Gastrointestinal nematode infection affects overall activity in young sheep monitored with tri-axial accelerometers

Animals suffering from parasitism typically display altered grazing behaviour and a voluntary reduction in feed intake. These changes are potentially important as indicators of disease. Recent advances in sensor technologies provide the opportunity to objectively measure animal activity while on pasture. Tri-axial accelerometers measure body movement in terms of acceleration, which can then be used to estimate physical activity over time. This study investigated if tri-axial measures of overall activity can be used to assess the impact of gastrointestinal nematode (GIN) infection in young sheep. To address this, the overall activity, faecal nematode egg count (FEC) and body weight of two treatment groups of Romney X Suffolk ram lambs were compared. Animals were monitored for four days using tri-axial accelerometer sensors mounted on a ram mating harness after 42-days grazing on contaminated pasture. On Day 0, all lambs were given anthelmintics. Subsequently, a Suppressive Treatment Group (n = 12) was treated with anthelmintics every two weeks. An Untreated Group (n = 12) did not receive further anthelmintics. Overall activity levels were monitored from Day 42 - 46. Activity level was calculated as vectorial dynamic body acceleration (VeDBA). Anthelmintic treatment had a significant effect on FEC but there was no evidence found for a treatment effect on body weight growth over the 42-day period. An effect of treatment and lamb starting weight on overall activity was found (beta = -0.74, 95 % CI -1.17 to -0.30, p =  0.002), identifying a negative impact of parasitism on activity in heavier animals. These results highlight the usefulness of this approach in assessing the effect of GIN parasitism on sheep monitored remotely. If a threshold value of activity could be determined, it could provide a useful tool for farmers and managers that serves as an early indicator of parasitism in sheep.

Infection by cyst nematodes induces rapid remodelling of developing xylem vessels in wheat roots

Cyst nematodes induce host-plant root cells to form syncytia from which the nematodes feed. Comprehensive histological investigation of these feeding sites is complicated by their variable shape and their positions deep within root tissue. Using tissue clearing and confocal microscopy, we examined thick (up to 150 μm) sections of wheat roots infected by cereal cyst nematodes (Heterodera avenae). This approach provided clear views of feeding sites and surrounding tissues, with resolution sufficient to reveal spatial relationships among nematodes, syncytia and host vascular tissues at the cellular level. Regions of metaxylem vessels near syncytia were found to have deviated from classical developmental patterns. Xylem vessel elements in these regions had failed to elongate but had undergone radial expansion, becoming short and plump rather than long and cylindrical. Further investigation revealed that vessel elements cease to elongate shortly after infection and that they later experience delays in secondary thickening (lignification) of their outer cell walls. Some of these elements were eventually incorporated into syncytial feeding sites. By interfering with a developmental program that normally leads to programmed cell death, H. avenae may permit xylem vessel elements to remain alive for later exploitation by the parasite.

Effect of gastrointestinal nematodes on serum copper and phosphorus of growing beef calves in northwestern Argentina

The aim of this work was to study the effect of gastrointestinal nematodes (GINs) on copper (Cu) and phosphorus (P) in blood of beef cattle in two ranches (R1 and R2) located in northwestern Argentina. In 2015-2016 (R1) and 2016-2017 (R2), in each ranch, 22 weaned female calves were divided into two groups: calves treated systematically with 200 mcg/kg moxidectin every 45-50 days (TG) and untreated calves (UTG). The following parameters were measured: number of fecal eggs (epg), fecal cultures, serum Cu and P levels, and live weight gain (LWG). Differences between groups were compared using analysis of variance and Tukey test. GIN infections in both ranches were subclinical and moderate, showing the highest epg (R1 = 907 ± 754; R2 = 1049 ± 1040) by mid-winter. Epg values of TG groups were always negligible (> 93% of moxidectin efficacy). The dominant nematode genera were Cooperia and Haemonchus. The average serum Cu values (μg/dl) indicated low (R1 = 49.7 ± 18) and severe (R2 = 27.2 ± 14) deficiency. The effect of treatments was evident in both ranches from late winter, with TG showing significantly (p < 0.01) higher serum levels in winter, spring, and early autumn (R1 = 65.1, 50.9, and 60.3; R2 = 48.0, 25.7, and 22.4) than UTG (R1 = 44.3, 33.9, and 32.9; R2 = 25.5, 18.2, and 16.4). There were no differences in serum P levels between groups. LWG of TG increased significantly (p < 0.008) (27.2% in R1 and 38.6% in R2), with respect to those of UTG. This study showed a negative effect of GIN on serum Cu values in moderately infected growing calves.

The effect of gastrointestinal nematode infection level on grazing distance from dung

Avoiding grazing near feces is an efficient strategy to prevent parasitic infection and contamination; therefore, in the evolution of herbivorous species, this behavior may have developed as a mechanism to protect the host against infection by gastrointestinal nematodes. The aim of this study was to assess whether grazing distance from dung is related to the level of parasitic infection in cattle. Based on Fecal Egg Count (FEC) means, 18 castrated male steers, aged 18 months, were divided into three groups: High (FEC ≥ 315); Medium (FEC = 130–160); and Low (FEC = 40–70). To analyze the response to a new natural infection by gastrointestinal nematodes and to standardize infection levels, all animals received anthelmintic treatment at twenty days prior to field observation. Three observers simultaneously collected data on grazing behavior for 2.5 hours/week for 12 weeks. Observers recorded the distance when grazing occurred at less than one meter from dung. Every two weeks, fecal samples were collected for FEC, as well as serum samples to measure immunoglobulin G (IgG) levels against larvae and adult antigens of the parasitic species Haemonchus placei. All groups grazed farther from the dung on days of greater insolation (r = 0.62; P = 0.03). Animals with high levels of parasitism grazed farther from the dung (P < 0.05) but had lower levels (P < 0.0001) of IgG serum levels compared to those with medium and low levels of infection. FEC values varied over the experiment, remaining below 200 for the low and medium group and reaching 1000 (P < 0.01) for the animals with the highest rates of parasitism. Our results indicate that cattle showing high levels of parasitism are more likely to avoid contaminated areas than animals with lower infection levels, and the immune system seems to be involved in such behavior.

Spectral-domain optical coherence tomography appearance of a retinal nematode

A 65-year-old man presented with decreased visual acuity in his left eye of 10 days' duration. Ocular examination revealed visual acuity of 20/200 in the left eye caused by a visible retinal nematode (roundworm) located close to the fovea. Spectral-domain optical coherence tomography imaging showed the nematode in the retinal nerve fiber layer. The patient was followed up without treatment, and the nematode disappeared spontaneously after 5 weeks. Visual acuity in the affected eye improved to 20/25.

A pathogenic parasite interferes with phagocytosis of insect immunocompetent cells

Phagocytosis activity of hemocytes of the host Galleria mellonella (Lepidoptera) was modulated by the infection of the entomopathogenic nematode Steinernema feltiae (Rahbditida) and was found to be correlated with the opsonization of bacteria by hemolymph factors. The presence of nematodes resulted in a significative decrease in phagocytosis of bacteria by host hemocytes, both in in vivo and in in vitro assays. Host interacting proteins (HIPs), which appear to function as opsonic factors and are essential to perform immune responses, were removed by S. feltiae from host hemolymph, by means of its epicuticle binding properties. Host humoral factors sequestered by the parasite have been identified by monodimensional and 2D electrophoretic analysis. The data suggest that S. feltiae, living in association with symbiontic bacteria (Xenorhabdus nematophilus), develop an immune suppressive strategy to support its bacteria, which diminished the effectiveness of immunological surveillance by the host.

