Most eukaryotic parasites are obligately heteroxenous, requiring sequential infection of different host species in order to survive. Toxoplasma gondii is a rare exception to this rule, having a uniquely facultative heteroxenous life cycle. To understand the origins of this phenomenon, we compared development and stress responses in T. gondii to those of its its obligately heteroxenous relative, Hammondia hammondi and have identified multiple H. hammondi growth states that are distinct from those in T. gondii. Of these, the most dramatic difference was that H. hammondi was refractory to stressors that robustly induce cyst formation in T. gondii, and this was reflected most dramatically in its unchanging transcriptome after stress exposure. We also found that H. hammondi could be propagated in vitro for up to 8 days post-excystation, and we exploited this to generate the first ever transgenic H. hammondi line. Overall our data show that H. hammondi zoites grow as stringently regulated, unique life stages that are distinct from T. gondii tachyzoites, and implicate stress sensitivity as a potential developmental innovation that increased the flexibility of the T. gondii life cycle.

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Neospora caninum is protozoan parasite with domestic and wild dogs, coyotes and grey wolves as the definitive hosts and many warm-blooded animals as intermediate hosts. It was cultivated and named in 1988. Neosporosis is a major disease of cattle and has no public health significance. Since 1990's N. caninum has emerged as a major cause of abortion in cattle worldwide, including in Brazil. N. caninum also causes clinical infections in several other animal species. Considerable progress has been made in understanding the biology of N. caninum and there are more than 200 papers on this subject from Brazil. However, most of the reports on neosporosis from Brazil are serological surveys. Overall, little is known of clinical neosporosis in Brazil, particularly cattle. The few reports pertain to sporadic cases of abortion with no information on epidemics or storms of abortion. The objective of the present review is to summarize all reports from Brazil and suggest topic for further research, including prevalence of N. caninum oocysts in soil or in canine feces, and determining if there are additional definitive hosts, other than the domestic dog. There is need for a national survey in cattle using defined parameters. Future researches should focus on molecular characterization of N. caninum strains, possibility of vaccine production and relationship between wildlife and livestock epidemiology.Keywords: Neospora caninum, neosporosis, domestic animals, wild animals, Brazil. ResumoNeospora caninum é um protozoário parasita que possui os canídeos domésticos e selvagens, coiotes e lobos cinzentos como hospedeiros definitivos e vários animais de sangue quente como hospedeiros intermediários. Foi cultivado e nomeado em 1988. A neosporose é uma das principais doenças em bovinos e não tem significância em saúde pública. Desde 1990, N. caninum tem emergido como uma das principais causas de aborto em bovinos em todo o mundo, inclusive no Brasil. N. caninum também causa infecções clínicas em várias outras espécies animais. Consideráveis avanços foram feitos na compreensão da biologia desse parasita e há mais de 200 trabalhos sobre o assunto no Brasil. No entanto, a maioria dos relatos de neosporose do Brasil são relacionados a sorologia. Em geral, pouco se sabe sobre a neosporose clínica no Brasil, particularmente em bovinos. Os poucos relatos referem-se a casos esporádicos de aborto sem informações sobre epidemias ou surtos de aborto. O objetivo da presente revisão é resumir todos os relatos sobre N. caninum no Brasil e sugerir tópicos para pesquisas futuras, incluindo a prevalência de oocistos de N. caninum no solo ou em fezes caninas e determinar se há hospedeiros definitivos adicionais, exceto o cão doméstico no país. Uma pesquisa nacional em bovinos usando parâmetros definidos seria de grande importância. Pesquisas futuras deveriam ser focadas na caracterização de cepas de N. caninum, possibilidade de produção de vacinas e a relação epidemiológica entre a vida selvagem e o gado.Palavras-chave: Neospora caninum, neospo...

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Recent decline of sea ice habitat has coincided with increased use of land by polar bears (Ursus maritimus) from the southern Beaufort Sea (SB), which may alter the risks of exposure to pathogens and contaminants. We assayed blood samples from SB polar bears to assess prior exposure to the pathogens Brucella spp., Toxoplasma gondii, Coxiella burnetii, Francisella tularensis, and Neospora caninum, estimate concentrations of persistent organic pollutants (POPs), and evaluate risk factors associated with exposure to pathogens and POPs. We found that seroprevalence of Brucella spp. and T. gondii antibodies likely increased through time, and provide the first evidence of exposure of polar bears to C. burnetii, N. caninum, and F. tularensis. Additionally, the odds of exposure to T. gondii were greater for bears that used land than for bears that remained on the sea ice during summer and fall, while mean concentrations of the POP chlordane (ΣCHL) were lower for land-based bears. Changes in polar bear behavior brought about by climate-induced modifications to the Arctic marine ecosystem may increase exposure risk to certain pathogens and alter contaminant exposure pathways.

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