The first part of the thesis concerns phylogenetic relationships of eimerian coccidia from arvicoline rodents based on nuclear 18S rRNA, and mitochondrial COI and COIII genes, as well as morphological and morphometrical analyses of the eimerian oocysts. Population-genetic structure of eimerian coccidia was also analyzed and haplotype networks were constructed. The second part of the thesis is based on elucidation of the origin of infections of arvicoline rodents with Isospora spp. using three different approaches - phylogenetic analyses (18S rRNA, COI, and COIII genes), morphological and morphometrical data, and experimental infections. Techniques of field parasitology, laboratory methods of parasitological examination, molecular-genetic diagnostics, phylogeny, and taxonomy were used in the course of both parts of the study.

No description available.

Cryptosporidium is a genus of apicomplexan unicellular epicellular parasite with worldwide distribution causing watery diarrhea in humans and animals. The life cycle is completed in one host, where Cryptosporidium parasitizing epithelial cells of gastrointestinal tract and in birds can cause disease of respiratory or urogenital tract. Course of disease depends on condition of immune system. For immunodeficient individuals could be life threatening. One of problems especially in developing countries is early and correct diagnostic, particularly no effective treatment currently exist. The aim of this thesis was to compare efficiency of immunochromatographic tests in samples stored under different conditions. The comparison of sensitivity and specificity of these tests with molecular and microscopic techniques was also performed. Additionaly, suitability of immunochromatographic tests for detection of active infection during prepatent period was evaluated. The theoretic part includes general information about Cryptosporidium. Its taxonomy, cycle of evolution or transmission and course of disease. Using of immunochromatographic test is also mentioned. No differences in sensitivity of used immunochromatographic tests was observed in this thesis. The detection rate for most of tests was 200 oocyst per sample. The presence of coproantigen is depend upon presence of oocysts in a sample. False negative results of immunochromatographic assays was caused by i) low concentration of oocysts in a sample (sensitivity) or ii) antibodies in used test don´t react with antigen of Cryptosporidium spp. (specificity). Results of this thesis show that combination of immunochromatographic tests and other techniques is convenient. During prepatent period is not possible to detect specific DNA, antigen or oocysts of Cryptosporidium. The active infection could not be distinguish from passage of oocysts using of immunochromatographic assays even if PCR is also used.

Orientador: Katia Denise Saraiva Bresciani / Banca: Luiz Eduardo Corrêa Fonseca / Banca: Alex Akira Nakamura / Banca: Luiz da Silveira Neto / Banca: Jancarlo Ferreira Gomes / Resumo: Este estudo foi elaborado com o objetivo de investigar a ocorrência de Cryptosporidium spp. em quirópteros da região sul do Brasil. Cento e quarenta e sete amostras fecais de morcegos foram colhidas na cidade de Maringá (PR) e submetidas aos processos de purificação para a microscopia e extração de DNA genômico. A microscopia óptica de luz convencional foi utilizada com o uso da coloração negativa de verde malaquita para pesquisa de oocistos de Cryptosporidium spp. e a PCR foi utilizada para a amplificação de fragmentos do gene da subunidade 18S do rRNA na detecção de Cryptosporidium spp. A presença de Cryptosporidium spp. não foi constatada nas amostras fecais dos morcegos. Esse resultado pode ser considerado bom no aspecto que os morcegos são possíveis reservatórios e consequentemente, dispersores deste patógeno, sendo estes parques visitados diariamente por um grande número de pessoas. Esta é a primeira investigação do referido protozoário em morcegos nesta região. / Abstract: This study was elaborated with the objective to investigate the occurrence of Cryptosporidium spp. in chiroptera of southern Brazil. One hundred and forty-seven fecal samples of bats were collected in the city of Maringá (PR) and submitted to purification processes for microscopy and extraction of genomic DNA. Optical microscopy of conventional light with negative malachite green staining was performed to investigate oocysts of Cryptosporidium spp. and PCR for the amplification of fragments of the 18S rRNA subunit gene in the detection of Cryptosporidium spp. This coccidium was not found in faecal samples of bats. This result can be considered good in the aspect that bats are possible reservoirs and consequently dispersers of this pathogen, being these parks visited daily by a large number of people. It is the first investigation of this protozoan into bats in this region / Doutor

