Protozoan Diseases

Protozoan Diseases www.HourlyBook,com


• Protozoans are diverse group of eukaryotic, unicellular organisms.
• Human diseases caused by protozoa are relatively few, but are individually of devastating consequences.
Amoebiasis or Amoebic dysentery
• Amoebiasis is a protozoan infestation of upper part of large intestine which is caused by monogenetic protozoan (having one host i.e., man) known as Entamoeba histolytica.
Mode of transmission of Amoebiasis
• Incubation period is 2-4 weeks or more.
• The infection occurs by the cysts of Entamoeba present in the stool of infected person.
• It spreads through faecal – oral route, sexual contact and vectors like flies, cockroaches etc.
• Inside the intestine, the cyst germinates and releases 4-8 Entamoebae where they secrete an enzyme called cytolysin. The enzyme partially dissolves the wall of large intestine.
• The parasites reach blood capillaries and feed on red blood corpuscles.
• The feeding stage of parasite is called trophozoite or magna. It stops feeding prior to cyst formation.
• The non-feeding pre-cystic stage is called minuta form (7-20 p.m).
• The infective stage is tetranucleate cyst.
Symptoms of Amoebiasis
• Amoebiasis disease is characterised by abdominal pain, diarrhoea with loss of blood in stools, fever, nausea, vomiting.
• It is diagnosed by the presence of Charcot-Leydin crystals in the cytoplasm of eosinophils.
Prevention and treatment
• To prevent the infection, the sanitary disposal of faecal matter and cleanliness in the preparation of food should be carefully done.
• This disease can be cured by administering drugs like emetine, stremetine (strychnine + emetine), carborsome, metronidazole and tinidazole.

Ciliary dysentery (Balantidiasis)
• Ciliary dysentery is caused by ciliated protozoan named Balantidium coli.
• The protozoan inhabits the human large intestine (colon). It is also seen in pigs and monkeys. In pigs they are non-pathogenic.
• It reproduces asexually by transverse binary fission and sexually by conjugation. The latter is followed by cyst formation. Cysts pass out in the host’s faeces.
Mode of transmission of Ciliary dysentery
• Incubation period is of few days.
• Infection occurs by ingesting cysts with food and drinks.
Symptoms of Ciliary dysentery
• The protozoan causes ulcers in the colon and invades mucous membrane by secreting an enzyme hyaluronidase.
• This generally results in vomiting, abdominal pain, weight loss and diarrhoea, but may also lead to severe or fatal dysentery.
Prevention and treatment of Ciliary dysentery
• This disease can be prevented by adopting hygienic measures.
• Tetracycline and iodoquinol are effective treatments against the disease.

• Giardiasis is caused by Giardia intestinalis, ‘The Grand Old Man of the intestine’.
• It is the first human parasitic protozoan known.
• It inhabits upper part of small intestine (duodenum and jejunum).
Mode of transmission of Giardiasis
• Incubation period is 1 to 3 weeks.
• Infection occurs by contamination of food and drink with cysts.
Symptoms of Giardiasis
• It is characterised by epigastric pain, abdominal discomfort, headache, diarrhoea and sometimes fever.
Prevention and treatment of Giardiasis
• Clean water supply, infection free food, properly washing hands, fruits and vegetables before eating etc. are some of the preventive measures.
• Drugs like metronidazole, tinidazole, ornidazole are used to treat giardiasis.

• Malaria is caused by a digenetic (have two hosts to complete its life cycle) protozoan parasite known as Plasmodium.
• The primary host is female Anopheles mosquito and secondary host is man.
• Sir Ronald Ross (1897), a doctor in Indian Army, established that malarial parasite is transmitted by the bite of a female Anopheles mosquito for which he got Nobel Prize in 1902.
human being, the malarial parasites enter into the mosquito’s body and undergo further development to form sporozoites that finally move to the salivary glands of the insect.
• The bite of these mosquitoes introduces the sporozoites inside the body, thus initiating the above mentioned cyclic process again.
• The attack of malaria is preceeded by yawning, tiredness, headache and muscular pain.
• There are four species of Plasmodium which causes four main types of malaria in human.
Mode of transmission of Malaria
• The malarial parasite, Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito.
• The sporozoites reach the liver cells via blood where they initially multiply. These then attack the red blood cells (RBCs) resulting in their rupturing.
• The rupture of RBC is associated with the release of haemozoin, a toxin which causes the chill and high recurring fever every two to three days.
• The female Anopheles mosquito when bites an infected human being, the malarial parasites enter into the mosquito’s body and undergo further development to form sporozoites that finally move to the salivary glands of the insect.
• The bite of these mosquitoes introduces the sporozoites inside the body, thus initiating the above mentioned cyclic process again.

