Reservoirs of Giardia spp. in southwestern Alberta

A survey of potential hosts of Giardia spp. was carried out during 1982 and 1983 in the Kananaskis Valley and Banff National Park, Alberta, Canada. Diagnosis was based mainly on fecal analysis but a few animals were examined at necropsy and scrapings from the small intestine analyzed. A total of 304 specimens was examined from humans (Homo sapiens L.) and a variety of animal species. Cysts and/or trophozoites of Giardia were found in 10.5% of the specimens examined. Positive samples were found from 20 of 21 red-backed voles (Clethrionomys gapperi Vigors), two of six meadow voles (Microtus pennsylvanicus Ord), one of three long-tailed voles (Microtus longicaudus Allen), five of 50 deer mice (Peromyscus maniculatus Mearns), and two of 58 beavers (Castor canadensis Kuhl). Cysts obtained from a beaver were successfully introduced to gerbils (Meriones unguiculatus Milne-Edwards) and the trophozoites obtained were cultured in vitro.     

High-resolution electron microscopic evidence for the filamentous structure of the cyst wall in Giardia muris and Giardia duodenalis

High-resolution morphological studies of the cyst wall of Giardia spp. were performed using low-voltage scanning electron microscopy (LVSEM) and transmission electron microscopy (TEM). The cyst wall was composed of membranous and filamentous layers. The membranous layer consisted of an inner and an outer cyst membrane separated by a thin layer of cytoplasm. The filamentous layer contained individual filaments that ranged from 7 to 20 nm in diameter when measured by LVSEM, formed a dense meshwork with branches or interconnections, and were occasionally arranged on the surface in whorled patterns. Cysts of Giardia muris from mice, Giardia duodenalis from dogs, pigs, voles, beavers, muskrats, and humans, and Giardia psittaci from a bird (parakeet), possessed an essentially identical wall composed of filaments. Inducement of excystation in viable Giardia cysts produced a dramatic increase in the interfilament spacing over an entire cyst, but none was observed in heat-killed or chemically fixed control cysts. These results demonstrated that the cyst wall of Giardia spp. was composed of a complex arrangement of filaments, presumably formed during the process of encystment.     

Excystation and culturing of human and animal Giardia spp. by using gerbils and TYI-S-33 medium.

Mongolian gerbils were used as an animal model to excyst and host Giardia spp. isolated from meadow voles, dogs, beavers, and humans. Both cysts and trophozoites were used to establish infections. Gerbils were infected with Giardia duodenalis from beaver, dog, and human sources, and the trophozoites were extracted and cultured in Diamond TYI-S-33 medium. The use of gentamicin and ampicillin in the medium, coupled with treatment of gerbils with gentamicin before they were sacrificed, permitted the elimination of trophozoite purification techniques before culturing. An extract of whole bovine calf blood, CLEX, was substituted for fetal bovine serum in TYI-S-33 medium and was found to be both adequate and less expensive.     

Excystation and culturing of human and animal Giardia spp. by using gerbils and TYI-S-33 medium

Mongolian gerbils were used as an animal model to excyst and host Giardia spp. isolated from meadow voles, dogs, beavers, and humans. Both cysts and trophozoites were used to establish infections. Gerbils were infected with Giardia duodenalis from beaver, dog, and human sources, and the trophozoites were extracted and cultured in Diamond TYI-S-33 medium. The use of gentamicin and ampicillin in the medium, coupled with treatment of gerbils with gentamicin before they were sacrificed, permitted the elimination of trophozoite purification techniques before culturing. An extract of whole bovine calf blood, CLEX, was substituted for fetal bovine serum in TYI-S-33 medium and was found to be both adequate and less expensive.     

