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Mycology & Parasitology

Terms in this set (98)

Homoxenous
Requires only one host
Heteroxenous
Infects more than one host
Trophozoite
Active feeding stage
Merozoites
Daughter cell resulting from schizogony (merogony, endopolyogeny)
Bradyzoite
Slow dividing cell
Tachyzoite
Rapid dividing cell, result from endodyogeny
Merogony
Multiple fissions for produce merozoites
Macrogamete
Large, quiescent, "female" gamete, waiting to be fertilized by a microgamete
Microgamete
Slender, active, "male" gamete
Oocyst
Fertilized egg
Sporocyst
In protozoa -- the stage of development found within a membrane within the oocysts (in trematodes, it is an asexual stage of development)
Sporozoite
Zoite that is inside the mature sporulated oocyst and is infections; result of sexual reproduction
1-host tick
Spends its entire developmental period, from larva to adult, on one animal

Note: The only other place we find a 1-host tick is in the environment -- adult female laying eggs, or unfed larval stage questing
2-host tick
Leaves the host as mature larva or mature nymph, molts on the ground, and seeks a second host
3-host tick
1. Feeds as larva on one host, leaves to molt

2. Feeds on 2nd host, leaves to molt

3. As adults, feed and mate on 3rd host
Primary myiasis
Requires living tissue for larvae to feed
Secondary myiasis
Feeds on dead, decaying tissues
Oviparous
Adults lay eggs
Ovoviviparous
Larva already developed in egg when it is laid
Viviparous
Live larvae passed from adults
Trichostrongyloidea
Smaller
Hairlike
Grazing animals

e.g. Ostertagia (brown stomach worm - cattle, ruminants)
Strongyloidea
Larger, stouter than Trichostrongyloidea
Ancylostomatoidea
Blood suckers
Arrested larvae

e.g. Ancyclostoma caninum (hookworm - dogs & cats)
Haemonchus contortus (Barber pole worm - sheep, goats, camelids; "essentially the hookworm of ruminants")
Oxyuroidea
Long, slender tail on females
Direct life cycle
Spiuridea
Insect or crustacean as IH
Trichinelloidea
Stichosome esophagus
Oviparous/viviparous
Rhabditoidea
Free-living form
Small, thin-shelled, larvated eggs
Filarioidea
Mosquito vector
Viviparous

e.g. Dirofilaria immitis (heartworm)
Metastrongyloidea
Usually indirect life cycle
Terrestrial snail/slug

e.g. Parelaphostrongylus tenuis/meningeal worm (White tail deer is DH, snail/slug is IH)
Ascaridoidea
Largest, most familiar roundworms of dogs, cats, horses

e.g. Toxocara canis (roundworm - dogs)
Parascaris equorum (roundworm - equine)
Toxocara canis
Dog roundworms

Transplacental transmission → puppies infected with L33* stage at birth

Somatic migration: Infective eggs ingested → larvae hatch, burrow through GI wall, portal vein to liver → circulate to alveolus (coughed up, swallowed, reside in GI tract) or somatic tissues → immunity develops → larval stages start to encyst w/in muscle → dampening of immunological response during pregnancy → L3 are released & infect fetuses

Non-somatic/GI only: Immunity does not develop, or Toxascaris leonina stays w/in lumen of GI tract (no trans-tracheal migration; does not travel to liver or lungs); re-exposure can occur
Parascaris equorum
"Sort of the analogy of Toxocara in the horse"

Predilection site for adult worms is the small intestine -- younger horses will present with potbelly, poor hair coat, potentially still larval stages migrating (older horses resistant to migration)

Infective stage is the larvated egg in the environment (egg containing L2)

There is no transplacental or transmammary transmission of Parascaris equorum -- entirely oral/fecal route!
Ancyclostoma caninum
Dog hookworm

Puppies are infected shortly after birth through migration of L3 → transmammary transmission
L3 undergoes molt w/in puppy → L4 → L5 adult stages can produce patent infection w/in 10 days (eggs being passed in the feces)

Most important thing isn't necessarily migration of larvae, but what the adults do -- i.e. attach, detach, and re-attach to the GI tract ("messy eaters") → leakage of blood & proteins from GI tract
Haemonchus contortus
Barber pole worm

Feeds in the same way as the dog hookworm -- adults latch on, take a plug of mucosa, etc.

