Direct measurement of dispersal of Dictyocaulus viviparus in sporangia of Pilobolus species

Parasites in ungulates of Arctic North America and Greenland: a view of contemporary diversity, ecology, and impact in a world under change

Parasites play an important role in the structure and function of arctic ecosystems, systems that are currently experiencing an unprecedented rate of change due to various anthropogenic perturbations, including climate change. Ungulates such as muskoxen, caribou, moose and Dall's sheep are also important components of northern ecosystems and are a source of food and income, as well as a focus for maintenance of cultural traditions, for northerners. Parasites of ungulates can influence host health, population dynamics and the quality, quantity and safety of meat and other products of animal origin consumed by people. In this article, we provide a contemporary view of the diversity of nematode, cestode, trematode, protozoan and arthropod parasites of ungulates in arctic and subarctic North America and Greenland. We explore the intricate associations among host and parasite assemblages and identify key issues and gaps in knowledge that emerge in a regime of accelerating environmental transition.

A field survey on the status of internal parasites in calves on organic dairy farms in southwestern Sweden

Infections with internal parasites are one of the most important causes of reduced productivity in first-grazing season cattle (FGSC). In conventional herds, nematode infections can be controlled by prophylactic anthelmintic treatments, but this is prohibited in organic production. The purpose of this investigation was to monitor the status of internal parasitism on 15 organic cattle enterprises in southwestern Sweden during the 1997 and 1998 grazing seasons, and to estimate the benefits of some management practices in parasite control. On each farm, the numbers of Eimeria alabamensis oocysts per gram of (opg) faeces were counted in seven fresh dung pats collected from the paddock 8-10 days after the turnout of FGSC. Faecal samples from 5 to 15 FGSC were also analysed for nematode eggs per gram (epg) faeces at four occasions during each grazing season. In addition, the FGSC and one group of second-grazing season cattle (SGSC) were weighed at turnout and housing and at the same time blood samples were collected, and analysed for serum pepsinogen concentration and antibodies against the lungworm, Dictyocaulus viviparus. On seven farms, 1-6 samples with more than 100000 opg were found, indicating considerable pasture contamination by E. alabamensis. However, clinical signs of coccidiosis were not observed. The highest outputs of nematode eggs were observed 45-55 days after turnout. More than 500 epg were only observed in 12 (2.2%) of the calves in 1997 and in three (0.6%) animals in 1998. Only 1% of the serum samples had pepsinogen values exceeding 3.6 U tyrosine, indicative of subclinical Ostertagia ostertagi infection. Lungworm infection was detected in five and nine herds in 1997 and 1998, respectively. The number of seropositive animals on these farms ranged between one (10%) and seven (70%). Clinical signs of dictyocaulosis were observed on two farms. The results indicate that dictyocaulosis is a problem in organic dairy herds in Sweden. On the other hand, the study shows that good management such as usage of parasite safe pastures and supplementary feeding may help control gastrointestinal parasites.

An experimental field study on the build up of lungworm infections in cattle

The build up of lungworm infections was studied in four groups of calves. Calves of Group 1 were infected experimentally with 6 x 10 larvae during the first 3 weeks after turnout. The pasture of Group 2 was contaminated with approximately 35,000 larvae in June and the pasture of Group 3 with approximately 1.3 million larvae in August. Group 4 served as the helminth free control group for challenge infections with 5,000 larvae in October. In Group 1 faecal larval counts increased 5 weeks after the beginning of patency and decreased after another 3 weeks, indicating the development of immunity after the second lungworm generation. In contrast, the development of immunity in Groups 2 and 3 occurred after the first lungworm generation as maximal faecal larval counts were seen within 3.5 weeks after the beginning of patency. Infection levels were highest in Group 3 which was the only group showing clinical signs. These signs became worse after oxfendazole treatment.

The prevalence of patent lungworm infections in herds of dairy cows in The Netherlands

The results of a survey on the prevalence of patent lungworm infections in herds of dairy cows in the Netherlands are presented. Low patent infections were recorded in February-March on six out of 40 farms in at least one out of 40 cows. Between mid-April and mid-June low patent infections were detected on 28 out of 39 of these farms in one to four of 40 cows. Two farms on which cows were positive in the first round were negative in the second round. One to three positive cows were found on six out of a total of 15 farms revisited in July-August. These results show that lungworm infections are cycled within herds of dairy cows in the Netherlands at a low level. This indicates that dairy cows are important as carriers for lungworm, particularly in spring. The increased patency of lungworm in cows from winter to spring may be explained by maturation of inhibited larvae.

