Obligate intracellular parasite

Vimses are obligate intracellular parasites. They only exhibit activity by infecting other living organisms, thus they are not a practical concern in industrial microbiological fields. The exception is where viral contamination of the product or process represents a threat of transmission of disease. Microscopic insects and protozoans are also not addressed in this article (see Insectcontroltechnology). 

The identification of bacteria has traditionally required the establishment of a pure culture before any other steps are taken. Pure cultures of bacteria may sometimes be obtained from blood and spinal fluid, which are normally sterile, or from extreme environments like hot springs. However, because there are few such situations in nature, individual bacteria must generally be isolated from other cells and grown for one to five days to obtain pure cultures before identification. Some pathogenic bacteria are obligate intracellular parasites that are difficult or impossible to grow outside their mammalian host cells 37 for these, pure cultures are not feasible. 

Hackstadt,T. The diverse habitats of obligate intracellular parasites. Curr. Opin. Microbiol. 1998,1, 82-87. 

Infections caused by C. trachomatis are believed to be the most common STD in the United States that has more than doubled in the past 10 years. C. trachomatis is an obligate intracellular parasite that has some similarities to viruses and bacteria. 

Viruses are obligate intracellular parasites that use many of the host cell s biochemical mechanisms and products to sustain their viability. A mature virus (virion) can exist outside a host cell and still retain its infective properties. However, to reproduce, the virus must enter the host cell, take over the host cell s mechanisms for nucleic acid and protein synthesis, and direct the host cell to make new viral particles. 

Viruses are obligate intracellular parasites their replication depends primarily on synthetic processes of the host cell. Therefore, to be effective, antiviral agents must either block viral entry into or exit from the cell or be active inside the host cell. As a corollary, nonselective inhibitors of virus replication may interfere with host cell function and... 

In a relationship of parasitism the population that benefits, the parasite, normally derives its nutritional requirements from the population that is harmed, the host. The host-parasite relationship is characterized by a relatively long period of contact, which may be directly physical or metabolic. Normally, the relation is as specific as for example the viruses, which are obligate intracellular parasites of bacterial, fungal, algal, and protozoan populations. 

Toxoplasmosis is a recurrent, potentially blinding, disease caused by the obligate intracellular parasite Toxoplasma gondii. Toxoplasmosis affects millions of people worldwide. Cats are the definitive host for the parasite but not the primary source of human infection. Environmental contamination of the soil, water, fruits and vegetables, and infection in other animals cause most human infections. Human infection may be either congenital or acquired, and acquired disease appears to be the most prevalent. 

Chlamydiae are obligate intracellular parasites that depend on the host cell to carry out metabolic biosynthe-sis.The genus includes two major species C. trachomatis, which causes disease in humans, and Chlamydia psittaci, which infects primarily nonhumans. The many different serotypes cause a wide spectrum of disease states, including inclusion conjunctivitis, trachoma, lymphogranuloma venereum, and cervicitis or urethritis. 

Viruses (from the Latin virus referring to poison) are nonliving obligate intracellular parasites composed of protein and nucleic acid (DNA or RNA) that manipulate the host cell to produce and manufacture more viruses. Viral infection occurs by tire attachment of virus particles to specific cell receptors within the host cell. After fusion of the host cell plasma membrane with the virus outer envelope, the protein-based viral nucleocapsid (containing the viral DNA) is transported to the host cell nucleus, where components of the viral particle inhibit macromolecular synthesis by tire host cell. Herpes viral DNA and new viral nucleocapsid synthesis occurs within the host nucleus, with the acquisition of new viral envelopes via a budding process through the inner membrane of the host nucleus. The mature newly synthesized viral particles are subsequently... 

VIRUSES Viruses lack most of the properties that distinguish life from nonlife. For example, viruses cannot carry on metabolic activities on their own. Yet under the appropriate conditions they can wreak havoc on living organisms. Often described as obligate, intracellular parasites, viruses can also be viewed as mobile genetic elements because of their structure, that is, each consists of a piece of nucleic acid... 

Being an obligate intracellular parasite, host cell entry is a necessary and specific requisite for Plasmodium in the vertebrate host. As such, the molecular mechanisms of invasion have been considered the Achilles heel that might be exploited for the development of new therapies for malaria. Despite half a century of invasion research a practical and effective means for interrupting the entry process into red blood cells has not been achieved. However, hope for novel interventions remains. 

The pathogenic vims is the quintessential parasite. It is a totally obligate, intracellular parasite that replicates only within the host cell diverting components of the host s nucleic acid synthesizing machinery to build more of itself. While carrying out this rapacious process, the virion is actually protected by the victimized cell s plasma membrane. 

Malaria is a devastating human disease that causes more than 850 000 deaths each year. The disease is caused by a protozoan parasite of the genus Plasmodium, which is obligate intracellular protozoan parasites of humans and animals, and the symptoms of the disease are largely a consequence of the asexual multiplication of these parasites within erythrocytes in the host. The Human disease is caused by the Plasmodium species P. falciparum, P. vivax, P. ovale and P. malariae. The life cycle of the Malaria parasite is extremely complex involving distinct cellular morphologies for infection of the host organism (human or other animal) and the infectious vector, the mosquito... 

Hall, B. F. and Joiner, K. A. (1991) Strategies of obligate intracellular parasites for evading host defences. Immunoparasitol. Today 12 124 129. 

Viruses, in general, utilize only the enzyme-system of the host-cell for two purposes, namely first, to synthesize DNA and secondly, to replicate virus, thereby enabling it to perform their usual metabolic activities. They may carry out either the transformation or the replication processes of the cell at the same time. By virtue of the fact that viruses are obligate intracellular parasites, therefore, their replication phenomenon solely depends on the host s cellular processes. 

Background Viruses are obligate intracellular parasites composed of either DNA or RNA wrapped in a protein nucleocapsid. Some viruses produce a glycoprotein envelope that surrounds the nucleocapsid. Viruses shed their capsid after invading a host cell. The host cell then synthesizes new viruses using the message encoded by the viral DNA or RNA. Relatively few viral infections are treatable. 

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