Lungworm Burdens Research Articles

Paratuberculosis, syn. Johne's disease

The annual ewe mortality rate from Johne's disease in some flocks in south-east Scotland is between 2 and 5%. Affected sheep void pelleted faeces until the terminal stages unless there is significant parasitic infection. Very high lungworm burdens are common and may cause coughing. Affected sheep have profound hypoalbuminaemia (serum concentration <15 g/L; normal range greater than 30 g/L) and a normal globulin concentration (protein-losing enteropathy). Thickening of the ileum with prominent ridging is not always obvious but the mesenteric lymph nodes are visibly enlarged. Encouraging results have been reported following vaccination with significantly reduced disease prevalence.

Candidate gene microsatellite variation is associated with parasitism in wild bighorn sheep

The loss of genetic variation in host populations is thought to increase host susceptibility to parasites. However, few data exist to test this hypothesis in natural populations. Bighorn sheep (Ovis canadensis) populations occasionally suffer disease-induced population declines, allowing us to test for the associations between reduced genetic variation and parasitism in this species. Here, we show that individual mean heterozygosity for 15 microsatellite loci is associated with lungworm abundance (Protostrongylus spp.) in a small, recently bottlenecked population of bighorn sheep (linear regression, r2=0.339, p=0.007). This association remains significant for seven microsatellites located in genes (p=0.010), but not for eight neutral microsatellites (p=0.306). Furthermore, heterozygotes at three of four microsatellites located within disease-related genes had lower lungworm burdens. This study corroborates theoretical findings that increased parasitism and disease may be a consequence of reduced heterozygosity in wild populations, and that certain individual loci influence parasite resistance. The results illustrate the usefulness of using genomic information, strong candidate genes and non-invasive sampling for monitoring both genetic variation and fitness-related traits, such as parasite resistance, in natural populations.

RELATIONSHIPS AMONG FECAL LUNGWORM LOADS, FECAL GLUCOCORTICOID METABOLITES, AND LAMB RECRUITMENT IN FREE-RANGING ROCKY MOUNTAIN BIGHORN SHEEP

Most wild Rocky Mountain big-horn sheep (Ovis canadensis canadensis) in northern latitudes are infected with lungworms. Indirect effects of lungworms on bighorn sheep are unknown, but high pulmonary burdens might increase stress (i.e., elevated glucocorticoid levels), and chronic stress could in turn decrease fitness. We hypothesized that high lungworm burdens in Rocky Mountain bighorn ewes increase stress, thereby increasing lamb mortality. To test our hypothesis, one subherd of bighorn sheep in Custer State Park, South Dakota was provided a free-choice loose mineral mix containing the anthelmintic fenbendazole every six weeks from March 1999 to August 2000 to eliminate lungworms; another subherd served as the control. Daily, individually marked ewes were located telemetrically from the ground and uniquely marked animals were observed until they defecated. After the herd moved from the area, fecal samples were collected and stored at -23 C. A consistent number of samples per season per herd (x-=16.56+/-3.99 samples) were collected. Fecal larval lungworm levels (LPG) in the treatment subherd were lower than levels in the control subherd; however, there was no difference in fecal glucocorticoid metabolite (FGM) levels between the two subherds. Fecal glucocorticoid metabolite levels varied by season in both subherds, with levels in winter lower than during the other three seasons. Lamb:ewe ratios were not different between the control and treatment subherds at the end of summer 1999. In contrast, the treatment group had a lower lamb:ewe ratio at the end of summer 2000 despite having lower LPG. However, this result was attributed to lower ewe production, not lower lamb survival. The LPG levels were not correlated with FGM concentrations; instead, FGM levels might reflect normal seasonal patterns. Other factors, including contagious ecthyma, were more important for determining lamb mortality than LPG and FGM levels during our study. We suggest further experimental work over a longer duration to address these relationships.

