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== Mortality from infectious diseases ==
The [[World Health Organization]] collects information on global deaths by [[ICD|International Classification of रोग (ICD) code categories]]. The following table lists the top infectious रोग killers which caused more than १००,००० deaths in २००२ (estimated). १९९३ data is also included for comparison.
{| cellpadding=3 cellspacing=0 border=1
|
|
|2002
|
|''1993''
|
|-
|
|World population
| 6.2 billion
|
| 5.5 billion
|-
|
|Total deaths from all causes
| 57 million
| 100%
| 51 million
|-
| '''Rank'''
| '''Cause of death'''
| '''Number'''
| '''Percentage of total'''
| ''Number''
| ''1993 Rank''
|-
|
| I. Communicable diseases category
| 14.9 million
| 26.0%
|-
| 1
|
:[[Lower respiratory tract infection|Lower respiratory infections]]
| 3.9 million
| 6.8%
| 4.1 million
| 1
|-
| 2
|
:[[HIV]]/[[AIDS]]
| 2.8 million
| 4.9%
| 0.7 million
| 7
|-
| 3
|
:[[Gastroenteritis|Diarrheal diseases]]
| 1.8 million
| 3.2%
| 3.0 million
| 2
|-
| 4
|
:[[Tuberculosis]] (TB)
| 1.6 million
| 2.7%
| 2.7 million
| 3
|-
| 5
|
:[[Malaria]]
| 1.3 million
| 2.2%
| 2.0 million
| 4
|-
| 6
|
:[[Measles]]
| 0.6 million
| 1.1%
| 1.1 million
| 5
|-
| 7
|
:[[Pertussis]]
| 0.30 million
| 0.5%
| 0.36 million
| 7
|-
| 8
|
:[[Tetanus]]
| 0.21 million
| 0.4%
| 0.15 million
| 12
|-
| 9
|
:[[Meningitis]]
| 0.17 million
| 0.3%
| 0.25 million
|8
|-
| 10
|
:[[Syphilis]]
| 0.16 million
| 0.3%
| 0.19 million
| 11
|-
| 11
|
:[[Hepatitis B]]
| 0.10 million
| 0.2%
| 0.93 million
| 6
|-
|
|
:[[Tropical रोग]]s (6)
| 0.13 million
| 0.2%
| 0.53 million
| 9, 10, 16, 17, 18
|}
<!-- following is indented as a footnote for the table -->
:''(Note: The other categories of death are maternal र perinatal conditions (५.२%), nutritional deficiencies (०.९%), noncommunicable conditions (५८.८%), र injuries (९.१%).)''
----
The top three single agent रोग killers are [[HIV]]/[[AIDS]], [[tuberculosis|TB]] र [[malaria]]. From १९९३ to २००२, the death ranking for AIDS went up from ७th to २nd र Hepatitis B went down from ६th to ११th. While the number of deaths has decreased in almost every रोग, it has increased four-fold in [[AIDS]].
Lower respiratory infections, which include various [[pneumonia]]s, र diarrheal diseases are caused by many different [[virus]]es, [[bacterium|bacteria]] or [[parasite]]s.
Childhood diseases include [[pertussis]], [[poliomyelitis]], [[diphtheria]], [[measles]] र [[tetanus]]. Children also make up a large percentage of lower respiratory र diarrheal deaths.
Tropical diseases include [[Chagas रोग]], [[dengue fever]], [[filariasis|lymphatic filariasis]], [[leishmaniasis]], [[onchocerciasis]], [[schistosomiasis]] र [[trypanosomiasis]].
=== Historic pandemics ===
A [[pandemic]] (or global [[epidemic]]) is a रोग that affects people over an extensive geographical area.
* The Influenza Pandemic of १९१८ or [[Spanish Flu]] killed २५ to ४० million in १ year (about २% of world population of १.७ billion).
** [[Influenza]] now kills about २५०,००० to ५००,००० worldwide each year.
* The [[Black Death]] of १३४७ to १३५२ killed २५ million in Europe over ५ years (estimate of २५ to ५०% of Europe, Asia, र Africa - world population was ५०० million).
=== नयां रोगहरु र pandemics ===
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]]).
With most new infectious diseases, some human action is involved, changing the environment so that an existing [[microbe]] can take up residence in a new ecological [[niche|niche.]] Once that happens, a [[pathogen]] that had been confined to a remote habitat appears in a new or wider region, or a microbe that had infected only animals suddenly begins causing human रोग.
Several human activities have led to the emergence र spread of new diseases:
:'''Encroachment on wildlife habitats.''' The construction of new villages र housing developments in rural areas brings people into contact with animals--and the microbes they harbor.
:'''Changes in agriculture.''' The introduction of new crops attracts new crop pests र the microbes they carry to farming communities, exposing people to unfamiliar diseases.
:'''Destroying rain forests.''' As tropical countries make use of their rain forests, building roads through forests र clearing areas for settlement or commercial ventures, people encounter insects र other animals harboring unknown microorganisms.
:'''Uncontrolled urbanization.''' The rapid growth of cities in many developing countries concentrates large numbers of people in crowded areas with poor sanitation, which foster the transmission of contagious diseases.
:'''Modern transport.''' Ships र other cargo carriers often harbor unintended "passengers," such as insects र rats, that can spread diseases to faraway destinations.
:'''High-speed globe-trotting.''' With international jet-airplane travel, people infected with a new रोग can carry the रोग to the far side of the world before their first symptoms appear.
The relationship between virulence र transmission is complex, र has important consequences for the long term evolution of a pathogen. If a रोग 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 रोग that death rates are highest.
== Diagnosis र therapy ==
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