Adult worms as a factor in the inhibition of development of Ostertagia ostertagi in the host

The removal, by anthelmintic treatment, of adult worms from calves that had been infected daily for 204 days with larvae of Ostertagia ostertagi, stimulated the resumed development of inhibited early fourth stage larvae. The calves remained susceptible to the establishment of worms and the continued administration of infective larvae after the 204th day reduced the rate at chich the burden of inhibited forms decreased. The relevance of these findings to the regulation of worm burdens is discussed.     

Ostertagia ostertagi: establishment of patent infections in calves by intravenous inoculation

In two experiments calves raised free of parasite infection were given parenteral injections of Ostertagia ostertagi infective larvae to determine if patent infections might result. Patency was achieved by intravenous injection of larvae. Ten calves of different age (3–8 months) and sex were given intravenous, subcutaneous, and intraperitoneal injections of infective larvae. These calves were not necropsied; patency was based on fecal egg counts. Six calves injected intravenously all achieved patency (17–21 days after inoculation). Two calves each were inoculated subcutaneously and intraperitoneally; patency was observed in none. Calves given primary intravenous inoculation responded with higher levels of ova production to subsequent oral challenge inoculation.In a second experiment, six 2–3-month-old calves were injected intravenously with 186,000 infective larvae. Calves were killed at 2, 7, 12, 20 and 30 days after inoculation and had a tissue reaction in the lungs to migrating larvae characterized by focal granulomas, interstitial thickening of alveolar walls, and some hemorrhage. Infective larvae were recovered from the lungs at 2, 7 and 12 days, fourth stage larvae from the abomasum at 7 and 12 days, and adults only from the abomasum at 20 and 30 days. It was considered that larvae reached the abomasum by way of the trachea and by then being swallowed. Clinical signs of disease were not observed.     

The effect of genetic factors on the vulval flap of Ostertagia ostertagi.

Michel J. F., Lancaster M. B. &; Hong C. 1976. The effect of genetic factors on the vulval flap of Ostertagia ostertagi. International Journal for Parasitology6: 83–86. Ostertagia ostertagi, selected according to the form of the vulval flap, were implanted into calves and larvae cultured from the faeces. Larvae obtained in this way were administered to groups of susceptible calves and to groups of calves sensitized by previous infection. Examination of worms recovered post mortem showed that the incidence of worms with reduced flaps was smaller among the progeny of worms with fully developed flaps than among the progeny of worms in which the flap was greatly reduced or absent. This difference was, however, much smaller than that between the worms from sensitized and from susceptible calves.     

Babesia major in Britain: blood-induced infections in splenectomized and intact calves

A strain of Babesia major, originally isolated from field collections of Haemaphysalis punctata in Kent, England was maintained in splenectomized calves by the intravenous inoculation of infected blood. Rapid passage from carrier calves, that had recovered from a tick-induced infection, resulted in a marked increase in virulence; 4 out of 6 calves of the second passage underwent fatal infections and the others suffered severe reactions.Five splenectomized and 5 intact calves of the same breed and age were infected with the same number of infected erythrocytes (RBC). The intact calves reacted mildly with maximum parasite counts ranging from < $\text{1}\text{1000}$ RBC to $\text{5}\text{1000}$ RBC; haemoglobin levels and packed cell volume values, however, fell sharply but recovered swiftly. The group of splenectomized calves exhibited one fatal case, 2 severe reactions and 2 mild infections; maximum parasitaemias varied from $\text{7}\text{1000}$ RBC to $\text{322}\text{1000}$ RBC. Packed cell volumes and haemoglobin concentrations declined to low levels and took several weeks to return to normal.It is concluded that B. major should be regarded as a potential pathogen of British cattle.     

The effect of age, acquired resistance, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi

An experiment is described in which the effects of age, previous infection, pregnancy and lactation on some reactions of cattle to infection with Ostertagia ostertagi were studied. It was found that an acquired resistance to the establishment of worms developed more rapidly in 20-month-old heifers than in calves, that it was unaffected by pregnancy of the host but that it was largely lost by heifers in early lactation. The rate at which populations were turned over, i.e. the mean life-span of worms through the late 4th and 5th stages was unaffected by the factors studied. Although, in the conditions of the experiment, development of the worms was not arrested in susceptible calves, both age of the host and its previous experience of infection were significant causes of arrest, and in previously infected 20-month-old cattle 86% of the worms of a challenge infection were arrested. Pregnancy did not affect the proportion of worms that was arrested but in lactating heifers only marginally more worms were arrested than in calves. Worms that were not arrested grew more rapidly in calves and in lactating heifers than in empty heifers or those in mid-pregnancy.     

