Gastrin and pepsinogen changes during an Ostertagia ostertagi challenge infection in calves

Biomarkers of gastrointestinal nematodes in beef cattle raised in a tropical area

Biomarkers are specific molecular, histological, or physiological characteristics of normal or pathogenic biological processes and are promising in the diagnosis of gastrointestinal nematodes (GINs). Although some biomarkers have been validated for infection by Ostertagia sp. in cattle raised in temperate regions, there is a lack of information for tropical regions. The aim of this project was to assess potential biomarkers and validate the most promising. In the first study, 36 bovines (Nelore breed) naturally infected by GINs were distributed into two groups: infected (not treated with anthelmintic) and treated (treated with fenbendazole on days 0, 7, 14, 21, 28, 42, and 56). The variables of interest were live weight, fecal egg count, hemogram, serum biochemical markers, phosphorus, gastrin, and pepsinogen. In the second step, pepsinogen was assessed in cattle of the Nelore breed distributed among three groups: infected (not treated with anthelmintic), MOX (treated with moxidectin), and IVM + BZD (treated with ivermectin + albendazole). In the first study, no difference between groups was found for weight, albumin, hematocrit (corpuscular volume [CV]), erythrocytes, or hemoglobin. Negative correlations were found between pepsinogen and both CV and albumin, and albumin was negatively correlated with the percentage of Haemonchus sp. in the fecal culture. Among the biomarkers, only pepsinogen differentiated treated and infected (beginning with the 28th day of the study). In the second study, a reduction in pepsinogen was found after anthelmintic treatment. Therefore, pepsinogen is a promising biomarker of worms in cattle naturally infected by the genera Haemonchus and Cooperia in tropical areas.

Analysis of cell hyperplasia and parietal cell dysfunction induced by Ostertagia ostertagi infection

Infections in cattle with the gastric nematode Ostertagia ostertagi are associated with decreased acid secretion and profound physio-morphological changes of the gastric mucosa. The purpose of the current study was to investigate the mechanisms triggering these pathophysiological changes. O. ostertagi infection resulted in a marked cellular hyperplasia, which can be explained by increased transcriptional levels of signaling molecules related to the homeostasis of gastric epithelial cells such as HES1, WNT5A, FGF10, HB-EGF, AREG, ADAM10 and ADAM17. Intriguingly, histological analysis indicated that the rapid rise in the gastric pH, observed following the emergence of adult worms, cannot be explained by a loss of parietal cells, as a decrease in the number of parietal cells was only observed following a long term infection of several weeks, but is likely to be caused by an inhibition of parietal cell activity. To investigate whether this inhibition is caused by a direct effect of the parasites, parietal cells were co-cultured with parasite Excretory/Secretory products (ESP) and subsequently analyzed for acid production. The results indicate that adult ESP inhibited acid secretion, whereas ESP from the L4 larval stages did not alter parietal cell function. In addition, our data show that the inhibition of parietal cell activity could be mediated by a marked upregulation of inflammatory factors, which are partly induced by adult ESP in abomasal epithelial cells. In conclusion, this study shows that the emergence of adult O. ostertagi worms is associated with marked cellular changes that can be partly triggered by the worm’s Excretory/secretory antigens.

Abomasal secretion in sheep receiving adultOstertagia circumcinctathat are prevented from contact with the mucosa

AIMS

Both adult and larval Ostertagia circumcincta infections raise abomasal pH and serum gastrin and pepsinogen concentrations, either because of physical effects of the worms or from their chemical secretions. The study was designed to examine whether adult worms require contact with the gastric mucosa to effect changes in gastric secretion.

METHODS

Abomasal pH and serum gastrin and pepsinogen concentrations were measured in four groups of sheep: Group A (n = 4): abomasal contents containing about 18,000 adult O. circumcincta were obtained from donor sheep, concentrated and infused into 5 microm mesh porous bags attached to surgically implanted abomasal cannulae. A second worm transplantation was carried out 1 week later to assess worm survival after 16 hours. Group B (n = 4): about 9000 adult worms, recovered after migration out of abomasal contents set in agar, were placed in small 5 microm mesh bags which were inserted through indwelling abomasal cannulae and left for 3 days. Group C (n = 2): about 3000 adult worms from the population recovered from agar were infused through abomasal cannulae which allowed. free movement in the abomasum. Group D (n = 3) was left uninfected.

