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K Snowden

Publications and source records attributed to K Snowden.

At least 19 recordsLinked to original sources
PubMed2000

Restriction-fragment-length polymorphism analysis of small-subunit rRNA genes of Blastocystis hominis isolates from geographically diverse human hosts.

Genomic diversity among 14 isolates of Blastocystis hominis from 4 different geographic locations was examined by small-subunit rRNA (ssu rRNA) restriction-fragment-length polymorphisms (RFLP) using 5 different restriction endonucleases. On the basis of the observed RFLP patterns among the isolates, a total of 12 genotypes were identified, with 7 isolates exhibiting mixed RFLP genotypes. There was no correlation between B. hominis geographic origin and RFLP banding pattern or genotype.

Animals↗
PubMed2000

Restriction-fragment-length polymorphism analysis of small-subunit rRNA genes of Blastocystis isolates from animal hosts.

The anaerobic enteric protozoan organism Blastocystis sp. has been identified from mammalian, avian, reptilian, and arthropod hosts. Eight Blastocystis isolates from five animal host species (cow, goat, sheep, guinea pig, and rhea) were compared by small-subunit ribosomal RNA (ssu rRNA) restriction-fragment-length polymorphism (RFLP) analyses using five restriction endonucleases. The isolates sorted into five genotypes. Multiple genotypes were found in isolates from a single animal host species, and multiple host species shared a single genotype. A molecular method such as RFLP analysis of ssu rRNA genes facilitates the characterization of Blastocystis isolates from various host species.

Animals↗
PubMed1999

Parasite diversity and anthelmintic resistance in two herds of horses.

Diversity of parasite populations was compared between two herds of horses, one a regularly treated herd the other a feral herd which has bad no anthelmintic treatment for at least 25 years. Eggs obtained from fecal samples of both herds were tested for anthelmintic resistance by use of an in-vitro larval hatch/development assay (LDA), DrenchRite. A fecal egg reduction test was also performed with the domesticated herd using fenbendazole, pyrantel pamoate and ivermectin. Cyathostomes were the predominant group of worms present in both herds. Trichostrongylus axei was seen in both herds, but Strongylus equinus, Strongylus vulgaris, Gyalocephalus capitatus, Poteriostomum spp. and Strongyloides westeri were only found in the feral horses. Larvae of Strongylus edentatus were found in a single domesticated horse. Fecal egg reduction tests with the domesticated herd showed a 32% egg count reduction for fenbendazole, a 93% reduction with pyrantel, and a 99% reduction with ivermectin. From the LDA, anthelmintic resistance was evaluated by determining the resistance ratio of the domesticated herd compared with the feral herd. For benzimidazoles in the domesticated herd, 45% of the cyathostome population was 9.4 times more tolerant than the feral herd's parasite population. The parasite population in the domesticated herd was 1.5 times more tolerant to Levamisole, and 1.7 times more tolerant to the benzimidazole/levamisole combination than the parasite population within the feral herd. 9% of the parasite population in the domesticated herd was 90 times more tolerant to avermectins than the feral herd's parasite population, even though a subpopulation of worms in the feral herd were tolerant to low concentrations of avermectins despite never being previously exposed to this class of anthelmintic.

Animals↗
PubMed1999

Encephalitozoon cuniculi strain III is a cause of encephalitozoonosis in both humans and dogs.

Microsporidia are obligate intracellular eukaryotic organisms found in a wide range of vertebrate and invertebrate hosts. Encephalitozoon cuniculi is commonly found in domestic rabbits and rodents and also occurs in dogs, other canids, and primates, including humans. DNA sequencing of the ribosomal RNA genes has been used to identify these parasites to a species level and to define E. cuniculi strains I, II, and III. Eight new dog isolates were characterized as E. cuniculi strain III by use of molecular methods. This strain has also been identified in isolates from immunocompromised humans, suggesting the zoonotic potential of this parasite species. Prolonged microsporidial spore shedding from asymptomatic dogs is also reported.