The combined effect of environmental factors and neighbouring populations on the distribution and abundance of Arvicola terrestris. An approach using rule-based models

We investigated how the interplay between environmental factors and presence of neighbouring populations determines the distribution and abundance of a small, endangered rodent, the water vole ( Arvicola terrestris ). We studied thriving and non-fragmented populations of water voles in the absence of their main predator, the introduced American mink ( Mustela vison ). A low degree of population fragmentation, such as the one characterizing the studied populations, was probably typical of water voles before their decline started. We found that under these conditions water voles' distribution is mainly determined by three environmental factors: presence of freshwater, adequate food, and cover. Variance in other factors is well tolerated by water voles. We obtained this result by the use of rule-based models in two separate areas. The two models correctly classified 81% and 83% of the observed cases, respectively. When optimised on one area and cross-validated on the other area the performance of the models was still high (73% and 79%) indicating that the models were robust and generalizable. We also found that the density of animals was lower in sub-optimal than in optimal habitat. We then tested the hypothesis that the number of neighbouring colonies determines the probability of finding voles in a given section. We found that the presence of nearby colonies was an important factor in determining the presence of water voles in sub-optimal habitat, while isolated patches of suitable habitat were less likely to host water voles. These observations suggest the possible presence of a source-sink dynamic, where an optimal habitat acts as a source for populating sub-optimal habitats that may be considered a sink habitat. These findings are discussed in the context of water vole conservation.     

Between-year variation and spatial dynamics of Cryptosporidium spp. and Giardia spp. infections in naturally infected rodent populations

Prevalence and abundance of Cryptosporidium spp. and Giardia spp. infections were studied over the 8-year period in 3 species of rodents in N.E. Poland (bank vole Myodes glareolus-1523; yellow-necked mouse Apodemus flavicollis- 638; common vole Microtus arvalis- 419). Prevalence was 53.8, 28.1 and 62.3% respectively for Cryptosporidium spp. and 58.3, 24.4 and 74.2% respectively for Giardia spp. Prevalence and abundance of infection varied markedly across 8 years of the study with 1998 and 2002 being years of higher prevalence and abundance, following changes in the densities of host species. The distribution of intestinal protozoa in forest rodents did not vary in the 3 isolated sites during the 4-year study. In the case of Cryptosporidium, fewer older animals carried infection and infections of the oldest bank and common voles were relatively milder. In the case of Giardia in yellow-necked mice, infections were more common in older age classes (2 and 3). The two species showed significant co-occurrence and in animals carrying both species there was a strong significant positive correlation between abundance of infection with each. These data are discussed in relation to the parasite genotypes identified in this region and in respect of the role of various ecological factors in shaping of intestinal protozoa communities.     

Small rodents and other mammals associated with mountain meadows as reservoirs of Giardia spp. and Campylobacter spp

Sixty-five percent (469 of 722) of the fecal samples collected from small rodents in the central Washington Cascade mountains were positive for Giardia spp. Trapping studies showed that microtines of the genus Microtus were heavily infected with the parasite. Morphologically the cysts and trophozoites were of the Giardia duodenalis type. Small-rodent populations appear to maintain their infection throughout the year. Our data suggest that there is no difference in the percentage of positive animals in areas receiving a lot of human use as opposed to animals in those areas receiving very little or no human use. Giardia spp. were also found in elk and beaver fecal samples. Campylobacter spp. were recovered infrequently from the small rodents inhabiting alpine meadows. Of 551 specimens cultured, less than 1% were positive for the bacterium, and the isolates were identified as Campylobacter coli. Water voles were susceptible to a human isolate of Campylobacter jejuni and shed the bacterium for several weeks. C. jejuni was also isolated from a bear fecal sample collected from a protected watershed. Our studies indicate that microtines and possibly other small rodents inhabiting mountain meadows have a potential to act as a reservoir for both Giardia spp. and Campylobacter spp. Because these animals may carry human pathogens, they should be included in animal surveys designed to assess the health risks associated with mountain watersheds.     

Small rodents and other mammals associated with mountain meadows as reservoirs of Giardia spp. and Campylobacter spp.

