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)

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

sporozoa and microspora – 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.

• Example parasitic amoeba– Acanthamoeba (eye)– Entamoeba (intestines)– Naeglaria (brain)

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

• Flagellates posses one or more long, slender flagella used for locomotion.

• Two groups1. 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 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. • 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.

Apicomplexa

• 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

Apicomplexa

4,516 species in 339 genera Impt. groups• Coccidia

– Ex. Toxoplasma, Neospora, Sarcocystis

• Haemosporidia– Ex. Plasmodium (malaria)

• Piroplasm– Ex. Babesia

Babesia

Apicomplexa

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.

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• 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 lifetime.

Toxoplasmosis in other animals• Consumption of meat containing tissue cysts

(carnivores, scavengers) ingestion of cat feces containing oocysts (all warm-blooded 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 phase)

• Tissue cysts in the host remain viable for many years, and possibly for the life of the host.

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,

hydrocephalus

• but can cause devastating disease in immunocompromised individuals

• and transplacental infection can result in:•blindness•mental retardation