1. What are pathogens?
A pathogen is an organism that causes disease.
Your body is naturally full of microbes. However, these
microbes only cause a problem if your immune system is
weakened or if they manage to enter a normally sterile
part of your body.
Pathogens are different and can cause disease upon entering
the body.
All a pathogen needs to thrive and survive is a host. Once
the pathogen sets itself up in a host’s body, it manages to
avoid the body’s immune responses and uses the body’s
resources to replicate before exiting and spreading to a new
host.
Pathogens can be transmitted a few ways depending on the
type. They can be spread through skin contact, bodily fluids,
airborne particles, contact with feces, and touching a
surface touched by an infected person.
Pathogen types

2. There are different types of pathogens, but we’re going to
focus on the four most common types: viruses, bacteria,
fungi, and parasites.
Viruses
Viruses are made up of a piece of genetic code, such as DNA
or RNA, and protected by a coating of protein. Once you’re
infected, viruses invade host cells within your body. They
then use the components of the host cell to replicate,
producing more viruses.
After the replication cycle is complete, these new viruses are
released from the host cell. This usually damages or destroys
the infected cells.
Some viruses can remain dormant for a time before
multiplying again. When this happens, a person appears to
have recovered from the viral infection, but gets sick again.
Antibiotics do not kill viruses and therefore are ineffective
as a treatment for viral infections. Antiviral medications
can sometimes be used, depending on the virus.
Bacteria
Bacteria are microorganisms made of a single cell. They are
very diverse, have a variety of shapes and features, and
have the ability to live in just about any environment,

3. including in and on your body. Not all bacteria cause
infections. Those that can are called pathogenic bacteria.
Your body can be more prone to bacterial infections when
your immune system is compromised by a virus. The disease
state caused by a virus enables normally harmless bacteria
to become pathogenic.
Antibiotics are used to treat bacterial infections. Some
strains of bacteria have become resistant to antibiotics,
making them difficult to treat. This can happen naturally,
but also happens because of the overuse of antibiotics,
according to the World Health Organization (WHO)Trusted
Source.
Fungi
There are millions of different fungal species on Earth.
Just 300Trusted Source or so are known to cause sickness.
Fungi can be found just about everywhere in the
environment, including indoors, outdoors, and on human
skin. They cause infection when they overgrow.
Fungi cells contain a nucleus and other components
protected by a membrane and a thick cell wall. Their
structure can make them harder to kill.

4. Some new strains of fungal infections are proving to be
especially dangerous, such as Candida aurus, and have
prompted more research into fungal infections.
Parasites
Parasites are organisms that behave like tiny animals, living
in or on a host and feeding from or at the expense of the
host. Though parasitic infections are more common in
tropical and subtropical regions, they can occur anywhere.
Three main types of parasites can cause disease in humans.
These include:
 protozoa, which are single-celled organisms that can
live and multiply in your body
 helminths, which are larger, multi-celled organisms
that can live inside or outside your body and are
commonly known as worms
 ectoparasites, which are multimulti-celled organisms that live
on or feed off your skin, including some insects, such
as ticks and mosquitos
They can be spread several ways, including through contaminated soil,
water, food, and blood, as well as through sexual contact and via insect bites.

5. Diseases caused by
pathogens
Pathogens can cause a number of diseases that range in severity and how
they’re transmitted. Let’s look at some of the diseases caused by the
different types of pathogens
Viruses
Viruses can cause a number of infections, many of which are contagious.
Examples of viral diseases include:
 common cold viral infection that affects the upper respiratory tract.
 flu and with it comes sniffling, sneezing, coughing, fatigue, and all the
familiar trappings of the flu
 meningitis an inflammation (swelling) of the protective membranes covering
the brain and spinal cord
 warts, including genital warts Genital warts are a common sexually
transmitted infection caused by a virus called Human Papilloma Virus (HPV). This
virus is passed on through direct skin-to-skin contact with someone who has HPV
on their skin. It can be passed from person to person during vaginal and anal sex.
 oral and genital herpes Oral herpes caused by HSV-1 can spread from
the mouth to the genitals through oral sex.
 chickenpox/shingles Shingles is caused by varicella zoster virus (VZV), the
same virus that causes chickenpox. After a person recovers from chickenpox, the
virus stays dormant (inactive) in their body. The virus can reactivate later,
causing shingles. Most people who develop shingles have only one episode
during their lifetime.

