Protozoa

Dr. Linroy Christian

Definition

• Eukaryotic• Lack cell wall• Usually obtain food by ingesting other

organisms or organic matter• Found in fresh water and marine habitats

and also in soil• Can be parasites of animals and humans

Definition

• Most are motile

• They feed by ingesting their prey or organic material via:– Pinocytosis – Phagocytosis– A gullet

Mastigophora – The Flagellates

• Motile via a flagella

• Many are free-living, but some are parasitic to animals and humans

• Two important examples are the trypanosomes and giardia

Trypanosomas gambiense• Etiologic agent of chronic African Sleeping

Sickness• Spread by the bite of some species of the tsetse

fly• Disease can be transmitted from animal to

human or from human to human• Parasite can eventually invade the nervous

system• Infected individuals may be infected for months

or years without symptoms

Symptoms of Chronic Sleeping Sickness

• Initially can include bouts of fever, joint pain and itching

• After infection of the central nervous system:– Confusion– Sensory disturbances– Poor coordination– Disturbance of the sleep cycle

• Without treatment the disease can be fatal

T. gambiense

Giardia Lamblia• Etiologic agent of Giardiasis, an acute form of

gastroenteritis

• Usually transmitted to human by faecally contaminated water and food and less frequently via sexual intercourse

• The disease is generally transmitted by the encysted form of the parasite

• Cysts are generally resistant to chlorination

Symptoms of Giardiasis

• Explosive, foul-smelling, watery diarrhoea• Intestinal cramps• Flatulence• Nausea• Malaise

G. Lamblia

Sarcodina – The Amoebas• Can be free-living in habitats such as ponds

• Move via amoeboid movement

• One of the most significant amoebas is Entamoeba histolitica, the etiologic agent of amoebic dysentery (amebiasis)

• It is transmitted from person to person by water and food contaminated with the cysts of the parasite

E. histolitica

• Symptoms include:– Ulceration of the intestinal tract– Diarrhoea– Severe intestinal cramps

• Diarrhoea is replaced by dysentery which is characterised by the passage of blood and mucus

• The infection if untreated can migrate to the liver, lung and brain

E. histolitica

Ciliophora – The Ciliates

• Possess cilia in some stage of their life cycle

• Not as many parasitic species as other protozoa

• They feed via a mouth part that leads to the gullet

• Cilia can be used in defense or to paralyse prey

The Ciliates

• One of the best known genera is Paramecium

• Balantidium coli is a parasite of animals and humans causing symptoms similar to E. histolitica

Paramecium

Sporozoa• Are obligate parasites• Lack a motile adult stage• Do not generally ingest food, but absorb it

through the outer wall• Produce a spore-like structure called a

sporozoite which are involved in the transmission into a new host

Plasmodium

• The Plasmodia are one of the most important Sporozoa groups

• Plasmodia are the etiologic agent of malaria

• Most prevalent in Africa, but can be found in parts of the middle east and Europe

• Transmitted by the Anopheles mosquito

Malaria

• Symptoms after 10-15 days may include:– Fever, headache, chills and vomiting

• If left untreated:– Cerebral malaria, anemia and kidney failure– Can result in death

• The symptoms may not present for years depending on the infecting species

Malaria cycle