Infective Larvae Of Ostertagia Ostertagi Research Articles

Survival of infective Ostertagia ostertagi larvae on pasture plots under different simulated grazing conditions

This study was carried out to examine the survival of infective Ostertagia ostertagi larvae (L 3) on pasture under different simulated conditions of grazing, i.e. mixed grazing of cattle and nose-ringed sows, or grazing by cattle alone. Standardised pats of cattle faeces containing O. ostertagi eggs were deposited on three types of herbage plots, which were divided into zone 1: faecal pat; zone 2: a circle extending 25 cm from the edge of the faecal pat; zone 3: a circle extending 25 cm from the edge of zone 2. For “tall herbage” (TH) plots, the herbage in zone 2 was allowed to grow naturally, while the herbage in zone 3 was cut down to 5–7 cm fortnightly, imitating a cattle-only pasture. For “short herbage” (SH) plots, the herbage in both zones 2 and 3 were cut down to 5–7 cm fortnightly, imitating mixed grazing of cattle and sows. The grass in the “short herbage and scattered faeces” (SH/SF) plots were cut as for SH plots, and the faeces were broken down 3 weeks after deposition and scattered within zone 2, imitating the rooting behaviour of co-grazing sows. Five faecal pats from each plot group were collected on monthly basis, along with the herbage from zones 2 and 3 cut down to the ground. Infective larvae were then recovered from both faeces and herbage. The numbers of L 3 recovered from zone 1 were higher in the TH plots than in the other two groups and, furthermore, the larval counts from SH plots were always higher than from SH/SF plots. The three groups followed a similar pattern during the season regarding numbers of L 3 in zone 2, and no clear patterns between plot types were obtained. The presence of L 3 in zone 3 was almost negligible. Important differences were seen throughout the study from the biological point of view; more L 3 were able to survive in faeces on the TH plots, presumably reflecting a better protection from heat and desiccation compared to those in the other plots. The overall results support the idea that mixed grazing of cattle and pigs favour the reduction of O. ostertagi larval levels in pasture. This reduction is mainly due to the grazing behaviour of pigs, which by grazing up to the very edge of the cattle faeces, will either expose the larvae in faeces to adverse environmental summer conditions or ingest cattle parasite larvae, or both.

Persistent efficacy of doramectin against experimental challenge with Ostertagia ostertagi in cattle

Two studies were conducted in North America to evaluate the persistent efficacy of doramectin injectable solution against experimental challenge with infective larvae of Ostertagia ostertagi. In both studies, four groups of 10 randomly-assigned calves, negative for trichostrongyle-type eggs on fecal examination, were treated subcutaneously in the midline of the neck with saline (1 ml 50 kg −1) on Day 0 or doramectin (200 μg kg −1 = 1 ml 50 kg −1) on Day 0, 7, or 14. Two additional calves from the same pool of animals were randomly assigned as larval-viability monitors and received no treatment. Beginning on Day 14 and continuing through Day 28, the 40 treated calves each were given ∼ 1000 infective larvae of O. ostertagi by gavage daily; the two larval-viability monitors were inoculated in a similar manner with ∼ 30 000 larvae as a single dose on Day 28. Animals were slaughtered on Day 42 in one study and on Days 42, 43, or 46 in the second. The abomasum from each calf was harvested and processed for worm recovery. A 2% aliquot of abomasal contents plus wash was examined for worm quantification and identification. Geometric mean O. ostertagi burdens were calculated from the log ( O. ostertagi count + 1) and were used to estimate percentage reduction. In both studies, doramectin injectable solution was ≥99.6% efficacious in reducing infection resulting from challenge with infective larvae of O. ostertagi for at least 21 days postreatment; by 28 days posttreatment, efficacy was 87.3% in one study and 99.7% in the other.

Gastrin and gastrin-related responses to infection with Ostertagia ostertagi in the half

The effects of a single challenge with 60,000 infective Ostertagia ostertagi larvae on blood and gastrointestinal mucosal gastrin concentrations, gastrin-producing G-cell numbers in the pyloric mucosa and growth of different parts of the gut were investigated in 16, two-and-a-half-month-old calves. Infected calves exhibited a rise in abomasal pH which was accompanied by a 145 per cent increase in wet weight of the fundic mucosa (P<0·05) and a significant rise in blood total gastrin concentrations (P<0·01). Circulating little gastrin (G-17) was unaffected. Pyloric mucosal total gastrin concentrations remained unaltered in the infected calves until day 28 when levels fell to 36·9 per cent of control group values (P<0·01). Pyloric mucosal G-cell numbers declined during the experiment in the infected group. It is suggested that release of previously stored tissue gastrin and not a change in Gcell numbers contributes to the hypergastrinaemia associated with ostertagia infection in the calf.