Sixty-five percent (469 of 722) of the fecal samples collected from small rodents in the central Washington Cascade mountains were positive for Giardia spp. Trapping studies showed that microtines of the genus Microtus were heavily infected with the parasite. Morphologically the cysts and trophozoites were of the Giardia duodenalis type. Small-rodent populations appear to maintain their infection throughout the year. Our data suggest that there is no difference in the percentage of positive animals in areas receiving a lot of human use as opposed to animals in those areas receiving very little or no human use. Giardia spp. were also found in elk and beaver fecal samples. Campylobacter spp. were recovered infrequently from the small rodents inhabiting alpine meadows. Of 551 specimens cultured, less than 1% were positive for the bacterium, and the isolates were identified as Campylobacter coli. Water voles were susceptible to a human isolate of Campylobacter jejuni and shed the bacterium for several weeks. C. jejuni was also isolated from a bear fecal sample collected from a protected watershed. Our studies indicate that microtines and possibly other small rodents inhabiting mountain meadows have a potential to act as a reservoir for both Giardia spp. and Campylobacter spp. Because these animals may carry human pathogens, they should be included in animal surveys designed to assess the health risks associated with mountain watersheds.     

Evaluation of an internal positive control for Cryptosporidium and Giardia testing in water samples

AIMS: An internal positive control for Cryptosporidium and Giardia monitoring was evaluated for use in routine water monitoring quality control. The control, known as ColorSeed C&G (BTF Pty Ltd, Sydney, Australia), is a suspension containing exactly 100 Cryptosporidium oocysts and 100 Giardia cysts that have been modified by attachment of Texas Red to the cell wall, allowing them to be differentiated from unmodified oocysts and cysts. The control enables recovery efficiencies to be determined for every water sample analysed. METHODS AND RESULTS: A total of 494 water samples were seeded with ColorSeed C&G and with unlabelled Cryptosporidium and Giardia and then analysed. Additionally, the robustness of the ColorSeed labelling was challenged with various chemical treatments. Recoveries were significantly lower for the ColorSeed Texas Red labelled Cryptosporidium and Giardia than recoveries of unlabelled Cryptosporidium and Giardia. However, the differences in recoveries were small. On average ColorSeed Cryptosporidium recoveries were 3.3% lower than unlabelled Cryptosporidium, and ColorSeed Giardia recoveries were 4% lower than unlabelled Giardia. CONCLUSIONS: ColorSeed C&G is suitable for use as an internal positive control for routine monitoring of both treated and raw water samples. SIGNIFICANCE AND IMPACT OF THE STUDY: The small differences in recoveries are unlikely to limit the usefulness of ColorSeed C&G as an internal positive control. The ColorSeed labelling was found to be robust after different treatments.     

Volume and ion regulating renal functions in the big gerbil (Rhombomys opimus L.) and the water vole (Arvicola terrestris L.)

1. After iso-osmotic salt loading (1% NaCl, 1.25% KCl, 0.75% MgCl2 solutions, each load making up 5% body weight) the water voles excreted 66.2% sodium, 84.4% potassium, 18.8% magnesium over a 4 hr period. The big gerbil excreted 20%, 58.9% and 7.1% respectively over the same period. The volume of the water excreted was greater in the case of the water vole. 2. There were no considerable changes in plasma ion concentration in rodents of the species studied after salt loading. 3. The gerbils and water voles had no significant changes in the renal cortex electrolyte concentrations as a result of isotonic salt loads. The highest sodium cortico-papillar gradient was found in the gerbils when experimenting with the isotonic NaCl loading. It was somewhat lower with the KCl load, and significantly lower with water and MgCl2 loads. 4. Under the same experimental conditions, no major changes in the papilla sodium concentration were found in the water voles. 5. The concentrations of potassium, calcium and magnesium were practically alike in all zones of the renal tissue of both rodent species, ion loads producing no effect. 6. The comparison of the renal volume and ion regulating function in rodents with different urine osmotic concentration systems proves the independent existence of renal functions. The greater rate of renal fluid and ion excretion in the water voles is coupled with less specific ion regulation.     

