Protozoal Diseases of Wildlife

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