Anthelmintics

Anthelmintics remain the principal means for the prevention and control of subclinical and clinical ostertagiasis. The selection of an appropriate anthelmintic depends on whether one is controlling or preventing Type I ostertagiasis (caused by the establishment of adult worms derived from recently acquired infective larvae), preventing Type II (treating pre-Type II or inhibited larvae) or controlling Type II ostertagiasis (caused by the development of inhibited larvae to adults), or using the anthelmintic as part of an epidemiologically based plan to reduce pasture contamination with infective Ostertagia ostertagi larvae. In the latter case, the choice of an anthelmintic may depend on whether the targets for treatment are only adult worms and developing larvae or whether the targets include hypobiotic larvae. Thus for Ostertagia control, anthelmintics must be divided into those that normally controll all stages, such as the avermectin group (ivermectin, abamectin and moxidectin) and some of the benzimidazoles (albendazole, oxfendazole and fenbendazole at appropriate does rates), and those that only control adult worms and developing larvae (levamisole, morantel, coumaphos, phenothiazine and thiabendazole).

Inoculation of conventionally and specific-pathogen-free reared rabbits with Ostertagia ostertagi isolated from cattle

Summary Eleven trials were conducted to collect helminthologic and pathologic data from 27 conventionally reared (cr) and 53 specific-pathogen-free (spf) 6- to 13-week-old male New Zealand White rabbits. These rabbits were given 2 to 100,000 ensheathed third-stage infective Ostertagia ostertagi larvae (L3) orally. The L3 had been isolated from the feces of cattle. Fecal egg counts were conducted and worm populations were determined after euthanasia 3 to 56 days after inoculation. At necropsy, nodules were observed in a confluent pattern in the mucosa of cardiac region of the stomach in all inoculated rabbits, except in cr rabbits inoculated at 6 weeks of age, which had no nodules or worm burdens 42 days after inoculation. Confluent areas were not observed in spf rabbits euthanatized 5 days or less after inoculation; however, small, transparent nodules were evident in the mucosa of the cardiac region of the stomach. Fourth-stage larvae (L4) were obtained from the mucosal nodules after digestion of stomach of both types of rabbits. There were more L4 in spf than cr rabbits. In addition, greater numbers of L4 were found in spf rabbits euthanatized 14 days or less after inoculation. Petechial hemorrhages were in the fundic area of the stomach mucosa in spf rabbits inoculated with 100,000 L3 and euthanatized 14 days later. Mature O ostertagi or worm eggs in feces were not found in inoculated cr or spf rabbits. The pathologic changes had characteristics similar to those in cattle and goats infected with O ostertagi. Specific-pathogen-free rabbits inoculated orally with ≥ 50,000 L3 were determined to be a host/parasite laboratory test model for use in chemotherapeutic, immunogenic, or pathogenic studies.

Ostertagia ostertagi infection in the calf: effects of a trickle challenge on appetite, digestibility, rate of passage of digesta and liveweight gain

The effects of a trickle challenge with the equivalent of 10,000 infective Ostertagia ostertagi larvae per day on appetite, digestibility, rate of passage of digesta and liveweight gain were investigated in 12 calves assigned to infected, pair-fed control and ad libitum-fed control groups. Digestibility of cellulose, nitrogen, organic matter and dry matter was determined using insoluble acid detergent fibre as a marker on two occasions during the study: (i) Between days 31 and 38, when abomasal dysfunction was greatest; and (ii) between days 52 and 58, beginning approximately one week after anthelmintic treatment (day 46). Rate of passage of digesta was measured using chromium mordanted hay, fed to each calf after each digestibility study period. Voluntary feed intake of the infected group was significantly reduced from day 37 with the greatest depression (77 per cent) occurring just before anthelmintic treatment. The drop in appetite was responsible for nearly 73 per cent of the difference in liveweight gain between the infected and ad libitum fed control groups. The apparent digestibility coefficient of nitrogen was significantly depressed (22 per cent) in the infected group though was restored to control levels by anthelmintic treatment. The rate of passage of digesta was significantly reduced in both pair-fed control (50 per cent) and infected (74 per cent) groups. Anthelmintic treatment increased the latter though only to pair-fed control group levels. It is suggested that the marked hypergastrinaemia seen in the infected calves may have been in part responsible for the decreased rate of passage of digesta and in turn for the drop in appetite.