The parasitic phase of Ostertagia ostertagi: quantification of the main life history traits through systematic review and meta-analysis

Predictive models of parasite life cycles increase our understanding of how parasite epidemiology is influenced by global changes and can be used to support decisions for more targeted worm control. Estimates of parasite population dynamics are needed to parameterize such models. The aim of this study was to quantify the main life history traits of Ostertagia ostertagi, economically the most important nematode of cattle in temperate regions. The main parameters determining parasite density during the parasitic phase of O. ostertagi are (i) the larval establishment rate, (ii) hypobiosis rate, (iii) adult mortality and (iv) female fecundity (number of eggs laid per day per female). A systematic review was performed covering studies from 1962 to 2007, in which helminth-naïve calves were artificially infected with O. ostertagi. The database was further extended with results of unpublished trials conducted at the Laboratory for Parasitology of Ghent University, Belgium. Overall inverse variance weighted estimates were computed for each of the traits through random effects models. An average establishment rate (±S.E.) of 0.269 ± 0.022 was calculated based on data of 27 studies (46 experiments). The establishment rate declined when infection dose increased and was lower in younger animals. An average proportion of larvae entering hypobiosis (±S.E.) of 0.041 (±0.009) was calculated based on 27 studies (54 experiments). The proportion of ingested larvae that went into hypobiosis was higher in animals that received concomitant infections with nematode species other than O. ostertagi (mixed infections). An average daily adult mortality (±S.E.) of 0.028 (±0.002) was computed based on data from 28 studies (70 experiments). Adult mortality was positively correlated with infection dose. A daily fecundity (±S.E.) of 284 (±45) eggs per female was found based on nine studies (10 experiments). The average female sex ratio of O. ostertagi based on individual animal data (n = 75) from six different studies was estimated to be 0.55. We believe that this systematic review is the first to summarise the available data on the main life history traits of the parasitic phase of O. ostertagi. In conclusion, this meta-analysis provides novel estimates for the parameterization of life cycle-based transmission models, explicitly reports measures of variance around these estimates, gives evidence for density dependence of larval establishment and adult mortality, shows that host age affects larval establishment and, to our knowledge, provides the first evidence for O. ostertagi of a female-biased sex ratio.     

Seasonal changes of gastrointestinal nematode populations in yearling beef cattle in Louisiana with emphasis on prevalence of inhibition in Ostertagia ostertagi

Investigation of seasonal changes in the composition of nematode populations, principally Ostertagia oslertagi, was conducted over 3 years at three locations in Louisiana. This is the most commonly occurring parasite of cattle in the state. Naturally infected yearling cattle were killed monthly over extended periods and tracer calves were grazed for monthly intervals from late autumn to summer at two locations in 1978–1979. Major objectives were to determine seasonal incidence of common gastrointestinal nematodes and for O. ostertagi, in particular, the time period during which larval inhibition was prevalent, circumstances under which larvae were conditioned to inhibition, and the duration of inhibition. Small numbers of inhibited O. ostertagi were recovered between November and February. Large numbers were found initially in March and increased numbers in April and May. Both normally developing and inhibition prone larvae were acquired during late winter-early spring, with the proportion of the latter being more prevalent in April and May. Evidence from tracer calves indicated that few O. ostertagi larvae were acquired after early June. Large burdens of inhibited larvae persisted in yearling cattle through summer; numbers of developing larvae and adults were minimal. Maturation of inhibited larvae occurs from August to October and in one instance was associated with cases of clinical parasitism. Factors responsible for inhibition were not defined, but increasing temperatures of late winter-early spring, host resistance, and density-dependence of populations were considered. Other abomasal genera were most prevalent in spring while intestinal genera were most common during autumn through spring.     

