Modification of the ultrastructure of the muscle larva of Trichinella pseudospiralis following exposure to acidified pepsin solution.

Examination of the cuticle of Trichinella pseudospiralis by transmission electron microscopy revealed an epicuticle, exocuticle, and mesocuticle, each divided into several layers. The epicuticle consisted of an outermost thin plasmalemmalike infracuticular material covering an inner trilaminar membrane. The exocuticle was granular and could be divided into 2 regions on the basis of density. The mesocuticle was fibrillar and 3 regions could be distinguished based on the orientation of fibrils. The cuticle appears attached to the hypodermis by hemidesmosomes. The infracticular structure was altered following isolation of larvae by pepsin-HCl digestion of host muscle.

Susceptibility of corneas from various animal species to in vitro binding and invasion by Acanthamoeba castellanii [corrected].

A crucial requirement for establishing corneal infection by the extracellular protozoal parasite, Acanthamoeba, is the ability of the parasite to bind to the corneal surface. In a series of in vitro studies, we examined the ability of Acanthamoeba castellanii [corrected] to adhere, invade, and damage normal, intact corneas of 11 mammalian and one avian species. A. castellanii [corrected] (80-90% trophozoites and 10-20% cysts) were incubated with corneas for 24 hours in vitro and examined by scanning electron microscopy (SEM). Results of several independent SEM experiments revealed that parasites not only failed to produce cytopathic effects but did not even bind to the corneal epithelium of mice, rats, cotton rats, horses, guinea pigs, cows, chickens, dogs, and rabbits. However, parasites adhered, invaded, and produced severe damage to human, pig, and Chinese hamster corneas during the 24-hour in vitro incubation period. Additional in vitro experiments quantified the binding of A. castellanii [corrected] to the corneas of selected susceptible and nonsusceptible species. In vitro binding assays revealed scant binding of parasites to mouse, rat, and rabbit (range = 5-20 parasites/7.07 mm2 corneal button). In contrast, extensive binding was observed on Chinese hamster, pig, and human corneas (range = 100-200 parasites/7.07 mm2 button). The results indicate that A. castellanii [corrected] exercises rigid host specificity at the host cell surface.

A pig model of Acanthamoeba keratitis: transmission via contaminated contact lenses.

A model of contact lens-induced Acanthamoeba keratitis was developed in Yucatan micropigs. Pigs fitted with parasite-laden soft contact lenses developed corneal infections that clinically and histopathologically mimicked the human counterpart. Three distinct stages of disease became apparent and were categorized as: acute, condensed infiltrate, and resolution stages. Viable parasites were isolated from corneal scrapings and smears were taken during the acute and condensed infiltrate stages. In addition, cysts could be identified deep within the stroma of histological specimens taken during the resolution stages. The characteristic dense, white ring-like infiltrates, stroma edema, keratic precipitates, and the chronic nature of the infections were similar to those observed in human Acanthamoeba keratitis. Histopathological examination of infected corneas revealed extensive neutrophilic infiltrates, stromal necrosis, and disorganization of the collagen lamellae. The strong correlation between the clinical and histopathologic features of contact lens-induced Acanthamoeba keratitis in the pig as well as the anatomical similarity of the pig eye with the human eye make the porcine model a valuable tool for investigations of the immunology, cell biology, and therapy for Acanthamoeba keratitis.

In vitro penetration of human corneal epithelium by Acanthamoeba castellanii: a scanning and transmission electron microscopy study.

Human corneal buttons were exposed to Acanthamoeba castellanii trophozoites and cysts for 12 hours at 35 degrees C. The buttons examined by light microscopy and scanning and transmission electron microscopy had severe epithelial ulceration and penetration by trophozoites. Observations on trophozoites below the surface suggest that penetration is accomplished by both secreted cytolytic enzymes and phagocytosis. It is likely that the secretion of one or more enzymes constitutes the initial step in preparing the host tissue for endocytosis or that the secretory mechanism is used by the amebas to move through the outer squamous layer to the basement epithelium where phagocytosis occurs. Based on this study and a previous study, it appears that entry into the cornea is a two-step process involving adherence and penetration by trophozoites.

In vitro intercellular adherence of Acanthamoeba castellanii: a scanning and transmission electron microscopy study.

Human corneal buttons were exposed to trophozoites and cysts of Acanthamoeba castellanii for 12 hours. Examination of the buttons by scanning electron microscopy showed numerous trophozoites on the surface of the epithelium. Trophozoites examined by transmission electron microscopy had limited regions of attachment to the epithelium but extensive regions of attachment to each other. Attachment regions were characterized as plaque-like maculae of an incomplete desmosome junction. Firm attachment mechanisms may explain how penetration of the human cornea occurs.

Ultrastructural and immunohistological characterization of the SIRC corneal cell line.

