This document discusses different types of pathogens that can cause disease in animals. It defines pathogens as microbes or agents that cause disease. The main types of pathogens discussed are bacteria, viruses, fungi, protozoa, and prions. For each type, examples are provided of diseases they cause along with associated symptoms. Common bacterial, viral, fungal and protozoal diseases affecting multiple body systems in animals are outlined. The document provides an overview of pathogens and infectious diseases in a veterinary context.

1. Copyright 2011. PEER.tamu.edu
Pathogens

2. Think about it:
• What sicknesses have
you had?
• Can you name an
infectious disease that
causes people or animals
to die?
• What is an infectious
disease that has been in
the news recently?

3. Epidemiology
• The branch of medical science dealing with the
transmission and control of disease.
• There are human physicians that study
epidemiology and also veterinarians that study
animal epidemiology. Both of these types of
epidemiologists also deal with diseases that are
transmitted from humans to animals and from
animals to humans.

4. Infectious
Diseases are
Caused by
Pathogens
What’s a
pathogen?

5. • Pathogens are microbes (microscopic
living organisms) or other agents that
cause diseases.
• Example: Foot and mouth disease is a
highly contagious disease of cattle,
swine, and other cloven-hoofed animals.
– It is caused by a viral pathogen called
picornavirus.
– It causes blisters in the mouths and
hooves of animals.
What are Pathogens?

6. Not all microbes are pathogens
• There are many types of microbes that are
actually beneficial to animals.
• Examples include the symbiotic bacteria
found in the digestive system of cattle and
horses that help them digest cellulose in
roughage.
• There can be one trillion or more microbes in
1 ounce of rumen fluid from a cow!*

7. Common Types of Pathogens
Fungi
Bacteria
Viruses
Protozoa
Prions

8. Bacteria
• Bacteria are single celled
organisms that are
prokaryotic.
• There are countless
numbers of bacteria on the
Earth but less than 1% of
them cause diseases.
• Bacterial infections make
an animal noticeably sick.
• Bacteria reproduce rapidly
and many give off toxins
which damage body tissue.
Bacteria are shaped like
cocci (spheres), bacilli
(rods), or spirilla (spirals).
A Closer Look at the types of Pathogens:

9. Bacteria
• Symptoms of bacterial infections
depend on the type of bacteria
but can include fever, pain,
swelling, vomiting, diarrhea,
formation of pus, and even
abortion.
• Body fluids can be sampled and
cultured to grow and identify the
bacterial pathogen.
• Antibiotics are the usual
treatment for bacterial infections,
but treatment can vary.
• Bacteria adapt quickly and may
become resistant to antibiotics.
Strangles in horses is caused by
Streptococcus equi bacteria
A positive culture for Streptococcus bacteria
A broad spectrum antibiotic

10. Common Bacterial Diseases
Disease Body System Symptoms Examples
Dermatitis Skin Inflammation, pruritus (itching)
skin lesions (bumps, blisters, scales,
crusts)
Staphylococcus aureus
Pyoderma Skin Purulent exudate (pus) from skin
lesions
Staphylococcus intermedius
Keratocunjunctivitis Eye Inflammation of cornea and
conjunctiva , pain, sensitivity to
sunlight, tears, squinting
“Pinkeye” is common name
Staphylococcus aureus
Otitis Externa Ear Inflammation of external ear canal
with reddening, drainage and itching
Staphylococcus
Rhinitis and Sinusitis Respiratory Inflammation of the membranes of
the nasal passages and sinuses.
Mucus nasal discharge, open-mouth
breathing, sneezing.
Strangles in horses caused by
Streptococcus equi
Pneumonia Respiratory Deep cough and difficulty breathing Staphylococcus aureus, including
methicillin-resistant S. aureus
(MRSA), Streptococcus species
Gastroenteritis Digestive Inflammation of stomach and
intestines, excessive salivation,
vomiting, diarrhea, straining,
abdominal pain.
Salmonellosis, colibacillosis,
eneterotoxemia
Metritis Reproductive Inflammation of uterus. Purulent
vaginal discharge, abortion,
premature birth.
Contagious Equine Metritis (CEM)
Abortion Reproductive Premature birth (expelling) of fetus
by pregnant female.
Brucellosis, leptospirosis and
camphylobacteriosis (vibriosis)
Mastitis Reproductive Inflammation of mammary gland or
udder tissue. Swollen, warm and
painful mammary glands.
Pseudomonas aeruginosa and
many other bacteria
Anthrax Skin, Digestive, Respiratory Sudden death in cattle
Varied in humans depending on
exposure method
Bacillus anthracis is reportable
disease responsible for outbreaks
in cattle. Zoonotic, possible
bioterrorism agent

