Mode of Transmission of Diseases

Mode of Transmission of Diseases

The traditional epidemiologic triad model holds that infectious diseases result from the interaction of agent, host, and environment. More specifically, transmission occurs when the agent leaves its reservoir or host through a portal of exit, is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host.  An infectious agent may be transmitted from its natural reservoir to a …

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Shiga toxin-producing Escherichia coli (STEC)

Shiga toxin-producing Escherichia coli (STEC)

The Shiga toxin-producing E. coli (STEC), is also alternatively referred to as verocytotoxin-producing E. coli (VTEC), and enterohemorrhagic E. coli (EHEC). All members of this group are defined by the presence of Shiga toxin 1 (Stx1) or 2 (Stx2). Some but not all EHEC strains are LEE positive and form A/E cytopathology, resembling EPEC strains. The most common serotype associated …

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Enterotoxigenic E. coli (ETEC)

Enterotoxigenic E. coli (ETEC)

Enterotoxigenic E. coli (ETEC) is defined as containing the E. coli strains that elaborate at least one member of two defined groups of enterotoxins: heat-stable toxin (ST) and heat-stable toxin (LT). Enterotoxigenic Escherichia coli, or ETEC, is thus the name given to a group of E. coli that produces special toxins that stimulate the lining of the intestines causing them to secrete excessive fluid, …

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Endemic Diseases

Endemic Diseases

Communicable diseases are termed endemic when they have a relatively stable pattern of occurrence in a given geographical area or population group at the relatively high prevalence and incidence. It refers to the constant presence of a disease or infectious agent within a given geographic area or population group, without importation from outside. It may also refer to the “usual” …

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Disease Prevention

Disease Prevention

Disease prevention is a procedure through which individuals, those with risk factors for a disease or without the risk factors, are treated in order to prevent a disease from occurring. Treatment normally begins either before signs and symptoms of the disease occur, or shortly thereafter. Prevention includes a wide range of activities — known as “interventions” — aimed at reducing …

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Enteroinvasive E. coli (EIEC)

Enteroinvasive E. coli (EIEC)

Enteroinvasive E. coli (EIEC) strains are rare in both developed and developing countries. EIEC infections are characterized by a period of watery diarrhea that precedes the onset of scanty dysenteric stools containing blood and mucus. Pathogenic strains are primarily associated with a few restricted O serotypes: O124, O143, and O164. EIEC strains are biochemically, genetically, and pathogenetically related closely to Shigella spp. …

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Enteroaggregative E. coli (EAEC)

Stages of pathogenesis of EAEC

Enteroaggregative E.  coli (EAEC) are a heterogeneous collection of strains characterized by their autoagglutination in a “stacked-brick” arrangement over the epithelium of the small intestine and, in some cases, the colon. EAEC strains are currently defined as  E. coli strains that do not secrete enterotoxins LT or ST and that adhere to HEp-2 cells in an AA pattern. The prevalence of disease …

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The Germ Theory of Disease

Germ Theory of Disease

Before the Germ theory of disease, the causes suggested for the occurrence of disease were the effect of supernatural phenomena like planetary alignments, effect of bad bodily humors and the faulty environment. For example, in ancient Greece, it was thought that disease was spread not via direct contact with other infected individuals, but rather via infectious “seeds” in the air …

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WHO Global Tuberculosis Report 2018

WHO Global Tuberculosis Report 2018

WHO has published a global TB report every year since 1997. The main aim of the report is to provide a comprehensive and up-to-date assessment of the TB epidemic, and of progress in prevention, diagnosis and treatment of the disease at global, regional and country levels. This is done in the context of recommended global TB strategies and targets endorsed …

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Enteropathogenic Escherichia coli (EPEC)

Enteropathogenic Escherichia coli (EPEC)

Two groups of E. coli are responsible for enteric disease: Enteropathogenic E. coli [EPEC] and some Shiga toxin–producing E. coli [STEC]. They both possess a cluster of virulence genes located on a chromosomal pathogenicity island called the locus of enterocyte effacement (LEE). The EPEC are however, defined by: Presence of LEE and Absence of Shiga toxin. Enteropathogenic Escherichia coli (EPEC), one of …

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