Made available in DSpace on 2016-12-08T16:24:15Z (GMT). No. of bitstreams: 1 PGCA13MA115.pdf: 2445554 bytes, checksum: 3ef0e43758000b9d20b09e8f978e7502 (MD5) Previous issue date: 2013-07-10 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The species of the genus Eimeria are responsible for the greatest economic impact among the parasitic diseases that affect broilers. The control of coccidiosis is mainly performed with anticoccidial, however, the development of resistance to these drugs, together with the public opinion against the use of drugs in food, they tend to promote the use of vaccines, increasing the importance of the identification of species of Eimeria circulating. Aiming to identify the species of Eimeria and study the occurrence of these species in poultry farms in the southern state of Santa Catarina, samples were collected (pool of feces) in 21 municipalities, from 251 flocks of broilers aged 28 to 48 days. The oocysts were recovered by techniques of filtration, centrifugation and flotation using supersaturated solution of NaCl and quantified using a Neubauer chamber. The samples were stratified by age of the birds in three intervals (28 to 34, 35 to 41 and 42 to 48). The species were identified by Multiplex PCR technique. Amplicons of the seven species of Eimeria originating from the PCR positive samples have been cloned and sequenced. The occurrence of the genus Eimeria was 96.02%. It was found that in chickens aged 42 to 48 days the average number of oocytes was significantly reduced when compared to the intervals age of 28 to 34, and 35 to 41 days (p<0.05). Were found Eimeria acervulina (63.3%), Eimeria maxima (63,7%), Eimeria tenella (54.6%), Eimeria praecox (25.1%), Eimeria mitis (38.6%), Eimeria necatrix (24.3%) and Eimeria brunetti (13.1%). The average number of species detected by property was 2.96 and was the most frequent combination of E. acervulina, E. maxima and E. tenella (9.16%). The sequencing of the clones confirmed the specificity and effectiveness of the Multiplex PCR technique for identification of species of Eimeria. It can be concluded that in the South of the State, prophylactic measures should consider the control of the seven Eimeria species that parasitize chickens / As espécies do gênero Eimeria são responsáveis pelo maior impacto econômico dentre as doenças parasitárias que acometem frangos de corte. O controle da coccidiose é realizado principalmente com anticoccidianos, porém, o desenvolvimento da resistência a esses fármacos, aliada à opinião pública contra o uso de drogas na ração, tendem a fomentar a utilização de vacinas, aumentando a importância da identificação das espécies de Eimeria circulantes. Com os objetivos de identificar as espécies de Eimeria e estudar a ocorrência destas em instalações avícolas da mesorregião Sul do estado de Santa Catarina, foram coletadas amostras (pool de fezes) em 21 municípios, provenientes de 251 lotes de frangos de corte com idade entre 28 a 48 dias. Os oocistos foram recuperados por meio de técnicas de filtragem, centrifugação e centrífugo-flutuação utilizando solução hipersaturada de NaCl e quantificados utilizando câmara de Neubauer. As amostras foram estratificadas, por idade das aves em três intervalos (28 a 34; 35 a 41 e 42 a 48). As espécies foram identificadas por meio da técnica de Multiplex PCR. Amplicons das sete espécies de Eimeria originados da PCR de amostras positivas foram clonados e sequenciados. A ocorrência do gênero Eimeria foi de 96,02%. Verificou-se que em frangos com idade entre 42 a 48 dias a média do número de oocistos foi significativamente menor quando comparada com os intervalos de idade de 28 a 34 e 35 a 41 dias (P<0,05). Foram encontradas Eimeria acervulina (63,3%), Eimeria maxima (63,7%), Eimeria tenella (54,6%), Eimeria praecox (25,1%), Eimeria mitis (38,6%), Eimeria necatrix (24,3%) e Eimeria brunetti (13,1%). O número médio de espécies detectadas por propriedade foi de 2,96 e a associação mais frequente foi de E. acervulina, E. maxima e E. tenella (9,16%). Por meio do sequenciamento dos clones confirmou-se a especificidade e eficácia da técnica de Multiplex PCR para a identificação das espécies de Eimeria. Concluí-se que na mesorregião Sul do Estado, a adoção de medidas profiláticas deve considerar o controle das sete espécies de Eimeria que parasitam frangos

