Haemonchus and Oesophagostomum occurred in 91.7%, Cooperia in 83.3%, Trichuris and Strongyloides in 4.1% of the animals. Adult and immature worms co-existed in proportions that varied with seasons, where Haemonchus survived the dry season mainly as hypobiotic larvae and Trichostrongylus species as an adult worm population. The mean wet season worm counts in both seasons were considered moderate, usually associated with sub-clinical helminthosis and decreased productivity. There is need, therefore, to control such infections in sheep within the study area in order to achieve higher productivity. Bulletin of Animal Health and Production in Africa Vol. 54(1) 2006: 1-6

Previous or Ongoing Schistosome Infections Do Not Compromise the Efficacy of the Attenuated Cercaria Vaccine

A current or previous schistosome infection might compromise the efficacy of a schistosome vaccine administered to humans. We have therefore investigated the influence of infection on vaccination, using the baboon as the model host and irradiated Schistosoma mansoni cercariae as the vaccine. Protection, determined from worm burdens in test and controls, was not diminished when vaccination was superimposed on a chronic infection, nor was it diminished when it followed a primary infection terminated by chemotherapy. Protection was also assessed indirectly based on fecal egg output and circulating antigen levels, as would be the case in human vaccine trials. In almost all instances, these methods overestimated protection, sometimes with discrepancies of >20%. The overwhelming immune response to egg deposition in infected animals made it difficult to discern a contribution from vaccination. Nevertheless, the well-documented immunomodulation of immune responses that follows egg deposition did not appear to impede the protective mechanisms elicited by vaccination with attenuated cercariae.

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

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