The application of mass spectrometry to identify immunogenic components of excretory/secretory products from adult Dictyocaulus viviparus

Proteomics has come to the forefront in the post-genomic era. The ability to compare and identify proteins expressed in a particular cell type under specific physiological or pathological states requires a range of technologies, including separation of complex protein or peptide mixtures, densitometry-based or isotope-coded methods for comparison of multiple proteomes, and mass spectrometric methods for identification of individual low abundance proteins. Although an emergent technology, thus far, proteomics has provided new perspectives on many problems in biomedical science. In parasitology, proteomics has been used to answer specific biological questions relating to survival and development, and also to identify candidates for vaccines. Here, we describe an ongoing research programme in which proteomics is being used to identify potential vaccine candidates for the bovine lungworm, Dictyocaulus viviparus. This work is focusing on antibody responses to the adult parasite excretory/secretory (ES) products, with selection of candidate antigens based on differential screening with serum from immune versus non-immune animals to simplify the proteome and the ensuing analytical challenges. Thus far, we have identified seven candidate proteins using this strategy. Of these, one protein showed significant identity to a previously cloned gene from D. viviparus, whilst the other six proteins have shown no significant identities. Isolation of further peptide sequences is now warranted to facilitate cloning of the genes encoding these antigens.

DifferentialN-glycan- and protein-directed immune responses inDictyocaulus viviparus-infected and vaccinated calves

Calves with naturally acquiredDictyocaulus viviparusinfection mount an effective immune response. In the search for protection-inducing antigens, we found that severalD. viviparusthird-stage larval (L3) and adult ES products carry N-glycans. Deglycosylation of the worm antigens using PNGase F resulted in reduced IgA, IgE, IgG1 and IgG2 (but not IgM) reactivities in sera of primary infected animals, suggesting that the carbohydrate moieties contained immunodominant epitopes. Challenge infection resulted in increased specific serum antibody levels against ES and L3 in the re-infected and challenge control groups. Testing of sera by enzyme-linked immunosorbent assay (ELISA) demonstrated a significant increase in IgG1 and IgE (but not IgA or IgG2) reactivity against the deglycosylated antigens in the re-infected group compared with the challenge control group. Sera from calves vaccinated with irradiated larvae showed a strong anti-N-glycan response, but no booster response against the protein backbone after challenge infection, consistent with the absence of a memory response. Together, our results suggest thatD. viviparusproteins carry immunodominant N-glycan moieties that elicit a strong but short-lived immune response during infection and after vaccination, whereas the protein backbones effectively induce a memory response which results in a long-lasting, potentially protective immune response in re-infected, but not in vaccinated calves.

Preventive vaccination of lactating and pregnant heifers against lungworm: safety and protection in three dairy herds

A study of the safety of a vaccine against lungworm was carried out with pregnant and lactating heifers from three dairy herds with a previous history of lungworm outbreaks in adult cows. Half of the heifers were vaccinated while the other half were not. A slight temporary cough following the vaccination was only observed in one herd. No adverse effects on pregnancy or milk production were seen. All heifers were serologically and coprologically examined before the first, before and after the second immunization, 3 months after introduction to pasture and at the end of the grazing season. Serological and faecal examination of the dairy cows before introduction into pasture confirmed the presence of at least one Dictyocaulus viviparus carrier in each herd. Lungworm infection occurred in all herds during the grazing season, most prominently in the herd with the highest number of heifers. In this herd, mild coughing associated with the lungworm infection was noticed, especially in the non vaccinated heifers. No other signs or symptoms were observed. It is concluded that a vaccine against D. viviparus can be used safely in heifers, before they are introduced into the adult herd, and that this vaccine can be used as a preventive measure against lungworm outbreaks in adult cattle.

Efficacy trial of an irradiated cattle lungworm vaccine in red deer (Cervus elaphus)

Lungworm (Dictyocaulus sp.) is the parasite of most concern to the New Zealand deer industry. Although lungworm can be controlled by anthelmintics there is an increasing concern over excessive drenching programmes and reliance on chemicals for parasite control. A live irradiated larval vaccine developed for cattle has been available in Europe for the past 40 years but has never been evaluated in red deer in New Zealand. Four groups of red deer and two of cattle were hand reared from birth in parasite-free conditions. The cattle acted as a control group to ensure that the vaccine was still efficacious on arrival in New Zealand. Two groups of deer were vaccinated, and all four groups were challenged with either D. viviparus or deer origin Dictyocaulus, tentatively identified as D. eckerti. The vaccine provided excellent protection to cattle under New Zealand conditions, there was no larval output in the vaccinated cattle and no adults were found in their lungs at necropsy. In red deer, patency was delayed in the vaccinated groups regardless of challenge species and larval output was lower but was not prevented. Adult lungworms were found in the lungs of all deer at necropsy but fewer were recorded in the vaccinated deer. Although Huskvac provided a degree of protection for red deer it was not effective enough to recommend its use.

[Lungworm disease in dairy cattle: symptoms, diagnosis, and pathogenesis on the basis of four case reports]

Clinical lungworm disease appears to occur frequently in Dutch dairy herds. Because the clinical diagnosis is difficult to make in adult cattle, the clinical diagnosis, laboratory diagnosis, differential diagnosis, therapy, and prevention are discussed in this article. In addition, four cases of lungworm disease in adult cattle are presented. The main clinical complaints were coughing, decreased milk production, and weight loss. Several lactating cows died in one herd. The disease history of four herds revealed that introduction of susceptible cows or heifers to herds with cows with subclinical patent lungworm infections had resulted in a pasture infection, leading to clinical problems in both the newly introduced and 'resident' cows of the herd. Further history analysis of the fourth herd revealed that re-introduction of lungworm infection by newly purchased cows in a lungworm free herd resulted in clinical lungworm problems in adult and young animals. The fourth case led to the conclusion that lungworm infection must have been re-introduced by cows purchased from another farm.

