Infectious agent

The final criterion of satisfactory sterilization of domestic water is the reduction in bacterial concentration to very low values. Bacteriological examination of drinking water uses the coliform bacteria Escherichia coli—often referred to as E, coli) as an indication of the purity of the water since these bacteria are the normal inhabitant of the intestinal tract and constitute about 30% of the dry weight of adult human feces. Water suitable for human consumption should contain less than one viable coliform per 100 mL. 

Three different types of standard tests are used  

Multiple-type fermentation method. The various aliquots of samples are incubated for 48 h at 35°C in a culture medium. The absence of gas formation indicates a negative test for coliform. 

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Tolerance The ability of a person to withstand adverse conditions of air quality, infectious agents, noise, vibration, or light without showing signs of infection or disease. 

Viruses are small infectious agents composed of a nucleic acid genome (DNA or RNA) encased by structural proteins and in some cases a lipid envelope. They are the causative agents of a number of human infectious diseases, the most important for public health today being acquired immunodeficiency syndrome (AIDS), hepatitis, influenza, measles, and vituses causing diarrhoea (e.g., rotavirus). In addition, certain viruses contribute to the development of cancer. Antiviral drugs inhibit viral replication by specifically targeting viral enzymes or functions and are used to treat specific virus-associated diseases. 

Rheumatoid arthritis (RA) is a chronic inflammatory disease of unknown aetiology with some autoimmune features. Current thinking favours the hypothesis that interplay between genetic factors, sex hormones, and possibly an infectious agent or another immune activating agent initiates an autoimmune pathogenic mechanism that culminates in a disease with inflammatory and destructive features. 

Operations involving infectious agents or organisms will require further measures to ensure bio-security and safety. This usually involves the use of biosafety cabinets, which are designed to protect both the product and the user from contamination. Appropriate disinfection and bio-containment procedures must be adopted to prevent unwanted release of dangerous organisms. 

The terms allergy and atopy are in close proximity of our lives in the new millennium since our lifestyles have enormously changed. Encounters with various new molecules in air, water and diet, living in a more polluted world with less exposure to infections, and infectious agents are supposed to be the major causative factors added to the genetic propensity of developing IgE antibodies responsible for symptoms and... 

DNA sequences as short as 50-100 bp and as long as 10 kb can be amplified. Twenty cycles provide an amplification of 10 and 30 cycles of 10. The PCR allows the DNA in a single cell, hair follicle, or spermatozoon to be amplified and analyzed. Thus, the applications of PCR to forensic medicine are obvious. The PCR is also used (1) to detect Infectious agents, especially latent viruses (2) to make prenatal genetic diagnoses (3) to detect allelic polymorphisms (4) to establish precise tissue types for transplants and (5) to study... 

Immunologic abnormahties (eg, transfusion reactions, the presence in plasma of warm and cold antibodies that lyse red blood cells, and unusual sensitivity to complement) also fall in this class, as do toxins released by various infectious agents, such as certain bacteria (eg, Clostridium). Some snakes release venoms that act to lyse the red cell membrane (eg, via the action of phospholipases or proteinases). 

The most resistant of all infectious agents to chemical inactivation are the prions, which cause transmissible degenerative encephalopathies. 

The body possesses a number of non-specific antimicrobial systems which are operative at all times against potentially pathogenic microorganisms. Prior contact with the infectious agent has no intrinsic effect on these systems. 

A more general example fiom virus vaccine produetion is the rigorous examination of tissue cultures to exclude contamination with infectious agents fiom the sonrce animal or, in the cases of human diploid cells or cells fiom eontinuous cell lines, to detect... 

Infectious diseases may either be spread Irom a common reservoir of the infectious agent that is distinct from diseased individuals (common source) or they might transfer directly firm a diseased individual to a healthy one (propagated source). 

Table 5 Examples of immunoassays developed for anti-infectious agents...

Routine antibiotic use is not warranted because the primary infectious agents associated with asthma exacerbations are viruses.2,3 Antibiotics should be reserved for situations when bacterial infection is strongly suspected (e.g., fever and purulent sputum, pneumonia, and suspected sinusitis). 

Compare and contrast diarrhea caused by different infectious agents. 

Bacteria are likely precipitants in many other cases including Escherichia coli, Salmonella species, Shigella species, Vibrio cholerae, and Clostridium difficile. The term dysentery has often been used to describe some of these bacterial infections when associated with serious occurrences of bloody diarrhea. Additionally, acute diarrheal conditions can be prompted by parasites-protozoa such as Entamoeba histolytica, Microsporidium, Giardia lamblia, and Cryptosporidium parvum. Most of these infectious agents can be causes of traveler s diarrhea, a common malady alflicting travelers worldwide. It usually occurs during or just after travel subsequent to the ingestion of fecally-contaminated food or water. It has an abrupt onset but usually subsides within 2 to 3 days. 

Over 20 infectious agents have been incriminated as etiologic agents for many the causal relationship has been disproved, and for others there is conflicting evidence. Human herpesvirus 6 (HHV-6) is currently the most likely causative virus. HHV-6 may initiate the autoimmune processes of MS in one of two ways. First, HHV-6 is structurally similar to myelin basic protein. When T cells become sensitive to HHV-6, the cells may attack myelin basic protein. Second, HHV-6 may directly stimulate the complement cascade, activating autoimmune processes.5 Infection with HHV-6 alone cannot fully explain MS, because HHV-6 is found in 75% of all people, but MS is much more rare. 

Even though exposure to environmental agents such as agricultural chemicals, pesticides, and radiation has been associated with leukemia, none of these agents is linked conclusively with the development of leukemia. An increased frequency of ALL is associated with higher socioeconomic status. It is postulated that less social contact in early infancy and thus a late exposure to some common infectious agents may have some impact.7 In most individual instances, there is no reasonable or obvious explanation for the development of leukemia. 

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