Protozoa are microscopic, eukaryotic, unicellular organisms that are classified into four subphyla based on their structures and methods of locomotion and nutrition. They exhibit a variety of reproductive strategies including asexual reproduction through binary fission or multiple fission and sexual reproduction through conjugation or syngamy. Many protozoa alternate between parasitic and free-living stages in their life cycles or can live as commensals with other organisms. Common protozoan diseases affecting humans include malaria, amoebiasis, African sleeping sickness, and giardiasis.

1. General Characters and
Classification of Protozoa

3. General Characters:
Phylum Protozoa are microscopic, eukaryotic, unicellular, solitary
or colonial, commonly motile and phagocytic heterotrophic
animalcules without tissues and organs. They have one or more
nuclei.
Almost about 50,000 species are known till date.
Anton Van Leeuwenhoek (1676) was the first to observe protozoa
(Vorticella convellaria) and called them animalcules. Gold
fuss coined the term Protozoa (1818).

4.  They may be free living (Amoeba) or symbiotic (Parasitic,
mutualistic or commensalistic)
 Body symmetry is symmetrical (Actinopodeans) or radial (sessile
forms) or bilateral (Giardia) or absent (Amoeba).
 Locomotion is brought about by pseudopodia or flagella or cilia or
myonemes.

5.  Nutrition is holozoic or holophytic or osmotrophic (Saprophytic
or parasitic). Digestion is intracellular. Some forms like Euglena
are mixotrophic (perform more than one type of nutrition)
 Excretion occurs by diffusion across general body surface or by
contractile vacuoles. Contractile vacuoles serve mainly for
Osmoregulation and are common in freshwater forms.
Excretion

6.  Exchange of respiratory gases takes place by diffusion through the
general body surface. Respiration is aerobic or anaerobic in some
parasitic forms.
 Asexual reproduction takes place by binary fission or multiple
fission or plasmotomy or budding.

7.  Sexual reproduction takes place by conjugation or by fusion of
gametes (Syngamy).
 Many forms undergo encyctment to tide over unfavorable
conditions
 Somotoplasm and germplasm are not differentiated. Hence they
are immortal (exempt from natural death).
Syngamy
Sexual
Reproduction
Sexual Reproduction Encyctment

8. Classification of Phylum Protozoa
Classification given by BM Honigberg and the society of
Protozoologists divides this phyla into 4 subphyla.

10. Superclass 1: Mastigophora (Gr. Mastix=whip; phoros=bearing)
The body of animals belonging to this super class is covered by
pellicle. The locomotory organelles are flagella. Asexual reproduction
occurs by longitudinal binary fission.
This super class includes 2 classes:
Class 1: Phytomastigophora (Gr. Phyton=plant; Mastix=whip;
phoros=bearing)
They have chromatophores with chlorophyll. The nutrition in these
organisms is mainly holophytic which takes place by phototrophy.
These are free living organisms. The reserve food in is starch. These
organisms may have 1 or 2 flagella. Ex: Euglena, Ceratium, Noctiluca
Ceratium
Euglena Noctiluca

11. Class 2: Zoomastigophora (Gr. Zoon=animal; Mastix=whip; phoros=bearing)
These organisms do not have chlorophyll bearing chromatophores.
These are mostly parasitic. The nutrition in these organisms is
holozoic or saprozoic. The reserved food is glycogen. They may have
one to many flagella.
Ex: Leishmania, Trypanosoma, Trichomonas, Trichonympha
Trichonympha

12. Superclass 2: Opalinata
The organisms belonging to this super class live as commensals or
parasites in the gut of anurans (Frog).
Their body is covered by oblique rows of cilia-like flagella. These
organisms may have 2 or many nuclei.
They undergo asexual reproduction by binary fission or by syngamy.
Sexual reproduction takes place by anisogamy.
Ex: Opalina, Zelleriella
Zelleriella

