Parasite: Protozoan Parasites, Giardia & Hexamita

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5 Groups of Protozoan Parasites

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1. Flagellates - all possess flagella at some life stage

2. Ciliates - all possess cilia at some life stage

3. Amoebae - all use pseudopodia for locomotion at some life stage

4. Apicomplexa - the coccidians & hemosporidians

5. Microsporida - Highly specialized (protozoa-like) fungi - dominant life stage is a spore

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Flagellates

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- all possess flagella at some life stage

1. Giardiasis

2. Spironucleosis (Hexamitosis)

3. Trichomoniasis - Bovine, Avian, and Feline

4. Histomoniasis

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Ciliates

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- all possess flagella at some life stage

1. Balantidiosis

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Amoebae

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- all use pseudopodia for locomotion at some life stage

1. Intestinal amoebiasis - mammals

2. Intestinal amoebiasis - reptiles

3. Amoebic meningoencephalitis

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Apicomplexa

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- The coccidians & hemosporidians

1. Enteric Coccidians - Avian, Bovine, Ovine/Caprine, Equine, Rabbit, Swine, Canine, Feline

2. Cryptosporidiosis

3. Tissue cyst-forming cociccidians

- Toxoplasmosis

- Neosporosis

- Sarcocystosis

- EPM

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Microsporida

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- Highly specialized (protozoa-like) fungi - dominant life stage is a spore

1. Encephalitozoonosis

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Protozoan Parasites: General Characteristics

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- protozoa are a heterogenous group of approximately 50, 000 known species, many of which are parasitic

- protozoa are responsible for some of the most important diseases of animals & humans

- protozoan parasites kill, debilitate & mutilate more people in the world than any other group of disease organisms

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Host Range

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- all animals are susceptible

- some protozoan parasites have highly specific host ranges (e.g. Eimeria)

- Others are less discriminate and will infect any host e.g. Giardia & Cryptosporidium

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Site of Infection

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- most organs & tissues e.g. intestine, muscle, brain, liver & blood

- some live free within the intestine or blood while others are intracellular

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Morphology

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- single-celled eukaryotes & therefore most have a typical complement of organelles (nucleus, mitochondria, endoplasmic reticulum, golgi apparatus) surrounded by a plasma membrane

- simple appearance but some have developed complexity through specialized organelles that aid in attachment, locomotion, feeding & cell entry

- Glycosomes (contain glycolytic enzymes)

- Kinetoplasts (contain extrachromosomal DNA - modified mitochondria)

- Rhoptries (cell invasion)

- Locomotion occurs by the use of flagella, cilia, pseudopodia or other specialized methods

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Life Cycle

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- Reproduction can be asexual, sexual or a combination of both

- Asexual e.g. budding, binary fission or schizogony (multiple fission)

- Sexual reproduction involves fusion of identical gametes (isogametes) or gametes that differ in size (anisogametes)

- Some have a cyst stage (infective or resting stage) with a resistant covering that protects from environmental factors. Some protozoa also encyst within the host's tissue (e.g. Toxoplasma)

- Life cycles may be simple occurring with a single host (e.g. Isopora) while others are complex and involve multiple hosts (intermediate & paratenic)

- Some infect hosts directly while others rely on a vector (e.g. insects) for successful transmission

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GI Protozoa Parasites: Dog

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- Giardia Small Intestine

- Cryptosporidium Small Intestine

- Isopora Small Intestine

- Sarcocystis Small Intestine

- Neospora Small Intestine

- Entamoeba Colon

- Balantidium Colon

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GI Protozoa Parasites: Cat

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- Giardia Small Intestine

- Trichomonas Large Intestine

- Cryptosporidium Small Intestine

- Isospora Small Intestine

- Sacrocystis Small Intestine

- Toxoplasma Small Intestine

- Besnoitia Small Intestine

- Entamoeba Colon

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GI Protozoa Parasites: Cattle

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- Giardia Small Intestine

- Trichomonas Reproductive Tract

- Cryptosporidium Small Intestine & Abomasum

- Eimeria Small & Large Intestine

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GI Protozoa Parasites: Sheep & Goats

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- Giardia Small Intestine

- Cryptosporidium Small Intestine

- Eimeria Small & Large Intestine

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GI Protozoa Parasites: Swine

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- Giardia Small Intestine

- Cryptosporidium Small Intestine

- Eimeria Small Intestine

- Entamoeba Colon

- Balantidium Colon

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GI Protozoa Parasites: Horses

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Giardia Small Intestine

Cryptosporidium Small Intestine

Eimeria Small Intestine

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GI Protozoa Parasites: Pet Birds

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Giardia Small Intestine

Trichomonas Crop

Cryptosporidium Small Intestine/Airways

Eimeria Small Intestine

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GI Protozoa Parasites: Poultry

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Giardia Small Intestine

Trichomonas Crop

Hexamita Small Intestine

Histomonas Cecum & Liver

Cryptosporidium Small Intestine

Eimeria Small & Large Intestine, Cecum

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GI Protozoa Parasites: Rodents & Rabbits

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Giardia Small Intestine

Cryptosporidium Small Intestine

Encephalitozoom Kidney, liver, brain

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GI Protozoa Parasites: Reptiles & Amphibians

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Giardia Small Intestine

Entamoeba Intestine

Cryptosporidium Stomach/SI

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Giardiasis: Agent & Host Range

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- common intestinal disease of mammals& birds found worldwide (cosmopolitan), esp. in warmed climates, causes by various Giardia spp.

