Protozoal Diseases of Wildlife• Eukaryotes• Unicellular• Multiple stages
trophozoite
cyst • Complex life cycles
• reproduce asexually• some also have a sexual reproductive stage
Phyla Important for Infectious Disease
1. Amoebozoa (amoebae)
2. Ciliophora (ciliates)
3. Archaezoa (flagellates)
4. Euglenozoa (flagellates)
5. Microspora
6. Apicomplexa (sporozoa)
Major differences in modes of locomotion
amoebae – pseudopodia
ciliates – cilia
http://video.google.com/videosearch?q=amoeba%20movement&hl=en&source=vgc&um=1&ie=UTF-8&sa=N&tab=wv#
http://video.google.com/videosearch?q=paramecium+darkfield&emb=0&aq=f#
flagellates – flagella
microspora and sporozoa – intracellular
http://video.google.com/videosearch?q=flagellates+dancing&emb=0&aq=f#
Amoeba• The typical life cycle
involves infection of the host with the trophozoite, multiplication, and in some cases, producing cysts.
Ingestion in contaminated food or water
Ciliates 2 examples• Balantidium coli - a
common intestinal parasite of man, lower primates, and hogs.
• Ichthyophthirus multifillis - agent of "ich“ - a parasite infecting fish.
Flagellates• 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– infects a variety of
domestic and wild animals – the most common intestinal
parasite of people in North America.
– 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.
Apicomplexa• all members are parasitic• obligate intracellular• non motile• 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.– Acts like a drill bit, and secretes
enzymes that allow the parasite to enter other cells
Toxoplasma invading host cell
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. Definitive
host
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• Mouse – infected by ingesting an oocyst
• Oocysts transform into tachyzoites
shortly after ingestion. These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites.
• Once parasite is in tissue cyst stage it stimulates the mouse immune system so that only parasites within tissue cysts will survive, in this way the infection will not kill the mouse before the mouse gets eaten.
Toxoplasmosis in felids• Mice lose their fear of cat smell, and
actually seek out cats.• Mouse containing tissue cysts with
bradyzoites is ingested by feline
Toxoplasmosis in felids• Bradyzoites are released from tissue cysts
during digestion, invade cat’s intestinal epithelium, and undergo sexual replication, passing through a tachyzoite stage, culminating in the release of oocysts in cat feces.
• 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 lifetime.
Toxoplasmosis in other animals• Toxoplasmosis is one of the most commonly
diagnosed causes of abortion in sheep and goats
Toxoplasmosis in other animals• Recent research has shown that T. gondii is
one of the primary killers of sea otters.
• Toxoplasmosis is a fatal disease in the eastern bandicoot
Toxoplasmosis in other animals• and wombats
• and wallaby, which can transmit to humans
Toxoplasmosis in humans
Toxoplasmosis in humans
hydrocephalus
• Parasites form tissue cysts, most commonly in skeletal muscle, myocardium, brain, and eyes; these cysts may remain throughout the life of the host.
Toxoplasmosis• Domestic and wild
cats = definitive host
• British Columbia = cougars
Toxoplasmosis• Intermediate hosts
– Moose– Pronghorn– Mule deer– WTD– Black bear– Red fox– Skunks– Opossum– Mink– Small mammals
Neosporosis• Neospora caninum • Structurally/biologically
similar to Toxoplasma; 1988
• Definitive hosts = canids (1998)
• Intermediate hosts = livestock
• Dogs deposit feces into pastures or food stuffs or water
Neospora caninum• Structurally/biologically
similar to Toxoplasma; 1988
Tissue cyst with bradyzoites (thicker wall)
Neosporosis• Forms cysts in the tissue
and remains dormant as bradyzoites. Dogs that eat infected meat from deceased cattle will ingest the bradyzoites and become infected, thereby shed more Neospora caninum oocysts.
Neosporosis• fetal abortions,
stillbirth, low milk yield, reduced weight gain, weakened condition, premature culling in cattle
• economic loss to farmers
Neosporosis• Woodbine et al. (2008) BMC
Veterinary Research. 4:1471-8219 • England: seroepidemiological study of
N. caninum antibodies from 114 herds visited on 3 occasions, annually
• 94% of herds: at least 1 seropositive cow; 12.9% of adult cattle had at least 1 seropositive test
• 90% of herds: seropositive at all visits • median seroprevalence in + herds was
10% (range 0.4% to 59%) • positive association between the
serostatus of offspring and dams that were seropositive
• Between-herd movements of infected cattle enhance spread, particularly into low seroprevalence herds
Neosporosis• >40% of white-tailed deer
sampled from Illinois exhibited antibodies to Neospora caninum
• Seroprevalence in WI wildlife species:– 19.0% WTD– 14.7% coyotes – 11.1% foxes – 0% raccoons & opossums
Neosporosis• Transmission from
deer & cattle to dogs & coyotes – demonstrated
• Incidence of Neospora higher where high cattle densities and high numbers of wild canids
Neosporosis* Potential for crossover
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