Early exposure of infants to GI nematodes induces Th2 dominant immune responses which are unaffected by periodic anthelminthic treatment

We have previously shown a reduction in anaemia and wasting malnutrition in infants <3 years old in Pemba Island, Zanzibar, following repeated anthelminthic treatment for the endemic gastrointestinal (GI) nematodes Ascaris lumbricoides, hookworm and Trichuris trichiura. In view of the low intensity of worm infections in this age group, this was unexpected, and it was proposed that immune responses to the worms rather than their direct effects may play a significant role in morbidity in infants and that anthelminthic treatment may alleviate such effects. Therefore, the primary aims of this study were to characterise the immune response to initial/early GI nematode infections in infants and the effects of anthelminthic treatment on such immune responses. The frequency and levels of Th1/Th2 cytokines (IL-5, IL-13, IFN-γ and IL-10) induced by the worms were evaluated in 666 infants aged 6–24 months using the Whole Blood Assay. Ascaris and hookworm antigens induced predominantly Th2 cytokine responses, and levels of IL-5 and IL-13 were significantly correlated. The frequencies and levels of responses were higher for both Ascaris positive and hookworm positive infants compared with worm negative individuals, but very few infants made Trichuris-specific cytokine responses. Infants treated every 3 months with mebendazole showed a significantly lower prevalence of infection compared with placebo-treated controls at one year following baseline. At follow-up, cytokine responses to Ascaris and hookworm antigens, which remained Th2 biased, were increased compared with baseline but were not significantly affected by treatment. However, blood eosinophil levels, which were elevated in worm-infected children, were significantly lower in treated children. Thus the effect of deworming in this age group on anaemia and wasting malnutrition, which were replicated in this study, could not be explained by modification of cytokine responses but may be related to eosinophil function.

Infants and very young children commonly become infected with intestinal nematode infections. However, the worm burdens are generally very light, so a beneficial effect of deworming on wasting malnutrition and anaemia in this age group which we have demonstrated was unexpected and the mechanism unclear. To investigate this, we have, for the first time, determined whether such worm infections in infants induce significant immune reactions which might be detrimental to nutrition and growth e.g. by inducing inflammation in the gut or by cytokine effects on erythropoiesis. We also determined if such responses are modulated by regular deworming over a 9 month period. Peripheral blood cells from infants infected with Ascaris and hookworms in particular responded to stimulation with worm antigens, producing predominantly Th2 cytokines. Although the Th2 cytokine responses in the periphery were not significantly altered by deworming, the levels of eosinophils, which are regulated by the Th2 cytokine, IL-5, were lower after treatment. It is possible that eosinophils play a role in gut pathology leading to wasting malnutrition and anaemia in the very young and that this effect is reduced by deworming.

In silico exploration of the effects of host genotype and nutrition on the genetic parameters of lambs challenged with gastrointestinal parasites

An in silico mathematical model was used to explore the effect of, and the interaction between, (i) nutrition, (ii) genotype for growth and (iii) genotype for resistance, on the estimates of genetic parameters for resistance and performance in a population of lambs trickle-challenged daily with 3,000 L3s of Teladorsagia circumcincta. A previously published model for nematode infections in sheep was developed to include heritable variation in sheep growth traits, as well as in immunologically controlled traits such as establishment of incoming larvae, mortality of the adult worms and fecundity of the adult female worms. The simulated population comprised 10,000 lambs, these being the offspring of 250 sires mated to 5,000 dams. The model assumed the lambs to be parasitologically naïve at weaning (2 months of age), at which point the trickle challenge commenced and the model was updated daily until slaughter (at 6 months of age). Dietary treatments included a good and a poor quality feed, offered ad libitum. Two genotypes for growth were assumed: (i) fast and (ii) slow growing. Three genotypes for resistance were used: (i) benchmark, (ii) susceptible and (iii) resistant, differing in their ability to cope with nematode infections. Genetic parameters for output traits, including growth rate, food intake, worm burden and faecal egg count were estimated using a linear mixed model, fitting sire as a random effect to capture genetic effects. Heritabilities and correlations were found to change over time. In general, the heritabilities of immunity traits increased over time, whereas genetic correlations between production and immunity traits became weaker. Diet had a significant effect on the means and the estimated correlations of output traits, while genotypes for growth and resistance had smaller effects. These results suggest that discrepancies between published genetic parameters for nematode resistance may be a function of environmental factors rather than differences in host genotype.

The pathogenic helminth parasites of eels

Although 63 and 55 species of helminths have been reported from each species of Atlantic eel and from 29 to 19 for each species of Pacific eel only the monogeneans Pseudodactylogyrus bini and P. anguillae and the nematode Anguillicola crassus, originally specific to species of Pacific eels, can be considered serious pathogens. None of the three are normally pathogenic to their preferred natural eel host species in the wild. Pseudodactylogyrus spp. only cause serious local gill damage when present on a host in large numbers under optimal conditions that facilitate transmission. This is the case in eel aquaculture, where infections can be controlled by drugs. Anguillicola crassus is only pathogenic to Anguilla anguilla and A. rostrata when Atlantic eels are introduced to the far east or when the parasites have been introduced to Europe. Here the parasite life cycle differs in that A. crassus can infect a wide range of intermediate hosts, employ paratenic hosts and survive as larvae for months in the swimbladder wall. This makes it an excellent colonizer. Its major pathogenic effects on eels result from haemorrhaging in, and thickening of, the swimbladder wall. It reduces the oxygen concentration in the swimbladder, reducing its ability to function as a hydrostatic organ, and increases the stress response of eels. In shallow lakes at warm temperatures this can result in mass mortalities. It is also feared that the parasite affects the ability of eels to migrate to the Sargasso Sea and so contributes to the decline in eel populations. Control by drug treatment is possible in culture, but not in the wild.

Parasitic pulmonary eosinophilia

Parasitic infections, although common in tropical and subtropical regions, are prevalent worldwide because of changing immigration patterns and in international travel. The burden of worm infection is enormous and the intensity of infection is usually high among the poor and in immunocompromised individuals. Pulmonary eosinophilia occurs in almost all metazoan infections. In the Western world, the most common infections are caused by Strongyloides, Ascaris, Toxocara, and Ancylostoma species. Most of the nematodes multiply within the human host and cause pulmonary eosinophilia during larval migration through the lungs. Despite larval migration through the lungs, there is usually no permanent lung damage. The result is an increased number of eosinophils in the airways or lung parenchyma with or without peripheral eosinophilia. Löffler's syndrome, visceral larva migrans, and tropical pulmonary eosinophilia are the most common infections that cause pulmonary eosinophilia. The most serious parasitic eosinophilic lung disease is tropical pulmonary eosinophilia, a disorder caused by the filarial worms Wuchereria bancrofti and Brugia malayi, in which cases have typically been reported to masquerade acute or refractory bronchial asthma. Increasing awareness, newer diagnostic techniques, preventative measures, and antiparasitic drugs are important in reducing the worldwide morbidity and mortality from parasitic helminths and protozoa. This review focuses on common and some uncommon causes of pulmonary parasitic eosinophilia and their manifestations, diagnosis, and management.

