Parasitology

General Parasitology

Parasites are generally considered pathogenic, even if the host shows no signs, because they can carry disease.
Endoparasite: Lives inside the host's body.
Ectoparasite: Lives on the surface of the host.
Obligate parasite: Requires a host to survive (e.g., lice).
Periodic parasite: Can live off-host but needs a host for nourishment (e.g., ticks).
Infections: Internal parasite invasion.
Infestations: External parasite invasion.
Size varies from microscopic to 1 yard in length.

Modes of Transmission

Bite
Blood transfer
Vomitus
Fecal-oral
Urine
Skin/hair contact
Eating infected host

The Host

Provides nutrients and protection.
Definitive host: Final host during the adult reproductive stage.
Intermediate host: Organism harboring the parasite during the larval or non-reproductive stage; often called vectors.
Life cycle: Developmental stages within intermediate or definitive hosts, including egg, nymph, larva, and adult stages.

Symptoms and Clinical Signs

Usually proportional to parasitic load.
Diarrhea, constipation, vomiting, and bloody stool from gastric endoparasites.
Lethargy and dull coat from ectoparasites.
Dehydration and anemia from blood parasites.
Coughing or dyspnea from respiratory parasites.
Heartworm symptoms: coughing, valve blockage, poor blood pressure, irregular heart rate.

Ectoparasites

Two common classes:
- Insecta: Fleas, lice, flies, mosquitoes (3 body parts, 6 legs).
- Arachnida (Acarina): Ticks and mites (2 body parts, 8 legs).

Collection Methods

Immobilizing species with sprays (e.g., alcohol) and picking them off.
Skin scrapings for burrowing species:
- Equipment: clippers, scalpel, mineral oil.
- Mineral oil slows down critters.
- Deep scrapings to draw capillary blood.
Cellophane tape: For superficial ectoparasites (clear tape, no mineral oil).
Swab for Ear Mites:
- Cotton-tipped applicator to collect dark, tar-like residue.
- Examine under low power with mineral oil.

Order Hemiptera (True Bugs)

Can be intermediate hosts for other parasites.
Bed bugs: Flattened, wingless pests affecting humans and animals.
Cause bites and allergic reactions.

Order Siphonaptera (Fleas)

Ctenocephalides felis: Common cat flea, also on dogs.
Laterally compressed, wingless, with jumping legs.
Siphon-like mouthparts for blood feeding.
Intermediate vectors for roundworms and tapeworms.
Flea dirt (digested blood feces) can be diagnosed on white paper.
Many pets are allergic to flea saliva.

Order Diptera (Flies)

Adults feed on blood, saliva, tears, mucous.
Larvae can develop under the skin or inside organs.
Bots: Larval stage of flies, tunnel under the skin.
Example: Horse bot burrows into mucous membranes, migrates to stomach/intestines, and passes in feces.
Cuterebra

Order Diptera (Mosquitoes)

Affect large and small animals; blood-sucking.
Spread malaria, yellow fever, elephantiasis, equine encephalomyelitis, and West Nile Virus.
Culex species are intermediate hosts for Dirofilaria immitis (heartworm).

Order Diptera (Deerflies and Horseflies)

Large with scissor-like mouths, inflicting painful bites.
Common to large animals, vectors for:
- Anthrax bacteria
- Equine Infectious Anemia
Musca flies feed on saliva, tears, and mucous.
- Transmit bacteria causing bovine pinkeye.

Myiasis-Producing Flies

Myiasis: Maggot infestation in skin wounds or matted hair with feces.
Larvae (maggots) feed off skin and tissues.
Can cause death by shock.

Order of Lice

Infestation: Pediculosis.
Dorsoventrally flattened, wingless insects.
Head: Mouthparts, suckers, antennae.
Thorax: Three pairs of legs, no wings.
Abdomen: Larger than thorax.
Egg (nit) cemented to hair shaft, hatches into nymph (like adult but without reproductive organs) in about 10 days, then adult.
Transmission by direct contact or via bedding/grooming items.
Generally species-specific.

Mallophaga (Biting/Chewing Lice)

Head larger than thorax.
Large mouthparts for biting and chewing.
Most often species-specific.

Anoplura (Sucking Lice)

Narrower head than biting lice.
Piercing and sucking mouthparts.
Infest all kinds of animals.
Can cause anemia.
Usually species-specific.

Class Acarina: Mites and Ticks

Not insects: 2 body parts, 8 legs, no wings.
Mites: Smaller than ticks.
Ticks: Largest ectoparasite.
Life cycle: egg, larva, nymph, adult.
Mite infestation: Acarisiasis.
Very small, round/oval bodies; legs may have suckers.

