From Simple English Wikipedia, the free encyclopedia
A
pathogen
is an
infectious
thing, such as a
virus
,
bacteria
,
fungi
or
parasite
, which causes a
disease
. This ability is called
pathogenicity
.
The body has many ways to defend against some of the common pathogens (such as
Pneumocystis
) in the form of the human
immune system
and by some "helpful"
bacteria
present in the human body's normal human
flora
. However, if the
immune system
or "good" bacteria is damaged in any way (for example,
chemotherapy
,
HIV
, or
antibiotics
being taken to kill other pathogens), pathogenic
bacteria
that were being held back can grow and cause harm to the host. Such cases are opportunistic infections.
Some pathogens cause
epidemics
. These include the bacterium
Yersinia pestis
which may have caused the
Black Death
, the
Variola
virus, and the
malarial
protozoa. They hurt or even kill large numbers of people.
The most famous and lethal outbreak was the
1918
Spanish flu
pandemic
(type A influenza,
H1N1
subtype), which lasted from 1918 to 1919. It is not known exactly how many it killed, but estimates range from 20 to 100 million people.
[1]
[2]
This pandemic has been described as "the greatest medical holocaust in history" and may have killed as many people as the
Black Death
.
[3]
The huge death toll was caused by an extremely high infection rate of up to 50% and the extreme severity of the symptoms. One observer wrote, "One of the most striking of the complications was hemorrhage from
mucous membranes
, especially from the nose, stomach, and intestine. Bleeding from the ears and skin also occurred".
[1]
The majority of deaths were from bacterial
pneumonia
, a
secondary infection
caused by influenza, but the virus also killed people directly, causing massive bleeding and
oedema
in the lungs.
[4]
In plants, fungi are the main cause of infectious disease.
- ↑
1.0
1.1
Institute of Medicine (US) Forum on Microbial Threats; Knobler, S. L.; Mack, A.; Mahmoud, A.; Lemon, S. M. (2005-03-09).
The Threat of Pandemic Influenza: Are We Ready? Workshop Summary
. Washington, D.C.: National Academies Press.
doi
:
10.17226/11150
.
ISBN
978-0-309-09504-4
.
PMID
20669448
.
- ↑
Patterson, K. D.; Pyle, G. F. (Spring 1991). "The geography and mortality of the 1918 influenza pandemic".
Bull Hist Med
.
65
(1): 4?21.
PMID
2021692
.
- ↑
Potter, C.W. (2001).
"A history of influenza"
.
Journal of Applied Microbiology
.
91
(4): 572?579.
doi
:
10.1046/j.1365-2672.2001.01492.x
.
ISSN
1364-5072
.
PMID
11576290
.
S2CID
26392163
.
- ↑
Taubenberger, Jeffery K.; Reid, Ann H.; Janczewski, Thomas A.; Fanning, Thomas G. (December 29, 2001).
"Integrating historical, clinical and molecular genetic data in order to explain the origin and virulence of the 1918 Spanish influenza virus"
.
Philos Trans R Soc Lond B Biol Sci
.
356
(1416): 1829?39.
doi
:
10.1098/rstb.2001.1020
.
PMC
1088558
.
PMID
11779381
.