Economic Importance of Protozoa
Introduction
Protozoa are unicellular microscopic organisms found almost everywhere, in water, in moist
surface of soil, in the air or even within the bodies of other animals and plants. In this fast
moving age of mammals, dominated by man, it may appear at first glance that this minute
animals would have little or economic significance. However, such is not the case, protozoa
exert far more influence in the worldly affairs and are generally thought, they are harmful as well
as useful, but harmful species are relatively smaller in numbers as compared with useful species.
Protozoa are important components of aquatic and soil ecosystems. They control microbial
populations and also a major route to transfer of biomass within the food chain in aquaculture.
Flagellate protozoa are the primary components in the marine food chain. They have some roles
in soil fertility which has great impact to agriculture. Skeletons of Foramininfera make up much
of the limestone and chalk on the Earth. Many protozoa can cause diseases in humans. Common
examples include malaria, amoebic dysentery, sleeping sickness, etc.
It has a great impact on the economy due to the medical costs incurred and due to days of labour
lost due to sickness. Costs of treatment and for control, and lost workdays affects economic
factors greatly.
In this assignment, we would like to discuss the economic importance of protozoa - its harmful
effects, useful effects and its role in causing diseases as well as in the treatment of diseases –
since all these aspects constitute their major economic importance.
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Objectives of the Assignment
On completion of the assignment we would like to fulfill the following objectives:
 Name as many economically important protozoa as possible
 Name the useful protozoa and explain how they are useful
 Name the harmful protozoa and explain how they are harmful
 Name some parasitic protozoa and the diseases that they cause
Useful Protozoa
Helpful in Sanitation
Numerous holozoic protozoa feed on putrefying bacteria in various bodies of water and thus,
help indirectly in the purification of water. These protozoa play an important role in sanitary
betterment and improvement of the modern civilized world in keeping water safe for drinking.
Planktonic protozoa as Food
Protozoa floating in the plankton of the sea provide directly or indirectly the source of food
supplies for man, fish and other animals. They form one of the first links in the numerous and
complicated food chains that exists in the oceans of the world. Clams and young fish feed
extensively on aquatic insect larvae, small crustaceans, worms etc., all of which take protozoa as
food. Thus, protozoa indirectly form the food of fish, clams and other animals, which in their
turn are consumed by man.
Symbiotic Protozoa
Some protozoa are found in symbiotic relationship with other organisms. This association is
usually beneficial to both the partners. The two partners become so dependent on each other that
one cannot get along without the other and their separation results in the death of both. Most
outstanding examples of symbionts among the protozoa are several intestinal flagellates
(Trichonympha, Colonympha etc) of termites and wood roaches. According to Cleveland, these
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flagellates are extremely vital for the existence of their hosts. They digest cellulose converting it
into soluble glycogen for their hosts as well as for themselves.
Oceanic Ooze and fossils Protozoa
The tiniest skeletons of dead pelagic foraminiferida, radiolaria and heliozoan sink to the sea
bottom forming the soft mud or the oceanic ooze. These tiny skeletons are made of silica or
calcium carbonate. Over countless millions of years these skeletons, deposited on the f lour of
the ocean, became solid and focilized and converte into some important sedimentary rocks strata
found all over the world. These have been put to various commercial uses such as filering agents,
abrasives, chalk; building stones etc. the white chalk cliffs of Dover, England, and the limestone
beds if Paris, Cairo and Noth America are composed almost exclusively of the fossils
foraminiferida.
It is hard to believe that the great city of Paris is indebted to these obscure animals. Most of the
buildings of Paris are made of limestone composed almost exclusively of the shells of
foraminiferida genus, Millionia. Similarly, the great pyramids of Egypt were carved from the
limestone deposits made tests of an early Tertain foraminiferida , Nummulites. The radiolarian
fossils are abundant in the hard rock of the nature of flint and chert. They also constitute a part of
the ripoli stone, which is used in abrasive powders of polishing.
Protozoa in Study
Protozoa re singles-celled organisms, possessing forms and functions like those of metazoan
cells. They are studied in the laboratories for comprehension and application of the biological
principles. Due to their minute size and quick reproduction, they are studied by geneticist for
heredity and variations. The knowledge fossil protozoa are essential for the students of geology
and paleontology. Protozoa are the progenitors of all the metazoans alive in the world today.