RESULTS

Worms transplanted directly into the abomasum (Group C) caused rapid and marked effects on abomasal secretion. Adult O. circumcincta died within 16 hours of transfer into the abomasum when they were restrained within porous bags. Nevertheless, in sheep receiving 18,000 worms, abomasal pH increased soon after new feed was presented on Days 1, 2 and 4 after worm transfer; serum gastrin was elevated in three sheep from 113 hours and serum pepsinogen increased in one animal. Sheep receiving 9000 worms showed similar trends but the results were equivocal.

CONCLUSIONS

Adult O. circumcincta prevented from physical contact with the gastric mucosa by restraint in porous bags are able to raise abomasal pH. This study implicates parasite excretory-secretory products in mediating changes in gastric secretion caused by adult abomasal worms.

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.

Infection of sheep with adult and larval Ostertagia circumcincta: gastrin

Gastric endocrine cell populations and serum and tissue gastrin have been examined in sheep which were infected either intraruminally by tube with 150,000 Ostertagia circumcincta larvae followed by a trickle infection of 10,000 larvae thrice weekly for 8 weeks or by the transfer of 15,000 adult worms directly into the abomasum and killed 8 days later. Depletion of both antral gastrin and somatostatin was evident in both groups: tissue gastrin concentrations were reduced by 85% in the trickle infection and both G cells (gastrin-containing) and D cells (somatostatin-containing) were pale and fewer after adult worm transfer. The concurrent depletion of antral gastrin and somatostatin supports the contention that the hypergastrinaemia in parasitised sheep is largely secondary to the increase in abomasal pH. Although there was no change in the proportions of G34 and G17 in the tissues, there was an increase in the longer form of gastrin in the circulation of the larval-infected sheep, suggesting that there may be differential secretion of G17 and G34 which may be exaggerated as the rate of secretion increases. Although the fundic mucosa was thicker following trickle infection, there was no evidence of enterochromaffin-like cell hyperplasia in either infected group. It is suggested that hyper-gastrinaemia may be beneficial to the host, as it may allow the abomasum to regain the ability to acidify its contents during continued exposure to the parasites.

Effects of adult and larval Haemonchus contortus on abomasal secretion

Abomasal pH and serum pepsinogen and gastrin were increased in parasite-naive sheep by infection with either larval or adult H. contortus. Four sheep received 10000 larvae intraruminally and 9000 adult worms were given directly via an abomasal cannula to another 4 sheep. The latter animals were dosed orally with 0.4 mg kg-1 ivermectin 4 days after worm transfer and their recovery was monitored for a further 8 days. Whereas the presence of adult worms rapidly induced changes in the secretory activity of the abomasum, the early larval stages had minimal effects up to the 4th day post-infection. After either larval or adult infection, the initial hypergastrinaemia began at the same time as the increase in abomasal pH, but serum gastrin continued to increase after abomasal pH had reached a maximum and returned more slowly to normal values after drenching. The increase in serum pepsinogen did not precede those in the other parameters, unlike the earlier hyperpepsinogenaemia which occurs with Ostertagia infection. Three of the 8 infected sheep had no detectable serum pepsinogen increase during the parasitism while showing typical effects on abomasal pH and serum gastrin. The rapidity of the responses to the transfer of adult worms and to their removal by treatment with anthelmintic supports a role for worm excretory/secretory (ES) products which possibly are not produced by the early larval stages. The similarity of responses to H. contortus and O. circumcincta infection suggests the involvement of the same or very similar ES products.

Pathophysiological aspects of Mecistocirrus digitatus (Nematoda: Trichostrongylidae) infection in calves

Three groups of four calves were experimentally infected with infectious larvae of Mecistocirrus digitatus. One group received a trickle infection of 5000 L3 per day for 8 days, the other two groups received a single infection of 5000 and 40,000 L3, respectively. All animals were necropsied 120 days after infection. Prepatent periods varied between 61 and 79 days, and maximal faecal egg output was reached between 80 and 100 days after infection. Repeated infections were not additive and worm counts at 120 days after infection varied between 100 and 440 in the first two groups and between 120 and 1700 in the last group. There was no significant difference in worm counts between the different infection regimes. However, there was a significant positive relationship between worm burden and faecal egg counts. In addition, there were significant negative relationships between worm burden and packed cell volume, and weight gain. The relative decreases in packed cell volume and weight gain emerged 70-80 days after infection. Serum pepsinogen levels were significantly elevated by the end of the trial, but the observed positive relationship between worm burden and pepsinogen was not significant. An enzyme immunoassay based on crude adult antigen was able to detect M. digitatus infection at 90 and 100 days after infection, but again there was no significant association between worm burden and antibody levels. Therefore, anaemia and a reduction in weight gain caused by the haematophagous activity of adult stages seem to be the most important pathogenic effects of M. digitatus infection in calves.