Ostertagia ostertagi infection in the calf: effects of a trickle challenge on the hormonal control of digestive and metabolic function

Metabolic effects of a trickle challenge with the equivalent of 10,000 infective Ostertagia ostertagi larvae per day were investigated in 12 calves allocated to infected, pair-fed control or ad libitum-fed control groups. Changes in hormone levels reflecting abomasal, pituitary and pancreatic function were monitored using radioimmunoassay techniques previously validated for use in cattle. A range of metabolic profile parameters and blood metabolites was also measured. Feed intake of the infected calves began to decline as blood gastrin and pepsinogen levels reached a peak. The depression in appetite recorded in this group was responsible for significant increases in plasma urea and non-esterified fatty acid levels and associated with an increase in growth hormone/insulin ratio. No significant difference in glucagon levels was recorded between groups. A decline in blood albumin values was also shown in the infected group and associated with a drop in nitrogen digestibility. A significant depression in circulating calcium levels was related to either the hypoalbuminaemia or impaired mineral absorption in the intestine. A decrease in plasma cholesterol values in the infected group was associated with changes in digestive function.

Factors influencing rain splash dispersal of infective larvae of Ostertagia ostertagi (Trichostrongylidae) from cow pats to the surroundings

Laboratory experiments were conducted to investigate rain splash dispersal of infective Ostertagia ostertagi larvae (L 3) from cow pats to the surroundings during simulated rainfall. Simulated rainfall on dry cow pats resulted in dispersal of only very few L 3. When cow pats were watered prior to the experiments, many infective larvae were stimulated to migrate up onto the surface of the pats, where they might be hit by water drops. When pre-watered pats were hit by falling drops, a considerable proportion of L 3 was translocated. More than 90% of the translocated larvae were transported passively by splash droplets and only a minor part of the larvae migrated actively in water films or were transported passively by water run-off to the soil surrounding the pats. A reduction of the fall height of the simulated raindrops resulted in a significant reduction of the number of translocated L 3. When cow pats were hit by drops of diameters between 2 and 5 mm, it was found that small raindrops were just as effective as large drops in splash dispersal of L 3, provided the amount of rain was the same; but individual small drops were less effective in this respect than individual large drops. When splash droplets could travel freely, most of the splash-dispersed L 3 were found within a horizontal distance of 90 cm from the pats; this applied for all sizes of drops. Most splash droplets carrying L 3 were travelling within a vertical distance of 30 cm from the ground.

Induction of Nematode-Trapping Organs in the Predacious Fungus Arthrobotrys oligospora (Hyphomycetales) by Infective Larvae of Ostertagia ostertagi (Trichostrongylidae)

Laboratory experiments were designed to study the influence of temperature, concentrations of nematodes, oxygen tension, light, and nutrient levels, on the induction of nematode-trapping hyphal nets in the predacious fungus Arthrobotrys oligospora. When induced by infective Ostertagia ostertagi larvae, a maximum number of nets was produced at 20 degrees C, at which temperature nets in surplus were produced at larval concentrations up to 1,000 larvae per cm2. A. oligospora did not produce nets in an anaerobic atmosphere containing 21% CO2 (v/v), and net induction was suppressed to a certain degree by exposure to light. The composition of the medium had an important influence on the saprophytic growth and the net-forming capability of A. oligospora as a maximum number of nets was induced at a relatively low concentration of corn meal supporting the relatively sparse mycelium. It was shown that a proportion of trapping nets in A. oligospora maintained their trapping potential for more than 7 weeks when the temperature was below 25 degrees C. Induction of nematode-trapping organs in A. oligospora is discussed in relation to control of infective nematode parasite larvae in cow pats.