Behavioural defense against parasites: interaction with parasite invasiveness

Behavioural patterns involved in avoiding, repelling, or removing parasites allow mammalian hosts to defend themselves from an array of parasites that threaten the host's fitness in the natural world. Some examples of behavioural defenses and the presumed target parasites are: grooming to remove ticks, grouping to reduce attack rate of biting flies, fly repelling movements to reduce parasitic flies, and selective grazing to reduce intake of faecal-borne parasites. These behavioural defenses are discussed with regard to effectiveness in controlling the target parasites. Parasites have sometimes evolved behavioural strategies of evading, penetrating or disabling these behavioural defenses. These parasite behavioural strategies, though less studied, are discussed. Also discussed is the possibility that host behavioural patterns that may defend against one parasite may be exploited by a different type of parasite to facilitate its own transmission. The interplay between host defensive strategies, the cost versus the effectiveness of such strategies, and a parasite's evasion or exploitation of such strategies, may be useful in understanding some aspects of host-parasite dynamics in nature.

Infection build-up and development of immunity in calves following primary Dictyocaulus viviparus infections of different levels at the beginning or in the middle of the grazing season

An experiment was carried out to study the build-up of infection and development of immunity against Dictyocaulus viviparus infections in calves. Six groups of four calves were used. Groups 1-5 grazed on separate pastures and Group 6 served as a permanently housed control group. To simulate 'low' and 'very low' overwintered pasture infectivity, Groups 1 and 2 were infected experimentally six times with ten and two larvae, respectively, during the first 3 weeks on pasture in May. From the middle of July, Groups 2-4 were experimentally infected six times in 3 weeks with 10, 10 and 100 larvae, respectively, to simulate 'low' and 'moderate' pasture contamination by carriers. Group 5 served as a non-infected pasture control group. After housing of Groups 1-5 in October, all calves were treated with oxfendazole and challenged with 5000 larvae of D. viviparus to evaluate the development of immunity. The results showed a similar population build-up of lungworm infections in Groups 1-4. After the beginning of patency, 24-35 days after primary infection, an increase in faecal larval counts occurred 31-35 days later as a result of re-infection. For Group 2, this was only true when the infections with a total of 12 larvae in May were ignored, as these did not result in patent infections. Faecal larval counts were highest in Group 4, which was the only group with mild signs of lungworm disease occurring in the re-infection period. The worm counts at necropsy showed the development of immunity in Groups 1-4 but not in Group 5. This is consistent with the fact that Group 5 did not develop patent lungworm infections throughout the grazing season.

The effect of rotational grazing for periods of one or two weeks on the build-up of lungworm and gastro-intestinal nematode infections in calves

An experiment was carried out with three groups of grazing calves and one housed control group to study the effect of rotational grazing for periods of 1 and 2 weeks on the build up of lungworm and gastro-intestinal nematode infections respectively. The experiment demonstrated that rotational grazing for periods of 1 week on six plots prevented the build-up of heavy lungworm infections. A build up of heavier lungworm infections was observed in a group that was rotationally grazed for periods of 2 weeks on three plots and a group which remained on one plot throughout the grazing season; there was no difference between these two groups. In all three situations, there was an adequate development of immunity against D. viviparus, as measured by worm recovery after challenge infection at the end of the experiment in comparison with worm recovery of the similarly challenged control group. Neither rotational grazing scheme protected the calves against gastrointestinal helminthiasis, because tracer calves, which grazed for 4 days only in August or October, acquired infections which would have resulted in severe illness or even death if necropsy had been postponed for a week.

Dictyocaulus viviparus in calves: effect of rotational grazing on the development of infections

A study was made of the possibility of reducing lungworm infections in young grazing calves by rotational grazing for weekly periods on six paddocks. For this purpose three groups of four calves each were grazed on separate pastures in 1989, whereas a fourth group served as a permanently housed control group. Two groups of calves were infected experimentally with six doses of 10 larvae of Dictyocaulus viviparus during the first 3 weeks on pasture. In the third group, low natural infections with overwintered larvae occurred. One of the experimentally infected groups was rotationally grazed for weekly periods on six small plots while both other groups were set-stocked. Faecal larval counts and worm counts in tracer calves demonstrated lower lungworm infections in the rotationally grazed group than in both set-stocked groups. However, the numbers of worms found after challenge infection and subsequent necropsy were relatively high in the rotationally grazed group, indicating that development of immunity was less than in both other groups. Owing to the dry weather conditions in the summer of 1989, no serious clinical signs of husk developed in any of the three groups. These dry conditions, however, did not prevent the build-up of heavy pasture infectivity with gastrointestinal nematodes resulting in heavy worm burdens and serious clinical signs in tracer calves grazing for 4 days in August and September-October, respectively. This implies that rotational grazing did not have a clear effect on build-up of gastrointestinal nematode infections.