Cryptosporidium spp. est un protozoaire parasite du système gastro-intestinal largement répandu chez les vertébrés et causant la cryptosporidiose, une zoonose occasionnant des troubles digestifs sévères pouvant entrainer la mort chez les individus immunodéficients. Au Canada, la déclaration de cette maladie est obligatoire depuis l’an 2000. Ainsi, il est pertinent de mieux comprendre l’infection chez les animaux de compagnie, puisqu’ils sont potentiellement un réservoir du parasite. Durant l’année 2008, des échantillons fécaux provenant de 1 202 chats (n = 371) et chiens (n = 831) de la province du Québec ont été analysés par comptage des ookystes de Cryptosporidium spp. au moyen de la technique de centrifugation en solution de sulfate de zinc. Dans cette étude,la prévalence de Cryptosporidium spp. chez les chats (28/371 : 7,55 %) et chez les chiens(88/831 : 10,59 %) de compagnie confirme leur potentiel en tant que réservoir du parasite. Au Québec, de par leur nombre, les chats sont potentiellement un réservoir zoonotique du parasite plus important que celui des chiens, bien qu’il n’existe pas de différence significative entre la prévalence du parasite chez le chat et le chien pour l’année 2008. L’âge (p = 0,0001) et l’infection concomitante par Giardia spp. (p = 0,0001) se sont avérés être des facteurs associés avec la présence de Cryptosporidium spp. chez le chien. Parmi l’ensemble des variables testées chez le chat (l’âge, le sexe, la saison et l’infection concomitante par Giardia spp.), aucune n’a été associée de manière significative à la présence du parasite chez le chat. Ceci peut être dû au nombre limité d’individus testés pour cette espèce. Un suivi de l’excrétion des ookystes de Cryptosporidium spp. chez deux chats suggère que l’excrétion des ookystes peut se faire sur une période de sept mois et que le taux d’excrétion varie dans le temps. Le diagnostic moléculaire des espèces et génotypes de Cryptosporidium spp. isolés à partir des échantillons de matières fécales devait être réalisé par la technique de PCR emboîtée des fragments des gènes ARNr 18S et HSP70 et du séquençage des produits de PCR. Aucun résultat positif n’a toutefois été obtenu. Afin d’augmenter la puissance statistique des analyses épidémiologiques sur la prévalence de Cryptosporidium spp., il serait nécessaire à l’avenir de travailler sur un nombre d’animaux beaucoup plus important. / Cryptosporidium spp. is a protozoan parasite from the gastro-intestinal tract with a large range of vertebrate hosts causing cryptosporidiosis, a zoonotic disease which may lead to severe digestive troubles and sometimes death for immunocompromised people. It is a noticeable disease in Canada since 2000. It is thus relevant to study the infection in cats and dogs as they may represent an important zoonotic reservoir for the parasite. A total of 1,202 stool samples from cats (n = 371) and dogs (n = 831) from the province of Quebec were examined during the year 2008 for this research. The prevalence of Cryptosporidium spp. was calculated using coprology tests using centrifugation in a zinc sulfate solution. The prevalence in cats (28/371: 7,55 %) and dogs (88/831: 10,59%) corroborates that pets living in the province of Quebec may be a reservoir for Cryptosporidium spp. While we did not find a significant difference in the prevalence of Cryptosporidium spp. between cats and dogs, cats may represent a larger reservoir as they represent a larger population within the province. We identified age (p = 0,0001) and concomitant infection with Giardia spp. (p =0,0001) as risk factors for dogs. Among all the variables tested on cats (age, sex, season, concomitant infection with Giardia spp.), none were significantly associated with the presence of the parasite in cats. This may be caused in part by the small number that was analyzed. A follow-up study with two cats showed the excretion of oocysts can last for a minimum of seven months and varies in intensity through time. The molecular diagnostic of species and genotypes of Cryptosporidium spp. isolated from fecal samples should have been done by using the amplification of the gene fragments ARNr 18S and HSP70 nested PCR reactions and the sequencing of PCR products. Although this technique was attempted in this study, no positive result was obtained. It is recommended to work on larger animal populations to increase the statistical power of epidemiological analysis of the prevalence of Cryptosporidium spp.