Immune-mediated regulation of chronic intestinal nematode infection

Gastrointestinal nematode infection is extremely prevalent worldwide in humans and animals. Infection levels vary between individuals in infected populations and exhibit a negative binomial distribution, and some individuals appear to be predisposed to certain infection levels. Moreover, infection tends to be chronic, despite evidence for the acquisition of some degree of acquired immunity. The host is subject to constant and repeated antigenic challenge, and individuals vary in the response they make. While a considerable amount of information is emerging on the immunoregulatory mechanisms operating during acute nematode infection from a variety of laboratory model systems, relatively little work has been carried out on the immune mechanisms underlying chronic infection. This review details some of the work that has addressed this important facet of gut nematode infection, highlighting studies from model systems that give insight into the induction of nonprotective immunity, while at the same time avoiding the induction of host-damaging pathology.

Impact of eprinomectin on grazing behaviour and performance in dairy cattle with sub-clinical gastrointestinal nematode infections under continuous stocking management

Forty spring-calving cows and heifers (20 of each) were allowed to acquire infection with gastrointestinal (GI) nematodes naturally during grazing. The control group (10 cows and 10 heifers) were compared with 20 similar animals treated with eprinomectin in order to evaluate the effect of GI nematodes on grazing behaviour, milk production, body condition score and live weight. The animals were paired according to parity and milk yield during the week prior to treatment, then within replicate pair randomly allocated to a different treatment group. The grazing area was sub-divided into 20 replicated paddocks of equivalent size and topography. Grazing pairs of either control or treated animals were randomly assigned to each paddock over the duration of the study (one pair per paddock). Grazing behaviour was recorded for both groups over a 10-day period commencing 4 days after treatment with eprinomectin. Milk yield was recorded daily and milk quality was recorded weekly. Live weight and body condition score were recorded on the day of allocation, the day of initial treatment and thereafter at weekly intervals until the end of the 4-week trial. Faecal samples were collected from each animal prior to, and after, allocation and submitted for counts of nematode eggs. Additional faecal samples were taken at the end of the study for culture and nematode identification. Individual faecal samples were also analysed for residual digestibility. Pasture samples for nematode larval counts were taken at the same time as faecal sampling. The parasitological results showed low levels of faecal nematode egg output throughout the study, with the heifers having higher counts than the cows. Faecal culture yielded species of Ostertagia, Cooperia, and Trichostrongylus. Pasture larval levels were very low throughout with no value exceeding 68 larvae/kg dry matter (DM) of herbage. There were significant (P < 0.05) effects of treatment on grazing time, eating time, total bites, total grazing jaw movements (TGJM), idling time and mean meal duration. Treated cows and heifers grazed for 47 and 50 min longer per day, respectively, than controls (P = 0.016). Mean meal duration was extended as a result of anthelmintic treatment by 11 and 38 min, in cows and heifers, respectively (P = 0.012). There were no significant (P > 0.05) treatment effects on ruminating time or residual faecal digestibility, but idling time was significantly reduced in both treated cows and heifers, by 50 and 110 min, respectively (P = 0.010). In the treated cattle, there was an increase in solids-corrected milk yield compared with the control cattle, which was significant (P < 0.05) in weeks 2 and 3 after treatment. The response was particularly marked in heifers, where the difference in yield between treated and controls was up to 2.35 kg/day. The differences in live weight gain and condition score over 28 days post-treatment were significant (P < 0.05) in both cows and heifers, in favour of the treated animals.

Early-stage diffuse unilateral subacute neuroretinitis: improvement of vision after photocoagulation of the worm

PURPOSE

To evaluate the visual outcome after direct laser photocoagulation of the worm in patients with early-stage diffuse unilateral subacute neuroretinitis (DUSN).

METHODS

We report on four patients with DUSN diagnosed in its early stage, in whom the worm was identified and destroyed by laser photocoagulation.

RESULTS

In all the four cases, resolution of the inflammatory multifocal lesions was achieved within 1 month of treatment. After that period and during follow-up (mean 11.5 months), visual acuity improved in three eyes and remained unchanged in one eye.

CONCLUSION

The diagnosis of DUSN in its early stage followed by prompt location and destruction of the worm by photocoagulation may improve vision of affected patients.

Enteric nematodes induce stereotypic STAT6-dependent alterations in intestinal epithelial cell function

Infection with gastrointestinal nematodes exerts profound effects on both the immune and physiological responses of the host. We showed previously that the Th2 cytokines, IL-4 and IL-13, induce STAT6-dependent changes in intestinal epithelial cell permeability, absorption, and secretion that are similar to those observed in a secondary infection with Heligmosomoides polygyrus. In the current study we investigated whether nematode-induced effects on epithelial cell function were 1) generic, 2) dependent upon STAT6, and 3) attributable to direct effects on the epithelial cells themselves or mediated by effects on enteric nerves. Our results demonstrate that infection of BALB/c mice with three different gastrointestinal nematodes (H. polygyrus, Nippostrongylus brasiliensis, and Trichinella spiralis) alters intestinal epithelial cell function by decreasing resistance, glucose absorption, and secretory responses to 5-hydroxytryptamine and acetylcholine, two critical mediators in the submucosal reflex pathway. These modified responses are dependent on STAT6 and are the result of both direct effects and indirect effects mediated through enteric nerves.

Impact of mass chemotherapy on the morbidity due to soil-transmitted nematodes

This review summarises current knowledge of the ill-effects of soil-transmitted helminthiasis and takes a detailed look at studies that have been published over the past decade describing the effect of mass anthelminthic use on the health of endemic communities. Mass chemotherapy appears to give maximal returns in terms of improved health in areas where hookworm is a major problem and albendazole is used regularly, along with iron supplements; in children it improves physical growth and iron stores, and in pregnant women it reduces the prevalence of iron-deficiency anaemia. In areas where ascariasis is common, the directly attributable benefits of chemotherapy may be minimal, but it can facilitate the entry of other health care programmes in children, because deworming for ascariasis is often much desired and appreciated by the community. In areas with Vitamin A deficiency and endemic ascariasis, Vitamin A supplementation can be combined with deworming: anthelminthics do not impair Vitamin A absorption but the worms may interfere with Vitamin A uptake by reducing fat absorption. Where trichuriasis is a major problem, single dose chemotherapy may take some time to reduce prevalence, but reduction of heavy infections will reduce the incidence of Trichuris Dysentery Syndrome, probably benefit the learning abilities of affected schoolchildren, and may reduce anaemia and stunting. In general, children should be treated as early as possible, and in areas of very high prevalence, thrice-yearly mass chemotherapy probably improves health better than twice-yearly treatment.