Dictyocaulus viviparus: re-emerging or never been away?

For over 40 years a highly effective vaccine against the bovine lungworm has been commercially available. The use of it successfully reduced the number of outbreaks in calves. However, the past decade has seen a dramatic increase in lungworm outbreaks in adult cows in the UK. This might indicate that Dictyocaulus viviparus is re-emerging as a significant parasite in the dairy cattle industry. Much is still unknown, and here the most important aspects requiring urgent attention are put into perspective.

Treatment vs non-treatment of helminth infections in cattle: defining the threshold

Helminth infections are an important cause of lost productivity in livestock world-wide, often necessitating anthelmintic treatment. However, a large part of the anthelmintics are used indiscriminately because the parasite levels are too low to justify treatment or because the treatments are not correctly programmed, resulting in undertreatment or overtreatment. The objective of this paper is to discuss possible thresholds for anthelmintic treatment of some of the more important helminth infections in livestock, i.e. gastrointestinal nematodes, lungworms and liver fluke, to promote a more appropriate use of anthelmintics. When possible, a distinction is made between therapeutic thresholds, production-based thresholds and preventive thresholds. A "therapeutic threshold" is intended to identify (an) animal(s) with parasite levels that necessitate immediate treatment. The therapeutic threshold is basically the diagnosis of clinical disease, and can be determined relatively easily for the parasites discussed in this paper. A "production-based threshold" is intended to measure the effects of sub-clinical parasitism on productivity parameters, such as weight gain and milk yield, before clinical disease occurs. Finally, a "preventive threshold" is meant to predict future infection levels, to enable the application of appropriate control measures.

Immunisation of cattle with recombinant acetylcholinesterase from Dictyocaulus viviparus and with adult worm ES products

Dictyocaulus viviparus causes a serious lung disease of cattle. For over 30 years, a radiation-attenuated larval vaccine has been used with success; however, this vaccine has several disadvantages. A more stable vaccine against D. viviparus, capable of stimulating prolonged protective immunity, would be beneficial. Recent research has been directed at adult worm ES components that may be involved in parasite survival in the host. One component is the secreted enzyme, acetylcholinesterase (AChE), a target for circulating antibody in infected calves. Here, we describe a study where protection was investigated in calves immunised with either native adult ES products or a recombinant parasite AChE. These antigens were administered twice with Freund's incomplete adjuvant. Subsequently, all calves were challenged with 700 L3 and their worm burdens and immune responses compared with those in calves that received an anthelmintic-abbreviated infection and challenge control calves. Significant levels of protection were not obtained in the immunised groups but significant immunity was achieved in the calves that received the anthelmintic abbreviated infection. Antibody responses amongst the groups were different, with significantly higher IgG1 responses in the immune, infected group and in adult ES recipients. Significantly higher IgG2 responses were found in the latter group. Following challenge, the groups that received the abbreviated infection and the fusion protein produced specific antibody that bound the native enzyme. No differences were observed between groups in peripheral blood mononuclear cell responsiveness to either antigen. However, adult ES products appeared to have a mitogenic effect on these cells, whilst the fusion protein exhibited an inhibitory effect. These results suggest that in this form, AChE is not a potential vaccine candidate and that adult ES products, in contrast to previous experiments in guinea pigs, do not contain protective components.

Vaccine development and diagnostics of Dictyocaulus viviparus

Parasitic bronchitis is a serious disease of cattle and is caused by the nematode, Dictyocaulus viviparus. For over 30 years, a radiation-attenuated larval vaccine has been used for prevention of this disease. This vaccine has been used with considerable success in the UK and parts of Western Europe, however, it has several disadvantages. It has a short shelf-life and the vaccine has to be produced annually necessitating the use of donor calves. Following vaccination, calves must receive further boosting from natural challenge to maintain protective immunity. Sales of the irradiated larval vaccine have decreased dramatically since the 1970s. This is thought to be due to increased reliance of farmers on anthelmintic programmes to control lungworm infection. It is possible that, under certain circumstances, these programmes do not allow sufficient parasite exposure to stimulate protective immunity to further Dictyocaulus challenge. This is borne out by the recent documented increase in the number of outbreaks of parasitic bronchitis in the UK. A stable vaccine against D. viviparus that is capable of stimulating a more prolonged immunity would be beneficial. Recent research has been directed at identification and isolation of components thought to be involved in parasite survival in the host and examination of their potential as vaccine candidates. One of these components is acetylcholinesterase (AChE), an enzyme secreted by adult worms. This review describes the development of the secreted AChE as a vaccine candidate, as well as documenting recent developments in the immunodiagnosis of D. viviparus.

