Protozoa III

1. Sporozoa
Endoparasites in animals
Possess microtubules and organelles
Two groups
1. Gregarines – parasitize insects and other
invertebrates
2. Coccidians – parasitize both vertebrates and
invertebrates. Some are blood-cell parasites to
human.
Malaria
Agent – Plasmodium spp
Present victims – 300 to 500 million over the world
Death rate – 1 person every 12 seconds

2. • Adult apicomplexans are endoparasites that
completely lack locomotory organelles. Its life
cycle includes sexual reproduction through
gamete fusion and asexual reproduction by
means of fission, and the production of
resistant or infective pores.
• Female mosquitoes are excellent vectors of
malaria, easily transmitting it from one person
to another, because they must continually
ingest blood from vertebrate host to nourish
their developing embryo.

5. Life cycle of mosquitos
• Haploid gametes, quiescent within the RBC of their human
host are obtained from the human bloodstream through the
bite of the female.
• Gametocytes mature within the mosquitoes either male or
female after it quickly emerge from the RBC.
• The female gametes are fertilized within 30 minutes
• Diploid zygotes (ookinetes) move to the stomach, encyst in
the wall and grow.
• Encysted ookinete (oocyst) undergoes meiosis and large
number of fission events. It matures into infective haploid
sporozoites. 10,000 sporozoites are produced from an
individual zygote.

6. • Mature sporozoites migrate to the salivary glands to
be injected into human host at the next blood meal.
• After injection, sporozoites begin infecting human
liver cells. The immune system remove them from
direct attack but they form a resistant cyst and
asexually divides again numerously.
• a single fissioning sporozoite (schizont) can give rise
within 1 week nearly 40,000 genetically identical
offspring called merozoites which rupture the liver
cell housing them, enter the blood stream and invade
the hosts RBC.
• After entering a blood cell, they alter the cell surface
chemistry so that the cell sticks to the tissue lining of
the blood vessels

7. • After the removal of RBC from the
circulation, the hosts spleen prevents the
destruction of the blood cell.
• Within the RBC, merozoite multiplies asexually
to form 10 to 20 merozoites over the next 48
hours. The new ones quickly invade new RBC’s
for another round of asexual replication. This
may lead to anemia. Fever and chills
characterize malarial infection.
• Gametocytes can continue the life cycle only if
the RBC they reside in are ingested by a
mosquito

9. Key elements
• Only the haploid gametocytes living within the
human RBC, infect the mosquito vector
• Only the haploid sporozoites which
accumulate in certain of the mosquito’s
salivary gland cells can infect humans
• Pathological effects in human are caused only
by RBC (merozoite) stage of life cycle.
• Parasite is haploid for most of its life. A
diploid stage occurs only in the mosquito
vector.

10. Control strategies
1. Production of antibodies
2. Disarming the specific sporozoite surface proteins that
recognize and binds to the receptor of the liver cells
3. Prevent the diploid zygotes (ookinetes) from producing the
chintenase that enables them to penetrate the chitinous
membrane lining.
4. Genetically engineer mosquitoes that will prevent gametocytes
from maturing in the mosquito vector.
5. Genetically alters the bacteria or protozoans living
symbiotically with the mosquito vector
6. Disrupting the binding sites on the parasite that interact with
the mosquito’s salivary gland receptor.
7. Disable the vasodilators and anticlotting and anti platelet
compounds found in mosquito saliva

11. Microsporidea
• Intracellular parasites
• Lack mitochondria apical complex and flagella
• Has a polar filament
• Life cycle includes production of dispersive (
chitinous) spores. The polar filament discharges from
its capsule and anchors the spore to the host tissue. A
single amoeboid sporoplasm exits through the everted
polar filament of the attached spore and invades the
hosts tissues. The sporoplasm replicates itself many
times asexually.
• Recent molecular analyses indicate that most
microsporans are actually degenerate fungi.

12. Myxozoa
• Extracellular, spore-forming parasites
• The infective spores are
multicellular, dispersing the parasite from one
host to another.
• Mostly infect fishes and aquatic annelids
• Spores possess polar filaments
• Recent molecular data indicate that
myxozoans are degenerate multicellular
animals.