Seasonal dynamics of endosymbiotic ciliates and nematodes in Dreissena polymorpha

We report the results of a two-year study in the Svisloch River (Minsk, Belarus) on the dynamics of infection in Dreissena polymorpha by nematodes and three ciliate species Conchophthirus acuminatus, Ophryoglena sp., and Ancistrumina limnica. Although these endosymbionts were present in most of the samples, their prevalence and infection intensity differed significantly. C. acuminatus and A. limnica infection intensities in both years of the study had a maximum in summer and were positively correlated with water temperature. In contrast, Ophryoglena sp. and nematode infection intensities were considerably lower in summer versus winter and were negatively correlated with temperature. In the first long-term study to monitor the size and reproductive rate of C. acuminatus, we found that mean length was negatively correlated with temperature and that temperature was positively correlated with asexual reproduction, with a peak of cell division in April as water temperatures increased.

Sub-clinical parasitism in spring-born, beef suckler calves: epidemiology and impact on growth performance during the first grazing season

Sub-clinical parasitism in spring-born single suckled beef calves was investigated from the middle of their first grazing season until weaning or housing later the same year. The study was conducted on four beef suckler herds in southern England over a 3-year period and involved a total of 334 spring-born beef suckler calves and their dams. The animals were grazed extensively on pastures naturally infected with nematode larvae. At the start of each period of observation, faecal samples were taken from calves and cows and subjected to routine worm egg counts; calves were re-sampled at the end of the grazing season. In July in each year and at each location the calves were ranked by initial weight within sex, paired according to rank and randomly allocated to either an untreated control group or a group in which the calves were each treated with an ivermectin sustained-release (SR) bolus. The calves in both trial groups, and their dams, were grazed together until weaning or housing. The calves were weighed at the initial allocation and at the end of the study. The adult cows were not treated with any anthelmintic during the study. The faecal nematode egg counts (FECs) conducted in July showed that the suckler cows were excreting worm eggs at low concentrations: range 0-100 eggs per gram (epg), with one individual count of 500epg, 88% of the cows sampled had counts of <50epg. Similarly, the counts from the calf samples were fairly low in July: range 0-250epg, 73% of the calves sampled had counts of <50epg. By the end of the grazing season, the faecal samples from the untreated control calves showed higher values: range 0-650epg, with only 58% having an epg of <50. The average rate of daily liveweight gain in the untreated heifer calves was 0.79kg per day, the corresponding figure for the heifer calves treated with the ivermectin SR bolus in mid-summer was 0.88kg per day; the difference of 90g per day was significantly different (P=0.0118). The average rate of daily liveweight gain in the untreated bull calves was 0.91kg per day, the corresponding figure for the bull calves treated with the ivermectin SR bolus in mid-summer was 1.01kg per day; the difference was significantly different (P=0.0169).

Multifocal electroretinography response after laser photocoagulation of a subretinal nematode

PURPOSE

To describe multifocal electroretinography findings before and after laser photocoagulation of a subretinal nematode in diffuse unilateral subacute neuroretinitis.

METHOD

Observational case report. A 45-year-old woman with left eye inflammation, subretinal tracts superior and temporal to the fovea, and a subretinal coiled mobile parasite was treated with laser photocoagulation to destroy the nematode. Multifocal electroretinography was performed before and after laser photocoagulation.

RESULTS

In the left eye, multifocal electroretinography before treatment showed decreased foveal response density and increased parafoveal and perifoveal waveform amplitudes. Two months after laser photocoagulation, multifocal electroretinography showed full recovery of normal findings and the visual acuity remained 20/20.

CONCLUSION

Multifocal electroretinography appears to be useful in evaluating the retinal findings after photocoagulation of a parasite associated with diffuse unilateral subacute neuroretinitis.

Mermithid nematode infections and drift in the mayfly Deleatidium spp. (Ephemeroptera)

Alterations in host phenotype induced by parasitic infection are often interpreted as either host or parasite adaptations, depending on which of the two appears to benefit. Mermithid nematodes typically castrate their insect hosts and, therefore, any change in host behavior has no further fitness consequences for the host; the adaptive value of the modified behavior must be assessed with respect to parasite fitness only. In a New Zealand stream, mermithid-infected nymphs of mayflies in the genus Deleatidium were disproportionately represented in drift samples compared with benthic samples, suggesting that infection by mermithids results in an increased tendency to drift. Drifting mayflies face a higher predation risk from trout, and the mermithid nematodes they harbor die if ingested by a fish. The change in mayfly behavior induced by mermithids thus appears to have negative fitness effects for the parasite, and one possible explanation for this phenomenon is that it is a nonadaptive, pathological side effect of infection.

Induction of stress by the swimbladder nematode Anguillicola crassus in European eels, Anguilla anguilla, after repeated experimental infection

The purpose of this study was to determine under laboratory conditions over a period of 311 days if infection with the nematode Anguillicola crassus induces stress in European eels (Anguilla anguilla), and stimulates the endocrine stress axis as measured by serum cortisol levels. Eels were experimentally infected with 3rd-stage larvae (L3) in different doses to simulate natural conditions with varying infection pressures. Blood samples were drawn from the caudal vein every 2 weeks and serum cortisol concentrations were determined by radioimmunoassay (RIA). The results showed that the application of L3 resulted in a significant increase in the cortisol levels. The period of time at which elevated cortisol values were observed was consistent with the time of larval development and the appearance of adult A. crassus. Thus, there is a stress response to the larval and young adult stages, but no chronic response to older adults. Therefore, it is likely that infection of eels under natural conditions especially with a high number of larvae may be a considerable stressor, in combination with different environmental factors like water temperature, pH, oxygen concentration, pollution and interindividual relationships.

Animal models of intestinal nematode infections of humans

In this paper we discuss several established and potential animal models for human parasitic infection, with a focus on rodent, pig and primate models and the nematodes Ascaris, Trichuris and Toxocara spp. Firstly, we discuss the relevance of choosing a suitable animal host to fit the particular study hypothesis, and the interaction between mathematical modelling and animal models. Secondly, we review the use of animal models for the study of nutrition-parasite interaction, evaluation of treatment and control strategies, and bacteria-parasite interactions. We show that rodent, pig and primate models are all very useful in parasitological research, and that each model has its limitations. However, based on recent experience with the pig-Ascaris and pig-Trichuris models, a more extensive use of the pig-parasite model is advocated, especially for the study of the interaction between human malnutrition and helminth infection, and congenital helminth infection.

Distribution and repeatability of faecal egg counts and blood parameters in dairy goats naturally infected with gastrointestinal nematodes

The frequency, distribution and repeatability of measurements related to infection with gastrointestinal nematodes have been estimated in dairy goats. Monthly faecal and blood samples were taken over two grazing seasons from a flock of 120 naturally infected goats. The frequency distribution of egg excretion was positively skewed at each sampling date, suggesting an aggregative distribution of parasites. Overdispersed distributions were also apparent for pepsinogen and inorganic phosphate values. Repeatabilities for each parameter were estimated within each year. The values ranged between 0.23 to 0.43 and were relatively similar during the 2 years, with the highest coefficients recorded for pepsinogen. For each parameter, moderate to high repeatabilities were also estimated between the 2 years. Overall, the data suggest that, in dairy goats, the distribution of worms is overdispersed with a few individuals repeatedly harbouring large worm populations. These results have practical implications for genetic selection for resistance to worm infection and for selective administration of anthelmintics.

