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Biomedical subjects

G A Schad

Publications and source records attributed to G A Schad.

At least 19 recordsLinked to original sources
PubMed1992

Efficacy of milbemycin oxime against experimentally induced Ancylostoma caninum and Uncinaria stenocephala infections in dogs.

Twenty-eight helminth-naive Beagles, 16 to 26 weeks old, were inoculated with 200 third-stage larvae each of Ancylostoma caninum and Uncinaria stenocephala 5 times at weekly intervals. Dogs were randomly allocated to 4 groups of 7 on the basis of fecal egg counts, and treatments were randomly assigned. Groups 1 and 3 were given milbemycin oxime at a dosage of 500 micrograms/kg of body weight, PO, on day 0 and on days 0 and 30, respectively; groups 2 and 4 were nontreated controls. Fecal egg counts were evaluated before and after treatments. Feces were collected daily for 7 days after the final treatment for recovery of worms passed, and all dogs were euthanatized 7 days after the final treatment for recovery of worms retained. A 65.7% reduction from the pretreatment value for geometric mean hookworm egg count was found 7 days after the first treatment, and a 97.1% reduction 7 days after the second treatment. Although milbemycin oxime had 96.5% and 99.5% controlled efficacy against A caninum after 1 or 2 treatments, respectively, it lacked efficacy against U stenocephala. The geometric mean number of U stenocephala and the total number of hookworms retained after 1 or 2 treatments were not significantly different from the numbers retained by the corresponding control groups.

Ancylostoma↗
PubMed1992

Ivermectin treatment of naturally acquired and experimentally induced Strongyloides stercoralis infections in dogs.

Treatment of Strongyloides stercoralis infection was investigated in 2 dogs with naturally acquired, chronic-active infections, and in 3 dogs with corticosteroid-enhanced, experimentally induced hyperinfections. A single oral dose of ivermectin was given to naturally infected (200 micrograms/kg of body weight) and experimentally infected (800 micrograms/kg) dogs. Five dogs with experimental hyperinfections served as controls. Dogs with naturally acquired infections ceased to shed first-stage larvae in the feces 1 week after treatment, but 1 dog had recrudescence and required a second dose. Ivermectin was 100% effective in removing adult S stercoralis from the intestinal tract of the experimentally infected dogs, but it was not effective in removing third-stage larvae from parenteral sites. Ivermectin-treated dogs had few intestinal parasites of any stage, whereas at necropsy, 4 of 5 experimentally infected dogs not treated had massive infections (greater than 100,000 adults, greater than 92,000 larvae) in the intestinal tract, and 3 of 5 had larvae (greater than 2,500) in parenteral sites.

Administration, Oral↗
PubMed1992

Ancylostoma caninum: reduced glutathione stimulates feeding by third-stage infective larvae.

The resumption of feeding in vitro has been proposed as an indicator of the reactivation of development by arrested third-stage hookworm larvae. The tripeptide glutathione was tested for its ability to induce in vitro feeding by third-stage infective larvae of the canine hookworm Ancylostoma caninum. Reduced glutathione, but not oxidized glutathione, stimulated larval feeding in a specific, concentration-dependent manner. Feeding began at 5-10 mM, and reached a plateau at 25-50 mM. Incubation in reduced glutathione for 3 hr was sufficient to stimulate the maximum feeding response at 24 hr. Larvae began feeding within 6 hr of incubation with reduced glutathione, and feeding reached a maximum percentage by 24 hr. The reducing agents dithiothreitol and 2-mercaptoethanol failed to stimulate feeding, whereas S-alkyl derivatives of reduced glutathione were stimulatory. Reduced glutathione synergistically increased serum-stimulated feeding to greater than 90% of the sample population, and low concentrations of glutathione appeared to enhance feeding by sensitizing the larvae to a stimulatory component in serum and not by a chemical interaction with a serum component. The data suggest that reduced glutathione might participate in the transition from the free-living third-stage larva to the parasitic third-stage larva during infection.

Amino Acids↗
PubMed1992

Efficacy of an ivermectin/pyrantel pamoate chewable formulation against the canine hookworms, Uncinaria stenocephala and Ancylostoma caninum.

The effectiveness of the combination of pyrantel pamoate (5 mg kg-1) and ivermectin (6 micrograms kg-1) against the canine hookworms Uncinaria stenocephala and Ancylostoma caninum was determined. This combination is intended for monthly use as a heartworm preventative and for treatment and control of canine hookworms. The formulation was found to be effective (99.6% reduction in worm burdens) against both species of hookworms in experimentally infected dogs. No adverse effects due to the drug combination were observed in any dog during the course of this study.