13. Superclass 3: Sarcodina (Gr. Sarcode=fleshy)
The locomotion is brought about by pseudopodia. Their body is
amoeboid without definite pellicle. The nutrition is holozoic or
saprozoic. This super class is further divided into 3 classes:
Class 1: Rhizopodea (Gr. Rhizo= root; poda – foot).
The pseudopodia of the animals in this class are in the form of
lobopodia, filopodia or reticulopodia without axial filaments. This
class includes amoebas, foraminiferans and mycetozoans. These
animals are mostly free living and a few are also parasitic. In
foraminiferans the body is covered by porous calcareous shell.
Ex: Amoeba, Entamoeba, Elphidium

14. Class 2: Piroplasmea (pear shape)
The animals belonging to this class are parasitic. Locomotory
structures and Spores are absent. These are the small parasites in
the red blood cells of vertebrates.
Ex: Babesia
Class 3: Actinopodea (Gr. Actis=ray; podos=foot)
The pseudopodia of the animals belonging to this class are in the
form of axopodia with axial filaments, radiating from the spherical
body. These are planktonic. This class includes Heliozoans,
Radiolarians and acanthareans. Radiolarians and acanthareans are
marine forms whereas heliozoans are both marine and fresh water
forms. Skeletons of radiolarians have siliceous shells. The shells of
dead radiolarians accumulate on the ocean floor to form radiolarian
ooze.
Ex: Collozoum, Actinophrys, Acanthometra

15. radiolarian ooze under microscope at X250 magnification.

16. SUBPHYLUM II: SPOROZOA
The animals are exclusively endoparasites. Special locomotory
organelles are absent in these animals. Sometimes pseudopodia are
present which are useful only for ingestion of food. Merozoites bear
anterior apical complex that helps penetrate host cells. This
subphylum includes 3 classes:
Class 1: Telosporea
The Sporozoites are long in these animals. Reproduction is both
asexual and sexual. They are blood and gut parasites of vertebrates.
Sexual reproduction is by isogamy or anisogamy.
Ex: Monocyctis, Eimera, Plasmodium
Eimera

17. Class 2: Toxoplasmea
In this class reproduction is only asexual type which takes place by
internal budding where two daughter cells are produced within the
mother cell and the mother cell is finally destroyed in the process of
reproduction. Spores are absent.
Ex: Toxoplasma
Class 3: Haplosporea
The spores in this class are amoeboid. Also reproduction is only
asexual type taking place through multiple fissions.
Ex: Haplosporidium, Ichthyosporidium

18. SUBPHYLUM III: CNIDOSPORA (Gr. Cnide=needle; spora=seed)
The animals are parasitic. Spores are present with one or more
polar filaments. Polar filaments are special and unique features of
these animals. When these spores infect a host, the polar filament
is discharged and it gets attached to the host tissue. This
subphylum includes 2 classes:
Class 1: Myxosporidea
The spores of the animals of this class are large and develop from
several nuclei. These are generally extracellular parasites. The
spores of this class have two polar filaments and have two to three
valves.
Ex: Myxobolus
polar filaments

19. Class 2: Microsporidea
The spores of the animals of this class are small and are
developed from only one nucleus. These spores have single
valve. These are generally intracellular parasites. Many of the
animals of this class have a single polar filament.
Ex: Nosema bombycis
polar filament

20. SUBPHYLUM IV: CILIOPHORA (La. Cilium=eye lid with lashes;
phoros=bearing)
Ciliophorans are complex of all the protozoans.
The locomotory organelle of all the animals of this subphylum is cilia.
These cilia also help in feeding at some stage of the life cycle of the
animals.
The nuclei of these organisms are dimorphic. Macronucleus is
vegetative and polyploid.
Micronucleus is reproductive and diploid. Asexual reproduction takes
place by binary fission.
Sexual reproduction takes place by conjugation.
Only one class is included in this subphylum: Class 1: Ciliatea

21. Class 1: Ciliatea
The locomotory organelles of these animals are numerous hair-like
cilia. One or more contractile vacuoles are present in these forms.
The nucleus is dimorphic including both macro nucleus and
micronucleus.
Ex: Paramoecium, Vorticella, Balatidium
Paramoecium Balatidium