Animals↗
PubMed1999

Detection of Cryptosporidium parvum in horses: thresholds of acid-fast stain, immunofluorescence assay, and flow cytometry.

Feces collected from three asymptomatic horses and seeded with Cryptosporidium parvum oocysts (10(1) to 10(6)/g of feces) were evaluated by acid-fast staining (AF), an immunofluorescent antibody (IFA) technique, and flow cytometry. The thresholds of detection were 5 x 10(5) oocysts/g of feces for the IFA and AF techniques and 5 x 10(4) oocysts/g for flow cytometry.

Animals↗
PubMed1999

Rabbit intestinal xenograft model for human Encephalitozoon infections in mice.

BACKGROUND AND PURPOSE: The gastrointestinal tract is a common portal of entry for Encephalitozoon cuniculi, one of several microsporidial organisms emerging as opportunistic pathogens in immunocompromised humans. Although most human microsporidial pathogens can be propagated in vitro and in a variety of laboratory animals, an experimental animal system to specifically study intestinal uptake and systemic spread of these organisms does not exist. METHODS: Paired segments of near-term fetal rabbit small intestine were implanted subcutaneously into 25 athymic nude or 10 severe combined immune deficient mice. Five weeks after surgery, 65 xenografts were inoculated intraluminally with E. cuniculi (n = 14), E. intestinalis (n = 27), E. hellem (n = 20), or RK-13 cells (n = 2), or were left uninoculated (n = 2). RESULTS: Intestinal xenograft infection with E. cuniculi (n = 11), E. intestinalis (n = 17), and E. hellem (n = 18) was determined by light microscopy; control xenografts remained uninfected. Extraintestinal infection with E. cuniculi developed in host mouse brain, respiratory tract, spleen, salivary glands, and gastrointestinal tract (3 of 3 mice), and infection with E. intestinalis developed in the liver (8 of 15 mice). CONCLUSION: Intestinal xenografts provide a unique, sterile, and biologically relevant animal model system for studying host enterocyte/parasite interactions, mechanisms of microsporidial pathogenicity, antimicrosporidial chemotherapeutic agents, and immune effector mechanisms. This model provides evidence for persistent graft infection with three Encephalitozoon spp., and for intestinal spread of E. cuniculi and E. intestinalis from infected enterocytes in immunoincompetent mice.

Animals↗
PubMed1998

Prevalence of and risk factors for fecal shedding of Cryptosporidium parvum oocysts in horses.

OBJECTIVE: To determine prevalence of and risk factors for fecal shedding of Cryptosporidium parvum oocysts among 3 populations of horses. DESIGN: Cross-sectional study. ANIMALS: 152 horses participating in the 1996 Texas State 4-H Horse Show, 144 horses examined by the veterinary teaching hospital, and 70 broodmares and their 10- to 21-day-old foals. PROCEDURE: Information on signalment and potential risk factors for fecal shedding of oocysts was obtained. Fecal samples were evaluated for oocysts by means of acid-fast (AF) staining, immunofluorescence assay (IFA), and, for selected samples, flow cytometry (FC). RESULTS: Results of the 3 diagnostic tests were significantly different. The best agreement was between results of the IFA and FC; AF staining and FC were more sensitive than the IFA, but AF staining was less specific. Fecal samples from 13 horses were classified as positive for oocysts. Risk factors for fecal shedding of oocysts included residence on 2 of 4 breeding farms involved in the study, age < 6 months, and history of diarrhea during the preceding 30 days. A municipal water source was implicated as a risk but could not be verified because of insufficient data. CLINICAL IMPLICATIONS: Mature horses and exposure to cattle did not appear to be important sources of cryptosporidial infection for foals. Overall prevalence of C parvum infection among these horses was low, and C parvum infection appeared to be associated with particular farms, rather than an endemic opportunistic infection in horses.