Cross-sectional serological survey on gastrointestinal and lung nematode infections in first and second-year replacement stock in the netherlands: relation with management practices and use of anthelmintics

A cross-sectional survey was carried out on 86 farms randomly distributed in The Netherlands. After housing following the first and the second grazing season (FGS and SGS) serum samples were collected to determine IgG levels against Cooperia oncophora and Dictyocaulus viviparus, and the pepsinogen content. A questionnaire was used to inquire on grazing management practices and the use of anthelmintic drugs. On 80.7 and 60.2% of the farms FGS and SGS animals, respectively, were treated at least once with an anthelmintic drug. The percentage for the SGS animals indicates that the use of anthelmintic drugs in those animals has increased enormously over the last 10-15 years. Generally, parasitic nematode control in the FGS is good on most farms, but it can be characterised as being overprotective. There is a tendency that if anthelmintic drugs are used in the FGS they also are used more often in the SGS. On 12 farms (14%), no anthelmintic drugs were given in the FGS and the SGS. These farms did not differ from the others with respect to management practices in any obvious way. The serological results were in general very low, indicating low levels of exposure to gastrointestinal nematode infection in both FGS and SGS animals. This was not surprising in view of the good to high level of nematode control practices reported by the farmers. Although not statistically significant, a consistent result was that serological results for the SGS animals were more often positive or on average higher on those farms where FGS parasite control tended to be excessive. For D. viviparus, a prevalence rate of 41% positive farms was found. Following comparison with previous data, it is speculated that lungworm (sero-)prevalence in replacement stock may be declining as a result of continuing high levels of parasite control in replacement stock. It is concluded that the results confirm previous surveys, lending support to the conclusion that parasitic nematode control on Dutch dairy farms, certainly in FGS calves, is good but tends to be overprotective.

The efficacy of two isolates of the nematode-trapping fungus Duddingtonia flagrans against Dictyocaulus viviparus larvae in faeces

A series of experiments was carried out to examine the effects of two different isolates of the nematode-trapping fungus Duddingtonia flagrans to reduce the number of free-living larvae of the bovine lungworm, Dictyocaulus viviparus. A laboratory dose-titration assay showed that isolates CI3 and Troll A of D. flagrans significantly reduced (P < 0.05 to P < 0.001) the number of infective D. viviparus larvae in cultures at dose-levels of 6250 and 12,500 chlamydospores/g of faeces. The larval reduction capacity was significantly higher for Troll A compared to CI3 when lungworm larvae were mixed in faecal cultures with eggs of Cooperia oncophora or Ostertagia ostertagi and treated with 6250 chlamydospores/g of faeces. Both fungal isolates showed a stronger effect on gastrointestinal larvae than on lungworm larvae. Two plot trials conducted in 1996 and 1997 involved deposition of artificial faecal pats containing free-living stages of D. viviparus and C. oncophora on grass plots. Herbage around the pats was collected at regular intervals and infective larvae recovered, counted and identified. These experiments showed that both D. flagrans isolates reduced the number of gastrointestinal as well as lungworm larvae in faecal pats. During both plot trials, the transmission of C. oncophora larvae, but not D. viviparus, from faecal pats to the surrounding herbage was clearly affected by climatic conditions. After collection of faecal pats from the grass plots one month after deposition, the wet and dry weight of pats as well as organic matter content were determined. No differences were found between the fungus-treated and non-treated control pats. This indicated that the rate of degradation of faeces was not affected by the addition of the fungus.

Strategic control of gastrointestinal nematode and lungworm infections with eprinomectin at turnout and eight weeks later

Two groups of 10 first-year grazing cattle were either left untreated as controls (group 1) or treated with eprinomectin as a pour-on application at turnout and eight weeks later (group 2). The control group developed a mild infection with gastrointestinal nematodes and lungworms during the season, whereas the treated animals remained healthy. The interval between the treatments allowed the establishment of adult worms, but the egg counts remained negligible. The total number of eggs shed by the treated cattle during the grazing season was significantly smaller than by the controls.

[Prevention of gastrointestinal and lungworm infections in alpine calves: use of doramectin pour-on in before and after the alpine grazing season]

The effect of doramectin pour-on (Dectomax 0.5% pour-on, Pfizer) against gastrointestinal nematodes (GIN) and lungworms was investigated in calves grazed on alpine pastures in Switzerland. Doramectin pour-on (0.5 mg/kg body weight) was administered topically to calves (n = 57, Group D) before and after the alpine grazing season (mid-June to end of September) when the calves were kept on altitudes between 1800 and 2600 m together with 20 untreated calves (Group K). Calves of both groups were grazed together during the alpine season and were subsequently moved to prealpine and home pastures where they were kept until stabling (end of November). Faecal examinations, performed 4 to 5 weeks after anthelmintic treatment of Group D calves showed a marked reduction of the trichostrongyle egg output, which was also low in the untreated calves. Low numbers of Dictyocaulus-larvae were excreted by the calves at turnout to the alpine pastures. At the end of September the mean excretion of Dictyocaulus-larvae had increased markedly in both groups. After treatment of Group D calves the larval output remained negative until stabling. In contrast, the larval excretion of the untreated calves (Group K) reached highest levels at the end of October and 4 calves exhibited clinical signs of dictyocaulosis. The results indicate that the strategic use of doramectin pour-on in June and in late September provided good protection against severe infections with D. viviparus. The infection level with GIN confirmed that these parasites are of minor relevance under the extensive grazing conditions on high alpine pastures.

