Infectious disease is disease caused by a pathogen which enters the body and triggers the development of an infection. Infectious diseases have a range of causes, and they can be found all over the world. These diseases are considered contagious or communicable, meaning that they can be passed from person to person. It is also possible for such diseases to spread indirectly through unhygienic conditions, or from animals to people, in which case they are known as zoonotic diseases.
A variety of pathogens can be responsible for infectious disease, including viruses, bacteria, fungi, protozoans, and prions. Within these large categories of infectious organisms, there are numerous modes of transmission and a colorful assortment of symptoms, although surprisingly few organisms cause infectious disease, when one considers the diversity of viral, bacterial, fungal, and protozoan life. In order to treat an infectious disease, doctors must be able to knock out the source of the infection and repair the damage it has done to the body. Many infectious diseases make the body vulnerable to secondary infections, in which other organisms move in to take advantage of a weakened immune system, and this can be very problematic.
The study of infectious disease is known as epidemiology. Epidemiologists work to determine the source of an infectious disease so that they can develop new treatment approaches. They also identify emerging outbreaks, which may develop into epidemics or pandemics, and areas where a disease is endemic, meaning that it occurs regularly. Malaria, for example, is endemic to some regions of Africa and Southeast Asia. Read more »
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Posted in medicalmatrix | February 13, 2010 | 
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Background
Anemia, like a fever, is a symptom of disease that requires investigation to determine the underlying etiology. Often, practicing physicians overlook mild anemia. This is similar to failing to seek the etiology of a fever. The purpose of this article is to provide a method of determining the etiology of an anemia.
Anemia is strictly defined as a decrease in red blood cell (RBC) mass. Methods for measuring RBC mass are time consuming, are expensive, and usually require transfusion of radiolabeled erythrocytes. Thus, in practice, anemia is usually discovered and quantified by measurement of the RBC count, hemoglobin (Hb) concentration, and hematocrit (Hct). These values should be interpreted cautiously because they are concentrations affected by changes in plasma volume. For example, dehydration elevates these values, and increased plasma volume in pregnancy can diminish them without affecting the RBC mass.
Pathophysiology
Erythroid precursors develop in bone marrow at rates usually determined by the requirement for sufficient circulating Hb to oxygenate tissues adequately. Erythroid precursors differentiate sequentially from stem cells to progenitor cells to erythroblasts to normoblasts in a process requiring growth factors and cytokines. This process of differentiation requires several days. Normally, erythroid precursors are released into circulation as reticulocytes.
Reticulocytes remain in the circulation for approximately 1 day before reticulin is excised by reticuloendothelial cells with the delivery of the mature erythrocyte into circulation. The mature erythrocyte remains in circulation for about 120 days before being engulfed and destroyed by phagocytic cells of the reticuloendothelial system. Read more »
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Background
Intracranial abscesses are uncommon, serious, life-threatening infections. They include brain abscess and subdural or extradural empyema and are classified according to the anatomical location or the etiologic agent. The term brain abscess is used in this article to represent all types of intracranial abscesses.
Intracranial abscesses can originate from infection of contiguous structures (eg, otitis media, dental infection, mastoiditis, sinusitis) secondary to hematogenous spread from a remote site (especially in patients with cyanotic congenital heart disease), after skull trauma or surgery, and, rarely, following meningitis. In at least 15% of cases, no source can be identified.
In recent years, the complex array of etiologic agents that cause brain abscess has become better understood.
Pathophysiology
Brain abscess is caused by intracranial inflammation with subsequent abscess formation. In at least 15% of cases, the source of the infection is unknown (cryptogenic). Infection may enter the intracranial compartment directly or indirectly via 3 routes.
Contiguous suppurative focus (45-50% of cases)
Direct extension may occur through necrotic areas of osteomyelitis in the posterior wall of the frontal sinus, as well as through the sphenoid and ethmoid sinuses.This direct route of intracranial extension is more commonly associated with chronic otitic infection and mastoiditis than with sinusitis. Odontogenic infections can spread to the intracranial space via direct extension or a hematogenous route. Contiguous spread could extend to various sites in the central nervous system, causing cavernous sinus thrombosis; retrograde meningitis; and epidural, subdural, and brain abscess. Read more »
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