Quantitative estimation of the level of exposure to gastrointestinal nematode infection in first-year calves

In two experiments groups of calves were exposed to different levels and patterns of infection with Ostertagia spp. and Cooperia spp. The experimental design simulated the stereotypic pattern of herbage infestation, including a normal or a delayed midsummer increase, under conditions of set-stocking. The purpose of the experiments was to investigate the accuracy of egg counts, pepsinogen and gastrin values and antibody titres as estimators of the level of exposure to infection. Faecal egg counts significantly reflected levels of exposure during the first half of the simulated grazing season. Antibody titres and pepsinogen values reflected levels of exposure best during August and September, partly depending on the pattern and range of levels of exposure. Antibody titres against Cooperia spp. were particularly useful when levels of exposure to gastrointestinal nematode infection were low. Gastrin values were elevated only at high levels of exposure, which caused large weight gain reductions, in the later part of the simulated first grazing season. It is suggested that antibody titres and pepsinogen values can be used for prognostic diagnosis, indicating whether or not control measures should be taken. Both estimators of infection correlated significantly with the realised weight gain at the end of the simulated grazing season. Egg counts in the second month after the initial infection (turnout) also may be of significant value to support decisions concerning control measures. Comparisons with data from field trials and experiments conducted by others under various conditions suggested that the conclusions of the present experiments are also valid under field conditions. Furthermore, the results supported the conclusions drawn from previous field work, that levels of exposure are often very low on commercial farms in the Netherlands.

Evaluation of pepsinogen, gastrin and antibody response in diagnosing ostertagiasis

Ostertagia ostertagi is widely distributed and is one of the most important parasites affecting young bovine livestock. There is, therefore, a substantial need for sensitive and specific parameters in support of diagnosis of ostertagiasis, especially for subclinical disease related to production losses. In this review, the value and application of pepsinogen, gastrin and antibody response as diagnostic tools are discussed. These three parameters are useful and comparable for confirming clinical disease in calves during their first grazing season. However, their value for detecting subclinical parasitism is questionable. Differences in the course of gastrin and pepsinogen late in the grazing season can be correlated with larval inhibition and the possibility of ostertagiasis Type II. Relatively few serological methods have been developed for the immunodiagnosis of Ostertagia and until now the indirect antibody-detecting enzyme-linked immunosorbent assay (ELISA) has been the method of choice. Antibody measuring methods have several disadvantages, most notably a lack of sensitivity and specificity, which limits their use in longitudinal epidemiological studies. Considering the necessity of cost effectiveness and ease of use, it is anticipated that additional work will result in the enhancement and quality of current immunodiagnostic methods.

Current and future prospects for control of ostertagiasis in northern Europe--examples from Denmark

This review primarily discusses the status and prospects for control of bovine ostertagiasis in northern Europe, with examples from Denmark. There are different ongoing developments in agricultural systems and practices, and methods and possibilities for practical control depend on the intensity and specialisation of these; the modern dairy farm remains at highest risk of parasitism, owing to increasing stocking densities and limited natural control elements at hand. Epidemiology and course of infections are significantly influenced by the gradual build-up of acquired immunity, which usually contributes to prevent loss-producing effects in second season and older animals. It may be of doubtful value to exaggerate worm control in first season animals, because this may reduce development of immunity with the risk of translocating parasite problems from the young to the older, economically more important age categories of animals. A number of reasons for adopting an overall consideration on worm control and performance throughout adolescence is emphasised. Control by management relies on a fairly detailed insight into local transmission factors of Ostertagia ostertagi and related trichostrongyles. No doubt future investigations will provide important additional knowledge in this area. Anthelmintics will continue to constitute a major control measure, but it is unlikely that there will be any acceleration in the rate of commercial release of new compounds. However, ongoing modifications and new formulations of existing anthelmintics will continue to be produced, and implementation at the farm level of the proper use of anthelmintics and other control measures will be one of the important tasks of the coming century. Until now, the development of anthelmintic resistance in cattle has been negligible, but it may possibly pose a potential risk over the coming decades. With regard to some new anthelmintics that have environmental concerns related to their faecal excretion, this should be carefully examined in the future. Control in the form of vaccination or biological control by microfungi or others would be attractive alternatives that should be given a high research priority. Yet, at present it is not easy to predict which of these may lead to feasible, practical control.