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Biomedical subjects

H M Seitz

Publications and source records attributed to H M Seitz.

At least 37 records · Page 2Linked to original sources
PubMed1998

Opportunistic infections caused by protozoan parasites.

Parasitic protozoa have played a major role in the discovery of the HIV epidemic. It was the occurrence of clustered cases of Pneumocystis pneumonia which caught the attention of the epidemiologists indicating that something unusual was going on. Very recently remarkable progress was made in understanding the epidemiology. Knowledge is evolving that Pneumocystis is host-specific to an extent which seems to justify species rank for the cause of death in AIDS patients for many years. Toxoplasma gondii infections were also recognized very early in AIDS patients. Cerebral toxoplasmosis has now replaced Pneumocystis pneumonia as a fatal infection in many cases. AIDS patients with CD4 cells below 200/microl have a high risk to develop this complication. Cryptosporidium parvum was recognized as the cause of diarrhea in AIDS patients and also in immunocompetent humans where it only leads to a diarrheal episode lasting a few days. In AIDS patients the persisting diarrhea leading to loss of fluid and electrolytes can be life-threatening. Another group of parasites previously unknown to infect humans are the microsporidia, which are wide-spread parasites in nature. Increasing numbers of such infections are observed but many questions regarding pathogenesis and epidemiology are still unclear.

AIDS-Related Opportunistic Infections↗
PubMed1998

Infection and stage conversion during murine pulmonary toxoplasmosis: a study with three different strains of Toxoplasma gondii.

A murine model of pulmonary toxoplasmosis was examined morphologically and immunochemically using 3 strains of Toxoplasma gondii. BALB/c and NMRI mice were infected with tachyzoites of a virulent strain (RH) or with brain cysts of an avirulent (GAIL), or moderately virulent, strain (NED). Depending on the strain of T. gondii, the degree of infection, number of parasites, and replicative potential of T. gondii in lungs varied. In lungs of mice infected with the RH strain, the number of parasites increased in mice during the survival period. Only tachyzoites were found, as confirmed by stage-specific monoclonal antibodies. In lungs of mice infected with the GAIL strain or the NED strain, different stages of parasites were detected. Up to day 14 after infection, only tachyzoites were present, followed by bradyzoites between days 14 and 20 after infection. The number of cysts decreased and finally could not be detected in this organ. In general, the number of cysts that developed in the lungs was smaller than the number that developed in the brain.

Animals↗
PubMed1997

In vivo and in vitro studies on the sonographical detection of Ascaris lumbricoides.

Intestinal ultrasound, a frequently applied diagnostic tool in industrialized nations, has recently also been introduced in tropical regions. This study attempts to describe the anatomical and sonographical features of Ascaris lumbricoides in the human intestine. In the course of a schistosomiasis morbidity study in Madagascar, 581 inhabitants of a rice-farming village on the high plateau of the island had their stools examined by means of a modified Kato-Katz thick smear technique (four slides per sample); 53% had eggs of Ascaris lumbricoides in their stools. Twenty-two individuals underwent intestinal ultrasound examination and, in six cases, Ascaris lumbricoides was visualized. All six patients showed eggs upon stool examination. At ultrasound, the parasite was seen as a large, curved echogenic strip (4-6 mm in diameter) with an inner, anechoic, longitudinal canal. The image resembled a winding highway, the central structure representing the pseudocoel of the parasite. Patients were treated with mebendazole. The excreted worms of one patient were scanned under water, showing the same characteristics as in vivo. We conclude that Ascaris lumbricoides has a characteristic sonographical appearance and should not be a confounding factor in studies using intestinal ultrasound.

Aged↗
PubMed1997

Cyst formation by Toxoplasma gondii in vivo and in brain-cell culture: a comparative morphology and immunocytochemistry study.

Formation of Toxoplasma gondii cysts was examined in cultured murine brain cells and was compared with the development of cysts in mouse-brain tissue. Cultures of mixed glial cells from neonatal mouse brain were infected with bradyzoites of the avirulent T. gondii strain DX. The development and maturation of Toxoplasma cysts was monitored for up to 63 days after inoculation. Transmission electron microscopy indicated that in-vitro-derived cysts were morphologically similar to tissue cysts and were located intracellularly, even for up to 63 days postinfection. For immunohistological and immunocytochemical examination of both in-vivo- and in-vitro-infected material, monoclonal antibody (mAb) CC2 was used. MAb CC2 was shown to detect specifically the underlying granular material of the cyst wall without binding to the limiting membrane of the parasitophorous vacuole. This reactivity of mAb CC2 allows the distinction of bradyzoite-containing cysts from parasitophorous vacuoles harboring tachyzoites both in vitro and in vivo.

