"सरुवा रोग" का संशोधनहरू बिचको अन्तर

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Infectious diseases are the invasion of a [[host (biology)|host]] organism by a foreign [[replicator]], generally microorganisms, often called ''microbes,'' that are invisible to the naked eye. Microbes that cause illness are also known as ''pathogens.'' The most common pathogens are various bacteria र viruses, though a number of other microorganisms, including some kinds of [[fungi]] र [[protozoa|protozoa,]] also cause disease. [[Prions]] are borderline, र [[meme]]s would not usually be considered in this scope. An infectious disease is termed ''contagious'' if it is easily transmitted from one person to another.

An organism that a microbe infects is known as the host for that microbe. In the human host, a microorganism causes disease by either disrupting a vital body process or stimulating the immune system to mount a defensive reaction. An immune response against a pathogen, which can include a high fever, inflammation, र other damaging symptoms, can be more devastating than the direct damage caused by the microbe.

 

Infectious disease requires an ''agent'' र a ''mode of transmission'' (or ''[[Vector (biology)|vector]]''). A good example is [[malaria]], which is caused by Plasmodial [[parasite]]s, chiefly ''[[Plasmodium falciparum]]'' but does not affect humans unless the vector, the [[Anopheles]] [[mosquito]], is around to introduce the parasite into the [[human]] bloodstream.

 

The vector does not have to be biological. Many infectious diseases are transmitted by droplets which enter the airway (e.g. [[common cold]] र [[tuberculosis]]).

 

The [[World Health Organization]] collects information on global deaths by [[ICD|International Classification of Disease (ICD) code categories]]. The following table lists the top infectious disease killers which caused more than 100,000 deaths in 2002 (estimated). 1993 data is also included for comparison.

{| cellpadding=3 cellspacing=0 border=1

| 1

|

| 3.9 million

| 6.8%

| 3

|

| 1.8 million

| 3.2%

Tropical diseases include [[Chagas disease]], [[dengue fever]], [[filariasis|lymphatic filariasis]], [[leishmaniasis]], [[onchocerciasis]], [[schistosomiasis]] र [[trypanosomiasis]].

 

A [[pandemic]] (or global [[epidemic]]) is a disease that affects people over an extensive geographical area.

* The Influenza Pandemic of 1918 or [[Spanish Flu]] killed 25 to 40 million in 1 year (about 2% of world population of 1.7 billion).

* The [[Black Death]] of 1347 to 1352 killed 25 million in Europe over 5 years (estimate of 25 to 50% of Europe, Asia, र Africa - world population was 500 million).

 

In some cases, a microorganism र its host live in reasonable harmony. Such is the case for many tropical viruses र the insects, monkeys, or other animals in which they have lived र reproduced for thousands or millions of years. Because the microbes र their hosts have co-evolved together, the hosts have gradually become resistant to the microorganisms. But when a microbe jumps from a long-time animal host to a human being, it may cease being a harmless parasite and—simply because it is new to the human species—become a pathogen. (See [[infection]]).

 

The relationship between virulence र transmission is complex, र has important consequences for the long term evolution of a pathogen. If a disease is rapidly fatal, the host may die before the microbe can get passed along to another host. However, this cost may be overwhelmed by the short term benefit of higher infectiousness if transmission is linked to virulence, as it is for instance in the case of cholera (the explosive diarrhoea aids the bacterium in finding new hosts) or many respiratory infections (sneezing, coughing etc create infectious aerosols). Since it takes time for a microbe र a new host species to co-evolve an emerging pathogen may hit its earliest victims especially hard. It is usually in the first wave of a new disease that death rates are highest.

 

The field of ''infectious diseases'' also occupies itself with the [[diagnosis]] र [[Medication|therapy]] of [[infection]].

 

''Diagnosis'' is initially by medical history र physical examination, र imaging (such as [[X-ray]]s), but the principal tool in infectious disease is the [[microbiological culture]]. In a culture, a [[growth medium]] is provided for a particular agent. After inoculation of a specimen of diseased fluid or tissue onto the medium, it is determined whether bacterial growth occurs. This works for a number of [[bacterium|bacteria]], for example [[Staphylococcus]] or [[Streptococcus]].

 

A more recent development is direct detection of [[virus|viral]] proteins and/or DNA in [[blood]] or [[secretion]]s. This can be done by [[PCR]] (polymerase chain reaction), involving the amplification of viral DNA र its subsequent detection with anti-DNA probes.

 

One way of proving that a given disease is "infectious", is to satisfy [[Koch's postulates]] ([[Robert Koch]]), which demand that the [[infectious agent]] is identified in patients र not in controls, र that patients who contract the agent also develop the disease. These postulates were tried र tested in the discovery of [[Mycobacteria]] as the cause for [[tuberculosis]]. Often, it is not possible to meet some of the criteria, even in diseases that are quite clearly infectious. For example, ''[[Treponema pallidum]]'', the causative [[spirochete]] of [[syphilis]], cannot be [[microbiological culture|cultured]] in vitro - however the organism can be cultured in rabbit testes].

 

[[Epidemiology]] is another important tool used to study disease in a population. For infectious diseases it helps to determine if a disease [[outbreak]] is sporadic (occasional occurrence), [[endemic (epidemiology)|endemic]] (regular cases often occurring in a region), [[epidemic]] (an unusually high number of cases in a region), or [[pandemic]] (a global epidemic).

 

When a [[microbiological culture|culture]] has proven to be positive, the sensitivity (or, conversely, the [[antibiotic resistance]]) of an agent can be determined by exposing it to test doses of [[antibiotic]]. This way, the [[microbiology|microbiologist]] determines how sensitive the target [[bacterium]] is to a certain antibiotic. This is usually reported as being: '''S'''ensitive, '''I'''ntermediate or '''R'''esistant. The ''[[antibiogram]]'' can then be used to determine optimal therapy for the patient. This can reduce the use of [[broad-spectrum antibiotic]]s र lead to a decrease in [[antibiotic resistance]].

 

 

The services of the infectious disease team are called for when:

* The disease might be dangerous to other patients, र the patient might have to be isolated.

 

 

[[Anton van Leeuwenhoek]] ([[1632]]-[[1723]]) advanced the science of microscopy, allowing easy visualization of bacteria.

 

[[Gerhard Domagk]] develops [[Sulphonamides]], the first broad spectrum synthetic antibacterial drugs.

 

* [[Infection]]

* [[Microbiology]]

* [[Big killer]]

 

* Table: [http://www.who.int/whr/en/ The World Health Report] - 2004 Annex Table 2 र 1995 Table 5

 

* [http://www.idsociety.org IDsociety] - The Infectious Disease Society of America

* [http://www.GIDEONonline.com GIDEON] - [[GIDEON-Global Infectious Diseases र Epidemiology Network|Global Infectious Diseases र Epidemiology Network]]

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