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Seminar Thursday
“Migrating birds and their potential role in the spread
of zoonotic disease.” Dr. Jen Owen, MSU
My research focuses on the role
migrating birds play in the spread
of zoonotic disease, particularly
arthropod-borne viruses. I am
interested in how environmental
and physiological stressors impact
an animal’s ability to mount
effective immune responses and
how that impacts both their
susceptibility to disease and their
ability to serve as competent
reservoirs and dispersal vehicles
for zoonotic pathogens.
Protozoal Diseases of Wildlife
• Eukaryotes
• Unicellular
• Usually aerobic
• Feeding growing stage – trophozoite
• Adverse conditions – some form a cyst
• Life cycle
• reproduce asexually
• some also have a sexual reproductive stage
Phyla Important for Infectious Disease
1. Amoebozoa (amoebae)
4. Euglenozoa (flagellates)
Ciliophora (ciliates)
5. Microspora
Archaezoa (flagellates)
6. Apicomplexa (sporozoa)
Major differences in modes of locomotion
amoebae – pseudopodia
ciliates – cilia
flagellates – flagella
sporozoa and microspora – intracellular
• The typical life cycle
involves infection of the host
with the trophozoite,
multiplication and in some
cases, producing cysts.
• Example parasitic amoeba
– Acanthamoeba (eye)
– Entamoeba (intestines)
– Naeglaria (brain)
Ingestion in
food or water
2 examples
• Balantidium coli - a
common intestinal parasite
of man, lower primates,
and hogs.
• Ichthyophthirus multifillis agent of "ich“ - a parasite
infecting fish.
• Flagellates posses one or more long, slender
flagella used for locomotion.
• Two groups
1. within Archaezoa (intestinal & urogenital)
2. within Euglenozoa (blood)
Flagellates – intestinal and urogenital
• Trichomonas spp
– agent of trichomoniasis in a
variety of animals
– transmitted sexually
• Giardia lamblia
– infections a variety of
domestic and wild animals
– the most common intestinal
parasite of people in North
– transmitted fecal-oral
Flagellates - haemoflagellates
live in blood, lymph, and tissue spaces
transmitted from host-host by blood-feeding arthropods
most important genera: Trypanosoma and Leishmania.
infection in mammalian hosts occurs
– through the bite of the infected arthropod
– through contamination of the host's mucus membranes or abraded
skin by the arthropod's infected feces.
• A unique group because all
members are parasitic
• Not motile
• Obligate intracellular
• All have complex life cycles
• The common feature of all
members is the presence of an
apical complex in one or more
stages of the life cycle.
– Secretes enzymes that allow the
parasite to enter other cells
Toxoplasma invading host cell
4,516 species in 339 genera
Impt. groups
• Coccidia
– Ex. Toxoplasma, Neospora, Sarcocystis
• Haemosporidia
– Ex. Plasmodium (malaria)
• Piroplasm
– Ex. Babesia
Complex life-cycle, involving both asexual and
sexual reproduction.
A host is infected by a sporocyst (or
oocyst) (1)
The parasites divide to produce
sporozoites (2) that enter the host cells.
The infected cells burst, releasing
merozoites (3) that infect new cells
Cycle may repeat several times.
Eventually gamonts (4) are produced,
forming gametes that fuse to create new
cysts (1)
Toxoplasma gondii
• infects humans and other
warm-blooded animals,
including birds
• found worldwide
Toxoplasma gondii
• Only felids are
definitive host - both
wild and domestic cats
serve as the main
reservoir of infection.
Toxoplasma gondii
3 infectious stages of T. gondii
• tachyzoites (trophozoite)
• bradyzoites (within tissue cysts)
• sporozoites (within oocysts)
Toxoplasma gondii
• transmitted by
– consumption of sporocysts in
cat feces
– consumption of bradyzoites
within tissue cysts
– transplacental transfer of
tachyzoites from mother to fetus
Toxoplasmosis in felids
Bradyzoites are released from tissue cysts
during digestion, invade intestinal epithelium,
and undergo sexual replication, culminating in
the release of oocysts in feces.
Oocysts are first seen in the feces at 3 days
after infection and may be released for up to
20 days.
Oocysts sporulate (forming infectious
sporocysts) outside the cat within 1-5 days,
and remain viable in the environment for
several months.
Cats generally mount a powerful immune
response to the parasite and develop
immunity after the initial infection, and
therefore shed oocysts only once in their
Toxoplasmosis in other animals
Consumption of meat containing tissue
cysts (carnivores, scavengers) ingestion of
cat feces containing oocysts (all warmblooded animals).
Bradyzoites or sporozoites, respectively, are
released and infect intestinal epithelium.
Tachyzoites emerge and disseminate via the
bloodstream and lymph, infect tissues
throughout the body and replicate
intracellularly until the cells burst, causing
tissue necrosis.
Young and immunocompromised animals
may succumb to generalized toxoplasmosis
at this stage.
Older animals - immune response drives
parasite into tissue cyst form (dormant
Tissue cysts in the host remain viable for
many years, and possibly for the life of the
Toxoplasmosis in humans
• Nearly one-third of world population has been exposed to this parasite.
– 16-40% in the U.S. and the U.K
– 50-80% in Central and South America and continental Europe
• In most adults it does not cause serious illness,
• but can cause devastating
disease in immunocompromised
• and transplacental infection can
result in:
•mental retardation