Novel integrated ozone contactor design and optimization tools which consist of an instrument that measures ozone decay kinetics, a program that performs predictive simulation, and an experimental method to examine mixing characteristics within the ozone contactor, were developed in this study. A multi-channel stopped-flow reactor (MC-SFR) is an instrument that performs automatic, real-time, and continuous analysis of ozone decay kinetics in natural waters. Ozone Contactor Model (OCM) is the software to simulate the performance of full-scale ozone bubble-diffuser contactors in support of current and future regulations regarding pathogen and bromate control in drinking water. The MC-SFR and OCM developed in this study were further applied to simulate Cryptosporidium parvum oocyst log inactivation and bromate formation in Linnwood Water Plant Ozone Facility (LWPOF) at Milwaukee Water Works, Milwaukee, WI and model predictions were verified with experimental results. Three dimensional laser induced fluorescence(3DLIF) allowed real time characterization of mixing conditions in a physical model ozone contactors by capturing fluorescence image emitted from a laser dye (i.e. Rhodamine 6G) using a high speed CCD camera. 3DLIF system was applied to analyze the hydrodynamics of two representative types of ozone contactor: direct discharge side-stream venturi injector (SVI) and multi-chambered fine bubble diffuser (FBD). Experimental results verified the presence of circulative swirling related for low dispersion for SVI reactor and the existence of non-ideal flow including short circuiting and internal recirculation in FBD reactor. Finally, integrated tools were applied to the design of a new ozone contactor under planning stage to assess current design and to recommend the improvement.

Cryptosporidium spp. est un protozoaire parasite du système gastro-intestinal largement répandu chez les vertébrés et causant la cryptosporidiose, une zoonose occasionnant des troubles digestifs sévères pouvant entrainer la mort chez les individus immunodéficients. Au Canada, la déclaration de cette maladie est obligatoire depuis l’an 2000. Ainsi, il est pertinent de mieux comprendre l’infection chez les animaux de compagnie, puisqu’ils sont potentiellement un réservoir du parasite. Durant l’année 2008, des échantillons fécaux provenant de 1 202 chats (n = 371) et chiens (n = 831) de la province du Québec ont été analysés par comptage des ookystes de Cryptosporidium spp. au moyen de la technique de centrifugation en solution de sulfate de zinc. Dans cette étude,la prévalence de Cryptosporidium spp. chez les chats (28/371 : 7,55 %) et chez les chiens(88/831 : 10,59 %) de compagnie confirme leur potentiel en tant que réservoir du parasite. Au Québec, de par leur nombre, les chats sont potentiellement un réservoir zoonotique du parasite plus important que celui des chiens, bien qu’il n’existe pas de différence significative entre la prévalence du parasite chez le chat et le chien pour l’année 2008. L’âge (p = 0,0001) et l’infection concomitante par Giardia spp. (p = 0,0001) se sont avérés être des facteurs associés avec la présence de Cryptosporidium spp. chez le chien. Parmi l’ensemble des variables testées chez le chat (l’âge, le sexe, la saison et l’infection concomitante par Giardia spp.), aucune n’a été associée de manière significative à la présence du parasite chez le chat. Ceci peut être dû au nombre limité d’individus testés pour cette espèce. Un suivi de l’excrétion des ookystes de Cryptosporidium spp. chez deux chats suggère que l’excrétion des ookystes peut se faire sur une période de sept mois et que le taux d’excrétion varie dans le temps. Le diagnostic moléculaire des espèces et génotypes de Cryptosporidium spp. isolés à partir des échantillons de matières fécales devait être réalisé par la technique de PCR emboîtée des fragments des gènes ARNr 18S et HSP70 et du séquençage des produits de PCR. Aucun résultat positif n’a toutefois été obtenu. Afin d’augmenter la puissance statistique des analyses épidémiologiques sur la prévalence de Cryptosporidium spp., il serait nécessaire à l’avenir de travailler sur un nombre d’animaux beaucoup plus important. / Cryptosporidium spp. is a protozoan parasite from the gastro-intestinal tract with a large range of vertebrate hosts causing cryptosporidiosis, a zoonotic disease which may lead to severe digestive troubles and sometimes death for immunocompromised people. It is a noticeable disease in Canada since 2000. It is thus relevant to study the infection in cats and dogs as they may represent an important zoonotic reservoir for the parasite. A total of 1,202 stool samples from cats (n = 371) and dogs (n = 831) from the province of Quebec were examined during the year 2008 for this research. The prevalence of Cryptosporidium spp. was calculated using coprology tests using centrifugation in a zinc sulfate solution. The prevalence in cats (28/371: 7,55 %) and dogs (88/831: 10,59%) corroborates that pets living in the province of Quebec may be a reservoir for Cryptosporidium spp. While we did not find a significant difference in the prevalence of Cryptosporidium spp. between cats and dogs, cats may represent a larger reservoir as they represent a larger population within the province. We identified age (p = 0,0001) and concomitant infection with Giardia spp. (p =0,0001) as risk factors for dogs. Among all the variables tested on cats (age, sex, season, concomitant infection with Giardia spp.), none were significantly associated with the presence of the parasite in cats. This may be caused in part by the small number that was analyzed. A follow-up study with two cats showed the excretion of oocysts can last for a minimum of seven months and varies in intensity through time. The molecular diagnostic of species and genotypes of Cryptosporidium spp. isolated from fecal samples should have been done by using the amplification of the gene fragments ARNr 18S and HSP70 nested PCR reactions and the sequencing of PCR products. Although this technique was attempted in this study, no positive result was obtained. It is recommended to work on larger animal populations to increase the statistical power of epidemiological analysis of the prevalence of Cryptosporidium spp.