Ingested L3 from pasture stays in the abomasal mucosa → molts to L4 → molts to L5 (adult)

Hypobiosis (dormancy)
Ostertagia
Hypobiosis: Larvae stay dormant in gastric glands for mos. before maturing into L4 and emerging into the lumen; ability of parasite to be immediately infective or undergo hypobiosis produces 2 unique clinical presentations of dz

Type I: Young animals ingest infective L3, which mature immediately into adults → watery green diarhhea, weight loss; diagnosis via fecal flotation (many eggs)

Type II: Young animals ingest infective L3, which undergo hypobiosis before massive maturation during the next grazing seaseon → extensive damage to abomasum, bottle jaw, watery diarrhea, weight loss; diagnosis via incr. abomasal pH & blood pepsinogen (because few eggs in fecal)
Parelaphostrongylus tenuis
Usually indirect life cycle via terrestrial snail/slug

White tail deer is the "true host"

Alpaca's meningeal worm
Aberrant migration of parasite into CNS can occur in small ruminants, horses, camelids; usually spinal cord, infrequently brain → inflammation
Clinical presentation: Ataxia, hindlimb weakness or paralysis with progression to forelimbs, circling, head tilt, twisted neck, depression, blindness
Diagnosis: Compatible history (deer in pasture w/ small ruminants), physical & neurologic exam, CSF analysis, necropsy is confirmatory
Dirofilaria immitis
Heartworm -- a viviparous parasite

The adults that reside in the pulmonary arteries are the disease-causing stage! "Bump up against" artery walls → inflammation; can become "knotted" and impede blood flow

Microfilaria are the infective stage to the mosquito -- L3 are the infective stage to the dog
Heartworm preventatives do not prevent infection -- they prevent disease!

Tx: Need to pre-treat dogs with doxycycline to eliminate the Wolbachia (carried by Dirofilaria immitis) before treating for heartworm disease; also decreases worm's ability to resist adulticide, for some reason
If you transfused a dog with blood infected with microfilaria, would that progress to heartworm disease in the recipient dog?
NO, it wouldn't!

Microfilaria are the infective stage to the mosquito -- L3 are the infective stage to the dog
Taenia pisiformis
Cysticercus metacestode form in IH

Rabbit is IH, dog is DH -- would find sexually mature adult passing eggs in a canine host; generally causes little harm to the DH

Life Cycle:
Proglottids have oncospheres inside; rabbit ingests egg from environment → w/in rabbit, egg passes through GI tract → evaginated oncosphere passes through GI tract wall, enters peritoneal tissues and liver → embryo develops into cystocercus → when dog eats rabbit, ingests cystocercus, which enters GI tract of dog and evaginates, passes through GI tract wall, elongates → amplification occurs in DH
Anaplocephala
Equine DH, environmental/oribatid mite IH

"The equine tapeworm" -- Anaplocephala spp. have a tendency to want to hook onto the ileocecal junction, which is important because can cause colic when heavily infected!

Cysticercoid metacestode stage

Contains tiny hooks that attach to the GI tract

Start growing and eventually producing proglottids
Dipylidium caninum
Flea larvae feed on environmental debris, ingesting D. caninum egg packets → within flea, egg packet pupates into cystocercoid → dog must ingest flea to perpetuate life cycle

Q: Why do we care?
A: Zoonotic; "tickles" dogs' perineum, causing "scooting"; offensive to client; reveals underlying flea or biting lice problem