Differential impact of a shared nematode parasite on two gamebird hosts: implications for apparent competition

If the deleterious effects of non-specific parasites are greater on vulnerable host species than on reservoir host species then exclusion of the vulnerable host through apparent competition is more likely. Evidence suggests that such a mechanism occurs in interactions between the ring-necked pheasant (Phasianus colchicus), the grey partridge (Perdix perdix), and their shared caecal nematode Heterakis gallinarum. Modelling of the system predicts that the reduced parasite impact on the pheasant compared to the partridge results in the force of infection transmitted from pheasants to partridges being sufficient to cause partridge exclusion. Since the parasite impacts are currently estimated from correlational work, controlled infections were conducted to experimentally compare the impact of H. gallinarum on the two hosts and verify cause and effect. While challenged partridges showed reduced mass gain, decreased food consumption, and impaired caecal activity, in comparison to controls, the only detectable effect of parasite challenge on the pheasant was impaired caecal activity. The impact of H. gallinarum on challenged partridges conforms with previous correlational data, supporting the prediction that parasite-mediated apparent competition with the ring-necked pheasant may result in grey partridge exclusion. However, the observed decrease in the caecal activity of challenged pheasants could imply that H. gallinarum may also have an impact on the fecundity and survival of pheasants in the wild, particularly if food is limiting. If this is the case, the associated decrease in the force of infection to which the partridge is exposed may be sufficient to change the model prediction from partridge exclusion to pheasant and partridge coexistence.

[The influence of intestinal nematode infection on the productivity of gilts at pig testing stations]

On the basis of the faecal egg counts (epg), the effect of intestinal nematode infection on the productive traits of gilts fattened at Pig Testing Stations (PTS) during 1994-1995 was evaluated. Presumably due to a full-constituent pelleted feed mixture given ad libitum, only in some cases the infection significantly lowered the daily gain, feed convertion or meat content in carcass of gilts, and in some--the phenomenon of resilience was observed. The highest influence on the productivity had station factors.

Ecology of the free living stages of cattle nematodes during summer contamination in Argentina Western Pampas

Development, migration and survival of infective larvae (L3) were studied in the Western Pampeana Region. Faeces of naturally nematode infected cattle were deposited as artificial pats on plots during mid-spring-summer of 1994/1995 and 1995/1996. Since the start and during 1995, the study coincided with a severe drought, rainfalls being 29% below the 45-year means. The predominant genera recovered were Cooperia, Ostertagia and Haemonchus. Initial and peak recovery of L3 from pats occurred 8-15 and 15-21 days later respectively. A low percentage of L3 survived from November (0.3% L3) and January (0.06% L3) to the following autumn and winter. The mean persistence of larvae detected in pats or herbage was around 200 days from deposition. The migration of L3 from faecal pats to herbage started 15 to 30 days after deposition according to rainfall occurrence. Maximum herbage recoveries of L3 from pats deposited in late summer occur during autumn rainfalls. Only, few L3 were occasionally recovered from soil. Summer conditions were associated with rapid development and translation of L3 to herbage, but also with low L3 detection after initial recoveries. Faecal pats deposited from mid-summer were the main source of autumn herbage contamination.

Effects of the initial level of milk production and of the dietary protein intake on the course of natural nematode infection in dairy goats

The level of dietary protein is known to alter the establishment and the pathophysiology of gastrointestinal nematodes in sheep. On the other hand, high-producing dairy goats are less resistant and/or resilient than low-producing ones to experimental nematode infection. During a 2-year study, we have investigated the course of a natural nematode infection (mainly T. colubriformis) in a high-producing dairy goat flock. In year 1, 50 grazing goats divided in high (HP) or low producer (LP) were compared from April to October for parasitological and milk parameters. In year 2, the 25 HP goats were only considered and were allocated to two levels of dietary protein, high level (HPr) with a protein coverage of 125% or normal level (NPr) with a protein coverage of 106%. They were monitored as above. In year 1, HP goats showed a greater nematode egg output (1856 vs. 1000epg) associated with higher values in T. colubriformis IgG in autumn than LP ones whereas the decrease in serum phosphate concentration was similar in both groups. In year 2, HPr goats exhibited lower egg output in autumn (2219 vs. 2817) vs. NPr ones. Moreover, milk yield and fat content were significantly higher in HPr vs. NPr in the 2nd part of the study. HP goats are less resistant to nematode infection in natural conditions. Resistance and resilience of HP goats may partially be improved by a protein supplementation in the diet.

Evaluation of the effects of nematode parasitism on grazing behaviour, herbage intake and growth in young grazing cattle

Parasitic nematodes, even in the absence of any clinical disease, can cause a reduction in voluntary feed intake in housed ruminants. This trial examined these effects on young cattle grazing pastures. Twenty dairy heifer calves, born in the previous autumn, were blocked according to liveweight and allocated to one of two groups: either untreated or dosed with an IVOMEC((R)) (ivermectin) SR Bolus 10 days prior to turnout on 1 May 1998. The groups grazed separately on two paddocks on predominately ryegrass swards. Liveweights were recorded every 28 days and faecal samples taken for worm egg counts at the same time. In mid-May and mid-July, for two 14-day periods, animals were paired within treatment groups and transferred to one of 10 replicate paddocks of similar sward height and herbage mass. Grazing behaviour and herbage intake were measured during these periods. In mid-May, 2 weeks after turnout, treated and untreated animals showed no difference in grazing behaviour or daily intake of grass. By mid-July, 10 weeks after turnout, the untreated heifers spent on average 105min less per day in grazing time and their daily herbage intake was 0.78kg dry matter (DM) per day lower than that of the treated animals. Residual sward height, mass and composition in the trial paddocks reflected these differences. There were no clinical signs of gastrointestinal parasitism in the untreated group up to this time; in July, the mean worm egg count in this group was 120 eggs per gram (e.p.g.) of faeces. Faecal samples from several untreated animals were positive for lungworm larvae by July, mild clinical signs of bronchitis were observed in two of these animals in mid-July. Over the period from turnout until mid-July, the untreated heifers showed a reduction in mean daily liveweight gain of 150g, compared to the treated animals.

Do intestinal nematodes affect productivity in adulthood?

Intestinal nematode infections have been associated with many physical and mental developmental insults. These include anaemia, wasting, stunting, cognitive impairment and lowered educational achievement, all of which have in turn been shown to interfere with productivity and wage-earning capacity in adults. Although there is no direct evidence for an effect of intestinal nematodes on productivity, circumstantial evidence suggests such an effect. Here, Helen Guyatt reviews the indirect evidence for an effect of intestinal nematodes on productivity in adults through current infection and associated morbidity, and on early ill-health in children, which might affect productivity later in life.