22. TYPE STUDY ELPHIDIUM or POLYSTOMELLA
Phylum : Protozoa
Class : Rhizopoda
Order :Foraminifera.

23. Elphidium is a marine form and found creeping on Sea weeds to a
depth of 1800 feet.
Structure :
Elphidium is also called 'Polystomella is a 'dimorphic rhizopod'. It is a
unicellular microscopic protozoan, and" 1 mm in diameter. It is pale
yellow in colour.
The body is covered by a biconvex shell. The first formed chamber is
proloculum. The shell contains spirally arranged V shaped chambers.
Hence it is called "polythalamus or multilocular. They overlap one
another.

24. These chambers show perforation. The cytoplasm of the whole body
of the animal is not divided into compartments but it is continuous.
The cytoplasm extends through the pores of the shell to form a layer
over the shell. The cytoplasm is produced into a number
reticulopodia. which will form a network.
From hinder end of each chamber cytoplasmic processes will
develop. They are directed backwards. They are called retral
processes'.
1. The cytoplasm contains one or many nuclei.
2. Cytoplasm contains food vacuoles which takes up the process of
digestion.

25. Dimorphism: Polystomella exhibits dimorphism. The individual
occurs in two distinct forms.
1. Megalosperic form.
2. Microspheric form.
1. Megalospheric form:
Its proloculum is big in size. A single large nucleus is present in one
of the chambers. It takes up sexual reproduction.
2. Microspheric form: Its proloculum is small in size. Many nuclei are
present in the cytoplasm. This form reproduces by asexual
reproduction.
proloculum
Megalospheric Microspheric

26. ( granular endoplasmic
reticulum)

27. Locomotion and Nutrition:
Polystomella show slow creeping movements with the help of
reticulopodia. It is a holozoic feeder. These reticulopodia will capture
the prey. When it comes in contact with the prey, it kills the prey by
secreting toxic substance. The prey is digested in the food vacuole,
the digested food is absorbed by the cytoplasm.

28. Reproduction and Life Cycle of Elphidium:
Elphidium exhibits an alternation of generation in its life cycle.
The megalospheric forms alternate with the microspheric forms.
The microspheric forms always develop by the conjugation or
syngamy and megalospheric forms develop without conjugation or
syngamy.
The microspheric form reproduces asexually by fission to produce a
number of amoebulae. The inner cytoplasmic mass containing
several nuclei creeps out of the shell and remains as a lump around
it.
A small amount of cytoplasm collects around each nucleus.

29. As a result, a large number of amoeboid cells (amoebulae) are
formed.
Each amoebula secretes the proloculum, forms rhizopodia, then it
grows and forms other chambers of the shell to become a
megalospheric form.

30. The megalospheric form reproduces sexually by syngamy or
conjugation.
During sexual reproduction in megalospheric forms, nucleus first
breaks up into many small nuclei and the cytoplasm collects around
each of these nuclei.
The nuclei divide twice giving rise to a large number of tiny cells.
The cells develop flagella and come out of the shell.
The biflagellate cells are haploid and known as isogametes. The
isogametes of two different individuals fuse (conjugate) in pairs to
form zygotes. (The fusion of similar size gametes is known as
isogamy).
The zygotes, thus, formed develop into microspheric forms.

