Prevalence of the poultry red mite, Dermanyssus gallinae, in different types of production systems for egg layers in Sweden

This study was undertaken between May and December 1994 to investigate the prevalence of hematophagous mites in Sweden. A particular aim was to establish the relationship between occurrence of mites and certain types of production systems for egg layers. Initially a postal questionnaire study was performed. Some months later this was followed up by inspections, sampling, and interviews on farms. The only mite species found was the red poultry mite, Dermanyssus gallinae. Although this species was found to be present in cage batteries, deep-litter systems, and backyard flocks, it was less prevalent among birds housed in cages. About 4% of the cage systems were found to be affected both according to the results of the postal inquiry and from the field study. However, discrepancies in prevalence were found when comparing the results obtained with these two investigations regarding alternative, deep-litter systems and backyard flocks. According to the inquiry, 21% of the deep-litter flocks were afflicted whereas 33% were found to be afflicted in the field investigation. Among the backyard flocks, 19% were afflicted whereas as many as 67% of the flocks were found to be afflicted upon inspection. These discrepancies were probably due to the fact that the situation had actually changed in some farms during the study period, but possibly also to inherent methodological errors. Farmers were also interviewed with focus on methods of husbandry and control strategies. Most farmers answered that they were combatting the mites by cleaning the empty houses and using chemicals such as organophosphorous compounds, carbamates, and synthetic pyrethroids. In several instances the problems were still not solved despite these curative or preventive measures. A control program for D. gallinae is suggested by regular screening and certification of the ectoparasite status of the birds before their transfer to production sites.

Enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to Anoplocephala perfoliata in horse sera

A scolex antigen of the horse tapeworm Anoplocephala perfoliata containing at least 14 different proteins was employed in an enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to A. perfoliata in equine sera. The assay was applied to sera from 426 slaughtered horses with different numbers of worms and with varying degrees of intestinal lesions. As measured by the ELISA, there was a very strong effect on the antibody levels both from the number of tapeworms present and from the intestinal lesion score. However, considerable individual variation was observed between horses with similar worm counts. The ELISA values of horses that were either negative for strongyles and tapeworms or positive only for strongyles were similar, whereas both of these groups differed significantly from animals that harboured only A. perfoliata. Thus it seemed that cross-reactivity with concurrent nematode infections did not occur. Furthermore, a significant seasonal pattern in antibody levels was observed which reflected the establishment of newly acquired infections. No observations were made of confounding effects owing to age and previous anthelmintic treatment of the horses. It is concluded that the ELISA presented here has a potential for monitoring A. perfoliata infection on a herd level and can be used as a complementary diagnostic tool in epidemiological studies. The present study indicates that transmission of A. perfoliata in Central Sweden occurred during a short period in spring and more consistently in late autumn.

Anoplocephala perfoliata in horses in Sweden: prevalence, infection levels and intestinal lesions

Distal ileum, caecum and proximal colon of 470 horses were examined for helminths during 1 year at an abattoir in central Sweden. The infection levels of the horse tapeworm Anoplocephala perfoliata, their stage of development, site of attachment and gross pathological lesions caused by the worm were recorded. Faecal samples from 395 of the horses were examined specifically for tapeworm segments and eggs in order to correlate these findings with the numbers in the alimentary canal. In total 65% of the horses were infected with A. perfoliata and the mean intensity of infection was 79 worms per infected horse with a maximum of 912. The level of infection was significantly higher in (1) 3rd and 4th than in 1st and 2nd quarter of the year; (2) older horses than in yearlings; (3) females than in males and geldings; (4) thoroughbred and cold-blooded horses than in Swedish standard breeds and ponies. The level of infection was unaffected by the usage of anthelminthics against nematodes. Of the horses examined 51% had 1-100 worms whereas 14% were infected with more than 100 worms. Of the tapeworm positive horses 72% had mixed infections with both adult and juvenile worms, 20% solely juveniles, and 8% solely adults. The severity of intestinal lesions exacerbated by increasing numbers of A. perfoliata. About 11% of the intestines examined had severe lesions, but there was no history of acute abdominal distress in any of the horses included in this study. Although the number of detectable eggs was significantly higher for horses heavily infected with A. perfoliata, the egg recovery among infected horses was only 35%. An additional field survey comprising 218 horses on 88 premises in central and southern parts of Sweden showed that the prevalence of A. perfoliata egg positive horses was the same as found on faecal examination during the abattoir survey.