6.  measles Measles is an acute viral respiratory illness. It is characterized by a
prodrome of fever (as high as 105°F) and malaise, cough, coryza, and
conjunctivitis -the three “C”s -, a pathognomonic enanthema (Koplik spots)
followed by a maculopapular rash.
 viral gastroenteritis, including norovirus and rotavirus Rotaviruses are
the principal agent of sporadic, severe gastroenteritis in young children and are
responsible for the death of approximately 1600 children daily worldwide, mainly
in developing countries (Fig. 388-1 ). Noroviruses are the principal agent of
epidemic infectious gastroenteritis in both infants and adults.
 hepatitis A, B, C, D, E
 yellow fever Yellow fever is a serious disease caused by the yellow
fever virus. Most people infected with yellow fever virus do not get sick
or have only mild symptoms. People who do get sick will start having
symptoms (e.g., fever, chills, headache, backache, and muscle aches)
3–6 days after they are infected.
 dengue fever bitten by an infected mosquito. Dengue fever causes a
high fever — 104 F (40 C) — and any of the following signs and
symptoms: Headache. Muscle, bone or joint pain. Nausea
 HIV and AIDS HIV (human immunodeficiency virus) is a virus that
attacks the body's immune system. If HIV is not treated, it can lead to
AIDS (acquired immunodeficiency syndrome)
Bacteria

7. Here are some examples of bacterial infections:
 strep throat
 urinary tract infection (UTI)
 bacterial gastroenteritis, such as salmonella food poisoning or E.coli
infection
 bacterial meningitis Bacterial meningitis is serious. Some people with
the infection die and death can occur in as little as a few hours.
However, most people recover from bacterial meningitis. Those who do
recover can have permanent disabilities, such as brain damage,
hearing loss, and learning disabilities.
 Lyme disease caused by the bacterium Borrelia burgdorferi and rarely,
Borrelia mayonii. It is transmitted to humans through the bite of infected
blacklegged ticks. Typical symptoms include fever, headache, fatigue,
and a characteristic skin rash called erythema migrans.
 tuberculosis Tuberculosis (TB) is a disease caused by germs that are
spread from person to person through the air. TB usually affects the
lungs, but it can also affect other parts of the body, such as the brain,

8. the kidneys, or the spine. A person with TB can die if they do not get
treatment.
 gonorrhea a sexually transmitted disease (STD) caused by infection
with the Neisseria gonorrhoeae bacterium. N. gonorrhoeae infects the
mucous membranes of the reproductive tract, including the cervix,
uterus, and fallopian tubes in women, and the urethra in women and
men
 cellulitis a common bacterial skin infection that causes redness,
swelling, and pain in the infected area of the skin. If untreated, it can
spread and cause serious health problems. Good wound care and
hygiene are important for preventing cellulitis
Fungi
Some examples of common fungal infections are:
 vaginal yeast infections A vaginal yeast infection is a fungal infection
that causes irritation, discharge and intense itchiness of the vagina and
the vulva — the tissues at the vaginal opening. Also called vaginal
candidiasis, vaginal yeast infection affects up to 3 out of 4 women at
some point in their lifetimes.
 thrush is a fungal (yeast) infection that can grow in your mouth, throat
and other parts of your body. With oral thrush (oral candidiasis),
 ringworm Ringworm is a common skin infection that is caused by a
fungus. It's called “ringworm” because it can cause a circular rash
(shaped like a ring) that is usually red and itchy.
 athlete’s foot Athlete's foot occurs when a certain fungus grows on the
skin of your feet. The same fungus may also grow on other parts of the
body.
 jock itch tinea cruris) is a fungal infection that causes a red and itchy rash in
warm and moist areas of the body.

