Apicomplexans
Apicomplexans are a group of single-celled parasites known for causing diseases in animals, including humans. They possess a unique organelle called the apicoplast, which is essential for their survival and has become a target for drug development. Apicomplexans include the causative agents of diseases such as malaria (Plasmodium spp.) and toxoplasmosis (Toxoplasma gondii).
5 Key excerpts on "Apicomplexans"
eBook - ePubThorp and Covich's Freshwater Invertebrates
Ecology and General Biology
- James H. Thorp, D. Christopher Rogers, James H. Thorp, D. Christopher Rogers(Authors)
- 2014(Publication Date)
- Academic Press(Publisher)
...The organisms now referred to as Apicomplexans used to be an important component of the “sporozoans.” All are intracellular parasites of animals, and some cause life-threatening diseases of humans. They share the distinctive morphological feature of an “apical complex” at certain stages in the polymorphic life cycle. The degree of host specificity of many Apicomplexans is not known. They include the “gregarines” that infect insects, marine polychaetes, and other invertebrates (e.g., Monocystis in earthworms), and also the “coccidian” parasites including Toxoplasma gondii (the domestic cat is the final host, but intermediate infection in the human can cross the placenta) and about 1050 species of Eimeria infecting mammals, chickens, and other farmed birds. Cryptosporidium infects the digestive and respiratory systems of vertebrates and is an important parasite of humans and domestic livestock. There are 16 well-characterized species of Cryptosporidium, eight of which have been reported from humans, although only two are common, namely Cryptosporidium hominis and Cryptosporidium parvum. The main route of transmission in humans is thought to be the ingestion of oocysts in contaminated water, completing the fecal–oral cycle. Infection can cause life-threatening diarrhea in immunocompromised humans. Cryptosporidium may be sufficiently different from other coccidians to warrant creation of the new higher taxon “cryptosporidia.” Plasmodium, the causative agent of malaria, is the most important protozoan parasite of humans in terms of its morbidity and mortality rates. There are approximately 4000 nominal species of Apicomplexans. Pneumocystis is an enigmatic parasite that can persist in the human lung for long periods. Pneumocystis carinii (currently renamed as Pneumocystis jiroveci) causes Pneumocystis pneumonia in human immunodeficiency virus patients...
- Charles M. Hendrix, Ed Robinson(Authors)
- 2016(Publication Date)
- Mosby(Publisher)
...The Apicomplexans are parasites of almost every animal phylum. In domesticated animals, they are found primarily in the epithelium of the intestine, within blood cells, and within cells of the reticuloendothelial system. The life cycles of these protozoans vary among the genera that affect domesticated animals; however, they do have a common trait in that their life cycles are complex and intimately integrated into the physiology of the host's body. The locomotory organelles of the flagellates, amoebae, and ciliates (i.e., flagella, pseudopodia, and cilia, respectively) are discernible. In contrast, the locomotory organelles of the Apicomplexans are not visible to the naked eye; their locomotory organelles are internal. The Apicomplexans are often banana-, comma-, or boomerang-shaped (Figure 10-6) and move via undulations. Some of the most important genera of parasitic Apicomplexans of domestic animals are Eimeria, Cystoisospora, Toxoplasma, Sarcocystis, Cryptosporidium, Plasmodium, Haemoproteus, Leukocytozoon, Babesia, Theileria, Cytauxzoon, and Hepatozoon. These protozoans are perhaps the most diverse, complicated members of the Protista kingdom. Technician's Note The apicomplexan parasites do not have visible locomotory organelles but move via undulations...