11. Prions
• A prion is an infectious particle
(not a cell) made from an
abnormally folded protein found
on the surfaces of nerve cells.
• Prions are highly resistant to
heat, radiation, and disinfectants.
• The best known prion forms holes
in brain tissue, making the brain
look like Swiss cheese.
• The prion causes mad-cow
disease and may cause some
forms of Alzheimer's Disease.
Ribbon diagram
of prion*
Click here for PEER curriculum on proteins

12. Viruses
• A virus consists of a piece of
genetic material (RNA) housed
within a protective coat. Viruses
are not cells.
• The virus reproduces by
hijacking the cell of another
organism (host) and getting the
host cell to reproduce more
viruses.
• Most viruses cause disease and
are specific as to which type of
cell they will attack.
Rabies Virus

13. Viruses
• Symptoms of viral diseases are varied
and related to the types of tissues that
are infected. Viral diseases are
commonly associated with infections of
the skin, blood, liver, uterus, fetus,
brain, lungs, stomach, and intestines.
• Diagnosis is done by virus isolation,
ELISA* and PCR* testing. A decrease in
lymphocytes on a CBC can also indicate
a viral infection.
• Treatments are mainly supportive in
nature. This can include administering
fever reducers and allowing the animal
to rest. Antiviral medications are being
developed, but many are cost
prohibitive. Antibiotics kill bacteria and
have no effect on viruses.
Horses can be infected by at least
four different papilloma viruses
that cause warts
*See slide notes for more information

14. Common Viral Diseases
Disease Body System Symptoms Examples
Hepatitis General-many
organs involved
Vary from slight fever to
death
Infectious canine
hepatitis-
canine adenovirus 1
Anemia Blood Fever, weight loss,
abortion, low iron level in
blood
Equine infectious
anemia-equine
infectious anemia virus
Warts Skin Fibrous tumors of the skin
an mucous membranes
Papilloma virus
Pox Skin Skin lesions-bumps,
blisters, pustules, and
crusts
Cowpox
Pneumonia Respiratory Labored or “flank”
breathing, hard deep
cough, fever, leukocytosis
Bovine Respiratory
Disease (BRD)-
Mannheimia
haemolytica
There are MANY viruses
that cause Pneumonia
Abortion Reproductive Loss of fetus Equine
Rhinopneumonitis-
equine herpesvirus 1
Meningitis and
encephalitis
Nervous Invfammation of the brain
covering causing
blindness, paralysis,
wobbling, seizures, coma
and delirium
Encephalomyelitis,
distemper, parvovirus,
swine pseudorabies
Rabies Nervous Throat paralysis, behavior
change, change in bark
(dog), aggression in later
stages, lack of fear
Rabies virus
Typically fatal

15. Protozoa
• Protozoa are unicellular microbes
that can be parasites or predators
of other microbes. Many are
motile.
• Most need a moist environment to
live and many are transmitted
through water.
• Infections of small numbers of
protozoa are common, they are
seen quite often on microscopic
fecal examinations with the animal
showing no evidence of diseases.
• Infected animals are recognized as
carrier animals and as possible
sources of infection for susceptible
animals.
Protozoa found in human stool
sample
Giardia

16. Protozoa
• Symptoms vary considerably
depending on the protozoa involved
but often include intestinal
disorders such as diarrhea, weight
loss, and anorexia. Some protozoa
cause fever, flu-like symptoms, or
anemia.
• Diagnosis is conducted through
examination of blood, feces, or
urine for the presence of the
microscopic organisms. ELISA and
PCR tests can also be done.
• Many antiprotozoal agents are
available for treatment of protozoal
infections.
Direct fecal smear stained to detect
Cryptosporidium sp., a protozoan
parasite. (Source: CDC)
Toxoplasmosis is a zoonotic parasite
that causes disease in humans and
animals

