1. Copyright 2011. PEER.tamu.edu
Pathogens
Copyright PEER.tamu.edu

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?
Answers will vary:
1. The cold, flu, stomach virus, strep throat, bronchitis, ear infection, chicken pox….
2. AIDS, pneumonia, H1N1 virus, yellow fever, anthrax, foot and mouth, rabies, malaria….
3. H1N1, SARS, Avian Influenza, Food-bourne e.coli

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. What are Pathogens?
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.
USDA Reference:
Images from:

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!*
*Reference:

7. Common Types of Pathogens
Viruses
Bacteria
Protozoa
Prions
Fungi

8. Bacteria A Closer Look at the types of Pathogens:
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.
An exercise: ask students how many kinds of bacteria can they name (anthrax, brucellosis, tetanus, diphtheria, E. coli, salmonella, and a few others are among those that many students should have heard about).
Prokaryotic is a cell that has no membrane bound nucleus or membrane bound organelles.
Eukaryotic cells have a membrane bound nucleus and organelles.
Bacteria are shaped like cocci (spheres), bacilli (rods), or spirilla (spirals).

9. Bacteria
Strangles in horses is caused by
Streptococcus equi 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.
A positive culture for Streptococcus bacteria
A broad spectrum antibiotic
Images from:
References:

10. Common Bacterial Diseases
Body System
Symptoms
Examples
Dermatitis
Skin
Inflammation, pruritus (itching)
skin lesions (bumps, blisters, scales, crusts)
Staphylococcus aureus
Pyoderma
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
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
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
Premature birth (expelling) of fetus by pregnant female.
Brucellosis, leptospirosis and camphylobacteriosis (vibriosis)
Mastitis
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
References:
Veterinary Assistant Handbook
Floron C. Fairies, Jr.
Instructional Material Service
Texas A&M University
First Edition
Pages X-1-1 through X-1-4
Merck Veterinary Manual
Centers for Disease Control:

11. Prions
Ribbon diagram
of prion*
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 diagrams are 3D schematic representations of protein structure and are one of the most common methods of protein depiction used today. The ribbon shows the overall path and organization of the protein backbone in 3D, and serves as a visual framework on which to hang details of the full atomic structure.
PEER Curriculum on Proteins found at
Mad Cow Disease Resource:
Alzheimer's Disease Resource:
Prion Resource:
Brain picture from:
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.
Currently, viruses are not considered living organisms, but there is debate among the scientific community on this topic.
Images from:
Rabies Virus

13. Viruses *See slide notes for more information
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
References:
Veterinary Assistant Handbook
Floron C. Fairies, Jr.
Instructional Material Service
Texas A&M University
First Edition
Page x-2-1
ELISA TESTING:
See last slide in the Immune System PowerPoint in this module.
Merck Manual General Information on viruses including PCR testing:
SNAP Tests for cats:
*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 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
Throat paralysis, behavior change, change in bark (dog), aggression in later stages, lack of fear
Rabies virus
Typically fatal
References:
Veterinary Assistant Handbook
Floron C. Fairies, Jr.
Instructional Material Service
Texas A&M University
First Edition
Page x-2-1 – x-2-3
Merck Veterinary Manual:

15. Protozoa found in human stool sample
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
Reference:
Veterinary Assistant Handbook
Floron C. Fairies, Jr.
Instructional Material Service
Texas A&M University
First Edition
Page x-4-4
Merck Veterinary Manual:
Fish and Whales use protozoa as food, making them an important part of the marine food web.
Giardia (pictured) is a common cause of food poisoning.
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
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
Hexamitiasis
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
References:
Veterinary Assistant Handbook
Floron C. Fairies, Jr.
Instructional Material Service
Texas A&M University
First Edition
Page x-4-4
Merck Veterinary Manual:
Pubmed Health:
More information on Toxoplasmois in humans:

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.
An exercise: ask students how many kinds of fungi can they name (ringworm and athletes foot are ones they may know about). Tell them how they can recognize ringworm in pets.
Images from:

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
Images from:
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
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
References:
Veterinary Assistant Handbook
Floron C. Fairies, Jr.
Instructional Material Service
Texas A&M University
First Edition
Page x-3-2
Merck Veterinary Manual:

21. Quick Check #1: What is a pathogen? Name five kinds of pathogens.
How are these five kinds of pathogens alike?
How are these five kinds of pathogens different?
A microscopic organism
Bacteria, viruses, fungi, protozoa, prions
The all have the ability to cause infectious diseases. They are very tiny, even microscopic.
Some are made of cells, some are not. Some have a nucleus, some do not. They belong to different Domains and Kingdoms.
They cause diseases in different ways.