eBook - ePubImmunology
Mucosal and Body Surface Defences
- Andrew E. Williams(Author)
- 2011(Publication Date)
- Wiley(Publisher)
...For purposes of clarity, we shall look at the ultrastructure of the flagellates, which include the trypanosomes, and those species that cause leishmaniasis and giardiasis. Although most protozoa reside in cells within the bloodstream and therefore do not directly infect mucosal sites, they represent an important group of parasites responsible for causing devastating diseases worldwide. Most of these parasites are also transmitted via the bite of an insect vector and often induce an immune reaction within the skin. Therefore, due to their significant effect on human health they will be discussed in this chapter. Leishmania species, which directly infect the skin, and giardia, which infects the intestines, shall also be discussed in this chapter. Furthermore, the apicomplexan malaria parasites are also responsible for millions of deaths in tropical and sub-tropic regions and, due to their impact on human health, will also be discussed. Trypanosomes are flagellate parasites that are responsible for many human and veterinary diseases such as sleeping sickness and Chagas's disease (human) and nagana and surra (animals). Trypanosomes are typically small and elongate being 15–30 μm in length and 2–3 μm in width (Figure 14.1). They are characterized by a cytoplasmic structure known as the kinetoplast, which contains its own nucleus and kinetoplast DNA. Trypanosomes are characterized by the flagella apparatus, which consists of a basal body where the structure originates and a flagellum that is continuous with an undulating membrane running along the length of the body. Trypanosomes also possess a nucleus, mitochondria, Golgi body, endoplasmic reticulum and various vacuoles. Figure 14.1 Structure of the trypanosome cell. Trypanosomes are unicellular protozoan parasites with a cellular structure similar to other eukaryotes. The plasmodium parasite that is the causative agent of malaria has a number of life cycle stages characterized by slightly different body structures...
eBook - ePub- Peter L. Long(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...gondii and Sarcocystis spp. were coccidian parasites, another coccidian gained recognition as an important pathogen of man and domesticated animals. In 1982, our concept of Cryptosporidium spp. began to change from that of a rare organism infecting mammals into that of important, widespread causes of diarrheal illness in several animals species, including humans. 23 Cryptosporidium parvum is now recognized as a common cause of sell-limited diarrheal illness in immunocompetent persons and as a cause of prolonged, life-threatening, cholera-like illness in immunocompromised persons, especially patients with AIDS. Reports of infections of the respiratory tract, pancreatic ducts, and biliary tree demonstrate that the developmental stages of this protozoan are not confined to the gastrointestinal tract and suggest that C. parvum may also be an under-reported cause of respiratory and biliary tract disease, especially in the immune deficient host. 5 III Taxonomy As a direct result of the rapid advances in our understanding of the fine structure of parasitic protozoa that occurred in the early 1960s, 13, 14 the phylum Apicomplexa Levine 1970 was established in an attempt to make some sense of the “Sporozoa” that contained diverse groups of protozoan parasites. 24 The phylum Apicomplexa brings together all protozoa that possess an apical complex, an assemblage of organelles at the anterior end of certain life cycle stages that facilitate attachment to or entry into host cells...
eBook - ePub- Britannica Educational Publishing, Kara Rogers(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
...This capability has made Stentor a favourite subject for studies of regeneration in protozoans. Trichomonad Trichomonads are zooflagellate protozoans that possess three to six flagella, one of which commonly trails or borders an undulating membrane. Most trichomonads inhabit the digestive systems of animals. They may be uninucleate or multinucleate. Reproduction is by division. The genus Trichomonas is a common parasite in the digestive system of many animals. Trichomonas cells are pear-shaped and may have four flagella anteriorly and a fifth bordering the undulating membrane. A mouth and a basal rod (costa) are found along the membrane. An axostyle, a stiff rod of cytoplasm used for support, often protrudes posteriorly. Three species occur in humans: T. hominis in the intestine, T. vaginalis in the vagina, and T. buccalis in the mouth. Tritrichomonas foetus is a pathogenic form in cattle. Trypanosoma Trypanosoma is a genus of parasitic zooflagellate protozoans. Adult trypanosomes are mainly blood parasites of vertebrates, especially fishes, birds, and mammals. Most species require an intermediate host (often an insect or a leech) to complete their life cycle. Sleeping sickness (also called African trypanosomiasis), for example, caused by T. gambiense or T. rhodesiense, is transmitted by tsetse flies. In South and Central America, T. cruzi, the agent of Chagas’ disease, and the harmless T. rangeli are transmitted by bloodsucking insects. Other species of trypanosomes induce economically important diseases of livestock: nagana, surra, mal de caderas, and dourine. Trypanosomiasis Trypanosomiasis is an infectious disease in both humans and animals that is caused by certain members of the flagellate protozoa genus Trypanosoma and spread by certain bloodsucking insects...
