Waterborne zoonoses *
Jamie Bartram, Rachel Baum, Peter A. Coclanis, David M. Gute, David Kay, Stéphanie McFadyen, Katherine Pond, William Robertson, Michael J. Rouse in Routledge Handbook of Water and Health, 2015
Oocysts of the organism are widely distributed in both the terrestrial and aquatic environments. It has a low infectious dose (as few as 10 oocycts) and is highly resistant to chlorine and other bactericidal agents used for disinfection and water treatment. The resistance of the oocycts to these agents explains how outbreaks of gastrointestinal illness associated with treated drinking water and swimming pools and waterparks occur. In the developed world, large outbreaks of waterborne cryptosporidiosis have been associated with failures of water treatment systems or high loads of oocysts that result from flooding or overt fecal contamination of water sources that overwhelm water treatment systems. Fortunately, cryptosporidia are sensitive to UV light disinfection procedures.
A Case of Toxoplasmosis in Pregnancy
Meera Chand, John Holton in Case Studies in Infection Control, 2018
T. gondii is an obligate intracellular parasite belonging to the subclass Coccidia and phylum Apicomplexa, as are Plasmodium species, the causative agents of malaria. There are three infective stages of the parasite: the sporulated oocyst, the tissue cyst, and the tachyzoite. Sporulated oocysts are ovoid structures measuring about 12 μm in length. Each mature oocyst contains two sporocysts, which each contain four sporozoites. Oocysts have a multilayered wall that allows them to survive in the external environment. Tissue cysts may be found in any organ but are most common in brain and muscle tissue. They measure between 10 and 100 μm in diameter and are circular. Each tissue cyst can contain up to hundreds of bradyzoites and are surrounded by an outer membrane. Bradyzoites are elliptical, replicate slowly, and have a low metabolism, which allows for long-term survival and lifelong persistence of infection. Tachyzoites have a crescent shape and are about 5 μm in length (Figure 22.1). They are the rapidly dividing, highly metabolically active dissemination forms and are more vulnerable to physical or chemical changes in their environment than the other stages. Antimicrobial agents are only effective against these forms.
The Protozoa
Donald L. Price in Procedure Manual for the Diagnosis of Intestinal Parasites, 2017
The three genera of coccidia that infect man, Isospora, Sarcocystis, and Cryptosporidium, are quite different in their life cycle and in their structure (refer to Plate 6). All three species form oocysts. In the definitive host, the zygote produced by the union of the male and female gametes rounds up and secretes a resistant cyst wall consisting of outer and inner portions, the oocyst. Within the cyst, the zygote may develop into a sporoblast and then directly into four sporozoites (Cryptosporidium), or it may divide to form two sporoblasts (Isospora and Sarcocystis) or four sporoblasts (Eimeria). A wall is formed around each sporoblast to produce a sporocyst. Within each sporocyst, the sporozoites are formed. In both Isospora and Sarcocystis of man, there are two sporocysts each with four sporozoites.
Immunogenicity and protection efficacy of enhanced fitness recombinant Salmonella Typhi monovalent and bivalent vaccine strains against acute toxoplasmosis
Published in Pathogens and Global Health, 2021
Fei-Kean Loh, Sheila Nathan, Sek-Chuen Chow, Chee-Mun Fang
It is estimated that one-third of the global human population has been exposed to Toxoplasma gondii [1], an opportunistic intracellular protozoan which stays active as tachyzoites but converts to bradyzoites in response to stress [2]. The parasite replicates sexually within the guts of feline families and the oocysts are excreted to the environment. The oocysts are then ingested and usually transmitted through food sources between the definitive hosts and intermediate hosts which include almost all mammals [2]. Most T. gondii infections are asymptomatic as the parasite is suppressed by effective host immune control. However, the tissue cysts can recrudesce in immunocompromised hosts and cause diverse complications. For instance, AIDS/HIV patients have an increased frequency of toxoplasma encephalitis [3]. In pregnant women, T. gondii may transmit across the placenta and cause miscarriage of the fetus. Infants with congenital infection have been diagnosed with manifestations including chorioretinitis, calcification and hydrocephalus [4]. Meta-analyses have also deduced positive correlation between T. gondii seropositivity and psychotic symptoms such as schizophrenia and bipolar disorder [5,6]. To date, there is only one live attenuated vaccine developed from the T. gondii S48 strain, Toxovax, mainly used to prevent sheep and goat abortions in United Kingdom, New Zealand, France and Ireland. All the drugs used in clinical practice are solely active against tachyzoites and are not able to clear cysts formed during chronic infection [7].
A review on inactivation methods of Toxoplasma gondii in foods
Published in Pathogens and Global Health, 2018
Adel Mirza Alizadeh, Sahar Jazaeri, Bahar Shemshadi, Fataneh Hashempour-Baltork, Zahra Sarlak, Zahra Pilevar, Hedayat Hosseini
It has been found that the oocyst wall is bilayered, with the outer layer being thinner than the inner layer [57]. Experimental results have shown that layers are not tightly bound together and the outer layer can be stripped off easily using chemical agents [58]. Furthermore, the oocyst wall is composed of more than 90% cysteine- and tyrosine-rich protein [59] and thermal methods such as high heating, cooking or physical methods can denature the proteins and cause inactivation or killing of T. gondii. The use of drugs or freezing can inactivate or prevent T. gondii infection by preventing the parasite from attaching and entering cells [60] or by disrupting metabolism and the formation of ice crystals [61,62], respectively. Under experimental and industrial conditions, physical methods (thermal and non-thermal) or other applied technologies (chemical and biochemical methods) can be used to control, remove or inactivate T. gondii. The prevention of cross-contamination in raw and processed food products is significant in this regard (Figure 2).
4-Arylthiosemicarbazide derivatives as a new class of tyrosinase inhibitors and anti-Toxoplasma gondii agents
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2021
Adrian Bekier, Lidia Węglińska, Agata Paneth, Piotr Paneth, Katarzyna Dzitko
T. gondii exists in three infectious stages, such as oocysts (with sporozoites), tissue cysts (with bradyzoites), and rapidly proliferated tachyzoites, which form the parasitophorous vacuole (PV), a structure created by apicomplexan parasites in the host cells. Oocysts are only produced in the definitive hosts – members of the Felidae family (domestic cats and their relatives). Unsporulated oocysts are excreted in feline faeces of infected individuals. Each sporulated oocyst contains two sporocysts which hold four sporozoites. Even if a single sporulated oocyst is ingested or inhaled by the intermediate host, including all classes of warm-blooded vertebrates, sporozoites transform to tachyzoites, which localised in neural and muscle tissues including brain, eye, skeletal muscle, kidney, spleen, blood, liver, and heart tissue, and convert to bradyzoites enclosed in cysts that persist chronically10. In the case of infected pregnant women, tachyzoites can penetrate into the foetus via the bloodstream or placenta during the acute phase or reactivation of the infection. Ingestion of the tissue cysts in contaminated meat is also a source of infection, as bradyzoites transform back into tachyzoites upon entering a new host11.
Related Knowledge Centers
- Biochemistry
- Morphology
- Multinucleate
- Cell Nucleus
- Cytokinesis
- Organelle
- Intracellular Parasite
- Biological Life Cycle
- Fission
- Theileria