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Biomedical subjects

Ana Flisser

Publications and source records attributed to Ana Flisser.

At least 19 recordsLinked to original sources

Control of the taeniosis/cysticercosis complex: future developments.

Cysticercosis is due to the establishment of the larval stage of the zoonotic cestode parasite Taenia solium. The infection causes substantial human morbidity and mortality, particularly in several Latin American countries and parts of Africa and Asia, as well as economic losses in pig husban dry due to condemnation of infected pork meat. The life cycle of T. solium includes human beings as definitive hosts and pigs as intermediate hosts. Cysticercosis is acquired by the ingestion of eggs released by human tapeworm carriers, who become infected after ingesting pork meat contaminated with cysticerci. Taenia solium transmission has been associated with poverty, lack of sanitary services and practices of rearing backyard pigs with free access to the areas that villagers use as toilets, as well as cultural behaviour. Nonetheless, due to the recent increase of migration and tourism, industrial countries are also reporting cases of human cysticercosis. There are many epidemiological studies that have been conducted mainly in Latin American countries that have evaluated intervention measures for control of cysticercosis including the development and testing of vaccines. Furthermore, the involvement of international agencies and institutions, such as the World Health Organization, the Food and Agriculture Organization and the International Livestock Research Institute, as well as the commitment of policymakers, scientists and field workers, are key means for the sustainable control and, hopefully, eradication of T. solium infections.

Animal Husbandry↗

Informed consent in clinical research at a general hospital in Mexico: opinions of the investigators.

In Mexico informed consent is a legal requirement that ensures that patients who are invited to participate in clinical trials are provided with all the information needed to decide whether to participate, or not, in a research protocol. To improve our understanding of the problems physicians in developing countries encounter, when obtaining informed consent (IC), we examined their opinion on the importance of IC in clinical research, the quantity and quality of the information provided to the participant, and the conditions in which the IC is obtained. Investigators considered that IC was useful to the patients, providing information that helped the patient to make a decision about his/her participation. Nevertheless, they felt that for some aspects of the research, like drug development in general, the use of placebos, and the randomization process, many of the patients were not capable of fully understanding the information provided, referring to the complexity of the information and illiteracy as the main reasons. Many investigators were not acquainted with some of the guidelines established in the Mexican General Law of Health,(1) 36% of them admitting to not having completed their IC letters. Most investigators gave only minutes to the patient to make a decision and 20% of ICs were obtained while the patient was hospitalized. Except for one investigator, all of them considered that specific training in medical ethics would be useful for the daily clinical work.

Attitude↗

Molecular diversity of rabies viruses associated with bats in Mexico and other countries of the Americas.

Bat rabies and its transmission to humans and other species in Mexico were investigated. Eighty-nine samples obtained from rabid livestock, cats, dogs, and humans in Mexico were studied by antigenic typing and partial sequence analysis. Samples were further compared with enzootic rabies associated with different species of bats in the Americas. Patterns of nucleotide variation allowed the definition of at least 20 monophyletic clusters associated with 9 or more different bat species. Several lineages associated with distinctive antigenic patterns were found in rabies viruses related to rabies in vampire bats in Mexico. Vampire bat rabies virus lineages associated with antigenic variant 3 are widely spread from Mexico to South America, suggesting these lineages as the most likely ancestors of vampire bat rabies and the ones that have been moved by vampire bat populations throughout the Americas. Rabies viruses related to Lasiurus cinereus, Histiotus montanus, and some other not yet identified species of the genus Lasiurus were found circulating in Mexico. Long-range dissemination patterns of rabies are not necessarily associated with migratory bat species, as in the case of rabies in Desmodus rotundus and Histiotus montanus. Human rabies was associated with vampire bat transmission in most cases, and in one case, rabies transmission from free-tailed bats was inferred. The occurrence of rabies spillover from bats to domestic animals was also demonstrated. Genetic typing of rabies viruses allowed us to distinguish trends of disease dissemination and to address, in a preliminary fashion, aspects of the complex evolution of rabies viruses in different host-reservoir species.

Amino Acid Sequence↗

Differential expression of calreticulin in developmental stages of Taenia solium.