Their study helps in understanding the probable beginning of organic matter and origin and
evolution of life on earth. The physiology of protozoa has contributed much to know about the
study of cell.
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Harmful Protozoa
Soil Protozoa
Several soil protozoa present in large numbers hinder the nitrifying bacteria in their activity and
consequently tent to decrease the amount of germ.
Water pollution
Whenever protozoa are helpful in water sanitation, others become responsible for water
contamination or pollution. The protozoa of faecal origin belong to this later category. Some free
living protozoa (eg. Urolenopisis) also pollute water by producing aromatic and oily secretion
with objectionable odours, which render water for human consumption.
Some bioluminescent din flagellates, such as noctiluca, gynodiniun and gonyauls living sea
sometimes multiplies so extensively as to turn the water red with their bodies. The phenomenon
is known as blooming and is the cost of red tides, often experienced in the sea. Out breaks of this
red water often gives foul an disagreeable to the ocean water. The large concentrations of these
flagellate protozoa may even lead to the destruction of fish and poisoning of edible mollascs
such as clams, oysters and mussels, etc. making them unfit for human consumption.
Pathogenic Protozoa
Protozoa producing disease are termed pathogenic protozoa. They occur in all classes of
protozoa.
Pathogenic sarcodines: there are two common genera of parasitic amoeba- Endamoeba and
Entamoeba, which live in the intestine of man and other animals. Two pathogenic protozoa E.histolyica of man and other mammals and E.invadens of reptiles. E.histolutica is responsible
for amoebic dysentery in man. E.invadens, occurring in the colon of reptile causes reptilian
amoebiasis.
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Pathogenic flagellates: The pathogenic species of parasitic flagellates are included in the genera
Leishmania, Trypanosome,Trychomonas and Giardia. Some species of Leishmania have caused
severe diseses in man.L.donovani causes Yala-azar, a disease of the spleen and liver, L.tropica
causes a peculiar type of skin lesion and L.braziliensiscuaes infection of nasopharynxand skin
infection. These are transmitted by sandflies of the genus Phlebotomus. The parasitic species of
trypanosome
in
mammals
cause
worst
diseases.T.gambiense,
T.rhodesiense,
T.
cruzi,T.equiperdum, T.evansi, and T.brucei are common pathogenic pecies.
Histomonas meleagridis is the parasitic mastigamoeba of the parasitic species of trichomonas, T.
vaginalis is the causative organism of vaginal trichonmoniasis or vaginitis in the human female,
T. foetus and T.galinae is pathogenic in doves, pigeons, turkeys and chickens. Of the numerous
species of giardia, giardia intestinalis (= G.limblia)of man is of pathogenic significance.
Pathogenic sporozoans
The protozoa supperclass sporozoa is exclusively of parasitic forms. Though a majority of
sporozoa is harmless, some genera like Plasmodium, Eimeria, Isospora and Babesia include
pathogenic species. The species of plasmodium are called malaria paresites as they cause the
disease malaria. Four species of plasmodium -P. vivax, P. malariae, P. ovale, and P. falciparum
cause malaria in man. Malaria is cause by P. cyanomolgi in monkeys, by P. vergher in tree reds
and by P. gallinaceun in jungle fowl of Asia. Pathogenic species of Eimeria cause cocidiosis in
chickens and rabbits. E. canis in dogs, E. feline in cats, E. bovis in cattle and E. intricate in sheep
and goats are also common.
Isosporas, intesinalis in man and other animals, include one truly patheogenic species of man, I.
hominis. I. felis, I. bigemina and I. rivolta infect cats and dogs and occur in the mucous
membranes of ileum. The tramission is by cylindrical oocysts. The species of Babesia are intra
erythrocytic of various vertebvrates. Baesia bigemina of cattle causes the lethal haemoglobinuric
fever, red water fever or taxas fever. B. equi kin horses, B. rodhani in rodents, B. felis in cats, B.
motasi in goats, etc cause malignant jaundice, anaemia and fever in their respective hosts.