9.  fungal nail infections (onychomycosis) Fungal nail infections, also
known as “onychomycosis,” are very common. They may affect up to
14% of the general population. Fungal toenail infections are more
common than fungal fingernail infections.
Parasites
Some examples of diseases caused by parasites include:
 giardiasis Giardiasis is a diarrheal disease caused by the microscopic
parasite Giardia duodenalis (or “Giardia” for short). Once a person or
animal has been infected with Giardia, the parasite lives in the
intestines and is passed in stool (poop). Once outside the body,
Giardia can sometimes survive for weeks or even months.
 trichomoniasis Trichomoniasis (or “trich”) is a very common STD
caused by infection with Trichomonas vaginalis (a protozoan parasite).
Although symptoms vary, most people who have trich cannot tell they
have it.
 malaria is a mosquito-borne disease caused by a parasite. People
with malaria often experience fever, chills, and flu-like illness.
 toxoplasmosis What is toxoplasmosis? Toxoplasmosis is an infection
caused by a single-celled parasite called Toxoplasma gondii. While the
parasite is found throughout the world, more than 40 million people in the
United States may be infected with the Toxoplasma parasite.
 intestinal worms Parasitic worms, also known as helminths, are large
macroparasites; adults can generally be seen with the naked eye. Many are
intestinal worms that are soil-transmitted and infect the gastrointestinal tract.
Other parasitic worms such as schistosomes reside in blood vessels.
 pubic lice The crab louse or pubic louse is an insect that is an obligate
ectoparasite of humans, feeding exclusively on blood. The crab louse usually is
found in the person's pubic hair.

10. Protecting against
pathogens
The following are ways that you can protect yourself and others against
pathogens.
 Wash your hands often.
 Get vaccinated and ensure vaccinations are up to date.
 Prepare, cook, and store meat and other foods properly.
 Stay home when you’re sick, especially if you have
a fever or diarrhea, or are vomiting.
 Don’t share personal items, such as razors or toothbrushes.
 Don’t share drinking glasses or utensils.
 Protect against insect bites.
 Practice safe sex.
 Travel wisely by getting informed about health risks and special
vaccinations.
Takeaway
Pathogens have the ability to make us sick, but when healthy, our bodies can
defend against pathogens and the illnesses they cause.
Treatments are available for many of the illnesses caused by the different
types of pathogens. There is also symptom relief for those that can’t be
treated, such as some viral infections.

11. There are five stages of infection:
Incubation The incubation stage includes the time from exposure to an
infectious agent until the onset of symptoms.
Viral or bacterial particles replicate during the incubation stage.
Duration
The exact time frame of the incubation stage varies depending on the
infection. Here are a few examples:
Flu
The flu virus incubates for 1–4 daysTrusted Source, but symptoms can
appear as early as 2 days after the virus enters the body.
Hepatitis B

12. The incubation period for hepatitis B virus (HBV) ranges from 1.5–6
months.
Salmonella
Salmonella, a common foodborne bacterium, causes symptoms within 6
hours to 6 days. They can include:
 diarrhea
 vomiting
 stomach cramps
 Prodromal
 Illness

13.  Decline
 convalescence
Convalescence is the gradual recovery of health and strength after illness or injury. It
refers to the later stage of an infectious disease or illness when the patient recovers and
returns to previous health, but may continue to be a source of infection to others even if
feeling better

14. 5 Common Ways Germs are Spread
Nose, mouth, or eyes to hands to others: Germs can spread to the hands by
sneezing, coughing, or rubbing the eyes and then can be transferred to other
family members or friends
Hands to food: Usually germs are transmitted from unclean hands to food by
an infected food preparer who didn’t wash his or her hands after using the
toilet. The germs are then passed to those who eat the food. This is easily
prevented by always washing your hands after using the toilet and before
preparing food items
Food to hands to food: Germs are transmitted from raw foods, such as chicken,
to hands while preparing a meal. The germs on the hands are then transferred
to other uncooked foods, such as salad. Cooking the raw food kills the initial
germs, but the salad remains contaminated.
Animals to people: Wash your hands after petting animals or touching any
surfaces they come into contact with.
Infected child to hands to other children: Germs are passed from an child with
diarrhea to the hands of the parent during diaper changing. If the parent
doesn’t immediately wash his or her hands, the germs that cause diarrhea are
then passed to others.
1. Incubation
The incubation stage includes the time from exposure to an infectious agent until the
onset of symptoms.
2. Prodromal The prodromal stage refers to the period after incubation and before the
characteristic symptoms of infection occur.
3. Illness The third stage of infection is an illness or clinical disease. This stage
includes the time when a person shows apparent symptoms of an infectious disease.
4. Decline During the decline stage, the immune system mounts a successful defense
against the pathogens, and the number of infectious particles decreases.
5. Convalescence The final stage of infection is known as convalescence. During this
stage, symptoms resolve, and a person can return to their normal functions.Depending
on the severity of the infection, some people may have permanent damage even after
the infection resolves.