A ten-year survey of Giardia cysts in drinking water supplies of Seoul, the Republic of Korea

To understand the distribution of Giardia cysts in drinking water supplies in Seoul, Korea, we collected water samples quarterly at 6 intakes in the Han River, its largest stream and 6 conventional water treatment plants (WTPs) serving drinking water, from 2000 to 2009. Giardia cysts in each of 10 L water were confirmed in 35.0% of intake water samples and the arithmetic mean was 1.65 cysts/10 L (range 0-35 cysts/10 L). The lowest cyst density was observed at Paldang and Kangbuk intakes, and the pollution level was higher at 4 intakes downstream. It seemed that these 4 intakes were under influence of Wangsuk stream at the end of which cysts were found in all samples with the mean of 140 cysts/10 L. The annual mean number of cysts was 0.21-4.21 cysts/10 L, and the cyst level at the second half of the 10 years was about 1/5 of that at first half on average. The cysts were more frequently found in winter, and their mean density was 3.74 cysts/10 L in winter and 0.80-1.08 cysts/10 L in other seasons. All finished water samples collected at 6 WTPs were negative for Giardia in each of 100 L sample for 10 years and cyst removal by physical process was average 2.9-log. It was concluded that conventional water treatment at 6 WTPs of Seoul appears to remove the cysts effectively under the present level of their source water. Domestic wastewater from the urban region could be an important source of Giardia pollution in the river.     

Physiological consequences of captive conditions in water voles (Arvicola terrestris)

Re-introductions of captive-bred animals are increasingly common in wildlife conservation and it is important that they fulfil their potential. To foster this goal we examined variations in stress levels in a captive-bred population of water voles Arvicola terrestris in response to housing conditions and radio-collaring, using weight loss and leukocyte coping capacity (LCC) as measures of relative stress, to investigate the impacts of housing conditions, handling and radio-collaring on this species. Thirty-eight water voles (22 males and 16 females) were used in the investigation, 25 housed in outdoor enclosures and 13 in laboratory cages. During the 6-week study, LCC, body weight and urine refractive index (URI, an indicator of hydration levels) were recorded once a week for each individual in weeks 1, 2, 4 and 6. After the first sample, radio-collars were attached to 20 individuals (10 males and 10 females) taken from both housing types. Throughout the experiment laboratory-cage housed voles weighed less, had lower LCC scores – indicating a reduced ability to combat infection – and had higher URIs than outdoor-enclosure voles. This suggests that the laboratory-cage voles were more stressed and dehydrated than the outdoor-enclosure voles. Weights and LCC scores of both housing groups decreased as the study progressed, suggesting that elements of the study, such as repeated handling, may have caused stress to both groups. Evidence suggested a short-term effect of radio-collaring on immuno-competence. We conclude that captive housing conditions, repeated manipulation and radio-collaring had demonstrable physiological effects on the water voles studied. We recommend that the effects of husbandry and tagging practices upon captive-bred mammals be closely studied as part of the quest to improve the success of the re-introductions to which they contribute.     

European water voles in a reconnected lowland river floodplain: habitat preferences and distribution patterns following the restoration of flooding

Water voles have suffered large population declines in the United Kingdom due to habitat degradation and predation by invasive American mink. Habitat restoration of floodplain wetlands could help to reverse this decline, but the detailed habitat preferences of water voles in these environments have not been well studied, and the impacts of restoration practices on water vole populations are not known. This study investigated the habitat preferences of water voles in a reconnected lowland river floodplain. The results show that water voles preferred wider water bodies, and taller and more diverse vegetation. The impact of flooding on water voles was also investigated by comparing their occurrence between two survey periods which were separated by large flood events, and by comparing distribution patterns before and after restoration. Contrary to previous reports, there was no observed negative impact of flood events on water vole distribution, which has slightly expanded since the floodplain was reconnected to the river in 2009. Overall this study demonstrates that restored wetlands can provide suitable habitat for water voles, and provides guidance on some of the factors which should be considered when designing floodplains for water vole conservation.     

Occurrence of Giardia and Cryptosporidium spp. in surface water supplies.