The efficacy of Michel's dose and move system on gastrointestinal nematode infections in diary calves

The efficacy of a move to aftermath in July combined with moxidectin or fenbendazole treatment for the control of parasitic gastroenteritis (PGE) in calves was evaluated in three field experiments in the Netherlands. In all five treated groups high gastrointestinal nematode infections and PGE were prevented by a dose and move in July. Cooperia infections increased to moderate levels in two groups treated with moxidectin and one group treated with fenbendazole. In both other groups and also for Ostertagia in these three groups, low to extremely low infections were acquired. In the first experiment high primary infections, resulting in high faecal egg counts and a moderate increase of blood pepsinogen values occurred before the dose and move. Nevertheless, these primary infections were not high enough to result in PGE. In both other experiments primary infection levels were low and faecal egg counts increased to 100-650 eggs/g faeces at the end of the grazing season. The blood pepsinogen values of non-treated control groups demonstrated that it took more than a month after their move to aftermath before substantial reinfection occurred on the new pasture. In the first and the last experiment only, high Ostertagia and Cooperia infections developed in the control group at the end of the grazing season, though it did not result in clinical PGE. The experiments demonstrate all theoretical risks of the dose and move system: (1) PGE early in the grazing season as a result of high overwintered pasture infectivity. (2) PGE just before the move as a result of an early midsummer increase in pasture infectivity. (3) PGE around housing as a result of insufficient suppression of pasture infectivity late in the grazing season. (4) Underexposure to nematode infections due to a high suppression of nematode infections. Nevertheless, it can be concluded that under normal conditions the dose and move system remains to be a valuable and easily applicable system for the control of PGE.

Field evaluation of a topical doramectin formulation for the chemoprophylaxis of parasitic bronchitis in calves

A study was conducted to evaluate the efficacy of two topical treatments with doramectin on the season-long control of lungworm and gastrointestinal infections in first grazing season (FGS) calves. At the start of the study, 20 FGS calves were randomly allocated into two treatment groups of 10 animals each. Calves in the D-group were treated with doramectin pour-on on days 0 and 56, at a dosage of 500 microg kg(-1) BW: calves in the C-group were designated as controls. A permanent pasture was divided in two blocks and these were randomly allocated to the treatment groups. Throughout the study, tracers (n = 32) were grazed on each paddock at 3-week intervals. Clinical signs of parasitic bronchitis (PB) were observed in the C-group in July and this necessitated two salvage treatments with levamisole. From day 28, post-turnout lungworm larvae were recovered from faeces of the C-calves until housing. No signs of PB were observed in the D-group during the entire grazing season. Shedding of lungworm larvae in the principals of the D-group did not occur until 112 days post-turnout. From the data obtained from the tracer calves. it appeared that larvae had overwintered on both pastures. On the C-pasture, the number of lungworms recovered from the tracer calves gradually increased to a peak in September, whereas on the D-pasture, the increase was observed only at the end of the pasture season. Both strongyle faecal egg counts and pepsinogen levels were relatively low in both groups throughout the present study. At the end of the grazing period (day 161). the principals were housed and treated with oxfendazole. During the housing period, all principal animals (D- and C-groups) and a third group of four helminth free animals (N-group) received a challenge infection with Dictyocaulus viviparus. It appeared that the different exposure to the parasite during the grazing season resulted in different establishment rates, i.e.. group C < group D < group N. The present results show that overwintering of lungworm larvae occurs in Belgium and that in such conditions, doramectin pour-on given at turnout and at 8 weeks controls PB in calves during the first grazing season.

Protection against Dictyocaulus viviparus in second year cattle after first year treatment with doramectin or an ivermectin bolus

Forty-five calves were assigned randomly to three groups of 15 at turnout (day 0) in the spring of their first grazing season on to separate paddocks on a pasture known to carry infective larvae of Dictyocaulus viviparus. Group 1 calves were left as untreated controls, group 2 were injected with doramectin at 200 micrograms/kg at turnout and again on day 56, and group 3 were treated with an intraruminal bolus containing ivermectin. From day 42 onwards group 1 calves developed parasitic bronchitis which required repeated treatment with levamisole. The two endectocide regimes controlled lungworm infection, although some calves in group 2 developed some coughing during the week before the second dose of doramectin. After the end of the grazing season and again in May of the following year, five cattle from each group were infected experimentally with lungworm larvae and slaughtered 28 days later for lungworm counts and measurements of length to be made. At both times group 1 calves were found to be largely resistant to reinfection; group 2 were slightly more susceptible although the differences from group 1 were not statistically significant. Group 3 calves were more susceptible with no significant difference in worm counts from naive infection controls.

An attempt to control lungworm disease and parasitic gastroenteritis on commercial dairy farms by the use of an adaptation of Michel's dose-and-move system

On seven dairy farms an attempt was made to control lungworm disease in calves by turnout on a pasture grazed earlier by cows, followed by a move to aftermath and ivermectin treatment 2 months later. Transmission of lungworm was observed on all farms. Lungworm disease occurred on four farms at treatment. Coughing re-occurred on three of these farms in some animals 2 months later. Owing to poor performance between turnout and treatment, weight gain was below the norm on the farm with the highest infections and most severe respiratory signs. On the other farms respiratory signs did not result in poor weight gain. Gastrointestinal nematode infections remained low on all farms. The conclusion is that this dose and move scheme cannot be recommended for the control of lungworm.

Persistent efficacy of topical moxidectin against Dictyocaulus viviparus and Ostertagia ostertagi

The persistent activity of moxidectin topically administered at the dose rate of 0.5 mg kg-1 bodyweight was evaluated against experimental nematode infection in 30 calves randomly allocated to six groups. Five groups were treated on days -42, -35, -28, -21 and -14. The 6th group remained untreated as a control. On Day 0, the calves were infected experimentally with 1000 Dictyocaulus viviparus and 50,000 Ostertagia ostertagi larvae and killed 3 weeks later. The formulation of moxidectin showed excellent activity against both parasites for up to 5 weeks (> 99%). Six weeks after treatment the reduction in the number of D. viviparus was still high (> 90%). No adverse reactions to moxidectin were observed in any of the animals.

