6.6 Protists 3 Flashcards
Haemospororid Parasites
-Leucocytozoon spp.
-Haemoproteus spp.
Leucocytozoon spp.; host, site of infection, transmission
- found within erythrocytes wild or domestic birds
- locally, domestic ducks highly susceptible
- wild species (esp. Black ducks) are resistant
- transmitted by simuliid flies (blackflies)
Leucocytozoon spp. transmission, effects
- transmitted by simuliid flies (blackflies)
- transmitted in the spring to ducklings shortly after hatch
- may get high mortality
Haemoproteus spp.; host, site of infection, stages of life that cause pathogenicity
- found within erythrocytes of wild and domestic birds
- gamonts cause no pathological changes
- asexual stages within endothelium appear to be the primary cause of pathogenicity
Haemoproteus spp. transmission, when they are a problem
- usually transmitted by midges (no-see-ums) or hippoboscid flies
- often seen as a problem in captive wild birds (especially raptors)
- merogonic development may be activated by stress/brooding
Flagellates; General Characteristics; hosts, site of infection, type of life cycles
- Found in any animal, host-specific or not
- Some infect mucosal sites
- Mucosal parasites generally form cysts and have direct life cycles
- Some infect blood
- Blood borne parasites generally use vectors and have complex, multi-host life cycles
Flagellates; Major Groups
- Diplomonads (Giardia, Hexamita)
- Trichomonads (Trichomonas)
- Amoeboflagellates (Histomonas, Dientamoeba)
- Kinetoplastids (Trypanosoma, Leishmania)
Giardia spp.; Site of Infection
Duodenum and upper small intestine
Giardia spp.; Morphology
Pyriform trophozoite with:
> 8 flagella
> 2 nuclei
> prominent ventral disc
(highly characteristic “face-like” appearance)
Cyst is a rounded up trophozoite:
> about 9 to 12 um
> containing 4 nuclei when mature
Giardia spp.; Life Cycle
- like most mucosal flagellates, Giardia spp. have a simple, direct (monoxenous) life cycle involving the formation of cysts
- fecal-oral contamination with encysted forms is main route of infection
- cysts excyst in new host to form 2 trophozoites to initiate new infection
cysts passed in feces
>ingested by difinitive host
>excystation
>trophs attach to epithelial cells of intestine
>reproduce by binary fission
>trophozoite in intestine
>encystation…
Giardia spp.; Pathogenesis
- known to cause diarrhea in a variety of hosts
- cross-transmission between hosts is still controversial
(strains are better adapted to particular hosts but can infect other hosts – c.f. Cryptosporidium) - blanket epithelium of duodenum and upper small intestine causing a malabsorptive enteritis with diarrhea
- fat absorption affected > fatty diarrhea
Giardia spp.; Clinical Signs
- foul smelling, fatty diarrhea
- blood may be found in feces, especially with the chinchilla
- lesions at site of infection consist of acute focal inflammation, increased mucus
- may migrate to bile duct causing clinical signs
Giardia spp.; Diagnosis
- small oval cysts can be found on standard fecal flotations using ZnS04 (NOTE: sodium nitrate collapses cysts)
- smears can be stained using IFA for specific diagnosis–usually in human diagnostic labs only
- trophozoites may be seen in very watery diarrhea if kept warm and examined in saline directly - floats will kill trophozoites
- solid substrate ELISA tests now available for fecal antigen shed by Giardia spp. (e.g. ProSpecT® Giardia Rapid Assay - ~$25/test)
Giardia spp.; Treatment
- metronidazole (Flagyl) off-label
(50 mg/kg daily for 5 consecutive days) - fenbendazole (off-label) – efficacy?