Amylopectin↗
PubMed1996

Classification system and case definitions of Toxoplasma gondii infection in immunocompetent pregnant women and their congenitally infected offspring. European Research Network on Congenital Toxoplasmosis.

Classification systems and case definitions provide the foundations upon which clinical and epidemiological studies are based. The European Research Network on Congenital Toxoplasmosis acknowledged the lack of such a system or definitions within its field of interest and established a working group to address the issue. Congenital Toxoplasma gondii infection was defined as occurring in four separate patient groups: pregnant women, fetuses, infants, and individuals > 1 year of age. The likelihood of Toxoplasma gondii infection was separated into five mutually exclusive categories: definite, probable, possible, unlikely, and not infected. Inclusion within a specific category is dependent upon the case definition, which is in turn derived from criteria based on serological, parasitological, and clinical information. Notes are included within the classification not only to clarify the definitions, but also to improve the reliability and quality of diagnosis. The goal is to construct a system that encompasses all aspects of congenital toxoplasmosis, which is applicable to different countries and health services, suitable for large epidemiological studies, aids the diagnosis and management of individual cases, and lends itself to computerisation.

Female↗
PubMed1996

Occurrence of an unusual polymerase chain reaction product during identification of Anopheles gambiae sibling species (Diptera: Culicidae).

Using the polymerase chain reaction (PCR) for species differentiation within the Anopheles gambiae complex, we examined several hundred Cameroonian mosquito specimens. Applying an approved routine protocol for DNA extraction and PCR conditions, apart from the indubitable identification of most of the specimens, we came across ten PCR products that did not correspond in length to any of the hitherto known amplification products of the sibling species. Sequencing experiments showed the ten products to be of identical length (117 bp) and nucleotide sequence. The total sequence of the novel product is included in the PCR product specific for A. melas, which is known to occur in the same collection area as the ten unidentifiable mosquito specimens. On alignment of the novel PCR product sequence and the A. melas one starting at the 3'-end primer annealing site, the last 20 nucleotides of the novel product, reflecting the sequence of the 2nd PCR primer, showed only 60% homology with the then-corresponding A. melas DNA site. Explanations for the occurrence of the unusual PCR products are given and discussed.

Animals↗
PubMed1996

Possible contamination of surface waters with Giardia spp. through muskrats.

Muskrats were examined for Giardia infections. Collected faecal samples were processed by means of sucrose density gradient centrifugation, using a 1 M sucrose solution. Identification of cysts was done by phase contrast microscopy, by the immunofluorescence test, or by both methods. From July 1994 to September 1995, a total of 234 muskrats from two different geographical areas in western parts of Germany were examined for the presence of Giardia cysts. 176 animals (75.2%) were found to be Giardia-positive. This study corroborates the assumption that animals such as muskrats living close to surface water bodies could contaminate water bodies with parasites such as Giardia.

Animals↗
PubMed1996

Nonimmunological factors affecting the release of excreted/secreted antigens from Toxoplasma gondii cysts.

The phenomenon of released Toxoplasma gondii cyst antigens was studied immunohistochemically and cytochemically. It could be demonstrated that the preservation and localization of excreted/secreted antigens depended not only on the technique of preparation and fixation of the infected tissue but also on the preservation of the host cell. The soluble, bradyzoite-secreted amorphous cyst matrix material is released either after host cell destruction or permeabilization of the cyst wall. Ultrastructural studies could prove that the liberation of the cyst from its host cell does not affect the basic structure of the cyst wall but causes stretching of the invaginated limiting membrane.

Animals↗
PubMed1996

Recovery efficiency of Cryptosporidium from water with a crossflow system and continuous flow centrifugation: a comparison study.