Dipetalonema viteae: Microfilariae production in various mouse strains and in nude mice

Adult female Dipetalonema viteae worms obtained from hamsters were introduced beneath the dorsal skin of $\text{Balb}\text{c}$, $\text{C}{}_{57}\text{Bl}\text{6}$, and $\text{C}{}_3\text{H}\text{He}$ mice. The microfilaraemia from the transplanted worms in $\text{Balb}\text{c}$ mice was higher and persisted longer than in $\text{C}{}_{57}\text{Bl}\text{6}$, and in $\text{C}{}_3\text{H}\text{He}$ mice was intermediate between these two strains. The transplanted adult worms were killed earlier in $\text{C}{}_{57}\text{Bl}\text{6}$ compared to $\text{Balb}\text{c}$ mice; adult worms were killed before the microfilariae were cleared from the circulation. D. viteae infective larvae did not reach maturity in mice but when female worms were implanted into mice which had been infected with third-stage infective larvae 6 or 19 days previously, microfilarial production was inhibited. Outbred as well as inbred nude mice infected with 10 or 20 infective larvae died by Day 15, whereas the normal littermate control mice that received the same number of infective larvae remained alive and healthy. There was no difference in the duration and level of microfilaraemia from implanted female worms in outbred nudes and their heterozygous littermate control mice. In contrast, microfilaraemia in inbred $\text{Balb}\text{c}$ Nu+ was similar to that of inbred $\text{Balb}\text{c}\text{Nu}\text{Nu}$ only until Day 45; thereafter the microfilaraemia declined to zero around Day 160 in the Nu+, at which time it was still high and persisted longer in the $\text{Balb}\text{c}\text{Nu}\text{Nu}$. Transplanted adults were viable in inbred $\text{Balb}\text{c}\text{Nu}\text{Nu}$ for a longer time than in $\text{Balb}\text{c}$ Nu+. When infected, amicrofilaraemic nudes, littermate controls, and three strains of mice were challenged, a very low level short-lasting microfilaraemia resulted.     

Oesophagostomum radiatum in calves: intestinal hemorrhage associated with larval emergence

Intestinal blood loss in calves infected with various numbers of Oesophagostomum radiatum was measured using ⁵¹Cr-labeled erythrocytes, and compared with the subsequent changes in the packed cell volume of jugular blood. Emergence of histotropic fourth-stage larvae from the submucosal cysts was associated with intestinal hemorrhage in all infected calves but only in the calves given a near lethal dose of larvae was the bleeding sufficient to cause anemia. At the lower infection rates the hemorrhage caused by larvae was considerably less than that produced by the ensuing adult population. The proportion of adult worms recovered from the infecting dose diminished as the dose increased.     

Experimental inoculations with Ostertagia ostertagi or exposure to artificial illumination alter peripheral cortisol in dairy calves (Bos taurus)

A series of experiments were conducted on dairy calves (Bos taurus) to assess, by way of circulating cortisol, the impact of a parasitic infection as a systemic stressor. The first study was designed to assess the effects of chronic stress on dairy calves resulting from a large bolus inoculation of the nematode parasite, Ostertagia ostertagi. Peripheral cortisol concentrations and adrenal cortical competency to adrenocorticotropic hormone (ACTH) challenge were utilized as indicators of chronic stress for 5 weeks. Calves were cleared of nematodes by anthelminthic treatment after the third week of infection. Calves were challenged with ACTH on weeks 0 and 2, and blood samples were obtained at a 12 x 10-min bleeding schedule. Cortisol concentrations were significantly higher (P < 0.05) in the infected calves than in the uninfected calves. The maximal response level to the ACTH challenge was also higher while the calves were infected. Two additional experiments were conducted to investigate the effects of experimental procedures that became evident during Experiment 1. Firstly, calves that had previously been fitted with jugular cannulae were sampled from 3 hr predawn until 5 hr after dawn under red- or white-light incandescent illumination. Calves under red lights had lower initial cortisol concentrations but increased to the concentrations in calves under white lights, indicating a compounding effect of lighting with the procedures of blood-sample acquisition. Secondly, 12 calves were inoculated with 10,000, 100,000, or 200,000 third-stage, infective larvae of O. ostertagi. Blood samples were obtained similarly to the regimen in Experiment 1. Cortisol concentrations were elevated only in the 200,000-dose group during week 3, correlating with the period immediately after emergence of the young adult parasites from the gastric glands. Continuous emergence of these parasites might induce chronic hyperadrenocorticism and the concomitant negative consequences on metabolic and immunological processes.     