Nematode-trapping fungi in biological control of Dictyocaulus viviparus

Larvae of the cattle lungworm Dictyocaulus viviparus were cultured in experimental units of 200 g cattle faeces placed in semi-transparent trays in the laboratory. In each of 4 experimental series using this experimental unit, chlamydospores (chl) of the nematode-trapping fungus Duddingtonia flagrans were admixed to half of the faecal cultures in a concentration of 50.000 chl/g. In all 4 series there was a significant reduction in the development and subsequent release of infective lungworm larvae from faecal cultures containing chlamydospores. The average reduction in larval release, caused by fungal spores, was 86%.

Prophylaxis of bovine trichostrongylidosis and dictyocaulosis in the alpine region: comparison of an early and late administration of the oxfendazole pulse release bolus to first year grazing calves

The effect of the oxfendazole pulse release bolus (OPRB) administered at turnout, in May, or in mid-July on the development of infections with gastrointestinal nematodes and lungworms in first year grazing calves was investigated with three groups of nine animals, all grazing the same pastures in the Swiss midland region. In the calves of Group A (OPRB on 21 May) less than 20 eggs per gram of faeces (e.p.g.) and less than three Dictyocaulus larvae per 10 g (1.p.10 g) of faeces were shed for a period of 126 and 140 days respectively. Towards the end of the grazing period calves of this group excreted significantly higher levels of lungworm larvae (P < 0.05) compared with the other groups. Prior to OPRB administration on 14 July, the calves of Group B developed subclinical infections with trichostrongyles and lungworms which were similar to the untreated control Group C. By 4 weeks after bolus-administration the excretion of trichostrongylid eggs and lungworm larvae declined to levels below 20 e.p.g. and six l.p.10 g respectively. Serum pepsinogen values of the calves of Groups A and B were significantly lower (P < 0.05) compared with the control animals on days 84 and 98 after turnout and reflected mainly subclinical infections. With the exception of one Group A calf developing clinical parasitic gastroenteritis (p.g.e.) at the end of the season, clinical disease was not observed in the treated calves, while seven out of nine control animals grazing on the same pastures exhibited clinical p.g.e. with mean serum pepsinogen values exceeding 4400 mU tyrosine. Calves of Groups A and B gained significantly more weight (P < 0.01) compared with Group C (+36 kg and +41 kg respectively); differences between Groups A and B were not significant. The results indicate that in mixed grazing systems of treated and untreated calves, which are often found in the alpine region, administration of the OPRB in May or July provided good results with respect to performance of the calves. However, late administration of the OPRB has the additional advantage of coverage of the period of higher infection risk with trichostrongyles and lungworms in the late season until stabling, and should therefore be recommended.

Comparison between fenbendazole and moxidectin applied in a dose and move system for the control of Dictyocaulus viviparus infections in calves

A grazing study was performed with the main objective to compare the effect of moxidectin (MDT) and fenbendazole (FBZ) in a 'dose and move' system on nematode infections in calves with special emphasis on Dictyocaulus viviparus. Three groups of six calves were grazed from May to October 1994. All groups grazed together until 9 weeks after turnout when they were moved to separate mowed pastures. One group (MM) was then treated with 0.5 mg kg-1 MDT pour-on, the second group (FM) was treated with 7.5 mg kg-1 FBZ drench and the third group served as untreated pasture control group (PC). Two calves from MM and two from FM were experimentally infected with 20 lungworm larvae at turnout in order to initiate low infections in the herd. Pairs of tracer calves grazing during the first 7, 8 or 9 weeks after turnout acquired mean burdens of 218, 255 and 1156 lungworms, respectively. MDT and FBZ treatment removed adult lungworms from MM and FM. In PC faecal larval counts increased until the end of July, when most animals were suffering from lungworm disease. No lungworm disease occurred in both dose and move groups. In FM larvae reappeared in the faeces of some of the calves from 1 month after treatment and low patent infections remained to be present in FM in some calves until the end of the experiment. No reappearance of larvae after treatment was observed in MM. The mean Optical Density (OD) values of the three groups on pasture closely followed the infection patterns. After housing in October all calves, and also a group of five permanently housed non-infected control calves (HC), were infected experimentally with 5000 D. viviparus larvae to evaluate development of immunity. The worm counts at necropsy showed that groups on pasture had developed immunity. However, the degree of immunity was lower in MM than in FM and PC.

Evaluation of the effect of the fenbendazole sustained-release intraruminal device on the immunity of calves to lungworm

Each of 10 set-stocked calves was given a fenbendazole sustained-release intraruminal bolus at turnout for the control of parasitic bronchitis while a group of 10 similar calves was left untreated. The respiratory rates of the control calves were not greatly increased during the grazing season, but persistent coughing was evident from early July when they all had patent lungworm infections. Only occasional coughing was reported from the bolus-treated calves except for a transient increase in its frequency in late September. In mid-August, one of the treated calves was passing lungworm larvae and when they were housed six of the 10 had patent infections. In August tracer calves picked up an average of 23.5 lungworms per day from the control paddock but only 2.1 from the paddock grazed by the treated calves. In September the corresponding figures were 7.6 and 19.2 lungworms per day, respectively, from the control and 'treated' paddocks. After housing, the post mortem worm counts after an experimental challenge with Dictyocaulus viviparus larvae were reduced by 99.2 and 98.7 per cent (P < 0.0001), respectively, for the control and bolus-treated calves in comparison with weight-matched parasite-naive calves. Thus, despite a relatively low level of challenge during the grazing season, the treated animals had developed a considerable degree of protective immunity.