Effect of forage legumes containing condensed tannins on lungworm (Dictyocaulus sp.) and gastrointestinal parasitism in young red deer (Cervus elaphus)

To investigate the effect of feeding forage legumes containing condensed tannins (CT) on internal parasitism, red deer calves were fed either lucerne (Medicago sativa; 0.1 per cent CT), birdsfoot trefoil (Lotus corniculatus; 1.9 per cent CT) or sulla (Hedysarum coronarium; 3.5 per cent CT) and trickle-infected with deer-origin gastrointestinal nematode and lungworm (Dictyocaulus sp.) larvae for 5 weeks, then slaughtered at 7 weeks. There was a significant negative linear relationship between dietary CT concentration and abomasal nematode burdens. No significant differences in faecal egg counts, lungworm burdens or voluntary feed intake were found. Deer fed sulla had higher liveweight gain, carcass weight and carcass dressing-out percentage, higher serum total protein and albumin concentration and lower serum gastrin concentration and faecal lungworm larval count, compared with lucerne-fed deer. Inclusion of sulla in diets for young red deer may reduce the impact of internal parasites and/or reduce the dependence on anthelmintic treatment.

A quantitative approach to nematode lungworm burdens in goats.

Nematode lungworm burdens are difficult to evaluate of necropsy. The recovery of protostrongylid worms was achieved by three different post-mortem quantification techniques. Perfusion of the lungs under watertap pressure was successful in washing out Protostrongylus rufescens and Cystocaulus ocreatus but not Muellerius capillaris and Neostrongylus. Incubation of the lungs by pepsin and hydrochloric acid solution prior to perfusion helped to recover trapped Muellerius and Neostrongylus. Worm nodules were classified into type A, B and C, on increasing calcification process. Examination of these nodules showed that 75 to 80% of type A and B contained a parasite. Worms recovered by perfusion added to the sum of type A and B nodules were used to construct formula for quantifying the total lungworm burdens from naturally infected goat lungs and may provide a reasonable basis for assessing anthelmintic efficacy.

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, lungworm 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.

Necator americanus in inbred mice: a re-evaluation of primary infection kinetics

The course of a primary Necator americanus infection was studied in the lungs and small intestines of syngeneic mice. Following percutaneous infection no difference in initial larval establishment in the lungs was found between male BALB/c, NIH or B10.G mice. However, significant differences in the subsequent kinetics of infection were demonstrated between the BALB/c and NIH strains. Lung worm burdens declined more slowly in NIH mice than in BALB/c strain. Surprisingly, however, a greater proportion of larvae remaining in the lungs of BALB/c mice, 9 days p.i., were trapped than in NIH mice. Nevertheless, establishment in the small intestines of the BALB/c strain was consistently greater than in NIH mice. Host immunosuppression resulted in increased larval retention in the lungs of both the BALB/c and NIH strains as well as in the small intestines of BALB/c mice. Treatment with hydrocortisone acetate did not increase intestinal worm burdens in NIH mice. The data presented suggest that, in this complex, dynamic model system, designation of 'susceptible' and 'resistant' strains is inappropriate. The factors underlying the observed strain differences in resistance to infection are discussed.

Trickle Infections with Nippostrongylus brasiliensis in Rats: Larval Migration through the Lungs

The effects of exposure of rats to repeated low-level (trickle) infections with Nippostrongylus brasiliensis were assessed by measuring intestinal and lung worm burdens. Worm recoveries from the intestine, made during a period of trickle infection in rats of different ages, showed a virtually complete rejection of intestinal worms in old rats and a partial rejection in young rats. Recoveries from lungs were made in young rats after challenge infection with 500 third-stage (L3) larvae, given after a 2- or 4-wk period of sensitization, during which rats were infected with 10 or 20 doses of 25 larvae. Such trickle infections elicited a strong host response to a challenge infection, manifested by low recoveries of larvae and an increased duration of larval retention in lungs. In another group of rats sensitized by a single dose of 250 L3 larvae, the recovery of larvae from challenge infection and their clearance from the lungs were similar to these observed in rats uninfected prior to challenge. The effect of trickle infections on preintestinal stages was most pronounced and consistent in rats exposed to larvae the greater numbers of times and over the longest period.