A widely utilized rabbit corneal cell line, SIRC, was characterized ultrastructurally and immunohistologically. Although SIRC cells are often described as being of epithelial origin, important ultrastructural and antigenic characteristics indicate that these cells are fibroblastic and not epithelial. SIRC cells lack desmosomes, cytoplasmic filaments, and cytokeratin-structures that are characteristic of corneal epithelial cells. By contrast, the dendritic morphology, presence of vimentin, and the extensive dense accumulations of ribosomes and rough endoplasmic reticulum are consistent with a fibroblastic phenotype. Collectively, the morphology, ultrastructural features, and antigenic composition favor the hypothesis that SIRC cells are fibroblastic cells (keratocytes) and not corneal epithelial cells.

Vascularization of corneas of hairless mutant mice.

During the course of experiments examining the immunobiology of corneal transplants, the corneas of athymic, nude mice (nu/nu) were found to contain blood vessels that extended through the entire superficial stroma into the centermost portion of the cornea. The presence of corneal vessels was not related to the immunodeficient condition of the nude mouse since corneas from the severe combined immunodeficiency (SCID) mutant mouse strain were avascular and indistinguishable from corneas obtained from immunocompetent BALB/c mice. Furthermore, Langerhans cells were not found to accompany the blood vessels in the corneas of any of the nude mice examined. Corneal vascularization that was similar to that seen in the nude mouse was found in the cuthymic, hairless mutant mouse strain (SKH1; hr/hr). Although vascularization of the corneal stroma was associated with the heritable loss of hair, the genes responsible for hair loss in these two mutant mouse strains reside on different chromosomes. Understanding the processes involved in either promoting or preventing corneal vascularization may have significant impact in preventing corneal allograft rejection and in controlling inflammatory diseases of the corneal surface. The two mutant mouse strains described here may serve as valuable tools for such investigations.

A role for elevated plasma corticosterone in modulation of host response during infection with Trichinella pseudospiralis.

Suppression of host inflammatory response in mice infected with Trichinella pseudospiralis was associated with host plasma corticosterone levels significantly higher than those seen in uninfected mice or in mice infected with T. spiralis. Increases in the population of mitochondria and depletion of lipid droplets in cells of the zona fasciculata were seen in the adrenals of mice infected with T. pseudospiralis. Elevations in enteritis, myositis and myocarditis accompanied 100% mortality in adrenalectomized mice infected with T. pseudospiralis, while lower levels of inflammation and no mortality were observed in sham operated or intact animals infected with this parasite. The severe myositis normally accompanying infection with T. spiralis was suppressed by concurrent infection with 1000 or 2000 T. pseudospiralis to levels equivalent to those seen in animals receiving 0.15 and 0.41 mg cortisone acetate/25 g mouse/day, respectively.

Hematologic and coagulation studies on cotton rats, Sigmodon hispidus.

1. Blood coagulation factor levels and the normal ranges of commonly used coagulation tests were established for Sigmodon hispidus. 2. The white cell, red cell and platelet counts have been determined together with the red cell parameters as measured by the Coulter model S-plus. 3. The relationship between the results reported here and those published for related species are discussed.

Systematics of species referred to the genus Angiostrongylus.

Based on morphological criteria of the male bursa, angiostrongylid nematodes often placed in the genus Angiostrongylus Kamensky (1905) were found to be heterogeneous, comprising species which are relegated to 5 distinct genera: Angiostrongylus Kamensky, 1905 (syn. Haemostrongylus Railliet and Henry, 1907); Parastrongylus Baylis, 1928 (syn. Pulmonema Chen, 1935, Rattostrongylus Schulz, 1951, Morerastrongylus Chabaud, 1972, Chabaudistrongylus Kontrimavichus and Delyamure, 1979); Angiocaulus Schulz, Orlov and Kutass, 1933; Gallegostrongylus Mas-Coma, 1977 (syn. Thaistrongylus Ohbayashi, Kamiya and Bhaibulaya, 1979 n. syn); and Stefanskostrongylus Drozdz, 1970. These genera all contain species located primarily in specific host groups: Angiostrongylus in carnivores; Parastrongylus in rodents (Muridae), Angiocaulus in mustelids; Rodentocaulus in rodents (Cricetinae), Gallegostrongylus in rodents (Muridae), and Stefanskostrongylus in insectivores. Species in each genus include: Angiostrongylus (A. vasorum, A. raillieti, A. chabaudi); Parastrongylus (P. tateronae, P. cantonensis, P. mackerrasae, P. sandarsae, P. sciuri, P. petrowi n. comb., P. dujardini, P. schmidti, P. costaricensis n. comb., P. malaysiensis n. comb., P. ryjikovi n. comb., P. siamensis n. comb.); Angiocaulus (A. gubernaculatus, A. ten n. comb., A. sp. Caballero, 1951); Rodentocaulus (R. ondatrae) and Gallegostrongylus (G. ibicensis, G. andersoni, G. harinasutai n. comb.). Angiostrongylus pulmonalis is likely similar to Stefanskostrongylus soricis and is transferred to this genus. Angiostrongylus minutus is removed to Stefanskostrongylus.