A crossflow system and continuous flow centrifugation were tested with regard to the recovery rate of Cryptosporidium oocysts from water. Equal volumes of tap water were contaminated with specific numbers of oocysts. With the crossflow system, an average recovery of 9.8% was obtained when using a concentration of 2 x 10(2) oocysts/L. Recovery rates achieved with the continuous flow centrifuge were more satisfactory: Starting with a concentration of 80 oocysts/L, we obtained an average recovery of 12.9%. The technique of continuous flow centrifugation was found to be more efficient for collection of Cryptosporidium oocysts from water than the crossflow system.

Animals↗
PubMed1996

Giardia and Cryptosporidium in backwash water from rapid sand filters used for drinking water production.

Backwash water from rapid sand filters of a treatment plant using surface water from small rivers for drinking water production was examined with the aim of determining the degree of their potential contamination with Giardia cysts and Cryptosporidium oocysts. Simultaneous investigations were carried out for both protozoans from November 1993 to February 1994. Water samples were concentrated by continuous flow centrifugation (11 backwash water samples) or by using polypropylene cartridge filters (12 raw water samples and 39 backwash water samples). Parasites were identified by the direct immunofluorescence assay. Ten out of 12 raw water samples tested were positive for Giardia (range: 2-103/ 100 L) and 8 out of 12 were positive for Cryptosporidium (range: 0.8-109/100L). Eight of 11 backwash water samples collected by continuous flow centrifugation were positive for Giardia (range: 3-86/100 L) or Cryptosporidium (range: 1-69/100 L). Out of 39 samples collected using cartridge filters, 34 were positive for Giardia (range: 1.4-374/100 L) and 33 for Cryptosporidium (range: 0.8-252/100 L). Overall, Giardia, Cryptosporidium, or both were detected in 92% of the backwash water samples. The results have clearly shown that backwash waters were contaminated with Giardia and Cryptosporidium and the supernatant returned to the raw water after the sedimentation process was not free from cysts and oocysts.

Animals↗
PubMed1996

The use of short-term cultures of Pneumocystis for drug testing.

A method for short-term drug testing for Pneumocystis is described. Up to now there was no successful cultivation method without feederlayers. Parasites for inocula were obtained from nude rats, kept under conventional conditions. Pneumocystis separation was done by two centrifugation steps from lung homogenates. Cultivation in a modified Tegoshi medium resulted in preservation of parasites for five days, however there was no growth of P. carinii. Quantification was done microscopically by counting trophozoites in triplicate cultures. The percentage of cysts with intracystic bodies did not exceed 2% of parasites. Tests with pentamidine isethionate as a reference drug demonstrated the suitability of this system for drug evaluation.

Animals↗
PubMed1996

Enhanced efficacy of a liposomal pentamidine preparation in Pneumocystis carinii in an ex vivo/in vitro culture model without feederlayer cells.

The effects of pentamidine isethionate, phosphatidylcholine-liposomes (PPC-lip) and combinations of both on the survival of Pneumocystis carinii trophozoites in a culture system without feederlayer cells were quantified. Pentamidine or PPC-lip alone reduced significantly the number of cells, with a clear dose dependence. Combinations of both drugs showed overadditive effects on cell counts reduction. Additional EM-investigations showed a rapid destruction of cell structures especially with the pentamidine/phospholipids-combinations. Our results could justify clinical tests with these combinations in AIDS patients in order to reduce the pentamidine dose, reduce local side effects with inhaled pentamidine while at least maintaining efficacy.

Animals↗
PubMed1995

Infestation of rodents with larval Ixodes ricinus (Acari: Ixodidae) is an important factor in the transmission cycle of Borrelia burgdorferi s.l. in German woodlands.