- Giardiasis is recognized zoonosis

- Often called "beaver fever" in humans

Broad host range: Giardia duodenalis = intestinalis = lamblia

- most important species of Giardia in vet med

- wide range: dogs, cats, cattle, sheep, birds & humans

- animals = potential reservoir for human infections and vice versa

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Giardiasis: Site of Infection

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- duodenum & upper small intestine

- Giardia attached to the brush border of epithelial cells by a ventral sucking/adhesive disk

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Giardiasis: Morphology (Trophozoite)

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- 2 life stages: Trophozoite & Cyst

Trophozoite

- motile feeding stage, non-infectious

- bilaterally symmetrical, pyriform to ellipsoidal in shape, convex dorsal surface, a ventral sucking/adhesive disk, axostyle & 2 median bodies (specialized microtubules)

- approimately 12-20um long, by 7-10 um wide

- 4 pairs of flagella, binucleate (2 diploide nuclei) "Monkey Face"

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Giardiasis: Morphology (Cyst)

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- infectious stage (immediately infectious to host)

- environmentally resistant ~2 months w/ideal conditions (temp/hum)

- oval shaped, 9-12um long by 7-9um wide

- internal structures visible with light microscopy

- contains 4 nuclei (ie. 2 trophozoites/cyst)

- axostyle

- median bodies

- karyogamy (fusion of nuclei) ie. "Sex in the cyst"

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Giardiasis: Life Cycle

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- simple direct life cycle, cysts ingested by the host & excyst after exposure to both acid of stomach & alkaline of small intestine to release 2 trophozoites into duodenum

- trophozoites reproduce by asexual binary fission & feed & colonize SI

- severity of disease is dependant on the number of feeding trophozoites

- trophozoites encyst in response to increasing conc. of bile in feces

---> ie. reabsorption of water, dehydrated feces as it passes through intestine towards, rectum, therefore bile conc. increase at same time as free cholesterol decreases

- both cysts & more rarely, trophozoites can be passed in feces

- cysts resistant & survive (infectious stage), where as trophozoites are fragile & die quickly (non-infectious)

- 10^6 cysts per g of feces

- intermittent shedding of cysts

- PPP = 7-10 days

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Giardiasis: Transmission

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- via cysts (immediately infectious)

- direct: fecal-oral route is most important

- waterborne transmission common in human outbreaks

- cysts highly contagious & ingestion of a few as 10-100 cysts can establish an infection

- cysts are susceptible to desiccation but remain viable in cool moist areas for ~2 months

- cysts are resistant to "conventional" water disinfectants (ie. chlorination, filtration)

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Giardiasis: Prevalence

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- ubiquitous in the environment but varies among populations and geographic regions

- infections are most common in young animals (including humans) & exacerbated by stressful situations, poor sanitation/hygiene & crowded confinement conditions (eg. barnyards, kennels, catteries, shelters, pet stores, puppy mills & for humans, day care facilities)

Dogs & Cats Livestock Birds

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Giardiasis: Pathogenesis

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- highly variable & still controversial in some species as both parasite & host factors contribute to disease

- severity of disease dependent on dose of infection ie. number of cysts ingested

- trophozoites do not invade tissue (normally) but instead attach to the brush border of the mucosal epithelium of the duodenum & upper small intestine

- trophozoite colonies result in diffuse shortening of microvilli (sometimes villus atrophy) which reduces the absorptive surface area (malabsorption) of the SI & results in decreased intestinal enzyme activity (eg. disaccharidases) & malabsorption of nutrients (glucose esp.), electrolytes and water

---> results in increased intestinal motility of digesta (decreased transit time)

- in some animals, enterocyte injury by the parasite disrupting tight junctions thereby increasing intestinal permeability & destruction of enterocytes

- this may lead to more severe chronic intestinal disorders eg. Inflammatory bowel disease, Chron's disease & food allergies by exposing immune system to novel antigens

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Giardiasis: Clinical Signs

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- most infection are asymptomatic

- if so; typically small bowel diarrhea (usually self-limiting) but can be acute of chronic & often will reoccur

- clinical signs range from slight abdominal discomfort to severe abdominal pain and cramping, explosive water, pale, foul-smelling diarrhea with malabsorption

- steatorrhea (fat in stool) is common as is anorexia & some vomiting

- in people, acute giardiasis develops after 1-14 days (avg ~7 days) & can last 1-3 weeks

- dogs, PPP 1-2 weeks & can last 1 day to months

- extra-intestinal signs of urticaria & pruritus (allergic diseases) have been reported in both dogs, humans & birds

Eg. feather picking (allergic disease) in cockatiels (associated with giardiasis)