Predicting effects of naturally acquired abomasal nematode infections on growth rate and food intake in reindeer using serum pepsinogen levels

An experiment was performed on semiwild reindeer with naturally acquired parasite infections to assess whether measures of serum pepsinogen concentration and fecal egg counts can be used to predict effects of abomasal nematodes on reindeer weight gain and food intake. Food intake and weight gains were lower in infected calves compared with calves where parasites had been removed by anthelmintic treatment. Among the infected animals, concentration of pepsinogen in serum was correlated with food intake and weight gains. Concentration of abomasal nematode eggs in feces was not. Our results suggest that measures of pepsinogen levels in serum, but not fecal egg counts, may be used to predict the effects of abomasal nematodes on food intake and weight gain of reindeer.

Internal parasitism of steers grazing extensively at different stocking rates

Eighty-four first-year grazing Holstein-Friesian steers were observed through 2 years on 40 ha of reclaimed unfertilized grassland with the objective of investigating the influence of stocking rate (SR) on internal parasitism under extensive grazing conditions. Three groups of steers were grazed each year at low, medium and high SR in separate paddocks (0.53, 1.05 and 1.55 steers/ha). The faecal egg counts of predominantly Cooperia and Ostertagia spp. were influenced by SR in the first year (p < 0.05) with maximum geometric means of 135, 182 and 217 epg in the low, medium and high SR groups, respectively, and part of the second year (p = 0.08) with maximum geometric means of 88, 134 and 195 epg. In the second year, all steers were treated with levamisole by 26 July due to diarrhoea, being particularly severe at high SR and 7 steers were withdrawn from this group at the same time. Serum pepsinogen levels indicated a higher rate of uptake of Ostertagia larvae in higher SR groups in the second season before treatment (p < 0.01). The mean weight gains (+/- s.d.) for the first year were 630 +/- 58, 341 +/- 97 and 300 +/- 151 g/day in the low, medium and high SR groups, respectively, and in the second year the corresponding figures were 565 +/- 109, 357 +/- 135 and 247 +/- 129 g/day. Although the SRs were much lower than commonly found on improved pastures, we conclude that feed on offer was a limiting factor in late season and secondly, that the levels of exposure and uptake of nematodes in steers were affected by SR. The levels of parasitism at the medium and high SR were high enough to have affected production.

[Cerebrospinal nematodiasis in seven goats]

Clinical findings in seven goats affected with cerebrospinal nematodiasis are described. The animals originated from different parts of Switzerland. The disease occurred mainly in winter. The animals were admitted to the clinic because of progressive pelvic limb ataxia, recumbency, vestibular disease and circling. Clinical findings were complete or incomplete posterior paresis, pelvic limb ataxia, circling, reduced cutaneous sensation and proprioceptive deficits as well as cranial nerve reflexes deficits. The general condition was slightly reduced and the appetite was normal. In three goats predominance of mononuclear and eosinophilic cells in the cerebrospinal fluid was interpreted as typical findings for parasite infestation in the central nervous system. Histopathological changes and the finding of a nematode in cross sections in two affected animals confirmed the diagnosis. Infection with Elaphostrongylus cervi is discussed due to close contact with deer.

Pathophysiology of infection with gastrointestinal nematodes in domestic ruminants: recent developments

Infection with gastrointestinal nematodes, particularly Ostertagia species in domestic ruminants, continues to represent an important cause of impaired productivity in temperate parts of the world. The mechanisms responsible for such losses include changes in feed intake, gastrointestinal function, protein, energy and mineral metabolism, and body composition, and were described in detail at the last Ostertagia Workshop (Fox, M.T. 1993. Pathophysiology of infection with Ostertagia ostertagi in cattle. Vet. Parasitol. 46, 143-158). Since then, research into the pathophysiology of infection has focused on three main areas: mechanisms of appetite depression; changes in gastrointestinal function; and alterations in protein metabolism. Studies on the mechanisms responsible for appetite depression in Ostertagia-infected cattle have continued to support a close association between impaired feed intake and elevated blood gastrin concentrations. Alternative explanations will have to be sought, however, to account for the drop in feed intake associated with intestinal parasitism in which blood gastrin levels normally remain unaltered. Such work in sheep, and more recently in laboratory animals, has shown that central satiety signals are associated with inappetance accompanying intestinal infections, rather than changes in peripheral peptide levels. Changes in gastrointestinal function have also attracted attention, particularly the mechanisms responsible for increases in certain gut secretions, notably pepsinogen and gastrin. Elegant experimental studies have established that the gradient in pepsinogen concentration between abomasal mucosa and local capillaries could alone account for the increase in blood concentrations seen in Type 1 ostertagiosis. Additional factors, such as increases in capillary permeability and in surface area, probably contribute to such responses in cases of Type 2 disease. The increase in blood gastrin concentrations that accompanies Ostertagia infections in cattle is associated with the concurrent rise in abomasal pH. However, in sheep, additional factors appear to contribute to the hypergastrinaemia which may occur independent of parasite-induced changes in gastric pH. Alterations in protein metabolism have been well documented in ruminants harbouring monospecific infections with either abomasal or intestinal nematodes. More recently, however, the effects of dual abomasal and intestinal infections have been investigated and demonstrated that the host is able to compensate for impaired abomasal digestion provided that the intestinal parasite burden does not occupy the main site of digestion and absorption in the latter organ. An alternative method of improving the host's protein balance, dietary supplementation, has been shown not only to improve productivity, but also to enhance the innate resistance of susceptible breeds of sheep to Haemonchus and to accelerate the development of immunity to Ostertagia in lambs.

Substituted (pyridylmethoxy)naphthalenes as potent and orally active 5-lipoxygenase inhibitors; synthesis, biological profile, and pharmacokinetics of L-739,010

Dioxabicyclooctanyl naphthalenenitriles have been reported as a class of potent and nonredox 5-lipoxygenase (5-LO) inhibitors. These bicyclo derivatives were shown to be metabolically more stable than their tetrahydropyranyl counterparts but were not well orally absorbed. Replacement of the phenyl ring in the naphthalenenitrile 1 by a pyridine ring leads to the potent and orally absorbed inhibitor 3g (L-739,010, 2-cyano-4-(3-furyl)-7-[[6-[3-(3-hydroxy-6,8-dioxabicyclo[3.2.1] octanyl)]-2-pyridyl]methoxy]naphthalene). Compound 3g inhibits 5-HPETE production by human 5-LO and LTB4 biosynthesis by human PMN leukocytes and human whole blood (IC50S of 20, 1.6, and 42 nM, respectively). Derivative 3g is orally active in the rat pleurisy model (inhibition of LTB4, ED50 = 0.3 mg/kg) and in the anesthetized dog model (inhibition of ex vivo whole blood LTB4 and urinary LTE4, ED50 = 0.45 and 0.23 microgram/kg/min, respectively, i.v. infusion). In addition, 3g shows excellent functional activity against ovalbumin-induced dyspnea in rats (60% inhibition at 0.5 mg/kg, 4 h pretreatment) and Ascaris-induced bronchoconstriction in conscious sheep (50% and > 85% inhibition in early and late phases, respectively at 2.5 micrograms/kg/min, i.v. infusion) and, more particularly in the conscious antigen sensitive squirrel monkey model (53% inhibition of the increase in RL and 76% in the decrease of Cdyn, at 0.1 mg/kg, po). In rats and dogs, 3g presents excellent pharmacokinetics (estimated half-lives of 5 and 16 h, respectively) and bioavailabilities (26% and 73% when dosed as its hydrochloride salt at doses of 20 and 10 mg/kg, respectively, in methocel suspension). Based on its overall biological profile, compound 3g has been selected for preclinical animal toxicity studies.