Otodectes cynotis (Ear Mite)

Common ear mite, spread by contact.
Diagnosed by otoscope and ear swab with mineral oil.
Eats waxy buildup, causes black, gooey discharge.
Extremely pruritic, foul odor.

Sarcoptes scabiei

Causes sarcoptic mange by burrowing in epidermis.
Each species has its own specific scabies mite.
Found on head, ears, ventral abdomen.
Extremely contagious and zoonotic.
Infestation: Pruritic rash, scaling, crusting.
Diagnosis: Skin scraping.
Notoedres cati: Feline scabies mite (also on rabbits).
- Found on ears, neck, face, feet; causes yellowish/brownish crusting.

Demodectic Mange (Demodex spp)

Clinical infestation: Demodicosis.
Reside in hair follicles and oil glands.
Cigar-shaped.
Infests dogs on head, muzzle, legs; cats on head.
Diagnosis: Deep skin scraping.
Clinical signs: Alopecia, scaling, follicular keratinizatio

Cheyletiella spp

"Walking dandruff".
Surface-dwelling, non-burrowing.
Motile, resemble dandruff flakes.
Round shape, large jaws.
Ingest dead tissue and fluids.

Knemidokoptes spp

Scaly leg/face mites.
Affects birds (budgies).
Clinical signs: Thick scaling on face around beak and leg area.
Burrow under skin, live off dead skin cells.

Tromibicula spp

Chiggers (red color).
Only larval stage (6 legs) is parasitic.
Attracted to CO2.
Eat dead tissue and fluids, do not burrow or feed on blood.
Digestive fluid causes pruritic rash.

Ticks

Orders based on scutum (shell) on backs.
Larger than mites.
Large biting parts (chelicerae) and sucking organ.
Voracious blood feeders, may cause anemia.
Intermediate carriers of diseases, zoonotic.
Life Cycle: egg, larva (6 legs), nymph, adult.

Family Argasid (Soft Shell)

Otobius: Spinose ear tick (SW deserts).
- Larval and nymph stages are parasitic, producing ulcers.
- Adults found in environment.

Family Ixodid (Large Scutum)

Ixodes pacificus (West Coast Deer Tick) and Ixodes scapularis (East Coast): Black-legged tick, carry Lyme Disease, very zoonotic.
Rhipicephalis: Brown Dog Tick (kennels).
- Vector for Babesia canis.
Dermacentor: American Dog Tick/Wood Tick (US).
- Carriers for Rocky Mountain Spotted Fever (RMSF), zoonotic.

Lyme Disease

Caused by Borrelia burgdorferi bacterium.
Black-legged tick (Ixodes scapularis) is the carrier.
Diagnosed via blood sample.

Rocky Mountain Spotted Fever (RMSF)

Caused by Rickettsia rickettsii bacterium.
Carriers: American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and brown dog tick (Rhipicephalus sanguineus).

Ixodes holocyclus (Paralysis Tick)

Females responsible for paralysis
Males not toxic.

Diseases Carried by Ticks

80 species in the U.S., only a dozen with health concerns.
Lyme disease: Bacterial infection via tick bite (36-48 hours attachment).
- Black-legged tick (deer tick) is primary vector in the east; western black-legged tick in the west.
Rocky Mountain Spotted Fever: Bacterial disease.
- American dog tick (east) and Rocky Mountain wood tick (west) are carriers.

Endoparasites

Live inside the body: intestines, organs, blood, heart, lungs, kidneys, eyes, brain, liver, bladder.
Signs and Symptoms of parasitic load (infection):
- D & V
- Constipation
- Anorexia
- Blood in the stool
- Excessive Mucous in the stool
- Lethargy
- Dehydration & Dysuria
- Anemia
- Coughing
- Dyspnea (difficulty breathing)
Parasites can infect:
- Oral Cavity Esophagus
- Stomach Intestines
- Other abdominal organs Bladder, Kidneys, Liver
- Lungs, Trachea, Tongue Heart and Cardiovascular
- Brain, sensory organs Skin, etc.

Collection

Fecal samples from ground or litter box.
Digital: Extracting feces from rectum with fingers.
Manual: Using a fecal loop.

Analysis

Analyze fresh feces within 6 hours or refrigerate for 24 hours.
Minimum of 1 gram of material.
Wear GLOVES during collection and lab process.
Frequent hand washing, workspace disinfection with bleach.