Development of immunity to lungworm in vaccinated calves treated with an ivermectin sustained release bolus or an oxfendazole pulse release bolus at turnout

The ivermectin sustained release bolus (IVSRB), when used at turnout as recommended, will provide season-long control of parasitic bronchitis, thus obviating the need for use of a lungworm vaccine. However, some concerns have been expressed that calves treated with an IVSRB will receive so little exposure to Dictyocaulus viviparus that it will compromise their immunity in subsequent grazing seasons, which would be of particular importance in dairy herds. Although there is evidence that IVSRB-treated calves can develop immunity to D. viviparus when exposed to pasture infection, it was considered worthwhile to evaluate the compatibility of the IVSRB and lungworm vaccination to allow veterinary surgeons the option of using these products concurrently when they have particular concerns about the long term immune status of replacement dairy heifers. Thirty-two dairy replacement heifers were vaccinated with two doses of lungworm vaccine and, at turnout, half the calves received an IVSRB and the remainder an oxfendazole pulse release bolus (OPRB). At the end of the grazing season four replicate bolus treated pairs and four parasite-naive calves were challenged with 1000 D. viviparus infective larvae. At slaughter there was a 95% and 93% reduction in D. viviparus burdens in the IVSRB and OPRB treated calves respectively, compared with the unvaccinated, untreated controls. These results indicate that where it is considered necessary to use lungworm vaccination in addition to an IVSRB or an OPRB, the compatibility of these products with lungworm vaccine will allow development of a protective level of immunity to D. viviparus.

The therapeutic efficacy and prophylactic activity of doramectin against Dictyocaulus viviparus in cattle

Three groups of 8, 4-month-old male Jersey or Jersey-cross calves were infected with 2400 Dictyocaulus viviparus L3 larvae and either left untreated or injected subcutaneously with 200 micrograms/kg doramectin 5 or 25 days after infection (DAI). Lungworms were found in all untreated cattle (geometric mean = 49) at necropsy 39 or 40 DAI. None was found in any of the treated cattle. In a second experiment, groups of 6, 8-month-old calves were untreated or injected with 200 micrograms/kg doramectin 28, 21 or 14 days before each calf was challenged with 2700 D viviparus larvae. Lungworms were recovered at necropsy 32 to 34 DAI. The geometric mean worm burden in the untreated cattle was 550. This was reduced by 100%, 99.5% and 94.1% in calves treated with doramectin 14, 21 or 28 days, respectively, before infection. It was concluded that doramectin is a highly effective anthelmintic against D viviparus adult or L4 infections of cattle, and that reinfection of treated cattle will be significantly reduced for at least 28 days after treatment.

Immunisation of guinea pigs against Dictyocaulus viviparus using adult ES products enriched for acetylcholinesterases

The adult ES products of Dictyocaulus viviparus are a source of protective antigens against challenge in the guinea pig laboratory model. High levels of acetylcholinesterase (AChE) activity are present in these products and these enzymes are immunogenic in infected cattle. Here, the potential role of these enzymes in protective immunity was investigated using a fraction enriched for AChE to immunise guinea pigs. The antibody response stimulated by immunisation with AChE-enriched ES products and the worm burdens obtained following challenge with infective larvae were compared with those in animals immunised with whole ES products and challenge controls. The AChE-enriched preparation stimulated high levels of enzyme-specific antibody in immunised animals, which was not the case for those which received unfractionaed ES products. Worm burdens of guinea pigs which received the AChE-enriched fraction were significantly lower than those obtained in adjuvant controls. The animals which received the unfractionated ES products were not significantly protected against challenge. These results suggest that AChEs may be potential candidates for incorporation in a sub-unit vaccine against D. viviparus.

Protective immunisation of guinea pigs against Dictyocaulus viviparus using excretory/secretory products of adult parasites

Parasite preparations were examined for their ability to induce protective immunity against Dictyocaulus viviparus in guinea pigs. Dunkin-Hartley strain guinea pigs were immunised with somatic extracts of adult parasites, somatic extracts of third stage larvae or excretory/secretory (ES) products from adult parasites. The groups were immunised twice with Freund's adjuvant four weeks apart and challenged with 6000 infective L3. Significant levels of protective immunity were observed only in the adult ES-immunised animals. The antibody responses of the different groups were compared following analysis by ELISA and immunoprecipitation. To examine the protective role of antibody, guinea pigs were passively immunised with serum from animals immunised with adult ES products or serum from guinea pigs exposed to experimental D. viviparus infection. Following challenge with infective L3, lung-worm burdens of these groups were significantly lower than in guinea pigs which received normal sera. The results suggest that D. viviparus adult ES products contain protective antigens and that antibody-mediated mechanisms contribute to immune protection.