Taenia solium, a cestode that causes neurocysticercosis and taeniasis in humans, has a complex life cycle. The adult tapeworm develops in the intestine of human beings and is also responsible for neurocysticercosis, which is caused by the metacestode or cysticercus that develops in the brain. Recently, we have cloned the coding region for T. solium calreticulin (TsCRT) as a functional Ca(2+)-binding protein. Calreticulin is a ubiquitous protein involved in cellular Ca2+ homeostasis and protein folding. These important functions affect several aspects of cell physiology. To explore the expression of TsCRT during the T. solium life cycle, we used a specific polyclonal antibody raised against recombinant TsCRT to localize this protein by immunolabeling techniques. In sections of cysticerci obtained from swine muscle, as well as of adult tapeworms obtained after infection of hamsters with cysticerci, TsCRT was preferentially localized in tegumentary and muscle cytons of the suckers and rostellum. In mature proglottids obtained from infected humans, positive staining was observed in spermatogonia, ovogonia, uterine epithelium, and cells of the vas deferens. In the gravid uterus, the morula and early stage embryos were highly positive to TsCRT. However, expression diminished as embryonic development progressed and was absent in fully developed oncospheres that were surrounded by an embryophore. A similar down regulation was observed during spermatogenesis. Although early spermatocytes showed a high expression of TsCRT, mature spermatozoa present in the vas deferens were completely negative. These data indicate that calreticulin expression is spatially and temporally regulated during development of T. solium, especially during germ cell development and embryogenesis. In addition, these original images illustrate, for the first time, these processes at a histological level.

Animals↗

Laboratory animal models for human Taenia solium.

Human beings are the only hosts of adult Taenia solium; thus, many aspects of the host-parasite relationship are unknown. The development of successful experimental models of taeniasis allows in-depth investigations of the host-parasite relationship. We established experimental models in hamsters, gerbils and chinchillas. Here we review our findings regarding the characteristics of the tapeworms, their anchoring site and development, as well as the humoral and cellular immune response they elicit. We also used statistics to analyze the data obtained in different infections performed along several years. Furthermore, we compared the size of T. solium rostellum and strobila recovered from hamsters and gerbils to those obtained from humans. Our data indicate that these rodents are adequate experimental models for studying T. solium in its adult stage; that parasites induce immune responses and that hamsters seem to be more permissive hosts than gerbils, since parasites survive for longer times, grow longer and develop more, and the inflammatory response in the intestinal mucosa against T. solium is moderate. Finally, chinchillas are the most successful experimental definitive model for adult T. solium, since tapeworms with gravid proglottids are obtained, and the life cycle can be continued to the intermediate host.

Animals↗

Where are the tapeworms?

This review analyzes the literature in search of an answer to the fact that, in general, tapeworms are very difficult to recover. The results and comments of the authors that have searched for Taenia solium, either to define the local prevalence in different countries of Latin America, to assess the efficacy of cestocidal treatment or to evaluate alternatives for controlling cysticercosis, are presented. The difficulties in tapeworm recovery and the possible explanations for this phenomenon are discussed.

Animals↗

Molecular epizootiology of rabies associated with terrestrial carnivores in Mexico.

Epizootiological patterns of rabies are described, using antigenic and genetic analysis of samples obtained from infected domestic and wild mammals in 20 Mexican states during 1976-2002. Two independent origins are suggested for rabies in Mexican carnivores. One group shares ancestry with canine rabies, while the other group appears to share a common origin with bat rabies in North America. More than 12 sublineages were found in rabid dog populations, suggesting at least six major spatio-temporal foci. Coyote rabies was found as independent enzootic foci that probably emerged via spillover from dog rabies, translocated from major foci in the southcentral and western regions of Mexico. One focus of gray fox rabies was widely distributed in northwestern Mexico, overlapping with a focus in the same species in the southwestern United States. A skunk rabies focus distributed in the northcentral Mexican states appears to share a common origin with bat rabies foci in North America, and is a close relative of southcentral skunk and raccoon rabies in the United States. Two other skunk foci share a common ancestor with canine rabies and were distributed in northwest Mexico and Yucatan.

Animals↗

Short report: evaluation of a self-detection tool for tapeworm carriers for use in public health.