Examination

Macroscopic (Gross) Examination:
- Consistency: Formed, loose, watery, or hard.
- Color: Food present, unusual substances, vegetation.
- Blood: Bright red (fresh); Black (dried).
- Mucous: Digestive disorder or parasitic infection.
- Odor: Unique to Giardia or Coccidia.
- Visible parasites: Adult/larval worms, segments, eggs.
Microscopic
- Looking for ova or larva of parasites
- Direct smear
- Flotation
- Fecalyzer
- Sugar float and spin
- Cytology

Direct Smear

Put one drop of saline solution on a glass slide.
Using the applicator, retrieve a small sample of fecal matte from the sample container and add it to the solution drop.
Prepare a very thin film of the solution and fecal matter for microscopic examination by gently mixing the solution and fecal matter together.
Place a cover slip on the slide over the mixture
Examine under 4x first to focus, then increase 10x and 40x to view parasites.
Scan using the battlement pattern (snake like movement over the entire cover slip) to ensure reviewing the entire slide.

Why Direct?

Quick, inexpensive way to estimate parasites
Help with observation of motile (moving) protozoa
Only a small amount of fecal material needed
Use saline solution drop to slow down swimmers
Good way to see Giardia protozoa (protozoa to heavy to float)

Fecalyzer Flotation

Remove green inner piece and push the end into the fecal mater, collecting approx 1-2 teaspoons of fecal material.
Place fecal filled end of green tube back into the fecalyzer
Make sure the green inner tube of the fecalyzer is loose for mixing.
fill the container ½ full with Fecasol solution.
While holding the fecalyzer container, slowly twist the green inner tube to mix the contents of the fecalyzer.
After mixing, push the green inner tube firmly down in the fecalyzer.
Fill the container to the top with Fecasol solution forming a bubble on the top.
Place a cover slip on the bubble, very little will spill over.
Set the timer for 10-15 minutes
Once the timer has gone off, carefully pick up the cover slip and drop it onto the slide.
Review the slide completely on 10x and increase to 40x for detail examination.
Scan using the battlement pattern
Record your results on the patient chart and appropriate log.

How the float works

Able to examine larger amounts of fecal material in a concentration
Helpful if the parasite burden is low
Based on specific gravity of parasitic eggs vs. specific gravity of solution
Roundworm and Tapeworm Eggs are usually lighter than the Fecal Flotation solution, so they will float to the top
Solutions commonly used are Sodium Nitrate or Zinc Sulfate (Fecasol)
Fecal material and vegetation is heavier and will usually sink, but not always so there may be some need to thoroughly review; vegetation and pollen will collect near the top with eggs
You literally “look through the crap”

Specific Gravity of Solutions

Specific Gravity (SpGr) refers to the weight of an object compared to equal volume of water
SpGr of water is 1.000
Most parasite eggs are 1.05-1.24
Flotation solution needs to be greater than 1.24 so it is heavier then the eggs and therefore they float
Fecasol is less than or equal to 1.24 so some eggs will not float
Sugar solution is 1.27

Sugar Solution Flotation

Mix approx 2-5 grams fecal matter in a cup with 10mls sugar solution
Strain mixture into another cup
Place strained mixture into centrifuge tube
Place tube in centrifuge and spin at 1200rpm for 5 mins
Remove tube and fill the tube all the way to the top with more sugar solution forming a small bubble of fluid over the top of the tube
Place cover slip on top of tube
Let stand for 10 mins
Remove cover slip and place on a slide
Examine under scope at 10x and 40x
Record results

Common Endoparasitic Species

Protozoa
Nematodes
Cestodes
Trematodes

Protozoa

Unicellular organisms that can live on own and reproduce
Affect tissues within the definitive host—eat away at intestines, not just food
Some found in intestines—others found in blood
Simple and complex life cycles
Variety of hosts

Common Protozoa

Intestinal protozoans usually picked up by drinking stagnant water or more direct fecal-oral transmission
Giardia—Transmitted via fecal-oral route or contaminated water, has 2 stages the trophozoite mobile stage, and the oocyst egg stage, extremely small oocyst hard to find on a fecal float or direct, trophozoites don’t usually float.
Isospora—AKA coccidians common to puppies and kittens, very common to see in animals from puppy mills or kitten mills, very small eggs usually requiring 40x magnification, outside shell is thick
Toxoplasma—intestinal coccidian of cats, highly zoonotic, found in feline feces , only shed once by a feline, transmitted by fecal oral or inhalant route. It is more common to transmit to humans via improperly handled deli meat than cats.
Cryptosporidium—intestinal and respiratory, very small eggs need 40x, signs and symptoms of protozoan infection will be plenty

Common Protozoa cont.