32. Protozoan Diseases

33. Name of the
Disease
Causal
organism
Vector Pathogenesis Disease symptoms
Malaria Plasmodium
falciparum, P.
vivax, P.
malariae, P.
ovale
Female
Anopheles
mosquito
The parasite attacks the liver
and RBCs. It multiplies within
liver cells, enters the
bloodstream and ruptures
RBCs. It releases a toxic
substance
called ‘hemozoin’, which
causes fever. The sporozoite is
the infectious stage
Fever, headache, vomiting,
abdominal pain and it may
lead to fatal conditions if not
treated like organ failure and
convulsions
Amoebiasis
or Amoebic
dysentery
Entamoeba
histolytica
None. It gets
transmitted
by
contaminated
food or water
Invades intestinal mucosa and
spreads to other parts like
liver. Causes dysentery and
liver abscesses.
The infected stage is
trophozoites
Abdominal pain, loose bowel
movement, bloody stool, loss
of appetite, nausea, fever
African
Sleeping
sickness or
Trypanosomia
sis
Trypanosoma
brucei
gambiense, T.
brucei
rhodesiense
Tsetse fly B-lymphocyte proliferation
leading to tissue damage
High fever, muscle and joint
pain, irritability, swollen
lymph nodes, skin rashes. If
left untreated, neurological
problems develop, which
become fatal

34. Trichomoniasis Trichom
oniasis
vaginalis
Sexually
transmitted
disease
(STD)
Destroys epithelial cells and
cytotoxic substances are
released. Vaginal pH increases
and the number of leukocytes
also increases in response to
the toxic substance released
by the pathogen
Itching and burning in genital
organs and discharge.
Mostly asymptomatic in
males, but in females it may
lead to many complications
such as complication during
pregnancy and after birth.
Toxoplasmosis Toxoplas
ma
gondii
Transmission
by
contaminate
d water and
soil or get
attached to
fur of
animals
Sporozoites penetrate the
intestinal cells and multiply in
the intestine. It invades the
lymphatic system and blood
and damages the tissue leading
to necrosis
Redness of eye, blurred
vision, flu-like symptoms
Balantidiasis Balantidi
um coli
Pigs Excystation occurs in the small
intestine. Sporozoites migrate
to the colon
Ulcer due to lesion in the
colon, colitis, blood and
mucus in the stool,

35. Giardiasis Giardia lamblia
or duodenalis
None. It gets
transmitted by
contaminated food
or water
Mucosal damage is
related to the
mucosal
inflammation and
release of lectin or
proteinases.
Malabsorption may
also be due to
inhibition of
pancreatic enzymes
and depletion of
bile concentration
The parasite is
present in the
duodenum.
Watery or foul-
smelling diarrhoea,
nausea, flatulence,
weight loss
Leishmaniasis
or Kala-azar
Leishmania
donovani
Female Sandflies (of
the genus
Phlebotomus)
The flagellated
promastigotes of the
parasite bind to
macrophages
present in the skin.
There is marked
suppression of cell-
mediated immunity
Enlarged liver and
spleen, fever, skin
turns dark

36. Leishmania donovani
Classification:
Kingdom: Protista
Phylum: Protozoa
Subphylum: Sarcomastigophora
Super class: Mastigophora
Class: Zoomastigophora
Genus: Leishmania
Species: donovani

37. Leishmaniasis is a vectorborne disease that is transmitted by sand
flies and caused by obligate intracellular protozoa of the
genus Leishmania.
Leishmania is a digenetic parasite which requires two hosts to
complete its life cycle. These two parasites are named as primary
and secondary hosts. The primary host is the principal host which is
a vertebrate or man. In the primary host the parasite feeds and
multiplies itself asexually.
On the other hand the secondary host is the intermediate host or
vector which is usually an invertebrate or a blood sucking insect. In
the case of Leishmania it is sand-fly (Tse-tse fly). This sand fly
belongs to the genus Phlebotomus.

38. Life Cycle of Leishmania
1. People are infected when they are bitten by an infected female
sand fly. Sand flies inject a form of the protozoa (called
promastigotes) that can cause infection.
2. Promastigotes are ingested by certain immune cells called
macrophages.
3. In these cells, promastigotes develop into another form (called
amastigotes).
4. Amastigotes enter the cells of reticulo-endothelial system (consists
of the organs like spleen, bone marrow, liver and lymph nodes) and
undergo slow multiplication by binary fission and because of this the
respective organs become significantly enlarged. When the number of
parasites reaches 50 to 200 or more the macrophages get ruptured to
liberate the parasites.
5–6. When a sand fly bites an infected person or animal, it becomes
infected by ingesting blood containing macrophages with amastigotes
inside.

