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Sarcocystis
Published in Dongyou Liu, Handbook of Foodborne Diseases, 2018
B.B. Singh, R. Sharma, E. Jenkins
Members of the Sarcocystis genus are protozoan parasites belonging to the family Sarcocystidae, subphylum Apicomplexa, order Eucoccidia. Sarcocystis spp. tend to be specific for their hosts at the species, genus, or family level.2 Although multiple Sarcocystis species can infect intermediate hosts, the definitive hosts are usually infected by a few parasite species.2 Currently, the genus Sarcocystis has more than 200 named species that can infect mammals, birds, reptiles, and fish.8 Two Sarcocystis species viz. Sarcocystis hominis and S. suihominis are zoonotic and involve man as a definitive host. Other important Sarcocystis species circulating in intermediate hosts (food producing animals) and their definitive animal hosts are listed in Table 58.1.4,9–26
Cryptosporidium
Published in Dongyou Liu, Laboratory Models for Foodborne Infections, 2017
Due the fact that members of the genus Sarcocystis in the family Sarcocystidae produce oocysts with thin walls that often rupture to release sporocysts, each of which possesses four sporozoites similar to Cryptosporidium oocysts, a number of Cryptosporidium species were erroneously assigned to the genus Sarcocystis in the early days. However, subsequent ultrastructural examinations revealed the presence of a unique attachment organelle as a defining feature for the genus Cryptosporidium (indeed, the name Cryptosporidium refers to the absence of sporocysts within the oocyst) and the family Cryptosporidiidae. In addition, biological and molecular studies indicated that Cryptosporidium species are more closely related to gregarine parasites of the subclass Gregarinasina, class Conoidasida rather than to Coccidians (e.g., Isospora, Cyclospora, and Sarcocystis), since Cryptosporidium species undergo gregarine-like gamont stages and have the ability to complete their life cycles in the absence of host cells [1,2,5,6].
Cryptosporidium spp
Published in Peter D. Walzer, Robert M. Genta, Parasitic Infections in the Compromised Host, 2020
Excystation, the release of infective sporozoites from environmentally resistant oocysts, is a key event in the life cycle of every true coccidian. This infectioninitiating event usually occurs in the lumen of the gastrointestinal tract following ingestion of oocysts by a suitable host. In most coccidian species examined to date, excystation may also be triggered in vitro by exposing oocysts to conditions that simulate the gastrointestinal environment of the host (i.e., reducing conditions, CO2, host body temperature, bile salts, and trypsin). Much of our understanding of this process is based on in vitro excystation studies of coccidian species belonging to the families Eimeriidae (34,35) and Sarcocystidae (36-38) whose oocysts possess sporocysts, each containing infective sporozoites (Fig. 1B). Such investigations have suggested that there may be two major steps in excystation. The first step is alteration of oocyst wall permeability, allowing influx of proteolytic enzymes and bile salts. This can be triggered by exposure to host body temperature and CO2 and is often accomplished by a peeling away or dissolving of the micropyle, a thinning of the oocyst wall at one pole. This step can also be accomplished by removing the oocyst wall with a tissue grinder, releasing sporocysts. The second step is the release of sporozoites from sporocysts by the action of pancreatic enzymes and/or bile salts. Sporozoites of eimeriid coccidia (e.g., Eimeria spp. and some Isospora spp.) escape through an opening in one pole of the sporocysts that is formed by degradation of a plug, the Stieda body (Fig. 1B). It is believed that trypsin degrades the Stieda body and that bile salts stimulate sporozoite motility. Species of coccidia assigned to the family Sarcocystidae have sporocysts whose walls are composed of four plates joined by sutures. Trypsin and/or bile salts cause dissolution of the sutures, allowing sporozoites to escape between the collapsed plates.
Evaluation of a commercial enzyme-linked immunosorbent assay (ELISA) for detecting antibodies against Toxoplasma gondii from naturally and experimentally infected pigs
Published in Infectious Diseases, 2019
Giusi Macaluso, Santina Di Bella, Giuseppa Purpari, Elisabetta Giudice, Francesco Mira, Francesca Gucciardi, Anna Maria Fausta Marino, Carmelo Russo, Maria Angeles Gómez-Morales, Annalisa Guercio
Toxoplasma gondii is a protozoan parasite of the family of Sarcocystidae. Felids, the only definitive host, play an important role in the epidemiology of toxoplasmosis, because the parasite undergoes an asexual reproductive cycle in all species whereas in felidae, it simultaneously undergoes a sexual cycle or replication. Felids indeed shed oocysts in their feces, these sporulate in the environment and represent the main source of infection for grazing animals.