Muscle fiber selectivity of Trichinella spiralis and Trichinella pseudospiralis (1983).

The biceps, semimembranosus, biceps femoris, and soleus muscles of female Rockland Wistar mice infected with either 1,000 Trichinella spiralis or 1,000 Trichinella pseudospiralis larvae were removed on days 12, 14, 16, and 18 post-infection (PI), sectioned and stained histochemically for their myosin ATPase activity. Light microscopic examination of the sections revealed that larvae of T. spiralis invade only the slow twitch muscle fibers, and those of T. pseudospiralis invade both the fast twitch and the slow twitch fibers. In sections obtained from mice infected with either parasite and killed on days 16 and 18 PI, identification of the majority of the infected fibers as fast twitch or slow twitch was not possible due to pathological modification of infected fibers.

Experimental infection of Sigmodon hispidus with third-stage larvae of Angiostrongylus costaricensis.

Adult Sigmodon hispidus, were given 50 third-stage larvae of Angiostrongylus costaricensis orally, intraperitoneally, subcutaneously, and on abraded and unabraded skin. Larvae could not penetrate unbroken skin but established normal infections in the cecal vasculature by all other routes. Significantly more adults were recovered after oral and intraperitoneal inoculation than subcutaneously or through abraded skin. In a single animal given larvae subcutaneously, adult worms were recovered from the pulmonary arteries, an abnormal location for this species of metastrongylid nematode, which usually occurs in the ileocolic mesenteric arteries.

A unicellular endocrine gland in cestodes.

Unicellular glands are reported from the scolex and anterior neck region of Hymenolepis diminuta and H. nana. Despite positive staining reactions with the presumptive neurosecretory stains, paraldehyde-fuchsin and chrome-alum-hematoxylin, ultrastructurally these glands exhibit many non-neural characteristics. Glandular cell processes are frequently found in close proximity to muscular tissue, particularly in the suckers, suggesting a regulatory role in muscle modulation as a possible function. Two types of putative, neurosecretory cells are reported from the cephalic ganglia and the lateral nerve cords. Neurosecretory regulation of the unicellular endocrine glands is postulated based on the lack of direct innervation of the glands and the frequent close proximity of axons containing putative, neurosecretory granules.

Rhabdospora thelohani Laguessé, 1895 (Apicomplexa): new host and geographic records with taxonomic considerations.

New fish species and geographic records for Rhabdospora thelohani Laguessé, 1895 (rodlet cells) are presented. Additionally, the ultrastructure of R. thelohani in Alburnoides bipunctatus ohridanus Karaman, Borostomias antarcticus (Lönnberg), Leuciscus cephalus albus Bonaparte and Rutilus rubilio (Bonaparte) is compared with that reported by other authors and with members of Subphylum Apicomplexa. The ultrastructure of R. thelohani was similar in all the fish species examined; however, the organism was not present in all members of any single species and had intertissue density variations. Rhabdospora thelohani is pyriform, averaging in size 7 X 12 micrometer, with a basal nucleus. The surface complex is composed of a layer (0.5 micrometer diameter) formed by microfilaments (9.3 nm) and an outer trilaminar membrane (9.3 nm). The cytoplasm contains structures identical to rhoptries, micronemes and subpellicular microtubules. Mitochondria, Golgi apparatus, and rough endoplasmic reticulum were not observed, althouth free ribosomes were present and arranged in a vesicular pattern. The observations suggest that the organism moves between cell of epithelial layers and is either released into a lumen intact or passively or actively discharges its contents into a lumen. Results from this study indicate that R. thelohani should be considered a member of Apicomplexa unless definitive evidence is presented to the contrary.

The fine structure of spermatogenesis in Hymenolepis diminuta (Cestoda) with a description of the mature spermatozoon.

The processes of spermatogenesis and spermiogenesis in Hymenolepis diminuta were studied by electron microscopy using improved preparative techniques. Spermatogonia (Type A) are characterized by nuclei 3.79 (+/- 0.17) micrometer in diameter, dense cytoplasm packed with free ribosomes and aggregates of mitochondria. After mitoses, certain spermatogonia (Type B) assume syncytial rosettes containing eight nuclei. Primary spermatocytes maintain the rosette syncytium and have large nuclei (4.28 +/- 0.24 micrometer in diameter), smooth endoplasmic reticulum, and polysomes. The secondary spermatocyte is short-lived and is characterized by nuclei (2.0 +/- 0.11 micrometer in diai (2.0 +/- 0.11 micrometer in diameter) and perinuclear membranous lamellae. The syncytial spermatid cluster contains avoid nuclei which condense and elongate to a final diameter of 0.22 +/- 0.04 micrometer. Once elongated, these nuclei become delimited from the syncytium by invaginations of the plasma membrane. During delimitation, cortical peripheral microtubules arise beneath the spermatozoon plasmalemma and a 9 + 1 axoneme extends the length of the mature lance-shaped spermatozoon.