39. 7. In the middle part of the fly's gut (midgut), amastigotes develop
into promastigotes.
8. In the fly's midgut, promastigotes multiply, develop, and migrate to
the fly's mouth parts. They are injected when the fly bites another
person, completing the cycle.

40. DUMDUM FEVER or Kala-azar.
Occurrence: Dumdum fever is the serious oriental disease of man
caused by Leishmania donovani . It is also known as black fever or
Kala-azar. The word kala-azar is derived from two Indian words Kala
meaning black and azar meaning sickness. This fever is prevalent in
India, China, Mediterranean countries and some parts of Arica and
South America.
The very early symptoms of dumdum fever include swelling, high
fever, enlargement of organs or reticulo-endothelial system like
spleen and liver. These symptoms are followed by general weakness,
anemia due to reduction in the number of blood cells and darkening
of the skin.
In the advanced stages the skin of the infected person becomes
completely dry, rough and dark with lot of pigmentation, hair
becomes brittle and fall out. If the patient does not receive proper
treatment it can lead to his death in 2 years.

42. Classification:
Kingdom: Protista
Phylum: Protozoa
Subphylum: Sarcomastigophora
Super class: Sarcodina
Class- Rhizopoda
Genus: Entamoeba
Species: histolytica
Entamoeba histolytica

43. The life cycle of E. histolytica (histo–lytic = tissue destroying) begins
and ends inside one single host, i.e., an individual human being.
Infection is also called as Amoebiasis or Amoebic dysentery.
Life Cycle of Entamoeba histolytica:
1) Cyst – Stage 1 –
Infection occurs by ingestion of mature cysts through fecally
contaminated water or food. Due to protection from walls, cysts
survive several days and sometimes weeks. They are responsible for
transmission.
2) Excystation – Stage 2 –
Excystation is the process by which cysts transform into
trophozoites. When the cysts enter the ileum of the small intestine
of the host, the process of excystation begins. Trophozoites are
released in the small intestine and from here they migrate to the
large intestine.

44. 3) Trophozoite – Stage 3 –
Trophozoites are unicellular parasites that measure from 14 to 18
mm in diameter. They multiply in the small intestine by binary
fission to produce cysts that exit via human stool. Several
trophozoites remain inside the lumen of the small intestine. The
rest attach themselves to the intestinal mucosa, enter the
bloodstream and further grow in the extraintestinal regions of the
host like lungs, liver, brain.
E. histolytica, is pathogenic; infection can be asymptomatic, or it
can lead to amoebic dysentery or amoebic liver abscess.
Symptoms can include fulminating dysentery, bloody diarrhea,
weight loss, fatigue, abdominal pain, and amoeboma. The amoeba
can 'bore' into the intestinal wall, causing lesions and intestinal
symptoms, and it may reach the blood stream. A common
outcome of this invasion of tissues is a liver abscess, which can be
fatal if untreated.

45. Life-cycle of Entamoeba histolytica

46. Classification:
Kingdom: Protista
Phylum: Protozoa
Subphylum: Sprozoa
Class- Teleospora
Genus: Plasmodium
Species: falciparum
Plasmodium falciparum

48. Life cycle of Plasmodium:
Plasmodium parasites have a complex life cycle that includes three
stages namely Gametocytes, Sporozoites and Merozoites.
1) Gametocytes – Stage 1 –
The male gametocytes called microgametocytes and female
gametocytes called macrogametocytes are transmitted through an
anopheles mosquito during a blood meal. The gametocytes within the
mosquito fuse to form a sporozoite.
2) Sporozoites – Stage 2 –
When the infected mosquito feeds on humans, the sporozoites are
transmitted through the saliva into the bloodstream.
After that, the sporozoites enter the liver cells and here they mature
into schizonts. Later, these rupture and release merozoites.

