Copyright 2011. PEER.tamu.edu

PathogensPathogens

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?

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.

Infectious Diseases are Caused by Pathogens

What’s a pathogen?

• 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?

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!*

Common Types of Pathogens

Fungi

BacteriaViruses

ProtozoaPrions

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:

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

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 nameStaphylococcus 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 cattleVaried in humans depending on exposure method

Bacillus anthracis is reportable disease responsible for outbreaks in cattle. Zoonotic, possible bioterrorism agent

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 diagramof prion*

Click here for PEER curriculum on proteins

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

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

Common Viral DiseasesDisease 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 virusTypically fatal

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

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

Protozoal DiseasesDisease Body System Symptoms ExamplesGiardiasis 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

TritrichomonasAffects 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 gondiiZoonotic, affects animals and humans

Babesiosis Circulatory Fever, anemia, sudden cardiac deathMalaria-like (Malaria is a protozoal disease)

Babesia microti in dogs transmitted by ticks

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.

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

Fungal DiseasesDisease System Symptom ExamplesDermatophytosis 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

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?

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

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 lotsof infectious agents

including arena viruses and hantavirus.

I can transmitEbola virus!

Think about it:Where Do Pathogens Hide When

Not Infecting People and Animals?

The soilBodies of waterSurfaces like farm equipmentThe skin of people and animalsIn the airIn body fluids

Where are those

pathogens?

Do you know the difference between “infectious” and

“contagious?” Infectious: pathogen can invade

the bodyContagious: pathogen can be

spread from one animal to another.

An animal that has a contagious condition will

probably have to be isolated from

otheranimals until it is determined that it

isno longer

contagious.

Quick Check #21. 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?

Different infectious diseases require different approaches for

prevention and control.

But for any disease, there are three key steps for dealing

with it.

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?

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.

• 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.

• 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.

• 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.

Some Current ResearchOver-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

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

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

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.

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.

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.

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?

Activity Time:Model on Disease Spread

ACHOO!

References:Veterinary Assistant HandbookFloron C. Fairies, Jr. Instructional Material ServiceTexas A&M UniversityFirst Edition

Merck Veterinary Manual http://www.merckvetmanual.com