Hymenolepis nana: Immunogenicity of a lumen phase of the direct cycle and failure of autoinfection in BALBc mice

When $\text{BALB}\text{c}$ mice were given $\text{BALB}\text{c}$ mouse-derived cysticercoids (cysts) of Hymenolepis nana, only $\text{1}\text{43}$ mice became autoinfected, whereas most ($\text{31}\text{38}$) of dd mice given the same infection became massively autoinfected with mature worms. When $\text{BALB}\text{c}$ mice initially given cysts were challenged with eggs on Day 7, just before the patency of the primary infection, there was normal development into cysts, but almost none of them developed into adult worms. Thus, the failure of autoinfection of H. nana in $\text{BALB}\text{c}$ mice was not a result of failure of eggs to differentiate into cysts in the intestinal tissue, but a result of failure of these cysts to develop into adult worms in the lumen. The reasons why autoinfection does occur in dd and other strains of mice and not in the $\text{BALB}\text{c}$ strain are discussed in terms of the difference in onset of the late response in these strains of mice, ie., the response that is acquired after egg inoculation, and is directed against the lumen phase of cyst challenges. It is strongly suggested that (1) the lumen phase which follows cyst inoculation is highly immunogenic, but clearly differs from tissue phase which follows egg inoculation, (2) the autoinfection which occurs in some strains of mice is therefore not a result of no or poor immunogenicity of the lumen phase but is due to a delay of onset of the late response with the result that a secondary generation may mature, and (3) in other strains of mice, including $\text{BALB}\text{c}$, which acquire the late response within 15 days of initial egg inoculation, autoinfection normally does not occur after cyst infections.     

The length of Ostertagia ostertagi in populations of uniform age

Michel J. F., Lancaster M. B. and Hong C. 1978. The length of Ostertagia ostertagi in populations of uniform age. International Journal for Parasitology8: 437–441. The conclusion that, in calves exposed to daily infection with larvae of Ostertagia ostertagi, adult worms are constantly lost and replaced was based, in part, on the observation that the length of the worms present decreased with time. The underlying assumption that worms do not shrink was examined in an experiment in which groups of calves received 8300, 25,000 and 75,000 larvae respectively in a single occasion and were killed at various times between the 20th and 132nd day thereafter.The length of the worms was inversely related to the initial worm burden but as worm burdens declined the worms did not grow. Instead, in the groups that received 25,000 and 75,000 larvae, decreases in worm length of 7% and 8% respectively were seen when most of the worms had been lost. Although it appears very probable that this was due to the more rapid loss of large worms than of small, the point could not be conclusively demonstrated.     

Experimental studies on the interaction between infections of Ostertagia leptospicularis and other bovine Ostertagia species

Experimental infections of calves were carried out with either isolates of predominantly Ostertagia ostertagi, pure O. leptospicularis or a mixed isolate of equal numbers of both these species. The total worms established on day 21 for the mixed species from a total inoculum of 100 000 infective larvae, was 1.2 times greater than from 100 000 larvae of the O. ostertagi isolate and 3.3 times that of the pure O. leptospicularis isolate. The increased establishment in the mixed inoculum referred to both O. ostertagi and O. leptospicularis (days 17 and 21). These differences were both highly significant (P less than 0.01). The severity of the pathological changes was also greater in the mixed infections. It is suggested that these findings must be taken into account when control measures involving alternate grazing of sheep and cattle are being employed.     

The segregation of lambs into ‘responders’ and ‘non-responders’: Response to vaccination with irradiated Trichostrongylus colubriformis larvae before weaning

Random bred Merino ram and ewe lambs were vaccinated at 1, 2 and/or 3 months of age with irradiated T. colubriformis larvae. An exponentially increasing challenge of normal larvae was given to all groups including unvaccinated controls commencing at 1 month of age. The results, based on faecal egg counts, showed a dissociation into animals which responded to vaccination (geometric mean egg count 441) and those which did not (geometric mean egg count 1567). The proportion of responders was greatest in groups first vaccinated at the earliest age (1 month). Wool growth and liveweight gains showed severe depression corresponding to peak egg counts, however, responders were less affected than non-responders. There was no correlation between haemoglobin type and resistance to challenge. Faecal egg counts after impulse challenge with 10,000 normal larvae given at about 6$\text{1}\text{2}$ months of age showed a significant ranked correlation with those obtained during the primary exponential challenge. These results confirm that a proportion of young lambs respond to vaccination with irradiated larvae, and that genetically-determined factors are implicated in the ability of animals to respond to vaccination at an early age.     

