Parasitology devision of Veterinary protozoology Protozoology is the study of protozoanHome | Contact Us | Sitemap | Login| Bookmark this site!   


Protozoology is the study of protozoan

The protozoa (Gr., protos =first; zoon = animals) consist of a single 'cell like unit' which is morphologically and functionally complete. The single cell performs all the functions like reproduction, digestion, respiration, excretion etc. This is the simplest and most primitive of all animals, with very simple body organization.


The structure of a protozoan cell is composed of
  1. A cytoplasmic body, and
  2. A nucleus.
The cytoplasmic body is divided into: peripheral clear ectoplasm; its function is protective, locomotive and sensory, and inner granular endoplasm; its function is nutritive, and reproduction.


Nucleus is the most important structure, as it controls the various functions and regulates reproduction.  It is situated inside the endoplasm.

  1. Bounded externally by a well defined nuclear membrane.
  2. Made up of a network of linin, enclosing within it the nuclear sap.
  3. Chromatin granules, lining the inner side of the nuclear membrane or appearing as condensation on linin threads.
  4. Karyosome situated inside the nucleus either centrally or peripherally.
  5. In most of the protozoa there is one nucleus. In ciliates two nuclei are present-a small micronucleus and a large macro nucleus, certain protozoan shown in addition to the nucleus, a non nuclear DNA-containing body called the kinetoplast, near which the flagellum originates; there is a small body at the point of origin of the flagellum known as the basal body.
Encystment:  The protozoan parasites possess the property of being transformed from an active (trophozoite) to an inactive stage, losing its power of motility and enclosing itself with in a tough wall. The protoplasmic body thus formed is known as a cyst. In this stage the parasite loses its power of growth and multiplication.

Organelles of Locomotion:

  • Pseudopodia: pseudopodia are generally temporary outgrowths of ectoplasm from any part of the body, seen in the class Rhizopodea.
  • Flagella: long delicate thread-like filaments, seen in class Zoomastigophora.    
  • Cilia:  Fine needle-like filaments covering the entire surface of the body, seen in class ciliatea.


The protozoan parasite exist in two stages
  1. Trophozoite
  2. Cyst
 The parasite multiplies only in the trophozoite stage and in cyst stage reproduction won't take place. Protozoan reproduces both sexually and asexually.

Asexual multiplication:

By simple binary fission:  In this process the individual parasite divides either longitudinally or transversely in to two parts. Before division all the parts are duplicated. By multiple fission or Schizogony: In this process the nucleus of the parent cell undergoes repeated divisions which are then surrounded by cytoplasm .when the multiplication is completed the parent cell ruptures and these daughter nuclei are liberated.

Sexual Reproduction:

By conjugation: conjugation is a temporary union of protozoa of the same species for an exchange of nuclear material with out the fusion of the cytoplasm. Later on, the two individuals separate. By syngamy: syngamy is a process in which, sexually differentiated cells called gametes unite permanently and a complete fusion take place. The resulting product is known as zygote.

Life cycle:

The protozoan parasite passes its lifecycle in one or two hosts.
  • Some parasites like intestinal flagellates, Rhizopodea and Ciliatea need not require a secondary host. The parasites in this group adapt themselves for passive transfer from one host to another by Encystment. The species in this parasite undergoes asexual multiplication and during unfavorable condition it secretes a resistant cyst wall, transforming in to a cyst. When the condition becomes favorable for its existence and continues its life in the trophozoite form. Thus Encystment is not a reproduction process, but a mean of protection of the species from extinction.
  • Some parasites like Trypanosoma, Leishmania and plasmodium  requires a secondary host for the development of a special cycle which is essential for the continuation of the species from one host to another. For example in plasmodium asexual multiplication is carried out in one host and asexual reproduction in another host.
Diagnostic Procedures | Helminths | Introduction to parasitology | Medical Parasitology | Protozoology