Submitted by Cláudia Bueno (claudiamoura18@gmail.com) on 2016-01-14T16:38:41Z No. of bitstreams: 2 Dissertação - Rebeka Cristine de Bastos Costa - 2015.pdf: 2127820 bytes, checksum: 8789b51096d386c4def09d0d1ee4da0d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-01-15T09:55:51Z (GMT) No. of bitstreams: 2 Dissertação - Rebeka Cristine de Bastos Costa - 2015.pdf: 2127820 bytes, checksum: 8789b51096d386c4def09d0d1ee4da0d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-01-15T09:55:51Z (GMT). No. of bitstreams: 2 Dissertação - Rebeka Cristine de Bastos Costa - 2015.pdf: 2127820 bytes, checksum: 8789b51096d386c4def09d0d1ee4da0d (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-08-25 / Toxoplasmosis is a zoonotic disease in which mammals and birds can join the cycle as intermediate hosts, and felids as definitive hosts. Felis catus is recognized as the main responsible for the environmental contamination by Toxoplasma gondii oocysts. Serological diagnosis reveals little about the elimination of oocysts of T. gondii into the environment, principally by F. catus, which plays an important role in Public Health. There are few data on the frequency of feline toxoplasmosis in the State of Goiás. Therefore, the aim of this research was to evaluate the frequency of toxoplasmosis infection in domestic cats and their potential role in its transmission through the oocyst elimination into the environment and the respective factors associated with the infection. For this, we collected 102 blood samples and 98 fecal samples from 102 cats from Goiânia, State of Goiás. The animals were divided into groups according to age, gender and free access to the street or not. Indirect hemagglutination test was performed to determine the level of anti-T. gondii and indirect ELISA for the detection of infection by feline immunodeficiency virus (FIV). For search and detection of T. gondii oocysts elimination in the feces of cats we performed a centrifugal-flotation with Sheather's solution, subsequently we extracted DNA and used conventional PCR. The results showed that 18.63% (19/102) of the cats were positive for T. gondii, with titers ranging from 1:32 to 1: 8.192, while none of the fecal samples were positive in the PCR. The frequency of positive animals for FIV was 55.91% (52/93), and 18.28% (17/93) presented coinfection. By multivariate logistic regression we found the associated factors were the same for both infections, but one did not interfere with another. The factors associated with infection by T. gondii and feline immunodeficiency virus were free life and age under six months, since the sex was not statistically related to any of the illnesses. / A toxoplasmose é uma zoonose na qual, mamíferos e aves podem participar do seu ciclo como hospedeiros intermediários e os felídeos como hospedeiros definitivos. O Felis catus é reconhecido como o principal responsável pela contaminação ambiental por oocistos de Toxoplasma gondii. O diagnóstico sorológico pouco revela sobre a eliminação de tal fase no ambiente, o que representa o real impacto daquela espécie na Saúde Pública frente à toxoplasmose. São escassos os dados da frequência da toxoplasmose felina no Estado de Goiás. Assim sendo, objetivou-se com esta pesquisa avaliar a frequência da infecção da toxoplasmose em gatos domésticos e o seu potencial papel na sua transmissão, através da eliminação de oocistos no ambiente e dos respectivos fatores associados à infecção. Para isto, foram coletadas 102 amostras de sangue e 98 amostras fecais, de 102 gatos provenientes de Goiânia-Goiás. Os animais foram divididos em grupos de acordo com a faixa etária, gênero e livre acesso à rua ou não. Foi realizada a hemaglutinção indireta para a determinação do nível de anticorpos anti-T. gondii e o ELISA indireto para a detecção da infecção pelo vírus da imunodeficiência felina (FIV). Para a pesquisa e detecção da eliminação de oocistos de T. gondii nas fezes dos gatos foi feita a centrifugo-flutuação em solução de Sheather, posterior extração de DNA e realização da PCR convencional. Os resultados revelaram que 18,63% (19/102) dos gatos foram positivos para o T. gondii, com títulos variando entre 1:32 a 1:8.192, sendo que nenhuma das amostras fecais foi positiva na PCR. A frequência de positivos para o FIV foi de 55,91% (52/93), com coinfecção de 18,28% (17/93). Com a regressão logística multivariada verificou-se que os fatores associados foram os mesmos para as duas infecções, porém uma não interferiu diretamente na outra. Os fatores associados para a infecção pelo T. gondii e pelo vírus da imunodeficiência felina foram a vida livre e a idade igual ou superior a seis meses, já o gênero não apresentou relação estatística com nenhuma das enfermidades.