Field evaluation of the efficacy of the fenbendazole slow-release bolus in the control of gastrointestinal nematodes of first-season grazing cattle

The ability of fenbendazole slow release bolus (Panacur SR Bolus, Hoechst) to control gastrointestinal parasitism in calves during their first grazing season at pasture was evaluated in two field trials. The infection level on both investigated farms was low and the control animals did not develop parasitic gastroenteritis. However, it was possible to demonstrate significant differences in the parasitological and biochemical parameters between the control and treated groups during the grazing season. Faecal egg counts and blood pepsinogen levels in the control cattle at both trials sites were significantly higher than those of the bolus-treated cattle.

[Epidemiology and control of lung worm infections in cattle]

The epidemiology and control of lungworm infections in cattle are reviewed. A short introduction is given on the prevalence of lungworm infections and lungworm disease. Thereafter important aspects of the life cycle, the causes of primary infections, the possible causes of outbreaks of lungworm disease and the predictability of lungworm disease are reviewed. Finally different control measures for lungworm disease, vaccination, strategic anthelmintic treatment, vigilance and anthelmintic treatment and grazing management are discussed. It is concluded that vaccination is still the best preventive method.

Parasitic bronchitis in goats and the possible use of Dictyocaulus filaria vaccine for its control

Parasitic bronchitis is widely prevalent in migratory flocks of small ruminants in the northwest Himalayan regions of India. The prevalence data collected from 5554 goats, maintained in 31 villages in different agroclimatic regions of the Himalayas, showed that the prevalence of the disease in goats varied from 18.7 to 47.6% with an overall prevalence of 21.8%. Interestingly, 27.6% of goats maintained at an altitude of 2700-3900 m above mean sea level in Kargil (Jammu and Kashmir), where the climate is cold and dry for the major part of the year, were positive for the lungworm infections. The common lungworms observed were Dictyocaulus filaria, Protostrongylus rufescens, Varestrongylus pneumonicus and occasionally Muellerius spp. The kids were more susceptible to lungworm infections than adult goats. In experimental studies, it was seen that goats were more susceptible to Dictyocaulus filaria infection than sheep and two vaccine doses comprising 1000 and 2000 gamma-attenuated D. filaria (ovine strain) infective larvae conferred 97% protection in male Beetal kids against a homologous challenge dose of 4200 normal D. filaria larvae. The importance of simultaneous control of the disease in goats and sheep is discussed.

Persistent efficacy of doramectin against experimental nematode infections in calves

Three studies were conducted involving cattle exposed to experimental nematode infections. These studies were designed to investigate the prophylactic activity of a single subcutaneous treatment of doramectin at 200 micrograms kg-1 body weight against infections of Ostertagia ostertagi, Cooperia oncophora and Dictyocaulus viviparus. For each study, parasite-naive calves were randomly allocated to either a treated or a matched control group. One group received doramectin and the other received doramectin and the other received either no treatment or an injection of saline at 1 ml per 50 kg body weight by the subcutaneous route. Thereafter, all calves received a daily oral challenge of infective larvae of the particular parasite species on test in each study. Challenge of each pair of treatment/control groups continued for periods of 14, 21 or 28 days. An interval of 14-21 days was then allowed to permit the parasites which had established to mature, after which all animals were slaughtered and their worm burdens determined using standard techniques. Geometric mean worm burdens were calculated from the log worm counts and used to estimate percentage efficacy. Accumulated burdens of C. oncophora in doramectin-treated cattle resulting from a daily challenge infection for 14 or 21 days were reduced by 99.2% and 90.7% respectively, in comparison with those of non-treated control animals. For D. viviparus, burdens were reduced by 100% and 99.9% after a 21 or 28 day challenge, respectively. The corresponding figures for O. ostertagi were 99.9% after a 21 day challenge and 93.7% after a 28 day challenge.

Characterization of excretory-secretory products of adult Dictyocaulus viviparus and the antibody response to them in infection and vaccination

In vitro released products of the adult stage of the bovine lungworm. Dictyocaulus viviparus, were characterized according to their SDS-PAGE profile, glycosylation pattern, in vitro synthesis and antigenicity in the context of infection and vaccination with irradiated larvae. Biosynthetic labelling experiments with 35S-methionine indicated active synthesis of ES throughout this time. There was, however, little incorporation of 3H-glucosamine into ES products, and lectin affinity chromatography and glycopeptidase F digestion identified only one glycosylated component. Immunoprecipitation of 125I-labelled ES products with sera from calves patently infected with D. viviparus demonstrated that all of these, with the exception of two components, are antigenic to the bovine host. One of those not immunoprecipitated was shown to be host serum albumin carried over into culture. A limited degree of cross-reactivity between nematode species was observed, with a D. viviparus female-specific antigen of 290 kDa being recognized by serum antibody from calves infected with the gastrointestinal nematodes Cooperia oncophora and Ostertagia ostertagi. Calves vaccinated with irradiated larvae of D. viviparus, despite not being exposed to the adult stage of the parasite, also showed some recognition of adult ES products. This might suggest that vaccination with irradiated larvae operates against both pre-pulmonary and pulmonary stages of the infection.