Administration, Oral↗
PubMed1992

Hyaluronidase from infective Ancylostoma hookworm larvae and its possible function as a virulence factor in tissue invasion and in cutaneous larva migrans.

During skin penetration, infective hookworm larvae encounter hyaluronic acid as they migrate between epidermal keratinocytes and through the ground substance of the dermis. A hyaluronidase would facilitate passage through the epidermis and dermis during larval invasion. Zoonotic hookworm larvae of the genus Ancylostoma were shown to contain a hyaluronidase activity that migrated on modified sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) hyaluronic acid gels with an apparent Mr of 49,000. A second form with an Mr of 87,000 was also identified. The major etiologic agent of cutaneous larva migrans, A. braziliense, was shown to have the greatest enzyme activity, hydrolyzing up to 3.3 micrograms of hyaluronic acid per h per micrograms of total parasite protein at pH 6.0, whereas A. caninum and A. tubaeforme each had much less enzyme activity. The differences in enzyme activities between species correlated with differences in the intensities of the lytic zones at 49 and 87 kDa on SDS-PAGE hyaluronic acid gels. Hookworm hyaluronidase activity exhibited a broad pH optimum between 6.0 and 8.0 and did not hydrolyze chondroitin sulfate, two features that suggest that the hookworm enzyme is more like the invertebrate leech hyaluronidase than mammalian testicular or lysosomal hyaluronidase. Larvae of A. braziliense were shown to release hyaluronidase activity and degrade radiolabeled hyaluronic acid in vitro. Gold sodium thiomalate was identified as an enzyme inhibitor. The hyaluronidase is the second major virulence factor that we have identified from infective hookworm larvae.

Ancylostoma↗
PubMed1992

Strongyloides stercoralis infection in IgA-deficient dogs.

Two litters of eight-week-old, IgA-deficient pups, each including one normal littermate control, were infected with 5,000 infective third-stage Strongyloides stercoralis larvae per pup. No significant differences between the dogs deficient in serum and mucosal IgA and the normal control dogs were observed in any of the parasitologic parameters measured during the course of infection. The time required to reach patency, the maximum number of larvae shed in the feces, the number of days postinfection at which larval shedding was at its maximum, and the time required to eliminate shedding were similar in the two groups. Once larval shedding ceased, there was no recrudescence, even though serum and fecal IgA were absent or low throughout the seven-month course of the investigation. All dogs remained asymptomatic, with complete blood counts and clinical chemistries within normal ranges. In addition, serum IgM and IgG levels were within the normal range for both groups of infected dogs. All dogs from which necropsy samples were obtained harbored low numbers of adult female worms, some of which were barren. An IgA deficiency apparently does not affect the course or severity of S. stercoralis infection in the dog.

Animals↗
PubMed1992

Developmental biology and migration of Strongyloides ratti in the rat.

Most recent authors suggest that larvae of the threadworm, Strongyloides ratti, migrate from a cutaneous infection site to the small intestine via the naso-frontal region of the head. However, the proportion of larvae that successfully reach the intestine having followed this pathway had not been determined. Using compartmental analysis we have obtained a comprehensive quantitative description of larval migration during a primary infection of rats with S. ratti. Mean residence times in organs through which larvae migrate were calculated and the proportion of the larvae arriving in the small intestine via the head was estimated as 0.5-0.86, depending on the mathematical model used to generate the estimate. With 50% or more of successful larvae using this pathway it is now reasonable to recognize the "head route" as an important migratory pathway for larvae traveling to their intestinal predilection site. During the first 12 hr in the host, larvae were difficult to recover from the skin and subjacent muscles of the infection site. Apparently, upon invading a host, many larvae enter a quiescent phase during which Baermannization, an active recovery technique, fails to recover them. Infections were short-lived, with the daily finite mortality rate for adult worms attaining 50-80% on day 16 of infection.

Animals↗
PubMed1992

Resumption of feeding in vitro by hookworm third-stage larvae: a comparative study.

Third-stage infective larvae of the canine hookworm Ancylostoma caninum resume feeding in vitro in response to several stimuli. Experiments were conducted to characterize the in vitro feeding behavior of several hookworm species. Reduced glutathione and, to a lesser extent, canine and human serum stimulated third-stage larvae of Ancylostoma duodenale to resume feeding. Glutathione-induced feeding reached a maximum by 16 hr and was concentration-dependent between 0- and 15-mM glutathione. Oxidized glutathione and the reducing agents dithiothreitol and L-cysteine failed to induce feeding, suggesting that reducing conditions alone were not stimulatory. Serum incubated with glutathione was the most efficient stimulus for Ancylostoma ceylanicum, Ancylostoma braziliense, and Ancylostoma tubaeforme larvae, whereas Uncinaria stenocephala larvae responded best to canine serum alone. Necator americanus larvae did not resume feeding in response to glutathione, serum, glutathione plus serum, or linoleic acid (0.1-10 mM). These differences in feeding behavior suggest that generalizations concerning hookworm biology must be interpreted cautiously.