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
This link is to the PEER curriculum on the Body’s Defenses. It explains in much more detail about how the body reacts to infectious agents.
For more on bodily reaction, if you have a live Internet connection, show the class a few pages of the PEER Web curriculum materials on bodily defenses in the Organ Systems module at peer.tamu.edu.
For more on the immune system, click here

23. viruses and hantavirus.
Species Specificity
I can transmit
Brucellosis
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.
We can transmit lots
of infectious agents
including arena
viruses and hantavirus.
I can transmit
Ebola virus!
Some carrier species are eventually killed by the organism, but can spread it to other species before they die. Other carrier species seem to co-exist without much damage from their infectious agents. As humans encroach on the habitats of wild animals, they get exposed to diseases that have not been a problem before to humans.

24. Where are those pathogens?
Think about it: Where Do Pathogens Hide When Not Infecting People and Animals?
Where are those pathogens?
The soil
Bodies of water
Surfaces like farm equipment
The skin of people and animals
In the air
In body fluids
Infectious agents can live on surfaces like a desk for hours or even days, like the cold virus.
This is why sanitary practices are needed to help prevent infections.

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.
The difference between infectious and contagious is that you can be infected without being contagious, but you cannot be contagious without being infected. Being infected may or may not produce symptoms of the disease.
Images from:
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 How can pathogens get in the body to cause infection?
What is an infectious disease that can be transmitted from an animal to a human called?
Where are pathogens commonly found?
What’s the difference between being infectious and being contagious?
Infectious agents can enter through air, food, water, sexual interactions, skin contact, blood transfusions, etc.
A Zoonotic Disease.
2. In the soil and on most surfaces.
3. Infected means the organisms has entered your cells but you may not show signs of the disease. Contagious means you can spread the organisms to others. You can be infected but not contagious. You cannot be contagious unless you are infected.

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

28. Three Key Steps reak the cycle of transmission
ill the infectious agent
Break the cycle: Keep animals isolated when sick, wash your hands often when working with sick animals, clean kennels/stalls/pens and replace bedding materials before using with another animal, limit exposure of healthy animals to animals whose health status is uncertain, when traveling with or showing animals, use own feed and water buckets, limit exposure to wild animals. People and animals that live/work/show in large groups or herds easily pass diseases from one to another.
Kill the Infectious Agent: Use antibiotics as directed, use hand sanitizers, disinfect surfaces with antibacterial/antifungal products.
Increase host resistance: Vaccinate animals, provide proper nutrition and exercise, allow newborn animals to receive colostrum from mother, reduce stress.
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.
Reference:
Merck Veterinary Manual:

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.
Reference:
Merck Veterinary Manual:

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.
Reference:
Merck Veterinary Manual:

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.
Reference:
Merck Veterinary Manual:
Vaccination schedule from:
Please do not use this as a vaccination schedule. This is included as an example ONLY.
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.
Reference:
Image from:
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
For more information on this study:
Nanoparticle reference:
Image from:

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
If your class has the sufficient biology background, this is a good place to talk about gene regulation. In this case, “alien” chemicals in the background produced by the competing bacteria have activated (or de-repressed) silent genes in the other bacterial strain.
Image of bacteria from:
Image of agar plate from:

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.
Story and picture from:
And

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.
For more information:
References:

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.
For more information on this topic see:
Image from:

39. Quick Check #3
What are the three key steps for dealing with infectious disease?
What is the purpose of vaccination?
What are some considerations when designing a vaccination protocol?
What are some current areas of research concerning vaccination and treatment of infectious diseases?
Break the cycle of transmission, kill the organism, increase host resistance
Increase host’s immunity
The age of the animal, the immune status of the animal, the type of vaccine, the amount of time since last vaccine
Research into new antibiotics to combat resistance, delivery of antibiotics by nanoparticles, using bacteria to create new antibiotcs, developing edible vaccines.

40. Activity Time: Model on Disease Spread
ACHOO!
See the notes in the Presentation Plan

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