The current study was designed to evaluate a tool for the self-identification of tapeworm carriers. Clinical and animal health care practitioners and schoolteachers were trained regarding the life cycle, risk factors, and control measures related to infection with Taenia solium. More than 120 small glass bottles with a few tapeworm segments fixed in formaldehyde and an instructional guide were distributed among all clinical practitioners (physicians and nurses) working in health centers. The guide contained 10 key points on how to ask questions about tapeworm infections. Information on taeniosis and cysticercosis was also provided to the general population via different media. Seven tapeworm carriers were recorded in the official epidemiology surveillance system the year previous to the study, compared with the year after the study, when 41 tapeworm carriers (37 Taenia saginata; 4 Taenia solium) were recorded. Six times more tapeworm carriers were notified after the study. All four persons with Taenia solium were treated, thereby eliminating the parasite and subsequently preventing any new cases of human and swine cysticercosis that might have arisen from them.

Anthelmintics↗

Isozyme analysis of Taenia solium isolates from Mexico and Colombia.

Mexican and Colombian Taenia solium cysticerci and some species of Taenia adults were assayed using cellulose acetate electrophoresis to distinguish between isolates. Isozyme patterns for ARK, GOT, G3PD, GPI, and MPI were identical in all cysticerci suggesting homozygotic profiles. G6PD and MDH showed different patterns between Mexican and Colombian cysticerci, suggesting regional differences. ME activity was mainly detected in the adult stage suggesting that this enzyme is active in anaerobic environment, while MDH, detected in cysticerci, could be related to an environment that contains oxygen. Finally, the species of taeniid adults analyzed showed different patterns among them.

Animals↗

Muscular myosin isoforms of Taenia solium (Cestoda).

Type II myosin, the primary component of the thick filament of muscle fibers, is organized as a dimeric high molecular weight protein, and is composed of a pair of heavy chains (MHC) and two pairs of light chains. Myosin II transforms ATP energy into mechanical force. All type II myosins are conserved proteins but they have two variable regions that are located in different places of the molecule. Myosin molecules are encoded by a multigene family and many isoforms are generated. The expression of myosins depends on the developmental stage and on the type and degree of contractile activity and tissue, therefore several myosin isoforms are found in the same organism. Here we describe the use of different techniques that allowed demonstrating the presence of isoforms of the heavy chain type II myosin of Taenia solium cysticerci (larvae) and tapeworms (adults), a cestode parasite of importance in public health in many developing countries. Myosin was purified and used in comparative proteolytic fragmentation, ATPase activity, detection of antigenic differences and electrophoretic separation. The results obtained showed biochemical and immunochemical differences among cysticerci and tapeworms, and demonstrate the presence of myosin isoforms in T. solium that are probably associated to physiological requirements of each developmental stage.

Adenosine Triphosphatases↗

Induction of protection against porcine cysticercosis by vaccination with recombinant oncosphere antigens.

Two recombinant Taenia solium oncosphere antigens, designated TSOL18 and TSOL45-1A, were investigated as vaccines to prevent transmission of the zoonotic disease cysticercosis through pigs. Both antigens were effective in inducing very high levels of protection (up to 100%) in three independent vaccine trials in pigs against experimental challenge infection with T. solium eggs, which were undertaken in Mexico and Cameroon. This is the highest level of protection that has been achieved against T. solium infection in pigs by vaccination with a defined antigen. TSOL18 and TSOL45-1A provide the basis for development of a highly effective practical vaccine that could assist in the control and, potentially, the eradication of human neurocysticercosis.

Animals↗

Cloning, characterization, and functional expression of Taenia solium calreticulin.

Calreticulin is an endoplasmic reticulum protein involved in the homeostasis of intracellular Ca++ and other physiological processes. A complementary DNA clone containing the complete coding sequence of Taenia solium calreticulin (TsCRT) was isolated and characterized. Recombinant TsCRT was expressed in bacteria as a 50-kDa protein that specifically bound calcium when tested in a radioassay. The deduced amino acid sequence has 47-50% identity with other reported calreticulins. Poor recognition of TsCRT by human and pig sera with confirmed cysticercosis discourages its use for diagnosis of the disease. However, further characterization and localization studies could provide insights into the role of TsCRT in T. solium physiology and host-parasite interactions.

Amino Acid Sequence↗

Portrait of human tapeworms.