Giardia and Cryptosporidium levels were determined by using a combined immunofluorescence test for source waters of 66 surface water treatment plants in 14 states and 1 Canadian province. The results showed that cysts and oocysts were widely dispersed in the aquatic environment. Giardia spp. were detected in 81% of the raw water samples. Cryptosporidium spp. were found in 87% of the raw water locations. Overall, Giardia or Cryptosporidium spp. were detected in 97% of the raw water samples. Higher cyst and oocyst densities were associated with source waters receiving industrial or sewage effluents. Significant correlations were found between Giardia and Cryptosporidium densities and raw water quality parameters such as turbidity and total and fecal coliform levels. Statistical modeling suggests that cyst and oocyst densities could be predicted on the basis of watershed and water quality characteristics. The occurrence of high levels of Giardia cysts in raw water samples may require water utilities to apply treatment beyond that outlined in the Surface Water Treatment Rule of the U.S. Environmental Protection Agency.     

Occurrence of Giardia and Cryptosporidium spp. in surface water supplies.

Giardia and Cryptosporidium levels were determined by using a combined immunofluorescence test for source waters of 66 surface water treatment plants in 14 states and 1 Canadian province. The results showed that cysts and oocysts were widely dispersed in the aquatic environment. Giardia spp. were detected in 81% of the raw water samples. Cryptosporidium spp. were found in 87% of the raw water locations. Overall, Giardia or Cryptosporidium spp. were detected in 97% of the raw water samples. Higher cyst and oocyst densities were associated with source waters receiving industrial or sewage effluents. Significant correlations were found between Giardia and Cryptosporidium densities and raw water quality parameters such as turbidity and total and fecal coliform levels. Statistical modeling suggests that cyst and oocyst densities could be predicted on the basis of watershed and water quality characteristics. The occurrence of high levels of Giardia cysts in raw water samples may require water utilities to apply treatment beyond that outlined in the Surface Water Treatment Rule of the U.S. Environmental Protection Agency.     

Diabetes in Danish bank voles (M. glareolus): survivorship, influence on weight, and evaluation of polydipsia as a screening tool for hyperglycaemia

Background

Previous studies have concluded that the development of polydipsia (PD, a daily water intake ≥21 ml) among captive Danish bank voles, is associated with the development of a type 1 diabetes (T1D), based on findings of hyperglycaemia, glucosuria, ketonuria/-emia, lipemia, destroyed beta cells, and presence of autoantibodies against GAD65, IA-2, and insulin.

Aim and Methods

We retrospectively analysed data from two separate colonies of Danish bank voles in order to 1) estimate survivorship after onset of PD, 2) evaluate whether the weight of PD voles differed from non-PD voles, and, 3), evaluate a state of PD as a practical and non-invasive tool to screen for voles with a high probability of hypeglycaemia. In addition, we discuss regional differences related to the development of diabetes in Scandinavian bank voles and the relevance of the Ljungan virus as proposed etiological agent.

Results

We found that median survival after onset of PD is at least 91 days (lower/upper quartiles = 57/134 days) with a maximum recording of at least 404 days survivorship. The development of PD did not influence the weight of Danish bank voles. The measures of accuracy when using PD as predictor of hyperglycaemia, i.e. sensitivity, specificity, positive predictive value, and negative predictive value, equalled 69%, 97%, 89%, and 89%, respectively.

Conclusion

The relatively long survival of Danish PD bank voles suggests potentials for this model in future studies of the long-term complications of diabetes, of which some observations are mentioned. Data also indicates that diabetes in Danish bank is not associated with a higher body weight. Finally, the method of using measurements of daily water intake to screen for voles with a high probability of hyperglycaemia constitutes a considerable refinement when compared to the usual, invasive, methods.     