Giardia spp.; Prevention
- a vaccine was marketed that is designed to reduce cyst shedding and severity of clinical disease in dogs – limited effectiveness – no longer on market
- Chemically-killed cultured trophozoites
- given annually
Trichomonas spp.; General - Order Trichomonadida; hosts, site of infection, transmission
- most animals infected, including humans
- usually in GI tract but also in urogenital organs
- found in crop and intestines of birds
- no cysts formed - direct transmission
Trichomonas spp.; Morphology
- single nucleus
- 3 to 5 flagella with one flagellum attached to body by an undulating membrane
Trichomonas spp.; Life Cycle
- divide by simple binary fission
- direct transmission of trophozoites
Trichomonas spp.; Pathogenesis in various species
- Cattle - a venereal disease
> cows suffer vaginitis, early abortions
> bulls remain infected for life if not treated - Pigs - non-pathogenic
- Horses - infects cecum and colon
- Birds - many susceptible to severe infections of the crop and esophagus
Trichomonas spp.; Diagnosis
- direct smears looking for trophozoites
- culture of swabs for 3 to 7 days
Trichomonas spp.; Birds - Pathogenesis
- oral trichomoniasis most common
- pigeons highly susceptible because they feed their young using “crop milk” – exfoliated crop epithelial cells (and parasites)
- oral cankers or plagues that may resemble “thrush” (oral candidiasis, a fungal infection)
Histomonas meleagridis; Life Cycle
- divides by binary fission, non sexual cycle
- direct fecal-oral transmission rare - NO cyst
- transmitted within Heterakis sp. (cecal nematode) eggs
- trophozoites eaten by worms and penetrate nematode’s digestive tract
- invades ovaries and uterus of nematodes
- multiplies within eggs of nematodes and in the developing larvae
+ - use Heterakis as paratenic host
- released when larval nematode ingested
- establish and divide in cecae
- invasive trophs penetrate mucosa
- trophozoites enter blood
- trophozoites migrate to liver
- multiply rapidly
- pathogenicity and invasion is host-specific – turkeys highly susceptible
Histomonas meleagridis; Pathogenesis/Lesions/Clinical Signs (Turkeys)
- turkeys severely affected, especially poults
- cecal lesions common with edematous mucosa
- liver lesions (up to 1 cm), yellow-green necrosis
- numerous parasites in both ceca and liver
- clinically, droopiness/ruffled feathers/hanging wings
- head sometimes darkens - “Blackhead Disease”
- yellowish diarrhea is characteristic
Histomonas meleagridis; Treatment:
- metronidazole (off label) - “Flagyl” (not in food production animals)
- control is generally preventative > management
- remove soil contact (what operations susceptible?)
- anthelmintics to eliminate the intermediate helminth host
Phylum Ciliophora
“The Ciliates”; Physical characteristics, relation to other parasites, habitat, reproductive strategy
- possess cilia, usually arranged in rows
- related to apicomplexan parasites and dinoflagellates (all are alveolates)
- free-living with some parasitic species
- divide asexually by binary fission but also have genetic exchange via
conjugation some form resistant cysts
Balantidium coli; Morphology, location, replication strategy
- large ciliated protist that lives principally within the large bowel as a trophozoite
(arrow marks the cytostome = “mouth”)- cyst form with obvious curved, dense nucleus and
dense cyst wall; found in formed stool
- cyst form with obvious curved, dense nucleus and
- replication is by binary fission
Balantidium coli; Life Cycle, hosts
- usual (and “reservoir”) hosts are swine (wild and domestic)
- infection via ingestion of cysts shed by pig or human
- zoonotic risk
Balantidium coli; Clinical Signs /Treatment
- persistent diarrhea, occasionally dysentery, abdominal pain, and weight loss
- responds to tetracyclines
Ichthyophthirius multifiliis; Morphology
- common parasite of fish in aquaria usually seen as white raised spots in/on skin of fish up to 1 mm in diameter
- ciliate is found within cyst in skin
Ichthyophthirius multifiliis; Life Cycle
- both parasitic and free-living forms are found in the aquarium
- tomites are the infective forms and actively seek out a host
> tomont released by fish, encysys
multiple cell divisions on substrate
cyst opens, tomites released
skin penetration
trophonts grow within epithelium
Microspora; Taxonomy
Kingdom Protoctista (Protozoa)
Phylum Microspora
Order Microsporidia
Microsporidia; Site of Infection
- usually digestive tract but can also be elsewhere on a mucous membrane
Microsporidia; Morphology
- single-celled spore with characteristic coiled filament
- other forms (e.g. sporoplasm) less easily determined to be a microsporidium
Microsporidia; how does it invade cells?
active penetration of host cells
Microsporidia; Life Cycle
- polar filament explosively penetrates host cells
- asexual mitotic divisions give rise to sporoplasm that then divides into spores that mature