The attack of malaria is preceeded by yawning, tiredness, headache and muscular pain.
There are four species of Plasmodium which causes four main types of malaria in human.

• The incubation period of Plasmodium ovale and P. vivax is about 14 days, of P. falciparum it is 12 days, and of P. malariae it is 28-30 days.
Symptoms of Malaria
• Malaria is characterised by fever at intervals, sudden acute chillness (cold or rigor stage) accompanied by shivering followed by rise in temperature.
• Peak fever (hot or febrile stage) is 41.1°C or 106°F which persists for 3-6 hours. After 2-4 hours of fever, there is profuse sweating (sweating or defervescent stage) which lowers the body temperature to near normal.
• Malaria is also accompanied by nausea, headache, laziness and muscular pains. It also results in anaemia and splenomegaly.
Prevention and treatment
• Spraying areas with DDT, BHC and other insecticides will kill the mosquitoes. Introducing Utricularia, ducks and larva eating fishes like Gambusia, stickle back, minnow and trout in large water reservoirs, putting oil (kerosene) in the water ponds can help to protect against the breeding of mosquitoes.
• Fitting doors and windows with wire nets, using mosquito nets while sleeping, applying mosquito repellants at night, taking smaller prophylactic dose of antimalarial drugs at weekly intervals during malarial season can prevent effectively from infection of malaria.
• Drugs like chloroquine and primaquine are administered to treat malaria.
• Other drugs like quinine obtained from the bark of Cinchona plant, camoquin, daraprim and artemesenin obtained from Artemesia annua (is effective against cerebral malaria) are also used to treat malaria.

African sleeping sickness (Trypanosomiasis)
• Trypanosoma is a flagellate protozoan whose different species cause different types of trypanosomiasis.
African sleeping sicknessis of three types:
(i) Gambian (W. African) sleeping sickness
caused by Trypanosoma gambiense by the bite of the blood sucking tse tse fly, Glossina palpalis.
(ii) Rhodesian (E. African) sleeping sickness caused by Trypanosoma rhodesiense by the bite of the tse tse fly, Glossina species.
(iii) Chagas’ disease (South American sleeping sickness) is caused by Trypanosoma cruzi which spreads by the bite of blood sucking Triatoma species.
• Trypanosoma is a protozoan which is digenetic having two hosts:
Primary host: man.
Secondary host: tse tse fly, Glossina sp.
Mode of transmission of African sleeping sickness
• Incubation period is long may be of weeks or months.
• The infection is initiated by the bite of tse tse fly which harbours the infective metacyclic forms in the lumen of its salivary glands.
• In human beings, the parasite lives in the blood stream and in the lymph, it invades the cerebrospinal fluid of the CNS and damages the brain.
Symptoms of African sleeping sickness
• This disease is characterised by swelling of lymphatic glands, irregular recurrent fever followed by weakness, loss of weight, anaemia, increase in pulse rate, severe headache, sleepiness and muscular spasms.
Prevention and treatment of African sleeping sickness
• Fly screens on doors and windows should be installed.
• Trypanosomiasis can be treated in early stages by the drugs pentamidine, atoxyl, tryparsamide, germanin etc. But, it is very hard to control it once the parasites have entered the cerebrospinal fluid.

Kala-azar (Dum-dum fever or Visceral leishmaniasis)
• Kala-azar also known as Black fever or Dumdum fever, is caused by the protozoan Leishmania donovanithrough the bite of the sand fly, Phlebotomus argentipus.
• Its primary host is man and secondary host is sand fly.
Mode of transmission of Kala-azar
• Incubation period is long from 3 to 6 months, and symptoms may appear even after 2 years.
• Early symptoms of kala-azar include high fever and enlargement of spleen and liver, followed by general weakness, emaciation (wasting of the body), anaemia due to reduction in number of blood cells, and a peculiar darkening of skin.
• In advanced stage, hair becomes brittle and falls out. The body immune system becomes so weak that secondary infections by bacteria or viruses lead to death.

Prevention and treatment of Kala-azar
• Eradication of the insect vector sandfly by insecticides, and avoiding the bite of sandfly are the prophylactic measures against kala-azar.
• Pentavalent antimony compounds like sodium- antimony tartrate and glyconate, urea stibamine, aminostiburea, neostibosan etc. are used for treatment of Kala-azar.

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