The capability of the predacious fungus Arthrobotrys oligospora (Hyphomycetales) to reduce numbers of infective larvae of Ostertagia ostertagi (Trichostrongylidae) in cow pats and herbage during the grazing season in Denmark.

Artificially prepared cow pats containing Ostertagia ostertagi eggs were deposited on two pasture plots in May, June and July 1986. Half of the cow pats, placed on one plot, were inoculated with 2000 conidia per gram faeces of the predacious fungus Arthrobotrys oligospora. On the other plot fungus-free control cow pats were placed at the same time. In the faeces generally fewer infective O. ostertagi larvae developed in the inoculated than in the control cow pats. On the herbage around the control cow pats deposited in May, June and July a maximum concentration of infective larvae was found at the same time on the 6th of August 1986. At that time the herbage larval infectivity around inoculated cow pats deposited in May, June and July was subject to a reduction of 48%, 89% and 46%, respectively, compared with fungus-free control cow pats. This experiment indicates that a concentration of 2000 A. oligospora conidia per gram faeces results in a significant lowering of the herbage larval infectivity during the grazing season in Denmark.

A Field Experiment on Rain Splash Dispersal of Infective Larvae of Ostertagia Ostertagi (Trichostrongylidae) from Cow Pats to Surrounding Grass

Ostertagia ostertagi is an important tricho-strongyle nematode parasite of cattle in several countries, including Denmark. It leaves its host as eggs with faeces. After hatching it develops in the cow pat up to the third and infective stage, which is then transmitted to the surrounding grass.

Endocrine effects of a single infection with Ostertagia ostertagi in the calf

Endocrine effects of a single dose of 100,000 infective Ostertagia ostertagi larvae in the calf were investigated. Changes in hormone levels reflecting digestive, thyroid, adrenal and pituitary function were monitored using radioimmunoassay techniques previously validated for use in cattle. A significant increase in pepsinogen and gastrin was recorded in infected calves reflecting changes in abomasal function. A decrease in insulin levels was also demonstrated following Ostertagia infection and may have been related to changes in protein metabolism. A depression in total thyroxine levels, reversed by anthelmintic treatment, was apparently associated with reduced feed intake and therefore seen in both infected and pair-fed control animals. The metabolic effects of this change were, however, unlikely to be marked since free (or unbound) thyroxine remained unaltered. A small drop in growth hormone levels in the infected group was also noted.

In vitro Cultivation of Ostertagia ostertagi, the Medium Stomach Worm of Cattle. I. Development from Infective Larvae to Egg-Laying Adults

When a 70-min exsheathing process and two-step roller culture system were used, infective larvae of Ostertagia ostertagi developed in large numbers to mature adult males and females in 28 and 29 days, respectively. Females laid fertile eggs in the 2- to 16-cell stages from day 34 on. Some of the expelled eggs developed to the morula stage, in the culture fluid, by day 52. Yields of mature adults and eggs were best when cultures were started with 100,000 larvae in 100 ml of medium. The optimal culture system produced from 20% to 35% mature adults, from days 28 through 52.

On Experimental Transmission of Ostertagia Ostertagi (Stiles, 1892) Ransom, 1907, to Sheep

Lambs were administered heavy doses of infective larvae of Ostertagia ostertagi. Those autopsied 29 days after infection had some worms while others autopsied at the 57th day had no worms. The vulval flap was absent in female worms and eggs were not detected in the faeces of the lambs. The sheep is considered to be an unsuitable host for O. ostertagi.

Some observations on the worm burdens of calves infected daily with Ostertagia ostertagi.

Two experiments are described in each of which three groups of calves received infective larvae of Ostertagia ostertagi daily, each group at a different rate. Changes in worm burdens were followed by the periodic slaughter of calves.Numbers of adult worms quickly rose to and remained at levels which bore a positive relation to the infection rate. There was evidence that a turnover of worms was occurring and it appeared that burdens of adult worms were regulated by a loss of worms which depended on the number present. As the host's experience of infection increased, the adult worms present were smaller and an increasing proportion of females lacked a fully developed vulval flap. Evidence is presented which suggests that these were effects of resistance and that they depended on separate mechanisms.Faecal egg counts of groups carrying different numbers of worms rose to the same peak and then declined according to the same logarithmic curve. This finding, together with data concerning the number of eggs in the uteri of the worms, suggested that the egg output of the entire population was restricted by the host to a limit which depended on previous egg-laying.Infection did not have an adverse effect on the growth of the calves unless the infection rate exceeded a critical value. The resistance of calves to infection was impaired by clinical ostertagiasis.