The ecology of Borrelia burgdorferi Johnson et al. s.l. was investigated from 1987 to 1993 in a preserved woodland in western Germany near Bonn. In selected biotopes, host-seeking Ixodes ricinus L. were regularly collected by blanket dragging in 1987, 1988, and 1989 and screened for infection with B. burgdorferi. Rodents were trapped monthly between April and October in 1988, 1990, 1991, and in the winter of 1992-1993, examined for antibodies to B. burgdorferi s.l., and inspected for feeding ticks. Ticks collected from rodents were screened for spirochete infection. High numbers of host-seeking nymphs were consistently collected within a biotope characterized by humid and acid soils. The mean number of ticks was significantly lower in biotopes with permeable soils. All small mammals captured belonged to the species Apodemus flavicollis Melchior, A. sylvaticus L., and Clethrionomys glareolus Schreber. Of 11,680 ticks obtained from rodents, 11,674 were I. ricinus, with 97.9% of the ticks being larvae, 2.0% nymphs, and 0.1% females. Mean numbers of feeding ticks ranged from 3.4 to 117 larvae per rodent and from 0.0 to 0.64 nymph per rodent, respectively. High levels of larval infestation on rodents were recorded in the same biotope where high numbers of host-seeking nymphs were present. Members of the genus Apodemus were more heavily infested with I. ricinus larvae than C. glareolus. The mean infection prevalence in host-seeking ticks was found to be 1% for larvae, 5% for nymphs, and 10-20% for adults. The infection prevalence in host-seeking nymphs ranged from 1.1 to 15.4% according to the particular biotope. The values for specific infectivity for the Apodemus populations were positively correlated with the mean larval infestation, but not with nymphal infestation. The respective estimates for C. glareolus were much higher than those for Apodemus spp. in biotopes with low tick densities. However, specific infectivity of C. glareolus was substantially reduced at sites with high tick abundances. In biotopes with high numbers of infected I. ricinus, significantly more rodents were found to have antibodies to B. burgdorferi than in biotopes with low abundances of ticks. The data show that C. glareolus plays a different role as reservoir host species compared with the 2 Apodemus species. This and previous studies suggest that the degree of infestation with larval I. ricinus differentially modulates infectivity of host species for ticks. We conclude that immune processes in natural reservoir hosts induced by B. burgdorferi or I. ricinus bites (or both) are important regulatory factors in the transmission cycle(s) of B. burgdorferi.

Animals↗
PubMed1995

Toxoplasma gondii antibodies in pregnant women and their newborns in Dar es Salaam, Tanzania.

The sera of 849 Tanzanian pregnant women were tested at delivery for Toxoplasma gondii antibodies with the Sabin-Feldman dye test (DT) and an immunosorbent agglutination assay. A total of 296 (35%) of these women had DT titers greater than 1:4. The percentage of women with dye test titers greater than 1:4 was 34-37% regardless of the individual ages. The rate of positivity for human immunodeficiency virus 1/2 (HIV-1/2) using Western blotting was 11.5%. There was no relationship between prevalence of a positive DT result and HIV infection nor between the intensity of the DT result and HIV infection. Sixty-four parturients had a DT titer of 1:1,000 or more. From 57 newborns of these mothers, cord sera were available and were screened by the DT and the immunosorbent agglutination assay. Seven of these were found to be positive for IgM and/or IgA antibodies. It was concluded that the rate of serologic evidence for prenatal Toxoplasma infection in cord blood samples in the present study of Tanzanian pregnant women was approximately 0.8%.

Adolescent↗
PubMed1995

[Parasitic diseases of the liver].

The liver seems to be very attractive for many parasites which may either inhabit the organ or pass through during their normal development or may be carried to the liver leading to destruction there. Malaria parasites have a short developmental stage in the hepatocytes, but they do not damage the organ. For the leishmanias (Leishmania donovani complex) are the Kupffer cells are the target cells causing visceral leishmaniasis or kala azar. Nematodes of the ascarid group have a special affinity for the liver. The larvae of the human Ascaris have to pass through the parenchyma once during their developmental cycle, the larvae of animal ascarids on the contrary migrate within the liver for longer periods of time. Eggs of the schistosomes are carried via the portal system into the liver and trapped there in the tissue. An inflammatory granuloma develops around them. If the egg load is high, fibrosis of the liver may finally develop leading to portal hypertension. While small liver flukes (Clonorchis, Opisthorchis) living in the bile ducts do little harm to the liver in most cases, the larger liver fluke Fasciola hepatica destroys liver tissue during an early migratory phase of several weeks duration. Larval cestodes of the genus Echinococcus are usually found in the liver as closed cysts growing by expansion (E. granulosus) or as more solid structures growing by infiltration and destruction (E. multilocularis). Destruction results also if ameba (Entamoeba histolytica) invade the liver. Large areas of necrosis, liver abcesses are formed.

Animals↗