Blood protozoa carried by vector; causes & immunity issues
Babesia canis most common and resides inside red blood cells (very small), two stages of life like most protozoans; vector is an ectoparasite (Brown Dog Tick) trophozoite stage is very small and looks pear shaped, will need blood sample and 100x oil immersion to see
Hepatozoon canis is found inside White Blood Cells; destroys immunity

Nematodes (Roundworms)

Found in almost any tissue of domestic animals from intestines, heart, skin, lungs, kidneys, blood, eye, nose, bladder and the brain
Diverse and complicated life cycles
Most eggs or larva are passed in the feces of the host
Wide range of size
Variety of hosts

Toxocara spp

Toxocara Canis, Toxocara Cati, Toxascaris leonia Common dog and cat roundworm
Referred to as ascarids
Live in the small intestines
Canis and Cati usually come from fecal–oral route and the life cycle is completed in the intestines
Leonia is usually found in rodents and the life cycle is completed by the carnivore eating the rodent and the worm settles in the intestines
Canis and Cati can also pass through the uterus into the fetus and into the mammary glands and the babies ingest the eggs during nursing.

Ancylostoma caninum (nematode)

Hookworm
Lives in the small intestines
Hooks onto the intestinal wall with very sharp teeth
Feeds by drinking the host’s blood
Causes anemia, and possibly long-time iron deficiencies

Trichuris Vulpis (nematode)

Whipworms
Lives in the large intestines and cecum
Burrow into intestinal wall and feed on the blood
Can cause diarrhea, anemia, mucus diarrhea, hemorrhagic diarrhea

Pin worms

Common in Horses
Worm comes out of rectum during dark hours and lays eggs around anus and then retreats back
Mainly resides in the large intestines
Horses are very itchy, get bristle brush looking tail from rubbing hind end on fence or trees
Use the tape technique to diagnosis

Strongyloides (nematodes)

Common Threadworm
Named after its thin diameter
Larva penetrates tissue into the bloodstream and migrates to lungs
Larva are coughed up and swallowed into intestines
Threadworms are found in all sizes in domesticated animals
Can also be free living; live and mate outside the body

Visceral larva migrans

Caused by roundworm larva able to migrate to visceral organs from intestines
Transmission by ingestion of contaminated food and many organs can be affected
Once the worm settles in the heart, lungs or brain, it’s almost always fatal, no cure

Cutaneous Larval Migrans

Caused by hookworm and threadworms
The larval stage penetrates the skin and migrates to the subepidermal layer
Causes crusty, scaly pruritic lesions
Larva can travel 1-2cm per day
Usually self limiting, 1-2 months
Can cause a secondary bacterial infection

Ocular larva migrans

Caused by ingested roundworms eggs migrating to eye
May cause permanent visual impairment, even blindness in some cases

Diroflaria immitis (nematode)

Heartworm
Culex mosquito is the vector , live in vector 7-14 days at temp of 80 degrees C or above, if temp falls below 80 development stops
Heartworm preventives should be administered 30 days prior to travel
Adult heartworms settle in the chambers of the heart and lead to clogged valves, inadequate blood volume and usually death

Heartworm cont.

Test for heartworm by blood sample looking for eggs and microflaria (young worms)
Prepatent period is 6 months for an immature worm to fully develop, signs of infection may not become apparent until months after full maturation
Prevention of the growth of the larva via medication is the key as is control of mosquitoes around the animal

Cestodes (Tapeworms)

Flatworms that are ribbon-like and divided into segments called Proglottids
Scolex (head) attaches to the wall of the intestines
Some have suckers on scolex and some have Rostellum (hooks) for anchoring
Much simpler life cycle than most roundworms, normally only found in the intestines.
Proglottids are released in the feces and when dried look like rice
Proglottids contain the egg packets for future generations
Cestode eggs are common in packets with 30 eggs in each packet
Variety of hosts

Dipylidium caninum

Intermediate host is the common flea

Taenia pisifermus

Intermediate host is rodents or rabbits

Echinococcosis Hydatid disease

Fecal oral ingestion of egg or larva and migrates to liver where it incysts and causes a large hepatic tumor

Trematodes (Flukes)

AKA flatworms, Unsegmented with leaf shaped bodies
Found in the intestines, liver or lungs of hosts
Hermaphroditic (A fluke is both a Male and Female with organs of each)
Eggs are passed with the feces of the host
Variety of hosts

Schistosomes

Clinical term for blood flukes in circulatory system
Lives as a parasite in snails
Needs avians to complete life cycle
Penetrating skin of mammals is an accident and will eventually die
Horrible red rash and very pruritic