Animals↗
PubMed1998

Human cystic echinococcosis in a Uruguayan community: a sonographic, serologic, and epidemiologic study.

A prevalence and transmission study of human cystic echinococcosis (CE), due to infection with the dog tapeworm Echinococcus granulosus, was undertaken in the village of La Paloma in central Uruguay. The human population was registered and screened for CE by abdominal ultrasound scan as well as a number of serologic tests. Dogs were screened for E. granulosus infection by arecoline purgation as well as specific coproantigen testing. The total prevalence of human CE (new cases and those with a previous history) was 5.6% (64 of 1,149); 3.6% (40) of the cases were new ultrasound detected asymptomatic cases (mean age = 45 years). Age prevalence increased from 1.1% in the 4-6-year-old group to > 11% in the > 60-year-old group; the 20-29-year-old group had a significantly higher CE rate of 7.4%, compared with younger and older age groups, and there was no difference between sexes. A CE rate of 3.9% (20 of 514) was also recorded by ultrasound for new cases in the population residing outside the village. Most of the hydatid cysts were located in the liver presenting as either univesicular cysts or a solid mass, and of those 71% and 63%, respectively, with such cyst presentations were seropositive against E. granulosus cyst fluid antigens. Two of eight individuals who were filter paper blood spot seropositive, but ultrasound scan negative, were subsequently diagnosed respectively with pulmonary hydatidosis after radiography, and hepatic hydatidosis after computed tomography scan. Of 36 households with a CE patient, 32 were single cases while four households each harbored two CE cases. This did not represent a clustered distribution within families (23 of 117). Almost 20% of the dogs from La Paloma were found infected with E. granulosus after purge examination, with a mean worm number of 67 (range = 1-1,020). An additional eight dogs that were purge negative were Echinococcus coproantigen positive. The study showed that human CE is highly endemic in Uruguay, with one of the highest local prevalence rates in the world. Transmission appears to occur readily within well-developed towns, as well as on rural sheep ranches. Mass screening by ultrasound scanning with confirmatory serologic testing is an effective approach to case detection at the community level.

Adolescent↗
PubMed1995

Diagnosis of canine echinococcosis: comparison of coproantigen and serum antibody tests with arecoline purgation in Uruguay.

Echinococcus granulosus is one of the most important and widespread of the helminth zoonoses. Diagnosis of E. granulosus infection in dogs currently relies on arecoline dosing and detailed examination of the purge for adult worms. Two immunodiagnostic tests (ELISA) based on genus specific coproantigen detection or serum antibody (IgG, IgA and IgE) detection were compared against arecoline purgation for the detection of Echinococcus in naturally infected dogs in Uruguay. The coproantigen ELISA had a sensitivity of 76.9% compared with 34.6% for the serum IgG ELISA when assessed against 26 purge positive dogs (purge worm count range 1-4331). Coproantigen reactivity was positively correlated (r = 0.65) to purge worm count, with a threshold at over 20 worms. There was no positive correlation of antibody levels with worm counts. In 26 matched Echinococcus positive dog samples, the overall sensitivity of serological detection increased to 69.2% when seroreactivity for IgA and IgE antibodies were included and to 96.2% for both coproantigen and antibody assays combined. The detection of current infection of individual dogs with E. granulosus by coproantigen ELISA has the potential to replace arecoline purgation, while specific serum antibody detection should be useful in assessing Echinococcus exposure in dog populations.

Animals↗
PubMed1994

A multiple antigen detection dipstick colloidal dye immunoassay for the field diagnosis of trypanosome infections in cattle.

