Question

Summarize the general life cycle of a protozoan, explaining the importance of the various stages in disease transmission and species identification

Answer 1

Protozoa are single cell organism which are seen worldwide either free living or parisitic feeding which do have the ability to cause disease in animal and humans. The life cycle of protozoa consist of two stages:

1. Trophoziote ( active, feeding and multiplying stage)

2. Cyst stage ( inactive, dormant but multiplying stage)

1. Trophoziote stage - this is an activated stage of the protozoa which helps them in

a)locomotion with help of flagella or cillia - flagella are primary locomotive organs for the protozoan but also helps In propulsion, adherence and protection of protozoan in case of threat. It also can detect change in temperature, cleranace mechanism . Flagella can help a protozoan to move inorder to invade a host, to seek nutrition as well as to reproduce.

Flagella do have a function in transmission of pathogenesis by adhering to the host substrate eg. E. Coli and salmonella can cause Food borne disease due to secondary host in fruits and vegetables that can infect humans and animals. Flagella can also make them blood borne , water borne or air borne as it helps them in propulsion. Eg infection in eye transmitted by wearing contact lenses infected with acanthameba.

B) sexual or asexual reproduction- asexual reproduction place in form of binary fission and budding whereas sexual reproduction takes place in form of single cell multiplying to daughter cells. This reproduction helps in multiplication or protozoan to an amount enough to cause a Disease eg. Diarrhea due to Entameoba histolytica. The number or organism and it's pathogenesis vary according to the immune system of human eg. Patient with AIDS will show early symptoms compared to healthy humans for whom the effect might be mild.

B) cyst stage - this stage is an inactive stage which may or may not undergo cell division within the cyst. Cyst may contain one or more infective forms. In many organism, first form cyst have single nuclues but as cyst matures and undergoes excystation to release four uninucleate organism. Cyst stage has a strong protection wall which enables it to survive in the external environment ranging from days to years. Thats how the cyst is being transferred from soil to human through faeco-oral route and transmission of organism occurs.

Species which can cause pathogenesis during trophoziote phase are as follows trichomonas vaginalis, leishmania

Disease transmission in cyst stage are - malaria, cryptosporidium, Entameoba histolytica, giardia lambia