Comparative Size of Infective Larvae of Cooperia oncophora in Feces of Cattle and Sheep

A cattle strain of Cooperia oncophora was used to infect a helminth-free calf and lamb. Sphagnum moss-feces cultures were made from the feces of the infected animals. In addition, eggs separated from the feces of each infected animal were incubated in cultures made from the feces of a helminth-free calf and lamb, respectively. The mean total length of larvae cultured in the feces of a parasite-free lamb was smaller, though not always significantly so, than the mean total length of larvae cultured in feces from any of the other sources. The mean total length of larvae cultured in the feces of a parasite-free calf was greater, though not always significantly so, than the mean total length of larvae cultured in feces from any other source. No consistent correlation could be made in either experiment between total length and other measurements such as distances between anus and tail tip, anus and sheath tip, tail tip and sheath tip, and total length of larvae minus sheath. These data indicate that a factor or factors operating within individual host animals are sufficient to affect significantly the size of the infective third-stage larvae developed from nematode eggs passed from the host. Various authors, working with nematodes parasitic in ruminants, have reported different average lengths and ranges of lengths for infective larvae of the same species. Several explanations of the causes of these differences have been advanced. Keith (1953) measured infective larvae of Ostertagia ostertagi, a parasite of cattle, and found the range of total length (784 to 928 [t) almost triple the range (850 to 900 A) noted by Threlkeld (1946). Infective third-stage larvae of 0. ostertagi, observed by Douvres (1956), were longer than those observed by either Threlkeld or Keith. In addition, Douvres noted that iodine-killed larvae were longer than those that had been heat killed, and that refrigerated larvae were longer than those that were nonrefrigerated. Shumard, Herrick, and Pope (1955) demonstrated that the nutrition of lambs parasitized with Haemonchus contortus influenced the size of infective larvae of a succeeding generation. These authors conjectured that differences between their measurements and those of Dikmans and Andrews (1933) might have been caused by the type of fluid in which the larvae were killed. Received for publication 30 August 1963. Keith (1953), working with Cooperia oncophora larvae cultured from eggs passed by infected cattle, found little difference in total length from that reported by Dikmans and Andrews (1933) for C. oncophora larvae cultured from eggs removed from worms recovered from sheep. Keith noted, however, that infective larvae of his study had longer tails than did those observed by Dikmans and Andrews and suggested that this was due to a strain difference. Isenstein (1963), working with C. oncophora from eggs passed by infected cattle, found the infective larvae considerably longer than those studied by either Dikmans and Andrews or Keith. In view of the foregoing, it was deemed desirable to compare the sizes of infective larvae of Cooperia oncophora cultured in cattle and sheep feces, wherein the diet of the host, strain of worms, and method of preparing the worms for measurement are kept constant. MATERIALS AND METHODS Thirty-two thousand infective third-stage larvae of Cooperia oncophora were administered per os to a parasite-free calf (1741). These larvae were of a cattle strain, having been passed through cattle for at least seven generations. A parasitefree lamb (102) was subsequently infected with 80,000 larvae cultured from the eggs passed in the feces of calf 1741.

The phenomena of host resistance and the course of infection of Ostertagia ostertagi in calves

A study of the changes in the worm burden in calves receiving daily doses of infective larvae of Ostertagia ostertagi indicates that the following processes occur:(1) A constant loss of adult worms at a rate depending on the number present.(2) An inhibition of development in the early fourth stage which depends partly on the presence of adult worms. This inhibition is not irreversible; larvae resume their development, the number which do so depending on the number present.(3)A stunting of adult worms, those developing late in the infection failing to grow as large as those which developed earlier.(4)An inhibition of ovulation, distinct from the stunting, which prevents worms developing later from becoming as prolific as those which developed earlier.(5)A resistance to the establishment of newly acquired worms, which begins to operate after prolonged exposure to infection.The loss of adult worms and their replacement by the further development of fourth stage larvae leads to a frequent exchange of populations of adult worms.The effect of these phenomena in determining the course of the infection is discussed.