Ancylostoma↗
PubMed1992

Efficacy of a chewable formulation of ivermectin against a mixed infection of Ancylostoma braziliense and Ancylostoma tubaeforme in cats.

The efficacy of a beef-based, chewable formulation of ivermectin against a mixed infection of Ancylostoma braziliense and A tubaeforme was determined in cats. Ivermectin administered orally at approximately 24 micrograms/kg of body weight was 92.8% effective against adult A braziliense and 90.7% effective against adult A tubaeforme. The number of eggs per gram of feces had decreased 98.1% by 7 days after treatment. Clinical signs of hookworm disease also decreased after treatment. Location of adult parasites within the small intestine, percentage of infecting larvae that developed to the adult stage, and egg size in cats with infections of A braziliense and A tubaeforme were similar to those reported for cats with separate infections of either species.

Administration, Oral↗
PubMed1991

Albumin and a dialyzable serum factor stimulate feeding in vitro by third-stage larvae of the canine hookworm Ancylostoma caninum.

Previous studies demonstrated that third-stage, developmentally arrested larvae of the canine hookworm Ancylostoma caninum resume feeding in vitro in response to canine serum and hostlike temperature. Experiments to determine the identity of the serum stimulus are described. Serum from several nonhost species stimulated feeding, but to levels lower than canine serum. Heating the serum to 57 C had no effect on its stimulatory ability. Dialysis reduced serum stimulatory activity by 50%, and ultrafiltration through 10- and 30-kDa molecular weight cut-off membranes decreased activity in both the filtrates and retentates similarly. Recombination of the filtrates and retentates restored activity to whole serum control levels. Commercial canine and bovine albumin stimulated feeding to serum control levels at 10 and 50 mg/ml, respectively. These results suggest that albumin and an unidentified low molecular weight compound(s) are capable of inducing in vitro feeding by A. caninum L3.

Ancylostoma↗
PubMed1990

The identification of a species-specific antigen from Necator americanus.

A 17 kD protein of Necator americanus was isolated by SDS-PAGE and used to raise monospecific antisera in rabbits. ELISA and Western blotting against a range of parasite extracts demonstrated the species specificity of this protein. It is expressed at all stages of the life-cycle, appears to be accumulated through the larval stages to adulthood, and can be localized in the oesophageal glands and cuticle of the adult parasite. The possible nature and diagnostic potential of this protein is discussed.

Animals↗
PubMed1990

Serum-stimulated feeding in vitro by third-stage infective larvae of the canine hookworm Ancylostoma caninum.

Developmentally arrested nonfeeding infective larvae of hookworms resume development after entry into the host, presumably in response to a signal encountered during invasion. Logically, an initial step in the resumption of development might be the resumption of feeding. An in vitro assay for feeding is described for the third-stage larvae of the canine hookworm Ancylostoma caninum. Populations of larvae incubated under hostlike conditions in the presence of 10% canine serum resume feeding within 6 hr, as evidenced by the uptake of fluorescein-labeled bovine serum albumin. Feeding is dependent on the presence of canine serum, and peaks by 24 hr incubation. Maximal feeding levels occur at temperatures above 34 C with a gas phase of 5% CO2/95% air, whereas culture medium and pH are unimportant for feeding. Serum concentrations between 0.1% and 1.0% (v/v) initiate feeding, and the response peaks at approximately 8.0% serum. Serum triggers feeding within 6 hr and is not required for feeding to continue once initiated. The saturation effect and the trigger phenomenon suggest that the initiation of feeding is a receptor-mediated response.

Ancylostoma↗
PubMed1990

Trichinella spiralis in an agricultural ecosystem: transmission in the rat population.

Four hundred forty-three Norway rats (Rattus norvegicus) were examined to determine their role in the transmission and maintenance of Trichinella spiralis on a pig farm. Rats, classified by sex and weight, were examined for trichinellosis by peptic digestion of muscle samples. Over a 25-mo period, 188 (42.4%) rats were found to be infected with T. spiralis. The mean intensity of infection was 293.2 larvae per gram (LPG) of muscle; 65 (34.6%) infected rats had intensities of infection greater than 100 LPG. Even in the absence of a known source of infected meat (garbage containing meat scraps or dead animals), the rat population maintained the infection, probably through cannibalism. Population reduction was an effective method for reducing the prevalence of infection within the rat population. Therefore, to reduce the likelihood of transmission of T. spiralis between rats and swine, it is essential that rat populations in a farmyard environment be controlled.