Parasiten durchlaufen in ihrem Lebenszyklus morphologisch verschiedene Stadien. Die Kontrolle des Übergangs zwischen den Stadien kann die Transmission in einen neuen Wirt begünstigen. Bei vielen Parasiten ist unbekannt, welche Faktoren die Progression des Lebenszyklus beeinflussen. Der Ablauf kann genetisch prädeterminiert sein (kanalisiert) oder von äußeren Einflüssen abhängen (phänotypische Plastizität). Hier wurde die Progression des Lebenszyklus zweier Darmparasiten in Mäusen untersucht. Die Oozysten von Eimeria falciformis wurden quantifiziert und die Transkriptome von Parasit und Wirt wurden in Mäusen unterschiedlicher Immunkompetenz analysiert. Wenngleich erwartet wurde, dass die Immunantwort einen Stressor für das Pathogen darstellt, hatte die Immunkompetenz des Wirts keine Auswirkungen auf den Zeitpunkt der Oozystenausscheidung und das Transkriptomprofil des Parasiten. E. falciformis konnte nicht von der Immunschwäche des Wirtes profitieren; ist also hinsichtlich der Immunantwort des Wirts genetisch kanalisiert. In G. duodenalis wurde untersucht, inwiefern die Progression des Lebenszyklus, d.h die Trophozoitenreplikation bzw. die Zystenausscheidung, von Arginin abhängt. Die Replikation der Trophozoiten war nicht von Arginin aus der Nahrung abhängig; die Ausscheidung infektiöser Zysten war unter argininarmen Bedingungen jedoch verringert. Dies lässt vermuten, dass der Ablauf des Lebenszyklus von G. duodenalis, insbesondere die Enzystierung, an die Argininzufuhr gekoppelt ist. Die Umstellung des Metabolismus von G. duodenalis hin zur Produktion eines wichtigen Zystenwandbestandteils wird hier als mechanistische Verbindung zwischen ATP-Erzeugung aus Arginin in Nichtsäugetieren (Arginindihydrolase-Stoffwechselweg), verringerter Glykolyse und der Zystenwandsynthese erörtert. Somit könnte Arginin als Stimulus für phänotypische Plastizität bei der Enzystierung von G. duodenalis dienen. / Eukaryotic parasites have life cycles with morphologically distinct stages. Accurate timing of the conversion from one stage into another can be beneficial for transmission into a new host. Often little is known about determinants for such life cycle progression or the genes involved. Timing can be genetically pre-determined (canalized) or depend on exposure to a stimulus (phenotypic plasticity). Here, life cycle progression of two unicellular intestinal parasites was investigated in mice. For Eimeria falciformis, oocyst stage parasites were quantified, and parasite and host transcriptomes analyzed in differently immune competent hosts. Host immune response stimuli are expected to induce stress on the pathogen, but different host immune competences did not change the timing of oocyst shedding or influence parasite transcriptome profiles. E. falciformis was unable to benefit from hosts with weakened immune responses. It is therefore an example of a genetically canalized parasite with regards to host immune stimulus. In Giardia duodenalis, dependence on arginine for life cycle progression was investigated. The in vivo relevance for parasite replication is unknown. Trophozoite stage replication and cyst shedding were assessed in hosts fed normal and arginine-free diets. G. duodenalis did not depend on dietary arginine for trophozoite replication, but infective cysts were reduced in number under arginine-poor conditions. Dependence on arginine for life stage switching suggests that G. duodenalis could time progression by encysting upon arginine exposure. G. duodenalis metabolic reprograming to generate a major cyst wall component is discussed as a strategy to mechanistically link 1) non-mammalian ATP generation (arginine dihydrolase pathway) from arginine with 2) decreased glycolytic flux and 3) cyst wall generation. Therefore, arginine may be an external stimulus for phenotypic plasticity of encystation in G. duodenalis.