Efficacy of abamectin against nematodes in cattle

Eight controlled trials were conducted, using 96 cattle of European breeds, to evaluate the efficacy of abamectin against natural and artificially acquired infections of adult and fourth-stage larvae of all the economically important gastrointestinal nematodes and lungworms in Germany and the United Kingdom. Half the animals were treated on one occasion with abamectin at a dose of 200 micrograms/kg bodyweight given subcutaneously while the other half remained untreated. Worms were counted 14 or 21 days after treatment or 28 days after the last infection. The treatment was highly effective (> 99 to 100 per cent) (P < 0.05) at removing immature (L4) stages and adult worms of the following species: Ostertagia ostertagi (inhibited larvae included), Trichostrongylus axei, Haemonchus contortus, Bunostomum phlebotomum, Cooperia species Oesophagostomum radiatum and Dictyocaulus viviparus. Naturally acquired adult C surnabada and Trichuris discolor infections were also significantly (P < 0.05) reduced. For Nematodirus helvetianus the efficacy varied from 89.8 to > 99 per cent (P > 0.1 to < 0.01). Abamectin gave full protection against the gastrointestinal nematodes O ostertagi, H contortus, Cooperia species and O radiatum for at least seven days and against the lungworm D viviparus for at least 14 days after treatment.

The antibody repertoire in infection and vaccination with Dictyocaulus viviparus: heterogeneity in infected cattle and genetic control in guinea pigs

The antigen recognition profiles of serum antibody from calves infected or vaccinated with irradiated Dictyocaulus viviparus larvae were analysed by immunoprecipitation of radio-iodinated in vitro-released excretory-secretory materials from live adult parasites. Immunoprecipitates were analysed by SDS-PAGE and considerable heterogeneity in antigen recognition between individual animals was observed, regardless of infection regimen. This heterogeneity was also found to occur amongst outbred guinea pigs infected with the parasite and permitted an examination of the genetics of the effect using inbred guinea pigs (Strains 2 and 13). The antibody repertoires of the two strains were distinct, with only slight variation occurring between individuals within a strain. Previous work on nematode infections in rodents has demonstrated a role for the major histocompatibility complex (MHC) in the control of the immune repertoire. If this, as is probable, holds for the guinea pig, then it can be ascribed to the MHC Class II region because Strain 2 and Strain 13 bear identical Class I alleles but disparate Class II alleles. Whilst there is no evidence to date that the efficiency of vaccination of cattle is influenced by genetic factors, the operation of vaccines based on a single or a few molecularly cloned parasite antigens might be seriously compromised by the kind of genetic restriction to the immune repertoire described here.

Use of an ELISA for serodiagnosis of parasitic bronchitis in cattle

The enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of parasitic bronchitis in cattle was evaluated in naturally injected, experimentally infected and vaccinated animals. Significant antibody titres could be demonstrated from five weeks after animals had been exposed to the parasite, so that infected animals could be identified during the summer. The test did not give false positive results in vaccinated animals. The technique proved particularly useful in revealing latent infections in milking herds in the autumn when heavy burdens of worms in the lungs do not generate any larvae in the faeces.

Immunity of calves treated with an oxfendazole pulse release bolus to challenge with Dictyocaulus viviparus

Two experiments were performed to study the effect of an oxfendazole pulse release intraruminal device (OPRB) on the development of lungworm infection and immunity in calves. Infections were monitored in OPRB-treated and control calves by faecal and pastural larval counts. Levels of immunity of grazing groups and helminth-free housed groups were compared by challenge infection. Even though signs of parasitic bronchitis were seen only in control animals, sufficient immunity had developed in OPRB-treated calves to prevent disease after a substantial challenge infection. However, the degree of immunity was less than in untreated grazing control groups and there were indications that it was related to initial infection levels. These results imply that the OPRB may successfully control parasitic bronchitis, provided that pasture larval infections are sufficient to allow the development of immunity.

Comparison of the efficacy of dermal formulations of ivermectin and levamisole for the treatment and prevention of Dictyocaulus viviparus infection in cattle

Four groups of six parasite-naive calves were infected at seven day intervals with three doses of infective larvae of Dictyocaulus viviparus. Twenty-one days after the first dose three of the groups were treated either with an injectable formulation of ivermectin at a dose rate of 200 micrograms/kg bodyweight, or with pour-on preparations of levamisole at 10 mg/kg or ivermectin at 500 micrograms/kg. On day 28 two calves from each group were slaughtered and their burdens of lungworms counted. On day 35 the remaining calves were reinfected with D viviparus infective larvae at a rate of 80 L3/kg. The levamisole preparation was 94.6 per cent effective and both ivermectin preparations were 100 per cent effective against the initial infections. The ivermectin-treated calves were protected from the reinfection which subsequently became patent in the levamisole-treated and control calves.

Comparison of a levamisole sustained-release bolus and ivermectin treatment to prevent bovine lungworm infection

The efficacy of a levamisole sustained-release bolus to prevent parasitic bronchitis in calves in their first grazing season was compared to ivermectin treatment at three, eight and thirteen weeks after turn out. Contamination of the pasture was established by experimentally infected seeder calves. Twenty calves were split into two groups. Ten calves of one group received a bolus at the start of the experiment. In the other group the calves were treated with ivermectin at 21, 56 and 91 days. Two principal calves from each group were killed during the experiment to study histopathological changes. Pairs of tracer calves were introduced on both pastures at intervals of four weeks throughout the grazing period. The permanent calves were challenged with lungworm larvae at housing and slaughtered four weeks later. Both systems prevented parasitic bronchitis. Larval output was completely reduced in the ivermectin-treated calves while all bolus-treated calves excreted larvae at certain times. The highest group average was 4 larvae per gram faeces. Eosinophilia, ELISA-titres and histopathological changes confirmed the differences in larval uptake. Challenge infection was not successful in either group and no worms were found at slaughter. Weight gain was significantly different at housing in favour of the ivermectin-treated calves, but after challenge this was reduced due to a higher weight gain in the bolus-treated calves. The practical consequences of the results have been discussed.