Dx: Proglottid brought in by client (can be found in feces, on animal, on furniture... 😱 ), egg packet seen in feces, history of fleas and no dewormer
Diphyllobothrium latum
Individual eggs passed from gravid segments in feces (at this point in the cycle, NOT infectious) → in water, hatch into a motile, ciliated coracidium → 1st IH (copepod crustacean) ingests coracidium, which develops to a procercoid → 2nd IH (freshwater fish) ingests crustacean → procercoids migrate to muscles or viscera to form 2nd larval stage, the plerocercoidcercoid* → human/dog/cat ingests IH, and the plerocercoid matures into an adult tapeworm

Pathogenesis: In humans, macrocytic anemia due to vitamin B12 deficiency (taken up by tapeworm); infections in humans can last up to 30 years, passing 2-40 million eggs/day (~1 billion viable eggs over lifetime)!

Dx: Fecal sedimentation of tapeworm eggs that look like trematode eggs (yellow, operculated)
Fasciola hepatica
Acute fluke disease: Invasion of young flukes tunneling about the liver → inflammation
Secondary bacterial infection e.g. by Clostridium novyi + poorly oxygenated tissue = multiplication and release of bacterial toxins

Chronic fluke disease: Associated w/ presence of flukes; fibrotic ducts calcify to "pipe stem" structures
Animals exhibit loss of condition, general weakness, anemia, hypoproteinemia, bile duct hyperplasia
Paragonimus kellicotti
Dog/cat must ingest crawdad/crayfish that has the metacercariae on/in it

This particular fluke has a trophism for the lung and likes (but doesn't need) to live in pairs, for some reason ( → cystic inflammation around the pair of the them)

Produce unembryonated eggs in the lung, which are coughed up, swallowed, and passed in the feces into the environment → hatch, enter snail, amplification → encyst in a crayfish

If paratenic host ingests crayfish, dog/cat must ingest paratenic host for the cycle to continue
Avian schistosomes (Trichobilharzia spp.)
Causes "swimmer's itch" (Cercarial dermatitis)

If cercariae infect humans, die w/in the skin (humans are an aberrant host); upon subsequent exposures, can develop allergic-type inflammatory response

Adult trematodes reside w/in nasal cavity of geese → females lay eggs which are passed by the geese → eggs develop in aqueous environment → larva seeks snail, infects it → amplification → release of cercariae
Nanophyetus salmincola
Salmon poisoning
Ixodes scapularis
Blacklegged/deer tick

Long mouthparts

3-host tick; difficult to control, extremely good dz vector
Note: 3-host ticks tend to start with small mammals and proceed to progressively larger host preferences
Long life cycle

All Ixodidae females drop to environment to lay their eggs (can hold onto them for a while if conditions are not quite right), and females die once they lay their eggs!
Dermacentor variabilis
American dog tick

Found throughout USA and Hawaii; will infest human dwellings; cold intolerant and will persist in temperate regions, though can tolerate lower humidity (how they get established indoors)

3-host tick
Larvae & nymphs prefer dogs, will also feed on rabbits & rodents
Adults prefer dogs, will also feed on other mammals

Vectors: Ehrlichia canis, Babesia gibsoni, RMSF
Amblyomma americanum
Lone Star tick

Larval "seed ticks" have 3 pairs of legs, while nymphs & adults have 4 pairs of legs

Long mouthparts, painful bite

Vectors: RMSF, tularemia
Rhipicephalus sanguineus
Brown dog tick

Rhipicephalus (Boophilus) annulatus is a federally reportable tick -- causes cattle Babesia
Otobius
Spinose ear tick

Argasidae (soft ticks)
Idiosoma has a soft, leathery surface (no scutum)

Adults are not parasitic!
1-host tick: Dogs, cats, horses, cattle, pigs, etc.