The course of primary infection with Necator Americanus in syngeneic mice

Wells C. and Behnke J. M. 1988. The course of primary infection with Necator americanus in syngeneic mice. International Journal for Parasitology 18: 47–51. A panel of syngeneic mouse strains was compared for susceptibility to infection with a hamster adapted strain of N. americanus. Lung worm burdens were compared 4–5 days after percutaneous exposure to 190–375 larvae. SJL and DBA/I were most susceptible. Balb/c, DBA/2 and CBA strains showed intermediate worm burdens and SWR, C 57BL 10, NIH and C3H/HR mice were the most resistant. NIH and Balb/c mice consistently showed significant differences in lung worm establishment and were selected for closer examination. The recovery of larvae from the skin on day 2 and the subsequent rate of loss from this site were similar in both strains. However, Balb/c mice developed significantly higher lung worm burden than NIH and the rate of loss from the lung was more rapid. L 4 larvae were first recovered from the small intestines of Balb/c mice on day 7, numbers reaching a peak on day 9 when the mean intestinal recovery corresponded to 10% of the peak lung burden. Intestinal stages were not found in NIH mice and no larvae were found in other tissue sites of either strain. The relevance of N. americanus in mice as a model for the study of host-parasite relationships of the invasive and migratory stages of hookworms is discussed.

Amoscanate as a Topically Applied Chemical for Prophylaxis against Schistosoma Mansoni Infections in Mice *

Amoscanate (0.1% w/v) in methanol solution applied to skin by tail immersion 1 day prior to cercarial exposure provided mice with better than 90% protection against mature Schistosoma mansoni infections. Cercariae penetrated and schistosomula migrated from treated skins as readily as in control skins. Lung incubation assays, however, indicated that day 7 lung worm burdens were only about half those of control values. By day 20, worm burdens were reduced further to approximately 15% of those for control mice. The delayed prophylactic activity was apparently not due to percutaneously absorbed compound. Wipe application of amoscanate to the skin was nearly as effective as immersion.

Studies on the interaction between an irradiated bovine lungworm vaccine and a morantel sustained release bolus.

The interaction of the morantel sustained release bolus with the development of immunity in calves vaccinated with two doses of gamma irradiated (40 Kr) Dictyocaulus viviparus larvae was investigated under laboratory conditions. A total of 37 helminth-naive calves were used. Eight calves were used in the first part of the study to test the efficacy of a larval vaccine prepared by using gamma rays delivered from a cobalt source. In the second part of the study, four groups of four groups of four calves each were vaccinated and of these, all the animals in two groups each received a bolus. The remaining three groups (two groups of four and one group of five calves each) remained nonvaccinated with each animal in one group receiving a bolus. All the calves were challenged with approximately 2000 lungworm larvae four months postvaccination. In order to simulate possible field conditions, two of the vaccinated groups and two of the nonvaccinated groups were given a trickle infection of 800 lungworm larvae over a four-week period, three months prior to challenge. Based on a comparison of clinical signs, pathology and lungworm burdens at necropsy, the vaccination of the calves conferred a significant degree of protection (P less than 0.001) to a subsequent challenge compared with controls. The introduction of a morantel sustained release bolus and/or a trickle infection had no effect on the high degree of protection engendered by the vaccination. Nonvaccinated calves given a trickle infection, with or without a bolus, were also highly immune to challenge.

Observations on the epidemiology of Dictyocaulus viviparus in north west England

A five year ley pasture was used as a source of natural infection with Dictyocaulus viviparus for cattle in anthelmintic trials. Pasture larval counts, faecal larval counts of permanently grazing calves and lungworm burdens harboured by tracer calves were monitored in three grazing seasons to assess the pattern of infection. Carrier calves were introduced at the beginning of the grazing season in the first two years of the study but not in the third. In the fourth year the pasture was subdivided into two paddocks where overwintered infection with and without carrier infection were compared. A control paddock exposed to carrier infection but no overwintered infection was also monitored. Pasture larvae survived the winter but carrier infection appeared to make a larger contribution to pasture larval counts and the onset of parasitic bronchitis in susceptible calves. In the absence of grazing cattle at the end of the grazing season the concentration of D viviparus larvae on the herbage fell rapidly to undetectable levels. Discrepancies between contamination of herbage by infective D viviparus larvae and infectivity of pasture for susceptible cattle occurred in all years but were particularly marked on the third year when natural immunity appeared to influence the number of lungworms accumulating in tracer calves. Failure to recover lung worms from tracer calves cannot be regarded as an accurate indication of lungworm free pasture. In the first three years the proportion of the lungworm population which was inhibited in tracer calves was higher early and late in the grazing season and negligible in mid season. This suggests that a predisposition to inhibition in larvae which have overwintered on pasture may influence the time of onset of parasitic bronchitis in the next grazing season, but results from the fourth year did not support this hypothesis.