Evaluation of a direct agglutination test for detection of antibodies against Toxoplasma gondii in cat, pig and sheep sera

The protozoan parasite Toxoplasma gondii is the causative agent of the zoonosis toxoplasmosis. In sheep and goats, it is one of the most prevalent causes of infectious abortion. Also in pregnant women, a primary infection can result in miscarriage. Humans acquire the infection either by ingestion of oocysts excreted by cats, the definitive host of the parasite, or by eating raw or undercooked meat from latently infected animals (Dubey & Beattie 1988). In Sweden, toxoplasmosis is a notifiable disease, and cases of clinical disease in humans as well as animals must be reported. In both veterinary and human medicine serological assays based on detecting the humoral antibody response of the host against the parasite are used as diagnostic tools. So far, solid phase assays, such as the indirect fluorescent antibody test (IFAT) and the enzyme-linked immunosorbent assay (ELISA), have been widely used to diagnose T. gondii infection in many species including cats, pigs and sheep (Dubey & Beattie 1988). However, both IFAT and ELISA require appropriate anti-species specific immunoglobulins (Ig) that must be carefully evaluated for each species prior to use. This makes these assays complicated and time consuming. Consequently, alternative, simpler methods that do not require specific antisera would be of great value. The direct agglutination test (DA), which is based on the principle that formalin-treated organisms agglutinate in the presence of specific IgG antibodies, is such an assay (Fulton & Turk 1959). The DA-test is widely used in human medicine as a screening test for T gondii infection but it has not yet been thoroughly evaluated for use in veterinary medicine (Uggla & Buxton 1990).

Hybridization and low numbers in isolated populations of the natterjack, Bufo calamita, and the green toad, B. viridis, in southern Sweden: possible conservation problems

Abstract

Two isolated rock pool localities in southern Sweden with breeding green toads (Bufo viridis) and natterjacks (B. calamita) were studied, one on the mainland coast (Vik) and one on an island in the Baltic (Utklippan). Both localities are isolated by at least 30 km from other known populations of either species. A new character, dark throat patches present in B. calamita, aided in species separation on Utklippan. Body length was larger (9-41 % ) than reported from continental Europe. Individuals intermediate between the two species in size, morphologv and mating calls were found on Utklippan, suggesting the occurrence of viable hybrids. In Vik, neither of these characters nor electrophoretic data indicated hybridization. We suggest that the number of suitable breeding ponds may explain why the two species hybridize on Utklippan since only one sympatric breeding pond could be found on this site and a number of suitable ponds were found on Vik. Thus the species may be spatially more scparated at the Vik site making hybridization less likely to occur. However, few green toad males could be found on Utklippan making the sex ratio highly skewed. Accordingly, the low number of male green toad may explain why the species hybridize. Hybridization may be a potential threat to the persistence of endangered populations already in low numbers, if a large proportion of female gametes are wasted in hybrid matings. Thus this possibility is important when considering the conservation of endangered species.