Larvae feed 5-10 days, then molt (2 nymphal stages) → nymphs remain in ear for weeks to months → engorged nymph drops from host and crawls into crevices where it develops into an adult

Not a dz vector, but "extremely painful" and produce considerable damage to host's ear
Demodex canis
Follicular mange mite

Usually part of the natural flora of dogs, but some dogs have a genetic predisposition for developing skin dz associated with Demodex (only treat if the cause of skin issues)

Demodex in cats (more rare) is different from Demodex in dogs -- host-specific

A burrowing mite -- acquired early in life, from dam; complete life cycle on host w/in hair follicle
Sarcoptes scabiei (general)
Mange mite

Direct life cycle

Transmitted via close contact
All stages on host

Pathology: Burrowing mites → erythema, pruritis, scales, kenatinocysts, IgE mediated hypersensitivity
Cheyletiella
Walking dandruff

Superficial dwellers
Adult is motile, lives @ base of hair/fur/feathers; pierce skin w/ stylet-like chelicerae, engorging lymph; strong palpal claws used for grasping fur/feathers during feeding

Pathology: Mild to severe scaling dermatosis w/ variable pruritis in dogs/cats/rabbits; heavy infestation → hair loss, inflammation

Zoonotic!
Trombicula
Chiggers

Only larval stage is parasitic!
Not very host-specific -- will parasitize almost all domestic mammals

Eggs hatch → larvae find a host + attach → use chelicerae to feed on host's serous tissues for 3 days before falling off → molt to nymph, and then to adult stage

Nymphs and adults are free-living
Only 1 generation/year
Knemidocoptes
Scaly leg mite

Astigmatid, burrowing mite of poultry and domestic birds
Spends entire life on host -- burrows into unfeathered, scaled skin of feet and shanks
Females are ovoviviparous

Pathology: Exudates, crusty proliferative masses; in large numbers → lameness, deformity of feet/legs/claws, extensive hypertrophy of stratum corneum
Hypoderma spp.
Q: Why do we care? A: Damage to hide

Do not treat if you suspect larval stages are around the esophagus or spinal cord -- can be fatal; if you use the incorrect products during larvae migration, can have serious consequences

Hatch → penetrate skin → undergo a very long migration; get into somatic tissue and, depending on species, go to forelimbs or spinal cord area → during springtime, larval stages make the journey to the back of the animal's hide, where they form a breathing hole before warbles/bots fall out and pupate in the environment (primary myiasisiasis*)
Gasterophilus
Not pathogenic, "don't bother the horse"
Ctenocephalides felis
Found on cats and dogs!

Flea adult lays eggs, which fall to bedding → larvae molts → spins coccoons/pupates → adults

Pass Dipylidium caninum tapeworms

Flea allergy dermatitis

Most fleas are in the environment; environmental control a major component of flea control
Giardia intestinalis/lamblia/duodenalis
Flagellates of intestine & mucosa; trophozoites adapted for attachment to mucous epithelial cells of upper portion of small intestine (use of sucking discs)

Direct life cycle
Asymptomatic to clinical presentation (diarrhea, gas, intestinal malabsorption → greasy stool, cramps, nausea, dehydration)
Prepatent period ~1 week
Infectious stage: Cyst (immediately infectious)
Diagnostic stage: Trophozoite, cyst
Assemblages; some debate on zoonotic potential
Eimeria
"Coccidia" and "tissue cyst apicomplex"
Location: Endothelial cells

Direct life cycle
Infective stave is sporulated oocysts
Shed unsporulated
Cystoisospora
"Coccidia" and "tissue cyst apicomplex"
Location: GI mucosal cells of DH

Puppies, kittens, and swine

Direct and potential paratenic host
Infective stage is sporulated oocysts
Shed unsporulated
Cryptosporidium
"Coccidia" and "tissue cyst apicomplex"
May undergo multiple rounds of merogony
Asexual reproduction

Usual site of infection: GI tract (stays w/in brush border of epithelium), respiratory tract in some species
Zoonotic!