Monoclonal antibodies (McAbs) were developed against aspartate aminotransferase purified from Trypanosoma brucei rhodesiense bloodstream form (bf) soluble extracts using a combination of anion-exchange and hydrophobic interaction chromatography. McAb 1A1 was Trypanozoon and Nannomonas specific while 2F1 was Trypanozoon bloodstream form specific. A dipstick colloidal dye immunoassay (DIA) was employed as a field diagnostic test for African trypanosome infections and designed using affinity purified polyclonal antibodies (PcAbs) raised against T. b. rhodesiense bf and the two McAbs, 1A1 and 2F1. PcAbs were adsorbed onto Palanil Red dye particles and used as dye reagents. Dipsticks were dotted with the three different antibodies, which captured trypanosomal antigens in samples tested, while the dye reagent bound to the captured antigens; the presence of coloured dots on the dipstick identified trypanosome infections. A field trial of the DIA was carried out in southeastern Uganda. A total of 1686 cattle from seven areas were bled and tested by DIA and haematocrit centrifuge technique (HCT). A total of 798 cattle (47.3%) were found to be trypanosomal antigen positive by DIA while only 162 (9.6%) were revealed to harbour trypanosomes by HCT, of which 151 (93%) were also positive by DIA.

Animals↗
PubMed1991

Antigen detection immunoassay using dipsticks and colloidal dyes.

A dipstick colloidal dye immunoassay (DIA) for multiple antigen detection is described. The test combines the concepts of double antibody (Ab) sandwich ELISA, dot blotting, and colloidal particle-linked Abs to produce a dipstick test for multiple antigen (Ag) detection. Dipsticks prepared from Ab coated nitrocellulose membrane mounted on acetate strips served as the assay capture matrix. Abs absorbed to colored dye particles from a family of commercially available textile dyes (Dye/Ab reagent) served as Ag detecting reagents. DIA and enzyme labelled dot blot assays showed similar Ag detection limits down to a sensitivity of 10 ng/ml. In a pilot study, an assay designed to detect species-specific IgG for use in mosquito bloodmeal identification demonstrated the feasibility of the technique. Experiments comparing bloodmeal analysis of mosquitoes using DIA and ELISA methods showed 100% agreement. This DIA method provides an inexpensive, simple, robust test for multiple Ag detection without instrumentation suitable for a wide variety of field applications.

Aedes↗
PubMed1990

Selective breeding of dogs for segregation of limb edema from microfilaremia as clinical manifestations of Brugia infections.

Three generations of beagles were monitored for microfilaremia (mf) and clinical disease during repeated infection with Brugia pahangi and were selectively bred for offspring manifesting limb edema and low or amicrofilaremia. A high microfilaremic female mated to a high microfilaremic male produced 7 pups, 6 of which maintained mf greater than 1,000/ml for greater than 2 years after 5 monthly infections of 10 infective larvae each. An uninfected female mated to another high mf male produced 5 pups, 4 of which did not exceed 1,000 mf/ml 7 months after initiation of the repeating infection regimen; 1 of these remained amicrofilaremic after 2 additional challenges. Neither the parents nor the offspring from these matings manifested chronic limb edema. Two matings were conducted with offspring from the microfilaremic female by breeding siblings with the lowest mf and breeding siblings with the highest mf. The high mf siblings produced 4/5 offspring manifesting chronic limb edema (greater than or equal to 7 months duration) and either no mf (in 2 dogs) or less than 100 mf/ml after the repeating infection regimen. The lower mf siblings produced 5 offspring, all with greater than 1,000 mf/ml 6 months after the initiation of the repeating infection regimen; none manifested edema. Comparisons of IgG antibody levels, specific for extracts of adult worms, showed no consistent differences between these 2 litters of dogs that could be associated with limb edema or mf when monitored for 16 months; however, the onset of lymph node enlargement was much earlier in the group of dogs manifesting limb edema than in the other litter.

Animals↗
PubMed1987

Dynamics of immune responses related to clinical status in Brugia pahangi-infected dogs.