17. Protozoal Diseases
Disease Body System Symptoms Examples
Giardiasis Digestive abdominal cramps, watery
diarrhea, vomiting, flatus
(gas), and fever
Giardia lamblia
Affects animals and
humans
Coccidiosis Digestive Thin, watery feces with
considerable amounts of
intestinal mucosa and
blood
Coccidia Eimeria and
Isospora, affects
animals and humans
Tricnomoniasis Reproductive venereal disease
characterized primarily by
early fetal death and
infertility
Tritrichomonas
Affects animals and
humans
Hexamitiasis Digestive Watery diarrhea, dry
unkempt feathers,
listlessness, and rapid
weight loss despite the fact
that the birds continue to
eat
Hexamita meleagridis
in turkeys and other
fowl
Toxoplasmosis Multiple Systems Cough, fever, loss of
appetite, and lethargy. Can
be passed to fetus
(congenital). Congenital
toxoplasmosis can damage
the baby's eyes, nervous
system, skin, and ears.
Toxoplasma gondii
Zoonotic, affects
animals and humans
Babesiosis Circulatory Fever, anemia, sudden
cardiac death
Malaria-like (Malaria is a
protozoal disease)
Babesia microti in
dogs transmitted by
ticks

18. Fungi
• A single or multi-cellular
microbe that can infect
various tissues in animals.
• Symptoms can include skin
lesions, hair loss and
respiratory or digestive
system disorders.
• Many antifungal drugs are
available and can be used
systemically as well as
orally.
Microsporum-the fungus that causes ringworm.

19. Fungi
• Diagnosis of fungal infections
may be done by examination of
skin lesions, fungal culture,
biopsies, skin immunologic
tests, or by blood tests.
• Treatment of skin lesions in the
patient usually includes a
combination of anti-fungal
drugs, topical medications and
anti-fungal medicated
shampoos for animals with skin
lesions.
• Systemic fungal diseases can
be serious and result in severe
tissue damage.
A horse with a severe case of ringworm,
which is cause by a fungus
Treatment includes bathing with
a medicated shampoo

20. Fungal Diseases
Disease System Symptom Examples
Dermatophytosis or
Ringworm
Skin Circular skin lesions with
hair loss, itching,
pruritus may or may not
be present
Microsporum canis in
dogs
Dermatophilosis or
Rain Gall/Rain Rot
Skin Lumpy, crusty, lesions
covered with hair that
can be pulled off
Dermatophilus
congolensis has a
variety of hosts-cattle,
sheep, goats, and horses
are affected most
frequently; and pigs,
dogs, and cats rarely
Aspergillosis Respiratory Fever, cough, chest pain
or breathlessness
Aspergillus fumigatus in
many species. Type of
mold.
Candidiasis or Yeast
Infection
Skin, Respiratory,
Digestive
Signs can be variable.
Diarrhea and listlesses
can be observed. Lesions
of the skin and mucosae
are generally single or
multiple, raised, circular,
white masses covered
with scabs.
Candida albicans in many
species.
Coccidiosis Digestive Diarrhea, dehydration,
hemorrhaging,
Eimeria and Isospora in
cattle, sheep, goats,
pigs, poultry, and rabbits

21. Quick Check #1:
1. What is a pathogen?
2. Name five kinds of pathogens.
3. How are these five kinds of pathogens
alike?
4. How are these five kinds of pathogens
different?

22. How Are Pathogens Spread?
• Pathogens can enter
the body through air,
food, water, sexual
interactions, skin
contact, blood
transfusions, etc.
• The body’s reaction to
an infection can vary
from a mild discomfort
to death.
Pathogen
For more on the immune
system, click here

23. Species Specificity
• Some infectious
diseases of animals
can be transferred
to humans.
• These are called
zoonotic diseases.
• All mammals can
transmit rabies but
raccoons and
skunks are the
most common
carriers.
I can transmit
Brucellosis
We can transmit lots
of infectious agents
including arena
viruses and hantavirus.
I can transmit
Ebola virus!

24. Think about it:
Where Do Pathogens Hide When
Not Infecting People and
Animals?
The soil
Bodies of water
Surfaces like farm equipment
The skin of people and animals
In the air
In body fluids
Where are
those
pathogens?

25. Do you know the difference
between “infectious” and
“contagious?”
Infectious: pathogen can invade
the body
Contagious: pathogen can be
spread from one animal to
another.
An animal that has
a contagious condition
will probably have to
be isolated from other
animals until it is
determined that it is
no longer contagious.

26. Quick Check #2
1. How can pathogens get in the body to
cause infection?
2. What is an infectious disease that can
be transmitted from an animal to a
human called?
3. Where are pathogens commonly found?
4. What’s the difference between being
infectious and being contagious?