The tapeworms of the genus Taenia that infect human beings are T. solium, T. saginata and T. saginata asiatica. Taenia solium and T. saginata exhibit unequivocal features that characterize them; in contrast, only recent DNA studies, morphological characteristics, and epidemiological and sanitary aspects indicate that T. saginata asiatica is a subspecies of T. saginata. These 3 tapeworms occur in humans in their adult stage, and the intermediate hosts are pigs for T. solium and T. saginata asiatica and cows for T. saginata. Their identification is crucial considering the migratory increase from Asia to the Western Hemisphere and the fact that these tapeworms coexist in the same environment in Asia; furthermore, it is estimated that movement in both directions across the United States-Mexico border exceeds 200 million persons per yr, and thus, opportunities for acquiring and transporting T. solium infections are multiplied. It is not easy to distinguish among these tapeworms; therefore, a comparative diagram of the 3 parasites is shown in this article, which will facilitate their identification. All morphological features, some of which allow for identification, are clear and can be easily distinguished among the 3 tapeworms.

Animals↗

Neurocysticercosis: regional status, epidemiology, impact and control measures in the Americas.

The analysis of epidemiological data concerning human cysticercosis point to important advances in understanding the magnitude and distribution of this parasitic disease in Latin America, as well as the relationship of the elements that conform the life cycle of Taenia solium. The data indicate that the main risk factor for acquiring human neurocysticercosis and swine cysticercosis is the presence of the tapeworm carrier in the household. Therefore, several intervention measures for the control of cysticercosis have been evaluated: mass treatment in order to cure tapeworm carriers, health education towards understanding the risk factors, pig control by restraining them, experimental vaccination of pigs and treatment of swine cysticercosis. In this paper, we review the information obtained in these areas. We hope it will be useful in other endemic countries that wish to elaborate an action plan for the control and ultimate eradication of T. solium.

Abattoirs↗

Actin expression in Taenia solium cysticerci (cestoda): tisular distribution and detection of isoforms.

Identification, localization and partial biochemical characterization of actins expressed in the larval stage of the cestode parasite Taenia solium has been carried out. Frozen tissue sections of cysticerci, the larval stage of this parasite, were reacted with rhodamine-phalloidin, parasite actin was purified by polymerization in the presence of K(+), Mg(++) and ATP actin was analyzed by SDS-PAGE and two-dimensional gel electrophoresis, and immunoblotting of actin was performed in PVDF membranes and with commercial anti-actin monoclonal antibodies. Parasitic tissues showed different fibrous actin fluorescence patterns, which correlated with the expression of isoactins. Purified globular actin had a similar molecular mass to rabbit commercial actin (approximately 44 kDa). Actin was resolved into seven isoforms, indicating a family of actin genes.

Actins↗

The U5/U6 snRNA genomic repeat of Taenia solium.

The U6 and U5 snRNA (small nuclear ribonucleic acid) genes were identified in Taenia solium with the aim of characterizing their sequence and genomic structures. They are contained within a shared 1,009-nt tandem genomic repeat and present at approximately 3 copies per haploid genome. The U6 snRNA gene shares 92 and 95% sequence similarity with the U6 homologs from humans and Schistosoma mansoni, respectively. The U5 snRNA gene of T. solium is 70% similar to the human U5 sequence in the 5' stem and loop 1 domains. The U6 and U5 snRNA genes are on complementary genomic strands and separated by 458 nt at their "heads" and 306 nt at their "tails." The nucleotides upstream of the U6 gene lack a recognizable TATA box and proximal sequence elements (PSEs), and the putative gene promoter for U5 snRNA does not resemble vertebrate examples. There are short blocks of similarity between the sequences upstream of the U5 and U6 snRNA genes, and these may be sites of shared transcription factor binding at the respective RNA polymerase II and III promoters. It is possible that this unusual allied U5/U6 snRNA genomic repeat may help mediate coordinated regulation of expression of the 2 snRNAs.

Animals↗

Detection of genetic variation in Taenia solium.

Genetic variability among Taenia solium isolates was studied in 160 cysticerci from 6 pigs, 4 from Mexico, 1 from Honduras, and 1 from Tanzania. Random amplified polymorphic DNA (RAPD) analysis performed with 4 commercial primers showed 88% polymorphic loci and an average heterozygosity of 0.077; however, several alleles were fixed within each isolate. Linkage disequilibrium analysis indicated that 3 of the 6 isolates had a random association of alleles, whereas the other 3 had a clonal structure. These results suggest the existence of local lineages in T. solium, with events of genetic recombination within them.

Animals↗