Clinical signs of lymph node enlargement, limb edema, lymph duct fibrosis, and microfilaremia were monitored in dogs with chronic Brugia pahangi infections. During the study a single rear limb of each dog was reinfected with multiple low doses of infective larvae. The changing immune responses to parasite antigens prepared from three sources--Brugia pahangi adult worm homogenate extract, adult worm excretory-secretory products, and microfilaria excretory-secretory products--were monitored by Western blot ELISA of antigens fractionated on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and by microtiter plate ELISA. Assays were used to detect antibodies in both the the IgG and IgE classes. A wide range of clinical manifestations was demonstrated in response to reinfection: asymptomatic, amicrofilaremic; asymptomatic, microfilaremic; acute short duration node enlargement and/or limb edema with microfilaremia; and chronic limb edema, amicrofilaremic. On microtiter plate ELISA, the dogs demonstrating the highest anti-adult worm homogenate titers were amicrofilaremic and were asymptomatic or developed chronic limb edema, dogs with high anti-mf ES titers were persistently amicrofilaremic, and the most marked increases against all three antigen sources upon reinfection occurred in low or amicrofilaremic dogs. Quantitative changes in antibody levels against the three crude antigen sources following reinfection were often paralleled by distinct changes in recognition of specific bands of antigens fractionated by SDS-PAGE.

Animals↗
PubMed1986

Clinical and xeroradiographic lymphangiography studies of acute and chronic Brugia pahangi infections in dogs.

Xeroradiographic lymphangiography was carried out at approximately monthly intervals on five dogs during the first 18 weeks following infection with 400 Brugia pahangi infective larvae in the left rear paw. Clinical signs, body temperatures and microfilaria counts were also monitored during this time. Similar observations were made on nine dogs with chronic infections (one to five years duration) of 200 infective larvae in unilateral inguinal sites. Standard thoracic radiography was conducted on all dogs. Surgical occlusion of the major afferent ducts to the popliteal lymph nodes of the infected and noninfected limbs of a chronically infected dog was performed to study oedema induction and resolution. This non-invasive lymphangiographic technique demonstrated marked differences in lymphatic changes among individual dogs. The severity of lymphatic pathology correlated with clinical signs of limb oedema and low microfilaria counts. Chronically infected dogs also demonstrated a variety of pathological manifestations: two dogs presented lymphatic cording and another showed transient lymphadenitis with fever and pulmonary arterial opacities. Surgical occlusion of major lymphatic ducts in an uninfected limb resulted in short-term oedema, while occlusion caused by B. pahangi in acutely infected dogs resulted in more persistent oedema. Surgical occlusion of a major duct in a chronically infected limb did not result in oedema. Xeroradiographic lymphangiography revealed a spectrum of lymphatic pathology in Brugia pahangi-infected dogs and demonstrated the value of this animal model for the study of the pathogenesis of chronic lymphatic filariasis.

Animals↗
PubMedDate not supplied

Encephalitozoon hellem in two eclectus parrots (Eclectus roratus): identification from archival tissues.

Members of the phylum Microspora are obligate, intracellular, single-celled parasites identified in a wide range of vertebrate and invertebrate hosts. Only a few cases of microsporidial infections have been documented in psittacine birds including peach-faced, masked, and Fischer's lovebirds (Agapornis roseicollis, A. personata, and A. fischeri, respectively), budgerigars (Melopsittacus undulatus), and a double yellow-headed Amazon parrot (Amazona ochrocephala). Parasite identification has typically been limited to phylum or genus, and no avian species of microsporidia has clearly been described. In this report, microsporidia were identified in the kidney and intestine of a new host, the eclectus parrot (Eclectus roratus). Parasites were identified as Encephalitozoon hellem using morphologic, ultrastructural, and small subunit ribosomal RNA gene sequence data obtained from archived tissues. This parasite species was first identified in immunocompromised humans and may be a potential zoonotic pathogen. The epidemiology and prevalence of this parasite in humans and birds should be further explored.

Animals↗