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Pathogenic ciliate
Balantidium coli are the only important ciliate psthogenic paracites. It is found in the intestine of
man and often in frogs.
Protozoa and Human Diseases
1. Amoebiasis
Amoebiasis, also known as amoebic dysentery, is caused by entamoeba histolytica. Its
trophozites that penetrates the wall of the intestine (colon) secretes histolytic enzymes and feed
upon its cells causing the formation of ulcers. These ulcers rupture and discharge blood and
mucous into the intestine that pass with stools. The trophozoites, under certain circumstances,
reach the liver, lungs and the brain and cause abscess formation.
No intermediate host is involved in the life cycle of parasite. Transmission of parasites from man
to man takes place through tetranucleatecysts. Prior to cyst formation the prophozoite changes
into a smaller minute form, which then encyst to form a tetranucleatecyst. These cysts are voided
with the faccal matter and contaminate food and water and spread into new hosts. Houseflies
help in its rapid spread.
Amoebic dysentery is endemic in warm countries. Emetin, Fumagillin, Erythromycin,
Aureomycin, etc., provide quick relief.
2. Diarrhoea
Diarrhea, which is characterized by loose bowels, is caused by a flagellate parasite, Giardia (=
Lamblia) intestinalise. It harbours the small intestine. Its call body is pear shaped with dorsal
side convex and ventral side flattened and deepened anteriorly to form a suction grove. It bears
two nuclei and four pairs of flagella arranged symmetrically.
The parasite divides by binary fission to multiply rapidly and feeds upon amino acids intestine.
This causes intestinal disorders leading to epigastric pain, abdominal discomfort, loss of appetite
and headache. Transmission of the parasite takes place through cysts which are voided with the
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faeces and enter the new hosts in food or water. The infection of Giaridia is more in children
than in adults. Chloroquine, Camoquine, Atebrin, etc., are effective in its treatment.
3. Trypanosomiasis
It is caused by the species of trypanosome which are flagellate parasites of the blood (In
vertebrate hosts) and gut (In invertebrate hosts). These are the most dreadful of all pathogenic
protozoa. Sleeping sickness is a dangerous disease of man in tropical Africa. Its causative agent
is T. gambiense and is transmitted by tsetse fly, Glosssina palpalis. Infestation of lymph system
leads to glandular swelling which is symptomatic for sleeping sickness. Later the parasites
penetrate into cerebro-spinal fluid, cause damage to the brain and bring about the lethargy
characteristic for sleeping sickness. If untreated, the disease leads to death. Germanin and
Lomidine are used to treat blood and lymph infections and tryparsamide for brain infection.
T.cruzi is the causative agent of American trypanosomiasis or chaga’s disease. It is wide spread
in south and central and is more common in children. It is transmitted by bugs of the genus
Triatoma. Tramission to man is not due to bug’s bite but through its faeces. Swelling of the body
parts, severe headache and continuous fever or symptomatic for the disease anemia and injury to
heart muscles lead to death. No permanent cure has been suggested yet. Premaquine and
puromycin are used for temporarily relief.
4. Leishmaniasis
It is caused by the species leishmania, the parasitic flagellates that inhabit blood in vertebrates
and gut in insect hosts. Leishmania donovani is the causative agent of Kala-azar or visceral
leishmaniasis. The disease is widespread in India, south China and the in the Mediterranean
countries. A major characteristic of the disease is a considerable enlargement of the spleen due to
blockage of reticulo-endothelium system of the parasites. It is usually fatal if untreated.
Treatment with antimony compounds proves useful. Sodium animonyl cogloconate, Neostibosan
and Urea stibamine are most effective medicines.
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L. tropica is the causative agent of skin leishmaniasis (oriental sore).the infection is restricted to
the endothelium of the skin capillaries and leads to lump-like boils. The disease is endemic in
warmer countries especially in south west Asia, eastern Mediterranean and tropical America.
Treatment includes regular cleaning and dressing of the boils and injecting Atebrine and
Berberine sulphate around them.