Autonomy for a specific gene product in oocytes: Experimental evidence in the polychaetous annelid,Platynereis dumerilii

Oocytes of Platynereis dumerilii in early vitellogenesis were injected into female worms with oocytes of similar diameter. The donor oocytes were labeled by the or gene controlling eye pigmentation and, after some weeks of growth, were spawned together with the host oocytes. In most cases, a few donor progeny could be found among the offspring produced by the hosts. Donor progeny were examined with respect to an or gene-dependent maternal effect which normally causes wild-type eye color in homozygous ($\text{or}\text{or}$) larvae originating from the crossings of heterozygous ($\text{or}{}^{\mathrm{+}}\text{or}$) females and homozygous ($\text{or}\text{or}$) males. This maternal effect was absent from homozygous ($\text{or}\text{or}$) larvae derived from homozygous ($\text{or}\text{or}$) donor oocytes which had developed in heterozygous females. Conversely, this maternal effect was observed in homozygous ($\text{or}\text{or}$) larvae derived from heterozygous ($\text{or}{}^{\mathrm{+}}\text{or}$) donor oocytes which had developed in homozygous ($\text{or}\text{or}$) host females. It is concluded that the oocyte genome is active at the or⁺ locus during oogenesis and that the oocyte is autonomous with respect to the product of synthesis of the or⁺ locus. In the present case, the “maternal effect” is therefore caused by synthetic activity in the growing oocyte. The results are discussed with respect to current information on gene products from animal genomes.     

Occurrence of a non-cellular suprazonary layer in embryos collected from prepuberal calves

Twenty Angus calves between 4 and 7 months of age were randomly assigned to one of two superovulation treatment groups. Group I consisted of ten calves which were injected intramuscularly with 50 mg of progesterone 4 and 2 days before injection with 1200 I.U. of PMSG followed 72 hrs later by 50 mg of LH given intravenously. Group II consisted of ten calves which were not injected with progesterone before receiving PMSG and LH as in Group I. Both groups of calves were inseminated by the rectal fixation method with two straws of frozen semen 72 hrs after PMSG injection and at subsequent 12 hr intervals for a total of four inseminations. All semen was extended from a single ejaculate from one bull. Embryos were recovered by surgery or slaughter 48 to 72 hrs following the last insemination. A total of 80 and 70 ovulations were recorded from treatment Group I and II, respectively. Recovery and fertilization rates were 66 and 57% following progesterone treatment and 67 and 51% in calves without progesterone pretreatment. Seventy-seven percent ($\text{23}\text{30}$) of the fertilized embryos recovered in treatment Group I exhibited a suprazonary layer. This suprazonary layer appeared to be non-cellular on the basis of eosin-hematoxylin staining and ranged in thickness from 3 to 24 μm. All fertilized embryos in treatment Group II and unfertilized eggs in treatment Groups I and II, possessed completely smooth zonae pellucidae with no evidence of a suprazonary layer. These observations suggest that the conditions of the progesterone treated prepuberal tract, coupled with the process of sperm penetration of the oocyte, result in the formation of a non-cellular layer which surrounds the zona pellucida to varying degrees of thickness. The influence of this suprazonary layer on embryo viability in prepuberal calves remains to be determined.     

Trichinella spiralis: mediation of the intestinal component of protective immunity in the rat by multiple, phase-specific, antiparasitic responses.