Direct life cycle
Infective stage is sporulated oocysts
Shed sporulated
Sarcocystis spp.
Likes the vascular endothelium, 1st and 2nd rounds of merogony → then enters striated muscle cell to form sarcocysts filled with bradyzoites

Generally a specific DH and a specific IH
Sarcocystis cruzi: canids & cattle

Indirect life cycle -- IH and DH
Toxoplasma gondii
"Coccidia" and "tissue cyst apicomplex"

Tachyzoites: Invasive, rapidly dividing
Bradyzoites: Quiescent
Neospora spp.
Neospora caninum -- similar to Toxoplasma gondii
Dog is DH, horses and ruminants may be IH

Vertical transmission -- variable outcome (paresis/incoordination, severe paralysis); several generations

Nonsuppurative inflammation, protozoa in perivascular spaces in brain stem and spinal cord

Dividing forms: Merozoites/tachyzoites and schizonts
Babesia spp.
Ticks as vector where sexual reproduction takes place
Tick picks up infected blood cells (larvae, nymphs, adults)

Transovarial transmission (between stages)
Transtadial transmission (into eggs/larvae)
Transtadial transmission
Between stages
Transovarial transmission
Into eggs/larvae
Prepatent
Developmental stage in an infection before agents produce evidence of their presence
Patent
Stage in an infection at which infectious agents produce evidence of their presence, such as eggs or cysts

Exposure to agent, incubation time are important
Trichuris vulpis
Whipworm

Direct life cycle (no IH!)
Infective stage: Larvated egg
Diagnostic stage: Eggs (in the feces)
Prepatent period: ~3 month period between when dog ingests egg, and when eggs can be found in the feces (Larvated egg ingested → encyst w/in mucosa of small intestine → undergo several molts)

Dogs (DH) are susceptible throughout their lives, but organisms can't be found in puppies younger than 2 months old, because parasites would still be in prepatent period!
Direct life cycle
Stage infective to host

No free-living stage

No other host involved for development (can be 1 host)

e.g. Trichinella
Indirect life cycle
Another host or vector required for development (2+ hosts)

Free-living stage

Parasite develops outside of host to an infective stage
Vector
Any agent (water, wind, or insect) that transmits a disease organism
Definitive host (DH)
Parasite reaches sexual maturity
Intermediate host (IH)
One that is required for parasite development, but one in which parasite does not reach sexual maturity; asexual
Paratenic/transport host
Does not undergo development, but remains alive and infective
Aberrant host
Incorrect host; may have infection, but can result in dead end for parasite (lacks adaptations)
What are the "big 5"?
1. Nematodes

2. Protozoa

3. Cestodes

4. Trematodes

5. Ectoparasites
a. Ticks & mites
b. Flies, fleas, and lice
Microsporum canis
Ringworm (dermatophyte)
Common for cats to carry it subclinically
Responsible for 40-70% of ringworm infections in dogs
Sporadically zoonotic

Contagious!

Septate hyphae
Microsporum persicolor
Epidermatophyte
Zoophilic and geophilic
Primarily seen in dogs
Microsporum gypseum
#1 dermatophyte of horses in the south

Poorly zoonotic
Trichophyton equinum
#1 dermatophyte of horses (outside of the south)
Trichophyton verrucosum
Most common dermatophyte in cattle
Microsporum nanum
Most common dermatophyte in swine
How is a Wood's lamp used to diagnose dermatophytes?
Tryptophan metabolites fluoresce

30-50% of Microsporum canis will fluoresce, but almost no Trichophyton will fluoresce (many false negatives)
What factors can cause false positives in a Wood's lamp diagnosis?
Ointments

Dead skin

Pseudomonas spp.
Malassezia spp.
Malassezia pachydermatis is the most significant Malassezia sp. in veterinary medicine

A dermatophyte; part of normal flora that causes infection due to underlying inflammation (allergies), antibiotic therapy, etc.