Influence of photoperiod, nutrition and water availability on reproduction of male California voles (Microtus californicus)

Male California voles were maintained in long (14L:10D) or short photoperiods (10L:14D) for 10 weeks and fed a standard diet of rabbit chow and water ad libitum. One additional group in each photoperiod received the standard diet plus supplements of spinach 3 times weekly. A fifth group was housed in 14L:10D and fed the standard diet, but for 10 weeks water availability was restricted to several hours each morning. Testes and seminal vesicles were heaviest in long-day voles fed spinach supplements and lightest in short-day voles fed only the standard diet; the latter animals manifested reduced testicular spermatogenesis. Testicular weights were also depressed in voles with restricted access to water. It is suggested that photoperiods that simulate those of winter induce regression of the reproductive organs of male California voles but the availability of green vegetation counteracts the inhibitory effects of short daylengths.     

Patterns in the production of latrines by water voles (Arvicola terrestris) and their use as indices of abundance in population surveys

Water vole latrines were studied on four of the principal rivers in the North Yorkshire Moors National Park. Water voles occupied 'core' and 'peripheral' sites on these rivers. Core sites were marked by latrines and held breeding colonies of voles; animals at core sites were readily captured. Peripheral sites were not marked by latrines, but showed erratic water vole activity as measured by activity indices (tracks m^-1 of muddy bank month^-1). It was never possible to catch voles at these peripheral sites, and there was no evidence of breeding.
Latrines on core sites were not maintained outside the breeding season. The appearance of latrines coincided with the start of the breeding season, and while they were maintained, latrines provided a useful guide to the number of animals in the area. A curvilinear response was obtained between latrine production and date, with production rising steadily from early spring until mid-to-late summer, which suggests that latrines signal sexual activity.
Future studies on the distribution of water voles should use a variety of techniques. Latrine surveys will only be applicable during the breeding season at core sites. Similarly, live-trapping will only detect water voles at core sites. Tracking provides the best evidence that water voles are present at peripheral sites even though they may not be breeding or entering traps.     

Verification of the color genotype based on morphological analysis of fur pigmentation of brown and black water voles Arvicola terrestris L.]

Qualitative and quantitative analysis of fur pigmentation in brown and black water voles (Arvicola terrestris L.) was performed. Morphology of pigment granules, their distribution along the hair layers and histology of hair bulbs were studied. Morphological data and the results of the analysis of segregation in the progeny, when brown voles were self-crossed and crossed with black ones, led to conclusion that fur colour of water voles is mediated by genes from the agouti series, precisely, black colour is determined by the extreme non-agouti allele (aeae genotype), and in brown voles which are homo- or heterozygous the colour is determined by the agouti allele (AA or Aae genotypes).     

Spatial segregation of two vole species (Arvicola sapidus and Microtus cabrerae) within habitat patches in a highly fragmented farmland landscape

Spatial segregation is one of the common mechanisms allowing the co-existence of similar interacting species in heterogeneous environments. Analysing spatial segregation requires information on individual home-range sizes and their degree of spatial overlap. In this study, we used radio-tracking to report for the first time the home-range and core-area sizes of sympatric Cabrera and water voles and to analyse intra- and inter-specific space sharing within habitat patches in a highly fragmented landscape. Results indicated that both species exhibited strong fine-scale site fidelity and reduced variation in range size across sexes and seasons. Monogamous mating system seemed to prevail for both species, although water voles may also exhibit polygynous breeding strategies. Mean home-range and core-area sizes of water voles (946.3 and 156.6 m²) were about twice that of Cabrera voles (418.2 and 55.1 m²). Within habitat patches, individuals of both species often overlapped their home ranges, particularly during the dry season (May–September), though intra-specific home-range overlap was generally higher than inter-specific overlap. Inter-specific space sharing was restricted to areas outside the centre of activity of animals, as no core-area overlap was ever recorded between Cabrera and water voles. Taken together, results support the view that co-existence of Cabrera and water voles in Mediterranean patchy habitats may in part result from spatial segregation among individuals, which may reflect competitive displacement or small-scale habitat partitioning. Results highlight the need to account for species interactions when designing conservation management strategies for sympatric Cabrera and water voles in fragmented landscapes.