27. Different infectious diseases
require different approaches for
prevention and control.
But for any disease, there are
three key steps for dealing
with it.

28. Three Key Steps
reak the cycle of transmission
ill the infectious agent
ncrease host resistance
Do you have some ideas on how to do these three things?

29. Vaccination
• Vaccination acts to increase the
host’s resistance to a pathogen.
• Vaccination is the administration of
a material that stimulates adaptive
immunity to a disease.
• Although it is not possible to devise
precise schedules for each vaccine,
certain principles are common to all
methods of active immunization.

30. • Newborn animals are passively
protected by maternal antibodies.
• If stimulation of immunity is
necessary at this stage, the
mother may be vaccinated during
late pregnancy.
• Because the exact time of loss of
maternal immunity cannot be
predicted, young animals are
often vaccinated at least twice to
ensure successful immunization.
Newborn animals acquire
immunity from nursing colostrum,
or the first milk produced by the
mother.

31. • The interval between vaccine doses depends on an
animal’s immunologic memory. The duration of this
memory depends on factors such as the nature of
the antigen, the use of live or dead organisms, and
the route of administration.
• Modern vaccines may induce immunity that persists
for an animal’s lifetime. Other vaccines may require
boosting only once every 2-3 years.
• Some vaccines, like Bordatella in dogs, are
recommended to be given every 6 months.

32. • Annual revaccination has been
the rule because this approach
is administratively simple and
has the advantage of ensuring
that an animal is regularly seen
by a veterinarian. It is likely
that this is more than sufficient
for most vaccines.
• The veterinarian in
a local area will be
most informed on
protocols for
vaccination.
PLEASE NOTE: Sample schedule only. Check with your local
veterinarian for a complete schedule for your area.

33. Some Current Research
Over-use of antibiotics has led to some bacteria
developing resistance. This is a big problem.
Scientists search for antibiotics that can replace
current ones to which bacteria have evolved
resistance.
Click here for more on antibiotic resistance

34. Delivery of nanoparticles to cells
to kill drug-resistant bacteria
• Nanoparticles are sized between 1
and 100 nanometers. Nanoparticles
are 100 times smaller than
bacteria.
• Antibiotics bound with nanoparticles
may be used one day to treat
infections, especially those that are
drug resistant.
• One study will allow nanoparticles
to be engineered as “small
machines that will carry large
numbers of antibiotic molecules to a
single bacterial cell, then release
and kill the cell.”
Artist’s rendition of nanoparticles

35. One New Strategy
•Many bacteria have genes
that can make products like
toxins or even antibiotics
against other bacteria.
•Forcing bacteria to grow
with another kind of bacteria
might cause them to start
secreting a new antibiotic to
kill off the competition.
•This new antibiotic could be
used to kill resistant
bacteria.
Staphylococcus aureus, cultured on an agar
plate for drug sensitivity test

36. Simple Dissolvable Patch for Vaccines
•Scientists have created a
dissolvable patch that is currently
being tested which will deliver
vaccine into the skin painlessly.
• Microscopic needles made from a
special blend of vinyl and freeze-
dried vaccine can be pressed against
the skin causing the needles to
dissolve in the body’s fluids.
•This eliminates risk of shared
needles and it can be easily
administered by health care
officials.

37. Edible Vaccines in Food
• Many studies are currently being
done to modify plants to contain
vaccines.
• Plant-based edible vaccines
would be safer, cheaper, and
could be grown—or freeze-dried
and shipped—anywhere.
• Vaccines delivered in food
trigger a two-way immune
response.
• Oral vaccines initiate a systemic
and mucosal immunity, which
fights infections in places where
germs first attack the body: in
the mucous membranes of the
nose, mouth, lungs, gut, and
genitals.

38. Using Plants to Make Vaccines
• Plants can be genetically modified to
produce vaccines as they grow.
• The process of growing the vaccine in a
plant is about three times faster, and
can cut costs by about 75 percent,
compared to conventional methods.

39. Quick Check #3
1. What are the three key steps for dealing
with infectious disease?
2. What is the purpose of vaccination?
3. What are some considerations when
designing a vaccination protocol?
4. What are some current areas of
research concerning vaccination and
treatment of infectious diseases?

40. Activity Time:
Model on Disease Spread
ACHOO!

41. References:
Veterinary Assistant Handbook
Floron C. Fairies, Jr.
Instructional Material Service
Texas A&M University
First Edition
Merck Veterinary Manual
http://www.merckvetmanual.com