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Giardiasis: Diagnosis

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- "most commonly mis, under or over diagnosed parasite in vets"

- Requires multiple fecal samples (3 consecutive or 3 over 5 days) as cyst shedding is intermittent

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Giardiasis: Fecal Flotation

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- Gold Standard: fecal flotation with centrifugation in ZnSO4 (with or without Lugol's iodine stain)

- cytoplasm within cysts collapses producing a crescent shaped refractile osmotic artifact

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Giardiasis: Direct Smear

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- saline smear of fresh diarrhea, trophozoites movement (via flagella) - "falling leaf"

- trophozoites die quickly so sample must be observed soon after collection (ie. per rectum sample collection) or within ~20-30 mins of 'deposit' & kept at body temperature in humid environment to avoid desiccation

- cysts may be observed in high number

- Lugol's iodine can be used to stain both trophozoites & cysts

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Giardiasis: Antigen Detection

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- detect Giardia - specific antigen

- ProSpec T Fecal ELISA (micro plate - multiple samples) - detect infections in cats & dogs (100 & 96%, sensitivity & specificity respectively)

- IDEXX SNAP Giardia test (lateral flow ELISA - individuals samples)

- based on cyst wall protein released into the feces during encystation

- approvved for cats & dogs (>90% sensitivity & specificity)

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Giardiasis: Treatment

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- no licensed treatments

- anti-giardial therapy focuses on the trophozoite stage not the cyst

- (Panacur) & (Flagyl) used off-label alone or combo

- Dtrol Plus is effective

- most current treatment protocols recommend fenbendazole

- clinical resistance

- many ases of treatment failure are most likely cause by re-infection

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Giardiasis: Vaccination

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- Giardia Vax to aid in prevention of disease & cyst shedding by Giardia in dogs

- Claim of 1 year protection in healthy animals 8 weeks of age & older

- Contains killed Giardia. Dosage: 1ml dose subcutaneously

- 2nd dose is given 2-4 weeks after 1st vaccination

- annual re-vaccination is recommended

- vaccinated dogs may still shed viable cysts & therefore owners should continue to use proper hygiene & sanitation practices

- a few studies showing variable efficacy (no significant differences between vaccinated animals & controls), dogs cats and cows!

- not recommended by American Animal Hospital Association 2006

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Giardiasis: Control

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- good hygiene & proper sanitation to limit exposure to infectious cysts

- remove or reduce stressful situations if possible

- cysts can stick to the fur & be a source of re-infection, the positive animal should receive a bath at least once during treatment

- disinfectant on surfaces - bleach & Lysol (VIM) with high contact times:

- 15-20 minutes to ensure inactivation of cysts

- hot, soapy water also works

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Spironucleosis (Hexamitiasis or Hexamitosis)

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General Taxonomy: Flagellate

Agent & Host Range:

- Spironucleus (Hexamita) meleagridis - turkeys & game birds

- Spironucleus (Hexamita) columbae - pigeons

- hexamitosis = infectious catarrhal enteritis of birds (turkeys, pigeons, quail, pheasants, partridge, ducks & peafowl)

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Spironucleosis: Morphology

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Trophozoites

- oval shaped, 6-12um long

- bilaterally symmetrical with 8 flagella

- binucleate with prominent nucleoli

Cyst

- rarely formed

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Spironucleosis: Life Cycle

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- direct life cycle: trophozoites is the infectious stage, reproduce via binary fission

- fecal-oral route of transmission (feces containing trophozoites or cysts contaminate food or water)

- trophozoites colonize crypts of duodenum & upper jejunum

- disease of young birds (1-9 weeks old) recovered adults act as asymptomatic carriers

- heavy losses in outbreaks in ring-necked pheasants

- chickens not typically affected

- hexamitosis is a problem in every commercial turkey-producing area

- major problems occur in localized areas during a particular year, followed by one or more years in which incidence is low

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Spironucleosis: Pathogenesis

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- catarrhal enteritis (inflammation of the mucous membranes) and atony

- results in distension of upper small intestine

- swollen, bulbous, liquid filled small intestine

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Spironucleosis: Clinical Signs

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- listlessness, inappetence, anorexia

- birds huddle together near heat source & chirp constantly (pain?)

- greenish-yellow, foamy or watery diarrhea

- rapid weight loss due to diarrhea (dehydration)

- convulsions due to lowered blood glucose levels shortly procede death

- affected birds that survive remain stunted

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Spironucleosis: Diagnosis

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- history, clinical signs & microscopic examination of intestinal contents

- trophozoites detected in fresh wet mounts of intestinal contents of the duodenum

- confounding flagellate organisms in the cecae are not disease producers

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Spironucleosis: Treatment & Control`

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- remove carrier birds & disinfect buildings, feeders & waterers

- separate adult & young birds or use an all-in/all-out strategy

- biosecurity: prevent contact between turkey poults & captive/wild birds

- chlortetracycline & oxytetracycline used w/food animals: variable success

- Drugs** for non-food animals (pet birds)

- treatment does not substitute for adequate sanitation & management programs