Animals↗
PubMed1989

Ancylostoma duodenale and Necator americanus: effect of temperature on egg development and mortality.

The development and mortality of the eggs of Ancylostoma duodenale and Necator americanus in distilled water were monitored over a range of temperatures between 15 and 35 degrees C. Egg demography was examined within the context of a four-parameter mathematical model of development and mortality. Over the range of temperatures studied, egg mortality (mu) was an increasing exponential function of temperature (T) measured in degrees Celsius. A single model adequately described the mortality of both species (In [mu] = 0.41*T-6.87). The minimum time (tau) to hatching was consistently less for A. duodenale (In [1/tau] = -(0.79 + 53.05*[1/T]) than N. americanus (In [1/tau] = -(0.99 + 53.05*[1/T]]. The hatching rate (sigma when t greater than tau) was an increasing function of time and temperature in both cases, but the precise functional relationship was species specific.

Ancylostoma↗
PubMed1989

Strongyloides stercoralis: is there a canonical migratory route through the host?

It is generally accepted that the skin-penetrating larvae of Strongyloides stercoralis travel from the skin to the intestinal habitat of the adult stage by an obligatory migratory route that includes the blood, lungs, trachea, and upper gastrointestinal tract in sequence (the pulmonary route). It is assumed, furthermore, that following autoinfective invasion of the bowel wall, S. stercoralis larvae follow this same route to return to the small intestine where they mature. We reexamined the parasite's migratory behavior using a canine isolate of S. stercoralis, specific-pathogen-free pups, radiolabeled larvae, and compressed tissue autoradiography. Compartmental analysis of the number of larvae found in the organ sets examined revealed no reason to reject the simple idea that the pulmonary route was just one of several possible pathways to the duodenum. This was true whether the larvae began their journey in the subcutaneous tissue of the inguinal area or in the distal part of the ileum. Direct sampling of the larvae traversing the trachea indicated that the number of larvae reaching the duodenum by way of the presumptive pulmonary route was insufficient to account for the estimated absolute number actually found there.

Animals↗
PubMed1989

Radiolabeling of infective third-stage larvae of Strongyloides stercoralis by feeding [75 Se]selenomethionine-labeled Escherichia coli to first- and second-stage larvae.

A technique is described for radiolabeling Strongyloides stercoralis larvae with [75Se]selenomethionine. Cultures of an auxotrophic methionine-dependent stain of Escherichia coli were grown in a medium containing Dulbecco's modified Eagle's medium supplemented with 5% nutrient broth, amino acids, and [75Se]selenomethionine. When the 75Se-labeled bacterial populations were in the stationary phase of growth, cultures were harvested and the bacteria dispersed on agar plates to serve as food for S. stercoralis larvae. Use of nondividing bacteria is important for successful labeling because the isotope is not diluted by cell division and death of larvae attributable to overgrowth by bacteria is prevented. First-stage S. stercoralis larvae were recovered from feces of infected dogs and reared in humid air at 30 C on agar plates seeded with bacteria. After 7 days, infective third-stage larvae were harvested. The mean specific activity of 6 different batches of larvae ranged from 75 to 330 counts per min/larva with 91.8 +/- 9.5% of the population labeled sufficiently to produce an autoradiographic focus during a practicable, 6-wk period of exposure. Labeled infective larvae penetrated the skin of 10-day-old puppies and migrated to the small intestine, where the developed to adulthood.

Animals↗
PubMed1988

Trichinella spiralis in an agricultural ecosystem. III. Epidemiological investigations of Trichinella spiralis in resident wild and feral animals.

As part of a larger epidemiological study examining the transmission of Trichinella spiralis in an agricultural ecosystem, resident wild and feral animals were trapped to determine the extent of their involvement in the natural, on-farm cycling of the parasite among swine. During a 21-mo-study, seven of 15 skunks (Mephitis mephitis), one of three opossums (Didelphis virginiana), two of two feral domestic cats and a raccoon (Procyon lotor) were found to be infected, while five shrews (Blarina brevicauda) and 18 deer mice (Peromyscus spp.) were uninfected. Most of the former hosts probably became infected by scavenging dead infected swine or rats (Rattus norvegicus). However, infections obtained through predation of living rats, particularly with regard to the cats, cannot be excluded. Our observations do not suggest that there was transmission of T. spiralis from the wild animals to swine. Therefore, transmission of T. spiralis appeared to occur only from the farm's swine and rats to the associated wild and feral animals.

Agriculture↗