L. brasiliensis causes a disease called Espundia, producing multiple sores over large areas of the
body. Development of ulceration in nasal cavities, mouth and pharynx is quiet frequent. Injection
of antinomy drugs has proved fruitful for curing the diseases. Leishmania species are transmitted
from man to man by bites of sandflies belonging to the genus Phlebotomus.
5. Trichocomoniasis
This disease is caused by the species of Trichomonas, the flagellae protozoa. Its body is rounded
with one nucleus, an axostyle, a parabasal body, 4-6 flagella and one backwardly directed
flagellum. The most common pathogenic species is Trichomonas vaginalis that inhabits in
vagina of women and cause vaginitis. The disease is characterized by burning sensation, itch and
frothy vaginal discharge. The transmission is always through sexual intercourse by male
members who act as intermediaries. Even in man the infection of the urethra and prostate is not
uncommon. Arsenic and iodine drugs and antibiotics, like Aureomycin and terramycin have
proved helpful in combating the disease.
6. Malaria
It is caused by the species Plasmodium, the sporozoan parasites. It is transmitted through the
bites of female anopheles mosquito. In man, the parasite attacks the live cell and the re d blood
cells. A toxic substance, the haemozoin, is released by parasites cause malaria.
Malaria is most destructive for man. It is widespread in the tropic and sub-tropic. It is
characterized by the periodic attack of fever. The fever is repeated in the tertian malaria caused
by P. vivax, every second day; in ovale malaria caused by P. ovale, every second day; in quatan
malaria caused by P. malaria e, every third day, and in malignant tertian malaria caused by P.
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falciparum, every second day. The various drugs which are now used in the treatment of malaria
include quinine, Atebrin, Chloroquine, Camowuin, Pamaquine, Paludrine, Daraprim, etc.
7. Toxoplasmosis
The disease is caused by toxoplasmagondii, a sporozoan parasite. It is widely distributed all over
the world. The parasites occupy the cells of the reticulo-endothelial and central nervous systems.
The parasites multiply by endodyogenybut under certain conditions large cysts are also
produced. Symptoms of the disease include hydrocephaulus and choriorentinitis. Infants infected
before birth usually die. Daraprim, combined with sulphadiazine, has been found to be an
effective remedy.
8. Balantidial dysentery
It is caused by balantidium coli, an intestinal ciliate. It is characterized by diarrhea and ulceration
of the large intestine. The transmission of the parasite to a new host takes place through cysts
with contaminated food or water. Carbarsone, Aureomycin and Teramycin are ideal for curing
the disease.
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Conclusion
Protozoa are abundant in the soil, in the air and everywhere possible yet it is felt that they are
least important to human lives owing to its minute size. However, through this assignment on
´´The Economic Importance of Protozoa´’, we came to know a lot of things about protozoa apart
from the negligible knowledge that we had prior to doing this assignment.
Protozoa are the most abundant animals in the world in terms of numbers and biomass. Their
principal importance is as consumers of bacteria. Bacteria play a vital role in maintaining the
earth as a suitable place for inhabitation by other forms of life and protozoa play a vital role in
controlling their numbers and biomass. Protozoa are also important as parasites and symbionts of
multicellular animals.
It is this assignment that ushered us to the pool of information about protozoa and its economic
importance through the research that we did to find out things about it. It is both harmful as well
as helping that contribute to finding solutions to a lot of problems that exists in this world.
In brief, this assignment was of immense importance to us because it is crucial to people like us
who should be thorough about the stuffs like that.
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References
Hoare, C. A. 1972. The Trypanosomes of Mammals. Blackwell Scientific Publications, Oxford
Wells, E. A. 1976. Biology of the Kinetoplastida. Academic Press.
Received September 12, 2009 from
http://answers.yahoo.com/question/index?qid=20071110015149AAKcRah
Received September 12, 2009 from
http://ukpmc.ac.uk/articlerender.cgi?accid=PMC2723921
Received September 14, 2009 from
http://malaysia.answers.yahoo.com/question/index?qid=20060902001607AANEZZu
Received September 20, 2009 from
file:///C:/Documents%20and%20Settings/std.SCE/Desktop/protozoan.htm#v=onepage&q
=&f=false
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