A high efficiency technique for the long-term preservation of infective nematode larvae

Improvements are suggested for the existing long term techniques for the preservation of nematode larvae. Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis and Cooperia curticei larvae exsheathed in sodium hypochlorite and then suspended in phosphate buffered saline (PBS pH 7.2) are cooled in the gas over liquid nitrogen at a cooling rate of -1 degree C min-1 down to -50 degrees C. Larvae are then stored in liquid nitrogen at -196 degrees C. After warming at 30 degrees C and reactivation at 20 degrees C for at least 12 h, their percent motility is maintained (approximately 85%) providing that no more than 3000 to 5000 larvae are suspended in 1.8 mL of PBS in cryotubes. Infectivity does not significantly decrease: 46% of larvae cooled for 2 or 6 mo develop to adult stages compared to 52% for larvae stored at 4 degrees C for 2 mo.

First case of Lagochilascaris minor infection in Bolivia

Few cases of human infection with Lagochilascaris minor have been reported in the literature. They occurred in Central and South America and the Caribbean. We describe the first patient with this nematode infection in Bolivia.

Impaired pulmonary gas exchange in ewes naturally infected by small lungworms

Respiratory rate and blood gases were studied in 2 groups of ewes: the ewes in group 1 (9 ewes) acted as uninfected controls and those in group 2 (6 ewes) were infected with small lungworms (Muellerius, Cystocaulus, Protostrongylus and < 1% Neostrongylus). The respiratory rate was higher in infected (49 +/- 19 breath min-1) than in uninfected ewes. (20 +/- 3 breath min-1); it was strongly reduced after treatment (49 vs 22) in infected ewes. The partial carbon dioxide arterial tension (PCO2), total CO2 and HCO3- were higher (respectively 77 vs 39 mmHg, 38 vs 23 mmol-1 and 35 vs 23 mmol-1) in infected compared with uninfected ewes, whereas arterial pH (7.2 vs 7.4) and partial oxygen tension PO2 were lower (41 vs 81 mmHg) in infected ewes. Group 2 was treated with fenbendazole (at 15 mg kg-1 bodyweight) to eliminate small lungworms, and the respiratory rate and blood gases were measured 3 weeks after treatment. The values after treatment were similar to those in uninfected ewes. It is concluded that heavy infections by small lungworms in ewes impairs gas exchange, but that gas exchange improves rapidly after treatment.

Anthelmintic resistant nematodes in goats in The Netherlands

A suspected case of anthelmintic resistance on a farm with Angora and Anglo-Nubian goats was confirmed in a controlled test. Twelve lambs of sheep were infected with larvae cultured from faeces of the goats. The lambs were allocated to four groups: untreated controls and lambs treated 21 days after infection with 5 mg kg-1 oxfendazole, 0.2 mg kg-1 ivermectin or 7.5 mg kg-1 levamisole. The lambs were slaughtered 1 week later and post-mortem worm counts were performed. Benzimidazole resistance was found in Haemonchus contortus, Teladorsagia circumcincta, Cooperia curticei and Trichostrongylus colubriformis with the efficacy of oxfendazole being 68%, 31%, 21% and 48% respectively. No resistance was found against levamisole or ivermectin.

Safety assessment of a nematode-resistant tomato by a simple, short-term rat feeding study

A simple, 11-week, weanling rat feeding period was used to determine general safety of a nematode-resistant tomato cultivar. Comparison of growth, mean blood hemoglobin, hematocrit, red blood cell count, and total white blood cell count of Fisher rats fed a complete diet containing 40% "VFN 8" tomato (nematode-resistant) cultivar to two other groups of rats, fed either a "New Yorker" tomato (nematode-susceptible) or a control diet, showed normal and similar results. Although the expressed product of the Mi gene necessary for nematode resistance is unknown, this short, comparative study of a whole plant food shows no unexpected toxicants influencing animal growth and hematology. However, human exposure of this resistant tomato would be needed to definitely determine consumer safety regarding allergenicity and hypersensitivity.

Nutrition and parasite interaction

This overview focuses on the interaction between nutritional status and gastrointestinal nematode infection in ruminants and considers: (i) the influence of the parasite on host metabolism; and (ii) the effect of host nutrition on the establishment and survival of parasite populations, the development of the host-immune response and the pathophysiology of infection. Gastrointestinal nematodes reduce voluntary feed intake and efficiency of feed utilisation, a key feature being an increased endogenous loss of protein into the gastrointestinal tract. Overall there is movement of protein from productive processes into repair of the gastrointestinal tract, synthesis of plasma proteins and mucoprotein production. Although reduction in feed intake is a major factor contributing to the reduced performance of parasitised ruminants, the underlying mechanisms of the anorexia are poorly understood. Supplementation of the diet with additional protein does not appear to affect initial establishment of nematode infections but the pathophysiological consequences are generally more severe on lower planes of protein nutrition. The main effect of protein supplementation is to increase the rate of acquisition of immunity and increase resistance to reinfection and this has been associated with an enhanced cellular immune response in the gastrointestinal mucosa. The unresponsiveness of the young lamb can be improved by dietary protein supplementation. Recent trials have shown that growing sheep offered a free choice between a low and a high protein ration are able to modify their diet selection in order to alleviate the increase in protein requirements which result from gastrointestinal nematode infection. Studies on the influence of nutrition on the expression of genotype have shown that the benefits of a superior genotype are not lost on a low protein diet whereas a high protein diet can partially emeliorate the disadvantages of an inferior genotype. In addition to dietary protein both macro-minerals and trace elements can influence the host-parasite relationship.

Why do some nematode parasites of the alimentary tract secrete acetylcholinesterase?

Many gastrointestinal nematodes secrete large amounts of acetylcholinesterases. Antibodies are produced against these secreted acetylcholinesterases and appear to give some protection against infection with some nematodes. The theory that acetylcholinesterase secreted by gastrointestinal nematodes may act as a biochemical holdfast by reducing contractions of the alimentary system has not been substantiated; a vasoactive intestinal polypeptide-like protein is secreted by some species and may be the biochemical holdfast. Secreted acetylcholinesterases may alter host cell permeability, have an anti-coagulant role, affect glycogenesis, and/or be important in certain aspects of acetate and choline metabolism. Probably the most important role for acetylcholinesterase secreted by nematodes is immune modulation and/or reduction of inflammation in the vicinity of the nematode. The reason why some species of gastrointestinal nematodes resistant to benzimidazoles contain elevated amounts of acetylcholinesterase is unclear.