Rats infected orally with Trichinella spiralis developed an immunity that was induced by and expressed against separate phases of the parasite's enteral life cycle. Infectious muscle larvae generated an immune response (rapid expulsion) that was directed against the very early intestinal infection and resulted in the expulsion of worms within 24 hr. This response eliminated more than 95% of worms in an oral challenge inoculum. Developing larvae (preadults) also induced an immune response that was expressed against adult worms. The effect on adults was dependent upon continuous exposure of worms to the immune environment throughout their enteral larval development. Immunity induced by preadult T. spiralis was not expressed against adult worms transferred from nonimmune rats. While adult worms were resistant to the immunity engendered by preadults they induced an efficient immunity that was autospecific. Both “preadult” and “adult” immunities were expressed in depression of worm fecundity as well as in the expulsion of adults from the gut. However, the two reactions differed in respect to their kinetics and their efficiency against various worm burdens. Preadult immunity was directed mainly against fecundity whereas adult immunity favored worm expulsion. All responses (rapid expulsion, preadult and adult immunity, and antifecundity) acted synergistically to produce sterile immunity against challenge infections of up to 5000 muscle larvae. These findings indicate that the host protective response to T. spiralis is a complex, multifactorial process that operates sequentially and synergistically to protect the host against reinfection.     

Nematospiroides dubius: arrested development of larvae in immune mice.

When immune NIH mice were killed 10 days after a challenge infection with Nematospiroides dubius, approximately 10% of the inoculated larvae were recovered from the intestinal lumen, irrespective of the dose administered. When such mice were treated with cortisone from Day 10 for a period of 8 to 14 days and were subsequently killed for worm counts, it was found that they had significantly more worms than the immune control mice killed on Day 10. During the week following the beginning of treatment with cortisone there was little change in the low worm burdens in immune mice. However, 9 to 11 days after this treatment worm counts indicated that worms were accumulating in the intestinal lumen, and concurrently eggs were recorded in the feces of the mice. These observations indicated that a period of 9 to 11 days was required after the initiation of cortisone treatment on Day 10 for the worms in immune mice to complete their development to the adult lumen-dwelling stage. It is suggested that the larvae in the challenge infection became arrested early in their development in the intestinal wall and that growth resumed only after cortisone treatment. When treatment with cortisone was initiated later after challenge, it was still effective in reactivating arrested worms, but the lower worm recoveries in these mice indicated that the arrested larvae were being slowly rejected by the host. In subsequent experiments it was established that the arrested larvae of N. dubius were insusceptible to the activity of pyrantel embonate, an anthelmintic which is 99% effective against adult worms in the intestinal lumen. The mechanism whereby the larvae of N. dubius became arrested in immune mice and subsequently resumed their development after cortisone treatment is discussed.     

The oxygen consumption of non-dormant and dormant larvae of Chironomus plumosus (Diptera)

The physiological expression of a short-day-induced dormancy (Oligopause) of 4th-instar Chironomus plumosus larvae was investigated by measuring the oxygen consumption. By means of a polarographic continuous-flow respirometer the oxygen consumption of single larvae or groups of larvae (up to 5) could be measured continuously over a period of several hours. The oxygen consumption of dormant larvae is lower than in non-dormant larvae: in relation to the individual it is reduced by about $\text{1}\text{3}$, in relation to 1 g of dry weight by about $\text{1}\text{2}$. Dormant larvae are heavier than non-dormant larvae. In the dormant larvae, the proportion of dry weight to total weight is higher than in the non-dormant larvae. The increased proportion of dry weight is composed of a size-specific (dormancy-independent) and a dormancy-specific component. Independent of the sex and dormancy state, the larger larvae have a lower oxygen consumption per weight unit than the smaller larvae. A sex-specific difference can be observed: when animals with identical oxygen consumption per weight unit are compared, the females are considerably heavier than the males.     

Regulation of Haemonchus contortus populations in sheep exposed to continuous infection

Groups of sheep were infected three times weekly for 15 weeks with infective larvae of Haemonchus contortus at four rates ranging from 600 to 4800 larvae per week. At 3-weekly intervals, sheep from each group were killed for total worm counts after receiving a dose of radiolabelled larvae which enabled a direct measurement of establishment of incoming larvae during the continuing infection. Peak H. contortus burdens were reached between 6 and 9 weeks of infection, and were related to infection rate. In the groups receiving 2400 and 4800 larvae per week, worm numbers then declined rapidly and by the end of the experiment were lower than those in the groups given 600 or 1200 larvae per week. Establishment of incoming larvae was not influenced by infection rate, and declined from 45% in the first 4 weeks of infection to insignificant levels during the final 6 weeks. The proportion of incoming larvae arrested in their development increased as the infection progressed. It was concluded that H. contortus numbers were regulated by development of resistance to infection and by a loss of established worms which was related to the current rate of larval intake, and to the host's previous experience of infection.