Very rarely zoonotic (only in severely immunocompromised individuals)
Sporothrix schenkii
Sporotrichosis is a subcutaneous mycosis

Thermal dimorphism
Septate hyphae

Typically head/neck/extremities; yeast form at body temp. can spread regionally
Rupture of granulomas → CMI (Th1, Th17)

Zoonotic purulent material in wound discharge!
Pythium insidiosum
Pythiosis is a subcutaneous mycosis

Typically appears in dogs & horses -- "swamp cancer," "leeches"

Chronic nonhealing granulomas can lead to bony involvement -- almost always require aggressive surgical treatment (debridement, excision, amputation) in addition to systemic antifungals
Zygomycosis
A subcutaneous mycosis caused by Mucor and Rhizopus spp. (aseptate hyphae)

Basiodiobolus, associated with the dung of tropical amphibians, reptiles, and bats, causes deep cutaneous infections

Mucomycosis only seen in severely immunocompromised patients

Common saprophyte contaminants in fungal cultures
Candida albicans
Candidiasis is an opportunistic systemic mycosis

A yeast that is part of the normal flora
Hyphae & pseudohyphae
Can cause mucosal infections of mouth, bladder (may ascend)

Peritonitis in dogs -- associated with rupture of upper GI/biliary tract -- results in dramatic thickening of serosa
Aspergillus fumigatus
Can cause an opportunistic systemic mycosis
Immunosuppression is NOT required for LOCALIZED disease

Ubiquitous in environment -- common contaminant
Rapid growth; mycetomas = fungal masses

Guttural pouch mycosis -- horse can bleed out if infection erodes internal carotid; aerial phase produces fruiting bodies -- conidia diagnostic for Aspergillus

Canine nasal Aspergillosus results in loss of bony detail in radiographs (DDx Pseudallescheria boydii)
Mycotic abortion in cattle due to A. fumigatus (or Mucor spp.) in feed
Mycotic keratitis in horses, dogs when spores invade corneal injury (Aspergillus, Fusarium, Alternaria spp.)
Cryptococcosis
An opportunistic systemic mycosis
Cryptococcus neoformans = ubiquitous, enriched in pigeon droppings
Cryptococcus gattii = associated w/ eucalyptus & Douglas firs; most often seen as nasal mass in a cat

Grows as a yeast -- tiny spore, gigantic capsule
Causes dz when immunosuppression OR high inoculum
Tropism for cooler tissues (respiratory, skin, CNS, eye); penetration of respiratory epithelium → granulomas

NOT ZOONOTIC because not acquired directly from animal!

One of the few fungal diseases for which there's an immunodiagnostic test available (detects exfoliation of capsular Ag)
Blastomycosis
A systemic mycosis = immunosuppression is NOT a requirement for infection

Dogs, humans (rare in other spp., "not really" zoonotic)
Thermally dimorphic (yeast at body temp.)
"Broad-Based Budding" is a diagnostic feature
Mold form is septate (an ascomycete)

Almost always inhaled from soil → almost always begins as a pulmonary infection (pyogranulomatous inflammation, CMI, multifocal nodules in the lungs)

Blastomyces dermatitidis infectious form is mold form; enhanced by corticosteroids; dx via urine Ag test (sensitive, specific, & affordable)
Histoplasma capsulatum
Found in bird/bat droppings
Cause disease in dogs/cats/humans

Thermally dimorphic, not zoonotic (similar to Blasto)
Looks almost just like capsule-deficient Crypto

Inhalation of mold → pulmonary lesions → dissemination to distant sites, especially GI → GI symptoms, wasting

Urine Ag test available, cross-rxn with Blasto but "tx is the same to doesn't matter"
Coccidioides immitis
"San Joaquin Valley fever"
Dogs, rarely cats, rarely horses
No direct animal → human spread = nott* zoonotic

TISSUE dimorphism
Grows much faster than other 2 systemic mycoses

Inhalation of infectious arthroconidia → spherules on alveoli → distribute endosporesres* systemically → severe hilar LN enlargement, multifocal granulomas in lungs, osteomyelitis (usually in extremities)
Variable prognosis -- disseminated dz is worse

Distinctive arthrospore fruiting bodies interdigitate between hyphae; serology is mainstay of diagnosis
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