49. 3) Merozoites – Stage 3 –
The merozoites enters RBCs, here they grow to form a ring shaped
trophozoites and multiply while destroying all blood cells in that
process. When the red blood cells are destroyed by the
merozoites, it releases a toxin that causes bone-shaking chills and
fever. Extreme cold chills and fever are classic symptoms of
malaria in human beings. Dizziness, muscle pain, abdominal
pain, nausea, vomiting, mild diarrhea, and dry cough are also
generally associated. High heartrate, jaundice, enlarged liver,
and enlarged spleen are also diagnosed.
Certain merozoites develop into gametocytes, which is later
ingested into the bloodstream by a mosquito and the whole cycle
starts again.
Some other species of plasmodium known to spread Malaria are
P. vivax, P. ovale, P. malariae, and P. knowlesi.

50. Trypanosomiasis, human African (sleeping sickness)
Classification:
Kingdom: Protista
Phylum: Protozoa
Subphylum: Sarcomastigophora
Super class: Mastigophora
Class: Zoomastigophora
Genus: Trypanosoma brucei
Species: gambiense

51. Human African trypanosomiasis, also known as sleeping sickness, is
a vector-borne parasitic disease. It is caused by infection with
protozoan parasites belonging to the genus Trypanosoma.
They are transmitted to humans by tsetse fly bites which have
acquired their infection from human beings or from animals
harbouring human pathogenic parasites.
Two subspecies that are morphologically indistinguishable cause
distinct disease patterns in humans: T. b. gambiense, causing
chronic African trypanosomiasis (“West African sleeping sickness”)
and T. b. rhodesiense, causing acute African trypanosomiasis (“East
African sleeping sickness”).
The third subspecies T. b. brucei is a parasite primarily of cattle and
occasionally other animals, and under normal conditions does not
infect humans.

53. Life Cycle of Trypanosoma brucei gambiense
1. When an infected tsetse fly bites a person (or animal), it injects a
form of the protozoa that can cause infection (called
trypomastigotes) into the skin. The protozoa move to the lymphatic
system and bloodstream.
2. Inside the person, they change forms and travel to organs and
tissues throughout the body, including lymph and spinal fluid.
3. The protozoa multiply in the bloodstream and other body fluids.
They circulate in the bloodstream.
5. A fly ingests the protozoa when it bites an infected person.
6. Inside the fly, the protozoa change forms and multiply.
7–8. The protozoa travel to the fly's salivary glands, multiply, and
change into trypomastigotes—the form that is injected when the fly
bites a person.

54. African trypanosomiasis symptoms occur in two stages: the
hemolymphatic stage and the neurological stage.
Hemolymphatic phase
Incubation period is 1–3 weeks for T. b. rhodesiense, and longer in T. b.
gambiense infection.
The first/initial stage, known as the hemolymphatic phase, is
characterized by non-specific, generalised symptoms like: fever,
headaches , joint pains, itching, weakness, fatigue, weight loss,
lymphadenopathy, and hepatosplenomegaly.
Invasion of the circulatory and lymphatic systems by the parasite is
associated with severe swelling of lymph nodes, often to tremendous
sizes.

55. Neurological phase
The second phase of the disease, the neurological phase (also called
the meningoencephalic stage, begins when the parasite invades
the central nervous system by passing through the blood–brain
barrier.
Progression to the neurological phase occurs after an estimated 21–
60 days in case of T. b. rhodesiense infection, and 300–500 days in
case of T. b. gambiense infection.
Sleep-wake disturbances are a leading feature of neurological stage
and gave the disease its common name African sleeping sickness.
Infected individuals experience a disorganized and fragmented
sleep-wake cycle.
Neurological symptoms include: tremor, general muscle
weakness, hemiparesis, paralysis of a limb, abnormal muscle tone,
gait disturbance, ataxia, speech disturbances, paraesthesia,
hyperaesthesia, anaesthesia, visual disturbance, abnormal reflexes,
seizures, and coma. Parkinson-like movements might arise due to
non-specific movement disorders and speech disorders.