Gastrointestinal nematodes depress food intake in naturally infected reindeer

Models have predicted that directly transmitted macroparasites may influence the abundance of forage plants in herbivore grazing systems by reducing the food intake of their host. Evidence of parasite-induced alterations in host food intake is, however, limited mainly to sheep, cattle and laboratory rodents. We estimated the effect of naturally acquired parasite infections on the appetite of reindeer. Food intake was significantly lower in infected reindeer compared to animals in which the parasites had been experimentally removed. Among the infected animals there was a significant negative relationship between intensity of the directly transmitted macroparasites (i.e. gastrointestinal nematodes) and mean food intake, indicating that the lower food intake was caused by these parasites. The time-specific onset of depression in food intake is also consistent with seasonality in the pathogenic effect from gastrointestinal nematodes. This shows that parasite-induced changes in herbivore food intake is not restricted to agricultural systems, and implies that parasites may have impact on the dynamics of a wide range of herbivore plant communities.

The haematological and biochemical effects of the gastrointestinal nematodes prevalent in camels (Camelus dromedarius) in central Saudi Arabia

Coprological examinations on 1200 Najdi camels (Camelus dromedartus) in the Gassim region of central Saudi Arabia between October 1992 and September 1993 revealed the presence of strongyle-type, Nematodirus and Strongyloides eggs. In addition, examination of the gastrointestinal tracts of 240 camels slaughtered in different abattoirs in the Gassim region from March to August 1994 revealed 11 species of helminths. Infection with gastrointestinal trichostronglyes resulted in normocytic, normochromic anaemia. Adult infected camels showed leukocytosis, a decrease in total serum protein concentration and increases in blood urea concentration and in serum creatine phosphokinase activity.

Monospecific nematode infections of donor calves with Cooperia punctata

During a 25 year period, 48 calves from three states were raised helminth-free from birth and inoculated with Cooperia punctata. These calves served sequentially as donors of the parasite. The following aspects of the monospecific infection were of value in successful donor management and contributed to understanding the host-parasite relationship. Calves with no previous experience with C. punctata were the best hosts for establishing initial infections. Male Holstein calves were satisfactory donors of the parasite. Inoculation of calves 6-24 weeks of age with 10,000-11,200 infective third-stage larvae (L3) over a 2 day period produced the desired donors. Occasional over-feeding of calves appeared to reduce the patent period. Superimposed infection was more likely when calves were still patent from previous infection, whereas reinfection was less likely after patency of the earlier infection had ended. Strong immunity eventually developed following oral administration of L3.

The effects of gamma radiation on the development of Heligmosomoides polygyrus bakeri in mice

The development of a Heligmosomoides polygyrus bakeri (H. polygyrus) primary infection in its definitive host was severely effected by a wide range of gamma radiation doses (10-400 Gy). Male worms were more susceptible to gamma radiation than female worms. A dose of 400 Gy prevented the development of L3 larvae to mature female worms and 200 Gy abrogated the maturation of males. At 300 Gy, a dose known to stimulate high levels of protective immunity, male worms were unable to moult to the L4 stage and females failed to develop into morphologically normal adults. An experiment to select for a radiation resistant parasite line provided data on the cumulative effects of gamma rays on successive parasite generations. Parasite fitness data demonstrated that worm development, at the level of embryogenesis, was far more sensitive to radiation damage than either post embryonic development or adult worm fecundity. The parasite line died out on the 14th generation of selection after receiving an accumulated dose of 420 Gy. It is concluded that gamma radiation profoundly alters the developmental biology of H. polygyrus in a dose-dependent manner, with maximal sensitivity exhibited during embryogenesis.

Effects of treatment with topical ivermectin three and eight weeks after turnout on nematode control and the performance of second-season beef suckler cattle

Two groups of yearling suckled beef calves born between January and May of the preceding year and another two groups of lighter and slightly younger calves born between the previous March and July were grazed during their second year on four separate paddocks known to be contaminated with infective larvae of gastrointestinal nematodes. One of the heavier and one of the lighter groups were treated with a topical formulation of ivermectin three weeks and eight weeks after turnout. The treatment of the heavier group had only relatively minor parasitological effects and no effect on weight gains, whereas the treatment of the lighter cattle resulted in increased weight gains due to effective nematode control. The paper highlights that small differences in previous performances, age and exposure to parasites can have a substantial impact on the benefits accrued from anthelmintic treatment.

Prevention of pathophysiologic and immunomodulatory effects of gastrointestinal nematodiasis in calves by use of strategic anthelmintic treatments

Effects of strategic anthelmintic treatment on pathophysiologic and immunomologic changes induced by infection with Ostertagia ostertagi and Cooperia oncophora were studied in 2 groups, of 12 calves each: an infected group, inoculated with 200,000 mixed O ostertagi and C oncophora third-stage larvae (L3) on day 1; and an infected-treated group, similarly inoculated, but treated with ivermectin at 9 and 33 days. All calves were also inoculated at 12 weeks with Brucella abortus vaccine, at 13 weeks with bovine rhinotracheitis vaccine (bovine herpesvirus 1), and at 14 weeks with a soluble O ostertagi L3 extract, then were allowed to graze on a contaminated pasture. Four calves from each group were slaughtered at 7, 11, and 19 weeks of the study. Calves of the infected group had significantly (P < 0.05) lower weight gain than did those in the infected-treated group (60.90 kg vs 75.86 kg). They also had high plasma pepsinogen and serum gastrin values, and low serum albumin concentration from 2 or 4 weeks. Calves in the infected-treated group had steady weight gain and no significant changes in albumin and gastrin values. They also had less severe abomasal lesions and higher carcass yield. Compared with calves of the infected-treated group, those of the infected group had significantly (P < 0.05) lower blood lymphocyte reactivity to phytohemagglutinin at 14 and 16 weeks, to concanavalin A at 10 weeks, to pokeweed mitogen at 14 weeks, and to soluble O ostertagi L3 extract at 2, 4, and 14 weeks. (ABSTRACT TRUNCATED AT 250 WORDS)

Epizootiology of Ostertagia ostertagi in cow-calf production systems in the American Midwest

The most common gastrointestinal nematodes found in cattle in the Midwest are Ostertagia ostertagi and Cooperia oncophora. Other parasites include Haemonchus placei, Bunostomum phlebotomum and Nematodirus helvetianus. Parasite numbers are generally low in this region, as indicated by fecal egg counts and tracer calf worm recoveries, and the numbers of parasites decrease as one travels farther north. This decrease in parasite numbers also corresponds to a similar reduction in the prevalence of clinical disease. The dynamics of fecal egg shedding are similar throughout the Midwest. Cow fecal egg counts begin to increase just prior to calving in the spring, continue to rise, reaching a peak in July and August, and return to low numbers (2 or less eggs per gram of feces (epg)) in October. Calves born in the spring (March-May) show increasing numbers of eggs in their feces throughout the grazing season, with peak recoveries in October and November, after which the numbers decline as the calves develop an immunological response. Tracer calf worm recoveries demonstrate pasture contamination for the period grazed. These recoveries show adult O. ostertagi increasing throughout the grazing season then falling to low levels over the winter. Larval inhibition of O. ostertagi, as shown by recovery of inhibited fourth stage larvae (L4) occurs throughout the year, with increasing numbers of larvae recovered in the fall. The production robbing effects of these parasites has been demonstrated by the use of a controlled strategic deworming program. Weaning weight advantages of 14 to more than 20 kg have been reported in this region of the country when compared with an untreated group.2+ !%"