Control of parasitic bronchitis in calves: vaccination or treatment?

A 16-day infection of Dictyocaulus viviparus in two groups of calves was treated with levamisole and fenbendazole respectively. Five days afterwards the calves were reinfected with 4000 larvae and necropsied 21 days later. Although the lungworm burdens of the two groups of calves were reduced by about 70 per cent compared to a control group the clinical signs of dyspnoea, tachypnoea and coughing were indistinguishable from a primary infection. This was due to pulmonary emphysema, oedema and an acute epithelialising pneumonia apparently associated with the death and disintegration of lungworms in situ, the result of an incompletely developed immune response. The results are compared with those obtained with the lungworm vaccine. It was concluded that the outcome of any system of "control" which depends on drug therapy and reinfection is unpredictable and that vaccination offers the only effective method of prophylaxis.

Speed of actin of some anthelmintics against Dictyocaulus viviparus infection in cattle.

In a study of the comparative speed of action of anthelmintics against Dictyocaulus viviparus infection in cattle levamisole reduced the lungworm burdens by 87 per cent within three hours of administration whereas fenbendazole and febantel required 36 hours to achieve 80 and 87 per cent reduction, respectively. The more rapid action of levamisole may be advantageous in the treatment of bovine parasitic bronchitis since it allows virtually immediate elimination of the majority of the lungworms and limits undesirable sequelae dependent on the continued presence of the parasite.

Efficacy of mebendazole against Dictyocaulus arnfieldi in the donkey

In a controlled trial in naturally infected donkeys the efficacy of mebendazole against Dictyocaulus arnfieldi infection was evaluated. A powder formulation of mebendazole given orally at a dosage rate of 4.3 to 5.7 mg per kg per day for five days had no apparent effect on existing lungworm burdens. However a paste formulation of mebendazole given orally at a higher dosage rate of 15.2 to 20.0 mg per kg per day for five days was 75 to 100 per cent effective in the removal of lungworms from individual animals.

Studies on immunisation of suckling calves with dictol

The immunisation of young milk-fed calves with two doses of the commercially available Dictyocaulus viviparus irradiated larval vaccine, Dictol, was studied. In the first experiment, vaccination of groups of pail-milk-fed calves at 3 and 7 weeks of age resulted in 96.7% reduction of lungworm burdens upon challenge when compared with non-vaccinated controls. Contemporaneous vaccination of calves aged 8 and 12 weeks resulted in a reduction in lungworm burden of 98.9% compared with controls of the same age. The clinical reaction upon challenge of both age groups was minimal compared with their respective controls. In the second experiment a group of six suckling calves were vaccinated with Dictol at 3 and 7 weeks of age and then challenged with infective larvae of D. viviparus together with non-vaccinated controls. At subsequent post-mortem examination the mean lungworm burdens of the vaccinates was 87% less than that of the controls. Some clinical reaction evidence by increased respiratory rates and bodyweight loss occurred in the vaccinates but this was not as severe as in the controls. At necropsy a concurrent pneumonia due to Mycoplasma spp. was present and it is suggested that this contributed to the poorer protection obtained compared with the pail-milk-fed calves of the fist experiment. In the third experiment a group of suckling calves were again vaccinated at 3 and 7 weeks of age and then exposed to a natural challenge together with parasite-naive controls. Although the level of challenge was relatively low, immunisation was apparently high successful as lungworms were completely absent in the vaccinates when examined at necropsy. In all three experiments numerous pulmonary lymphoid nodules, which are a useful guide to the immune status of calves, were present in the vaccinates and absent or scarce in the controls. It is concluded that the cumulative evidence from the three experiments suggest that immunisation against infections of D. viviparus of young milk-fed calves in the field may be a practical proposition.