Ultrastructural observations and radiometric assay on cercarial penetration and migration of the digenean Diplostomum spathaceum in the rainbow trout Oncorhynchus mykiss

The entrance into host tissues by the cercaria of the digenean Diplostomum spathaceum and the parasite's migration to the eyes of the fish host (post-penetration larvae) were studied by scanning and transmission electron microscopy at the ultrastructural level and by a radiometric assay in experimentally infected rainbow trout (Oncorhynchus mykiss). It was demonstrated that cercariae penetrated the host surface at several sites, although the major site involved the gill region. This observation was verified by the measurement of radioactivity in different regions of fish at intervals following their exposure to cercariae that had been radiolabeled with selenium in vivo. The migratory routes of the post-penetration-labeled cercariae (diplostomulum) were followed along with the distribution of radioactivity, which was altered with increasing time after exposure in the different regions of the host. A marked increase in radioactivity was noted, particularly in the eyes of the host, whereas the radiolabel decreased elsewhere. The results support the view that the cercariae of D. spathaceum contact the host by chance. The finding that the parasite mainly penetrates the host through the gills may be connected with fish ventilation hydrodynamics. The total amount of radioactivity retained in the fish gradually decreased with time, which may suggest that only a portion of the primarily attached cercariae actually penetrated the fish. The majority of the penetrating parasites reached the eyes of the host, where they became established as metacercariae within 24 h, thus indicating migration directed to the eye region. This is facilitated by the functional morphology of the migrating stage of D. spathaceum.

The epidemiology of the metacercariae of Diplostomum baeri and D. spathaceum in perch (Perca fluviatilis) from the warm water effluent of a nuclear power station

Thermal effects on the dynamics of infection with metacercariae of Diplostomum baeri and D. spathaceum were monitored between May and September, in a year-class of perch Perca fluviatilis, in an artificial lake receiving warm water discharges from a nuclear power station and in an unheated reference site, for a two year period. In the heated area the prevalence of infection of the retinal form, D. baeri, was always 100%, whereas in the unheated site there was an increase from 93% in May to 100% in June 1986. The relative density of D. baeri was found to increase gradually during the first summer in both areas, although the accumulation rate of metacercariae was significantly increased in the heated area. In August of the first year the relative density of D. baeri peaked in the heated area, whereas it continued to increase in the unheated control. However, in September of the following year, the relative densities were at the same level in both thermal regimes. A concomitant decline in the degree of overdispersion of metacercariae within the host population was observed in the heated area as the population density of metacercariae decreased, whereas the index of dispersion remained at the same level throughout the study in the unheated area. However, it was not possible to sample perch in the unheated area between October 1986 and May 1987 and changes in the parasite population could have occurred during this period. The prevalence and relative density of D. spathaceum, the lens form, was on the contrary low, especially in the unheated site where it was recorded only occasionally. The infection of D. baeri exhibited a convex pattern in both thermal regimens, although the peak infection was noticed earlier in the heated area. Regulation of the parasite infrapopulation may have been achieved by the combined effects of a decreased transmission rate of cercariae with increasing age of the host, the mortality of metacercariae as a natural termination of the life span and to selective predation of heavily infected hosts. However, regardless of an increased accumulation rate of metacercariae in the heated area, the relative densities of D. baeri became equal in both thermal regimes at the end of the study. The mortality rate of metacercariae in the heated area was therefore presumably increased as compared with the unheated reference site.

Random mating by size in a population of common toads (Bufo bufo)

Abstract

The mating system of a population of individually marked common toads (Bufo bufo) was studied during two years at a pond on the island Öland, southern Sweden. The mating system can be described as explosive breeding with scramble competition for mates. Males outnumbered females by approximately 2:1 and competed for the possession of females by guarding them prior to spawning and by displacing already paired males. Data on displacement patterns showed that smaller males were displaced more often than larger males. However, successful males were not larger than the male they displaced. Furthermore, thc mean size of spawning males was not different from the population mean and the size distribution of spawning males did not differ from the size distribution expected by chance. No size assortion could be detected among spawning pairs. Female fecundity showed a strong correlation with increasing body size. Males of all sizes showed capability of fertilizing all eggs of any female. Females apparently did not choose their mates. Though males would enhance their reproductive success by mating with large and more fecund females, this scenario was probably hampered due to a short breeding season and an operational sex ratio close to 2: 1.